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Central and peripheral components of the vasoactive actions of vasopressin and adrenergic amines King, Kathryn Anne 1987

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CENTRAL AND PERIPHERAL COMPONENTS OF THE VASOACTIVE ACTIONS OF VASOPRESSIN AND ADRENERGIC AMINES By KATHRYN ANNE KING B.Sc,  University of Victoria, 1982  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in THE FACULTY OF GRADUATE STUDIES (Department of Pharmacology & Therapeutics)  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA July 1987 ©Kathryn Anne King,  1987  In  presenting  degree  this  at the  thesis  in  University of  partial  fulfilment  of  of  department publication  this or of  thesis for by  his  or  her  representatives.  The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1 Y 3 1 8  August 1987  an advanced  agree that permission for extensive  It  this thesis for financial gain shall not  Department of Pharmacology & Therapeutics  for  that the Library shall make it  scholarly purposes may be  permission.  Date  requirements  British Columbia, I agree  freely available for reference and study. I further copying  the  is  granted  by the  understood  that  head of copying  my or  be allowed without my written  - ii  -  ABSTRACT Three  major  circulation: sympathetic  systems  participate  in  the  control  the  peripheral  the r e n i n - a n g i o t e n s i n , the arginine vasopressin (AVP) and the nervous systems.  These studies examined the r o l e s of the AVP  and the sympathetic nervous systems in the regulation both the central and the peripheral Anatomical  studies  have revealed that  reflex  cardiovascular  it  regulation.  (MAP)  catecholamine  arc,  and  fourth cerebroventricle  was  neurons  containing  (NTS) in the medulla.  of the afferent  The  effect  of  nerve  activity,  investigated.  and NTS of  central  The  in  AVP on mean estimated  injection  Since  neurons of  suggests that AVP may be involved  sympathetic  levels,  hypothalamic  solitarius  the NTS. i s the primary s i t e of termination baroreceptor  of blood pressure at  level.  AVP extend to the nucleus tractus  pressure  of  central arterial  from  of  plasma  AVP into  conscious, unrestrained  rats  the  the  increased  MAP and plasma noradrenaline and adrenaline l e v e l s , suggesting that AVP may act c e n t r a l l y at the NTS to modulate sympathoadrenal outflow. injection  of  a selective  vascular  antagonist  of  into the fourth v e n t r i c l e or NTS did not affect levels, stress,  either or  in in  normotensive  rats,  in  endogenously-released  AVP may  not  have  AVP, d(CH ) Tyr(Me)AVP, 2  subjected  rats. a  5  MAP or plasma catecholamine  rats  neurogenically-stressed  However, the  tonic  This  to  hypotensive  suggests  influence  on  that central  cardiovascular r e g u l a t i o n . (cont'd)  The r o l e  of  distribution The  was  i.v.  of  resistance  distribution  the  control  investigated  injection  peripheral  of  AVP in  in  of  MAP, cardiac  anesthetized,  d(CH ) Tyr(Me)AVP 2  (TPR),  not  alter  CO,  MAP  and  of blood flow (BF) to the stomach and s k i n .  AVP was found  renin-angiotensin  to  be  and the  greater  in  the  sympathetic  absence of  nervous  (CO) and  surgically-stressed  decreased  5  did  output  its  rats.  and  total  increased  the  The vascular r o l e influence  systems.  After  from  the  blockade of  the renin-angiotensin system by the infusion of s a r a l a s i n the AVP antagonist increased  BF  to  the  skin  and  a-adrenergic system with the  muscle,  infusion  markedly increased BF to the muscle. produced  by AVP in  endogenous  different  vasomotor  tone  of  after  phentolamine,  blockade  the  beds was found renin-angiotensin  of  the  the AVP antagonist  Thus, the amount of  vascular  from  while  vasoconstriction  to  depend on  and  the  a-adrenergic  systems. Cross-circulation peripheral  studies  and central  were  effects  conducted  of  designated rat A and B, r e s p e c t i v e l y .  to  a-agonists The i . v .  concurrently in  two  injection  observe  anesthetized  the rats,  of c l o n i d i n e  into  rat A was found to increase MAP and decrease HR in rat A, and reduce MAP and HR in rat B.  Since the stimulation  by  increased MAP, i t  clonidine  post-junctional pre-junctional  o^-adrenoceptors c^-adrenoceptors.  of peripheral  suggests  that  a-adrenoceptors in rat A  the  effects  predominate  over  those  In  the  contrast,  i.v.  of of  peripheral peripheral  injection  of  the  o ^ - a g o n i s t , methoxamine, in rat A increased MAP and decreased HR in rat A, (cont'd)  and  increased both  (^-adrenoceptors  MAP and HR in  rat  B.  This  suggests  that  central  may mediate responses in the opposite d i r e c t i o n  to  those  produced by o^-adrenoceptors. To v e r i f y the r e s u l t s of the c r o s s - c i r c u l a t i o n studies in animals free of the  influence of  surgery and anesthesia, and to  determine whether  the  responses to a-agonists were mediated by changes in sympathoadrenal outflow, clonidine centrally  and in  significantly  a  more  selective  conscious  rats.  decreased  MAP  c^-agonist,  The  i.e.v.  and  HR  B-HT 920,  injection  and  of  slightly  were  injected  clonidine  (1 ug)  decreased  plasma  noradrenaline and adrenaline l e v e l s ; however, contrary to expectations, the i.c.v.  injection  of  B-HT 920  (1,  10 yg)  increased MAP, decreased HR and  s l i g h t l y increased plasma noradrenaline and adrenaline l e v e l s .  To determine  whether the responses to central i n j e c t i o n of c l o n i d i n e or B-HT 920 were due to  the  stimulation  were  given  (^-antagonist.  of  after The  ©^-adrenoceptors, pretreatment  i.c.v.  i.c.v.  with  injection  of  increased MAP and plasma noradrenaline that  central  ag-adrenoceptors  cardiovascular system. produced the Further  may  However, i . c . v .  same responses in  studies with d i f f e r e n t  the  injections  rauwolseine, rauwolscine  in  and adrenaline  mediate  tonic  injections absence or  a-adrenergic  of a  drugs  selective  conscious  levels,  rats  suggesting  inhibition  of  the  of c l o n i d i n e or B-HT 920 presence of  agonists  rauwolscine.  and antagonists  various s e l e c t i v i t i e s are necessary before we can explain the e f f e c t s of central c l o n i d i n e and B-HT 920.  these  with  differential  -  V  -  TABLE OF. CONTENTS CHAPTER  Page  1 INTRODUCTION  1  1.1 General overview  1  1.2 The vasopressin system  2  1.2.1 1.2.2 1.2.3 1.2.4 1.2.5 1.2.6  Structure of AVP Synthesis of AVP Release of AVP P h y s i o l o g i c a l r o l e of AVP Role of AVP in hemorrhage, dehydration and s u r g i c a l s t r e s s Role of AVP in hypertension.  1.3 The sympathetic nervous system 1.3.1 1.3.2 1.3.3 1.3.4  21  Structure of the sympathetic nervous system C l a s s i f i c a t i o n of adrenoceptors Peripheral a-adrenoceptors Central a-adrenoceptors  21 24 26 29  1.4 Aims .of the studies  31  1.4.1 Role of AVP in cardiovascular regulation 1.4.2 Role of the a-adrenergic system in cardiovascular regulation 2 METHODS  2 2 4 11 16 18  -  37  2.1 Central AVP in conscious rats  37  2.1.1 Surgical preparation 2 . 1 . 1 . 1 Implantation of i n t r a c e r e b r o v e n t r i c u l a r 2.1.1.2 Implantation of vascular cannulae  31 34  37 cannulae  37 38  2.1.2 Experimental protocol  38  2.1.3 Catecholamine analysis by HPLC 2 . 1 . 3 . 1 Extraction of plasma samples  41 41  2.1.3.2 HPLC with electrochemical detection 2.1.4 S t a t i s t i c a l  analysis  42 42 (cont'd)  - vi -  CHAPTER  Page  2.2 Central AVP in hypotensive rats  43  2.2.1 Experimental protocol  43  2.2.2 S t a t i s t i c a l analysis  43  2.3 M i c r o i n j e c t i o n of AVP into the NTS  43  2.3.1 Experimental protocol 2.3.2 H i s t o l o g i c a l technique  43 45  2.3.3 S t a t i s t i c a l analysis  45  2.4 Central AVP in neurogenically-stressed rats  45  2.4.1 Experimental protocol  45  2.4.2 S t a t i s t i c a l analysis  46  2.5 Vascular r o l e of AVP  46  2.5.1 Surgical preparation 2.5.2 Microsphere technique 2.5.3 Experimental protocol 2.5.4 C a l c u l a t i o n s , 2.5.5 S t a t i s t i c a l analysis 2.6 Central and peripheral actions of a-agonists 2.6.1 C r o s s - c i r c u l a t e d rat preparation 2.6.2 Blood flow to the brain v i a the l e f t c a r o t i d artery 2.6.3 Microsphere technique 2.6.4 Determination of c i r c u l a t o r y leakage 2.6.5 E f f e c t s of c l o n i d i n e and methoxamine 2.6.6 C a l c u l a t i o n s 2.6.7 S t a t i s t i c a l analysis 2.7 Central ct2-agonists in conscious rats  46 46 48 49 49 50 50 52 53 53 53 54 54 54  2.7.1 Experimental protocol 2.7.2 S t a t i s t i c a l analysis 2.8 Drugs  54 56 56 (cont'd)  Page  CHAPTER 3 RESULTS  57  3.1 Central AVP in conscious rats  57  3.1.1 Central administration of AVP 3.1.2 Central administration of AVP antagonist  57 57  3.1.3 Peripheral administration of AVP and AVP antagonist  62  3.2 Central AVP in hypotensive rats  62  3.3 M i c r o i n j e c t i o n of AVP into the nucleus tractus s o l i t a r i u s  65  3.4 Central AVP in neurogenically-stressed rats  65  3.5 Vascular r o l e of AVP  70  3.5.1 E f f e c t of antagonism of pressor systems, on MAP, CO and TPR 3.5.2 E f f e c t of AVP antagonist on MAP, CO, and TPR  70 70  3.5.3 E f f e c t of AVP antagonist on the d i s t r i b u t i o n of blood flow  74  3.6 Central and peripheral actions of a-agonists 3.6.1 3.6.2 3.6.3 3.6.4  Blood flow to the brains of c r o s s - c i r c u l a t e d rats Blood flow to the brain v i a the l e f t c a r o t i d artery C i r c u l a t o r y leakage C r o s s - c i r c u l a t e d rat preparation  3.7 Central (^adrenergic agonists in conscious rat 4 DISCUSSION  78 78 78 78 82 82 93  4.1 Central AVP in conscious rats  93  4.2 Central AVP i n hypotensive rats  97  4.3 M i c r o i n j e c t i o n of AVP into the NTS  98  4.4 Central AVP in neurogenically-stressed rats  101  4.5 Vascular r o l e of AVP  102  4.6 Central and peripheral actions of a-agonists  (cont'd) 105  - viii  -  CHAPTER  Page  4.7 Central a2~agonists in conscious rats  109  4 . 8 General conclusions  113  4 . 8 . 1 Role of AVP in cardiovascular regulation 4 . 8 . 2 Role of the a-adrenergic system in cardiovascular regulation 5 REFERENCES •  113 114  - ix LIST-OF TABLES Table  Page  1  Control values of MAP, CO and TPR in Groups I,  2  Effects of AVP antagonist on MAP, CO and TPR in Groups I, and  3  II,  and III  71 II  73  III  Cpm in rats A and B expressed as a % of cpm detected in rat A  81  in 1 min 4  Control values of MAP, HR and plasma noradrenaline and adrenaline concentration in Groups I, administration  II,  III  and IV p r i o r to drug  87  -  X  -  LIST OF - FIGURES Fig.  Page  1  The structures of arginine vasopressin (AVP) and l y s i n e vasopressin  3  2  The biosynthetic pathway for noradrenaline and adrenaline  22  3  Vascular connections between rats A and B in the c r o s s - c i r c u l a t i o n preparation  51  4  The e f f e c t s of i . e . v . i n j e c t i o n s of AVP on MAP and plasma noradrenaline and adrenaline concentrations in r a t s from Group I and Group II  58  5  The e f f e c t s of i . e . v . i n j e c t i o n s of a r t i f i c i a l CSF on MAP and plasma noradrenaline and adrenaline l e v e l s in r a t s from Group III and Group IV  59  6  The effect of i . e . v . i n j e c t i o n of AVP antagonist on MAP and plasma noradrenaline and adrenaline concentrations in rats from Group V  60  7  The effect of pretreatment of the fourth v e n t r i c l e with AVP antagonist on MAP and plasma noradrenaline and adrenaline l e v e l s following i . e . v . i n j e c t i o n s of AVP in rats from Group VI  61  8  The e f f e c t of i . v . i n j e c t i o n s of AVP and AVP antagonist on MAP and plasma noradrenaline and adrenaline concentrations in rats from Group VII, Group VIII and Group IX  63  9  The effect of i . e . v . i n j e c t i o n s of a r t i f i c i a l CSF (Group I) and AVP 64 antagonist (Group II) on MAP and plasma noradrenaline and adrenaline l e v e l s in rats r e c e i v i n g i . v . infusions of nitroprusside  10  The e f f e c t of i n j e c t i o n into the NTS of 2 ul a r t i f i c i a l CSF, 2 ng AVP, 10 ng AVP, or 10 ng AVP antagonist on MAP and HR  66  11  The e f f e c t of i n j e c t i o n into the NTS of 2 yl a r t i f i c i a l CSF, 2 ng AVP, 10 ng AVP, or 10 ng AVP antagonist on plasma noradrenaline and adrenaline concentration  67  12  The effect of i n j e c t i o n into the NTS of a r t i f i c i a l CSF (Group I) and AVP antagonist (Group II) of rats subjected to neurogenic stress on MAP and HR  68  13  The effect of i n j e c t i o n into the NTS of a r t i f i c i a l CSF (Group I) and AVP antagonist (Group II) of rats subjected to neurogenic stress on plasma noradrenaline and adrenaline concentration  69  - xi Fig. 14  Page Effect of AVP antagonist on MAP, CO and TPR in anesthetized, s u r g i c a l l y stressed r a t s : intact and s a l i n e - p r e t r e a t e d (Group s a r a l a s i n - p r e t r e a t e d (Group II) and phentolamine-pretreated (Group III)  72 I),  15  Effect of AVP antagonist on regional d i s t r i b u t i o n of BF in rats from group I (saline-pretreated)  75  16  Effect of AVP antagonist on regional d i s t r i b u t i o n of BF in rats from group II (saralasin-pretreated)  76  17  Effect of AVP antagonist on regional d i s t r i b u t i o n of BF in rats from group III (phentolamine-pretreated)  77  18  BF to the l e f t and r i g h t brain hemispheres and brainstem before and after l i g a t i o n of the subclavian a r t e r i e s in r a t s A and B of c r o s s - c i r c u l a t e d rat preparations  79  19  BF to the l e f t and r i g h t brain hemispheres and brainstem in the presence and absence of functional subclavian a r t e r i e s in single r a t s  80  20  MAP and HR responses of rat A and rat B to i . v . of clonidine (25 yg/kg) in rat A  83  21  Representative recordings of MAP and HR responses in rat A and rat B following i . v . i n j e c t i o n of clonidine (25 yg/kg) in rat A  84  22  MAP and HR responses of rat A and rat B to i . v . of methoxamine (25 yg/kg) in rat A  85  23  Representative recordings of MAP and HR responses of rat A and rat B following i . v . i n j e c t i o n of methoxamine (25 yg/kg) in rat A  86  24  The effect of i . c . v . i n j e c t i o n of B-HT 920 (Group I) and c l o n i d i n e (Group II) on MAP and HR  88  25  The effect of i . c . v . i n j e c t i o n of B-HT 920 (Group I) and c l o n i d i n e (Group II) on plasma noradrenaline and adrenaline l e v e l s  89  26  The effect of i . c . v . i n j e c t i o n of 10 yg rauwolscine followed by 1 yg B-HT 920 (Group III) and 10 yg rauwolscine followed by 1 yg c l o n i d i n e (Group IV) on MAP and HR  91  27  The e f f e c t of i . c . v . i n j e c t i o n of 10 yg rauwolscine followed by 1 yg B-HT 920 (Group III) and 10 yg rauwolscine followed by 1 yg clonidine (Group IV) on plasma noradrenaline and adrenaline l e v e l s  92  injection  injection  -xii  -  ACKNOWLEDGEMENTS I  am grateful  to both the B.C. and Canadian Heart Foundations, without  whose f i n a n c i a l support t h i s work would not have been p o s s i b l e . I would l i k e to express my appreciation to Dr. M.C. S u t t e r , Dr. M.J.A. Walker, Dr. V.W. Yong, Dr. M . J . C u r t i s and Caroline Bruce f o r t h e i r and encouragement. write.  I am also grateful to Wee f o r providing me with space to  I would l i k e to thank Dr. R. Wall f o r  the HPLC a n a l y s i s , and for his endless patiencel Fedrick  support  Wong and Maureen Murphy f o r  their  his expert advice regarding I would also l i k e to thank  assistance in  several  of  the  studies. I would l i k e to thank Ron f o r his patient support. his help, and f o r  his sense of  I thank Reza for  lunacy and his exceptional  insight.  all I am  very grateful to my supervisor, Dr. C . C . Y . Pang f o r her careful guidance and encouragement, and e s p e c i a l l y for her enthusiasm f o r s c i e n c e .  - xiii  -  LIST OF ABBREVIATIONS arginine vasopressin  AVP  adenosine triphosphate  ATP  blood flow  BF  cardiac output  CO  central nervous system  CNS  cerebrospinal f l u i d  CSF  counts per minute  cpm  deoxycorticosterone/salt  DOC/salt  3,4-dihydroxybenzylamine  DHBA  heart rate  HR  high performance l i q u i d chromatography  HPLC  hour(s)  h  international  units  IU  intracerebroventricular  i.c.v.  intraperitoneal  i.p.  intravenous  i.v.  mean a r t e r i a l  pressure  MAP  minute(s)  min  nucleus tractus s o l i t a r i u s  NTS  paraventricular nucleus  PVN  polyethylene  PE  second(s)  sec  spontaneously hypertensive r a t ( s )  SHR  standard deviation  SD  standard error of the mean  SEM  t o t a l peripheral r e s i s t a n c e  TPR  1  INTRODUCTION  1.1  General overview The c i r c u l a t i o n of the blood was f i r s t described by William Harvey in  his t r e a t i s e " E x c i t a t i o anatomica de motu cordis et sanguinis in animalibus" in  1628.  Since  peripheral  the  time  circulation  remove  regulate  body temperature  flow  or  to  materials,  the  it  maintain  is  flow of  autoregulation  has  provide  and f a c i l i t a t e  r o l e of the c i r c u l a t i o n  mechanisms regulate blood  Harvey,  functions  oxygen,  primary  waste  of  been tissues  normal  food  occurs  at  the the  with  tissue  that  the  nutrients  and  fluid  absorption.  to maintain  blood to  established  In  homeostasis. tissues.  level  of  Local the  volume,  effect  the  A number  of  control  of  blood  vessel.  Autoregulation i s the tendency f o r blood flow to remain constant in s p i t e of changes in a r t e r i a l  pressure, and i t  i s achieved by non-neural mechanisms.  It may involve a myogenic mechanism, the a b i l i t y of the a r t e r i o l e to in response to a reduction in a r t e r i a l  pressure and to contract  in response  to an increase in pressure, and/or a metabolic mechanism, the of  metabolites  decreased f l o w .  by  tissues  which  cause  vasodilation  dilate  accumulation  during  periods  of  In addition to these non-neural regulatory systems, several  hormonal systems including the renin-angiotensin-aldosterone  and vasopressin  systems have been implicated in the control of the c i r c u l a t i o n .  s  Perhaps the  greatest influence on the peripheral c i r c u l a t i o n , however, i s exerted by the sympathetic  nervous  neurotransmitter causes contraction  system.  noradrenaline  The  sympathetic  released  from  nervous  system,  sympathetic  of vascular smooth muscles and therefore  the maintenance of blood pressure.  nerve  via  the  endings,  contributes  to  - 2 1.2  The vasopressin system 1.2.1  Structure  of  AVP.  The  discovery  that  extracts  of  the  posterior pituitary gland have an effect on blood vessels was f i r s t made by Oliver  and  Schafer  in  1895.  Krogh  (1929)  later  observed  that  local  application of posterior pituitary extracts to capillary beds in vivo in the webbed  feet  constrict. extracts  frogs  and  in  the  ear  of  The structure of the vasoactive was  subsequently time.  of  postulated  dogs  substance  by du Vigneud and his  synthesized  in 1954,  caused  an unprecedented  the  present  group  in  vessels  to  in pituitary 1953  accomplishment  and was at  this  Vasopressin was found to be a nonapeptide containing two cysteine  residues at positions one and six which participate in a disulfide so that  the f i r s t  biological  six  activity  Lysine vasopressin,  amino acids  (Fig. 1).  form a ring,  which is  linkage  essential  for  Two major naturally occurring forms exist.  which occurs in the pig and hippopotamus, contains a  lysine residue in position eight,  and arginine vasopressin  (AVP), the form  present in other mammals, contains an arginine residue at position eight. 1.2.2  Synthesis  neurosecretory neurosecretory  of  system cells  AVP.  for  which  The hypothalamohypophyseal  AVP, have  is  their  comprised perikarya  paraventricular nuclei of the hypothalamus.  of in  complex,  the  magnocellular  or  the  through the  neurohypophysis. synthesis,  pars  tuberalis  to  The secretory process  packaging into secretory  the release site, and release.  terminate  and their axons  on capillaries  for AVP consists  in  the  of four phases:  granules,transport of the granules  AVP and its  and  The magnocellular neurons form  the floor and ventrolateral walls of the third ventricle, project  supraoptic  to  binding protein neurophysin II  are synthesized within the cell bodies of the magnocellular neurons in the form of a precursor molecule,  and packaged  granules (Brownstein et a l . 1983).  into membrane-bound secretory  The granules are transported along the  - 3 -  Cys—Tyr—Phe—Glu—Asp—Cys—Pro—Arg—Gly(NH J 2  1  2  3  4  5  6  7  8  9  8-Arginine Vasopressin (ADH, AVP; mammals) Lys8-Lysine Vasopressin (lypressin, LVP; swine) Fig.  1.  The structures  of arginine vasopressin (AVP) and lysine vasopressin.  - 4 axons to the axon terminals  where they  are stored  (Russell et a l .  1981).  AVP i s released from the nerve endings into the systemic c i r c u l a t i o n 2+ Ca  -dependent  by e l e c t r i c a l  exocytosis  the  total  response to  membrane d e p o l a r i z a t i o n  impulses generated within the supraoptic  nuclei (Thorn 1978). of  in  pool  and  of  the  in response to stimulation  paraventricular  hormone stored  within the  neural  lobe  and McPherson 1977).  but at a slower r a t e .  The complete process of  of  1-8 min  in  1973;  Baumann and  Robertson 1977). Release of AVP.  AVP appears to be released in response to two  types of p h y s i o l o g i c a l s t i m u l i : or c e l l  osmotic and non-osmotic.  which can respond to changes in  accordingly influence AVP r e l e a s e , was f i r s t This proposal was based on experiments  The concept of an its  own volume and  postulated by Verney in 1947.  in which the i n t r a c a r o t i d  injection  of hypertonic solutions of solutes which are not r e a d i l y permeant to such as sodium c h l o r i d e , sucrose and sodium s u l f a t e , fall  to  Gazis and Sawyer 1978), 4-8 min in the dog (Gazis and  Sawyer 1978), and 17-35 min in humans (Robertson et a l .  osmoreceptor,  (Pickering  Once secreted into the blood stream, AVP i s subject  metabolic clearance by the kidney and l i v e r with a h a l f - l i f e the rat (Lauson 1974;  can be  occurs AVP secretion continues  synthesis, transport and storage i s completed in 1-2 h in the rat  1.2.3  elicited  Sachs et a l . (1971) have shown that only 10-20 percent  r e a d i l y and r a p i d l y released, and once t h i s  Dingman 1976;  by a  elicited  cells,  an immediate  in urine flow in dogs, while the administration of hypertonic  solutions  of solutes which r e a d i l y penetrate c e l l s , such as glucose or urea, were less effective. hypertonic  Subsequent  involving  administration  of  various  solutions c l e a r l y demonstrated that an increase in the  pressure of Verney  studies  1957;  the  extracellular  Eriksson et a l .  fluid  stimulates  1971; Athar  antidiuresis  and Robertson  et a l . 1977) and AVP release (Thrasher et a l . 1980a).  1974;  In v i t r o  osmotic  (Jewell  and  Robertson experiments  -  using rat  5  -  hypothalamo-neurohypophysial osmolality  explants  induced' with  also demonstrated that  hypertonic  solutions  of  saline  an  increase  in  or  mannitol  caused AVP r e l e a s e , and that reduction of osmolality reduced AVP  release (Sladek and Knigge 1977). A l t e r n a t i v e l y , Andersson (1971) proposed that AVP release i s regulated by a sodium-sensitive mechanism, or "sodium r e c e p t o r " , present in the walls of  the  third  ventricle,  concentration  of  the  evidence  a  sodium  for  would  of  sodium c h l o r i d e  (i.c.v.)  the  of  fluid  is  not  the  would  increase  (CSF).  of  The  by  the  osmolality  both  or  goats,  supporting  the  effect,  concept  osmoreceptor (Eriksson 1974). saccharide antidiuresis  solutions due to  (Olsson 1973).  into  of  the  yet  the  hypertonic  convincing  not  that  sodium  hypertonic  osmolality  produce a n t i d i u r e s i s  isotonic  sodium  sucrose s o l u t i o n ,  antidiuresis;  increase  the  observations  but  and  (Olsson 1969).  saccharide  into the t h i r d v e n t r i c l e , which would be expected to concentration by a d i l u t i o n a l  in most  hypertonic  produce  CSF, did  of  an  provided  increase the  which  administration  to  injection  CSF, did  solution,  sodium concentration The i . c . v .  receptor  be expected to  concentration  responds  cerebrospinal  intracerebroventricular which  which  solutions  decrease CSF sodium  i n h i b i t e d AVP release i n normovolemic a  sodium  receptor  rather  than .an  Moreover, infusions of i s o t o n i c or hypertonic  a lateral  intracarotid  ventricle  infusion  were shown to  of  hypertonic  inhibit  the  saline  solution  McKinley et a l . (1978) showed that the i n t r a c a r o t i d  infusion  of hypertonic urea s o l u t i o n in sheep caused a much greater increase in CSF sodium concentration solutions, This  would  influences blood-brain  and yet suggest  than  infusion  was much less that  AVP r e l e a s e , barrier  did  of  effective  an osmoreceptor and  since  that  hypertonic  the  circulating  in  saline  stimulating  rather  receptor hypertonic  than is  or  antidiuresis.  a sodium  located urea  sucrose  receptor  outside  solution  the  should  - 6 -  provide an osmotic stimulus to which i t i.c.v.  does not  rapidly  administration  of  a receptor within the  penetrate.  However, they  hypertonic  saline  in  blood brain also found  artificial  barrier that  the  CSF produced a  greater a n t i d i u r e t i c e f f e c t than the i . c . v . i n j e c t i o n of equiosmolar sucrose solutions  which  produced  an  identical  decreased sodium concentration. osmoreceptor-sodium  receptor  elevation  As a r e s u l t ,  system mediates  of  they  CSF osmolality proposed that  AVP r e l e a s e ,  osmoreceptors located outside the blood-brain b a r r i e r  but  a dual  involving  both  and sodium receptors  w i t h i n the blood-brain b a r r i e r . More clarified infusion  recent the  of  conscious  studies  issue of  by  osmoreceptors  hypertonic  solutions  dogs was shown to  concentration  of  the  Thrasher  of  et a l .  versus saline,  (1980a,b)  sodium receptors.  yet  only  osmolality  (Thrasher et a l . 1980a). by  a sodium  receptor  It  hypertonic  the CSF i s not  AVP  outside  release,  concentration. receptor  These  either  the  infusion of  saline  barrier.  or  of  with  the the  i.v.  urea  and  a stimulus f o r  blood-brain  in  sodium sucrose  elevation AVP release  outside  the  since  out  decreased the  plasma  existence  blood-brain  of  barrier.  of  On the other hand, the i . v .  osmoreceptors  within  in  sodium a  sodium  The  i.v.  increased both  CSF and the plasma AVP concentration, existence  hypertonic  as hypertonic s a l i n e s o l u t i o n  significantly rule  barrier  hypertonic sodium c h l o r i d e or sucrose solutions  the osmolality consistent  but  observations  within  The  i s also u n l i k e l y that AVP release i s mediated  sucrose s o l u t i o n was equally as e f f e c t i v e causing  have  and the  solutions increased plasma AVP concentration suggesting that the of the sodium concentration of  to  sucrose, glucose or  increase both the  CSF, and  appear  the  observations blood-brain  infusion of hypertonic glucose or urea  solutions also elevated both the osmolality and the sodium concentration of the  CSF, but  did  not  cause AVP release.  While these  substances  readily  - 7 penetrate  most c e l l s ,  they penetrate  the  blood-brain  barrier  very  slowly,  and should provide an osmotic stimulus within the b a r r i e r by causing osmosis of water across the b a r r i e r . cause AVP release after not  The observation that these solutions  i.v.  infusion  located within the blood-brain  such  as the  terminalis  subfornical were  organ  proposed  as  or  suggests that the osmoreceptors  barrier. the  a  The circumventricular  organum  possible  vasculosum of  anatomical  osmoreceptors (Thrasher et a l . 1980b), although i t that  neurons  in  the  supraoptic  do not are  organs,  the  lamina  of  these  site  has also been suggested  nucleus may detect  osmotic  stimuli  (Leng  et a l . 1982). Non-osmotic s t i m u l i  of AVP release include changes in blood pressure  or blood volume, hypoxia, nausea, hormones, surgery and other stimuli.  It  i s f a i r l y c l e a r that the c a r o t i d sinus baroreceptors  the release of AVP.  S c h r i e r and Berl  increasing  carotid  concentration  in  influence  Carotid occlusion has been shown to cause AVP release  or a n t i d i u r e s i s (Share and Levy 1962; 1967;  stress-related  1972).  sinus dogs  afferents, possibly a t r i a l  Stimulation  pressure  (Thames  Share 1965;  has  and  of  been  Schmid  Clark and Rocha e S i l v a arterial  shown  to  1981).  baroreceptors reduce  Receptors  by  plasma AVP with  vagal  receptors, have been shown to i n h i b i t AVP release  in anesthetized dogs with s i n o - a o r t i c denervation (Thames and Schmid 1979), as well as in conscious dogs with a o r t i c or s i n o - a o r t i c denervation et a l . 1984).  It  has also been reported that when c a r o t i d  (Bishop  sinus pressure  was held constant at 50 mmHg or 135 mmHg, vagal cold block increased plasma AVP  levels,  but  when c a r o t i d  sinus  pressure  was  increased to  200 mmHg,  plasma AVP l e v e l s decreased with vagal cold block (Thames and Schmid 1981). These studies suggest that there may be an i n t e r a c t i o n between baroreceptors and a t r i a l receptors i n the regulation of AVP r e l e a s e .  - 8 The l e f t (Gauer  atrial  and Henry  studies  showed  receptors  1963;  that  a small  abolished  by b i l a t e r a l  workers  showed  More  left  atrium was Vagotomy  Schrier  of  left  left  (Henry  shown  et a l .  of  cause d i u r e s i s cause  left  in  diuresis  which  was  shown  of dogs  antidiuresis  hypophysectomy (Schrier and Berl 1972). tachycardia,  to  1972).  pressure  1956).  1965;  atrial  receptors  which  AVP  (Ledsome  Linden  In a d d i t i o n , left  and  abolished  In contrast  by left  1968).  by  acute atrial caused  vagotomy  Kappagoda et a l .  (1975) did not observe a change in bioassayable AVP l e v e l s a f t e r distension in dogs.  and  pressure,  to these observations,  other levels  pacing-induced  atrial  was  achieved  vein  was  by  Johnson et a l .  in dogs which was abolished by acute hypophysectomy or  (Boykin et a l . 1975).  of  the pulmonary  which  increase  plasma  et a l .  Early  produced  A number  reduced  Shu'ayb  stimulation  to  atrial  distension  1965;  and Berl  atrium caused d i u r e s i s  balloon at the junction  shown to  was  the  atrial  (Share  localized  i n f l a t i n g a small  in  vagotomy  that  1964;  elevation  balloon  measured by bioassay 1969).  Perlmutt  the  inflating  have been proposed to regulate AVP release  left  atrial  These e a r l y studies were subject to the l i m i t a t i o n that  plasma AVP l e v e l s were e i t h e r not measured or the bioassay procedure used to measure AVP was not s e n s i t i v e enough to detect small changes in AVP l e v e l s . More recent studies using radioimmunoassay techniques showed that AVP l e v e l s decreased a f t e r et a l . 1975). in  atrial  Left a t r i a l  anesthetized  et a l . 1982;  left  dogs  distension  (Johnson et a l .  1969;,  de  Torrente  distension also reduced plasma AVP concentration  (Ledsome et a l .  1983)  and in  conscious dogs  Schultz et a l . 1982), but not after vagal cold block, or  cardiac denervation, r e s p e c t i v e l y .  Stimulation of  (Fater after  left  atrial  receptors  i n f l a t i o n of a balloon placed at the pulmonary v e i n - l e f t  atrial  junction was  also shown to decrease plasma AVP l e v e l s Ledsome 1983).  Direct stimulation  by  in anesthetized dogs (Wilson and  of cardiac receptors with vagal  afferents  - 9 by i n j e c t i o n although i t  of veratrum a l k a l o i d s has been shown to  i n h i b i t AVP r e l e a s e ,  i s not c l e a r whether the response was mediated by l e f t a t r i a l  or  v e n t r i c u l a r receptors (Thames et a l . 1980).  These studies provide evidence  to  atrial  suggest  that  the  stimulation  of  left  receptors  inhibits  AVP  release. Small  reductions  (<10  percent)  in  blood volume have been shown  increase the release of AVP, an e f f e c t which may be mediated by l e f t receptors  (Share 1968;  that  pathway may mediate AVP release in  this  hemorrhage Share  Claybaugh and Share 1973).  (Share 1968;  1974).  Moderate  Henry et a l . or  severe  It  atrial  has been suggested  response to  1968;  to  non-hypotensive  Claybaugh and Share 1973;  hemorrhage  has  been  shown  to  be  an  extremely potent stimulus f o r the release of AVP (Ginsburg and H e l l e r 1953; Weinstein  et a l .  1960;  Szczepanska-Sadowska 1973;  1972;  not c l e a r i f large  Silva  of  hypotensive hemorrhage.  and  Share  Rosenberg  1973;  Weitzman et a l . 1978;  Pullan et a l . 1980;  left atrial  elevations  e  Claybaugh and  Arnauld et a l . 1977;  Laycock et a l . 1979;  of  Rocha  1969;  Cousineau et a l .  Bierman et a l . 1979;  Fyhrquist et a l . 1981).  It  is  receptors play an important r o l e in the mediation plasma AVP concentrations  in  response  to  more  Vagotomy has been shown to s i g n i f i c a n t l y reduce the  increase in plasma AVP concentration which occurs in response to hypotensive hemorrhage  (Clark  relationship  was  concentration  in  and Rocha e S i l v a found  to  exist  anesthetized  dogs  1967;  between in  Share 1968). blood  which  volume  elevation  A  logarithmic  and  plasma AVP  of  blood  volume  resulted in a reduction in plasma AVP l e v e l s while reduction of blood volume led  to  an  increase  in  plasma AVP concentration  (Ledsome et a l .  1985).  However, i t was also found that the plasma AVP concentration was more highly correlated with mean a r t e r i a l suggesting that the l e f t a t r i a l  pressure than with mean l e f t a t r i a l  pressure,  receptors are u n l i k e l y to provide the major  -10  -  stimulus f o r AVP release during large changes in blood volume. studies  in  anesthetized rabbits  significant arterial  elevation  pressure  aortic,  of  1986).  type  and r i g h t  species  atrial  sinus  may stimulate  Whether t h i s is  not  baroreceptors  afferent  is  receptors  regulation of AVP r e l e a s e ;  even a f t e r  nerves,  studies do  hemorrhage caused  and reduction  hemorrhage  suggest  mean  of  that  (Rankin et a l .  that  both  in  the  another  or extends to  participate  however the r e l a t i v e  of  section  suggesting  unique to the rabbit  These  atrial  pressure,  AVP release during  finding  clear.  and  10 percent  plasma AVP concentration  vagus and c a r o t i d  receptor  showed that  Subsequent  the  other  arterial  non-osmotic  r o l e s of the two receptor  types in various pathophysiological conditions has yet to be e l u c i d a t e d . Other pathways have also been implicated in the non-osmotic release of AVP,  including  center  chemoreceptors  (Robertson 1977)  1973).  (Share and Levy 1966),  and a cerebral  Hypoxia has been shown to  (Forsling  and  Ullmann  conscious rats 1977) .  1977),  pain center  the  (Bhatia et a l . 1977)  sheep but  (Alexander  not  to  a surgical  anesthetized dogs et a l .  in man ( F o r s l i n g  Pain pathways may also influence AVP r e l e a s e .  reporting  emergency department  with  emetic  (Hayward and Jennings  cause AVP release in  fetal  cerebral  1972),  and Ullmann  A group of  pain  had  and  patients  significantly  higher l e v e l s of plasma AVP than a control group of p a t i e n t s , although there was no difference et a l .  1978).  Emesis  1978) are powerful which  AVP release  unclear,  it  baroreceptor  in  is tone  plasma osmolality (Robertson 1977)  stimuli is  that  during  in  these conditions (Schrier et a l . 1979).  the  two  groups  (Kendler  sickness ( F e l a l  et a l .  Although the mechanisms through hypoxia,  sympathetic  may p a r t i c i p a t e  the  and motion  of AVP r e l e a s e .  stimulated  possible  between  nausea and pain  stimulation mediation  of  or  remain  alteration  AVP release  of  under  - 11 Anesthesia has been implicated in the release of AVP, although  recent  evidence suggests that the large amount of AVP released i s more l i k e l y to be associated with s u r g i c a l stress since the induction of anesthesia was found to cause l i t t l e change in plasma AVP l e v e l s , but subsequent surgery released large amounts of AVP (Moran et a l . 1964; et a l . 1968; 1976;  Bonjour and Malvin 1970;  Ishihara et a l . 1978;  Moran and Zimmerman 1967;  Oyama et a l . 1971;  P h i l b i n and Coggins 1978;  Ukai  P h i l b i n et a l .  Wu et a l .  1980).  Moreover, inadequate anesthesia, indicated by the return of corneal or r e f l e x e s , was reported  to  increase plasma AVP concentrations  The l a t t e r  is  also consistent  observation  with the  (Ukai  involvement  of  limb  1971). a pain  pathway in the release of AVP. Hormones may also modulate (1970)  suggested  intra-arterially, dogs,  later  altered nor  water  showed  excretion  infusion  angiotensin  in  angiotensin  reported  cause AVP r e l e a s e , II  been shown to  to  AVP  II  angiotensin  Bonjour  infused  such  angiotensin  and Malvin  intravenously  II  in  isolated  (Claybaugh II  (Keil  pituitary  et a l .  infusions  et a l .  glands  suggesting that  may modulate AVP r e l e a s e .  1972).  1975) (Gagnon  neither  brain  and a p p l i c a t i o n  rather  1975) than  Centrally-administered  release AVP (Yamamoto et a l .  1978).  diuresis  However,  et a l .  or  anesthetized  anesthetized animals undergoing water  bioassayable of  that  angiotensin to  II,  While  increased bioassayable plasma AVP l e v e l s  studies  increased  i.c.v.  that  AVP r e l e a s e .  TSH, t h y r o i d  both of were  plasma  PGE2 has hormones  (Skowsky and Fisher 1977), estrogen, progesterone and androgens (Skowsky and Swan 1977) have a l l been suggested to modulate AVP r e l e a s e . 1.2.4  P h y s i o l o g i c a l r o l e of AVP.  Although i t was the pressor action  of AVP which was f i r s t observed, the conventional p h y s i o l o g i c a l r o l e of AVP i s that of an a n t i d i u r e t i c  hormone.  The p a r t i c i p a t i o n  conservation of water was f i r s t noted by Verney in 1947.  of AVP in the renal AVP i n t e r a c t s with  - 12 receptors on the basolateral surface of the c o r t i c a l of  the  collecting  duct,  increasing the  water and thereby f a c i l i t a t i n g designated V  and medullary segments  permeability  water reabsorption.  of  these segments  to  The renal AVP receptors,  receptors, act through the adenylate cyclase system (Michel 1  2  et a l . 1979). Many studies have attempted Krogh  (1929)  reported  that  to  in vivo  assess the  vascular e f f e c t s  application  of  posterior  extracts to the c a p i l l a r y bed in the webbed feet of frogs dogs caused v a s o c o n s t r i c t i o n , to  these v e s s e l s .  and peripheral  pituitary  and the ear of  and that hypophysectomy increased blood flow  More recent  crude p i t u i t a r y extracts  of AVP.  studies  have shown that  administration  or P i t r e s s i n increased systemic a r t e r i a l  vascular resistance in rats  pressure  (Bisset and Lewis 1962;  et a l . 1965), rabbits (Friedman and Pauls 1952), cats (Barer 1961; and Pauls 1952), dogs ( C a r l i e r et a l . 1960; (Davis  et a l .  1957).  Although  arterioles,  it  was generally  insensitive  to  the  Saameli 1968). fact  more  hormone  it  was  even than  clear  believed that (Sawyer 1961;  angiotensin  that  blood  Friedman  Mellander  II  (1977) in  AVP could  vessels  constrict  were  relatively  and Johansson 1968;  showed that AVP was  constricting  a r t e r i o l e s , mesenteric resistance vessels and a o r t i c  rat  strips.  It  at  10"  to  1 3  10"  1 2  M  (Altura  1973).  Vascular  should be levels  responses  appeared to be dependent on the species and the vascular bed.  in  terminal  noted that v a s o c o n s t r i c t i o n could be e l i c i t e d with p h y s i o l o g i c a l AVP  Altura  C o r l i s s et a l . 1968) and humans  However, A l t u r a and A l t u r a  potent  of  to  of AVP  AVP was found  to cause potent coronary vasoconstriction in the dog heart-lung  preparation  (Bodo 1927), in anesthetized dogs (Wegria et a l . 1940) and in conscious dogs (Essex  et a l .  constriction hepatic  1940). in  arterial  The  splenic beds  and  infusion  of  intestinal  (Cohen et a l .  AVP in vascular  1970).  anesthetized beds  but  The g r a c i l i s  cats  caused  dilatation muscle  is  in more  - 13 s e n s i t i v e than the mesenteric beds to the vasoconstrictor e f f e c t of AVP, and these in turn are more s e n s i t i v e than the renal (Schmid et a l . 1974). veins  (Sutter  bed in  AVP also appears to have l i t t l e  1965;  Stamm 1972),  although  in  anesthetized dogs effect  on i s o l a t e d  human umbilical  concentrations of AVP were shown to cause r e l a x a t i o n  vein,  (Somlyo et a l . 1966).  As w e l l , in vivo experiments have shown that AVP has l i t t l e e f f e c t c i r c u l a t o r y f i l l i n g pressure, an index of t o t a l Tabrizchi  1986).  The AVP receptors  present  body venous tone on  high  smooth  on mean (Pang and  muscles  (Michel 1  et a l . 1979), as well as those present on hepatocytes which mediate hepatic glycogenolysis  (Gopalnakrishnan  et a l .  1986),  have  been  classified  V}  receptors, and are believed to use phosphoinositides and calcium as second messengers. It  has been reported  blood pressure response to  that  subpressor doses of  noradrenaline  dogs (Bartelstone and Nasmyth 1965). the vasoconstrictor e f f e c t s in v i t r o  in  i s o l a t e d rat  response of  mesenteric  indomethacin,  of  AVP can enhance  the  and adrenaline in c a t s , rats  and  AVP has also been shown to  noradrenaline,  mesenteric a r t e r i e s artery  to  angiotensin  II  and potassium  (Karmazyn et a l .  AVP was diminished  in  1978).  the  suggesting that prostaglandins may play a r o l e  potentiate  The  presence  of  in  mediating  of  pituitary  the vascular e f f e c t of AVP (Manku and Horrobin 1977). Based  on  his  observations  of  the  vascular  effects  e x t r a c t s , Krogh (1929) proposed that p o s t e r i o r p i t u i t a r y hormones might have a tonic  constrictor  influence  on peripheral  p a r t i c i p a t e in the regulation of blood flow.  blood  vessels  and  therefore  Many studies have attempted to  determine whether AVP has a p h y s i o l o g i c a l r o l e in the maintenance of pressure.  To  produce  a  10 mmHg  conscious dogs (Cowley et a l . 1974; et a l .  1979;  Morton  et a l .  increase  in  blood  pressure  in  Montani et a l . 1980) and rats  1982),  AVP  was  infused  at  a  blood intact  (Mohring rate  of  - 14 1-2 ng/min/kg, a dose corresponding to a 30-80 pg/ml increase in plasma AVP concentration.  In humans, infusions of AVP which increase plasma AVP l e v e l s  by 50-500 pg/ml were shown to have l i t t l e e f f e c t on blood pressure (Padfield et a l .  1976;  Mohring  concentration 1977).  of  et a l .  AVP in  humans i s  Bussien et a l . (1984)  pressor  antagonist  1980);  the  in  the  normal range  of  reported that i n j e c t i o n  d(CH2)gTyr(Me)AVP  in  physiological 1-5 pg/ml  plasma  (Robertson  of the s e l e c t i v e AVP  healthy,  normally  hydrated  subjects did not affect blood pressure, heart rate or skin blood f l o w , even after  inactivation  of  the  renin-angiotensin  system with c a p t o p r i l .  Since  plasma l e v e l s of at least 50 pg/ml are required to elevate blood pressure a concentration  10-100 times  both the  normal  physiological  level  and the  l e v e l required to achieve maximal a n t i d i u r e s i s - and AVP pressor antagonists have l i t t l e effects  effect  of  AVP  significance. increase  1980).  have  been  However,  blood  et a l . 1974)  on blood pressure under normal c o n d i t i o n s , the vascular  pressure  considered  to  low concentrations after  and in patients  be of  baroreceptor with autonomic  of  little  AVP have  physiological  been reported  denervation  in  insufficiency  (Mohring  It was also shown that AVP antagonist decreased a r t e r i a l  conscious,  water-replete  rats  ganglionic  blockade  adrenalectomy  I r i u c h i j i m a to  or  suggest that  only  after  sinoaortic  (Iriuchijima  dogs  (Cowley et a l .  pressure in  denervation 1983).  the AVP system may be r e c r u i t e d  to  and  This to  led  maintain  blood pressure only a f t e r f a i l u r e of the sympathoadrenal system. It  has been suggested that AVP may increase the  sensitivity  of  baroreceptor r e f l e x , since AVP produces a greater reduction in heart rate  the in  response to equivalent increases in blood pressure than other pressor agents (Heyndrickx On the other  et a l . 1976;  Mohring et a l . 1981;  hand, Brattleboro  rats,  s e n s i t i v i t y of the baroreceptor r e f l e x  which  Lumbers and Potter  lack AVP, d i s p l a y  1982).  a decreased  system which can be restored by the  - 15 administration  of  AVP (Imai  et a l .  1983).  I.v.  infusions  of AVP produce  only small elevations of blood pressure in animals with i n t a c t (Cowley  et a l .  inactivation, significantly  1974;  infusion  of  et a l .  physiological  and  in  doses  After  of  conscious dogs  in  conscious  baroreceptor denervation,  identical  increased  a reduction  interaction  1974;  total  to  Cowley  a vertebral  Liard et a l .  artery  peripheral  in cardiac output;  Evidence suggests that  between AVP and the baroreceptor r e f l e x  nervous system (CNS).  AVP into  shown  AVP l e v e l s led to an increase in  blood pressure since cardiac output was not reduced.  central  was  (Cowley et a l .  dogs  r e s i s t a n c e , but not blood pressure, due to  this  AVP  baroreceptor  Moreover, Montani et a l . (1980) found that small increases in  plasma AVP concentrations  after  1980).  increase blood pressure in anesthetized dogs (Rocha e S i l v a  and Rosenberg 1969) et a l . 1983).  Montani  baroreceptors  (1981)  caused greater  occurs within  showed that infusion  reflex  bradycardia than  the of i.v.  infusion of the same dose of AVP.  Infusion of AVP in r a b b i t s was shown to  i n h i b i t lumbar sympathetic efferent  nerve a c t i v i t y but did not change a o r t i c  baroreceptor centrally  afferent  activity  (Guo et a l .  (1985) proposed the baroreflex  Based  on  It  is  Injection  anesthetized rabbits  not  lesion  of  AVP  into  produced a small  influence  the  the  sensitization  studies,  at which AVP acts to enhance  resting  the  isolated  activity  sensitize  carotid  increase in the a c t i v i t y It  occurs  Undesser et a l .  possible that AVP may also l o c a l l y  sinus nerves (Holmes and Ledsome 1984). AVP did  that  area postrema as a s i t e  activity.  baroreceptors.  1986).  suggesting  sinus of  carotid  has also been shown that of  single  fibres  from  while aortic  baroreceptors in anesthetized r a b b i t s , or from l e f t v e n t r i c u l a r receptors anesthetized c a t s ,  it  e l e v a t i o n of a r t e r i a l in rabbits  significantly  enhanced s i n g l e f i b r e  pressure and l e f t  and cats r e s p e c t i v e l y  ventricular  activity  end-diastolic  (Abboud et a l • 1986).  in  in  during pressure  Therefore AVP may  - 16 facilitate  the baroreceptor r e f l e x  This extremely e f f e c t i v e why AVP, although i t  buffering  by both central  of the pressor e f f e c t  actions.  of AVP may explain  i s a potent vasopressor agent, does not normally appear  to increase blood pressure in animals with i n t a c t In addition to i t s a n t i d i u r e t i c of other e f f e c t s .  and peripheral  baroreceptors.  and vascular a c t i o n s , AVP has a number  AVP has been found to be e f f e c t i v e  hemophilia and von Willebrand's  disease,  since i t  in the management of  can increase l e v e l s  f a c t o r VIII p o s s i b l y by inducing i t s release from vascular endothelium.  of The  secretion of adrenocorticotropic  hormone i s stimulated by AVP which reaches  the  hypophyseal  anterior  pituitary  via  the  portal  circulation  et a l . 1977).  An area which has generated much i n t e r e s t  possible  of  role  facilitate  AVP as  memory  a  central  consolidation  Weingartner et a l . 1981).  neurotransmitter.  (de  Wied  1976;  recently Central  Kovacs  Central AVP may p a r t i c i p a t e  (Zimmerman is  the  AVP may  et a l .  1979;  in the regulation  of  body temperature since a number of studies have shown that central AVP has antipyretic also  been  neurons 1980;  properties reported  since  it  Kasting  spontaneous  (Cooper et a l .  that  central  1979;  AVP may  can cause convulsions et a l .  water  1980).  intake  In  Veale et a l . influence  in  addition,  permeability of the brain to water  the  conscious central  (Szczepanska-Sadowska  1981).  It  has  excitability  rats  (Abood et a l .  AVP may  1982),  of  influence  regulate  (Raichle and Grubb 1978),  and  the  control  CSF absorption by the choroid plexus (Schultz et a l . 1977). 1.2.5 Since  the  hemorrhage,  Role of AVP in hemorrhage, dehydration levels  of  dehydration  AVP  detected  and in  in  and s u r g i c a l  volume-depleted  s t r e s s - r e l a t e d conditions  stress.  states  such  as  such as surgical  stress are much greater than required f o r maximal a n t i d i u r e s i s , a number of studies have examined the r o l e of these c o n d i t i o n s .  AVP in  blood pressure regulation  The amount of AVP secreted in  response to  under  hypotensive  - 17 hemorrhage  was found  to  be  sufficient  to  cause  a pressor  response  in  anesthetized dogs in which the baroreceptor r e f l e x e s were suppressed (Rocha e S i l v a and Rosenberg 1969).  Infusion of pathophysiological  amounts of AVP  (equivalent to l e v e l s of plasma AVP induced by conditions such as surgery or hemorrhage) increased blood pressure in conscious dogs (Szczepanska-Sadowska 1973). in  Blood loss of 1 percent of body weight did not affect blood pressure  control  rats,  but  decreased blood  pressure  diabetes i n s i p i d u s (Laycock et a l . 1979).  in  Brattleboro  rats  with  Dogs with diabetes i n s i p i d u s have  also been shown to be more susceptible to hemorrhage than normal  dogs, an  e f f e c t that can be reversed by the administration of P i t r e s s i n (Frieden and K e l l e r 1954).  An AVP pressor antagonist  subjected .to s u r g i c a l  stress  administered to  (Pang 1983a)  or  anesthetized  hypotensive  hemorrhage  1983b) was found to decrease blood pressure through  a reduction  peripheral  of  r e s i s t a n c e , and increase the d i s t r i b u t i o n  skin and stomach. the  maintenance  of  the pressor e f f e c t  blood  blood  pressure  denervation  after  in  total  blood flow to  non-hypotensive  administration  of  AVP was also found  after  hemorrhage  and i n a c t i v a t i o n  of  in  the  the in  hemorrhage  in  of a s e l e c t i v e antagonist  of  of AVP decreased blood pressure in  antagonist  pressure  (Pang  Schwartz and Reid (1981) found that AVP p a r t i c i p a t e s  conscious dogs, since the i . v .  vascular  rats  to  animals  prevent  dogs. the  subjected  renin-angiotensin  A selective  restoration to  of  baroreceptor  system, leading  the  authors to conclude that AVP released in hemorrhage can function as a rapid and potent system to maintain blood pressure (Cowley et a l . 1980). Dehydration r e s u l t i n g from r e s t r i c t i o n to  increase plasma AVP l e v e l s  produce  significant  hemodynamic  Aisenbrey et a l . 1981). conscious dehydrated  to  rats  of water intake has been shown  10-30 pg/ml, effects  The i n j e c t i o n  of  an increase s u f f i c i e n t  (Andrews  and  Brenner  a vascular antagonist  (Aisenbrey et a l .  1981)  and dogs  to  1981;  of AVP in  (Schwartz  and  - 18 Reid 1983) s i g n i f i c a n t l y decreased blood pressure. shown  that  the  injection  of  an  AVP  In c o n t r a s t ,  pressor  antagonist  dehydrated rats did not decrease blood pressure even a f t e r renin-angiotensin  system (Fejes-Toth  et a l .  1985).  i t has been  in  conscious  blockade of  Rascher  et a l .  found that an AVP vascular antagonist decreased t o t a l peripheral  the  (1985)  resistance  but did not decrease blood pressure in conscious dehydrated rats unless they were  also  subjected  administration  of  osmolality  pressure  sino-aortic  AVP antiserum  induced by g l y c e r o l plasma  to  (a condition increased)  (Hofbauer  in  et a l .  anesthetized  in  was  denervation.  which  found  1977).  It  Furthermore,  rats  with  plasma volume  to  renal is  significantly  may be  argued  the  failure  reduced  decrease  that  while  antagonist may not decrease blood pressure under some c o n d i t i o n s ,  and blood  an AVP it  does  decrease peripheral r e s i s t a n c e , suggesting that endogenous AVP has vascular actions. renal  In summary, in pathophysiological  failure  and  possibly  dehydration,  conditions AVP  may  such as hemorrhage, participate  in  the  short-term maintenance of blood pressure and peripheral r e s i s t a n c e . 1.2.6  Role of AVP in hypertension.  Since AVP may be involved  in  cardiovascular regulation and p a r t i c i p a t e s in the regulation of f l u i d volume through  its  antidiuretic  actions, i t  have a r o l e in hypertension.  development However,  of  (SHR),  this  a selective  speculate that  it  may  Both an increase in plasma AVP l e v e l and  s e n s i t i v i t y to the pressor e f f e c t rat  to  The r o l e of AVP in a number of animal models  of hypertension has been examined.  hypertensive  i s tempting  of AVP were reported in the spontaneously  suggesting  genetic model antagonist  of  that  of  AVP may  hypertension  the  pressor  but  play  a  (Hoffman not  the  role et a l .  in  the  1977).  antidiuretic  effect of AVP produced only a small reduction in blood pressure in ten-week old SHR.  It  has also been reported that s p e c i f i c AVP antiserum decreased  blood pressure in stroke-prone SHR with well-developed hypertension  (Mohring  - 19 et a l .  1979).  AVP i s  certainly  not  essential  for  the  development  of  spontaneous hypertension since Ganten et a l . (1983) have developed a s t r a i n of SHR which also develop hypothalamic diabetes i n s i p i d u s . possible that AVP may contribute  to t h i s form of  Therefore i t  hypertension only in  is its  l a t e r stages. Increases  in  both plasma AVP l e v e l s  (Matsuguchi  et a l .  1981; Share  et a l . 1982) and-urinary excretion of AVP (Share et a l . 1982) were observed in Dahl s a l t - s e n s i t i v e rats fed a high s a l t d i e t . responsiveness was also observed (Matsuguchi  Although enhanced pressor  et a l . 1981), suggesting that  AVP plays a r o l e in t h i s model of hypertension, i n j e c t i o n antagonist did not decrease blood pressure (Matsuguchi et a l . 1982). crucial  of an AVP pressor  et a l . 1981;  F a i r l y convincing evidence e x i s t s to suggest that AVP plays a  role  in  the  hypertension.  Friedman  contribute  the  to  development et a l .  of  another  (1960)  pathogenesis  of  first  form  of  suggested  the  development  denervation prevented Brattleboro  it.  1980)  Marchetti  hypertension,  This type of  and  et a l .  Furthermore,  Both plasma l e v e l s  renal  excretion  1980)  were  in rats  of  that  AVP  may  (DOC/salt)  of exogenous AVP  and  neurohypophyseal  hypertension cannot be induced  rats with diabetes i n s i p i d u s , except  (Berecek et a l . 1982). et a l .  of  salt-related  deoxycorticosterone/salt  hypertension based on studies in which the administration accelerated  Share  AVP  increased  in  after  treatment with AVP  (Mohring et a l . (Crofton  1977;  et a l .  DOC/salt  subjected to the administration  1979,  hypertensive of  either  Crofton 1980; rats.  a specific  AVP antiserum  (Mohring et a l . 1977) or an AVP pressor antagonist  et a l . 1979;  Mento et a l . 1982)  a significant  in  (Crofton  decrease in blood pressure  was observed. Although plasma AVP l e v e l s have been reported to be elevated in one kidney-one c l i p renal hypertensive rats (Pullan et a l . 1980), i t  is  unlikely  - 20 that AVP i s since i t  essential  for  the  development  can be produced in Brattleboro  50 percent  of  rats  subjected  to  two  of  rats  this  not  hypertension significant  critical  (Johnston role  to  et a l .  in t h i s  plasma concentration  the  development 1981)  type  of  and urinary  clip  a reduction  response to AVP antiserum (Mohring et a l . 1978). system i s  of  hypertension,  (Johnston et a l . 1981).  kidney-one  displayed elevated plasma AVP l e v e l s or  type  of  in  two  hypertension. of  hypertension  blood pressure  An i n t a c t  clip  AVP does not  Significant  However, i t  action of AVP i s s o l e l y responsible f o r  increases  AVP were observed in  1981).  It  is  possible  rats saline  the r e s u l t i n g hypertension since a  however,  hypertension through i t s a n t i d i u r e t i c  in  i s u n l i k e l y that the pressor  pressor antagonist did not decrease blood pressure in these rats et a l .  renal play a  which had 70 percent of the renal mass removed and were given normal to drink (Lee-Kwon et a l . 1981).  in  neurohypophyseal  kidney-one  suggesting that  excretion  renal  Only  that  effect,  AVP  (Lee-Kwon  contributes  since p a r t i a l  to  the  nephrectomy-salt  hypertension i s a volume-dependent model of hypertension. The r o l e  of  AVP i n  human e s s e n t i a l  Plasma AVP concentrations et a l .  1976;  Shimamoto  have et a l .  Elevated plasma AVP l e v e l s  been  effect  hypertension,  of but  AVP was the  level  reported  1979)  or  to  reported  be  elevated  have been observed in  hypertension (Padfield et a l . 1981). pressor  hypertension  is  controversial.  decreased  (Cowley  (Padfield  et a l .  patients  with  1981).  malignant  A small increase in s e n s i t i v i t y to the in  patients  was u n l i k e l y  with  sufficient  mild  to  to  account  moderate for  the  elevated blood pressure of these patients ( P a d f i e l d et a l . 1976). While  AVP l e v e l s  have  been shown to  hypertensive animal models, the r e s u l t i n g to  account  for  the  increase  in  blood  be  elevated  l e v e l s appear to pressure,  in  a number  of  be  insufficient  unless  appreciable  enhancement of the s e n s i t i v i t y to the pressor e f f e c t of AVP also occurs.  An  - 21 increased s e n s i t i v i t y AVP  levels,  as  salt-sensitive animals.  to AVP occurring in combination with elevated plasma  observed  rats,  in  DOCA-salt  may contribute  to  hypertensive elevated  rats,  blood  pressure  It has also been suggested that the a n t i d i u r e t i c  contribute  to  the  development  of  some forms  of  SHR and in  Dahl these  action of AVP may  hypertension,  especially  those i n v o l v i n g volume expansion (Share and Crofton 1984). 1.3  The sympathetic nervous system 1.3.1  Structure  of  the  sympathetic  nervous  system.  Injection  of  extracts of the adrenal gland were reported by O l i v e r and Schafer i n 1895 to increase blood pressure in animals.  The a c t i v e component, which was subse-  quently named adrenaline, was soon i s o l a t e d and i d e n t i f i e d Takamine 1901;  F i g . 2).  a l i n e (arterenol)  The primary homologue of adrenaline, d l - n o r - a d r e n -  was a r t i f i c i a l l y  that i t was as e f f e c t i v e mals  (Fig. 2).  similar  to  synthesized in 1904 by S t o l z , who observed  as adrenaline in increasing blood pressure in  The observation  stimulation  ( A l d r i c h .1901;  of  that  adrenal  sympathetic  extracts  nerves  led  to  produced responses the  suggestion  adrenaline was released from sympathetic nerves ( E l l i o t t 1904). was  suggested  responses  by  Barger  which were more  and  similar  those produced by adrenaline. substances  were  later  Dale  in to  Nerve, f i b r e s  classified  as  (Dale  it  produced  stimulation  which release  adrenergic  However  noradrenaline nerve  that  than  adrenaline-like  1933).  There  were  released by the sympathetic nerves  Through experiments involving stimulation of the hepat-  i c nerve, Cannon and U r i d i l  (1921) found evidence of a substance with sympa-  thomimetic actions which was not adrenaline. another series of  that  sympathetic  various i n d i c a t i o n s that the transmitter was not adrenaline.  1910  ani-  experiments  Cannon and Bacq (1931)  concluded that sympathetic  nerve  through  stimulation  led to the appearance of a substance other than adrenaline, which they named sympathin.  It was not u n t i l 1946 that von Euler established that the t r a n s -  mitter released by adrenergic nerves was noradrenaline.  -  L-Tyrosine  HO<f  22  >— C H — C H — N H 2  2  COOH Tyrosine hydroxylase  HO ,-DOPA  H  0  \  / ~  C  H  ^ - C H - N H  2  COOH l - D O P A decarboxylase  HQ. Dopamine  HO<(  7— C H — C H — N H 2  2  2  D o p a m i n e p-hydroxylase  HC Noradrenaline  HO<f  >-CH(OH)-CH -NH 2  2  Phenylethanoiamine W-mcthyltransferase  HQ Adrenaline  F i g . 2.  HO<f  7—  CH(OH)—CH —NH—CHj 2  The biosynthetic pathway for noradrenaline and adrenaline.  -23The general organization  and d i s t r i b u t i o n  system was described by Langley in 1921. is  comprised of  neurons  located  ganglia. (1933)  a chain of in  Early  the  at  by  established release  fibres that  of  as  neurons  (1933)  and  the  from  a  located  Feldberg  and  Rand  nicotinic  in  the  and Gaddum  chromaffin  (1959)  effect,  sympathetic  the  preganglionic  released by sympathetic  Burn  through  from  adrenaline  neurons:  of the transmitter  acetylcholine,  and  pathway  acetylcholine.  noradrenaline  noradrenaline  The sympathetic efferent  postganglionic  Kibjakow  led to the i d e n t i f i c a t i o n  preganglionic  nervous  least two types of  CNS and  experiments  of the sympathetic  nerve cells  then  caused  the  terminal of  the  and  adrenal  medulla which are anatomically r e l a t e d to autonomic g a n g l i a . Noradrenaline  is  synthesized  from  the  amino  acid  tyrosine  within  sympathetic nerve endings according to the pathway proposed by Blaschko in 1939  (Fig. 2).  adrenaline states  The  only  within  noradrenaline  in  synthetic  the  the  noradrenaline  chromaffin  neuron:  within within  pathway  where  it  chromogranins. 2+ Ca  -dependent  subsequently  is  Noradrenaline exocytosis acts  on  in  receptors  storage  exists  vesicles,  (Burnstock  ATP  and  released  and  the  acidic  from  to  the  nerve  effector  vesicles  by  The  Noradrenaline  subject  to  enzymatic  cells  catabolism  (uptake2). by  1975).  called  (uptake-^)  effector  bound  proteins  by reuptake  the  free  -dependent  impulses  organ.  and effects  a it of  i n t o the axons may  also  catechol-O-methyltransferase  monoamine oxidase, although enzymatic degradation i s much less important terminating the e f f e c t s of noradrenaline than reuptake.  of  three  and Costa  released noradrenaline are terminated p r i m a r i l y or  in  cytoplasm,  v e s i c l e s by an ATP and Mg  response on  in  synthesis  2+  with is  the  Noradrenaline  vesicles  stored  to  noradrenaline  membrane-bound  Noradrenaline i s taken up into the process  cells.  free  storage  continues  be and for  - 24 -  1.3.2  C l a s s i f i c a t i o n of  that the e f f e c t o r which  the  adrenoceptors.  1905, Langley proposed  c e l l s contained two d i f f e r e n t "receptive substances" with  released transmitter  excitatory  In  effects.  Cannon  combined  and  to  produce  Rosenblueth  (1933)  either  inhibitory  proposed  a  d i f f e r e n t concept of the receptor when they suggested that the sympathin combined with e i t h e r the  effector  properties rejected  tissues  on the after  available.  which  transmitter,  evidence in  somewhat  transmitter  of two receptive substances, E or I, conferred  either  respectively.  support  Although unaware of  its  of  excitatory This  theory  Langley s o r i g i n a l  within  or  inhibitory  was  eventually  proposal  1  or  s i g n i f i c a n c e at the time,  became  Dale  (1906)  made one of the f i r s t observations in support of the receptor theory when he blocked the pressor e f f e c t  of adrenaline in the spinal cat with  and provided the f i r s t demonstration of receptor antagonism.  Alquist  compared the r e l a t i v e potencies of a s e r i e s of sympathomimetic number of  different  adrenoceptors  into  tissues. two  This work resulted  distinctive  types:  ergotoxine (1948)  amines in a  in the c l a s s i f i c a t i o n  a-receptors  which  s e n s i t i v e to noradrenaline and adrenaline but are r e l a t i v e l y  are  of  highly  insensitive  to  isopropylnoradrenaline, and e-receptors at which the order of potency of the amines  was  isopropylnoradrenaline  >  adrenaline  >  noradrenaline.  The  a-adrenoceptors were found to be located p r i m a r i l y in the vasculature, while the B-adrenoceptors were found 6-adrenoceptors  in the heart,  muscles.  The  were  &2 types,  based on the d i f f e r e n t  vasculature and other  eventually  subclassified  sensitivities  of  smooth  into  a number of  and  tissues  to  various 3-adrenergic agonists (Lands et a l . 1967). It  also gradually  became apparent  comprise a d i s c r e t e population. the a-adrenoceptor  antagonists  the  noradrenaline  overflow  of  that  the  a-adrenoceptors  Brown and G i l l e s p i e (1957)  by  nerve  not  observed that  dibenamine and phenoxybenzamine elicited  did  potentiated  stimulation  in  the  --25 blood-perfused overflow  cat  spleen.  of transmitter  At  the  time  to occupation of  they  attributed  the  the p o s t - j u n c t i o n a l  increased  receptors  the antagonist, r e s u l t i n g in higher l e v e l s of unbound t r a n s m i t t e r the neuroeffector of  junction.  While phenoxybenzamine i n h i b i t s  noradrenaline released by nerve s t i m u l a t i o n ,  uptake,  it  was shown that  enhanced overflow  of  these e f f e c t s  noradrenaline  caused by  the  Starke et a l . hypothesis  terminals  was  phenoxybenzamine  that  decreased  negative  feedback  the  It  was  subsequent  1972;  release  (Langer  et a l .  Starke 1972;  Phenoxybenzamine was then  blocking p o s t - j u n c t i o n a l  proposed  on  the  that  of 1971;  to  the  Farnebo  findings,  be 30 times  nerve  neuroeffector through  a  and Hamberger  1973;  a-receptors than p r e - j u n c t i o n a l  other  pre-junctional  noradrenaline  Rand et a l .  found  and  adrenergic  in  the  Langer and Vogt  these  present  in  neuronal  Based on these  present  by noradrenaline  mechanism  Enero et a l .  were  a-receptors  postulated.  junction  1974).  Enero et a l . 1972).  when activated  a-receptors  1971;  1971;  its  account f o r  a-adrenergic antagonists such as phentolamine (Langer 1970; 1971;  present  the metabolism  and i n h i b i t s  alone could not  by  Langer 1973,  more  potent  receptors  in  mediating  noradrenaline r e l e a s e , suggesting that these two types of receptors were not identical Langer  pharmacologically  (1974)  classes  based  designated  (Dubocovich  suggested that on  the  anatomic  a^-adrenoceptors,  and  a-adrenoceptors  location: while  Langer  1974;  be subdivided  post-junctional  those  located  Langer  1974).  into  receptors  pre-junctionally  two were  on  the  nerve terminal were c a l l e d ag-adrenoceptors. The  receptor  post-junctional observed  in  post-junctional a-^-adrenergic  classification  scheme  of  Langer  (1974)  a-receptors were a homogeneous population. cats  and  rats  that  vasoconstriction  assumed  However, i t mediated  by  that was the  receptors could not be completely abolished by p r a z o s i n , an antagonist,  suggesting  that  perhaps  a  sub-population  of  -26 a-receptors was present p o s t - j u n c t i o n a l l y Jauernig (1977)  also reported  (Bentley et a l . 1 9 7 7 ) .  Moulds and  a s i m i l a r f i n d i n g in vivo in human a r t e r i e s .  The existence of two classes of a-receptors at the p o s t - j u n c t i o n a l f i n a l l y demonstrated by Drew and Whiting (1979) pithed  rat.  They  found  antagonist,  or yohimbine,  completely  antagonize the  response was abolished i f established  that  post-junctionally. post-junctional  while  the  selectivity  both  and  a-^  a^-  antagonist,  could  not  although  the  It was then  are  a2-adrenoceptors  led to confusion. refer  and  present  as those  and  only to  anatomical  the  the receptors f o r  were  where  pre-junctional  location  designate  designated  showed greater  sites  the  Therefore the terms pre- and  a2~adrenoceptor  phenylephrine  2  a^-adrenergic  phenylephrine,  a-j-adrenoceptors  a-j-Adrenoceptors  a -adrenoceptors  so-called  As a r e s u l t , Langer's o r i g i n a l proposal to designate the  based on the preference of  or  a  both antagonists were given together.  presently  and antagonists. methoxamine  prazosin,  pressor response to  receptors  terms  in the anesthetized cat and  a s e l e c t i v e a2~adrenergic  receptors a2-adrenoceptors post-junctional  that  s i t e was  the  as  potency reverse  of  receptors,  pharmacological certain  those  than order  agonists  sites  where  clonidine, of  and  potency was  observed (Berthelsen and Pettinger 1977). 1.3.3  Peripheral  a-adrenoceptors.  Pre-junctional  a2~adrenoceptors  have been demonstrated in a number of t i s s u e s , including the r a b b i t i s o l a t e d pulmonary  artery  (Starke  1981),  rabbit  ear  artery  (Drew  1979)  and  autoperfused hindlimb (Steppeler et a l . 1978), rat heart (Drew 1979; P i c h l e r and Kobinger 1978), anococcygeus muscle (Leighton et a l . 1979; and vas deferens (Doxey et a l . 1977; Kobinger 1978), dog heart (Marshall stimulation  at a l . of  1978).  Drew 1977), cat hindlimb  Doxey 1979) ( P i c h l e r and  (Lokhandwala et a l . 1977) and mouse vas deferens It  pre-junctional  has  been  clearly  a -adrenoceptors ?  demonstrated decreases  the  that  the  amount  of  -.11 noradrenaline released per impulse. which  could  account  s i g n i f i c a n c e of  for  this  Surprenant 1980; Qui 11 en 1984).  