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The actions of calcium antagonists on systemic hemodynamics, blood flow distribution and venous tone.. 1987

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THE ACTIONS OF CALCIUM ANTAGONISTS ON SYSTEMIC HEMODYNAMICS, BLOOD FLOW DISTRIBUTION AND VENOUS TONE OF THE RAT By ROBERT PATRICK WAITE B.Sc. (Hons), The U n i v e r s i t y o f B r i t i s h Columbia, 1985 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Pharmacology & T h e r a p e u t i c s ) We a c c e p t t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA August 1987 © R o b e r t P a t r i c k Waite, 1987 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Pharmacology & T h e r a p e u t i c s The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 August 13, 1987 ABSTRACT The purpose of my s t u d y was t o determine and compare the e f f e c t s o f t h r e e c a l c i u m a n t a g o n i s t s on s y s t e m i c hemodynamics, ECG, blood f l o w d i s t r i - b u t i o n , t i s s u e conductance and venous tone of the r a t . The e f f e c t s o f a r e p r e s e n t a t i v e drug from Spedding's (1985) t h r e e sub- c l a s s e s o f c a l c i u m a n t a g o n i s t s on s y s t e m i c hemodynamics, ECG, c a r d i a c o u t p u t and t h e d i s t r i b u t i o n o f blood f l o w were i n v e s t i g a t e d by the m i c r o s p h e r e t e c h n i q u e i n 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 r a t s . The r e p r e s e n t a t i v e drugs were: I, n i f e d i p i n e (12 and 35 pg/kg/min); I I , v e r a p a m i l (43 and 83 ng/kg/min) and I I I , f l u n a r i z i n e (174 and 275 yg/kg/min). Low and h i g h doses were s e l e c t e d t o g i v e a d e c r e a s e i n mean a r t e r i a l p r e s s u r e o f 10 and 20 mmHg, r e s p e c t i v e l y , compared w i t h c o n t r o l r a t s . At equal d e p r e s s o r l e v e l s , a l l t h e drugs s i m i l a r l y d e c r e a s e d t o t a l p e r i p h e r a l r e s i s t a n c e w h i l e s l i g h t l y but not s i g n i f i c a n t l y i n c r e a s i n g c a r d i a c o u t p u t (CO) and s t r o k e volume. Heart r a t e was d e c r e a s e d by v e r a p a m i l and f l u n a r i z i n e , but i n c r e a s e d by n i f e d i p i n e . The h i g h dose o f n i f e d i p i n e d e c r e a s e d c o n t r a c t i l i t y as measured by dP/dt and had no e f f e c t on P R - i n t e r v a l , w h i l e v e r a p a m i l d e c r e a s e d dP/dt and p r o l o n g e d the P R - i n t e r v a l . The low dose o f n i f e d i p i n e and both doses o f f l u n a r i z i n e s l i g h t l y but not s i g n i f i c a n t l y d e c r e a s e d dP/dt and had no e f f e c t on P R - i n t e r v a l . A l l t h r e e drugs s i m i l a r l y a f f e c t e d the d i s t r i b u t i o n o f b l o o d f l o w . Blood f l o w t o l u n g s , l i v e r , and h e a r t was i n c r e a s e d w h i l e f l o w t o the i n t e s t i n e , k i d n e y s , s p l e e n and s k i n was d e c r e a s e d . A r t e r i a l conduc- t a n c e s i n l u n g s , l i v e r , h e a r t and s k e l e t a l muscle were i n c r e a s e d by the t h r e e drugs. These r e s u l t s show t h a t r e p r e s e n t a t i v e drugs from the t h r e e - i i i - subclasses of calcium antagonists had s im i la r e f fects on the d is t r ibu t ion of blood flow and a r te r i a l conductances but d i f ferent chronotropic, dromotropic and inotropic e f fec ts . A f i n a l set of experiments were designed to evaluate calcium antagonist actions on venous tone, as venous tone i s a primary determinant of CO and the calcium antagonists general ly increase CO. The ef fects of three calcium antagonists, verapamil, n i fedip ine and f l unar i z ine on mean a r te r i a l pressure (MAP), heart rate (HR) and mean c i rcu la to ry f i l l i n g pressure (MCFP), an index of to ta l body venous tone, were investigated in the . conscious ra t . Infusions of a l l three drugs caused a dose-dependent decrease in MAP and an increase in MCFP, compared with the corresponding values in control ra ts . HR was decreased by verapamil and f lunar i z ine and s l i g h t l y increased by n i fed ip ine . Further experiments invest igated whether the increase in MCFP by verapamil was i nd i rec t l y caused by ref lex ac t iva t ion of the autonomic nervous system. Rats were pretreated with a continuous infusion of the gangl ionic blocker hexamethonium pr io r to infusion of verapamil. Af ter treatment with hexamethonium, verapamil did not increase the MCFP. In fact the highest dose of verapamil s i gn i f i can t l y decreased MCFP. The resul ts suggest that calcium antagonists have greater d i l a t o r e f fects in a r te r io les compared to veins. It appears that any d i rect venodilator ef fects of vera- pamil in conscious rats are masked due to ref lex act ivat ion of the autonomic nervous system. - i v - TABLE OF CONTENTS CHAPTER Page TABLE OF CONTENTS i v . ABSTRACT i i LIST OF TABLES v i LIST OF FIGURES v i i ABBREVIATIONS v i i i ACKNOWLEDGEMENTS i x 1. INTRODUCTION 1 1.1 H i s t o r i c a l a s p e c t s 1 1.2 C l a s s i f i c a t i o n o f c a l c i u m a n t a g o n i s t s 2 1.3 The r o l e o f c a l c i u m i n muscular c o n t r a c t i o n 6 1.4 The e f f e c t s o f c a l c i u m a n t a g o n i s t s on c a r d i o v a s c u l a r t i s s u e 7 1.4.1 In V i t r o a c t i o n s on: 7 1.4.1.1 C a r d i a c muscle 7 1.4.1.2 V a s c u l a r smooth muscle 8 1.4.2 In Vivo a c t i o n s on: 9 1.4.2.1 C a r d i a c muscle 9 1.4.2.2 V a s c u l a r smooth muscle 10 1.4.3 A c t i o n s i n e x p e r i m e n t a l and c l i n i c a l c a r d i o v a s c u l a r d i s e a s e 11 1.4.3.1 A c t i o n s i n e x p e r i m e n t a l c a r d i o v a s c u l a r d i s e a s e 11 1.4.3.2 A c t i o n s i n c l i n i c a l c a r d i o v a s c u l a r d i s e a s e 12 1.5 C a l c i u m a n t a g o n i s t a c t i o n s on c a l c i u m dependent p r o c e s s e s o t h e r than c a r d i a c and smooth muscle c o n t r a c t i o n 14 1.6 C a l c i u m a n t a g o n i s t a c t i o n s on n o n - c a l c i u m dependent p r o c e s s e s 16 1.7 C a l c i u m e n t r y i n t o t h e c e l l v i a membrane c h a n n e l s : m o l e c u l a r s i t e o f c a l c i u m a n t a g o n i s t a c t i o n 17 1.7.1 V o l t a g e dependent c a l r i u m channel 18 1.7.1.1 Types o f v o l t a g e dependent c a l c i u m c h a n n e l s 18 1.7.1.2 S t r u c t u r e o f the v o l t a g e dependent c a l c i u m channel 19 1.7.1.3 Ca l c i u m a n t a g o n i s t a c t i o n s on t h e v o l t a g e dependent c a l c i u m channel 20 1.7.2 R e c e p t o r o p e r a t e d c a l c i u m c h a n n e l s 23 1.8 E x p e r i m e n t a l Aims 26 1.8.1' Calcium a n t a g o n i s t e f f e c t s on hemodynamics and blood f l o w d i s t r i b u t i o n o f the 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 r a t 26 1.8.2 C a l c i u m a n t a g o n i s t a c t i o n s on venous tone o f t h e c o n s c i o u s r a t 27 2. MATERIALS AND METHODS 29 2.1 S u r g i c a l p r e p a r a t i o n s 29 - V - 2.1.1 M i c r o s p h e r e s t u d i e s 29 2.1.2 Mean c i r c u l a t o r y f i l l i n g p r e s s u r e (MCFP) s t u d i e s 29 2.2 M i c r o s p h e r e s used i n the blood f l o w d i s t r i b u t i o n s t u d i e s 30 2.3 E x p e r i m e n t a l p r o t o c o l 31 2.3.1 E f f e c t o f v e r a p a m i l , n i f e d i p i n e and f l u n a r i z i n e on s y s t e m i c hemodynamics and blood f l o w d i s t r i b u t i o n o f the 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 r a t 31 2.3.2 E f f e c t o f v e r a p a m i l , n i f e d i p i n e and f l u n a r i z i n e on MCFP o f the c o n s c i o u s r a t 32 2.3.3 Role of the autonomic nervous system on MCFP d u r i n g v e r a p a m i l a d m i n i s t r a t i o n 33 2.4 Drugs 34 2.5 C a l c u l a t i o n s 34 2.6 S t a t i s t i c a l a n a l y s i s 35 2.6.1 M i c r o s p h e r e S t u d i e s 35 2.6.2 MCFP S t u d i e s 36 3. RESULTS 37 3.1 C a l c i u m a n t a g o n i s t e f f e c t s on s y s t e m i c hemodynamics and ECG 37 3.2 Cal c i u m a n t a g o n i s t e f f e c t s on b l o o d f l o w d i s t r i b u t i o n 40 3.3 C a l c i u m a n t a g o n i s t e f f e c t s on t i s s u e conductance 44 3.4 Cal c i u m a n t a g o n i s t e f f e c t s on MAP, HR and MCFP 44 3.5 Ro l e o f the autonomic nervous system on MCFP d u r i n g v e r a p a m i l a d m i n i s t r a t i o n 55 4. DISCUSSION 60 4.1 Summary 67 5. REFERENCES 69 LIST OF TABLES TABLE PAGE 1 Chemical i d e n t i t y o f c a l c i u m a n t a g o n i s t s 3 2 P r e t r e a t m e n t v a l u e s of s y s t e m i c hemodynamic and ECG v a r i a b l e s f o r a l l r a t groups 38 3 P r e t r e a t m e n t v a l u e s of organ b l o o d f l o w (ml/min) f o r a l l r a t groups 41 4 Pr e t r e a t m e n t v a l u e s o f organ conductances (ml/min/mmHg x 10 ) f o r a l l r a t groups 45 5 B a s e l i n e v a l u e s o f MAP, HR and MCFP f o r a l l r a t groups 48 LIST OF FIGURES FIGURE PAGE 1 C a l c i u m a n t a g o n i s t e f f e c t s on s y s t e m i c hemodynamics and ECG o f 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 r a t s 39 2 Cal c i u m a n t a g o n i s t e f f e c t s on organ blood f l o w o f 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 r a t s 42 3 Cal c i u m a n t a g o n i s t e f f e c t s on organ blood f l o w o