these  effect  -  No mechanism has yet been demonstrated  effects.  In  addition,  has been questionned  F i t z G e r a l d et a l . 1981; This modulation  of  the  physiological  (Drew 1980;  Holman and  Kalsner 1982, 1983;  noradrenaline  release  Kalsner and  from the  terminal could p o s s i b l y play a r o l e in cardiovascular r e g u l a t i o n . a  selective  decrease 1974;  antagonist  in  blood  pressure  Safar et a l .  Graham et a l .  of  1974)  1976).  ag-adrenoceptors  a-j-adrenoceptors, but or  little  renin  Since the  inhibits  causes  reflex  release  (Lund-Johanssen  of  peripheral  released  by  pre-junctional  stimulation  post-ganglionic sympathetic nerves, i t  has been suggested that the  of  may account f o r  prazosin to  block  these receptors  and a  (Massingham and Hayden 1975;  activation  noradrenaline  Prazosin,  vasodilatation  tachycardia  nerve  the  of  the  inability  lack of  reflex  tachycardia and renin release observed in response to t h i s drug (Stokes and Oates  1978).  It  (^-adrenoceptors  has  also  been  suggested  that  pre-junctional  in the heart may contribute to the bradycardia induced by  drugs such as c l o n i d i n e , since c l o n i d i n e was shown to decrease the amount of noradrenaline overflowing Roach 1980), stimulation  into the coronary sinus blood in dogs (Cavero and  and also to in  pithed  inhibit rats  tachycardia  (de  Jonge  in  response to  et a l .  1981).  sympathetic However  the  p h y s i o l o g i c a l r o l e of these cardiac c^-adrenoceptors remains unclear. Post-junctional  a-adrenoceptors  which  mediate  the  effects  of  the  sympathetic nervous system in vascular smooth muscle were a l l considered to be  of  the  receptors  classical with  the  o^-adrenoceptors  were  Whiting 1979). into  a-^-adrenoceptor  type  pharmacological also  present  at  until  it  selectivity  was  realized  of  pre-junctional  post-junctional  The s u b d i v i s i o n of vascular p o s t - j u n c t i o n a l  ay- and a2-adrenoceptors  has  been  demonstrated  in  sites  (Drew  that  and  a-adrenoceptors rats  (Timmermans  - 28 et a l . 1979;  Drew and Whiting 1979), rabbits (Hamilton and Reid 1982), dogs  (Langer  et a l .  1981),  et a l .  1982;  Flavahan  post-junctional responses to  cats  (Timmermans  et a l .  vascular  sites  s e l e c t i v e ay-  and P i c h l e r 1982)  1981)  1987).  The  was determined  and o^-agonists  and pithed rats  and a^/ot  decapitated  1986)  suggest  suggested  that  that  the  extra-junctionally,  post-junctional  and that they  Catecholamines rather (Langer 1981;  ci2  to  that  - r e c e  of  P  f°  the  r  cats  (Kobinger  and i t  Vanhoutte 1982)  was  in  and i n  Pang and Tabrizchi veins.  o^-adrenoceptors  noradrenaline  t o r s  present  are p r i m a r i l y  W i l f f e r t et a l . 1982).  post-junctional identical  than  at  Both in v i t r o studies  Stevens and Moulds 1982;  o^-adrenoceptors. are  ratio  and P i c h l e r 1981)  in dog saphenous vein (de Mey and Vanhoutte 1981; (Greenway 1979;  Brummelen  receptor  2  suggested that both subtypes are of equal importance.  vivo studies  (van  by examining blood pressure  in  (Kobinger  humans  It  may  stimulated  released from the  by  has been  be  located  circulating  nerve  terminal  Although the r e l a t i v e a f f i n i t y of the  various  pre-junctional  agonists  and  q^-receptors,  the  antagonists  is  post-junctional  receptors were shown to mediate both vasoconstriction (Kobinger and P i c h l e r 1980a,b; Meel  Timmermans and Van Zwieten 1980a,b;  et a l .  1983;  venoconstriction et a l . 1984;  Hicks  (Schumann  et a l . and  1984;  Lues  Steen et a l . 1984;  Elliott  Pang  1983;  and  Shoji  agonists.  In  contrast,  vasoconstriction rats,  they  while  and maintain  have not  the  (^-adrenoceptors  peripheral  been found to  1986)  1986)  1983;  contribute  to  Van and  Kalkman  in response to  of s e l e c t i v e adrenergic were found  to  mediate  resistance and blood pressure  c i r c u l a t o r y f i l l i n g pressure, an index of t o t a l Tabrizchi 1986).  Tabrizchi et a l .  Pang and Tabrizchi  sympathetic nerve stimulation or the administration  and Reid 1983;  in  the maintenance of mean  body venous tone (Pang and  - 29 1.3.4 shown to et a l .  Central  be p r i m a r i l y  1977;  Central  a-adrenoceptors. a.^ in  Perry  and  nature  by  U'Prichard  binding  studies  Jarrott  et a l .  1981;  pharmacological  studies  1982).  a^-adrenoceptors have been shown to  Central  s i m i l a r to  (Timmermans  both  a-adrenoceptors have  both pre-junctional  post-junctional  muscle  (Kobinger  central  a -adrenoceptors are located on the  Pichler  It  neurons  or on the c e l l  (post-synaptic).  ag-adrenoceptors  is  A  supported  noradrenaline turnover  of  bodies or dendrites  that  inhibition  pre-synaptic  of  of  of  noradrenaline  with  reserpine  and  these  adrenergic  post-synaptic for  central  F u l l e r et a l . 1977), release  However,  inhibition  resulting  it  shown that c l o n i d i n e was able to produce a response even a f t e r central  smooth  c l o n i d i n e decreases  noradrenaline  a2-adrenoceptors.  (Doxey  whether  location  observation  and  Pichler  vascular  unclear  in the CNS (Anden et a l . 1970;  which could be a t t r i b u t e d to from stimulation  by the  and  vas deferens  nerve terminals  presynaptic  1979)  pharmacologically  on  remains  2  (pre-synaptic)  be  a2~adrenoceptors  1980b).  (U'Prichard  Kobinger  in the rat  1983)  and  1981;  a2~receptors  et a l .  nerves  and  et a l .  been  has  been  depletion  of  of  noradrenaline  synthesis with a - m e t h y l - p - t y r o s i n e in cats (Hausler 1974) and dogs (Kobinger and P i c h l e r 1975), and a f t e r  destruction of central  6-hydroxydopamine (Warnke and Hoefke 1977; also  no change  in  the  binding  catecholamine depletion effect,  clonidine  could s t i l l  Kubo and Misu 1981).  characteristics  (Greenberg et a l .  adrenergic neurons with  of  1976;  these  neuronal noradrenaline, which would not be p o s s i b l e i f from  a  reduction  Therefore provide  in  stimulation a  noradrenaline of  satisfactory  Alternatively,  the  central  from  pre-synaptic  explanation central  release  for  receptors  Langer et a l .  produce a response even  in  the  the  nerve  a2~adrenoceptors  effects may  of be  after  1983).  In  absence of  the e f f e c t  a2~adrenoceptors  the  There was  resulted terminal. does  not  clonidine. located  -  post-synaptically.  This  clonidine  effective  decrease  is in  still  would  noradrenaline  be  30  -  consistent  after  turnover  central could  with  the  observation  that  depletion.  The  catecholamine be  explained  by  an  inhibitory  neuronal feedback mechanism in which the post-synaptic neuron would exert an inhibitory  influence  on  the  projection  (Hausler  1982).  pre-synaptic Hausler  neuron  (1982)  through  has  a  neuronal  suggested  that  the  o^-adrenoceptors may be located on non-catecholamine neurons which release a  transmitter  other  than  o^-Adrenoceptors  noradrenaline.  located  p o s t - s y n a p t i c a l l y on such neurons could mediate decreases in MAP and HR i f these  neurons  had  On  the  system.  a  tonic  inhibitory  other  hand,  Clearly, defined.  released  the  normally  anatomical  site  the  in  on  MAP and HR i f  the  system.  c^-adrenoceptors has yet  central  solitarius  cardiovascular  cardiovascular  Within the CNS, o^-adrenoceptors are present  such as the nucleus tractus  the  (^-adrenoceptors  a reduction  stimulated  of  on  pre-synaptic  non-catecholamine neurons could mediate transmitter  influence  to  be  in brain stem areas  (NTS), the vasomotor center and the  nucleus motoris dorsal i s vagus (Chalmers 1975). A decrease in response to injection  the  of  blood pressure and heart  stimulation  clonidine  in  of  central  cats  rate  o^-adrenoceptors by  (Kobinger  1967)  1971), i n j e c t i o n of c l o n i d i n e into a vertebral van  Zwieten  responses  1967)  were  and  dogs  observed  a-methyl noradrenal i n e ,  a  (Constantine  after selective  the  was shown to  and dogs  artery  and  injection  o^-adrenergic  occur  intracisternal (Onesti  et a l .  in cats ( S a t t l e r  McShane of  1968).  and  Similar  noradrenaline  agonist  in  (de  or  Jonge  and  Nijkamp 1976; Kubo and Misu 1981) or c l o n i d i n e (Kubo and Misu 1981) into the NTS.  Clonidine was also shown to reduce or abolish spontaneous e l e c t r i c a l  discharges in preganglionic  and postganglionic  cats (Hukuhara et a l . 1968) and rats  sympathetic  and dogs (Schmitt  nerve f i b e r s  et a l . 196 7;  in  Klupp  - 31 et a l .  1970).  facilitate to i . v . but  It  is  also  possible  that  central  c^-adrenoceptors  the baroreceptor r e f l e x , since the r e f l e x bradycardia in response  injection  not  i.v.  experiments  of angiotensin II  injection were  of  in dogs was increased by  clonidine  performed  on  (Kobinger  animals  and  subjected  to  Central  (^-adrenoceptors  have  activity  by decreasing sympathetic outflow to the periphery.  the  o^-antagonist  bi laterally-vagotomized elicited sinus to  by i . v .  nerve  decrease blood  activity  yohimbine  of  et a l .  pressure  and a reduction  shown  inhibit  rate  sympathetic  enhance  the  baroreflex  The  injection  artery  reflex  or stimulation  of the  carotid appear  2  an  increase  in sympathetic nervous a c t i v i t y ;  in  bradycardia  a -adrenoceptors  through  The  vagally-mediated.  vertebral  Thus, central  and heart  is  to  a  noradrenaline  1983).  effect  into  dogs was shown to  injection  (Huchet  been  1971).  cardiac  suggesting that t h i s also  intracisternal  Walland  blockade with t o l i p r o l o l ,  of  may  in  vagal  the mechanism by  which stimulation of these receptors brings about such e f f e c t s remains to be elucidated. 1.4  Aims of the studies This  thesis  will  focus  on  the  roles  of  the  vasopressin  and  the  sympathetic nervous systems in the regulation of blood pressure, at both the central and the peripheral 1.4.1  level.  Role of AVP in cardiovascular r e g u l a t i o n .  f o r AVP as a neurotransmitter result  of  neuroanatomical  containing  AVP o r i g i n a t i n g  hypothalamus  extend  to  in the CNS has r e c e n t l y studies in  the  a number  Studies employing retrograde  A possible new r o l e  of  which  have  paraventricular areas  distribution  of  in  the  come to  revealed nucleus  light  as a  that  neurons  (PVN)  of  ventrolateral  the  medulla.  horseradish peroxidase (Saper  et a l . 1976) and dyes (Swanson and Sawchenko 1980)  and immunohistochemical  techniques  AVP-containing  (Swanson  1977)  have  shown  that  these  neurons  - 32 terminate  on catecholamine-containing  neurons of the A-^ group at the NTS.  Ascending catecholaminergic f i b r e s of the A-^ group have also been shown t o terminate  predominantly  (Swanson  and Sawchenko 1980).  connection  is  present  in the region of AVP-containing neurons in the PVN Therefore  between the  a descending-ascending  PVN and NTS.  Moreover,  neuronal  neurons  which  project from the medulla to the PVN can i n h i b i t the release of AVP (Blessing et a l . 1982), although a more recent study has shown that stimulation of the A^  cell  group  in  the  medulla  enhances  neurons in the PVN (Day et a l . 1984).  the  activity  AVP-secreting  The discharge rate of PVN neurons has  also been shown to be altered by stimulation of the buffer and C i r i e l l o 1980;  of  nerves (Calaresu  Yamashita et a l . 1984).  AVP projections to the NTS have been found to terminate  in axosomatic  and axodendritic contacts, which suggests that an i n t e r a c t i o n  with neurons  occurs rather than the release of hormone into the blood (Sofroniew 1980). Immuno-electron  microscopic studies have shown that the AVP present in PVN  neurons i s contained w i t h i n v e s i c l e s (Buijs and Swaab 1979; 1983).  Binding studies have also revealed s p e c i f i c binding s i t e s f o r AVP on  neural membranes in the NTS (Dorsa et a l . 1983; evidence suggests that AVP may function  baroreceptor  possible  that  reflex  AVP may  Brinton et a l . 1984).  as a neurotransmitter  Since the NTS i s the primary s i t e of termination the  Voorn and B u i j s  arc  (Cottle  1964;  be  involved  in  the  in the CNS.  of the afferent  Crill  and Reis  neurogenic  This  neurons of  1968),  control  it of  is the  circulation. A number  of  studies  have  possibility.  Nashold  et a l • (1961) showed that i n j e c t i o n of AVP into a l a t e r a l cerebral  ventricle  in cats elevated blood pressure.  investigated  I.c.v.  this  injections  shown to increase both blood pressure and heart  of AVP have since been  rate  in both anesthetized  (Pittman et a l . 1982) and conscious rats (Zerbe et a l . 1983).  In  contrast,  - 33 other  studies  have  pressure and heart  shown that rate  i.c.v.  injections  of  in anesthetized r a t s , yet  AVP decrease  increase blood pressure  and heart rate in conscious rats (Zerbe and Feuerstein 1985). AVP d i r e c t l y  into the  NTS of  anesthetized rats  V a l l e j o et a l . 1984) and conscious rabbits  blood  Injections of  (Matsuguchi  et a l . 1982;  (Martin et a l . 1983, 1985) have  also been shown to increase blood pressure, i m p l i c a t i n g the NTS as a s i t e of action  of  central  the  central  injection  pressor e f f e c t  of  AVP.  The pressor  responses  to  of AVP were abolished by ganglionic blockade (Matsuguchi  et a l . 1982), suggesting that they were mediated by the sympathetic nervous system. The purpose of  our  experiments  was f i r s t  of  all  to  examine more  d i r e c t l y whether the responses to central AVP are mediated by an increase in sympathetic nerve a c t i v i t y .  The e f f e c t of i . c . v .  i n j e c t i o n of AVP on blood  pressure and plasma noradrenaline and adrenaline concentrations was examined in conscious r a t s .  Plasma l e v e l s of noradrenaline and adrenaline have been  shown  a  to  provide  (Yamaguchi  reliable  and Kopin 1979;  estimate  of  Goldstein et a l .  sympathetic 1983;  nerve  Esler  activity  et a l .  1985;  Hubbard et a l . 1986).  As w e l l , in order to assess the r o l e of central AVP,  the e f f e c t  injection  of central  investigated. central  A second s e r i e s of experiments was c a r r i e d out to assess the  role  catecholamine  of a s e l e c t i v e AVP pressor antagonist was  of  endogenously-released  release  in  hypotensive  AVP  rats.  on In  blood these  pressure  experiments, AVP  antagonist was injected c e n t r a l l y into conscious rats subjected to of n i t r o p r u s s i d e .  In a f i n a l  and  infusion  s e r i e s of experiments, the possible r o l e  of  the NTS as a s i t e of action of central AVP was examined by i n j e c t i n g AVP and AVP antagonist d i r e c t l y into the NTS in conscious rats and monitoring blood pressure,  heart  rate  and  plasma catecholamine  responses.  In  order  to  determine i f endogenously-released AVP in the region of the NTS p a r t i c i p a t e s  - 34 in  cardiovascular regulation  during  neurogenic  s t r e s s , AVP antagonist  injected into the NTS of rats exposed to a 150 watt heat lamp. of  stress  has  pressure in  been  all  may i n t e r f e r e  the  shown  to  reproducibly  animals tested  elicit  an  with the responses to central  injections  This model  increase  (Chan et a l . 1985).  was  in  blood  Since anesthetics of AVP, a l l  studies  were c a r r i e d out in conscious, unrestrained r a t s . Another objective of our study was to i n v e s t i g a t e the vascular r o l e of AVP.  Surgery has been reported to cause the release of large amounts of AVP  (Moran et a l . 1964;  Bonjour and Malvin 1970;  Ishihara et a l . 1978).  Since  AVP has been shown to be a potent pressor agent ( A l t u r a and A l t u r a 1977),  it  i s l o g i c a l to speculate that AVP released during surgery may contribute  to  the maintenance of blood pressure. shown  to  vascular  participate resistance  in  the  (McNeill  AVP released by surgery has indeed been  control  of  blood  and Pang 1982;  Pang  vascular r o l e of AVP may have been underestimated buffering  reflex  renin-angiotensin sympathetic  systems, systems.  nervous  and  such It  as  the  pressure 1983a).  the  in the presence of  the  nervous  has been shown that a f t e r  released (Burnier et a l . 1983a;  peripheral  However,  sympathetic  renin-angiotensin  and  systems,  Waeber et a l . 1983;  and  antagonism of  the  amount  Dipette  Burnier et a l . 1983a;  I r i u c h i j i m a 1983;  of  et a l .  and i t s e f f e c t on blood pressure are increased (Cowley et a l . 1980; and Brenner 1981;  the the AVP 1984)  Andrews  McNeill 1983).  Therefore we investigated the influence of endogenous AVP on cardiac output and i t s d i s t r i b u t i o n  in p e n t o b a r b i t a l - a n e s t h e t i z e d ,  in the presence and absence of  s u r g i c a l l y - s t r e s s e d rats  influence from the renin-angiotensin or  the  a-adrenergic systems. 1.4.2  Role of the a-adrenergic system in cardiovascular r e g u l a t i o n .  The mechanism of antihypertensive  action of a2-agonists such as c l o n i d i n e ,  guanfacine and a-methydopa has generally been a t t r i b u t e d to the  stimulation  --35 -  of  central  c^-adrenoceptors leading  activity,  blood  Pichler  pressure  and  However,  clonidine  1982).  at  o^-adrenoceptors  to  heart  peripheral  rate  and  pre-junctional  central  hypotensive reported  effects  that  of  this sites,  blood pressure.  In  may also contribute to  the  to  its  peripheral  in  to  and  stimulate  resulting  in  less  in  the  heart  to and  vasculature  bradycardic  and  Pichler  (1980a,b)  also  at  and  peripheral  an  increase  an c ^ - a d r e n e r g i c agonist  (Timmermans  and van Zwieten  pharmacological of  and  the  vasoconstriction is  in  i s possible that  c^-adrenoceptors  clonidine  effects  shown  Therefore i t  Kobinger  stimulates  properties  Kobinger  sites,  contribute  clonidine.  addition,  a-^-agonistic  relative  may  resulting  nerve  stimulation of sympathetic outflow  o^-adrenoceptors  drug  sympathetic  1981;  been  pre-junctional  o^-adrenoceptors  post-junctional  partial  also  (Kobinger and P i c h l e r 1980a,b).  peripheral  in  (Kobinger  has  tachycardia in response to e l e c t r i c a l pithed rats  a reduction  effect.  1980a)  Therefore  c ^ - a d r e n e r g i c agonists  the  in  with which  central  are not  yet  clearly established. In  order  to  completely  separate  the  central  from  the  peripheral  e f f e c t s of adrenergic agonists we developed a c r o s s - c i r c u l a t i o n technique anesthetized peripheral  rats.  The  circulations  blood from one rat  two  rats  supplied the brain of  returned to the body of the f i r s t second r a t .  of  rat,  peripheral  effects  of  delivered  the  of  second, rat  brain  central e f f e c t s of the drug. from the  peripheral  The actions  of  investigated  in t h i s  the  drug,  that  and then  blood from the  in one r a t ,  and the  which  so  which  drug would be  would  exhibit  the  Using t h i s technique, we separated the central  component of  methoxamine,  the  a second rat  intravenously  would d i s p l a y the only  joined  and vice versa f o r  A drug could then be injected  to  were  in  the  cardiovascular  a selective  ctj-adrenergic  preparation to provide a contrast  effect  of  agonist,  clonidine. were  also  to c l o n i d i n e , since  -  methoxamine  increases  o^-adrenoceptors  but,  blood unlike  36  -  pressure  by  an  clonidine,  has  not  action been  on  peripheral  shown  to  decrease  blood pressure or heart rate by central a c t i o n s . A  disadvantage  requirement  for  neurotransmitter  of  the  anesthesia  cross-circulation and  surgery,  experiments  which  was  the  could  influence  and hormone release and the responses to drugs.  Due to the  s u r g i c a l stress to which these animals were subjected, i t to examine the e f f e c t s  was not  of these drugs on catecholamine r e l e a s e .  in order to determine f i r s t l y whether i t  feasible Therefore  was possible to extend the  results  of the c r o s s - c i r c u l a t i o n studies to conscious animals, and secondly whether the sympathetic  nervous system was involved  c l o n i d i n e , the e f f e c t s heart  rate  conscious  and rats.  of  plasma  also  antagonist, clonidine  agonist  investigated. rauwolscine, and B-HT 920  is  also  concentrations unclear  a c t i o n s , the e f f e c t s  s e l e c t i v e o^-adrenergic were  it  (Kobinger  The to  were  the responses to  i n j e c t i o n of c l o n i d i n e on blood pressure,  catecholamine  Since  agonists have s i m i l a r  i.c.v.  in mediating  block also  ability the  of  whether i.c.v.  a  to  in  c^-adrenergic  1980a,b),  selective  responses to  investigated  all  examined  injection  and P i c h l e r of  were  of  a more  B-HT 920,  ag-adrenergic  central  injection  of  determine  whether  the  responses to these drugs were a r e s u l t of ^ - a d r e n o c e p t o r  activation.  - 37 2  METHODS  2.1  Central AVP in conscious rats 2.1.1  Surgical  2.1.1.1 Wistar rats  preparation  Implantation  intracerebroventricular  (280-320 g, Charles River Canada, Inc.)  sodium pentobarbital (David  of  Kopf)  to  cerebroventricle. 2-3 cm i n c i s i o n  (65 mg/kg, allow  i.p.)  and mounted  implantation  The i n c i s o r  of  a  cannulae.  were anesthetized with in  a stereotaxic  cannula  into  the  bar was placed 5 mm above the  was made through  the  skin  Male  device fourth  ear bar..  A  and subcutaneous t i s s u e s .  The  t i s s u e was retracted with hemostats at each corner and the s k u l l was allowed to dry. using  The guide cannula p o s i t i o n was marked by measuring from the bregma the  stereotaxic  manipulator.  Stereotaxic  p o s i t i o n i n g of the cannula were 10.5 mm posterior ventral to the dura ( P e l l e g r i n o et a l . 1979). 280)  with a dental  drill  bit,  three  coordinates  used  Using a d r i l l  holes were d r i l l e d  (Dremel, Model  just  and s t a i n l e s s steel  inserted  cannula was then  The hole for  the  the  to the bregma and 7.8 mm  s k u l l at s i t e s around the cannula p o s i t i o n in the holes.  in  through  the  screws were  drilled  and a  s t a i n l e s s steel cannula (23-gauge, 15 mm long) was lowered into p l a c e . cannula was surrounded with gelfoam and held ( P l a s t i c Products Co.) s u f f i c i e n t screws.  The stereotaxic  of  15 mm of  crimped 19-gauge needle. suture.  place with dental  cement  to s t a b i l i z e the cannula and cover the 3  manipulator,  removed once the cement was hardened. consisting  in  The  a 30-gauge  with  the  guide  cannula holder,  was  Patency was maintained using a plug  needle fused  When necessary, the  to  a short  incision  length  of  a  was closed with a  Animals were i n d i v i d u a l l y housed and allowed to recover f o r 7 days.  - 38 -  2.1.1.2 experiment,  Implantation of  rats  femoral  artery  tubing.  The  were  briefly  and femoral tubing  was  vascular canriulae.  anesthetized  with  On the  day of  1.5% halothane  and  vein were cannulated with polyethylene filled  with  normal  saline  the the  (PE) 50  containing  heparin  (25 Ill/ml) to prevent c l o t t i n g .  The cannulae were held in place with three  silk  burrowed  ties.  All  cannulae were  secured at the back of the neck.  subcutaneously,  exteriorized  The cannulae were flushed and heat-sealed  by melting the end with a flame and squeezing with the f i n g e r s . were allowed to recover for  and  The animals  at least 4 h before the experimental  protocol  was begun in order to avoid the influence of anesthesia on the experimental results. 2.1.2  Experimental p r o t o c o l .  An i n j e c t i o n  device, c o n s i s t i n g of an  i n j e c t i o n needle (30-gauge, 15 mm) fused to a 19-gauge needle connected v i a PE 50 tubing to a Hamilton 10 ul s y r i n g e , was inserted into the v e n t r i c u l a r cannula f o r  i.c.v.  connected to  injections  of drugs.  a pressure transducer  PE 90 t u b i n g .  The femoral  arterial  cannula was  (Gould, Model P23ID) with a length  of  Conscious and unrestrained rats were placed in a small cage  and allowed to a c c l i m a t i z e for at least twenty min p r i o r to the s t a r t of the experiment.  Mean a r t e r i a l pressure (MAP) was continuously monitored using a  Grass polygraph (Model 7D).  MAP values were recorded immediately p r i o r  the removal of each blood sample. obtained from the femoral  arterial  A control  blood sample (1 ml)  cannula of  each rat  groups f o r the determination of plasma concentrations of adrenaline  by high  performance  liquid  chromatography  to  was then  from the  various  noradrenaline and  (HPLC).  All  blood  samples obtained f o r the assay were 1 ml in volume and a l l blood removed was replaced solution.  with  the  injection  of  an  identical  volume  Nine groups of animals were used in the study.  prepared with i . c . v .  cannulae f o r  central  injections  of  normal  saline  A l l animals were  of drugs, except  for  - 39 three  groups  which  were  prepared  with  cannulae only and which received i . v .  the  femoral  arterial  and venous  i n j e c t i o n s of drugs,  i  Five min a f t e r the control (n = 10)  were  artificial  given  i.c.v.  injection  of  23 ng/kg  of  AVP  in  I,  1 ul  CSF over 5 sec followed by the removal of a second blood sample  a f t e r 1 min.  Ten min l a t e r a second i . c . v .  3 ul of a r t i f i c i a l  i n j e c t i o n of 73 ng/kg of AVP in  CSF was given, followed by the removal of a f i n a l  sample 1 min l a t e r . whether  an  blood sample was obtained, rats in Group  Two d i f f e r e n t  a relationship  doses of  AVP were given  existed between dose and response.  to  blood  determine  The two doses  were given in sucession to achieve a cumulative dose of AVP. Animals in Group II  (n = 8)  received the same treatment  Group I except that the responses were examined at a d i f f e r e n t to assess the time course of the response to central AVP. was withdrawn  10 min rather  than 1 min a f t e r  i.c.v.  as those  in  time in order A blood sample  injection  of  the  low  dose of AVP. A f t e r 5 min, the high dose of AVP was i n j e c t e d ; 10 min l a t e r a f i n a l blood sample was obtained. Groups III effects  of  (n - 7)  the  vehicle,  concentration  were  respectively.  Following  artificial  and IV  (n = 6)  served as controls  artificial  assessed the  1  and  CSF,  on  10 min  protocol  MAP  after  described  and  in  1  injections, and  3 ul  of  in  the  CSF were injected in both groups.  To determine whether  endogenously released AVP plays a r o l e  modulation of sympathetic nervous a c t i v i t y , Group V (n = 5) was given injections  of  a  selective  antagonist  of  the  pressor  [l-(B-mercapto-e,s-cyclopentamethylenepropionic a c i d ) , arginine  the  catecholamine  i.c.v.  above,  which  vasopressin  and Leighton 1981;  (d(CH ) Tyr(Me)AVP) 2  5  (Kruszynski  Manning and Sawyer 1982).  and 1.5 ug/kg in 3 ul  artificial  effect  of  i.c.v. AVP,  2-(0-methyl)-tyrosine] et a l .  1980;  Pang  Two doses, 0.5 ug/kg in 1 ul  CSF, were given according to the  protocol  - 40 described  for  Group I I .  Since  the  antagonist  is  known to  have  a  long  duration of action (Pang and Leighton 1981), blood was sampled 10 min a f t e r each i n j e c t i o n only. In order to determine whether the receptors involved in mediating the pressor response to central administration of AVP are i d e n t i c a l to vascular AVP receptors present p e r i p h e r a l l y , the response to i . c . v . was observed in Group VI (n = 11) a f t e r AVP  antagonist.  Five  min  after  the  pretreatment first  i n j e c t i o n of AVP  of the rats with the  blood  sample  was  obtained,  2.0 ug/kg of AVP antagonist (the t o t a l cumulative dose used in the previous study) was injected into the fourth v e n t r i c l e 1 min  later.  Ten min  after  AVP antagonist  and a blood sample obtained was given,  96 ng/kg  AVP was  i n j e c t e d , and a f i n a l blood sample was removed 1 min l a t e r . To ensure that the reponses observed following drugs were not due to d i f f u s i o n AVP and AVP antagonist Group VII  were  central  injections  of drugs into the peripheral  injected  intravenously  in  of  circulation,  3 further  groups.  (n = 8) received doses of AVP i d e n t i c a l to those given to Group I  except that the drug was dissolved in Blood samples were obtained 1 min a f t e r Group VIII (n = 5)  a volume of i.v.  0.1 ml normal  i n j e c t i o n of each dose of AVP.  also received the same doses of AVP but  were removed 10 min after  i.v.  injections  saline.  of  AVP.  blood samples  Group IX  (n = 5) was  given the same dose of AVP antagonist ( i n 0.1 ml of normal s a l i n e ) as Group V.  Blood  samples  were  obtained  10 min  after  i.v.  injections  placed on  ice,  centrifuged  of AVP  antagonist. Blood samples were plasma removed adrenaline anesthetized  and stored  content. with  On  immediately at , -80°C  until  completion  sodium pentobarbital  (2 ul) was injected through the i . c . v .  of  assayed for the  and  the  noradrenaline  and  experiments,  (30 mg/kg,  i.v.).  rats  Methylene  cannula to permit l a t e r  were blue  verification  - 41 of  the  position  of  the  cannula in the fourth v e n t r i c l e .  Rats were then  perfused t r a n s c a r d i a l l y to allow in s i t u f i x a t i o n of the brain t i s s u e . thorax was cut open, the r i g h t out,  atrium was snipped to allow blood to  and 60 ml of normal s a l i n e followed by 60 ml of 10% buffered  formalin (BDH) was injected into the l e f t v e n t r i c l e .  The flow  neutral  The brain was removed,  stored in 10% neutral formalin f o r 10 days and l a t e r sectioned in a f r e e z i n g microtome (American Optical Corp., model 880) f o r v i s u a l inspection of cannula p o s i t i o n .  the  Data obtained from animals in which the cannula was not  present in the fourth v e n t r i c l e were discarded. 2.1.3  Catecholamine analysis by HPLC  2.1.3.1 obtained  E x t r a c t i o n of  and stored  plasma samples.  at -80°C as described in  The plasma samples were the  previous  section.  The  e x t r a c t i o n procedure used was a modification of the method of Davis et a l . (1981).  Polypropylene microcentrifuge tubes (Western S c i e n t i f i c Ltd.)  prepared with 20 mg alumina, 250 ul 10% EDTA. 10 pg/ul  To each tube,  0.5 ml  3,4-dihydroxybenzylamine  1.5 M T r i s buffer  plasma and 100 ul  were  (pH 8 . 7 ) ,  and 25 ul  internal  standard,  of  (DHBA), were added.  For each assay,  2  spiked samples were also prepared with 0.5 ml 0.1 M sodium phosphate buffer and 50 ul  each of 100 pg/ul  noradrenaline,  adrenaline and DHBA s o l u t i o n s .  The tubes were then shaken to mix the contents and placed on a r e c i p r o c a l shaker f o r 3200)  for  washed  5 min.  The tubes were spun in  30 sec, the  twice  catecholamines  supernatant  removed by a s p i r a t i o n  with  double-distilled  from  the  alumina,  tubes were again agitated f o r  an. Eppendorf centrifuge  water.  100 ul  5 min.  In  order  0.1 M HCIO^  and the to  was  (Model alumina  extract added  and  the the  The tubes were then centrifuged and  the supernatant drawn into a 1 ml disposable syringe and ejected through a disposable f i l t e r filtrate  was  (Millipore,  immediately  0.45 um pore s i z e )  stored  content by HPLC the same day.  at  -80°C  and  into  a fresh tube.  assayed for  The  catecholamine  - 42 2.1.3.2 assayed f o r  HPLC with  electrochemical  detection.  noradrenaline and adrenaline content  HPLC with electrochemical consisted of  a liquid  detection  The samples  were  by reverse-phase ion  pair  (Davis et a l .  chromatograph  (Waters  1981).  Associates,  12.5 cm x 4.6 mm 5 urn column packed with ODS H y p e r s i l . composed of  a 0.1 M KH P0 2  sodium octyl  sulphate  4  buffer  and a  The mobile phase was  50 ml methanol, of  100 mg  buffer.  The  The electrochemical detection system consisted of  a carbon paste detector electrode packed with a graphite:nujol potential  with  Model 590)  and 60 mg EDTA added to each l i t r e  flow rate was 1.2 ml/min.  electrode  (pH 3.77)  The HPLC system  (Bioanalytical  Systems I n c . ,  paste ( B i o a n a l y t i c a l Systems Inc.,  was maintained  electrode  (Bioanalytical  Systems  integrated  using an Apple l i e  at  +0.60V  Inc.,  Model  computer.  versus  Model TL-3) CP-0).  a Ag-AgCl  RE-1).  Peak  The recoveries  The  reference areas  were  averaged 75-80 .  Plasma catecholamine concentrations were calculated using the equation: . . , . (Catecholamine/DHBA) , Catecholamine = j ' sample (ng/ml) (Catecholamine/DHBA) ' , . standard r  3  The c o e f f i c i e n t s day) of  of  variation  for  10 r e p l i c a t e  •. , , x Catecholamine . , (ng/ml) stanaan ' r  3  analyses (run  on the same  a human plasma sample spiked with standard catecholamine  solutions  were 8 f o r noradrenaline and 14 f o r adrenaline. 2.1.4 Analysis  of  Statistical analysis. variance  with  A l l values reported represent mean ± SD.  repeated  measures  was  used  to  assess  the  s i g n i f i c a n c e of differences between drug responses and control values of MAP and plasma noradrenaline  and adrenaline  concentrations  within each group.  Since plasma catecholamine concentrations were not n o r m a l l y - d i s t r i b u t e d , analysis  was performed  Where s i g n i f i c a n t  after  logarithmic  transformation  differences  were found,  Tukey's multiple  used to compare group means.  A probability  preselected as the c r i t e r i o n f o r s t a t i s t i c a l  of  these  the  values.  range test  was  of e r r o r of less than 0.05 was significance.  - 43 2.2  Central AVP in hypotensive rats 2.2.1  i.c.v.  Experimental p r o t o c o l .  cannulae  previously  in  and  femoral  Male Wistar  arterial  section 2 . 1 . 1 .  and  rats  venous  were prepared with  cannulae  as  MAP, recorded from the femoral  heart rate (HR) of conscious, unrestrained rats were monitored using  a Grass  polygraph  and  tachograph  (Model  7P4G).  described  artery,  and  continuously  To  assess  the  influence of endogenously released central AVP in hypotensive animals, AVP antagonist infusion  was injected of  centrally  nitroprusside.  Control  beginning of the experiment for received a continuous i . v .  in  later  rats blood  made hypotensive samples were  by continuous  obtained  at  plasma catecholamine a n a l y s i s .  infusion of n i t r o p r u s s i d e  Rats in Groups I  and II  of 4.0 pi  injections  Rats  (0.083 mg/kg/min), and  a second blood sample was removed 10 min l a t e r . (n = 8) were then given i . c . v .  the  alone or with 2.0 pg/kg AVP antagonist, r e s p e c t i v e l y .  (n = 8)  a r t i f i c i a l CSF  A final  blood sample  was obtained 10 min l a t e r . The plasma was separated, stored and analyzed as described in Section 2.1.3.  