f 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 r a t s 43 4 Cal c i u m a n t a g o n i s t e f f e c t s on organ conductance o f 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 r a t s 46 5 C a l c i u m a n t a g o n i s t e f f e c t s on organ conductance o f 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 r a t s 47 6 E f f e c t o f n i f e d i p i n e and e t h a n o l on MAP, HR and MCFP of c o n s c i o u s r a t s 49 7 E f f e c t o f ve r a p a m i l and s a l i n e on MAP, HR and MCFP o f c o n s c i o u s r a t s 51 8 E f f e c t o f f l u n a r i z i n e and t a r t a r i c a c i d on MAP, HR and MCFP of c o n s c i o u s r a t s 53 9 E f f e c t o f time on MAP, HR and MCFP o f c o n s c i o u s r a t s . 56 10 E f f e c t of e t h a n o l , s a l i n e , t a r t a r i c a c i d , hexamethonium and time on MCFP as a f u n c t i o n o f time 57 11 E f f e c t o f hexamethonium + verap a m i l and hexamethonium on MAP, HR and MCFP o f c o n s c i o u s r a t s 58 - v i i i - ABBREVIATIONS Mean A r t e r i a l P r e s s u r e = MAP Heart Rate = HR L e f t V e n t r i c u l a r P r e s s u r e = LVP C a r d i a c Output = CO F i n a l A r t e r i a l P r e s s u r e = FAP Mean C i r c u l a t o r y F i l l i n g P r e s s u r e = MCFP T o t a l P e r i p h e r a l R e s i s t a n c e = TPR Venous P l a t e a u P r e s s u r e =VPP Counts Per Minute = cpm C o n t r a c t i l i t y = dP/dt Blood Flow = BF S t r o k e Volume = SV ACKNOWLEDGEMENTS I would l i k e t o thank Dr. C a t h e r i n e Cheuk Y i n g Pang and Dr. M i c h a e l Walker f o r t h e i r guidance and a d v i c e t h r o u g h o u t my gra d u a t e s t u d i e s . I e s p e c i a l l y thank Dr. Pang whose f i n a n c i a l s u p p o r t e n a b l e d me t o complete my s t u d i e s i n t h e l i f e s t y l e to which I am accustomed. S p e c i a l thanks t o my f e l l o w graduate s t u d e n t s (soon t o be Dr.) Kathy K i n g and Reza T a b r i z c h i f o r t h e i r a d v i c e and h e l p w i t h m a i n t a i n i n g t he double b l i n d n a t u r e o f the m i c r o s p h e r e s t u d i e s , t o Ms. J a n e l l e H a r r i s and Ms. E l a i n e Jan f o r t h e i r s e c r e t a r i a l a s s i s t a n c e and Mr. Glenn C o l l i n s f o r s t a t i s t i c a l a n a l y s i s . WAITE, R.P. 1 1. INTRODUCTION 1.1 H i s t o r i c a l a s p e c t s The development o f the c o r o n a r y v a s o d i l a t o r s p r e n y l amine and v e r a p a m i l ( i p r o v e r a t r i 1 , o r i s o p t i n ) (Haas and H a r t f e l d e r 1962) and the subsequent d i s c o v e r y o f t h e i r e f f i c a c y i n p a t i e n t s w i t h c o r o n a r y i n s u f f i c i e n c y ( T s c h i r d e w h a z and K l e p z i g 1963) and a n g i n a p e c t o r i s (Knoch e t a l . 1963) l e d t o the s e a r c h f o r t h e i r mechanism o f a c t i o n . I n i t i a l p h a r m a c o l o g i c a l and e l e c t r o p h y s i o l o g i c a l experiments i n d i c a t e d t h a t t h e s e drugs d e c r e a s e d c o n t r a c t i l i t y i n i s o l a t e d mammalian myocardium and i n t a c t i n s i t u h e a r t s w i t h o u t p r o d u c i n g major changes i n a c t i o n p o t e n t i a l c o n f i g u r a t i o n . These e f f e c t s were r e v e r s e d by a d d i t i o n o f c a l c i u m , e - a d r e n e r g i c c a t e c h o l a m i n e s o r c a r d i a c g l y c o s i d e s ( F l e c k e n s t e i n 1964). I n i t i a l l y i t was thought t h a t such e f f e c t s were mediated v i a blockade o f e - a d r e n o r e c e p t o r s ( M e l v i l l e and Benfey 1965) but f u r t h e r experiments d i s p r o v e d t h i s h y p o t h e s i s and i n d i c a t e d t h a t v e r a p a m i l ' s mechanism o f a c t i o n was e i t h e r i n h i b i t i o n o f c a l c i u m movement i n t o the c e l l , o r c o m p e t i t i o n f o r an i n t r a c e l l u l a r b i n d i n g s i t e o f c a l c i u m ( F l e c k e n s t e i n 1967; N a y l e r 1968). The e v i d e n c e t h a t such compounds i n t e r - f e r e d w i t h c a l c i u m dependent e x c i t a t i o n - c o n t r a c t i o n c o u p l i n g l e d F l e c k e n - s t e i n t o g i v e them the name " c a l c i u m a n t a g o n i s t s " ( F l e c k e n s t e i n 1969). Though the c o n c e p t o f c a l c i u m antagonism was f i r s t proposed by F l e c k e n s t e i n , G o d f r a i n d and c o l l e a g u e s reached s i m i l a r c o n c l u s i o n s as a r e s u l t o f t h e i r work on i s o l a t e d smooth muscle. In v i t r o experiments w i t h v a s c u l a r smooth muscle and two p i p e r i z i n e d e r i v a t i v e s , c i n n a r i z i n e and l i d o - f l a z i n e , i n d i c a t e d t h a t t h e s e agents i n t e r f e r e d w i t h the e x c i t a t i o n - c o n t r a c - t i o n c o u p l i n g i n v a s c u l a r smooth muscle ( G o d f r a i n d e t a l . 