Rats were t r a n s c a r d i a l l y perfused and the cannula p o s i t i o n  verified  h i s t o l o g i c a l l y as previously described in Section 2 . 1 . 2 . 2.2.2  Statistical  analysis.  measures and Duncan's m u l t i p l e significance.  Analysis  range test  A p r o b a b i l i t y of error of  with  repeated  statistical  less than 0.05 was preselected as A l l values represent mean ± SEM.  M i c r o i n j e c t i o n of AVP into the NTS 2.3.1  Experimental  protocol.  implanting  cannulae c e n t r a l l y  previously  except  Co.)  variance  were used to assess  the c r i t e r i o n for s t a t i s t i c a l s i g n i f i c a n c e . 2.3  of  were used,  ventricle.  that  Male Wistar  7 days p r i o r  commercially  were  to the experiment  available  and they were placed at  rats  the  prepared  by  as described  cannulae  (Plastic  NTS rather  than  Products  the  The stereotaxic coordinates used were 11.6 mm posterior  fourth to  the  •>  bregma and 7.8mm ventral  44  -  to the dura, in the m i d l i n e .  The guide cannula  (26-gauge, 20 mm long) was lowered in the dorso-ventral plane to a p o s i t i o n of  0.5 mm above the  NTS.  A dummy cannula  (33-gauge,  inserted into the cannula to maintain patency.  20 mm long)  Femoral a r t e r i a l  was  and venous  cannulae were also inserted on the day of the experiment at least 4 h p r i o r to the experiment. Conscious unrestrained rats were placed in a cage and MAP and HR were continuously tubing to inserted  monitored.  An internal  cannula  (33-gauge)  connected  by PE  a 1 ul Hamilton syringe and preloaded with drug or v e h i c l e was into the guide cannula.  that, the  guide  cannula  The i n t e r n a l  so that  when  inserted  cannula was 0.5 mm longer into  the  guide,  it  was  positioned at the l e v e l of the NTS. A f t e r allowing at least 20 min f o r each rat to a c c l i m a t i z e , a control blood sample was then obtained. its  vehicle, a r t i f i c i a l  F i f t e e n min l a t e r , the appropriate drug or  CSF, was injected  into the NTS of four  groups  of  rats.  Each animal received one i n j e c t i o n c o n s i s t i n g of a volume of 0.2 ul  given  over  10 sec.  0.2 ul a r t i f i c i a l  Animals  CSF.  minimally e f f e c t i v e  in  Group  I  Rats in Group II  pressor dose.  (n = 10)  received  injections  of  (n = 8) were given 2 ng AVP, the  Group III  (n = 10)  received 10 ng AVP.  Group IV (n = 8) rats were injected with 10 ng AVP antagonist.  This dose  has been shown to block the pressor e f f e c t of vascular responses to central i n j e c t i o n s of 1-30 ng AVP ( V a l l e j o et a l . 1984;  Berecek et a l . 1984).  MAP  and HR were recorded at the time of maximal pressor response, within 1 min of  drug  afterward.  injection,  and  a  On completion of  second the  blood  sample  experiment  perfused and the brain removed and stored least 10 days before sectioning and s t a i n i n g .  the  was rats  taken were  immediately  transcardially  in 30% sucrose formalin  for  at  -  2.3.2  45  H i s t o l o g i c a l technique.  -  The f i x e d brain t i s s u e was sectioned  on the f r e e z i n g microtome into 50 u s e c t i o n s .  Sections were transferred  gelatin-coated glass s l i d e s and dried 0.5-1 h at 30-60°C. hydrated xylene, were  to  water  through  100% ethanol,  stained  with  the  following  70% ethanol,  cresyl  series  35% ethanol  violet  for  in d i f f e r e n t i a t o r , in 2 changes of combining 12 ml  dehydrated xylene.  of  violet  working  solution  rinsed  solution  (0.02 g c r e s y l  water.  They  quickly  The d i f f e r e n t i a t o r  the s l i d e s with mounting medium (Permount)  in  and cleared was made by  violet  + 15 ml  consisted of 90 ml 95% e t h a n o l , Coverslips were f i x e d  to  and the s l i d e s were allowed  to  The placement of the cannula at the NTS was confirmed by examining the  cannula track marks with reference to a s t e r e o t a x i c a t l a s ( P e l l e g r i n o et a l . 1979).  Data obtained from animals in which the cannula was not present  at  the NTS were r e j e c t e d . 2.3.3 multiple  Statistical  range  test  analysis.  was  Analysis assess  variance  statistical  and  Duncan's A  p r o b a b i l i t y of error of less than 0.05 was preselected as the c r i t e r i o n  for  2.4  to  of  significance.  statistical significance.  used  A l l r e s u l t s are presented as mean ± SEM.  Central AVP in neurogenically-stressed rats 2.4.1  cannulae at  Experimental the  previous study.  protocol.  NTS, and femoral  Male Wistar arterial  rats  were prepared with  and venous cannulae as in  the  MAP and HR of conscious, unrestrained rats were monitored  continuously.  To  assess  cardiovascular  regulation  the during  _  (94 ml 0.1 M a c e t i c acid + 6 ml 0.1 M  10 ml chloroform and 3 drops g l a c i a l a c e t i c a c i d .  dry.  and  xylene,  The sections were then placed —  violet  d i s t i l l e d water) with 100 ml of buffer sodium acetate, pH 3 . 5 ) .  solutions:  in 50:50 absolute ethanol:xylene  The c r e s y l  cresyl  The sections were  and d i s t i l l e d  0.5-1 min  d i s t i l l e d water, 70% ethanol and 95% ethanol.  of  to  role  of  neurogenic  endogenous stress,  AVP  in  central  AVP antagonist  was  —  - 46 i n j e c t e d into the NTS in rats subjected to a 150 watt heat lamp. blood sample was obtained f o r  l a t e r plasma catecholamine analysis a f t e r  animals were allowed 20 min to later,  become accustomed to  the heat lamp was turned on, and a f t e r  lamp, a second blood sample was obtained. (n = 5)  and  artificial  II  (n = 5)  were  given  later.  the  cage.  After  injections  1 min, rats into  the  the  Ten min  ten min of exposure to  CSF and 10 ng AVP antagonist, r e s p e c t i v e l y .  was obtained 5 min  A control  the  in Groups I  NTS of  0.2 ul  A f i n a l blood sample  The plasma samples were prepared as described  p r e v i o u s l y , and the rats were t r a n s c a r d i a l l y perfused as described in 2.1.2 and the cannula p o s i t i o n v e r i f e d h i s t o l o g i c a l l y as described in 2 . 3 . 2 . 2.4.2  Statistical  analysis.  measures and Duncan's m u l t i p l e significance.  Analysis  range test  A p r o b a b i l i t y of error of  variance  were used to  with  assess  repeated  statistical  less than 0.05 was preselected as  the c r i t e r i o n for s t a t i s t i c a l s i g n i f i c a n c e . 2.5  of  A l l values represent mean  ±  SEM.  Vascular r o l e of AVP 2.5.1  Surgical p r e p a r a t i o n .  Male Sprague-Dawley rats  were anesthetized with sodium pentobarbital  (60 mg/kg, i . p . )  to a standard laparotomy with a 5 cm midline i n c i s i o n .  (375-450 g)  and subjected  A PE 50 cannula was  then inserted into the l e f t v e n t r i c l e v i a the r i g h t c a r o t i d artery with the help of the a r t e r i a l  pressure t r a c i n g , f o r  the i n j e c t i o n  of microspheres.  PE 50 cannulae were also introduced into the femoral vein f o r the  infusion  of drugs, and into the abdominal aorta through the caudal and i l i a c a r t e r i e s for  blood  pressure  recordings  and  the  withdrawal  of  blood  during  the  i n j e c t i o n of microspheres, r e s p e c t i v e l y . 2.5.2 distribution  Microsphere of  blood flow  technique.  Cardiac  (BF) were determined  output by the  (CO)  and  the  reference sample  method (Malik et a l . 1976) using r a d i o a c t i v e l y - 1 a b e l l e d microspheres (15 um diameter, New England Nuclear).  It  has been shown that these microspheres  - 47 are trapped within one c i r c u l a t i o n after i n j e c t i o n in rats (Nishiyama et a l . 1976).  Beginning 10 sec before  withdrawn  with  i l i a c arterial A 200 ul  an  the  injection  infusion-withdrawal  pump  of  microspheres,  (Harvard  blood was  Apparatus)  from  the  cannula at 0.35 ml/min for 1 min into a heparinized syringe.  sample of a vigorously vortexed precounted microsphere suspension 57  (containing  20,000-30,000  microspheres,  labelled  with  either  Co  or  113 Sn) was injected  and flushed with 200 y l  into the l e f t v e n t r i c l e . of  20,000  It  microspheres  in  of  normal  has been shown that three repeated rats  gave  reproducible  systemic hemodynamic changes; only a cumulative microspheres  caused  reductions  of  pressure (Tsuchiya et a l . 1977). AB,  Sweden)  distribution  between  oxygen  injections  distribution  injection  consumption,  of  10 sec  with  over  CO and  no  100,000 arterial  F i c o l l 70 (10%, Pharmacia Fine Chemicals  and Tween 80 (0.05%)  (Foster and Frydman 1978).  s a l i n e for  were used to  suspend the  microspheres  To avoid the p o s s i b i l i t y of a v a r i a t i o n  microspheres  labelled  with  ^Co  and  ^ S n  in  the  and  to  avoid v a r i a t i o n s r e l a t e d to differences in the counting e f f i c i e n c i e s of the 57 two d i f f e r e n t isotopes, in half the experiments Co was given before 113 1  Sn.  In the remaining experiments, the order  in which the isotopes were  administered was reversed.  At the end of the experiments, whole rats were  completely  organs  dissected.  All  were  removed,  weighed  v i a l s f o r counting, bones were charred at 300°C overnight were cut  and  into  and large organs  into small pieces and loaded into several v i a l s to  than 3.0 cm from the base.  loaded  a level  less  In rare instances ( l e s s than 5%) where BF to the  l e f t and r i g h t kidney d i f f e r e d by more than 20%, the experiment was rejected as i t  was assumed that  Blood  samples,  injection  of  radioactivity  tissue  the mixing samples,  microspheres  of  test  and the  the microspheres was not tubes,  collection  and of  syringes blood  used  were  adequate. for  the  counted  for  using a Beckman 8000 Gamma Counter with a 3 inch Nal c r y s t a l  -•48 at  energy  settings  respectively.  of  95-165  320-460 keV  At these energy s e t t i n g s ,  channel i s n e g l i g i b l e (0.03%) spillover.  and  the  for  5 7  spillover  and therefore  Co  of  and  1 1 3  Sn,  Co into the Sn  no c o r r e c t i o n was made f o r Co  The s p i l l o v e r of Sn into the Co channel was 16.7% and c o r r e c t i o n  of Co counts was done by subtracting Sn s p i l l o v e r from Co counts. 2.5.3  Experimental  protocol.  CO  and  its  distribution  were  determined by the i n j e c t i o n of r a d i o a c t i v e l y - l a b e l l e d microspheres into the l e f t v e n t r i c l e p r i o r to and f o l l o w i n g the administration of AVP antagonist. Rats were divided  i n t o 3 groups  infused (0.08 ml/min/kg) the  infusion  (n = 8 ) .  30 min a f t e r  was continued microspheres  until was  In  Group I,  normal  s a l i n e was  s u r g i c a l preparation of the rats  the made  end of 10 min  the  experiment.  after  The  start  of  infusion.  Ten min a f t e r the i n j e c t i o n of the f i r s t set of microspheres, AVP  supramaximal doses of AVP in rats (Pang and Leighton 1981). injection  of  AVP antagonist,  microspheres  isotope were injected into the l e f t v e n t r i c l e . to  i.v.  i n f u s i o n of  normal s a l i n e .  continuous  infusion  of  saralasin  blocked the pressor responses to pressor  effect  infusion of  of  angiotensin  s a r a l a s i n and a f t e r  at  i.v.  II  Ten min  with  (0.5 mg/kg/min)  a  Group III at  at 0.08 ml/min/kg  different  instead  this  rate  injections  was tested  for of  in  was subjected to i . v . started  of  injection  Preliminary studies showed that 10 min  10 min  completely  angiotensin  all  the second i n j e c t i o n  0.08 ml/min/kg  after  rats were subjected  rats  II.  prior  The  to  the  of microspheres.  a l l cases, s a r a l a s i n completely blocked pressor responses to i . v . of angiotensin I I .  the  infusions of  The i n f u s i o n of s a r a l a s i n was continued during the  of the microspheres and the AVP antagonist. a  labelled Group II  s a r a l a s i n (10 ug/min/kg)  saline  A dose of 4 ug/kg of  antagonist has been reported to block pressor responses to i . v .  the  of  first  injection  antagonist was injected into the l e f t v e n t r i c l e .  the  and  In  injections  i n f u s i o n of phentolamine prior  to  the  first  - 49 injection  of  microspheres  and  continued  during  the  injection  of  AVP  antagonist and the second set of microspheres.  Preliminary studies showed  that a 10 min infusion of phentolamine at t h i s  rate completely blocked the  pressor  responses to  i.v.  injection  of  methoxamine  B-HT 933 (1 mg/kg) and c l o n i d i n e (5 mg/kg). the f i r s t  and second i n j e c t i o n s  (Sigma,  250 ng/kg),  MAP recordings obtained during  of microspheres were used to  i n d i c a t e MAP  during control and drug treatment p e r i o d s , r e s p e c t i v e l y . 2.5.4 was  Calculations.  calculated  by  Total peripheral  dividing  MAP  (mmHg)  resistance (TPR, mmHg min/ml)  by  CO  (ml/min).  CO and  the  d i s t r i b u t i o n of BF were c a l c u l a t e d as f o l l o w s : CO (ml/min) =  r  a  t  e  Tissue BF (ml/min) =  r  a  t  Total  amount  °^ withdrawal of blood (ml/min) x t o t a l i n j e c t e d cpm cpm in withdrawn blood °^ withdrawal of blood (ml/min) x t i s s u e cpm cpm in withdrawn blood  e  of  radioactivity  (cpm)  injected  was  obtained  by  subtracting the amount of r a d i o a c t i v i t y l e f t in the tube, i n j e c t i n g s y r i n g e , and f l u s h i n g syringe from the amount of r a d i o a c t i v i t y o r i g i n a l l y present the tube.  in  R a d i o a c t i v i t y (cpm) i n blood was obtained by adding the amount of  radioactivity  in the blood sample, cannulae and syringe used f o r  collecting  blood. 2.5.5  Statistical  measures was used to determinations  of  CO.  analysis.  Analysis  compare data obtained Analysis of  used to compare data from d i f f e r e n t  of  during  variance the  with  first  repeated  and second  variance, complete random design, was groups of r a t s .  Duncan's m u l t i p l e range  test was used to compare group means of MAP, CO and TPR.  Tukey's m u l t i p l e  range t e s t was used to compare group means of t i s s u e BF where a more t e s t was desired f o r m u l t i p l e of  less  than  significance.  0.05  was  comparisons of data.  preselected  as  the  A probability  criterion  for  of  strict error  statistical  50 -  2.6  Central and peripheral actions of ot-agonists 2.6.1  rats  of  C r o s s - c i r c u l a t e d rat  identical  pentobarbital femoral  weight  (65 mg/kg,  artery  were monitored  preparation.  (350-400 g, i.p.),  n = 8 pairs)  male Sprague-Dawley  were anesthetized with  and a PE 50 cannula was inserted  and femoral vein of each r a t . continuously.  Two  The d i s t a l  into  a  The MAP and HR of each rat  end of  the  left  common  carotid  artery of each rat was cannulated with PE 50 t u b i n g , while the proximal end of  the  same artery  proximal PE 90  ends of  and  both  PE 50  heparinized  was  normal  cannulated  left  tubing,  with  and r i g h t  PE 90  jugular  respectively.  saline  (25 I l l / m l ) .  tubing.  distal  and  veins were cannulated  with  All The  The  tubing  was  cannulae  from  filled  with  corresponding  vessels of the two rats were then j o i n e d , allowing peripheral a r t e r i a l from the body of each rat blood  to  (Fig. 3).  drain  back  to supply the head of the other r a t ,  into  the  peripheral  The trachea was cannulated  allow a r t i f i c i a l  circulation  with  of  and venous  the  a stainless-steel  blood  first  rat  cannula  to  respiration.  A PE 50 cannula was inserted v i a the r i g h t common c a r o t i d artery the l e f t v e n t r i c l e of one r a t ,  designated rat A.  into  The r i g h t common c a r o t i d  artery of the other r a t , designated rat B, was l i g a t e d .  Preliminary studies  have shown that l i g a t i o n of the r i g h t common c a r o t i d artery of r a t s did not alter  MAP and  HR responses  to  various  l a b e l l e d with ^ C o or ^ S n were injected  vasoactive into  the  drugs. left  Microspheres  ventricle  of  rat  A in order to determine the d i s t r i b u t i o n of BF from rat A to rat B. Each rat  was then  artificially  opened along the sternum, and the ligated.  left  This abolished the vertebral  ventilated and r i g h t arterial  with  O2,  the  chest was  subclavian a r t e r i e s were  blood supply to the head of  each r a t , rendering the brain of each rat dependent on the peripheral blood supply from the other  rat.  Methoxamine (n = 6 p a i r s )  or c l o n i d i n e  (n = 4  - 51  Fig.  3.  Vascular connections preparation, vein.  ca  =  -  between r a t s common  carotid  A and B i n artery,  the jv  =  cross-circulation external  jugular  -  -52  pairs)  was  injected  intravenously  l a b e l l e d with a d i f f e r e n t  into  rat  A.  Afterward,  microspheres  isotope were injected into the l e f t v e n t r i c l e  rat A to determine BF from rat A to rat B a f t e r  of  l i g a t i o n of the subclavian  arteries. 2.6.2  Blood flow to the brain v i a the l e f t  cross-circulated left  carotid  rat  preparation  artery  of  the  one  c r o s s - c i r c u l a t i o n of  rat  to  r a d i o a c t i v e l y - l a b e l l e d microspheres. through the r i g h t c a r o t i d artery of  microspheres,  the  right  To ensure  provide  BF to  sufficient  artery the  brain,  not  carotid  experiments  occluder was placed  halothane-anesthetized rats  could  left  determine BF to the brain v i a the l e f t c a r o t i d A polyethylene  was  the  from  the  verified  into the l e f t v e n t r i c l e f o r the  that  the  another  blood  In  using  Since t h i s e n t a i l e d placing a cannula  carotid  cross-circulation.  carotid artery.  be  used  artery  were  injection in  alone  carried  the could  out  to  artery.  loosely  around  each subclavian  artery  of  and e x t e r i o r i z e d at the back of  the  neck.  These occluders, s i m i l a r to those designed by Johnston et a l . (1983),  consisted of a length of PE 10 tubing one end of which had been f l a r e d with a  soldering  iron.  A polythene  suture  was threaded  through  the  tubing,  around the artery and back through the f l a r e at the bottom of the  tubing,  where i t was melted down s l i g h t l y with a soldering iron to secure i t . the  rats  recovered  pentobarbital artery  and  Radioactively  while  1  week  they  were  anesthetized  with  sodium  (65 mg/kg, n = 6) and cannulae were inserted into the femoral via  the  right  carotid  l a b e l l e d ' microspheres  the l e f t v e n t r i c l e . suture  for  After  artery (Co^  or  into ^Sn)  the  left  were  ventricle.  injected  into  The subclavian a r t e r i e s were l i g a t e d by p u l l i n g on the  holding  suture and the guide.  the  polyethylene  guide,  and heat-sealing  Microspheres l a b e l l e d with a d i f f e r e n t  then injected into the l e f t v e n t r i c l e .  both  the  isotope were  -  2.6.3  Microsphere  -  53  technique.  BF  was  determined  microsphere technique as described in section 2 . 5 . 2 . of  microspheres,  blood  was withdrawn  rather than an i l i a c a r t e r i a l hemispheres  (cerebrum  and  from  cannula.  the  using  During the  femoral  injection  arterial  cannula  Blood samples, l e f t and r i g h t  cerebellum),  and  brain  stem were  the  brain  counted  for  r a d i o a c t i v i t y using a Picker Gamma Counter (Model 644-055 Dual Channel/Dual Window A n a l y z e r ) . 2.6.4  Determination of c i r c u l a t o r y  leakage.  Since internal  venous drainage from the head to the body of each rat was s t i l l the extent of c i r c u l a t o r y leakage from the head of rat c i r c u l a t i o n was assessed.  jugular  functional,  B to i t s  peripheral  Radioactive solutions were obtained by leaching  57 the normal  Co microspheres saline)  (approximately  with 150 ul  of  50,000  concentrated  microspheres  nitric  acid.  in  300 ul  of  The r a d i o a c t i v e  s o l u t i o n was neutralized to pH 6 with sodium bicarbonate and suspended in 0.5 ml  of  injected  10% F i c o l l intravenously  70  solution.  into  rat  A  This in  suspension  (150 ul)  cross-circulated  rat  was  then  preparations  (n = 4 p a i r s ) , and blood (0.5 ml) was removed from both rats A and B at 3, 6, 9 and 15 min a f t e r measurement of 2.6.5  the i n j e c t i o n  of the r a d i o a c t i v e  suspension f o r  radioactivity.  E f f e c t s of c l o n i d i n e and methoxamine.  The c r o s s - c i r c u l a t i o n  preparation was used to investigate both the central and peripheral of c l o n i d i n e (n = 4) and methoxamine (n = 6 ) . to the i . v . normal  injection  saline)  observed in  1,  effects  Maximum MAP and HR responses  in rat A of e i t h e r c l o n i d i n e (25 ug/kg in 100 ul  or methoxamine  (25 ug/kg in  both rats A and B.  In  all  100 ul  of  normal  saline)  of  were  cases MAP and HR responses were  observed within 2 min in rat A and between 2 and 3 min in rat B.  - 54 2.6.6 2.5.4.  Calculations.  Tissue BF was c a l c u l a t e d as shown in  section  C i r c u l a t o r y leakage was c a l c u l a t e d as f o l l o w s : % leakage =  '-  c 3  ™ blood sample from rat B at any time  ni  ^ ^  x  n n  cpm in blood of rat A, 1 min a f t e r i n j e c t i o n of ^ C o 2.6.7  Statistical  analysis.  Results were expressed as mean ± SEM.  A n a l y s i s of variance and Duncan's m u l t i p l e statistical  significance.  A probability  range t e s t of  preselected as the c r i t e r i o n f o r s t a t i s t i c a l 2.7  error  were used to  of  less  than  assess  0.05 was  significance.  Central a g - a g o n i s t s in conscious r a t s 2.7.1  Experimental  were prepared with  protocol.  i.c.v.  Male Sprague-Dawley rats  cannulae as described in  (280-320 g)  section 2 . 1 . 1 ,  except  that commercially a v a i l a b l e cannulae ( P l a s t i c Products Co.) were used.  The  guide cannula (22-gauge) and the dummy cannula (28-gauge) were both cut to a length of 20 mm. arterial  and  unrestrained monitored. tubing  to  After venous  rats  cannulae  as  previously  described.  were placed in a cage and MAP and HR were  An internal a 5 ul  recovering 7 days, r a t s were prepared with femoral  cannula (28-gauge, 20 mm l o n g ) ,  Conscious continuously  connected with PE  Hamilton syringe and preloaded with drug or  v e h i c l e was  inserted into the guide cannula. The experiments were conducted over 2 days. HR responses to  i.c.v.  agonists were observed. rats  in  Group  II  doses  (Kobinger  0.1,  1.0,  (n = 8)  received (B-HT 920),  a  more  and P i c h l e r 1980b, 1982).  a-adrenergic  selective  All  c^-adrenergic  drugs were dissolved  in  Doses were administered at  At the end of the day, the vascular cannulae were flushed  with heparin and r e s e a l e d , and the guide cannula.  of  6-allyl-2-amino-5,6,7,8-tetrahydro-  normal s a l i n e and injected in a volume of 2 y l . l e a s t 1 h apart.  10.0 ug)  Rats in Group I (n = 8) were given c l o n i d i n e , while  4H-thiazolo-[4,5-d]-azepine agonist  (0.01,  On the f i r s t day, MAP and  dummy cannula was reinserted  into  the  -  55 -  On the second day, MAP and HR were again monitored. given 20 min to a c c l i m a t i z e , a control  given  recorded  the  once  previous the  day  was  response  was  r a t s were  blood sample was obtained f o r  analysis of catecholamine concentration. drug  After  later  Twenty min l a t e r , 1 pg of the same  injected fully  centrally.  developed,  MAP and  within  HR were  2-5 min  after  i n j e c t i o n , and a second blood sample was taken immediately afterward.  After  30 min, 10 pg of the same drug was i n j e c t e d , MAP and HR were recorded and a final  blood  sample was obtained.  Each  animal  received  injections  of  a  s i n g l e drug o n l y . In  order  to  determine whether  the  responses to  c l o n i d i n e and B-HT 920 were mediated by c * 2 ~ also  injected  in  rats  pretreated  o ^ - a n t a g o n i s t , rauwolscine. obtained,  rats  in  Groups  (n = 8)  t o r s  centrally  Twenty min after III  P  a d r e n o c e  i.c.v. >  IV  with  (n = 8)  i n j e c t i o n s of 10 pg rauwolscine in 4 pi normal s a l i n e .  the  selective  blood sample was received  i.c.v.  MAP and HR responses  were recorded and a second blood sample was obtained w i t h i n 2-5 min. 30 min,  rats  clonidine testing  in  and  for  Group  1 pg  III  and  B-HT 920,  blockade  of  IV  received  respectively,  (^-adrenoceptors  i.c.v. in  with  1 pi  of  these drugs were  the control  and  injection  injections normal  various  After  of  saline.  agonists,  it  1 pg By has  been found that rauwolscine e f f e c t i v e l y blocks pressor responses to B-HT 920 for  at  least  40 min f o l l o w i n g  personal o b s e r v a t i o n ) .  i.v.  administration  in  rats  (Pang et a l . ,  MAP and HR responses were recorded and a f i n a l  blood  sample was obtained w i t h i n 2-5 min of i n j e c t i o n . On completion of  the  experiments,  rats  were t r a n s c a r d i a l l y  perfused  and the brain removed and sectioned to v e r i f y the cannula p o s i t i o n . samples were assayed by HPLC f o r plasma catecholamine concentrations.  Blood  - 56 2.7.2  Statistical  analysis.  Results were expressed as mean  Analysis of variance and Duncan's multiple statistical  significance.  A probability  range t e s t of  error  of  ±  SEM.  were used to assess less than  0.05 was  preselected as the c r i t e r i o n f o r s t a t i s t i c a l s i g n i f i c a n c e . 2.8  Drugs All  drug solutions were made fresh d a i l y except f o r AVP and the AVP  antagonist which were made up f r e s h l y each day from stock s o l u t i o n s . the central  AVP s t u d i e s , AVP (Calbiochem) and AVP antagonist  For  (the g i f t  of  Dr. M. Manning, Department of Biochemistry, Medical College of Ohio) were dissolved M  in a r t i f i c i a l  NaCl;  KH P0 ; 2  4  5.0 x 1 0 " 2.0 x 10~  3  CSF. The a r t i f i c i a l KC1;  3  M  2.6 x 10~  2  MgS0 7H 0; 4  2  CSF consisted of M  NaHC0 ; 3  M  AVP, AVP antagonist, s a r a l a s i n (the g i f t of Dr. K. 0. E l l i s , Pharmaceuticals) and angiotensin II intravenously (Boehringer  were Ingelheim  dissolved  in  Canada L t d . ) ,  CaCl .  saline.  The  3  M The  2  Norwich-Eaton  (Ciba-Geigy Canada) which were normal  -  1.25 x 1 0 "  3  2.65 x 10~  1.24 x IO '''  injected  clonidine  HCl  methoxamine  HCl (Burroughs Wellcome),  B-HT 920 HCl (Boehringer Ingelheim Canada L t d . )  and rauwolscine HCl (Carl  Roth) used in the c r o s s - c i r c u l a t i o n and CNS studies were also dissolved in normal s a l i n e .  - 57 3  RESULTS  3.1  Central AVP in conscious rats 3.1.1  Central  administration  of  AVP.  i n j e c t i o n of a low dose of AVP i n Group I,  One min  after  the  i.c.v.  there were s i g n i f i c a n t increases  in MAP and the plasma l e v e l s of adrenaline but not noradrenaline ( F i g . 4 a ) . There  were  increases  concentrations ( F i g . 4a).  in  MAP and  1 min a f t e r  the  increased ( F i g . 4b). injection  of  AVP  noradrenaline  injection  of  and  reached  a  maximum  made once the  within  However,  reductions  in  III  ( F i g . 5a).  plasma adrenaline  Catecholamine  There was no change in MAP  of  Group  1 min.  concentration  i . c . v . i n j e c t i o n s of both volumes of a r t i f i c i a l  i n j e c t i o n s of 1 and 3 y l small  but  significant  were observed 10 min  There were no changes  in MAP or plasma concentrations of noradrenaline or adrenaline a f t e r i n j e c t i o n s of both doses of AVP antagonist in Group V ( F i g . 6 ) .  central  if  the receptors  AVP were i d e n t i c a l  experiments injection  was of  noradrenaline  carried  AVP or  involved to  out  antagonist adrenaline  in mediating the  peripheral on  Group  did  not  (Fig. 7).  alter  As  in  i.c.v.  In order to  pressor response to  V-^ receptors,  VI.  after  CSF ( F i g . 5b).  3 . 1 . 2 Central administration of AVP antagonist.  determine  the  change in MAP reached a steady  i.c.v.  in  the high dose of AVP  The increase in MAP began within 0.5-1.0 min a f t e r  or plasma catecholamine l e v e l s 1 min a f t e r vehicle  adrenaline  i n j e c t i o n s of both high and low doses  Heart rate did not change s i g n i f i c a n t l y .  the  and  MAP and plasma noradrenaline and adrenaline l e v e l s were  measurements were therefore state.  i.c.v.  Ten min a f t e r the i . c . v .  of AVP in Group I I ,  plasma  a further  Group  MAP or  V,  plasma  However, AVP antagonist  the  set  of  i.c.v.  levels  of  prevented  both the pressor response and the increase in catecholamine l e v e l s following the central i n j e c t i o n of AVP ( F i g . 7 ) .  58  MAP  •  CONTROL  S  23 n g / k g AVP  |  73  ng/kg AVP  NA  A  —r-  F i g . 4.  The e f f e c t s  of  i.c.v.  injections  of  AVP on MAP and plasma  noradrenaline and adrenaline concentrations (a)  and Group  II  (b).  *  in r a t s  Responses in Groups  I  from Group I  (n = 10) and  (n = 8) were measured at 1 and 10 min, r e s p e c t i v e l y , after  II  i.c.v.  * injections different  of AVP. from control  Values represent (P < 0.05).  mean  ±  SD.  Significantly  -  The  effects  plasma (a)  i.c.v.  noradrenaline  and  ( n = 6)  of  Group were  injections  IV  and  (b).  measured at of  59 -  injections adrenaline Responses 1 and  artificial  Significantly different  of  •  CONTROL  0  1 ul VEHICLE  •  3 ul VEHICLE  artificial  levels in  Groups  10 m i n ,  CSF.  from c o n t r o l  in  CSF on  and  Group  III  rats  from  III  (n = 7)  respectively,  Values  MAP  represent  (P < 0 . 0 5 ) .  after  and  IV  i.c.v.  mean * S D .  -  60 -  •  CONTROL  0  0.5 pg/kg AVP ANTAGONIST  •  1.5 pg/kg AVP ANTAGONIST  NA  MAP  14 o r  X £ E  2  12 0  r-  oi c  iooU Fig.  6.  The e f f e c t  of  noradrenaline  i.c.v.  injection  and a d r e n a l i n e  o f AVP a n t a g o n i s t concentrations  in  o n MAP and p l a s m a rats  from  Group V  * (n = 5 ) . from  Values  control  represent  (P < 0 . 0 5 ) .  mean  ±  SD.  Significantly  different  -  61  -  •  CONTROL  0  2.0 ug/kg AVP ANTAGONIST  •  96 ng/kg AVP  MAP  NA  140  10O^-  Fig.  7.  The e f f e c t  of  gonist  MAP  ... (mean * VI  on  pretreatment and  SD) f o l l o w i n g  (n = 1 1 ) .  plasma i.c.v.  of  the  fourth  ventricle  noradrenaline  and  injections  AVP i n  Significantly different  of  with  AVP a n t a -  adrenaline  from c o n t r o l  rats  from  levels Group  (P < 0 . 0 5 ) .  - 62 3.1.3  Peripheral  administration  of  AVP  and  AVP  antagonist.  An  increase in MAP and reductions in plasma concentrations of noradrenaline and adrenaline were observed 1 min a f t e r ( F i g . 8a).  In  10 min a f t e r  i.v.  ( F i g . 8b). reduction  Group V I I I ,  The in  i.v.  injections  of AVP in  MAP and plasma catecholamine  Group  l e v e l s measured  i n j e c t i o n s of AVP were not d i f f e r e n t from control i.v.  injection  MAP but  no  of  AVP antagonist  change  in  plasma  in  VII  Group  noradrenaline  IX  values  caused a  or  adrenaline  concentrations ( F i g . 8 c ) . 3.2  Central AVP in hypotensive rats The continuous i . v .  I,  infusion of sodium nitroprusside in rats in Group  which served as c o n t r o l s ,  significant  led to  a significant  reduction  increases in plasma noradrenaline and adrenaline  a f t e r 10 min.  Ten min a f t e r the i . c . v .  of  MAP and  concentration  i n j e c t i o n of the v e h i c l e in Group I  during the continuous i n f u s i o n of n i t r o p r u s s i d e , there was a s l i g h t , but not significant  further  noradrenaline noradrenaline  reduction  and  Group II  adrenaline  concentration  observed 10 min a f t e r  of  the  was start  MAP and  a further  concentrations significantly of  the  increase  in  (Fig. 9). increased  nitroprusside  showed i d e n t i c a l responses to those in Group I.  plasma  Only  from  the  infusion.  the level  Rats  Ten min after  in the  i n i t i a t i o n of the n i t r o p r u s s i d e i n f u s i o n , MAP was s i g n i f i c a n t l y reduced from control  and plasma noradrenaline  increased. infusion  Ten min a f t e r of  noradrenaline  and adrenaline  the i n j e c t i o n  nitroprusside, and adrenaline  MAP was  of  l e v e l s were  the AVP antagonist  slightly  reduced  levels increased further, o  further although  increase in plasma noradrenaline concentration was s t a t i s t i c a l l y (Fig. 9).  significantly during  the  and plasma only  the  significant  - 63 •  CONTROL  S  23 n g / k g AVP  |  7 3 n g / k g AVP •  0  0.5 (jg kg A V P A N T A G O N I S T  ED 1.5 yg/kg MAP  Fig.  8.  The e f f e c t plasma Group  NA  of i . v .  injections  noradrenaline VII  (a),  Groups V I I  (n = 5)  were  o f AVP and AVP a n t a g o n i s t  VIII  i.v.  (b)  concentrations  and Group  IX  on MAP and  in  (c).  rats  Responses  from in  ( n = 5) w e r e m e a s u r e d a t 1 and 10 m i n ,  injections  obtained  10 m i n  Values  represent  from c o n t r o l  (P < 0 . 0 5 ) .  antagonist. different  Group  after  A  and a d r e n a l i n e  ( n = 8 ) and V I I I  respectively,  AVP ANTAGONIST  of AVP.  after  i.v. mean  ±  Responses  i n G r o u p IX  injections SD.  of  AVP  .Significantly  - 64a F i g . 9.  The e f f e c t of i . c . v . antagonist line  i n j e c t i o n s of a r t i f i c i a l  (Group II)  levels  in  rats  receiving  i.v.  control  values  nitroprusside  10 min of  represent values 10 min after ist  during  mean * SEM. (P < 0.05).  continuous a  and AVP  on MAP and plasma noradrenaline and adrena-  Open columns represent after  CSF (Group I)  values,  ^Significantly  of  nitroprusside.  shaded columns  infusion  represent  and s o l i d  columns  i n j e c t i o n of v e h i c l e or AVP antagon-  nitroprusside  Significantly  infusions  infusion.  different different  infusion of nitroprusside (P < 0.05).  from  from value  Values  represent  control reported  value after  - 65 3.3  M i c r o i n j e c t i o n of AVP into the nucleus tractus  solitarius  The e f f e c t s of the i n j e c t i o n of AVP and the AVP antagonist on MAP are shown in F i g . 10. II  and III  Injection of both 2 and 10 ng AVP into the NTS in Groups  s i g n i f i c a n t l y elevated MAP by 4 and 15 mmHg, r e s p e c t i v e l y .  The  r i s e in MAP began within 15-20 sec of i n j e c t i o n and the maximal response was reached within 1 min of i n j e c t i o n . Group I and the AVP antagonist the treatments  significantly  The i n j e c t i o n of the v e h i c l e (0.2 y l )  in Group IV had no e f f e c t  changed HR ( F i g . 10).  on MAP.  ( F i g . 11).  The administration  of the  None of  The i n j e c t i o n  10 ng dose of AVP s i g n i f i c a n t l y elevated plasma noradrenaline  of  lower dose of AVP, v e h i c l e , or AVP  adrenaline concentration was s i g n i f i c a n t l y increased after ( F i g . 11).  in plasma adrenaline l e v e l s a f t e r  the  concentration  antagonist did not s i g n i f i c a n t l y change plasma noradrenaline l e v e l s .  10 ng AVP into the NTS in rats  in  Plasma  the i n j e c t i o n  of  There was no s i g n i f i c a n t change  the i n j e c t i o n  of the  lower dose of AVP,  AVP antagonist or v e h i c l e . 