196 9; G o d f r a i n d and Kaba 1969a). The c o n t r a c t i l e response o f i s o l a t e d a r t e r i e s to K + d e p o l a r i z a t i o n and a d r e n a l i n e s t i m u l a t i o n was b l o c k e d by c i n n a r i z i n e , o r WAITE, R.P. 2 removal o f c a l c i u m ( G o d f r a i n d and Kaba 1969b). The c o n t r a c t i o n o f a o r t a t o a d r e n a l i n e c o n t a i n e d a t o n i c and p h a s i c component. The p h a s i c component was c a l c i u m i n s e n s i t i v e w h i l e the t o n i c component was a b o l i s h e d i n the absence of c a l c i u m o r p r e s e n c e o f c i n n a r i z i n e ( G o d f r a i n d and Kaba 1969a). Though the c o n c e p t o f c a l c i u m antagonism, o r c a l c i u m e n t r y b l o c k a d e , as a mechanism o f drug a c t i o n i s a r e l a t i v e l y r e c e n t i d e a the c l i n i c a l b e n e f i t o f such a drug a c t i o n has been u t i l i z e d f o r c e n t u r i e s . Tanshinone, the a c t i v e i n g r e d i e n t o f a t r a d i t i o n a l C h i n ese remedy f o r c o r o n a r y d i s o r d e r s has been shown t o e x h i b i t the same e f f e c t s on i s o l a t e d g u i n e a p i g p a p i l l a r y muscle as v e r a p a m i l , n i f e d i p i n e and d i l t i a z e m (Patmore and W h i t i n g 1982). In r e c e n t y e a r s , many more drugs w i t h c a l c i u m a n t a g o n i s t i c p r o p e r t i e s have been s y n t h e s i z e d and t e s t e d i n both e x p e r i m e n t a l and c l i n i c a l s e t - t i n g s . These compounds are heterogeneous i n . c h e m i c a l s t r u c t u r e and d i f f e r i n t h e i r t i s s u e s e l e c t i v i t y , and p o s s i b l y i n t h e i r e x a c t s i t e o f a c t i o n . T a b l e 1 g i v e s the name and c h e m i c a l c l a s s i f i c a t i o n o f a number of c a l c i u m a n t a g o n i s t s as w e l l as t h e newly dev e l o p e d c a l c i u m channel a g o n i s t s . Development o f a v a l i d c l a s s i f i c a t i o n scheme f o r the c a l c i u m a n t a g o n i s t s , based on t h e i r c h e m i c a l n a t u r e and p h a r m a c o l o g i c a l a c t i o n s , would be u s e f u l f o r both t h e i r t h e r a p e u t i c use and f u r t h e r f u t u r e development. 1.2 C l a s s i f i c a t i o n o f c a l c i u m a n t a g o n i s t s C a l c i u m a n t a g o n i s t s were o r i g i n a l l y c l a s s i f i e d i n t o two subgroups based on t h e i r potency and s p e c i f i c i t y f o r i n h i b i t i n g c o n t r a c t i o n s o f i s o l a t e d c a r d i a c and smooth muscle ( F l e c k e n s t e i n 1983). Group A c o n s i s t s o f the more p o t e n t and s p e c i f i c d r u g s , such as v e r a p a m i l , n i f e d i p i n e , d i l t i a z e m and D-600 w h i l e group B c o n s i s t s o f l e s s p o t e n t and s p e c i f i c agents such as p r e n y l a m i n e , f e n d i l i n e and c a r o v e r i n e . U n f o r t u n a t e l y t h i s c l a s s i f i c a t i o n does not take i n t o account t h e heterogeneous c h e m i c a l n a t u r e o f c a l c i u m a n t a g o n i s t s o r t h e i r d i f f e r e n t p h a r m a c o l o g i c a l s p e c i f i c i t y . WAITE, R.P. 3 TABLE 1. Chemical I d e n t i t y o f C a l c i u m A n t a g o n i s t s Chemical Group Ca>] c i urn A n t a g o n i s t D i h y d r o p y r i d i n e s D i h y d r o p y r i d i n e c a l c i u m a g o n i s t s N i f edi pi ne Nimodi p i n e N i t r e n d i p i n e N i l u d i p i n e D a r o d i p i n e (PY 108-068) N i s o l d i p i n e I s r a d i p i n e (PN 200-110) N i c a r d i p i n e F e l o d i p i n e Bay K 8644 CGP 28392 YC 170 Phenethylamines Verapami1 G a l l o p a m i l (D-600) A n i p a m i l Desmethoxyverapami1 Ronipamil Tiapami1 B e p r i d i 1 B e n z o d i a z e p i n e s Di l t i a z e m F o s t e d i l (KB-944) D i p h e n y l a l k y l a m i n e s C i n n a r i z i n e F l u n a r i z i n e L i d o f 1 a z i n e P erhexi 1ine P r e n y l amine WAITE, R.P. 4 Godfraind proposed a modified Fleckenstein c l a s s i f i c a t i o n of two groups, each with an A and B subgroup, to take into account the re la t i ve s p e c i f i c i t i e s of the d i f ferent drugs (Godfraind 1987). Group I compounds are the se lec t ive calcium antagonists; group IA being se lec t ive for myocardial calcium channels (dihydropyridines, phenylakylamines, benzod ia - zepines), and group IB having no detectable ef fect on myocardial calcium channels (c innar iz ine , f l una r i z i ne ) . Group II compounds are less spec i f i c agents; group 11A drugs act on both the slow calcium channel and the fast sodium channel at s im i la r concentrations ( b e p r i d i l , f end i l i ne , prenylamine, l i do f laz ine ) while group 11B includes drugs which have the i r primary s i t e of action at a d i f ferent locus (phenothiazines, loperamide e t c . ) . Glossman and colleagues (Glossman et a l . 1982) characterized the calcium antagonists into four groups based on binding s tudies. Group IA are the dihydropyridines which bind with high a f f i n i t y and displace other dihydropyridines in a competitive manner. Diphenylalkylamines, such as c innar i z ine , displace dihydropyridine binding in a competitive manner but with low a f f i n i t y and are classed as group IB. Group 2 drugs such as verapamil d isplace dihydro- pyridine binding in a negative a l l o s t e r i c fashion while group 3 drugs (di l t iazem) cause dihydropyridine binding to increase in a pos i t ive a l l o - s te r i c manner. S imi lar to Glossman's scheme, Murphy proposed that the calcium antagonists could be divided into two groups, I being the dihydropy- r id ines and II being the drugs which a l l o s t e r i c a l l y regulate th is s i t e (Murphy et a l . 1983). Rodenkirchen and colleagues (1983) proposed a three group ranking based on the cardiodepressive actions of these compounds; I, the cardiodepressive drugs which are frequency dependent (verapamil, d i l t i azem) , I I , the cardiodepressive drugs which are not frequency dependent (dihydropyridines) and I I I , the drugs which are non spec i f i c and affect calcium f luxes at only high concentrations (flurazepam, phenobarbital) . WAITE, R.P. • 5 Based on the i n o t r o p i c , c h r o n o t r o p i c and d r o m o t r o p i c e f f e c t s o f c a l c i u m a n t a g o n i s t s , T a i r a a l s o proposed a t h r e e group c l a s s i f i c a t i o n scheme ( T a i r a 1987). D i h y d r o p y r i d i n e s b e i n g r e l a t i v e l y more s p e c i f i c f o r the c o r o n a r y v a s c u l a t u r e (group I ) , v e r a p a m i l and d i l t i a z e m produce e q u i p o t e n t d e c r e a s e s o f c h r o n o t r o p y and dromotropy (group I I ) , w h i l e b e p r i d i l and MCI-176 are more p o t e n t at p r o d u c i n g n e g a t i v e dromotropy than n e g a t i v e c h r o n o t r o p y (group I I I ) . A l l such c l a s s i f i c a t i o n s are based on l i m i t e d e f f e c t s o f c a l c i u m a n t a g o n i s t s and do not t a k e i n t o account a l l l e v e l s o f a c t i o n ( i n v i t r o , i n v i v o , b i o c h e m i c a l ) . A c l a s s i f i c a t i o n o f c a l c i u m a n t a g o n i s t s has been proposed by Spedding (1985), based on l i p o p h i l i c i t y , c h e m i c a l s t r u c t u r e and p h a r m a c o l o g i c a l a c t i v i t y . Group 1 c a l c i u m a n t a g o n i s t s are the 1, 4 - d i h y d r o p y r i d i n e s which i n c l u d e n i f e d i p i n e and n i m o d i p i n e . Group 2 i n c l u d e s s t r u c t u r a l l y d i v e r s e agents such as v e r a p a m i l and d i l t i a z e m which are b a s i c compounds w i t h s i m i l a r 1 i p o p h i 1 i c i t i e s . Group 3 c o n t a i n s d i p h e n y l a l k y l a m i n e s such as c i n n a r i z i n e and f l u n a r i z i n e . In v i t r o experiments i n d i c a t e t h a t r e p r e s e n t a - t i v e drugs from the t h r e e c l a s s e s b i n d t o d i f f e r e n t s i t e s on the c a l c i u m channel and d i s p l a y d i f f e r e n t p h a r m a c o l o g i c a l a c t i o n s (Spedding 1982, 1983, 1984; Spedding and Berg 1984). Furthermore, t h i s c l a s s i f i c a t i o n h o l d s f o r the a c t i o n o f v a r i o u s c a l c i u m a n t a g o n i s t s on the ECG o f the p i t h e d r a t p r e p a r a t i o n (Spedding 1982). However, few comparative s t u d i e s o f drugs from t h e s e c l a s s e s have been done i n v i v o . The aim o f my r e s e a r c h was t o examine the a c t i o n o f a r e p r e s e n t a t i v e drug from each o f Spedding's t h r e e c l a s s e s on hemodynamics, b l o o d f l o w d i s t r i b u t i o n and venous tone i n the r a t . B e f o r e d i s c u s s i n g t h e s e e x p e r i - ments, some o f the more r e c e n t and r e l e v a n t c a l c i u m a n t a g o n i s t l i t e r a t u r e , w i t h emphasis on mechanisms and s i t e s o f a c t i o n , w i l l be d i s c u s s e d . I t i s a p p r o p r i a t e t o f i r s t b r i e f l y review t h e r o l e c a l c i u m . p l a y s i n m u s c u l a r WAITE, R.P. 6 c o n t r a c t i o n i n o r d e r t o b e t t e r u n d e r s t a n d why c a l c i u m a n t a g o n i s t s are e f f e c t i v e m y o c a r d i a l and v a s c u l a r smooth muscle r e l a x a n t s . 