3.4  Central AVP in neurogenically-stressed rats Rats in Group I,  MAP,  no  change  in  adrenaline l e v e l s None  of  these  which served as c o n t r o l s ,  HR and  after changes  slightly  increased  a 10 min exposure to were  had a s l i g h t l y  significantly  plasma  the  heat  different  increased  noradrenaline  and  lamp ( F i g . 12,13). from  pretreatment  levels.  MAP, HR and plasma noradrenaline and adrenaline concentrations were  further  increased 5 min a f t e r  injection  neurogenic s t r e s s , although t h i s  further  of  Group II  significantly  showed s i m i l a r responses  greater  v e h i c l e during  continuous  increase was s i g n i f i c a n t  the case of plasma adrenaline concentration. MAP was, however,  the  only  in  A f t e r i n j e c t i o n of the vehicle  than the control  level.  Rats  to neurogenic stress ( F i g . 12,13).  10 min exposure to the heat lamp, MAP of rats in Group II  in  After  was s i g n i f i c a n t l y  increased, while HR and plasma noradrenaline and adrenaline concentrations  (a)  .(b)  (a)  -(b)-  (c)  (d)  (c)  (d)  450  10. The e f f e c t (n = 10);  of (b)  injection  .  into the  2 ng AVP (n = 8 ) ;  10 ng AVP antagonist  (n = 8 )  NTS of  (a.)  (c)  10 ng  on MAP and HR.  2 ul  AVP (n = 10);  mean * SEM.  (P < 0.05).  *Significantly  different  CSF (d)  Open columns represent  control v a l u e s , shaded columns represent treatment are  artificial  from  values. control  Values value  - 67 -  .75-1  3  .60  -  .45  -  (a)  .75  ~\  .60  -  (b)  (a) F i g . 11. The e f f e c t (n = . 1 0 ) ;  of Cp)  (b) injection 2  into the  ng AVP (n = 8 ) ;  (c)  (d)  (c)  (d)  NTS of (c)  (a)  .  2 yl  artificial  CSF  10 ng AVP (n = 10);  (d)  10 ng AVP antagonist (n = 8) on plasma noradrenaline and adrenaline concentration. columns  Open  represent  columns  treatment  * S i g n i f i c a n t l y different  represent values.  control Values  values, are  from control value (P < 0.05).  shaded  mean •* SEM.  - 68a F i g . 12.  The e f f e c t of i n j e c t i o n and AVP antagonist stress  into the NTS of a r t i f i c i a l  (Group  on MAP and HR.  II)  of  rats  CSF (Group  subjected  Open columns represent  to  neurogenic  control  values;  shaded and s o l i d columns represent values obtained initiation vehicle  of neurogenic s t r e s s , and 5 min after or  mean ^ SEM. (P < 0 . 0 5 ) . after  AVP a  antagonist,  Significantly  respectively. different  ^Significantly different  from,  10 min  after  the i n j e c t i o n Values  of  represent  control  from value obtained  i n i t i a t i o n of neurogenic stress (P < 0.05).  I)  value 10 min  - 68 -  Adrenaline (ng/ml)  Noradrenaline (ng/ml) PJ  _1_  0)  00  PJ  _L  0)  J  CTS  73  O  CO  CD  O  - 69a F i g . 13.  Plasma noradrenaline  and adrenaline  the NTS of a r t i f i c i a l  CSF (Group I)  of  neurogenic  rats  control  subjected  to  values;  shaded  obtained 10 min after after  injection  of  Values  represent  control  value  and  mean * SEM.  (P < 0.05).  obtained 10 min after  stress.  of  or  into  (Group  II)  represent  represent  values  neurogenic s t r e s s , and 5 min antagonist,  Significantly  ^Significantly  initiation  injection  Open columns  columns  AVP a  after  and AVP antagonist  solid  initiation vehicle  levels  respectively.  different  different  from  from value  of neurogenic stress (P < 0.05).  - 70 were s l i g h t l y  but  not  significantly  elevated.  Five min a f t e r  the  i.c.v.  i n j e c t i o n of the AVP antagonist in rats subjected to neurogenic s t r e s s , MAP, HR and plasma adrenaline l e v e l s showed f u r t h e r plasma  noradrenaline  increased.  concentration  was  significant  slightly  Therefore, the AVP antagonist  but  elevations and  not  significantly  did not prevent the  increase in  MAP and plasma adrenaline l e v e l s caused by neurogenic s t r e s s . 3.5  Vascular r o l e of AVP 3.5.1  Effect  of  Table 1 shows control  antagonism of  pressor systems on MAP, CO and TPR.  values of MAP p r i o r  to and f o l l o w i n g the infusion of  s a l i n e or drugs in the various groups of r a t s . did  not  alter  MAP in  rats  from  Group  phentolamine decreased MAP in Groups II  I.  Infusions  and I I I ,  comparison of r e s u l t s between groups I and II saralasin, did  not  A 10 min infusion of s a l i n e  any  significant  change  and  However, a  during infusions of s a l i n e and  in  corresponding values in Group I (Table 1 ) .  saralasin  respectively.  r e s p e c t i v e l y , shows that the i n f u s i o n of cause  of  s a r a l a s i n in Group  MAP, CO,  or  TPR from  II the  Therefore, unlike comparisons of  MAP within the same animal, we were unable to detect a s i g n i f i c a n t decrease of MAP during the infusion of s a r a l a s i n in Group II in Group I which received infusion of s a l i n e . Groups I and III  Comparisons of values between  show that MAP and CO in Group III  than the corresponding values in Group I. between Groups I and  compared to control MAP  were s i g n i f i c a n t l y  There was no difference  lower in TPR  III.  3..5.2 E f f e c t of AVP antagonist on MAP, CO, and TPR.  The i n j e c t i o n  of  AVP antagonist decreased MAP and TPR but not CO in the three groups of rats ( F i g . 14).  Table 2 shows the MAP, TPR and CO responses normalized as a  percentage  of  control  antagonist  in  the  to  allow  different  comparisons  groups.  The  of  the  effects  antagonist  of  caused  decrease of percent control of MAP in Group II than in Group I.  the AVP a  greater  Although  - 71 Table 1.  Control values of MAP, CO and TPR in Groups I,  Groups  II,  and  III  I  II  III  MAP (mmHg)  a  103 ± 17  106 ± 14  95 ± 13  MAP (mmHg)  b  103 ± 17  91 ± 17  105 ± 26  90 ± 20  69 ± 2 0  1.04 ± 0.29  1.03 ± 0.15  1.20 ± 0.37  CO (ml/min)  b  TPR (mmHg min/ml)  b  A l l values represent mean ± SD. a  Groups I, c  II  and I I I ,  Significantly  c d  d  infusion.  Denotes readings of MAP, CO or TPR during the f i r s t the  79 ± i o  n = 8 in each group.  Denotes MAP readings p r i o r to drug ( s a l i n e )  at 10 min following  c  infusions  of  determination  of CO,  s a l i n e , s a r a l a s i n or phentolamine  respectively.  different  from  MAP p r i o r  to  the  infusions  of  drug  s a l i n e within the same group (p < 0.05). d  in  Significantly different  from corresponding values in Group I (p < 0.05).  or  -  72 -  150 n  '_! 1.5 1 £  100  f •  l.o 4  X  8  E  so A  e  -  Q_  GROUPS  Fig. 14.  Effect  X  0.5 -\  x  GROUPS  of  AVP antagonist  surgically stressed rats:  GROUPS  on MAP, CO and TPR in  anesthetized,  intact and saline-pretreated  (Group I),  saralasin-pretreated (Group II) and phentolamine-pretreated (Group III).  CO was determined twice in each group of rats.  AVP anta-  gonist was given to each group between the f i r s t and second deter-  * minations of  CO.  Significantly different  from the first determination (P < 0.05).  from values  obtained  - 73 Table 2. E f f e c t s of AVP antagonist on MAP, CO and TPR in Groups I,  and  Groups  I  % of control MAP  87 ± 12  75 ± I 0  % of control CO  105 ± 17  106 ± 22  118 ± 30  % of control TPR  85 ± 1 8  73 ± 15  61 ± 2 1  A l l values represent mean ± SD. TPR  obtained  during  the  II  II  III  determination  71 ± 1 3  a  n = 8 in each group.  second  III  a  a  Values of MAP, CO and of  CO  following  the  administration of AVP antagonist were expressed as a % of the corresponding values obtained during the f i r s t of III a  rats:  Group I  determination of CO in the various groups  (saline-treated);  Group II  (saralasin-treated);  (phentolamine-treated). S i g n i f i c a n t l y d i f f e r e n t from Group I (p < 0.05).  Group  the AVP antagonist caused a greater decrease in control TPR in Group II in  Group  I,  the  decrease was  not  statistically  significant.  The AVP  antagonist caused s i g n i f i c a n t l y greater decreases of percent control and TPR in Group III  than in Group I.  differential  in the percent of control  effects  than  of MAP  The AVP antagonist did not cause any CO.  the AVP antagonist exerts greater depressor e f f e c t s  The r e s u l t s show  that  in rats with antagonism  of the renin-angiotensin or a-adrenergic systems than in i n t a c t r a t s . 3.5.3 E f f e c t of AVP antagonist on the d i s t r i b u t i o n intact  rats  (Group I ) ,  the AVP antagonist  skin  ( F i g . 15) but did not  alter  that  AVP has the  vasoconstrictor  stomach  and  antagonist  greatest  skin.  During  influence of  in  saralasin  This the  indicates  area of  (Group  II),  the AVP lungs  Therefore in the absence of influence from angiotensin  AVP has the greatest vasoconstrictor e f f e c t s in the vascular beds in the  skin and muscles. AVP  any other organs.  infusion  In  increased BF to the stomach and  increased BF to muscles and skin and decreased BF to the  and l i v e r ( F i g . 16). II,  the  BF to  of blood f l o w .  antagonist  During a continuous i n f u s i o n of phentolamine (Group  markedly  decreased BF to the l i v e r ,  increased muscle BF (note  change of  III),  scale)  i n t e s t i n e , kidneys, and t e s t e s ( F i g . 17).  and  Thus,  in the absence of the a-adrenergic system, AVP has the greatest influence on BF to the muscle.  - 75 -  25 n  F i g . 15.  Effect of AVP antagonist on regional d i s t r i b u t i o n from Group I the  (saline-pretreated).  determination  of  BF.  All  of BF in  rats  Whole r a t s were dissected for values  represent  BF to  entire  organs.  Glands include t h y r o i d , parathyroid, s a l i v a r y and adrenal  glands.  BF was determined twice in each r a t .  given between the f i r s t ficantly different (P < 0.05).  AVP antagonist was  and second determinations of  from BF obtained from the f i r s t  BF. * S i g n i determination  - 76 -  30  25 -  e 20 -  5  o _l  15  Q O O. _l  10  Lu  CD  rift  r^l  3C  O  z  =3 —I  F i g . 16.  ac o <_i o UJ o  CC  «c  u» X  UJ O  m*a  r^h  W1 UJ I—  _ l  _j  o.  o  Effect of AVP antagonist on regional d i s t r i b u t i o n  of  from Group II  were dissected  for  (saralasin-pretreated).  the determination of  BF.  Whole r a t s  BF in  o co  A l l values represent BF to  rats  entire  organs.  Glands include t h y r o i d , parathyroid, s a l i v a r y and adrenal  glands.  BF was determined twice in each r a t .  given between the f i r s t ficantly different (P < 0.05).  AVP antagonist was  and second determinations of  from BF obtained from the f i r s t  BF.  Signi-  determination  -  77  50  |  40  E —  30 H  o H  1  Q O O m  20  -I  1.  10  r*Th z 2: o r> _ J CJ o  <  <  17.  Effect from  of  CO  Q z  entire adrenal  Group for  III  BF  regional  given  (P <  include was  BF.  thyroid,  the  different  0.05).  of  determined  between  Significantly  determination  on  determination  Glands  glands. was  2:  distribution  first from  All  o  of  and  CO  BF  Whole  in  rats  rats  were  values represent  BF t o  parathyroid, twice  z o  _J  co  CO  (phentolamine-pretreated).  the  organs.  antagonist BF.  -o  AVP a n t a g o n i s t  dissected  of  >-  LU C J CJ  Fig.  r*Tih  CO  in  each  second  BF o b t a i n e d  salivary rat.  and AVP  determinations from  the  first  - 78 3.6  Central and peripheral actions of a-agonists 3.6.1  ligation  Blood flow  to  the  brains of  of the subclavian a r t e r i e s ,  cross-circulated rats.  peripheral  Prior  to  blood from rat A supplied  the l e f t and r i g h t brain hemispheres and brainstem of rat A ( F i g . 18a) and only  the  left  ( F i g . 18b).  and  right  hemispheres  but  not  the  brainstem  of  rat  B  A f t e r l i g a t i o n of the subclavian a r t e r i e s peripheral blood from  rat A supplied n e g l i g i b l e BF to the brain of rat A but  instead a l l  diverted to both brain hemispheres and brainstem of rat B.  BF to a l l  of the brain of rat A was s i g n i f i c a n t l y decreased while BF to a l l the brain of rat  B was s i g n i f i c a n t l y  increased f o l l o w i n g  BF was parts  parts  of  of  the  ligation  subclavian a r t e r i e s . 3.6.2 Blood flow to the brain v i a the l e f t c a r o t i d a r t e r y . the brain before and a f t e r  l i g a t i o n of the subclavian a r t e r i e s  rat  In  is  shown in F i g . 19.  the control  condition,  supplied by the l e f t common c a r o t i d a r t e r i e s After only  ligation by the  ligation  of  of  both subclavian a r t e r i e s ,  left  common c a r o t i d  the  subclavian  hemispheres was s l i g h t l y  although not  in a s i n g l e  the. brain was  and both subclavian a r t e r i e s . BF to  arteries.  arteries  BF to  The BF to  the  brain was supplied  Our r e s u l t s  BF to  the  significantly  left  show that and  after  right  brain  increased while  BF to  the brainstem was s l i g h t l y but not s i g n i f i c a n t l y reduced. 3.6.3  Circulatory  leakage.  The amount of  radioactivity  detected  in  the blood samples removed from rats A and B, expressed as a percentage of the  radioactivity  originally  present  in  rat  A  (measured  1 min  after  57 injection 3 min,  of  Co),  is  shown in  and reached a maximum of  obtained from rat  A was found to  Table 3. 18% at  Leakage was less 6 min.  gradually  p r i m a r i l y as a r e s u l t of t i s s u e uptake.  than  Radioactivity  decrease with time,  10% at  in  blood  probably  - 79 -  CONTROL Q  LIGATION  ^  a) RAT A  i  —  uCO  MEAN + SE.  -i  N=8  .6  e  "\  E  • *  L. BRAIN  R. BRAIN  BRAINSTEM  b) RAT B  • 8 — e Lu CO  . 6-  1  E  \  J. •'' . 2  4  ^ 1I L. BRAIN  F i g . 18.  BF to the and a f t e r (b)  of  left  R. BRAIN  and r i g h t  BRAINSTEM  brain hemispheres and brainstem before  l i g a t i o n of the subclavian a r t e r i e s in r a t s A (a) and B cross-circulated  rat  preparations.  d i f f e r e n t from p r e - l i g a t i o n BF (P < 0.05).  * S i gn i f i c a n t l y  -  80  -  CONTROL Q  LIGATION MEAN + SE N=6  l - SH  1  .E  . 5-  L. BRAIN  Fig.  19.  BF t o  the  presence rats.  left and  R. BRAIN  and r i g h t  absence of  brain  BRAINSTEM  hemispheres  functional  and  subclavian  brainstem  arteries  in  in  the  single  - 81 Table 3.  Cpm in rats A and B expressed as a  min (n = 4 ) .  of cpm detected in rat A in 1  Values represent mean ± SEM. Time (min) 1  3  6  9  15  Rat A  100  74 ± 9  47 ± 5  43 ± 5  35 ± 5  Rat B  5 ± 2  8 ± 3  18 ± 4  10 ± 2  13 ± 3  - 82 3.6.4  C r o s s - c i r c u l a t e d rat  in rat A caused a s i g n i f i c a n t significant) reduction  preparation.  The i n j e c t i o n  increase in MAP, and a s l i g h t  in HR in rat A, and a s i g n i f i c a n t  (not s i g n i f i c a n t )  in HR in rat  of  clonidine  decrease  (not  decrease in MAP and a s l i g h t  B ( F i g . 20).  MAP and HR tracings  from a t y p i c a l experiment with c l o n i d i n e are shown in F i g . 21.  The response  of rat A to c l o n i d i n e became evident w i t h i n 5-10 sec and lasted about 2 min, while the response to c l o n i d i n e became apparent and lasted 3-5 min.  in  rat  B within  Conversely, i n j e c t i o n of methoxamine in rat A s i g n i f i -  cantly increased MAP and decreased HR in rat A, and, s i g n i f i c a n t l y MAP and s l i g h t l y but not s i g n i f i c a n t l y and HR tracings F i g . 23. of  10-30 sec  from a t y p i c a l  increased  increased HR in rat B ( F i g . 22).  experiment  with methoxamine  are  MAP  shown  in  The response of rat A to methoxamine was apparent w i t h i n 5-10 sec  injection,  and lasted 2-3 min, while the response of  rat  B was evident  within 10-30 sec and persisted 4-6 min. 3.7  Central o^adrenergic agonists in conscious rats The control  values of MAP and HR p r i o r  to the administration  various doses of the a-agonists are l i s t e d in Table 4. of B-HT 920 in rats  in Group I on the f i r s t  The i . c . v .  of  the  injection  day was found to increase MAP  and decrease HR in a dose-dependent manner ( F i g . 24).  On the second day of  the experiment, the i n j e c t i o n of 1 and 10 yg B-HT 920 caused changes in MAP and HR s i m i l a r to those on day 1 ( r e s u l t s not shown).  The e f f e c t s of 1 and  10 yg B-HT 920 on plasma catecholamine l e v e l s are shown in F i g . 25.  While  the accompanying changes in plasma catecholamine l e v e l s did not reach s t a t istical  s i g n i f i c a n c e , the  10 yg dose of  B-HT 920 appeared to  increase the  plasma concentration of noradrenaline, while the 1 yg dose had l i t t l e on noradrenaline  concentration.  Both doses of  increase the plasma l e v e l s of adrenaline.  effect  B-HT 920 had a tendency  In contrast, the i . c . v .  to  injection  of c l o n i d i n e in Group II on the f i r s t day led to a dose-dependent decrease  - 83 -  CONTROL . [ ]  MEAN + SE N=4  2 0 0 - 1  1 5 0 -  cn I  CL.  < 3;  E  ICO -  so-  CLONIDINE  1I  RAT B  RAT A  4 0 0 -  T  H  c  I  E. Q:  UI  2 0 0  -  I  •  RAT B  RAT A  Fig.  20.  MAP and HR r e s p o n s e s o f of  clonidine  control  (25 u g / k g )  (P < 0 . 0 5 ) .  rat in  A (a) rat  A.  and r a t  B (b)  to  *Significantly  i.v.  injection  different  from  - 84 -  200  200  r  •  r  CLONIDINE  Fig.  21.  1 min  Representative recordings  of  rat  injection  A.  B (b)  following  i.v.  MAP and HR r e s p o n s e s of  clonidine  in  rat  A (a)  (25 y g / k g )  in  and rat  -  85 -  Q  CONTROL  ^  MEAN + SE N=6  *  T  METHOXAMINE  1 I  T  |  1  RA1 B  RAT A  6OO-1  5 0 0 -  —  4 0 0 -  RAT A  Fig.  ?.?..  MAP and HR r e s p o n s e s o f of  methoxamine  control  RAT B  rat  (25 u g / k g )  (P < 0 . 0 5 ) .  A (a)  in rat  and r a t A.  B (b)  to  *Significantly  i.v.  injection  different  from  - 86 -  200  Fig.  23.  r  Representative recordings of rat  B  rat  A.  (b)  following  i.v.  MAP and HR r e s p o n s e s o f  injection  of  methoxamine  rat  A (a)  (25  pg/kg)  and in  - 87 -  Table 4.  Control values of MAP, HR and plasma noradrenaline and adrenaline  concentration in Groups I, Drug  I:  II:  III:  IV:  Dose  II,  III  and IV p r i o r to drug administration.  MAP  HR  Noradrenaline  (yg)  (mmHg)  0.01  104 ± 1  386  11  —  0.1  105 ± 2  398 ± 10  —  1.0  86 ± 4  10.0  101 ± 5  381 ± 11  0.01  105 ± 3  398 ± 14  —  —  0,1  102 ± 2  389 ±  9  —  —  1.0  104 ± 2  388 ±  7  0.20 ± 0.06  10.0  104 ± 4  384 ±  8  0.20  0.06  1.14  Rauwolscine  10.0  99 ± 3  358 ± 13  0.17  0.05  0.65  B-HT 920  1.0  104 ± 3  376 ± 11  0.17  0.05  0.65 ± 0.25  Rauwolscine  10.0  106 ± 2  354  12  0.16  0.04  0.53 ± 0.15  Clonidine  1.0  103 ± 2  364  11  0.16  0.04  0.53 ± 0.15  B-HT 920  Clonidine  (beats/min)  385  9  (ng/ml)  Adrenaline (ng/ml) —  0.39 ± 0.05  0.24 ± 0.07  0.39  0.24 ± 0.07  0.05  0.14 ± 0.06 ± 0.06  0.25  GROUP I F i g . 24.  The e f f e c t (Group ^  of i . c . v .  II)  = 1.0 yg,  control.  on  i n j e c t i o n of B-HT 920 (Group I)  MAP  ^|•=  GROUP II  and  HR.  10.0 yg.  *Significantly different  Q  = 0.01 jig,  Values  represent  from control  and c l o n i d i n e [jjff] = 0.1 yg, change  (P < 0.05),  from  -  ~  0.3  -i  0.3  i  -0.3  89  -  J  GROUP I Fig.  25.  The e f f e c t (Group ^  = 1.0  control.  of  II) pg,  i.c.v. -injection on  plasma H=  GROUP of  B-HT 9 2 0  noradrenaline  10.0 pg.  *Significantly different  II  Values  (Group  and  I)  and  clonidine  adrenaline  levels.  represent  from c o n t r o l  (P <  change 0.05).  from  -  in  both  MAP and HR in  the  90 -  dose  range  of  elevation of MAP and reduction of HR a f t e r i.c.v.  0.01-1 pg  a  significant  the 10 pg dose ( F i g . 24).  The  i n j e c t i o n of 1 and 10 pg of c l o n i d i n e on the second day also caused  s i m i l a r changes in MAP and HR ( r e s u l t s not shown). adrenaline  l e v e l s decreased in response to  ( F i g . 25).  The i . c . v . in  both  Plasma noradrenaline and 1 and 10 pg of  clonidine  However, only the noradrenaline l e v e l a f t e r the i n j e c t i o n  pg of c l o n i d i n e was s i g n i f i c a n t l y d i f f e r e n t  rats  and  injection  Group III  adrenaline  of  significantly different subsequent  from the pretreatment value.  the s e l e c t i v e c ^ - a n t a g o n i s t , rauwolscine,  increased MAP, HR, and  concentrations  i.c.v.  ( F i g . 26),  both  although  from the pretreatment  injection  of 10  of  B-HT 920  in  plasma noradrenaline these  and  were  not  values shown in Table 4.  The  these  changes  in  animals  increased MAP  s i g n i f i c a n t l y and decreased HR ( F i g . 26) compared to control values obtained after  the treatment  with rauwolscine (Table 4 ) .  The i n j e c t i o n  of B-HT 920  also increased plasma noradrenaline and adrenaline concentrations ( F i g . 27), although these changes were not s i g n i f i c a n t l y or  rauwolscine  treatment  rauwolscine in rats  values  (Table  different  4).  The  in Group IV s i g n i f i c a n t l y  from control i.c.v.  injection  of  increased MAP, s l i g h t l y  but  not s i g n i f i c a n t l y decreased HR, and s l i g h t l y but not s i g n i f i c a n t l y plasma  noradrenaline  effect  of rauwolscine on HR in rats in Group IV was d i f f e r e n t  Group I I I ,  slightly and  levels  these changes were small  pretreatment clonidine  and adrenaline  control  after but  slightly  not  values  pretreatment  shown  Table  (Figs.  26,27).  significantly 4.  The  i.c.v.  with rauwolscine s i g n i f i c a n t l y  significantly  increased  in  and not  plasma  increased  Although  concentration  the  from that different injection  in  from of  decreased MAP,  decreased HR and plasma adrenaline noradrenaline  values  levels,  ( F i g s . 26,27),  compared to control values or rauwolscine treatment values (Table 4 ) .  91  15 - i 10  1  JL  cn  5 CL.  0 -5  0) CD  c  ra  -10  JZ  o  -15  J  20 -,  =  io  J3  OJ Cn  •10 -  c  T  o  •20  J  GROUP Fig.  26.  The 1 pg  effect  of  B-HT 920  clonidine control.  920  (Group  (Group Open  rauwolscine; B-HT  i.c.v.  and  Significantly  IV)  GROUP  injection III)  and  of  represent  columns  IV  10 ug  rauwolscine  10 pg r a u w o l s c i n e  on MAP and HR.  columns  shaded  III  followed  followed  Values represent values  represent  after  values  after  clonidine  in  Groups  III  and  different  from  control  (P < 0 . 0 5 ) ,  IV,  by  by  1 pg  change  from  injection injection  of of  respectively.  92  rE cn  0.3 H 0.2 -  ^  o.i H  O) s_ •o  0  n3 JO  cn c:  -  1 MEL  -o.i H -0.2 -0.3  0.3 -i cn  <y  0.2 -  0.1  S-  -0.1 g, "0.2  c  5  -0.3  J  GROUP III F i g . 27.  The effect  of  i.c.v.  injection  1 yg B-HT 920 (Group III) clonidine levels.  (Group Values  IV)  values  of  10 yg rauwolscine followed  and 10 yg rauwolscine followed  on  plasma  represent  change  represent values after represent  GROUP IV  after  Groups  III  and IV,  control  (P < 0.05).  injection injection  respectively.  noradrenaline from  and  control.  of rauwolscine; of  B-HT 920  and  *Significantly  by  by 1 yg  adrenaline  Open  columns  shaded columns clonidine different  in from  - 93 4  DISCUSSION  4.1  Central AVP in conscious rats Neuroanatomical studies have provided evidence to suggest that AVP may  play a r o l e in the modulation of the cardiovascular r e f l e x . has been shown to increase catecholamine turnover 1977).  Therefore, i t  by a f f e c t i n g central  Moreover, AVP  in the NTS (Tanaka et a l .  i s possible that AVP modulates cardiovascular r e f l e x e s  sympathoadrenal outflow.  administration  In t h i s study, we determined  of AVP a l t e r s MAP and plasma l e v e l s of  and adrenaline in conscious r a t s .  noradrenaline  Numerous studies have shown that plasma  concentrations of catecholamines provide a r e l i a b l e estimate of nerve a c t i v i t y et a l . 1985;  (Yamaguchi and Kopin 1979;  Goldstein et a l .  sympathetic 1983;  Esler  Hubbard et a l . 1986).  The r e s u l t s show that i . c . v .  injection  of both a high and a low dose  of AVP produced increases in MAP and plasma concentrations of and  whether  adrenaline  1 and  10 min  after  drug  administrations.  noradrenaline The  level  noradrenaline detected 1 min after the i n j e c t i o n of a low dose (23 ng/kg) AVP was however, not s i g n i f i c a n t l y d i f f e r e n t from the control level.  of  AVP than  it  was after  10 min.  Yamaguchi  of  noradrenaline  The release of adrenaline was found to be greater 1 min after  injection  of  i.c.v.  and Kopin  (1979)  reported that sustained sympathetic stimulation of pithed rats resulted in a rapid ( l e s s than 1 min)  increase of adrenaline l e v e l but slow elevation  noradrenaline l e v e l which peaked a f t e r  4 min of s t i m u l a t i o n .  Therefore,  i s not s u r p r i s i n g that the r i s e in adrenaline l e v e l was found in t h i s to  be higher  greater  after  10 min after  1 min, while the  i.c.v.  the  increase  injection  of  the  results  suggest  that  the  pressor  effect  noradrenaline  level  AVP.  Since the  increase  was mediated  by  it  study  in  blood pressure was associated with increased plasma catecholamine  of  was in  levels,  increased  - 94 sympathetic  nerve  sympathoadrenal  activity.  outflow  It  by  is  possible  central  that  AVP r e s u l t s  this  from  an  activation  of  inhibition  of  baroreceptor r e f l e x e s . Our  results  from  conscious  rats  are  consistent  Matsuguchi et a l . (1982) who found that m i c r o i n j e c t i o n s of  the  NTS of  anaesthetized rats  those  of  of AVP in the area  increased MAP and HR, and that  responses could be abolished by ganglionic i.c.v.  with  blockade.  these  We have found  that  i n j e c t i o n s of a second higher dose of AVP did not produce a greater  response than that obtained with the f i r s t dose. injected were very high, so that i t had produced the maximal response.  However, the doses of AVP  i s possible that the f i r s t It  dose given  i s also p o s s i b l e that tolerance may  have developed to a high l o c a l concentration of AVP, since Matsuguchi et a l . (1982) have reported the development of tolerance to the pressor e f f e c t s consecutive i n j e c t i o n s of AVP c e n t r a l l y . doses  (1-4 ng/kg)  changes  in  of AVP were injected  blood  pressure  or  In preliminary experiments, into the fourth v e n t r i c l e ,  plasma  catecholamine  of  lower but no  concentrations  were  observed. Anatomical studies have revealed that AVP-containing neurons terminate on somata and dendrites Therefore  it  is  likely  in  the  area of  that the  local  the  NTS (Sofroniew et a l .  concentrations  higher than those normally detected in the CSF. i.c.v.  of AVP may be much  This may be the reason why  i n j e c t i o n s of low doses of AVP did not produce any response.  was no change in MAP or plasma catecholamine l e v e l s in Group I I I , the  1981).  responses were  observed  1 min  after  injections  of  There  in which  artificial  CSF.  However, in Group IV, s l i g h t but s i g n i f i c a n t reductions in plasma adrenaline l e v e l s were observed 10 min after  i.c.v.  reason f o r t h i s i s obscure at present.  injections  of  the v e h i c l e .  The  - 95 It  was  found  that  injections  of  AVP antagonist  into  the  fourth  v e n t r i c l e did not affect MAP or plasma concentrations of catecholamines. one assumes that  both AVP and the  AVP antagonist  have s i m i l a r  If  diffusion  p r o p e r t i e s , the r e s u l t s suggest that endogenously released AVP does not have a tonic  influence on cardiovascular r e f l e x e s .  To r u l e out the  possibility  that the receptors involved in the mediation of AVP responses c e n t r a l l y not  identical  antagonist i.c.v. not  to  those present  prior  to the  injection  produce  of AVP after  any  concentrations.  i.c.v.  change  peripherally, injection  central  in  we pretreated  of AVP.  plasma  with AVP  We have found that  administration  MAP or  rats  of AVP antagonist  noradrenaline  This indicates that the receptors  or  are  the did  adrenaline  involved were synonymous  with peripheral AVP receptors. It  i s c o n t r o v e r s i a l whether a d i f f u s i o n b a r r i e r f o r AVP e x i s t s between  the blood and CSF. Several studies have shown the existence of a blood-CSF b a r r i e r to AVP (Ang and Jenkins 1982;  Vorherr et a l . 1968;  1985).  However, Schmid et a l .  (1984)  AVP to  the  To ensure  CNS i s  possible.  Stark et a l .  have reported that access of plasma that  the  observed responses  to  central AVP i n j e c t i o n s were not secondary to the d i f f u s i o n of the drug into the peripheral  circulation,  the e f f e c t s  of  i.v.  injections  antagonist were also examined.  One min after  significantly  plasma noradrenaline  increased, while  were reduced. effect  levels.  i n j e c t i o n of AVP, MAP was and adrenaline  The increase in MAP can be a t t r i b u t e d to the d i r e c t  of AVP on the  sympathetic  i.v.  of AVP and AVP  nerve  vasculature,  activity,  which  as r e f l e c t e d  Ten min after the i . v .  leads to by  the  a reflex decreased  levels pressor  reduction  in  catecholamine  i n j e c t i o n of AVP, the pressor e f f e c t of AVP  and plasma noradrenaline and adrenaline concentrations had returned to basal levels.  I.v.  injections  of  AVP  antagonist  did  catecholamine l e v e l s , although they did reduce MAP.  not  affect  plasma  The dose (2 yg/kg)  of  - 96 antagonist  used  peripheral  should  have  been  sufficient  to  produce  blockade  pressor receptors for AVP (Pang and Leighton 1981).  Since the  responses to i . v .  i n j e c t i o n s of AVP and AVP antagonist were d i s t i n c t  those  injections,  to  cannot  central  be  attributed  to  the  effect  diffusion  of  of  central  the  drug  drug into  of  from  administration the  peripheral  circulation. Each rat was subjected to the removal of 1 ml blood three times with approximately  10 to  15 min  intervals  between  successive samplings.  blood removed was replaced with an equal volume of normal s a l i n e . from our control  experiments involving i . c . v .  injections  of  The  Results  a r t i f i c i a l CSF  have shown that t h i s procedure neither decreased MAP nor elevated the plasma levels  of  noradrenaline  or  adrenaline.  catecholamine release f o l l o w i n g been the  result  vasopressin  of  level  blood l o s s .  1983).  injections  However, i t  of  is  even  a non-hypotensive  of  MAP and  AVP should not  have  possible that the plasma removal  be a potent stimulus for  Rocha e S i l v a and Rosenberg 1969;  Indeed,  elevations  may have been elevated by the  hemorrhage has been shown to (Pang 1983b;  i.c.v.  Thus, the  of  blood  since  vasopressin release  Szczepanska-Sadowska et a l .  hemorrhage  has  been reported  to  increase the release of AVP (Claybaugh and Share 1972; Szczepanska-Sadowska 1972).  The i . v .  injection  of AVP antagonist  was found  in t h i s  study  to  cause a decrease in MAP but no change in plasma l e v e l s of noradrenaline and adrenaline.  Therefore, the decrease in "MAP f o l l o w i n g the i . v .  AVP antagonist  was l i k e l y  to  have been due to  the  injection  antagonism of  of  pressor  e f f e c t s of endogenously-released AVP. This study does not c o n c l u s i v e l y i d e n t i f y the brainstem s i t e of cardiovascular actions of AVP. to  a number  of  brainstem  the  AVP-containing neurons project from the PVN  sites,  including  the  nucleus motoris  dorsal i s  - 97 vagus,  and the  1980).  It  nucleus i n t r a m e d i o l a t e r a l i s  of  the  spinal  cord  (Sofroniew  i s p o s s i b l e that AVP mediates i t s cardiovascular e f f e c t s  through  any of these s i t e s . In  summary,  it  was found  that  injection  of  AVP into  the  fourth  v e n t r i c l e of conscious and unrestrained rats produced increases in MAP which could be a t t r i b u t e d to increased plasma catecholamine l e v e l s , and therefore increased  sympathetic  sympathoadrenal reflexes.  nerve  outflow,  activity.  possibly  Thus,  via  an  central  inhibition  AVP of  activates  baroreceptor  Since c e n t r a l l y - a d m i n i s t e r e d AVP antagonist did not influence MAP  or plasma noradrenaline or adrenaline l e v e l s , i t  i s u n l i k e l y that AVP exerts  a t o n i c influence on the central cardiovascular r e f l e x system. 4.2  Central AVP in hypotensive rats The previous study showed that the central i n j e c t i o n of AVP increased  plasma noradrenaline and adrenaline l e v e l s as well  as MAP, suggesting that  the blood pressure response to central AVP was mediated by an increase in sympathetic  nerve a c t i v i t y .  It  would be expected that  if  AVP played an  active r o l e in central cardiovascular r e g u l a t i o n , the central AVP  antagonist  opposition  would  to  produce  effects  those produced by AVP.  on  the  injection  cardiovascular  The r e s u l t s  of  the  system  previous  of in  study  indicated that the central i n j e c t i o n of AVP antagonist did not a f f e c t MAP or plasma noradrenaline or adrenaline l e v e l s , suggesting that AVP does not have a tonic  influence on the  cardiovascular system.  However, i t  i s possible  that under conditions in which the sympathetic nervous system i s a c t i v a t e d , the  central  AVP system may p a r t i c i p a t e  nerve a c t i v i t y .  In t h i s  the  modulation  study the p h y s i o l o g i c a l  system under conditions of administering  in  role  of  of  sympathetic  the central AVP  hypotensive stress was determined by  a pressor antagonist  of  continuous infusions of n i t r o p r u s s i d e .  AVP in  rats  centrally  made hypotensive  with  -  The control  results  group,  increased. further the  was  increases  of  the  of  by  the  group.  nerve  study rats  elevated  v e h i c l e alone the  consistent pressure also  showed  plasma  with and  increased  of  either  influence  the  under suggests  on c e n t r a l  does  which  response neither  does  that  result  of study  affect  either  received  identical  both not  i.c.v. to  that  MAP  nor  levels  studies  reduce  conditions  show  MAP  or  or  during  endogenously-released  cardiovascular  of  plasma  adrenaline  from  normal  in  decreased  and  and after  previous  not  of  antagonist  MAP  infusion  the  the  rats  results  levels  AVP  regulation.  o f AVP i n t o t h e NTS the  MAP  and  but of  sympathetic  not  nerve  did  not  dose  catecholamine  not that  plasma  a larger  on MAP o r  theory  MAP, i t  microinjection  plasma  r e s p o n s e was the  since  noradrenaline  AVP  This  likely  of  antagonist  the  concentration  increase  CSF a l o n e  a pattern  AVP  activity  had no e f f e c t  pressor  10 m i n ,  of  continued  and  was  The g r o u p  Therefore  shows t h a t  MAP  MAP  artificial  The i n j e c t i o n  both  in  in  adrenaline  reduction  CSF and t h e  for  levels.  in  increased  concentrations.  that  of  activation.  Microinjection  conscious  nitroprusside and  slight  concentrations  injection  have a t o n i c  This  of  and a d r e n a l i n e  artificial  The  increase  sympathoadrenal does not  infusion  further  nitroprusside  nitroprusside.  sympathetic  4.3  of  central  a  decrease  AVP a n t a g o n i s t  the  produced  of  adrenaline  injection  control  by  second  plasma catecholamine  prevented  that  and  i.c.v.  injections  the  plasma n o r a d r e n a l i n e  injection  infusion  that  following  followed  The  noradrenaline  MAP o r  in  i.c.v.  nitroprusside.  