1.3 The r o l e o f c a l c i u m i n m u s c u l a r c o n t r a c t i o n In the t y p i c a l s k e l e t a l muscle f i b e r , an a c t i o n p o t e n t i a l l e a d s t o r e l e a s e o f a s m a l l amount o f t r i g g e r c a l c i u m from t r i a d j u n c t i o n s o f the muscle c e l l and t h i s i n t u r n i n d u c e s a r e l e a s e o f s e q u e s t e r e d c a l c i u m from the s a r c o p l a s m i c r e t i c u l u m . Calcium r e l e a s e d from the s a r c o p l a s m i c r e t i c u - lum then i n t e r a c t s w i t h t h e a c t i n - t r o p o n i n - t r o p o m y o s i n complex o f t h e myofilament c a u s i n g a c o n f o r m a t i o n a l s h i f t which a l l o w s i n t e r a c t i o n of the myosin g l o b u l a r head w i t h the a c t i n f i l a m e n t and so i n i t i a t e c o n t r a c t i o n . With r e l a x a t i o n , c a l c i u m i s a c t i v e l y s e q u e s t e r e d i n t o t h e s a r c o p l a s m i c r e t i c u l u m and s t o r e d (Endo 1977). C a r d i a c muscle c o n t r a c t s i n the same manner as s k e l e t a l muscle but the s o u r c e o f a c t i v a t o r c a l c i u m i s d i f f e r e n t i n t h a t i t depends on i n t r a c e l l u l a r e n t r y o f e x t r a c e l l u l a r c a l c i u m . C o n t r a c t i o n s i n h e a r t c e l l s are thus v e r y s u s c e p t i b l e t o a l t e r a t i o n s i n e x t r a c e l l u l a r c a l c i u m c o n c e n t r a t i o n , o r i n h i b i t i o n o f c a l c i u m e n t r y i n t o t h e c e l l ( F l e c k e n s t e i n 1977). C o n t r a c t i o n o f smooth muscle i s d i f f e r e n t from t h a t i n h e a r t o r s k e l e t a l muscle. Calcium e n t r y from the e x t r a c e l l u l a r space i s n e c e s s a r y f o r c o n t r a c t i o n but the c o n t r a c t i l e apparatus d i f f e r s i n t h a t t h e r e i s a a c t i n - t r o p o m y o s i n - c a l m o d u l i n complex p r o d u c i n g a c a l c i u m s e n s i t i v e actomyo- s i n ATPase system ( P e r r y and Grand 1979). C a l c i u m e n t e r i n g the c e l l i s bound by c a l m o d u l i n , and t h i s complex a c t i v a t e s "myosin l i g h t c h a i n k i n a s e which i n t u r n p h o s p h o r y l a t e s t h e myosin l i g h t c h a i n a l l o w i n g a c t i n t o a c t i v a t e the MgATPase and induce muscle c o n t r a c t i o n ( A d e l s t e i n 1987). Thus, i n both m y o c a r d i a l and smooth muscle, c o n t r a c t i l e a c t i v i t y i s dependent on the e n t r y o f e x t r a c e l l u l a r c a l c i u m . I t i s f o r t h i s reason t h a t the c a l c i u m a n t a g o n i s t s , are p r e d o m i n a n t l y c a r d i a c and v a s c u l a r smooth muscle r e l a x a n t s . WAITE, R.P. 7 Calcium a n t a g o n i s t a c t i o n s i n v i t r o and i n v i v o demonstrate t h i s r e l a t i v e s p e c i f i c i t y as w e l l as the heterogeneous a c t i o n s o f d i f f e r e n t c a l c i u m a n t a - g o n i s t s . 1.4 The e f f e c t s o f c a l c i u m a n t a g o n i s t s on c a r d i o v a s c u l a r t i s s u e 1.4.1 In V i t r o a c t i o n s on: 1.4.1.1 C a r d i a c muscle. Compounds Bay a 1040 ( n i f e d i p i n e , F l e c k e n - s t e i n 1972), v e r a p a m i l ( S i n g h and Vaughn-Williams 1972) and d i l t i a z e m (Naka- j i m a e t a l . 1975) were shown t o i n h i b i t t h e c o n t r a c t i l e a b i l i t y o f i s o l a t e d g u i n e a p i g p a p i l l a r y muscle w h i l e having l i t t l e e f f e c t on the m y o c a r d i a l a c t i o n p o t e n t i a l . S t u d i e s on i s o l a t e d c a t myocardium i n d i c a t e d t h a t the i n h i b i t i o n o f c o n t r a c t i o n by v e r a p a m i l was f r e q u e n c y dependent w h i l e t h a t of n i f e d i p i n e was not (Bayer and Ehara 1978). D i l t i a z e m was shown t o have i n t e r m e d i a t e f r e q u e n c y dependence ( F l e c k e n s t e i n 1983). V e r a p a m i l ' s a c t i o n was demonstrated t o be s t e r e o s p e c i f i c u s i n g i s o l a t e d r i g h t a t r i a from the c a t (Bayer and Ehara 1978) and i s o l a t e d c a t p a p i l l a r y muscle (Bayer e t a l . 1975) w i t h (-)-verapami1 b e i n g more p o t e n t than the ( + ) - i s o m e r . F u r t h e r - more, the (+)-isomer o f verapamil had a s i g n i f i c a n t e f f e c t on the r i s e r a t e o f the a c t i o n p o t e n t i a l ( a sodium dependent a c t i o n ) at c o n c e n t r a t i o n s comparable t o t h a t which i n h i b i t e d c o n t r a c t i l e a c t i v i t y (Bayer e t a l . 1975). I s o l a t e d P u r k i n j e f i b e r s o f the dog showed no change i n membrane p o t e n t i a l , maximum u p s t r o k e v e l o c i t y , o r a c t i o n p o t e n t i a l amplitude upon a d m i n i s t r a t i o n o f n i f e d i p i n e . N i f e d i p i n e s h o r t e n e d the p l a t e a u o f the a c t i o n p o t e n t i a l and reduced a u t o m a t i c i t y when abnormal pacemaker a c t i v i t y was induced w i t h barium (Dandman and Hoffman 1980). Abnormal i n d u c t i o n o f pacemaker a c t i v i t y i n r a b b i t p a p i l l a r y muscle was i n h i b i t e d by the c a l c i u m a n t a g o n i s t s i n the o r d e r n i f e d i p i n e > d i l t i a z e m >_ v e r a p a m i l (Roy and Pruneau 1985). F u r t h e r m o r e , a l l t h r e e drugs produced n e g a t i v e c h r o n o t r o p y i n i s o l a t e d g u i n e a p i g h e a r t s ( M i l l a r d e t a l . 1984). C a l c i u m a n t a g o n i s t s a l s o WAITE, R.P. 8 i n h i b i t t h e c o n d u c t i o n o f a c t i o n p o t e n t i a l s a c r o s s the AV-node thu s t h e y demonstrate a n e g a t i v e d r o m o t r o p i c a c t i o n ( T a i r a 1987). In c o n c l u s i o n , c a l c i u m a n t a g o n i s t s a f f e c t the myocardium by: 1) i n h i b i t i n g e n t r y o f c a l c i u m i n t o the m y o c a r d i a l c e l l p r o d u c i n g n e g a t i v e i n o t r o p y , 2) i n h i b i t i n g t h e g e n e r a t i o n of c a l c i u m dependent a c t i o n p o t e n t i a l s i n pacemaker r e g i o n s of t he h e a r t p r o d u c i n g n e g a t i v e c h r o n o t r o p y and 3) i n h i b i t i n g c o n d u c t i o n of a c t i o n p o t e n t i a l s through the AV-node p r o d u c i n g n e g a t i v e dromotropy. 1.4.1.2 V a s c u l a r smooth muscle. C a l c i u m a n t a g o n i s t s d i f f e r i n t h e i r a b i l i t y t o i n h i b i t c a r d i a c muscle and v a s c u l a r smooth muscle c o n t r a c t - i l i t y . The d i h y d r o p y r i d i n e s are more p o t e n t i n i n h i b i t i n g v a s c u l a r smooth muscle c o n t r a c t i o n than i n i n h i b i t i n g c a r d i a c muscle c o n t r a c t i o n . F o r example, n i f e d i p i n e was 15x l e s s p o t e n t i n i n h i b i t i n g c o n t r a c t i o n o f human t r a b e c u l a r s t r i p s than i n r e l a x i n g human c o r o n a r y a r t e r i e s ( G o d f r a i n d e t a l . 1984). A n o t h e r d i h y d r o p y r i d i n e , f e l o d i p i n e , was lOOx more p o t e n t on i s o l a t e d v a s c u l a r smooth muscle than on i s o l a t e d myocardium (Lj u n g 1985). The d i p h e n y l a l k y l a m i n e s ( c i n n a r i z i n e and f l u n a r i z i n e ) have l i t t l e e f f e c t on c o n t r a c t i l e a c t i v i t y o f i s o l a t e d myocardium (van Neuten and Janssen 1973; van Neuten e t a l . 1978) but are p o t e n t i n h i b i t o r s o f smooth muscle c o n t r a c - t i o n . These drugs a l s o have a much l o n g e r o n s e t and d u r a t i o n o f a c t i o n than o t h e r c a l c i u m a n t a g o n i s t s (Van Neuten 1969; van Neuten and Janssen 1973; van Neuten e t a l . 1978). Verapamil has a s i m i l a r potency on both c a r d i a c and v a s c u l a r muscle w h i l e d i l t i a z e m i s i n t e r m e d i a t e between n i f e d i p i n e and v e r a p a m i l ( F l e c k e n s t e i n 1983). Potency o f c i n n a r i z i n e , f l u n a r i z i n e , and n i f e d i p i n e was shown t o be d i f f e r e n t w i t h r e g a r d t o s t i m u l u s ( d e p o l a r i z a - t i o n , NA, PGF^^) and v e s s e l ( G o d f r a i n d and M i l l e r 1983). T h e r e f o r e , w h i l e c a l c i u m a n t a g o n i s t a c t i o n s appear t o be due t o i n h i b i t i n g c a l c i u m e n t r y i n t o t h e c e l l , each drug does t h i s i n a c h a r a c t e r i s t i c manner. T h i s i s e x e m p l i - f i e d by s t r u c t u r e a c t i v i t y r e l a t i o n s h i p s f o r the d i f f e r e n t c a l c i u m antagon- i s t groups. WAITE, R . P . 9 The a c t i v i t y o f d i h y d r o p y r i d i n e analogues has been shown by Hansch a n a l y s i s t o depend o n l y on s t e r i c f a c t o r s (Loev 1974; Rodenkirchen 1979) whereas v e r a p a m i l analogues d i s p l a y both s t e r i c and e l e c t r o n i c i n f l u e n c e s f o r maximal a c t i v i t y (Mannhold 1978; G o l l e t a l . 