continued  that  -  MAP d e c r e a s e d and p l a s m a n o r a d r e n a l i n e  This  control  shows  show  98  of  2 ng AVP i n t o  noradrenaline (10  ng)  of  levels.  plasma catecholamine  or  AVP  AVP  the  NTS  to  Although  the  lower  activity. increase  plasma  significantly of  indicating  These r e s u l t s  catecholamine  of  adrenaline  levels  vehicle.  in  NTS  Administration  c a u s e d by t h e acts  the  increase dose levels.  are blood  of  AVP This  - 99 was l i k e l y assay.  to  be a r e s u l t  of  the  large  variability  associated with  the  Continuous sympathetic stimulation of pithed rats has been reported  to produce a rapid (<1 min) increase in plasma adrenaline concentration, but a slower (>4 min to peak l e v e l s ) (Yamaguchi and Kopin 1979).  elevation of plasma noradrenaline  levels  Since blood samples were obtained within 1 min  after i n j e c t i o n of the lower dose of AVP, we were able to detect a small but insignificant  increase  in  plasma  concentration.  Homozygous Brattleboro rats which lack hypothalamic AVP also  showed pressor responses to central  adrenaline  but  not  noradrenaline  i n j e c t i o n of AVP (Pittman et a l . 1982).  Therefore t h i s suggests that the a b i l i t y of central AVP to increase MAP may not n e c e s s a r i l y be i n d i c a t i v e of a f u n c t i o n a l central AVP pathway. In t h i s  study,  each rat  was subjected to the removal of  1 ml  blood  only t w i c e , with an i n t e r v a l of at least 15 min between the removal of each sample, and the f l u i d volume was replaced with 1 ml normal s a l i n e as in the previous s t u d i e s .  The r e s u l t s of control experiments in which rats received  an  artificial  injection  reduction  of  treatment.  of  CSF (Group I)  MAP nor elevation of  showed  there  was  neither  plasma catecholamine l e v e l s a f t e r  a  this  As w e l l , in the previous studies three 1 ml blood samples were  removed from conscious rats without a f f e c t i n g concentrations.  Therefore  the  elevation  of  MAP or plasma catecholamine MAP and plasma catecholamine  l e v e l s which occurred a f t e r central i n j e c t i o n of AVP cannot be a t t r i b u t e d to the loss of blood. It for  by  evidence  i s u n l i k e l y that the e f f e c t s of AVP within the NTS can be accounted diffusion suggests  physiologically (Ermisch Moreover,  drug  that  1985;  doses of  into  the  significant  et a l . the  of  the  peripheral  blood-brain amounts  Ang drugs  and  of  barrier AVP from  Jenkins  injected  circulation,  1982;  were  very  limits the  the  CSF to  Vorherr small  since access the  et a l . and  most  thus,  of  blood 1968). were  - 100 unlikely  to  addition,  have much d i r e c t  the  first  study  effect  in  showed that  the  the  peripheral  circulation.  systemic administration  In  of AVP  produced responses d i f f e r e n t from those to the central i n j e c t i o n of AVP. HR was not vehicle.  The  (Matsuguchi  significantly  central  et a l .  affected  injection  1982).  of  However,  by the  AVP was these  injection reported  experiments  anaesthetized rats in which r e f l e x e s were depressed. c a r r i e d out result  in  increase  of  AVP or  to were  increase HR performed  in  reduction  HR produced  in  AVP i n j e c t i o n .  Zerbe  predominant.  by tachycardia,  Therefore,  it  was  while  at  possible  higher that  direct  et a l .  reported that in conscious rats the response to lower doses of was characterized  could  HR which may have concealed any  by central  on  Since our studies were  in conscious animals, pressor responses to AVP i n j e c t i o n a reflex  the  (1983)  i . c . v . AVP  doses bradycardia was  the  higher  dose  of AVP  produced a greater elevation of MAP, hence stimulating the baroreceptors  to  a greater extent, causing r e f l e x bradycardia. The i n j e c t i o n  of the AVP antagonist into the NTS did not affect MAP,  HR or plasma noradrenaline or adrenaline concentrations.  These r e s u l t s  consistent with those of the previous two studies in which the e f f e c t s i.c.v. suggest outflow.  injection that  of  AVP antagonist  AVP does  not  have  were a  investigated,  tonic  influence  and together on  are of they  sympathoadrenal  In a d d i t i o n , the r e s u l t s from t h i s study allow us to i d e n t i f y the  NTS as one s i t e  of  action  of  the  central  cardiovascular e f f e c t s  of AVP.  However, we cannot exclude the p o s s i b i l i t y that exogenously-administered AVP or  AVP  antagonist  stimulates  or  blocks,  respectively,  extra-synaptic  receptors while endogenously released AVP stimulates synaptic receptors that may be r e l a t i v e l y i n a c c e s s i b l e .  - 101 4.4  Central AVP in neurogenically-stressed rats The  previous  studies  showed  that  the  i.c.v.  injection  of  AVP  antagonist alone did not affect MAP, HR or plasma catecholamine l e v e l s , even in conscious rats that  central  system.  subjected to hypotensive s t r e s s .  AVP does not  influence  on the  suggest  cardiovascular  Another study showed that the NTS could be a possible s i t e of  actions of central AVP. this  have a t o n i c  These r e s u l t s  the  The i n j e c t i o n of the AVP antagonist into the NTS in  study was also without  effect.  A final  study  was c a r r i e d  determine whether AVP acting at the NTS s p e c i f i c a l l y has a t o n i c  out  to  influence  on the cardiovascular system under conditions of neurogenic stress induced by exposing the rats to a 150 watt heat lamp. The r e s u l t s i n d i c a t e that a f t e r  10 min of exposure to the heat lamp,  the MAP and plasma noradrenaline and adrenaline l e v e l s of control Group I increased s l i g h t l y , further  increases in  significantly different noradrenaline  but HR was not a f f e c t e d .  MAP and plasma adrenaline  rats  This was followed by  concentration  which  after  the  i.c.v.  injection  of  artificial  into the NTS under conditions of neurogenic s t r e s s .  Rats in Group II  responses  both  10 min  the  injection  to  were  from c o n t r o l , and smaller increases in HR and plasma  concentration  similar  in  those of  initiation  of  neurogenic  antagonist  into the NTS.  the  stress  control  and  group,  5 min  As observed a f t e r  after the  i.c.v.  CSF  showed  after  the  of AVP  injection  of AVP  antagonist in rats subjected to hypotensive s t r e s s , AVP antagonist did not prevent the elevations of MAP, HR and plasma noradrenaline and adrenaline concentrations which occurred in response to neurogenic s t r e s s , and in f a c t MAP,  HR and plasma adrenaline  concentration  f u r t h e r a f t e r the i n j e c t i o n of AVP antagonist.  all  increased  Therefore a l l of our r e s u l t s  suggest that endogenously-released AVP does not the cardiovascular system.  significantly  act t o n i c a l l y  to  regulate  - 102 4.5  Vascular r o l e of AVP It  has been shown that  surgery  in  different  Malvin 1970;  large  species of  Ishihara  et a l .  amounts of AVP are released  animals  1978).  (Moran et a l .  The i n j e c t i o n  1964;  following  Bonjour  of AVP antagonist  and in  halothane-anaesthetized, s u r g i c a l l y - s t r e s s e d rats has been shown to decrease MAP by the reduction of TPR (Pang 1983a). response f o l l o w i n g  the  injection  It  i s expected that the depressor  of AVP antagonist  would r e s u l t  in  reflex  a c t i v a t i o n of other endogenous pressor systems, thereby masking the vascular effects  of  effects  of  influence  the  antagonism of  endogenously from  AVP.  released  other  This AVP  endogenous  study  in  investigates  the  presence  pressor  the  and  systems,  vascular  absence namely  of the  renin-angiotensin or the a-adrenergic systems. The i n j e c t i o n of the AVP antagonist decreased MAP and TPR but did not a l t e r CO in a l l groups of r a t s .  The AVP antagonist caused a s i g n i f i c a n t l y  greater decrease of % control MAP in Groups II well,  the AVP antagonist  decrease of % control  caused a s l i g h t ,  TPR in Group I I ,  of % control TPR in Group III absence of vasoconstrictor  but  and III not  than in Group I.  significantly  the  control  of  than in Group I.  The r e s u l t s show that in the  influences from e i t h e r  MAP  and  greater,  and a s i g n i f i c a n t l y greater decrease  the renin-angiotensin  the a-adrenergic systems, endogenously-released AVP has a greater on  As  vascular  resistance  in  or  influence  anaesthetized,  surgically-stressed rats. The administration  of  AVP antagonist  in  pentobarbital-anaesthetized,  in Group I  increased BF to the stomach  s u r g i c a l l y - s t r e s s e d and i n t a c t  rats  and skin  organs.  previously  but  not  reported  (Pang 1983a).  the  other  using  The  results  halothane-anaesthetized  are  similar  to  surgically-stressed  those rats  - 103 Surgery has been shown to et a l .  1967).  It  has  been  increase plasma renin  shown  previously  in  activity  (McKenzie  halothane-anaesthetized,  s u r g i c a l l y - s t r e s s e d rats that the infusion of s a r a l a s i n caused a decrease of MAP and TPR but no change in CO (Pang 1983a). of s a r a l a s i n in Group II group of animals. the  infusion  of  In t h i s study, the  also resulted in a decrease of MAP w i t h i n the same  Although the values of MAP i n Group II  due  differences  rats subjected to  s a r a l a s i n were less than the MAP values in  s a l i n e i n f u s i o n , the decrease was not s t a t i s t i c a l l y probably  to  the  between  infusion  difficulty animals  associated with  due to  biological  Group I  significant. the  This was  detection  variations.  given  of  small  Likewise,  the  infusion of s a r a l a s i n was found to decrease TPR in a previous study (Pang 1983a) and not made within different  in t h i s  the  one because comparisons in the previous  same animal  animals.  while  in  this  The administration  of  one,  they  study were  were made  the AVP antagonist  between  in Group  II  caused an increase of BF to the skin and muscle and a decrease of BF to the lungs  and l i v e r .  Therefore,  renin-angiotensin  in  the  absence of  system, AVP plays the greatest  vasomotor  tone  from  vasoconstrictor  influence  in the areas of the muscle and skin and the l e a s t in the lungs and It  should be emphasized that  saralasin  would  Therefore  one  injection  of  be expected should  not  the to  depressor response to  activate  expect  the AVP antagonist  to in  the  obtain  groups  I  the  sympathetic the  same  and II  liver.  infusion  nervous  effects  the  of  system.  from  the  which have d i f f e r e n t  endogenous vasomotor tones. The reduction  infusion of  of  CO but  phentolamine not  TPR.  This  in  Group  is  previous study (Tabrizchi and Pang 1987). result  of  reduced  a-adrenoceptors  in  venous veins.  return It  due to has  been  III  decreased  consistent  with  MAP by  results  the  from a  The decrease of CO was probably a the  blockade  shown  that  of i.v.  post-junctional infusions  of  - 104 noradrenaline and B-HT 920 (a s e l e c t i v e o^-agonist) s e l e c t i v e a^-agonist)  into conscious rats  but not methoxamine  (a  caused a dose-dependent increase  in MAP and mean c i r c u l a t o r y f i l l i n g pressure, an index of t o t a l body venous tone, suggesting that c^-adrenoceptors in veins play a r o l e of  venous  blocking  tone. venous  Therefore,  it  is  o^-adrenoceptors  quite  and  reduction in venous return and CO.  possible  decreasing  that  in the  control  phentolamine,  venous  tone,  by  caused  a  The administration of the AVP antagonist  during the infusion of phentolamine markedly increased BF to the muscle and decreased BF to the l i v e r , absence of  i n t e s t i n e , kidneys and t e s t e s .  influence from the a-adrenergic  vasoconstrictor  influence  in  i n t e s t i n e , kidneys and t e s t e s . phentolamine 1983b).  in  rats  the  muscle  It  increased  endogenously influence  in  system, AVP plays the and  the  plasma  renin  activity  areas  angiotensin II of  the  in  the  (Burnier  be increased by a reduction  pressure (Keeton and Campbell 1981). released  least  greatest liver,  has been shown that the administration  Renin release i s known to  renal a r t e r i a l  Therefore, in the  kidneys  played and  the  skin  It  et a l .  of MAP or  has been shown that  greatest (Pang  of  vasoconstrictor  1983a).  Increased  vasomotor tone from the renin-angiotensin system in rats from Group III  may  have overcome the influence of AVP antagonist on skin BF (compared to  the  e f f e c t of the AVP antagonist in rats from Groups I and I I ) . in rats from Group III  Control skin BF  during the i n f u s i o n of phentolamine was indeed very  low, 3.3 ± 0.8 verses 10.6 ± 3.8 and 8.6 ± 4.0 ml/min (mean ± SD) in Groups I and I I ,  respectively.  The r e s u l t s were not expressed as changes in vascular conductance (or resistance). of  all  femoral  The c a l c u l a t i o n of conductance (BF/MAP) involves the  BF readings by MAP obtained from an e a s i l y accessible s i t e artery).  This method  of  calculation  of  arterial  division (e.g.,  conductance  is  based on the assumption that the same MAP can be recorded from any a r t e r y .  - 105 It  has been reported that unlike the case in larger animals ( e . g . , dogs and  cats), In  large or medium sized a r t e r i e s  the  rat,  an a r t e r i a l  between the  carotid  Therefore,  pressure  artery  calculation  difference  and the  of  arterial  can o f f e r  femoral  resistance to BF in of  about  artery  conductance of  5-6 mm Hg  exists  (Pang and Chan  1985).  different  using MAP obtained in the femoral artery could r e s u l t values in many organs ( e . g . , b r a i n , heart,  etc.)  rats.  vascular beds  in higher conductance  than the true conductance  which can only be obtained by d i v i d i n g BF by MAP obtained at the  particular  vascular bed in question. In summary, t h i s significant AVP plays  role  in the control  a greater  renin-angiotensin vasoconstrictor  study shows that  or  pressor the  endogenously-released AVP plays a  of MAP and vascular r e s i s t a n c e .  role  in  the  sympathetic  absence of  nervous  influence exerted by AVP in d i f f e r e n t  systems.  a-adrenergic  In  the  absence  of  renin-angiotensin system, AVP has the greatest the vascular beds of the skin and muscle. the  influence  systems.  depending on the endogenous vasomotor tone from the  sympathetic  nervous  system,  AVP  Moreover,  The  from  the  extent  of  vascular beds varies angiotensin II  vasomotor  tone  vasoconstrictor  and/or  from  the  influence  in  In the absence of influence from  has  the  greatest  vasoconstrictor  influence in the vascular beds of the muscle. 4.6  Central and peripheral actions of a-agonists Most c r o s s - c i r c u l a t i o n techniques developed in the past have involved  connecting  both  left  and  right  (Bickerton and Buckley 1961;  common c a r o t i d  Takahashi and Bunag 1980).  connect only one common c a r o t i d single  rats  a r t e r i e s , the to the b r a i n .  have left  shown  arteries  that  artery in  common c a r o t i d  the artery  from each r a t . absence  of  of It  two  animals  i s possible to  Our studies  functional  using  subclavian  alone could provide s u f f i c i e n t BF  This i s to be expected since rats  have extensive  collateral  - 106 circulation  supplying the c i r c l e of W i l l i s  (Pulsinelli  and B r i e r l y  1979).  Although none of the changes in BF to the d i f f e r e n t areas of the brain were significant, it  i s i n t e r e s t i n g to note that a f t e r l i g a t i o n of the subclavian  a r t e r i e s , BF to the l e f t and r i g h t hemispheres was increased, while that to the brainstem was reduced.  This change i n the d i s t r i b u t i o n  of blood to the  brain suggests that the brainstem i s highly dependent on blood supplied by the subclavian a r t e r i e s .  There was s i m i l a r BF to  both brain hemispheres,  i n d i c a t i n g that the l e f t common c a r o t i d artery supplied both hemispheres. A c r o s s - c i r c u l a t i o n preparation was developed in which the l e f t common c a r o t i d a r t e r i e s and both the l e f t and r i g h t external jugular rats were connected. occlude  blood  veins of two  The subclavian a r t e r i e s of both rats were l i g a t e d  supply  to  the  vertebral  arteries.  Unlike  to  previous  preparations, in which one animal served as a donor and one as a r e c i p i e n t , t h i s technique involved complete c r o s s - c i r c u l a t i o n of blood between r a t s , so that each rat  acted both as a donor and a r e c i p i e n t .  In contrast  to  the  preparation of Takahashi and Bunag (1980), no p e r i s t a l t i c pump was required to i n i t i a t e or maintain BF.  Results from microsphere experiments  verified  that peripheral blood from one rat supplied the brain of another rat but not its  own b r a i n .  This  cross-circulation  completely separate the central of drugs.  preparation  from the peripheral  Thus, one can administer  makes  it  possible  to  cardiovascular e f f e c t s  a drug intravenously  into one r a t  observe the peripheral e f f e c t s in the same r a t , , and the central  effects  to in  another r a t . This preparation was used to separate the e f f e c t s of methoxamine and c l o n i d i n e into central  and peripheral  components.  The i . v .  administration  of these drugs to one rat e l i c i t e d completely d i f f e r e n t responses from the two r a t s .  The r e s u l t s show that c l o n i d i n e reduced MAP and HR by a central  a c t i o n , while  its  peripheral  action resulted  in  a pressor response and a  - 107 -  reflex view  bradycardia. that  These o b s e r v a t i o n s  clonidine  reduction  of  significant  stimulates  sympathetic reduction  was masked by a r e f l e x action  of  suggests  that  predominate  over  stimulate effect  may be o f  post-junctional  and  of  by b o t h  central  the observation  Fenard  rat  the  actions.  because  it  depressor  of  peripheral  studies  but  of to  activation increased  correlates  administered nerve  have  this  stimulation  methoxamine finding  sympathetic  it  C l o n i d i n e may  primarily  This  HR,  o^-adrenoceptors  effect  low doses o f p h e n y l e p h r i n e  binding  a  periphery,  contrast,  a  that  MAP. and d e c r e a s e d  the overall  and p e r i p h e r a l  addition,  possible  stimulation  in  In  In  is  mediate  to the central  attributed  and s p l a n c h n i c  which  c^-adrenoceptors.  since  c a n be  It  the established  post-junctional  (^"adrenoceptors.  pressure  3  to  increased  pre-junctional  importance  that  1971).  by  peripheral  o^-adrenoceptors  blood  response  o^-adrenoceptors  little  of  increase  of  pre-junctional  peripheral  with  effects  those  of  MAP  the  with  i n t h e second  i n HR i n r e s p o n s e  was c h a r a c t e r i z e d  the  and M A P .  HR was n o t o b s e r v e d  Since  well  o^-adrenoceptors  activity  increase  clonidine.  o^-adrenoceptors  central  nerve  in  correlate  well  centrally  activity revealed  (Schmitt sites  for  criteria  for  3 H-WB  and  4101  H-prazosin  within  a-|-adrenoceptors  (U'Prichard  Our  methoxamine,  in  results conflict  depressor and  with with  the  responses  adrenaline,  which  a^-adrenoceptors. injection of  a  of  rat  activity  (Takahashi  did  remove  the  of  the recipient may  However  our  decreased and Bunag  a^-agonist,  Taylor  and  after  and were  conflict  its  blood  1980).  It  with into  pressure should  blood  the and  be n o t e d  supply  Snyder  to  1979).  not n e c e s s a r i l y  (1951)  administration  a-j-agonist,  arterial  Page  the  o^-adrenoceptors  results  another  meet  U!Prichard  1978;  stimulate  vertebral  CNS w h i c h  a selective  results  phenylephrine,  recipient  not  in  et a l .  the  who  of  observed  noradrenaline  in  addition  observations head  the  that  circulation  sympathetic that  to  the brain  nerve authors of  the  - 108 recipient rat.  BF from the donor rat was found to be d i s t r i b u t e d mainly to  the cerebrum of the r e c i p i e n t r a t ;  BF to the brainstem of the r e c i p i e n t  was  responses  negligible.  Therefore,  the  to  phenylephrine  which  rat they  observed were due to e f f e c t s of the drug on the brain hemispheres. In our c r o s s - c i r c u l a t i o n preparation, the determination of BF from rat A to  the  brains  of  the  two  rats  revealed that  subclavian a r t e r i e s , most BF was d i s t r i b u t e d  before  ligation  of  the  to the brain of rat A, while  the l e f t and r i g h t hemispheres of rat B received some BF but the brainstem did not.  Thus the subclavian a r t e r i e s alone were found to supply a l l  areas in rat A.  brain  A f t e r l i g a t i o n of the subclavian a r t e r i e s the brain of  A did not receive any BF, while BF to a l l areas of the brain of rat s u b s t a n t i a l l y increased. subclavian  arteries  is  Therefore, the r e s u l t s show that e s s e n t i a l to  ligation  rat  B was of  the  achieve c r o s s - c i r c u l a t i o n between the  two rats v i a the c a r o t i d a r t e r i e s . Since the venous connections between the head and body of the rats this  preparation were not completely severed, the  circulatory  possibility  leakage from the head to the body of rat  B.  in  remained of  To determine  the  57  extent the  of  circulatory  radioactivity  leakage,  in the  Co isotope was injected  blood of  Leakage was less than 10% u n t i l  both  after  rats 3 min.  measured at  into  rat  A and  specific  times.  We observed drug responses  within 5-10 s of drug i n j e c t i o n in rat A, and within 10-30 s in rat B.  Drug  responses were measured within 2 min in rat A and between 2-3 min in rat B. Within 2-3 min, drug responses in rat A had disappeared while responses in rat  B had reached a maximum and c i r c u l a t o r y  minimal.  Therefore, i t  rat  B was  still  i s u n l i k e l y that the drug response observed in rat B  was due to a peripheral action of the drug. drugs with  leakage in  a long duration  of  However, i t  action were to  i s possible that  be investigated  using  if  this  - 109 technique, that the drug responses observed in rat B could be a consequence of c i r c u l a t o r y leakage from the head to the body of B. Using t h i s c r o s s - c i r c u l a t i o n preparation we found that c l o n i d i n e acted peripherally  to  increase  MAP,  while  its  central  action  reduced  MAP.  Methoxamine on the other hand increased MAP by a peripheral  action,  while  i t s central action increased MAP and HR. 4.7  Central o^-agonists in conscious rats The r e s u l t s of t h i s  0.01 to  study show that the i . c . v .  1 yg of c l o n i d i n e  The i . c . v .  injection  caused dose-dependent reductions  of doses of  in MAP and HR.  i n j e c t i o n of 1 yg was accompanied by reductions in the levels of  plasma noradrenaline and adrenaline.  These changes, however, were not found  to  have  be  significant,  variability  but  this  of the assay.  may  been  These r e s u l t s  the  result  of  the  large  are consistent with those of  the  c r o s s - c i r c u l a t i o n study, in which c l o n i d i n e was shown to decrease MAP and HR by a central action in anesthetized r a t s . likely  a sufficiently  where  it  high dose to  stimulated  vasoconstriction  and  masking  of  10 yg c l o n i d i n e  response  to  the  The  significant  non-significant  into  the  increase  MAP  by a central in  decrease in  peripheral  as  adrenaline  causing  decrease  decrease in HR a f t e r  well  as  an  noradrenaline concentration  may represent a baroreceptor reflex-mediated  reduction  in  the  i.c.v.  a  reflex  consequence of  action of c l o n i d i n e  plasma  circulation,  o^-adrenoceptors,  may have been the  in  decrease  the  centrally-mediated  The s i g n i f i c a n t  injection  reflex  leak  post-junctional  sympathoadrenal a c t i v i t y .  baroreceptor  The 10 ug dose of c l o n i d i n e was  enhancement  of  the  (Huchet et a l . 1983). level  and  with  10 yg  small  and  clonidine  in sympathetic  nerve  a c t i v i t y which p a r a l l e l s the decrease in HR. The oto-agonist  responses  to  B-HT 920  were  the  i.c.v.  unexpected.  injection Rather  of than  the  more  decreasing  selective MAP,  the  - 110 i.c.v.  injection  dose-dependent  of  B-HT 920  fashion.  In  increased  contrast  to  MAP  and  decreased  the  responses  HR  to  in  the  a  i.c.v.  i n j e c t i o n of c l o n i d i n e , the responses to a l l 4 doses of B-HT 920 were in the same d i r e c t i o n .  If a high dose of B-HT 920 were to leak out of the CNS into  the peripheral c i r c u l a t i o n , i t would be expected to cause an e f f e c t  additive  to  did  its  central  action.  While plasma noradrenaline  appear to change a f t e r  the  adrenaline concentration adrenaline  i.c.v.  injection  appeared to  concentrations  were  of  concentration  1 yg B-HT 920, the plasma  i n c r e a s e , and both noradrenaline and  increased  after  the  injection  B-HT 920, although none of these changes were s t a t i s t i c a l l y These r e s u l t s that  as  a  more  are opposite to our expectations. selective  agonist  B-HT 920 should produce a greater activity i.c.v.  after  i.c.v.  at  a ~  than  t  n  a  n  of  of  significant.  t  aj-adrenoceptors,  MAP and sympathetic  clonidine.  nerve  Paradoxically,  the  i n j e c t i o n of B-HT 920 produced MAP and plasma catecholamine responses  in the opposite d i r e c t i o n to those observed a f t e r clonidine.  injection  s i t e of i n j e c t i o n ,  It  i s not c l e a r whether differences in the  could account f o r  the difference  in response.  These r e s u l t s suggest that e i t h e r the centrally-mediated i n h i b i t o r y  central  the  in the species or the use of anesthesia in the study by  and Kobinger (1981)  clonidine  of  i n j e c t i o n of B-HT 920 in anesthetized cats decreased MAP and  HR ( P i c h l e r and Kobinger 1981).  Pichler  the i . c . v .  These r e s u l t s are not consistent with e a r l i e r reports that  intracisternal  of  10 yg  Our hypothesis was a  2  reduction  administration  not  are  not  mediated  pressor e f f e c t s  (^-adrenoceptors,  or  of  that  by central  (^-adrenoceptors,  or  effects that  B-HT 920 are mediated by receptors other the  activation  of  other  receptors  the than  by B-HT 920  masks the e f f e c t of a c t i v a t i o n of c^-adrenoceptors. In order to determine whether the response to B-HT 920 or  that  to  clonidine  was mediated  by  centrally-administered  c^-adrenoceptors,  i.c.v.  - Ill injections  of  these  drugs  were  given  after  the  s e l e c t i v e o ^ - a n t a g o n i s t , rauwolscine (Tabrizchi injection  of  rauwolscine alone was found to  central rauwolscine on HR was less c l e a r . III  but decreased i t  in Group IV.  change was of s t a t i s t i c a l small  (about  and Pang 1987).  increase MAP.  by  the  The  i.c.v  The e f f e c t  However, i t  should be noted that  when  control  values  of  HR  of  neither  were  above  Furthermore, rauwolscine may have central as well as r e f l e x  increases  in  both  plasma  The increase in MAP was  noradrenaline  and  concentrations,  although again, due to the large v a r i a b i l i t y  these  were  changes  of  Rauwolscine increased HR in Group  e f f e c t s on HR which may act in opposite d i r e c t i o n s . accompanied  injection  s i g n i f i c a n c e , and that the amount of change was  10 beats/min  350 beats/min).  i.c.v.  rauwolscine-sensitive  not  significant.  receptors  are  If  it  is  that these receptors may have a t o n i c  inhibitory  in the assay,  assumed  (^-adrenoceptors,  the  adrenaline  that  results  these suggest  influence on sympathetic  nerve a c t i v i t y and MAP. The i . c . v .  injection  of B-HT 920 a f t e r  the central  rauwolcine produced the same responses as in  its  administration  of  an increase  in  absence:  MAP and plasma noradrenaline and adrenaline concentrations, in HR.  This suggests that the e f f e c t s of i . c . v .  not mediated by central ag-adrenoceptors.  injection  and a decrease of B-HT 920 were  However, the e f f e c t s  i n j e c t i o n s of c l o n i d i n e were also not abolished by rauwolscine. plasma  adrenaline  pretreatment  concentration  were  also  with rauwolscine, although  decreased  the magnitude  plasma noradrenaline l e v e l was not as great. dose of rauwolscine used was not s u f f i c i e n t central  B-HT 920 used in t h i s  of  central  MAP, HR and  clonidine the  after  reduction  The r e s u l t s suggest that  in the  to achieve complete blockade of  However, the  ratio  of  study was higher  than  that  a^-adrenoceptors.  by  of  doses of required  rauwolscine to  to  completely  block the peripheral pressor actions of B-HT 920 (Tabrizchi and Pang 1987).  - 112 Due to s o l u b i l i t y problems, i t s o l u t i o n of rauwolscine.  was not p o s s i b l e to make a more concentrated  As w e l l ,  it  was not p o s s i b l e to  inject  a larger  volume of the drug since a 4 pi volume was already used to carry the 10 pg dose.  Thus, i t  is s t i l l  possible that neither the e f f e c t  of  B-HT 920 nor  that of c l o n i d i n e was mediated by c e n t r a l o^-adrenoceptors. Clonidine  has  (^-adrenoceptors observation  studies  o^-adrenoceptors  be  leads  have  partial  agonistic  properties  van  Zwieten  1980a).  However,  and  centrally  increased  MAP  suggest  that  would  to  system.  to  and  methoxamine  cross-circulation  readily  shown  (Timmermans  that  cardiovascular  been  activation  Therefore the  attributed  to  its  rather central  activity  on  HR  stimulation than  effects  of  suggesting that  it  of  clonidine  a^-adrenoceptors.  may stimulate  the in  central  depression  B-HT 920 has been shown to be a s e l e c t i v e c ^ - a g o n i s t , i t than c l o n i d i n e ,  of  on  the  cannot  Although  acted d i f f e r e n t l y  another type of  receptor  w i t h i n the CNS which leads to a c t i v a t i o n of the sympathetic nervous system. It  has been reported  that  B-HT 958,  an  analog of  central dopamine receptors (Brown and Harland 1986). or  i.c.v.  prevent  injections  the  reductions  produced by the abolished  by  sulpiride.  in  i.v.  the  idazoxan,  a  selective  injection  of  B-HT 958,  administration  However, since the responses to to  those  unlikely  that  the  receptors.  o^-antagonist,  observed  after  pressor e f f e c t s  central of  although  of  the  blockade of  studies  central  injection  not  concentration  these e f f e c t s  dopamine  of  i.v.  were  antagonist, opposite  B-HT 920,  it  is  B-HT 920 were mediated by dopamine and rather  unexpected  using s e l e c t i v e c ^ - a n t a g o n i s t s which can ensure  a - a d r e n o c e p t o r s , and other ?  could  B-HT 958 were in the  These studies produced some i n t e r e s t i n g Further  stimulates  It was shown that  MAP, HR and plasma noradrenaline  i.c.v.  direction  results.  of  B-HT 920,  a - a g o n i s t s with ?  varying  - 113 selectivities  for  c^-adrenoceptors are required  before an explanation  for  these paradoxical r e s u l t s can be obtained. 4.8  General conclusions 4.8.1  Role  demonstrated  of  that  AVP  in  AVP can  cardiovascular  increase  regulation.  MAP and  These  studies  plasma catecholamine  levels  through an action in the CNS. A possible s i t e f o r t h i s action of AVP may be the  NTS, the  primary  baroreceptor r e f l e x  site  of  termination  of  the  a r c , since the m i c r o i n j e c t i o n  afferent of  neurons of  small amounts of AVP  into t h i s s i t e could evoke responses s i m i l a r to those observed a f t e r injection  of  AVP.  However,  the  injection  of  AVP antagonist  e i t h e r the fourth v e n t r i c l e or the NTS was without e f f e c t . AVP antagonist  into the fourth v e n t r i c l e  HR  or  plasma  endogenously-released central  levels.  AVP does not  into  The i n j e c t i o n of  or the NTS of rats  catecholamine  i.c.v.  alone  subjected  hypotensive stress or neurogenic s t r e s s , r e s p e c t i v e l y , also did not MAP,  the  This  affect  suggests  have a t o n i c  influence  to  that on the  cardiovascular system under e i t h e r normal conditions or conditions in which the  sympathoadrenal  system may be  activated.  Therefore  the  ability  of  c e n t r a l l y - i n j e c t e d AVP to elevate MAP and sympathetic nerve a c t i v i t y may be of l i t t l e p h y s i o l o g i c a l s i g n i f i c a n c e . The i n j e c t i o n TPR.  of  in  control  This suggests that at the peripheral l e v e l ,  plays a s i g n i f i c a n t  r o l e in the control  surgically-stressed rats. of  AVP antagonist  influence  from the  rats  decreased MAP and  endogenously-released AVP  of MAP and vascular resistance  in  This r o l e was found to be greater in the absence renin-angiotensin  or  sympathetic  nervous  systems,  since the i n j e c t i o n of AVP antagonist in rats subjected to blockade of  the  renin-angiotensin or the a-adrenergic systems caused a greater reduction  in  MAP and TPR than greater  role  in  control  rats.  in the maintenance of  Therefore the peripheral  AVP system may have a  r e s i s t a n c e and MAP in  the  event of f a i l u r e of the renin-angiotensin and sympathetic nervous systems.  -  The  amount  appears  of  vasoconstriction  to  depend  on  renin-angiotensin  and  renin-angiotensin  system,  suggesting greatest  that  suggesting  system, that  vasoconstrictor 4.8.2 results  the  in  the  effect  Role  of  from  the  of  mediate  a reduction  of  tonic  inhibitory  injection  the  also  that  resulted  pre-junctional  MAP  and  of  shown  in  these  two  be  system  may  to  skin  has  the  of  the  blockade  AVP  the  has  the  muscle,  AVP  to  the  of  and  system,  BF  beds  from  absence  During  in  studies  muscle,  the  an  greatest  that  HR  central  consistent  increase  system,  of  with the  in  block  either  become to  i.c.v.  study  pre-junctional a2~adrenoceptors of  HR.  Until  post-junctional  available,  receptors  a  post-junctional  a reduction  the  the  cross-circulation  peripheral  MAP and  exert  noradrenaline  peripheral  of  accepted  may  since  peripheral of  involved  a2~adrenoceptors  a2~adrenoceptors  from the  those  regulation.  which  i n c r e a s e MAP and p l a s m a  stimulation  of  studies  cardiovascular  over  types  cardiovascular  and  central  effects  the  the  sympathoadrenal  or  the  relative activity  and  determined.  cross-circulation possibly  BF  system,  The r e s u l t s  2  a-^-adrenoceptors  this  to  a -adrenoceptors of  the  increased  suggested  the  preferentially  hemodynamics c a n n o t The  was  the  since  which  contribution  over  predominate  a2~adrenoceptors,  antagonists  antagonist  Moreover,  concentrations.  suggest  clonidine  skin.  vascular  tone  In  this  MAP and HR, o b s e r v a t i o n s  influence  ag-adrenoceptors  by  and  clonidine  rauwolscine  and a d r e n a l i n e  muscle  a-adrenergic  literature.  of  increased from  cross-circulation  injections  in  systems.  tone  absence  different  vasomotor  of  AVP  in  on m u s c l e .  central  views  a-adrenergic  the  AVP  endogenous  absence  in  by  AVP a n t a g o n i s t  the  influence  a-adrenergic  The  in  -  produced  the  the  114  by  mediate  studies a  also  central  responses  showed  that  action, in  the  methoxamine  suggesting  opposite  increased  that  direction  central to  those  - 115  produced  by  cxg-adrenoceptors.  -  However,  it  is  not  clear  whether  these  receptors have a p h y s i o l o g i c a l r o l e in cardiovascular r e g u l a t i o n . F i n a l l y , the observation of a paradoxical elevation of MAP in response to the i . c . v . central  injection  of B-HT 920 r a i s e s new questions about the r o l e  o^-adrenoceptors.  Since  the  central  produced the expected decrease in MAP and HR, i t to  B-HT 920  was  mediated  Unfortunately,  neither  abolished  ©^-adrenoceptor  by  cannot d e f i n i t e l y activation  of  by  receptors  the response to blockade  of  than  ©^-adrenoceptors.  c l o n i d i n e nor that to with  clonidine  suggests that the response  other  rauwolscine.  conclude that the response to  rauwolscine-sensitive  injection  of  clonidine  ©^-adrenoceptors  B-HT 920 was Therefore,  we  was due to  the  and that  the  pressor  response to B-HT 920 was not.  Further studies with d i f f e r e n t a-antagonists  and o^-agonists  selectivities  with  explain the d i f f e r e n t i a l  various  are  necessary  before  e f f e c t s of central c l o n i d i n e and B-HT 920.  we can  - 116 5  REFERENCES  ABBOUD, F . M . , AYLWARD, P . E . , FLORAS, O.S. and GUPTA, B.N. S e n s i t i z a t i o n of a o r t i c and cardiac baroreceptors by arginine vasopressin in mammals. J . P h y s i o l . (Lond.) 377:251-265, 1986. ABOOD, L . G . , KNAPP,. R., MITCHELL, T . , BOOTH, H. and SCHWAB, L. Chemical requirements of vasopressins for barrel rotation convulsions and reversal by oxytocin. J. Neurosci. Res. 5:191-199, 1980. AISENBREY, G . A . , HANDELMAN, W.A., ARNOLD, P. and MANNING, M. Vascular e f f e c t s of arginine vasopressin during f l u i d deprivation in the r a t . J . C l i n . Invest. 67:961-968, 1981. ALDRICH, T.B. A preliminary report on the active p r i n c i p l e of the suprarenal gland. Am. J . P h y s i o l . 5^:457-461, 1901. ALEXANDER, D . P . , FORSLING, M.L., MARTIN, M.S., NIXON, D.A., RATCLIFFE, J . G . , REDSTONE, D. and TURNBRIDGE, D. The e f f e c t of maternal hypoxia on f e t a l p i t u i t a r y hormone release in the sheep. Biol. Neonate 21:219-228, 1972. ALQUIST, R.P. A study of the adrenotropic receptors. P h y s i o l . 153:586-600, 1948.  Am. J .  ALTURA, B.M. S e l e c t i v e microvascular c o n s t r i c t o r actions of some neurohypophyseal peptides. Eur. J . Pharmacol. 24:49-60, 1973. ALTURA, B.M. and ALTURA, B.T. neurohypophyseal hormones.  Vascular smooth muscle and Fed. Proc. 36 1.853-1860, 1977. :  ALTURA, B.M., HERSHEY, S.G. and ZWEIFACH, B.W. Effects of a synthetic analogue of vasopressin on vascular smooth muscle. Proc. Soc. Exp. B i o l . Med. 119:258-261, 1965. ANDEN, N . E . , CORRODI, H . , FUXE, K., HOKFELT, B . , HOKFELT, T . , RYDIN, C. and SVENSSON, T. Evidence for a central noradrenaline receptor stimulation by c l o n i d i n e . L i f e S c i . 2:513-523, 1970. ANDERSSON, B. T h i r s t - and brain control of water balance. 59:408-415, 1971.  Am. S c i .  ANDREWS J R . , C . E . and BRENNER, B.M. R e l a t i v e contributions of arginine vasopressin and angiotensin II to maintenance of systemic a r t e r i a l pressure in the anesthetized water- deprived r a t . Circ. Res. 48:254-258, 1981. ANG, V.T.Y. and JENKINS, J . S . Blood- cerebrospinal f l u i d b a r r i e r to arginine-vasopressin, desmopressin, and desglycinamide a r g i n i n e vasopressin in the dog. J . Endocrinol. 93:319-325, 1982.  - 117 ARNAULD, E . , CZERNICHOW, P . , FUMOUX, F. and VINCENT, J . D . The e f f e c t of hypertension and hypovolaemia on the l i b e r a t i o n of vasopressin during haemorrhage in the unanaesthetized monkey. Pfluegers Arch. 371:193-200, 1977. ATHAR, S. and ROBERTSON, G.L. Osmotic control of vasopressin secretion in man. C l i n . Res. 22:335A, 1974. BARER, G.R. A comparison of the c i r c u l a t o r y e f f e c t s of angiotensin, vasopressin and adrenaline in the anaesthetized c a t . J . Physiol. (Lond.) 156:49-66, 1961. BARGER, G. and DALE, H.H. Chemical structure and sympathomimetic action of amines. J . P h y s i o l . (Lond.) 41:19-59, 1910. BARTELSTONE, H . J . and NASMYTH, P.A. Vasopressin p o t e n t i a t i o n of catecholamine actions in dog, r a t , cat and rat a o r t i c s t r i p . J . P h y s i o l . 208:754-762, 1965.  Am.  BAUMAN, G. and DINGMAN, J . F . D i s t r i b u t i o n , blood transport and degradation of a n t i d i u r e t i c hormone in man. J . C l i n . Invest. 57:1109-1116, 1976. BENTLEY, S . M . , DREW, G.M. and WHITING, S . B . Evidence for two d i s t i n c t types of postsynaptic alpha- adrenoceptor. Br. J . Pharmacol. 61:116P-117P, 1977. BERECEK, K . H . , MURRAY, R.D., GROSS, F. and BRODY, M . J . Vasopressin and vascular r e a c t i v i t y in the development of DOCA hypertension in rats with hereditary diabetes i n s i p i d u s . Hypertension 4_:3-12, 1982. BERECEK, K . H . , OPLE, H . , JONES, R.S.G. and HOFBAUER, K.G. M i c r o i n j e c t i o n of vasopressin into the locus coeruleus of conscious r a t s . Am. J . P h y s i o l . 247:H675-H681, 1984. BERTHELSEN, S. and PETTINGER, W.A. A functional basis for c l a s s i f i c a t i o n of a - adrenergic receptors. Life S c i . 1977.  21:595-606, —  BHATIA, B . , SUBRAMANIAN, S. and SIDDIQUI, H.H. S i g n i f i c a n c e of the changes in urine output on acute exposure to hypoxia. In: Respiratory Adaptations, C a p i l l a r y .Exchange and Reflex Mechanisms. EcC P a i n t a l , A . S . , G i l l - Kumar, P.) U n i v e r s i t y of D e h l i , D e h l i . 1977), pp. 244-252. BICKERTON R.K. and BUCKLEY, J . P . Evidence for a central mechanism in angiotensin induced hypertension. Proc. Soc. Exp. B i o l . Med. 106:834-836, 1961. BIERMAN, U . , FORSLING, M.L., ELLENDORFF, F. and MCDONALD, A . A . The cardiovascular responses of the. c h r o n i c a l l y catheterized pig fetus to infused l y s i n e vasopressin and to hemorrhage. J . Physiol. (Lond.) 296:28P, 1979.  - 118 BISHOP, V . S . , THAMES, M.D. and SCHMID, P.G. E f f e c t s of b i l a t e r a l vagal cold block on vasopressin in conscious dogs. Am. P h y s i o l . 246:R566-R569, 1984. BISSET, G.W. and LEWIS, G.P. A spectrum of pharmacological in some biologically active peptides. Br. J. 19:168-182, 1962. BLASCHKO, H. The s p e c i f i c action of IP h y s i o l . (Lond.) 96:50-51P, 1939.  dopa decarboxylase.  J.  activity Pharmacol. J.  BLESSING, W.W., SVED, A . F . and REIS, D . J . Elevated plasma vasopressin contributes to fulminating hypertension produced by functional impairment of A l catecholamine neurons in rabbit medulla. Clin. S c i . 63:289s-292s, 1982. BODO, R. The e f f e c t of the "heart- t o n i c s " and other drugs upon the heart- tone and coronary circulation. J . Physiol. (Lond.) 64:365-387, 1927-28. BONJOUR, J . P . and MALVIN, R.L. Plasma concentrations of ADH in conscious and anesthetized dogs. Am. J . P h y s i o l . 218:1128-1132, 1970. BOYKIN, J . , CADNOPAPHORNCHAI, P . , MCDONALD, K.M. and SCHRIER, R.W. Mechanism of d i u r e t i c response associated with a t r i a l tachycardia. Am. J . P h y s i o l . 229:1486-1491, 1975. BRINTON, R . E . , GEE, K.W., WAMSLEY, J . K . , DAVIS, T . P . and YAMAMURA, I. Regional d i s t r i b u t i o n of putative vasopressin receptors in rat brain and p i t u i t a r y by q u a n t i t a t i v e autoradiography. Proc. N a t l . Acad. S c i . (USA) 81:7248-7252, 1984. BROWN, G . L . and GILLESPIE, J . S . The output of sympathetic transmitter from the spleen of the c a t . J . P h y s i o l . (Lond.) 138:81-102, 1957. BROWN, M . J . and HARLAND, D. B- HT 958 lowers blood pressure and heart rate in the rat through stimulation of dopamine receptors. Br. J . Pharmacol. 87:361-370, 1986. BROWNSTEIN, M . J . Biosynthesis of vasopressin and oxytocin. P h y s i o l . 45:129-135, 1983. BUIJS, R.M. and SWAAB, D.F. Immuno- electron microscopical demonstration of vasopressin and oxytocin synapses in system of the r a t . C e l l Tissue Res. 204:355-365, 1979.  Ann. Rev.  the  limbic  BURN, J . H . and RAND, M . J . Sympathetic postganglionic mechanism. Nature (Lond.) 184:163-165, 1959. BURNIER, M., BIOLLAZ, J . , BRUNNER, D.B. and BRUNNER, H.R. Blood pressure maintenance in awake dehydrated r a t s : r e n i n , vasopressin, and sympathetic a c t i v i t y . Am. J . P h y s i o l . 245:H203-H209, 1983a.  - 119 BURNIER, M., BIOLLAZ, J . , BRUNNER, D.B., GAVRAS, H. and BRUNNER, H.R. Alpha and beta adrenoceptor blockade in normotensive and deoxycorticosterone (DOC)- hypertensive r a t s ; plasma vasopressin and vasopressin pressor e f f e c t . J . Pharmacol. Exp. Ther. 224:. 222-227, 1983b. BURNSTOCK, G. and COSTA, M. Adrenergic Neurons: t h e i r o r g a n i z a t i o n , f u n c t i o n and development in the peripheral nervous system. Chapman and H a l l , London, (197S), pp. 1-50. BUSSIEN, J . P . , WAEBER, B . , NUSSBERGER, J . , SCHALLER, M.D., GAVRAS, H . , HOFBAUER, K. and BRUNNER, H.R. Does vasopressin sustain blood pressure of normally hydrated healthy volunteers? Am. J . P h y s i o l . 246:H143-H147, 1984. CALARESU, F.R. and CIRIELLO, J . Projections to the hypothalamus from buffer nerves and nucleus tractus s o l i t a r i u s in the c a t . Am. J . P h y s i o l . 239:R130-R136, 1980. CANNON, W.B. and URIDIL, J . E . Studies on the conditions of a c t i v i t y in endocrine glands. V I I I . Some e f f e c t s on the denervated heart of stimulating the nerves of the l i v e r . Am. J . P h y s i o l . 58:353-364, 1921. CANNON, W.B. and BACQ, Z.M. Studies on the conditions of a c t i v i t y in endocrine organs. XXVI. A hormone produced by sympathetic action on smooth muscle. Am. J . P h y s i o l . 96:392-412, 1931. CANNON, W.B. and ROSENBLUETH, A. Studies on conditions of a c t i v i t y in endocrine organs. XXIX. Sympathin E and sympathin I. Am. J . P h y s i o l . 104:557-574, 1933. CARLIER, J . G . , LEJEUNE, G. and BARAC, G. E f f e t s hemodynamiques compares d'une vasopressine synthetique et de l a p i t r e s s i n e chez le chien. Arch. Int. Pharmacodyn. 125:287-303, 1960. CAVERO, I. and ROACH, A . G . Effects of c l o n i d i n e on canine cardiac neuroeffector structures controlling heart rate. Br. Pharmacol. 70:269-276, 1980.  J.  CHALMERS, J . P . Brain amines and models of experimental hypertension. C i r c . Res. 36:469-480, 1975. CHAN, T . C . K . , WALL, R.A. and SUTTER, M.C. Chronic ethanol consumption, s t r e s s , and hypertension. Hypertension 1985.  7:519-524,  CLARK, B . J . and ROCHA E SILVA J R . , M. An afferent pathway f o r the s e l e c t i v e release of vasopressin in response to c a r o t i d occlusion and hemorrhage in the c a t . J . P h y s i o l . (Lond.) 191:529-542, 1967. CLAYBAUGH, J . R . and SHARE, L. Role of the r e n i n - angiotensin system in the vasopressin response to hemorrhage. Endocrinology 90:453-460, 1972.  - 120 CLAYBAUGH, J . R . and SHARE, L. responses to continuous 224:519-523, 1973.  Vasopressin, r e n i n , and cardiovascular slow hemorrhage. Am. J . P h y s i o l .  CLAYBAUGH, J . R . , SHARE, L. and SHIMUZI, K. The i n a b i l i t y of infusions of angiotensin to elevate the plasma vasopressin concentration in the anesthetized dog. Endocrinology 90: 1647-1652, 1972. COHEN, M.M., SITAR, D . S . , MCNEILL, J . R . and GREENWAY, C V . Vasopressin and angiotensin on resistance vessels of spleen, i n t e s t i n e and l i v e r . Am. J . P h y s i o l . 218:1704-1706, 1970. CONSTANTINE, J.W. and MCSHANE, W.K. Analysis of the cardiovascular e f f e c t s of 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride (Catapres). Eur. J . Pharmacol. 4:109-123, 1968. COOPER, K . E . , KASTING, N.W., LEDERIS, K. and VEALE, W.L. Evidence supporting a r o l e for endogenous vasopressin in natural suppression of fever in the sheep. J . P h y s i o l . (Lond.) 295:33-45, 1979. CORLISS, R . J . , MCKENNA, O . H . , SIALER, S . , O'BRIEN, G.S. and ROWE, G.G. Systemic and coronary hemodynamic e f f e c t s of vasopressin. Am. J . Med. S c i . 256:293-299, 1968. COTTLE, M.K. Degeneration studies of primary afferents of i x t h and xth c r a n i a l nerves in the c a t . J . Comp. Neurol. 122:329-345, 1964. COUSINEAU, D., GAGNON, D . J . and SIROIS, P. Changes in plasma l e v e l s of vasopressin and renin in response to hemorrhage in dogs. Br. J . Pharmacol. 47:315-324, 1973. COWLEY J R . , A.W., MONOS, E. and GUYTON, A . C . Interaction of vasopressin and the baroreceptor r e f l e x in the regulation of a r t e r i a l pressure in the dog. C i r c . Res. 34:505-514, 1974. COWLEY J R . , A.W., SWITZER, S . J . and GUINN, M.M. Evidence and q u a n t i f i c a t i o n of the vasopressin a r t e r i a l pressure control in the dog. C i r c . Res. 46:58-67, 1980.  system  COWLEY J R . , A.W., CUSHMAN, W.C., QUILLEN J R . , E.W., SKELTON, M.M. and LANGFORD, H.G. Vasopressin elevation in e s s e n t i a l hypertension and increased responsiveness to sodium intake. Hypertension 3 ( S u p p l . l ) : 9 3 - l 0 0 , 1981. COWLEY J R . , A.W., QUILLEN J R . , E.W. and SKELTON, M.M. vasopressin in cardiovascular regulation. 42:3170-3176, 1983.  Role of Fed.  Proc.  CRILL, W.E. and REIS, D . J . D i s t r i b u t i o n of c a r o t i d sinus and depressor nerves in cat brain stem. Am. J . P h y s i o l . 214:269-276, 1968.  - 121 CROFTON, J . T . , SHARE, L . , SHADE, R . E . , LEE-KWON, W . J . , MANNING, M. and SAWYER, W.H. The importance of vasopressin in the development and maintenance of DOC-salt hypertension in the r a t . Hypertension 1^:31-38, 1979. CROFTON, J . T . , SHARE, L . , WANG, B.C. and SHADE, R.E. Pressor responsiveness to vasopressin in the rat with hypertension. Hypertension 2_:424-431, 1980. DALE, H.H. (Lond.)  On some p h y s i o l o g i c a l actions of ergot. 34:163-206, 1906.  DOC-salt  J . Physiol.  DALE, H.H. Nomenclature of f i b r e s in the autonomic system and t h e i r e f f e c t s . J . P h y s i o l . (Lond.) 80:10-11P, 1933. DAVIS, G . C , KISSINGER, P.T. and SHOUP, R. E. Strategies for determination of serum or plasma norepinephrine by reverse-phase l i q u i d chromotography. A n a l . Chem. 63:156-159, 1981. DAVIS J R . , W.D., GORLIN, R., REICHMAN, S. and STORAASLI, J . P . E f f e c t of p i t u i t r i n in reducing portal pressure in the human being. New E n g l . J . Med. 256:108-111, 1957. DAY, T . A . , FERGUSON, A . V . and RENAUD, L . P . F a c i l i t a t o r y influence of noradrenergic afferents on the e x c i t a b i l i t y of rat paraventricular nucleus neurosecretory c e l l s . J . P h y s i o l . (Lond.) 355:237-249, 1984. DE JONGE, W. and NIJKAMP, F . P . C e n t r a l l y induced hypotension and bradycardia a f t e r administration of a-methylnoradrenaline into the area of the nucleus tractus solitarii of the r a t . Br. J . Pharmacol. 58:593-598, 1976. DE JONGE, A . , TIMMERMANS, P.B.M.W.M. and VAN ZWIETEN, P.A. P a r t i c i p a t i o n of cardiac presynaptic a2~adrenoceptors bradycardiac effects of clonidine and analogues. Schmiedeberg's Arch. Pharmacol. 317:8-12, 1981.  in the Naunyn  DE MEY, J . G . and VANHOUTTE, P.M. Uneven d i s t r i b u t i o n of postjunctional alpha^- and alpha2~like adrenoceptors in canine a r t e r i a l and venous smooth muscle. C i r c . Res. 48:875-884, 1981. DE TORRENTE, A . , ROBERTSON, G . L . , MCDONALD, K.M. and SCHRIER, R.W. Mechanism of d i u r e t i c response to increased l e f t a t r i a l pressure in the anesthetized dog. Kidney Int. 8:355-361, 1975. DE WIED, D. Behavioural e f f e c t s of i n t r a v e n t r i c u l a r l y administered vasopressin and vasopressin fragments. L i f e S c i . 19:685-690, 1976. DIPETTE, D., GAVRAS, I., NORTH, W., DIPETTE, P. and GAVRAS, H. Vasopressin response to hyperosmotic stimulus: blood pressure e f f e c t in normal subjects and patients with impaired sympathetic system. C l i n . Exp. Hypertens. 6:851-861, 1984.  - 122 DORSA, D . M . , MAJUMDAR, L . A . F . , PETRACCA, M . , B A S K I N , D . G . and CORNETT, L.E. Characterization and localization of H-arginine -vasopressin binding to rat kidney and brain tissue. P e p t i d e s 4 : 6 9 9 - 7 0 6 , 1983. 3  8  DOXEY, J . P r e - and p o s t s y n a p t i c e f f e c t s o f a - a g o n i s t s i n t h e annococcygeus muscle of the pithed rat. E u r . J . Pharmacol.  5 4 : 1 8 5 - 1 8 9 , 1979.  DOXEY, J . C . , S M I T H , C . F . C . a n d WALKER, J . M . S e l e c t i v i t y o f agents for p r e - and postsynaptic a-adrenoceptors. Pharmacol. 6 0 : 9 1 - 9 6 , 1977.  blocking Br. J .  DOXEY, J . C , G A D I E , B . , L A N E , A . C . a n d TULLOCH, I . F . Evidence f o r pharmacological similarity between a2-adrenoceptors i n t h e vas d e f e r e n s and c e n t r a l n e r v o u s s y s t e m o f t h e r a t . B r . J . Pharmacol.  8 0 : 1 5 5 - 1 6 1 , 1983. DREW, G . M . P h a r m a c o l o g i c a l c h a r a c t e r i z a t i o n o f t h e p r e s y n a p t i c a-adrenoceptor in the rat vas deferens. E u r . J . Pharmacol.  4 2 : 1 2 3 - 1 3 0 , 1977. DREW, G . M . P r e s y n a p t i c a - a d r e n o c e p t o r s : t h e i r pharmacological characterization and f u n c t i o n a l significance. In: Presynaptic R e c e p t o r s , Advances i n t h e B i o s c i e n c e s , V o l . 18. (Eds~I Langer, S . Z . , S t a r k e , KT, and D u b o c o v i c h , M . L . ) Pergamon P r e s s , O x f o r d .  (1979),  pp.59-65.  DREW, G . M . P r e s y n a p t i c m o d u l a t i o n nerve stimulation in pithed  of heart rate responses to c a r d i a c rats. J . Cardiovasc. Pharmacol.  2_:843-856, 1980. DREW, G . M . and WHITING, S . B . E v i d e n c e f o r t w o d i s t i n c t t y p e s o f p o s t s y n a p t i c a - a d r e n o c e p t o r i n v a s c u l a r smooth m u s c l e i n v i v o . J . P h a r m a c o l . 6 7 : 2 0 7 - 2 1 5 , 1979.  Br.  DU VIGNEUD, H . , LAWLER, H . C . and POPENOE, E . A . E n z y m a t i c c l e a v a g e o f g l y c i n a m i d e f r o m v a s o p r e s s i n and a p r o p o s e d s t r u c t u r e for this pressor-antidiuretic hormone o f t h e p o s t e r i o r p i t u i t a r y . J . Am. Chem. S o c . 7 5 : 4 8 8 0 - 4 8 8 1 , 1953. DU VIGNEUD, H . , G I S H , D . T . and KATSOYANNIS, P . G . A s y n t h e t i c preparation possessing biological properties associated arginine-vasopressin. J . Am. Chem. S o c . _75:4751-4752, 1954.  with  DUBOCOVICH, M . L . and LANGER, S . Z . N e g a t i v e f e e d b a c k r e g u l a t i o n o f n o r a d r e n a l i n e r e l e a s e by nerve s t i m u l a t i o n i n the perfused c a t ' s spleen: d i f f e r e n c e s i n potency of phenoxybenzamine i n b l o c k i n g t h e p r e - and p o s t - s y n a p t i c a d r e n e r g i c r e c e p t o r s . J . P h y s i o l . (Lond.)  237:505-519, 1974. ELLIOTT, H . L . and REID, J . L . E v i d e n c e f o r p o s t j u n c t i o n a l v a s c u l a r a2-adrenoceptors i n p e r i p h e r a l v a s c u l a r r e g u l a t i o n i n man. Clin.  Sci.  6 5 : 2 3 7 - 2 4 1 , 1983.  - 123 ELLIOTT, T.R. On the action of a d r e n a l i n . 32:401-467, 1904.  J . Physiol.  (Lond.)  ENERO, M.A., LANGER, S . Z . , ROTHLIN, R . P . and STEFANO, F . J . E . The r o l e of the alpha adrenoceptor in regulating noradrenaline overflow by nerve s t i m u l a t i o n . Br. J . Pharmacol. 44:672-688, 1972. ERIKSSON, L. E f f e c t of lowered CSF sodium concentration on the central control of f l u i d balance. A c t a . P h y s i o l . Scand. 91:61-68, 1974. — ERIKSSON, L . , FERNANDEZ,. 0. and OLSSON, K. Differences in antidiuretic response to intracarotid infusions of various hypertonic solutions in the conscious goat. A c t a . P h y s i o l . Scand. 83:554-562, 1971. ERMISCH, A . , BARTH, T . , RUHLE, H . J . , SKOPKOVA, J . , HRBAS, P. and LANDGRAF, R. On the blood-brain b a r r i e r to peptides: accumulation of l a b e l l e d vasopressin, desglyNH^-vasopressin and oxytocin by brain regions. Endocrinologia experimental i s 19:29-37, 1985. ESLER, M.D., HASKING, G . J . , WILLETT, I . R . P . , LEONARD, W. and JENNINGS, G.L. Noradrenaline release and sympathetic nervous system activity. Journal of Hypertension 3^: 117-129, 1985. ESSEX, H . E . , WEGRIA, G . E . , HERRICK, J . F . and MANN, F . C . The e f f e c t of c e r t a i n drugs on the coronary blood flow of the trained dog. Am. Heart J . 19:554-565, 1940. FARNEBO, L-0. and HAMBERGER, B. Drug-induced changes in the release of H-noradrenaline from f i e l d stimulated rat iris. Br. J . Pharmacol. 43:97-106, 1971. 3  FATER, D . C , SCHULTZ, H.D., SUNDET, W.D., MAPES, J . S . and GOETZ, K . L . E f f e c t s of l e f t a t r i a l stretch in cardiac denervated and i n t a c t conscious dogs. Am. J . P h y s i o l . 242:H1056-1064, 1982. FEJES-TOTH, G . , NARAY-FEJES-TOTH, A. and RATGE, D. Evidence against r o l e of a n t i d i u r e t i c hormone in support of blood pressure during dehydration. Am. J . P h y s i o l . 249:H42-H48, 1985. FELAL, I.; GOTTSMAN, M., EVERSMANN, T . , JEHLE, W. and UHLICH, E. Influence of various stress s i t u a t i o n s on vasopressin secretion man. A c t a . Endocrinol. [Suppl.] (Copenh) 215:122-123, 1978.  in  FELDBERG, W. and GADDUM, J . H . The chemical transmitter at synapses in a sympathetic ganglion. J . P h y s i o l . (Lond.) 80:12-13P, 1933. FITZGERALD, G . A . , WATKINS, J . and DOLLERY, C T . Regulation of norepinephrine release by peripheral a2~receptor stimulation. C l i n . Pharmac. Ther. 29:160-167, 1981.  - 124 FLAVAHAN, N.A., COOKE, J . P . , SHEPHERD, J . T . and VANHOUTTE, P.M. Human postjunctional alpha-1 and alpha-2 adrenoceptors: differential distribution in a r t e r i e s of the limbs. J . Pharm. Exp. Ther. 241:361-365, 1987. FORSLING, M.L. and ULLMANN, E.A. Non-osmotic stimulation of vasopressin release. In: Neurohypophys i s . Int. Conf. Biscayne, F l o r i d a . Karger, BaseT (1977), pp. 128-135.  Key  FOSTER, D.O. and FRYDMAN, M.L. Comparison of microspheres and R b as tracers of the d i s t r i b u t i o n of cardiac output in rats indicates invalidity of Rb -based measurements. Can. J. Physiol. Pharmacol. 56:97-109, 1978. 8 6  86  +  FRIEDEN, J . and KELLER, A.D. Decreased resistance to hemorrhage in neurohypophysectomized dogs. C i r c . Res. 2_:214-220, 1954. FRIEDMAN, S.M. and PAULS, H. The e f f e c t of p i t r e s s i n infusion on blood pressure of the r a b b i t , c a t , and r a t . Am. Heart 44:131-142, 1952.  J.  FRIEDMAN, S . M . , FRIEDMAN, C L . and NAKASHIMA, M. Accelerated appearance of DCA hypertension in rats treated with p i t r e s s i n . Endocrinology 67:752-759, 1960. FULLER, R.W., SNODDY, H.D. and MARSHALL, U.S. Lowering of rat brain 3-methoxy-4-hydroxyphenylethylene glycol suphate (MOPEG sulphate) concentration by 2,6-dichlorobenzylidene aminoguanidine. J . Pharm. Pharmacol. 29:375-376, 1977. FYHRQUIST, F . , TIKKANEN, I. and LINKOLA, J . Plasma,vasopressin concentration and renin in the r a t : e f f e c t of dehydration hemorrhage. A c t a . P h y s i o l . Scand. 113:507-510, 1981.  and  GAGNON, D . J . , SIROIS, P. and BOUCHER, P . J . Stimulation by angiotensin II of the release of vasopressin from incubated rat neurohypophysis: possible involvement of c y c l i c AMP. C l i n . Exp. Pharmacol. P h y s i o l . ^:305-313, 1975. GANTEN, U . , RASCHER, W. and LANG, R.E. Development of a new s t r a i n of spontaneously hypertensive rats homozygous for hypothalamic diabetes i n s i p i d u s . Hypertension 5(Suppl.1):119-128, 1983. GAUER, O.H. and HENRY, J . P . C i r c u l a t o r y basis of f l u i d volume c o n t r o l . P h y s i o l . Rev. 43:423-481, 1963. GAZIS, D. and SAWYER, W.H. Elimination of infused arginine-vasopressin and i t s long-acting deaminated r a t s . J . Endocrinol. 78:179-186, 1978.  analogue  in  GINSBURG, M. and HELLER, H. A n t i d i u r e t i c a c t i v i t y in blood obtained from various parts of the cardiovascular system. J . Endocrinol. 9:274-282, 1953.  - 125 GOLDSTEIN, D . S . , McCARTY, R., POLINSKY, R . J . and KOPIN, I . J . Relationship between plasma norepinephrine and sympathetic activity. Hypertension 5_:552-559, 1983.  neural  GOPALAKRISHNAN, V . , TRIGGLE, C . R . , SULAKHE, P.V. and MCNEILL, J . R . Characterization of a specific, high affinity [^H]arginine° vasopressin-binding s i t e on l i v e r microsomes from d i f f e r e n t s t r a i n s of rat and the r o l e of magnesium. Endocrinology 118:990-997, 1986. GRAHAM, R . M . , MUIR, M.R. and HAYES, J . M . D i f f e r i n g e f f e c t s of the v a s o d i l a t o r drugs, prazosin and diazoxide on plasma renin a c t i v i t y in the dog. C l i n . Exp. Pharmacol. P h y s i o l . 3^:173-177, 1976. GREENBERG, D.A., U'PRICHARD, D.C. and SNYDER, S.H. Alpha-noradrenergic receptor binding in mammalian b r a i n : differential l a b e l i n g of agonist and antagonist s t a t e s . L i f e S c i . 19:69-76, 1976. GREENWAY, C V . E f f e c t s of sodium n i t r o p r u s s i d e , isosorbide d i n i t r a t e , isoproterenol, phentolamine and prazosin on hepatic venous responses to sympathetic nerve stimulation in the ' c a t . J. Pharmacol. Exp. Ther. 209:56-61, 1979. GUO, G . B . , SCHMID, P . G . and ABBOUD, F.M. S i t e s at which vasopressin f a c i l i t a t e s the a r t e r i a l baroreflex in r a b b i t s . Am. J . P h y s i o l . 251:644-655, 1986. HAMILTON, C A . and REID, J . L . A postsynaptic l o c a t i o n of alpha-2adrenoceptors in vascular smooth muscle: in vivo studies in the conscious r a b b i t . Cardiovasc. Res. 16:11-15, 1982. HAUSLER, G. Clonidine-induced i n h i b i t i o n of sympathetic nerve activity: no i n d i c a t i o n f o r a central presynaptic or an i n d i r e c t sympathomimetic mode of action. Naunyn-Schmiedeberg's Arch. Pharmacol. 286:97-111, 1974. HAUSLER, G. Central a-adrenoceptors involved in cardiovascular r e g u l a t i o n . J . Cardiovasc. Pharmacol. £:S72-S76, 1982: HAYWARD, J . N . and JENNINGS, D.P. Influence of sleep-waking and nociceptor-induced behaviour on the a c t i v i t y of supraoptic neurons in the hypothalamus of the monkey. Brain Res. 57^:461-466, 1973. HENRY, J . P . , GAUER, O.H. and REEVES, J . L . Evidence of the a t r i a l l o c a t i o n of receptors i n f l u e n c i n g urine flow. C i r c . Res. 4:85-94, 1956. HENRY, J . P . , GUPTA, P . D . , MEEHAN, J . P . , SINCLAIR, R. and SHARE, L. The r o l e of afferents from the low-pressure system in the release of a n t i d i u r e t i c hormone during non-hypotensive hemorrhage. Can. J . P h y s i o l . Pharmacol. 46:286-295, 1968.  - 126 HEYNDRICKX, G . R . , BOETTCHER, D.H. and VATNER, S . F . E f f e c t s of angiotensin, vasopressin, and methoxamine on cardiac function and blood flow d i s t r i b u t i o n in conscious dogs. Am. J . P h y s i o l . 231:1579-1587, 1976. HICKS, P . E . , MEDGETT, I.C. and LANGER, S . Z . Postsynaptic alpha-2 adrenergic receptor-mediated vasoconstriction in SHR t a i l a r t e r i e s in v i t r o . Hypertension 6^:112-118, 1984. HOFBAUER, K . G . , KONRADS, A . , BAUEREISS, K., MOHRING, B . , MOHRING, J . and GROSS, F. Vasopressin and renin in glycerol-induced acute renal f a i l u r e in the r a t . C i r c . Res. 41:424-428, 1977. HOFFMAN, W.E., PHILLIPS, M.I. and SCHMID, P.G. Central angiotensin II-induced responses in spontaneously hypertensive r a t s . Am. J . P h y s i o l . 232:H426-H433, 1977. HOLMAN, M.E. and SURPRENANT, A. An electrophysiooogical a n a l y s i s of the effects of noradrenaline and a-receptor antagonists on neuromuscular transmission in mammalian muscular a r t e r i e s . Br. J . Pharmacol. 71:651-661, 1980. HOLMES, A . E . and LEDSOME, J . R . E f f e c t of norepinephrine and vasopressin on c a r o t i d sinus baroreceptor activity anesthetized r a b b i t . E x p e r i e n t i a 40:825-827, 1984.  in  the  HUBBARD, J . W . , BUCHHOLTZ, R . A . , KEETON, T.K., and NATHAN, M.A. Plasma norepinephrine r e f l e c t s pharmacological a l t e r a t i o n s of sympathetic a c t i v i t y in the conscious c a t . J . Autonom. Nerv. S y s t . 15:93-100, 1986. ~" HUCHET, A . M . , DOURSOUT, M . F . , OSTERMANN, G . , CHELLY, J . and SCHMITT, H. Possible r o l e of cq-and ©^-adrenoceptors in the modulation of the sympathetic component of the b a r o r e f l e x . Neuropharmacology 22:1243-1248, 1983. HUKUHARA J R . , T . , OTSUKA, Y . , TAKEDA, R. and SAKAI, F. Die zentralen wirkungen des 2-(2,6-dichlorophenylamino)-2-imidazolin-hydrochloride. Arzneim. Forsch. 18:1147-1153, 1968. IMAI, Y . , NOLAN, P . L . and JOHNSTON, C . I . Endogenous vasopressin modulates the baroreflex sensitivity in rats. Clin. Pharmacol. P h y s i o l . 10:289-292, 1983.  Exp.  IRIUCHIJIMA, J . Conditions f o r secretion of vasopressin in pressor amounts in water-replete r a t s . Jpn. J . P h y s i o l . 33:887-894, 1983. ISHIHARA, H . , ISHIDA, K., OYAMA, T . , KUDO, T. and KUDO, M. E f f e c t s of general anaesthesia and surgery on renal function and plasma ADH l e v e l s . Can. Anaesth. Soc. J . 25:312-318, 1978. JARROTT, B . , LOUIS, W.H. and SUMMERS. R . J . The c h a r a c t e r i s t i c s of (3H)-clonidine binding to an a-adrenoceptor in membranes from guinea-pig kidney. Br. J . Pharmacol. 65:663-670, 1979.  - 127 JEWELL, P.A. and VERNEY, E.B. An experimental attempt to determine the s i t e of the neurohypophyseal osmoreceptors in the dog. Philos. Trans. Roy. Soc. London Ser. B 240:197-324, 1957. JOHNSON, J . A . , MOORE, W.W. and SEGAR, W.E. Small changes in l e f t a t r i a l pressure and plasma a n t i d i u r e t i c hormone t i t e r s in dogs. Am. J . P h y s i o l . 217:210-214, 1969. JOHNSTON, C . I . , NEWMAN, M. and WOODS, R. Role of vasopressin in cardiovascular homeostasis and hypertension. Clin. 61:129s-139s, 1981.  Sci.  JOHNSTON, K . M . , MACLEOD, B.A. and WALKER, M.J.A. Responses to l i g a t i o n of a coronary artery in conscious rats and the actions of antiarrhythmics. Can. J . P h y s i o l . Pharmacol. 61:1340-1353, 1983. KALKMAN, H.O., THOOLEN, M . J . M . C , TIMMERMANS, P.B.M.W.M. and VAN ZWIETEN, P.A. The influence of a\- and (^-adrenoceptor agonists on cardiac output in' rats and c a t s . J . Pharm. Pharmacol. 36:265-268, 1984. KALSNER, S. The presynaptic receptor controversy. Pharmacological Sciences 3-1:11-16, 1982.  Trends in  KALSNER, S. Evidence that transmitter release in sympathetic nerves i s not set by feedback v i a presynaptic receptors. Can. J . P h y s i o l . Pharmacol. 61:1197-1201, 1983. KALSNER, S. and QUILLAN, M. A hypothesis to explain the presynaptic effects of adrenoceptor antagonists. Br. J. Pharmacol. 82:515-522, 1984. KAPPAGODA, C T . , LINDEN, R . J . , SNOW, H.M. and WHITAKER, E.M. E f f e c t of destruction of the p o s t e r i o r p i t u i t a r y on the d i u r e s i s from l e f t a t r i a l receptors. J . P h y s i o l . (Lond.) 244:757-770, 1975. KARMAZYN, M.M., MANKU, S. and HORROBIN, D.F. Changes of vascular r e a c t i v i t y induced by low vasopressin concentration interaction with Cortisol and lithium possible i n v o l v e m e n t of p r o s t a g l a n d i n s . Endocrinology 102:1230-1236, 1978. KASTING, N.W., VEALE, W.L. and COOPER, K . E . Convulsive and hypothermic e f f e c t s of vasopressin in the brain of the r a t . J . P h y s i o l . Pharmacol. 58:316-319, 1980.  Can.  KEETON, T.K. and CAMPBELL, W.B. The pharmacologic a l t e r a t i o n of renin r e l e a s e . Pharmacol. Rev. 31:81-227, 1981. KEIL, L . C , SUMMY-LONG, J . and SEVERS, W.B. Release of vasopressin by angiotensin I I . Endocrinology 96:1063-1065, 1975. KENDLER, K . S . , WEITZMAN, E.A. and FISHER. D.A. The e f f e c t of pain on plasma arginine vasopressin concentrations in man. Clin. Endocrinol. (Oxf) 8:89-94, 1978.  - 128 KIBJAKOW, A.W. Uber humorale Ubertragung den Erregung von einem neuron auf das andere. Arch. i . d. ges. P h y s i o l . 232:432-443, 1933. , KLUPP, H . , KNAPPEN, F . , OTSUKA, Y . , STRELLER, J . and TEICHMANN, H. E f f e c t s of c l o n i d i n e on central sympathetic tone. Eur. Pharmacol. 10:225-229, 1970. KOBINGER, W. Uber den Wirkungsmechanismus einer neuen antihypertensiven substanz mit imidazolinstruktur. Schmiedeberg's Arch. Pharmacol. 258:48-58, 1967.  J.  Naunyn  KOBINGER, W. The r o l e of a-adrenoceptors in central nervous and peripheral vascular regulation. Jpn. J. Pharmacol. 31(Suppl.):13P-2QP, 1981. KOBINGER, W. and PICHLER, L. The central modulatory e f f e c t of c l o n i d i n e on the cardiodepressor r e f l e x after suppression of synthesis and storage of noradrenaline. Eur. J . Pharmacol. 30:56-62, 1975. KOBINGER, W. and PICHLER, L. I n v e s t i g a t i o n into d i f f e r e n t types of post- and presynaptic a-adrenoceptors at cardiovascular s i t e s r a t s . Eur. J . Pharmacol. 65:393-402, 1980a.  in  KOBINGER, W. and PICHLER, L. Relation between central sympathoinhibitory and peripheral pre- and postsynaptic a-adrenoceptors as evaluated by d i f f e r e n t c l o n i d i n e - l i k e substances in r a t s . Naunyn-Schmiedeberg s Arch. Pharmacol. 315:21-27, 1980b. 1  KOBINGER, W. and PICHLER, L. A l p h a i and a l p h a adrenoceptor subtypes: selectivity of various agonists and d i s t r i b u t i o n of receptors as determined in rats. ' Pharmacol. 73:313-321, 1981. 2  KOBINGER, W. and PICHLER, L. a-Adrenoceptor subtypes in cardiovascular r e g u l a t i o n . J . Cardiovasc. Pharmacol. 1982.  relative Eur. J .  4:S81-S85,  KOBINGER, W. and WALLAND, A. Involvement of adrenergic receptors in central vagus a c t i v i t y . Eur. J . Pharmacol. 16:120-122, 1971. KOVACS, G . L . , BOHUS, B . , VERSTEGG, D.H.G., DE KLOET, E.R. and DE WIED, D. E f f e c t s of oxytocin and vasopressin on memory c o n s o l i d a t i o n : s i t e s of action and catecholaminergic correlates after local microinjection into limbic-midbrain structures. Brain Res. 175:303-314, 1979. KROGH, A. The reactions of c a p i l l a r i e s to d i r e c t s t i m u l a t i o n . In: The Anatomy and Physiology of C a p i l l a r i e s . Yale U n i v e r s i t y Press, Hafner N . Y .  (1929), pp.182-208.  - 129 KRUSZYNSKI, M., LAMMEK, B . , MANNING, M., SETO, J . , HALDAR, J . and SAWYER, W.H. [l-(B-mercapto-B,B-cyclopentamethylenepropionic a c i d ) , 2-(0-methyl)tyrosine]arginine-vasopressin and [l-(B-mercaptoB,B-cyc1opentamethy1enepropi oni c a c i d ) ] a r g i n i n e - v a s o p r e s s i n , two highly potent antagonists of the vasopresssor response to a r g i n i n e - v a s o p r e s s i n . J . Med. Chem. 23:364-368, 1980. KUBO, T. and MISU, Y. Pharmacological c h a r a c t e r i z a t i o n of the a-adrenoceptors responsible f o r a decrease of blood pressure in the nucleus tractus s o l i t a r i i of the r a t . Naunyn-Schmiedeberg s Arch. Pharmacol. 317:120-125, 1981. 1  LANDS, A . M . , ARNOLD, A . , MCAULIFF, J . P . , LUDUENA, F . P . and BROWN J R . , T.G. Differentiation of . receptor systems activated by sympathomimetic amines. Nature 214:597-598, 1967. LANGER, S . Z . The metabolism of ^H-noradrenaline released by e l e c t r i c a l stimulation from the i s o l a t e d n i c t i t a t i n g membrane of the cat and from the vas deferens of the r a t . J . P h y s i o l . (Lond.) 208:515-546, 1970. LANGER, S . Z . The regulation of transmitter release e l i c i t e d by nerve stimulation through a presynpatic feedback mechanism. In: F r o n t i e r s in Catecholamine Research. (Ed. Usdin, E. and Snyder, ST) Pergammon Press, New York. (T973), pp. 543-549. LANGER, S . Z . Presynaptic regulation of catecholamine r e l e a s e . Biochem. Pharmac. 23:1793-1900, 1974. LANGER, S . Z . Presynaptic regulation of the release of catecholamines. Pharmacol. Rev. 32:337-362, 1981. LANGER, S . Z . and VOGT, M. Noradrenaline release from i s o l a t e d muscle of the n i c t i t a t i n g membrane of the c a t . J . P h y s i o l . (Lond.) 214:159-171, 1971. LANGER, S . Z . , ADLER, E . , ENERO, M.A. and STEFANO, F . J . E . The r o l e of the alpha receptor in regulating noradrenaline overflow by nerve s t i m u l a t i o n . XXV Int. Cong. P h y s i o l . Sciences (1971), p. 335. LANGER, S . Z . , SHEPPERSON, M.B. and MASSINHAM, R. P r e f e r e n t i a l noradrenergic innervation of alpha-adreneric receptors in vascular smooth muscle. Hypertension 3(Suppl. 1):1112—1118, 1981. LANGER, S . Z . , PIMOULE, C. and SCATTON, B. [ H]-RX781094, a preferential a2-adrenoceptor antagonist radioligand, labels a2~adrenoceptors in the rat brain cortex. Br. J . Pharmacol. 7 8 ( S u p p l . ) : l 0 9 P , 1983. 3  LANGLEY, J . N . On the reaction of c e l l s and nerve endings to c e r t a i n poisons; c h i e f l y as regards the reaction of s t r i a t e d muscle to n i c o t i n e and to curare. J . P h y s i o l . (Lond.) 33:374-413, 1905. LANGLEY, J . N . The Autonomic Nervous System, Part I. Cambridge. (1921). :  Heffer,  - 130 LAUSON, H.D. Metabolism of the neurohypophysial hormones. In: Handbook of Physiology Endocrinology Sect. 7, V o l . IV, P t . l . (Ed. Greep, R . O . , Astwood, E.B.) AirTi P h y s i o l . S o c . , Washington, D.C. (1974), pp. 287-393,. LAYCOCK, J . F . , PENN, W., SHIRLEY, D.G. and WALTER, S . J . The r o l e of vasopressin in blood pressure regulation immediately following acute hemorrhage in the r a t . J . P h y s i o l . (Lond.) 296:267-275, 1979. LEDSOME, J . R . and LINDEN, R . J . The r o l e of the l e f t a t r i a l receptors in the d i u r e t i c response to l e f t a t r i a l d i s t e n s i o n . J . Physiol. (Lond.) 198:487-503, 1968. LEDSOME, J . R . , NGSEE, J . and WILSON, N. Plasma vasopressin concentration in the anaesthetized dog before, during and a t r i a l d i s t e n s i o n . J . P h y s i o l . (Lond.) 338:413-422, 1983.  after  LEDSOME, J . R . , WILSON, N. and COURNEYA, C.A. Plasma vasopressin during increases and decreases in blood volume in anaesthetized dogs. Can. J . P h y s i o l . Pharmacol. 63:224-229, 1985. LEE-KWON, W . J . , SHARE, L . , CROFTON, J . T . and SHADE, R . E . Vasopressin in the rat with p a r t i a l nephrectomy-salt hypertension. C l i n . Exp. Hypertens. _3:281-297, 1981. LEIGHTON, J . , BUTZ, K.R. and PARMETER, L . L . E f f e c t of a-adrenergic agonists and antagonists on neurotransmission in the rat anococcygeus muscle. Eur. J . Pharmacol. 58:27-38, 1979. LENG, G . , MASON, W.T. and DYER, R.G. The supraoptic nucleus as an osmoreceptor. Neuroendocrinology 34:75-82, 1982. LIARD, J . F . , DERIAZ, 0 . , TSCHOPP, M. and SCHOUN, J . Cardiovascular e f f e c t s of vasopressin infused into the vertebral c i r c u l a t i o n conscious dogs. C l i n . S c i . 61:345-347, 1981.  of  LOKHANDWALA, M . F . , COATS, J . T . and BUCKLEY, J . P . E f f e c t s of several catecholamines on sympathetic transmission to the myocardium: role of presynaptic a-adrenoceptors. Eur. J . Pharmacol. 42:257-265, 1977. ~~ LUMBERS, E.R. and POTTER, E.K. The e f f e c t of vasoactive peptides on the c a r o t i d cardiac b a r o r e f l e x . C l i n . Exp. Pharmacol. P h y s i o l . Suppl. 7:45-49, 1982. LUND-JOHANSEN, P. Hemodynamic changes at rest and during exercise in lon-term prazosin therapy of essential hypertension. In: Prazosin: Evaluation of a new antihypertensive agent. (Ed. Cotton, D.W.K.) Exerpta Medica, Amsterdam, ( i y / 4 ) , p p . 4 B - b J . MALIK, A . B . , KAPLAN, J . E . and SABA, T.M. Reference sample method for cardiac output and regional blood flow determinations in the r a t . J . A p p l . P h y s i o l . 40:472-475, 1976.  - 131 MANKU, M.S. and HORROBIN, D.F. Indomethacin i n h i b i t s response to a l l vasoconstrictors in the rat mesenteric vascular bed. Restoration of response by prostaglandin Ep. Prostaglandins 12:369-376, 1977. ~~ MANNING, M. and SAWYER, W.H. Antagonists of vasopressor and a n t i d i u r e t i c responses to arginine vasopressin. Ann. Int. 96:520-522, 1982.  Med.  MARCHETTI, J . , THIBONNIER, M., GONZALES, M . F . , CORVOL, P. and MENARD, J. Dynamic study of antidiuretic hormone during benign mineralocorticoid hypertension. Acta Endocrinol. 95:444-453, 1980. MARSHALL, I., NASMYTH, P . A . , NICHOLL, C.G. and SHEPPERSON, N.B. a-Adrenoceptors in the mouse vas deferens and t h e i r e f f e c t s on response to e l e c t r i c a l s t i m u l a t i o n . Br. J . Pharmacol. 62:147-151, 1978. ~~ MARTIN, S . , MALKINSON, T . J . , VEALE, W.L. and PITTMAN, Q . J . Central e f f e c t of arginine vasopressin on blood pressure in the r a b b i t . Can. J . P h y s i o l . Pharmacol. ( J l ^ A x v i i - A x v i i i , 1983. MARTIN, S . , MALKINSON, T . J . , VEALE, W.L. and PITTMAN, Q . J . The action of c e n t r a l l y administered arginine vasopressin on blood pressure in the conscious r a b b i t . Brain Res. 348:137-145, 1985. MASSINGHAM, R. and HAYDEN, M.L. A comparison of the e f f e c t s of prazosin and hydralazine on blood pressure, heart r a t e , and plasma renin a c t i v i t y in conscious renal hypertensive dogs. Eur. J . Pharmacol. 30:121-124, 1975. MATSUGUCHI, H . , SCHMID, P . G . , VAN ORDEN, D. and MARK, A . L . Does vasopressin contribute to salt-induced hypertension in the s t r a i n ? Hypertension 3:174-181, 1981.  Dahl  MATSUGUCHI, H . , SHARABI, F . M . , GORDON, F . J . , JOHNSON, A . K . and SCHMID, P.G. Blood pressure and heart rate responses to m i c r o i n j e c t i o n of vasopressin into the nucleus tractus s o l i t a r i u s region of the r a t . Neuropharmacology 21:687-693, 1982. MCKENZIE, J . K . , RYAN, J.W. and LEE, M.R. plasma renin a c t i v i t y in the r a b b i t . 1967.  E f f e c t of laparotomy on Nature (London) 215:542-543,  MCKINLEY, M . J . , DENTON, D.A. and WEISINGER, R.S. Sensors f o r antidiuresis and thirst osmoreceptors or CSF detectors? Brain Res. 141:89-103, 1978.  sodium  MCNEILL, J . R . . Redundant nature of the vasopressin and renin-angiotensin systems in the control of mesenteric resistance vessels of the conscious fasted c a t . Can. J . P h y s i o l . Pharmacol. 61:770-773, 1983.  - 132 MCNEILL, J . R . and PANG, C.C.Y. Effect of pentobarbital anaesthesia and surgery on the control of a r t e r i a l pressure and mesenteric resistance in c a t s : r o l e of vasopressin and angiotensin. Can. J . P h y s i o l . Pharmacol. 60:363-368, 1982. MELLANDER, S. and JOHANSSON, B. Control of r e s i s t a n c e , exchange, and capacitance functions in the peripheral c i r c u l a t i o n . Pharmacol. Rev. 20:117-196, 1968. MENTO, P . F . , WANG, H.H. and SAWYER, W.H. R e l a t i v e contributions of arginine vasopressin (AVP) and the sympathetic nervous system in maintaining DOC-salt hypertension in r a t s . Fed. Proc. 41:1230, 1982. — MICHELL, R . H . , KIRK, C . J . and BILLAH, M.M. Hormonal stimulation of phosphatidyl i n o s i t o l breakdown with p a r t i c u l a r reference to the hepatic e f f e c t s of vasopressin. Biochem. Soc. Trans. 7:861-865, 1979. MOHRING, J . , MOHRING, B . , PETRI, M. and HAACK, D. Vasopressor r o l e of ADH in the pathogenesis of malignant DOC hypertension. Am. J . P h y s i o l . 232:F260-F269, 1977. MOHRING, J . , MOHRING, B . , PETRI, M. and HAACK, D. Plasma vasopressin concentrations and e f f e c t s of vasopressin antiserum on blood pressure in rats with malignant two-kidney Goldblatt hypertension. C i r c . Res. 42:17-22, 1978. MOHRING, J . , . KINTZ, J . and SCHOUN, J . Studies on the r o l e of vasopressin in blood pressure control of spontaneously hypertensive rats with established hypertension (SHR, stroke-prone s t r a i n ) . J. Cardiovasc. Pharmacol. 1^593-608, 1979. MOHRING, J . , GLANZER, K., MACIEL J R . , J . A . , DUSING, R., KRAMER, H . J . , ARBOGAST, R. and KOCH-WESER, J . Greatly enhanced pressor response to a n t i d i u r e t i c hormone in patients with impaired cardiovascular r e f l e x e s due to i d i o p a t h i c o r t h o s t a t i c hypotension. J . Cardiovasc. Pharmacol. 21:367-376, 1980. MOHRING, J . , KINTZ, J.,.SCHOUN, J . and MCNEILL, J . R . Pressor responsiveness and cardiovascular r e f l e x a c t i v i t y in spontaneously hypertensive and normotensive rats during vasopressin i n f u s i o n . J . Cardiovasc. Pharmacol. 3:948-957, 1981. MONTANI, J . P . , LIARD, J . F . , SCHOUN, J . and MOHRING, J . Hemodynamic e f f e c t s of exogenous and endogenous . vasopressin at low plasma concentration in conscious dogs. C i r c . Res. 47:346-355, 1980. MORAN, W.H. and ZIMMERMAN, B. Mechanism of a n t i d i u r e t i c hormone control of importance to the s u r g i c a l p a t i e n t . Surgery 62:639-644, 1967. —  MORAN, W.H., MILTENBERGER, F.W., SHU'AYB, W.A. and ZIMMERMAN, B. The r e l a t i o n s h i p of a n t i d i u r e t i c hormone secretion to s u r g i c a l s t r e s s . Surgery 56:99-108, 1964.  - 133 MORTON, J . J . , GARCIA DEL RIO, C. and HUGHES, M.J. E f f e c t of acute vasopressin infusion on blood pressure and plasma angiotensin II in normotensive and DOCA-salt hypertensive rats. Clin. Sci. 62:143-149, 1982. MOUILLE, P . , HUCHET, A . M . , CHELLY, J . , LUCET, B . , DOURSOUT, M.F. and SCHMITT, H. Pharmacological properties of AR-C239, 2-[2-[4(0-methoxyphenyl)-piperazine-l-Yl]-ethyl]4,4-dimethyl-l,3(2H-4 H) isoquinolinedione, a new a-adrenoceptor blocking drug. J. Cardiovasc. Pharmacol. 2^:175-191, 1980. MOULDS, R . J . and JAUERNIG, A.R. Lancet j . : 2 0 0 - 2 0 l , 1977.  Mechanism of prazosin c o l l a p s e .  NASHOLD, B . S . , MANNARINO, E.M. and WUNDERLICH, M. Pressor-depressor blood pressure response in the cat after intraventricular administration of drugs. Nature 193:1297-1298, 1961. NISHIYAMA, K., NISHIYAMA, A. and FROHLICH, E.D. Regional blood flow i n normotensive and spontaneously hypertensive r a t s . Am. J . P h y s i o l . 230:691-198, 1976. OLIVER, G. and SCHAFER, E.A. On the p h y s i o l o g i c a l action of extracts of p i t u i t a r y body and c e r t a i n other glandular organs. J . P h y s i o l . (Lond.) 18:277-279, 1895a. OLIVER, G. and SCHAFER, E.A. P h y s i o l o g i c a l e f f e c t s of extracts of the suprarenal capsules. J . P h y s i o l . (Lond.) 18:230-279, 1895b. OLSSON, K. Studies on central regulation of secretion of a n t i d i u r e t i c hormone (ADH) in the goat. A c t a . P h y s i o l . Scand. 78:465-474, 1969. OLSSON, K. Further evidence f o r the importance of CSF N a concentration in central control of f l u i d balance. A c t a . P h y s i o l . Scand. 88:183-188, 1973. +  ONESTI, G . , SCHWARTZ, A . B . , KIM, K . E . , PAZ-MARTINEZ, V. and SWARTZ, CH. Antihypertensive effect of clonidine. Circ. Res.> 28(Supp1.2):53-69, 1971. OYAMA, T . , KIMURA, K. and SATO, K. The e f f e c t of anesthesia and surgery on plasma a n t i d i u r e t i c hormone. Med. J . Osaka 21:113-120, 1971.  Univ.  PADFIELD, P . L . , LEVER, A . F . , BROWN, J . J . , MORTON, J . J . and ROBERTSON, J.I.S. Changes of vasopressin in hypertension: cause or effect? Lancet 1255-1257, 1976. PADFIELD, P . L . , BROWN, J . J . , LEVER, A . F . , MORTON, J . J . and ROBERTSON, J.I.S. Does vasopressin play a r o l e in the pathogenesis of hypertension? C l i n . S c i . 61:141s-143s, 1981.  - 134 PANG, C.C.Y. Vasopressin and angiotensin in the control of a r t e r i a l pressure and regional blood flow in anaesthetized, surgically-stressed rats. Can. J. Physiol. Pharmacol. 61:1494-1500, 1983a. PANG, C.C.Y. E f f e c t of vasopressin antagonist and s a r a l a s i n on regional blood flow following hemorrhage. Am. J . Physiol. 245:H749-H755, 1983b. PANG, C.C.Y. and CHAN, T . C . K . recordings from d i f f e r e n t Methods 13:325-330, 1985.  D i f f e r e n t i a l i n t r a - a r t e r i a l pressure a r t e r i e s in the r a t . J . Pharmacol.  PANG, C.C.Y. and LEIGHTON, K.M. Prolonged i n h i b i t i o n of pressor response to vasopressin by a potent specific antagonist, [l-(B-mercapto-B,B-cyclopentamethylenepropionic acid)2-(0-methyl)tyrosine]arginine-vasopressin. Can. J. Physiol. Pharmacol. 59:1008-1012, 1981. PANG, C . C . Y . and TABRIZCHI, R. The e f f e c t s of noradrenaline, B-HT 920, methoxamine, angiotensin II and vasopressin on mean c i r c u l a t o r y f i l l i n g pressure in conscious r a t s . Br. J . Pharmacol. 89:389-394, 1986. PELLEGRINO, L . J . , PELLEGRINO, A . S . and CUSHMAN, A . J . A Stereotaxic A t l a s of the Rat B r a i n . Plenum Press, New York (1979T: PERLMUTT, J . H . E f f e c t of vagotomy on renal function during water d i u r e s i s . Proc. Soc. Exp. B i o l . Med. 116:270-273, 1964. PERRY, B.D. and U'PRICHARD, D.C. ( H)-Rauwolscine (a-yohimbine): s p e c i f i c antagonist r a d i o l i g a n d f o r brain (^-adrenoceptors. J . Pharmacol. 76:461-464, 1981. 3  a Eur.  PHILBIN, D.M. and COGGINS, C H . Plasma a n t i d i u r e t i c hormone l e v e l s in cardiac surgical patients during morphine and halothane anesthesia. Anesthesiology 49:95-98, 1978. PHILBIN, D.M., WILSON, N . E . , S0K0L0SKI, J . and COGGINS, C. Radioimmunoassay of a n t i d i u r e t i c hormone during anesthesia. Anaesth. Soc. J . 23:290-295, 1976.  Can.  PICHLER, L. and KOBINGER, W. Presynaptic a c t i v i t y at peripheral adrenergic s i t e s and blood pressure e f f e c t of a-adrenoceptor stimulating drugs. Eur. J . Pharmacol. 52:287-295, 1978. PICHLER, L. and KOBINGER, W. C e n t r a l l y mediated cardiovascular effects of B-HT 920 (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]-azepine d i h y d r o c h l o r i d e ) , a hypotensive agent of the " c l o n i d i n e t y p e " . J . Cardiovasc. Pharmacol. 3:269-277, 1981.  - 135 PICKERING, B.T. and MCPHERSON, M.A. Progress in the study of biosynthesis and transport i n the neurohypophysial system. In: Neurohypophysis. Int. Conf. Key Biscayne, F l o r i d a . Karger, B a s e l . (197/), pp. 30-42. PITTMAN, Q . J . , LAWRENCE, D. and MCLEAN, L. Central e f f e c t s of arginine vasopressin on blood pressure i n r a t s . Endocrinology 110:1058-1059, 1982. PULLAN, P . T . , JOHNSTON, C . I . , ANDERSON, W.P. and KORNER, P . I . Plasma vasopressin in blood pressure homeostasis and in experimental renal hypertension. Am. J . P h y s i o l . 239:H81-H87, 1980. PULSINELLI, W.A. and BRIERLEY, J . B . A new model of hemispheric ischemia in the unanesthetized r a t . 1979.  bilateral Stroke 10:267-272, —  RAICHLE, M.E. and GRUBB, R.L. Regulation of brain water permeability by c e n t r a l l y - r e l e a s e d vasopressin. Brain Res. 143:191-194, 1978. RAND, M . J . , STORY, D . F . , ALLEN, G . S . , GLOVER, A . B . and MCCULLOCH, M.W. P u l s e - t o - p u l s e modulation of noradrenaline release through a prejunctional a-receptor a u t o - i n h i b i t o r y mechanism. In: Frontiers in Catecholamine Research. (Ed. Usdin, E. and Snyder^ S.) Pergammon Press, New York. (1973), pp. 579-581. RANKIN, A . J . , KELPIN, B . G . , COURNEYA, C . A . , WILSON, N. and LEDSOME, J.R. Plasma vasopressin in response to haemorrhage in the anaesthetized r a b b i t . Can. J . P h y s i o l . Pharmacol. 64:904-908, 1986. —  RASCHER, W., MEFFLE, H. and GROSS, F. Hemodynamic e f f e c t s of arginine vasopressin in conscious water-deprived r a t s . Am. J . P h y s i o l . 249:H29-H33, 1985. ROBERTSON, G.L. The regulation of vasopressin function in health and disease. In: Recent Progress in Hormone Research. 23:333-388, 1977. —  ROBERTSON, G . L . , MAHR, E . A . , ATHAR, S. and SINHA, T. Development and c l i n i c a l a p p l i c a t i o n of a new method for the radioimmunoassay of arginine vasopressin in human plasma. J. Clin. Invest. 52:2340-2352, 1973. ROBERTSON, G . L . , ATHAR, S. and SHELTON, R.L. Osmotic control of vasopressin f u n c t i o n . In: Disturbances in Body F l u i d Osmolality (Ed. A n d r e o l i , T . E . , Grantham^ J . J . , Rector, F.C.) IW. P h y s i o l . S o c , Washington, D.C. (1977), pp. 125-248. ROCHA E SILVA J R . , M. and ROSENBERG, M. The release of vasopressin in response to haemorrhage and i t s r o l e in the mechanism of blood pressure r e g u l a t i o n . J . P h y s i o l . (Lond.) 202:535-557, 1969.  - 136 RUSSELL, J . T . , BROWNSTEIN, M . J . and GAINER, H. Time course of appearance and release of [ " " S j c y s t e i n e l a b e l l e d neurophysins and peptides in the neurohypophysis. Brain Res. 205:299-311, 1981. SAAMELI, K. Neurohypophyseal hormones and s i m i l a r peptides. In: Handbook of Experimental Pharmacology, V o l . 23. (Ed. Berde, B.) S p r i n g e r - V e r l a g , Heidelberg. (1968), pp. 545-612. SACHS, H . L . , SHARE, L . , OSINCHAK, J . and CARPI, A. Capacity of the neurohypophysis to release vasopressin. Endocrinology. 81:755-770, 1971. SAFAR, M . E . , WEISS, Y . A . and LONDON, G.L. Short-term hemodynamic studies with prazosin. Prazosin: Evaluation of a new antihypertensi ve agent. (Ed"! Cotton, D.W.K.) Exerpta Medica, Amsterdam. (1974), pp.64-70. SAPER, C . B . , LOEWY, A . D . , SWANSON, L.W. and COWAN, W.M. Direct hypothlamoautonomic connections. Brain Res. 117:305-313, 1976. SATTLER, R.W. and VAN ZWIETEN, P.A. Acute hypotensive action of 2-(2,6-dichlorophenylamino)-2-imidazol ine hydrochloride (St 155) a f t e r infusion into the c a t ' s vertebral a r t e r y . Eur. J . Pharmacol. 2_:9-13, 1967. SAWYER, W.H. 1961.  Neurohypophysial hormones.  Pharmacol. Rev.  13:225-277, —  SCHMID, P . G . , ABBOUD, F . M . , WENDLING, M.G., RAMBERG, E . S . , MARK, A . L . , HEISTAD, D.D. and ECKSTEIN, J.W. Regional vascular e f f e c t s of vasopressin: plasma l e v e l s and c i r c u l a t o r y response. Am. J . P h y s i o l . 227:998-1004, 1974. SCHMID, P . G . , SHARABI, F . M . , GUO, G . B . , ABBOUD, F.M. and THAMES, M.D. Vasopressin and oxytocin in the neural control of the c i r c u l a t i o n . Fed. Proc. 43:97-102, 1984. SCHMITT, H. and FENARD, S. E f f e t s des substances sympathomimetiques sur les centres vasomoteurs. Arch. Int. Pharmacodyn. 190:229-240, 1971. . SCHMITT, H . , SCHMITT, H . , BOISSIER, J . R . and GUIDICELLI, J . F . Centrally mediated decrease in sympathetic tone induced by 2-(2,6-dichlorophenylamino)-2-imidazoline (St 155, Catapresan). Eur. J . Pharmacol. 2_:147-148, 1967. SCHRIER, R.W. and BERL, T. Mechanisms of the a n t i d i u r e t i c e f f e c t associated with i n t e r r u p t i o n of parasympathetic pathways. J . C l i n . Invest. 51:2613-2620, 1972. SCHRIER, R.W., BERL, T. and ANDERSON, R . J . Osmotic and nonosmotic control of vasopressin r e l e a s e . Am. J . P h y s i o l . 236:F321-F332, 1979.  - 137 SCHULTZ, H.D., FATER, D . C . , SUNDET, W.D., GEER, P.G. and GOETZ, K . L . Reflexes e l i c i t e d by acute s t r e t c h of atrial vs. pulmonary receptors in conscious dogs. Am. J . P h y s i o l . 242:1065-1076, 1982. SCHULTZ, W . J . , BROWNFIELD, M.C. and KOZLOWSKI, G.P. The hypothalamo-choroidal t r a c t I I . Ultrastructural response of the choroid plexus to vasopressin. C e l l T i s s . Res. 178:129-141, 1977. SCHUMANN, H - J . and LUES, I. Postjunctional a-adrenoceptors in the i s o l a t e d saphenous vein of the r a b b i t : characterization and influence of angiotensin. Naunyn-Schmiedeberg's Arch. Pharmacol. 323:328-334, 1983. SCHWARTZ, J . and REID, I.A. Effect of vasopressin blockade on blood pressure regulation during hemorrhage in conscious dogs. Endocrinology 109:1778-1780, 1981. SCHWARTZ, J . and REID, I.A. Role of vasopressin in blood pressure regulation in conscious water-deprived dogs. Am. J . P h y s i o l . 244:R74-R77, 1983. SHARE, L. E f f e c t s of c a r o t i d occlusion and l e f t a t r i a l d i s t e n t i o n on plasma vasopressin t i t e r . Am. J . P h y s i o l . 208:219-223, 1965. SHARE, L. Control of plasma ADH t i t e r in hemorrhage: r o l e of a t r i a l and a r t e r i a l baroreceptors. Am. J . P h y s i o l . 215:1385-1389, 1968. SHARE, L. Blood pressure, blood volume, and the release of vasopressin. In: Handbook of Physiology Endocrinology Sect. 7, V o l . IV, P t . 1. (Ed. K n o b i l , E . , Sawyer, W.H.) Am. P h y s i o l . S o c , Washington, D.C. (1974), pp. 243-255,. SHARE, L. and CROFTON, J . T . The r o l e of vasopressin in hypertension. Fed. Proc. 43:103-106, 1984. SHARE, L. and LEVY, M.N. a n t i d i u r e t i c hormone. SHARE, L. and LEVY, M. plasma a n t i d i u r e t i c 1966.  Cardiovascular receptors and blood t i t e r of Am. J . P h y s i o l . 203:425-428, 1962.  Effect of c a r o t i d chemoreceptor stimulation on hormone t i t e r . Am. 0. P h y s i o l . 210:157-161,  SHARE, L . , CROFTON, J . T . , R0CKH0LD, R.W. and RAPP, J . P . Vasopressin secretion and responses to c a p t o p r i l and a vasopressin antagonist in the Dahl r a t . Proc. Fourth Int. Symp. Rats Spontaneous Hypertens. Related Studies. (Ed. Rascher, W., Clough, D. and Ganten, D.) Schattauer V e r l a g , New York. (1982), 574-576. SHIMAM0T0, K., AND0, T . , NAKHASHI, Y . , NAKAO, T . , TANAKA, S . , SAKUMA, M. and MIYAHARA, M. Plasma and urinary ADH l e v e l s in patient with e s s e n t i a l hypertension. Jpn. C i r c . J . 43:43-47, 1979. SHOJI, T . , TSURU, H. and SHIGEI, T. A regional difference in the d i s t r i b u t i o n of postsynaptic alpha-adrenoceptor subtypes in canine v e i n s . Naunyn-Schmiedeberg s Arch. Pharmacol. 324:246-255, 1983. 1  - 138 SHU'AYB, W.A., MORAN, W.H. and ZIMMERMAN, B. Studies of the mechanism of antidiuretic hormone secretion and post-commissurotomy d i l u t i o n a l syndrome. Ann. Surg. 162:690-699, 1965. SKOWSKY, W.R. and FISHER, D.A. Arginine vasopressin secretion on thyroidectomized sheep. Endocrinology 100:1022-1026, 1977. SKOWSKY, W.R. and SWAN, L. E f f e c t s of androgens and estrogens on arginine vasopressin in the rat and the human. Abstract 370, 59th Meeting of Endocrine S o c i e t y , 1977. SLADEK, C P . and KNIGGE, K.M. Cholinergic stimulation of vasopressin release from the rat hypothalamo-neurohypophysial system in organ c u l t u r e . Endocrinology 101:411-420, 1977. SOFRONIEW, M.V., WEINDL, A . , SCHRELL, U. and WETZSTEIN, R. Immunohistochemistry of vasopressin, o x y t o c i n , and neurophysin in the hypothalamus and extrahypothalamic regions of the human and primate b r a i n . Acta histochemica, Suppl. Band XXIV:S79-95, 1981. SOMLYO, A . V . , WOO, C Y . and SOMLYO, A . P . Response of nerve-free vessels to vasoactive amines and polypeptides. Am. J . P h y s i o l . 208:748-753, 1966. STAMM, W. The influence of carbon dioxide on the reaction of i s o l a t e d veins to vasoconstrictor substances. Agents Actions 2:261-269, 1972. STARK, R . I . , DANIEL, S . S . , HUSAIN, H.K., TROPPER, P . J . and LAMB, L . S . Cerebrospinal f l u i d and plasma vasopressin in the f e t a l lamb: basal concentration and the e f f e c t of hypoxia. Endocrinology 116:65-72, 1985. STARKE, K. Influence of e x t r a c e l l u l a r noradrenaline on the stimulation evoked secretion of noradrenaline from sympathetic nerves: evidence f o r an a-receptor-mediated feeback i n h i b i t i o n of noradrenaline release. Naunyn Schmiedebergs Arch. Pharmacol. 275:11-23, 1972. STARKE, K. a-Adrenoceptor s u b c l a s s i f i c a t i o n . Biochem. Pharmacol. 88:199-228, 1981.  Rev. P h y s i o l .  STARKE, K., MONTEL, H. and SCHUMANN, H . J . Influence of cocaine and phenoxybenzamine on noradrenaline uptake and r e l e a s e . Naunyn Schmiedebergs Arch. Pharmacol. 270:210-214, 1971. STEEN, S . , SKARBY, T . V . , NORGREN, L. and ANDERSSEN, K . E . Pharmacological characterization of postjunctional alpha-adrenoceptors in i s o l a t e d human omental a r t e r i e s and v e i n s . Acta P h y s i o l . Scand. 129:109-116, 1984. STEPPELER, A . , TANAKA, T. and STARKE, K.A. A comparison of pre- and postsynaptic a-adrenergic e f f e c t s of phenylephrine and tramazoline on blood vessels of the rabbit in v i v o . Naunyn Schmiedeberg's Arch. Pharmacol. 304:223-230, 1978.  - 139 STEVENS, M . J . and MOULDS, R.F.W. Are the pre- and postsynaptic a-adrenoceptors in human vascular smooth muscle a t y p t i c a l ? Cardiovasc. Pharmacol. 4:129-133, 1982.  J.  STOKES, G.S. and OATES, H.F. P r a z o s i n : new alpha-adrenergic blocking agent in treatment of hypertension. Cardiovasc. Med. 3:41-57, 1978. STOLZ, F. Veber adrenalin und alkylaminoaceto-brenzcatechin. deutsch. chem. G e s e l l s c h . 37:4149-4154, 1904. SUTTER, M.C. The pharmacology of i s o l a t e d v e i n s . 24:742-751, 1965.  Ber.,  Br. J . Pharmacol.  SWANSON, L.W. Immunohistochemical evidence for a neurophysin-containing autonomic pathway arising in the paraventricular nucleus of the hypothalamus of the rat and monkey. Brain Res. 128:356-363, 1977. SWANSON, L.W. and SAWCHENKO, P . E . P a r a v e n t r i c u l a r nucleus: a s i t e f o r the i n t e g r a t i o n of neuroendocrine and autonomic mechanisms. Neuroendocrinology 31:410-417, 1980. SZCZEPANSKA-SADOWSKA, E. The a c t i v i t y of the hypothalamo-hypophysial antidiuretic system in concious dogs. I. The influence of iso-osmotic blood volume changes. Pfluegers Arch. 335:139-146, 1972. SZCZEPANSKA-SADOWSKA, E. Hemodynamic e f f e c t of a moderate increase of the plasma vasopressin l e v e l in conscious dogs. Pfluegers Arch. 338:313-322, 1973. SZCZEPANSKA-SADOWSKA, E . , SOBOCINSKA, J . and SADOWSKI, B. Central dipsogenic e f f e c t of vasopressin. Am. J . P h y s i o l . 242:R372-R379, 1982. SZCZEPANSKA-SADOWSKA, E . , GRAY, D. and SIMON-OPPERMANN, C. Vasopressin in blood and t h i r d v e n t r i c l e CSF during dehydration, t h i r s t , and hemorrhage. Am. J . P h y s i o l . 245:R549-R555, 1983. TABRIZCHI, R. and PANG, C.C.Y. Comparative e f f e c t s of rauwolscine, prazosin and phentolamine on blood pressure and cardiac output in anesthetized r a t s . Can. J . P h y s i o l . Pharmacol. 1987; (in p r e s s ) . TAKAHASHI, H. and BUNAG, R.D. Augmentation of c e n t r a l l y induced alpha-adrenergic vasodepression in spontaneously hypertensive Hypertension 2^:198-206, 1980.  rats.  TAKAMINE, J . Adrenaline; the active p r i n c i p l e of the suprarenal glands and i t s mode of preparation. Am. J . Pharm. 73:523-531, 1901. ~~ TANAKA, M., DE KLOET, E . R . , DE WIED, D. and VERSTEEG, D.H.G. Arginine°-vasopressin affects catecholamine metabolism s p e c i f i c brain n u c l e i . L i f e S c i . 20:1799-1808, 1977.  in  - 140 TAYLOR, R.D. and PAGE, I.H. Peripheral vasomotor e f f e c t s of adrenaline and noradrenaline acting upon the i s o l a t e d central nervous system. C i r c u l a t i o n :563-575, 1951.  perfused  THAMES, M.D. and SCHMID, P . G . Cardiopulmonary receptors with vagal afferents t o n i c a l l y i n h i b i t ADH release in the dog. Am. P h y s i o l . 237:H299-H304, 1979. THAMES, M.D. and SCHMID, P.G. Interaction between c a r o t i d and cardiopulmonary baroreflexes in control of plasma ADH. P h y s i o l . 241:H431-H434, 1981.  J.  Am. J .  THAMES, M.D., PETERSON, M.G. and SCHMID, P . G . Stimulation of cardiac receptors with veratrum a l k a l o i d s i n h i b i t s ADH s e c r e t i o n . Am. J . P h y s i o l . 239:H784-H788, 1980. THORN, N.A. Introductory remarks about the antidiuretic-hormone-releasing neuron system. In: Osmotic and - Volume Regulation. (Ed. Barker Jorgens, C. and Skadhuage, E.) Munksgaard, Copenhagen. (1978), pp. 225-228. THRASHER, T . N . , BROWN, C . J . , KEIL, L . C . and RAMSAY, D . J . T h i r s t and vasopressin release in the dog: an osmoreceptor or sodium receptor mechanism? Am. J . P h y s i o l . 238:R333-R339, 1980a. THRASHER, T . N . , JONES, R . G . , KEIL, L . C . , BROWN, C . J . and RAMSAY, D . J . Drinking and vasopressin release during v e n t r i c u l a r infusions of hypertonic s o l u t i o n s . Am. J . P h y s i o l . 238:R340-R345, 1980b. TIMMERMANS, P.B.M.W.M. Calcium antagonism and (^-adrenoceptor a c t i v a t i o n . Naunyn Schmiedeberg's Arch. Pharmacol. 316:57, 1981. TIMMERMANS, P.B.M.W.M. and VAN ZWIETEN, P.A. Postsynaptic c ^ - and ©^-adrenoceptors in the c i r c u l a t o r y system of the pithed rat: s e l e c t i v e stimulation of the o^-type by B-HT 933. Eur. J . Pharmacol. 63:199-202, 1980a. TIMMERMANS, P.B.M.W.M. and VAN ZWIETEN, P.A. Vasoconstriction mediated by postsynaptic ©^-adrenoceptor stimulation. Naunyn-Schmiedeberg's Arch. Pharmacol. 313:17-20, 1980b. TIMMERMANS, P.B.M.W.M., KWA, H.Y. and VAN ZWIETEN, P.A. P o s s i b l e s u b d i v i s i o n of postsynaptic a-adrenoceptors mediating pressor responses in the pithed rat. Naunyn Schmiedeberg s Arch. Pharmacol. 310:189-193, 1979. 1  TIMMERMANS, P.B.M.W.M., SCHOOP, A . M . C . , KWA, H.Y. and VAN ZWIETEN, P.A. Characterization of a-adrenoceptors p a r t i c i p a t i n g in the central hypotensive and sedative e f f e c t s of clonidine using yohimbine, rauwolscine and corynanthine. Eur. J . Pharmacol. 70:7-15, 1981. TSUCHIYA, M., WALSH, G.M. and FROHLICH, E.D. Systemic hemodynamic e f f e c t s of microspheres in conscious r a t s . Am. J . P h y s i o l . 235:H617-H621, 1977.  - 141 U'PRICHARD, D.C. and SNYDER, S.H. D i s t i n c t a-noradrenergic receptors differentiated by binding and p h y s i o l o g i c a l r e l a t i o n s h i p s . Life S c i . 24:79-88, 1979. U'PRICHARD, D . C , GREENBERG, D.A. and SYNDER, S . H . Binding c h a r a c t e r i s t i c s of a .radio-labeled agonist and antagonist at central nervous system alpha noradrenergic receptors. Mol. Pharmacol. 13:454-473, 1977. U'PRICHARD, D . C , CHARNESS, M . E . , ROBERTSON, D. and SYNDER, S . H . Prazosin: differential affinities for two populations of a-noradrenergic receptor binding sites. Eur. J . Pharmacol. 50:87-89, 1978. UKAI, M. A n t i d i u r e t i c hormone responses to s u r g i c a l and experimental v i s c e r a l s t i m u l a t i o n . Med. J . Osaka Univ. 21:121-129, 1971. UKAI, M., MORAN, W.H. AND ZIMMERMAN, B. The r o l e of v i s c e r a l afferent pathways on vasopressin secretion and urinary excretory patterns during s u r g i c a l s t r e s s . Ann. Surgery 168:16-28, 1968. UNDESSER, K . P . , HASSER, E . M . , HAYWOOD, J . R . , JOHNSON, A . K . and BISHOP, V.S. Interactions of vasopressin with the area postrema in a r t e r i a l baroreflex function in conscious r a b b i t s . C i r c . Res. 56:410-417, 1985. VALLEJO, M., CARTER, D.A. and LIGHTMAN, S . L . Haemodynamic e f f e c t s of arginine-vasopressin microinjections into the nucleus tractus solitarius: a comparative study of vasopressin, a s e l e c t i v e vasopressin receptor agonist and antagonist, and oxytocin. Neurosci. L e t t . 52:247-252, 1984. VAN BRUMMELEN, P . , VERMEY, P . L . , TIMMERMANS, P.B.M.W.M. and VAN ZWIETEN, P.A. Preliminary evidence f o r a postsynaptic alpha2 adrenoceptor in the vasculature of the human forearm. Br. J . C l i n . Pharmacol. 15:134-135, 1982. VAN MEEL, J . C . A . , TIMMERMANS, P.B.M.W.M. and VAN ZWIETEN, P.A. <*]and <x2-adrenoceptor stimulation in the isolated perfused hindquarters of the r a t : an in v i t r o model. J . Cardiovasc. Pharmacol. 5:S80-S85, 1983. VANHOUTTE, P.M. Heterogeneity of postjunctional vascular a-adrenoceptors and handling of calcium. J. Pharmacol. 4:91-96, 1982.  Cardiovasc.  VEALE, W.L., KASTING, N.W. and COOPER, K . E . Arginine vasopressin and endogenous a n t i p y r e s i s : evidence and s i g n i f i c a n c e . Fed. Proc. 40:2750-2753, 1981. VERNEY, E.B. The a n t i d i u r e t i c hormone and the f a c t o r s which determine i t s r e l e a s e . Proc. R. Soc. Lond. ( B i o l . ) 135:25-106, 1947.  - 142 VON EULER, U.S. A s p e c i f i c sympathomimetic ergone in adrenergic nerve fibres (sympathin) and its relation to adrenaline and noradrenaline. A c t a . P h y s i o l . Scand. 12^:73-97, 1946. VOORN, P. and BUIJS, R.M. An immuno-electronmicroscopical study comparing vasopressin, o x y t o c i n , substance P and enkephalin containing nerve terminals in the nucleus of the s o l i t a r y t r a c t of the r a t . Brain Res. 270:169-173, 1983. VORHERR, H . , BRADBURY, M.W.B., HOGHOUGHI, M. and KLEEMAN, C.R. A n t i d i u r e t i c hormone in cerebrospinal f l u i d during endogenous and exogenous changes in i t s blood l e v e l . Endocrinology 83:246-250, 1968. —  WAEBER, B . , NUSSBERGER, J . and BRUNNER, H.R. Blood pressure dependency on vasopressin and angiotensin II in prazosin-treated conscious normotensive r a t s . J . Pharmacol. Exp. Ther. 225: 442-446, 1983. WARNKE, E. and HOEFKE, W. Influence of central pretreatment with 6-hydroxydopamine on the hypotensive e f f e c t of c l o n i d i n e . Arzneim. Forsch. 27:2311-2313, 1977. WEGRIA, G . E . , ESSEX, H . E . , HERRICK, J . F . and MANN, F . C . The simultaneous action of c e r t a i n drugs on the blood pressure and on the flow in the r i g h t and l e f t coronary a r t e r i e s . Am. Heart J . 20:557-572, 1940. WEINGARTNER, H . , GOLD, P . , BALLENGER, J . C , SMALLBER, S . A . , SUMMERS, R., RUBINOW, D.R., POST, R.M. and GOODWIN, F.K. E f f e c t s of vasopressin on human memory f u n c t i o n s . Science 211:601-693, 1981. WEINSTEIN, H . , BERNE, R.M. and SACHS, H. e f f e c t of hemorrhage. J . Endocrinol.  Vasopressin in blood: 66^:712-718, 1960.  WEITZMAN, R . E . , GLATZ, T . H . and FISHER, D.A. The e f f e c t of hemorrhage and hypertonic s a l i n e upon plasma oxytocin and arginine vasopressin in conscious dogs. Endocrinology 103:2154-2160, 1978. WILFFERT, B . , TIMMERMANS, P.B.M.W.M. and VAN ZWIETEN, P.A. Extrasynaptic location of alpha-2 and non-innervated beta-2 adrenoceptors in the vascular system of the pithed normotensive r a t . J . Pharmacol. Exp. Ther. 221:762-768, 1982. WILSON, N. and LEDSOME, J . R . Distension of the pulmonary v e i n - a t r i a l junctions and plasma vasopressin in the chloralose anaesthetized dog. Can. J . P h y s i o l . Pharmacol. 61:905-910, 1983. WU, W., ZBUZEK. V.K. and BELLEVUE, C. Vasopressin release during cardiac operation. J . Thorac. Cardiovasc. Surg. _79:83-90, 1980. YAMAGUCHI, I. and KOPIN, I . J . Plasma catecholamine and blood pressure responses to sympathetic stimulation i n pithed r a t s . Am. J . P h y s i o l . 237:H305-H310, 1979.  - 143 YAMAMOTO, M., SHARE, L. and SHAD, R.E. E f f e c t of v e n t r i c u l o - c i s t e r n a l perfusion with angiotensin II and indomethacin on the plasma vasopressin concentration. Neuroendocrinology 25^: 166-173, 1978. YAMASHITA, H . , KANNAN, H . , INENAGA, K. and KOIZUMI, K. The r o l e of cardiovascular and muscle afferent systems in control of body water balance. J . Auton. Nerv. S y s t . 10:305-316, 1984. ZERBE, R.L. and FEUERSTEIN, G. Cardiovascular e f f e c t s of c e n t r a l l y administered vasopressin in conscious and anesthetized rats. Neuropeptides 6:471-484, 1985. ZERBE, R . L . , KIRTLAND, S . , FADEN, A . I . and FEUERSTEIN, G. cardiovascular e f f e c t s of mammalian neurohypophyseal conscious r a t s . Peptides 4-:627-630, 1983.  Central peptides  in  ZIMMERMAN, E.A. and DEFENDI, R. Hypothalamic pathways containing oxytocin, vasopressin and associated neurophysins. In: Neurohypophysis. Int. Conf. Key Biscayne, F l o r i d a . (Ed. Moses, M., Share, L.) Karger, B a s e l . (1977), pp. 9-21.  

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