1985). U n f o r t u n a t e l y t h e d i p h e n y l a l k y l amines and b e n z o d i a z e p i n e s have not undergone e x t e n s i v e s t r u c t u r e a c t i v i t y a n a l y s i s . R e c e n t l y the development of novel d i h y d r o p y r i - d i n e s which s t i m u l a t e the e n t r y o f c a l c i u m i n t o the c e l l , and thus s t i m u l a t e c o n t r a c t i o n , has p r o v i d e d an a d d i t i o n a l t o o l f o r i n v e s t i g a t i n g c a l c i u m e n t r y and c a l c i u m a n t a g o n i s t e f f e c t s . Bay K 8544 has been shown t o i n c r e a s e the c o n t r a c t i l e a c t i v i t y o f i s o l a t e d g u i n e a p i g myocardium and r a b b i t a o r t a i n a manner which i s i n h i b i t e d by n i f e d i p i n e (Schramm e t a l . 1983). Furthermore, enantiomers o f Bay K 8544 (Franckowiak 1985) as w e l l as a new d i h y d r o p y r i - d i n e analogue 202-791 (Hof e t a l . 1985), were found t o b l o c k , o r enhance, c a l c i u m uptake and K + d e p o l a r i z e d smooth muscle c o n t r a c t i o n . The heterogeneous e f f e c t s o f the c a l c i u m a n t a g o n i s t s seen i n v i t r o a r e f u r t h e r c o m p l i c a t e d i n v i v o by the p r e s e n c e of r e f l e x mechanisms. Thus, i n v i v o c a l c i u m a n t a g o n i s t a c t i o n s are not n e c e s s a r i l y the same as i n v i t r o c a l c i u m a n t a g o n i s t a c t i o n s . 1.4.2 In Vivo a c t i o n s on: 1.4.2.1 C a r d i a c muscle. The e f f e c t s o f d i h y d r o p y r i d i n e c a l c i u m a n t a g o n i s t s on the myocardium i n v i v o are v e r y d i f f e r e n t from t h o s e seen i n v i t r o . In normotensive animals n i c a r d i p i n e (Hof 1983), n i s o l d i p i n e ( D r e x l e r e t a l . 1985a), n i f e d i p i n e (Gross e t a l . 1979; Kanda and F l a i m 1984) and f e l o d i p i n e ( L j u n g 1985, N o r d l a n d e r 1985) a l l i n c r e a s e d h e a r t r a t e w h i l e n i m o d i p i n e (Duncker e t a l . 1986), d a r o d i p i n e (Hof 1983,1984,1985) and i s r a d i p i n e ^(Hof 1987, Hof e t a l . 1987) a l l s l i g h t l y d e c r e a s e d h e a r t r a t e . In a n e s t h e t i z e d dogs (Gross e t a l . 1979) the i n c r e a s e d h e a r t r a t e caused by n i f e d i p i n e d i s a p p e a r e d long b e f o r e h y p o t e n s i v e e f f e c t s d i s a p p e a r e d . WAITE, R.P. 10 N i f e d i p i n e , n i s o l d i p i n e , n i m o d i p i n e and n i c a r d i p i n e i n c r e a s e d the h e a r t r a t e i n r e n a l h y p e r t e n s i v e dogs ( T a k a t a and Kato 1986) w h i l e f e l o d i p i n e caused an i n c r e a s e i n h e a r t r a t e i n r e n a l h y p e r t e n s i v e r a b b i t s ( B o l t and Saxena 1984) and s p o n t a n e o u s l y h y p e r t e n s i v e r a t s ( N o r d l a n d e r 1985). C h r o n i c a d m i n i s t r a - t i o n o f f e l o d i p i n e t o SHR r a t s ( N o r d l a n d e r 1985) r e s u l t e d i n a s l i g h t l o w e r i n g o f h e a r t r a t e . N i f e d i p i n e was a l s o shown t o have no e f f e c t on the ECG o f the p i t h e d r a t (Spedding 1982). T h i s lack, of d e p r e s s a n t e f f e c t , f o r d i h y d r o p y r i d i n e s , on the c h r o n o t r o p y and dromotropy o f t h e h e a r t i n v i v o i s accompanied by a l a c k o f n e g a t i v e i n o t r o p y . In a l l s t u d i e s i n which the c o n t r a c t i l i t y of t h e myocardium was measured (Hof 1983; Hof 1984; Kanda and F l a i m 1984; Hof 1985; H o f 1987; Hof e t a l . 1987) the d i h y d r o p y r i d i n e s i n c r e a s e d o r m a i n t a i n e d c o n t r a c t i l i t y r a t h e r than d e p r e s s e d i t . Presumably t h e l a c k o f d i h y d r o p y r i d i n e d e p r e s s a n t a c t i o n s on the myocardium i n v i v o i s due t o : 1) r e f l e x i n c r e a s e i n s y m p a t h e t i c tone c o n c o m i t t a n t upon hypoten - s i o n and 2) t h e i r r e l a t i v e s p e c i f i c i t y f o r v a s c u l a r smooth muscTe. Verapamil and d i l t i a z e m i n a n e s t h e t i z e d c a t s (Hof 1983, 1984), SHR r a t s ( F l a i m e t a l . 1986), r a t s w i t h m y o c a r d i a l i n f a r c t i o n ( D r e x l e r e t a l . 1985c), normal Sprague-Dawley r a t s ( F l a i m and Z e l i s 1982) and a n e s t h e t i z e d c a t s (Hof 1983) caused a d e c r e a s e i n h e a r t r a t e and c o n t r a c t i l i t y . Verapa- m i l g e n e r a l l y reduced c o n t r a c t i l i t y t o a g r e a t e r e x t e n t than d i l t i a z e m , t h e l a t t e r even i n c r e a s e d c o n t r a c t i l i t y i n the a n e s t h e t i z e d c a t (Hof 1983) though not t o the same e x t e n t as n i c a r d i p i n e . Both v e r a p a m i l and d i l t i a z e m d e c r e a s e d h e a r t r a t e and p r o l o n g e d P R - i n t e r v a l of p i t h e d r a t s (Spedding 1982). L i t t l e work has been done w i t h d i p h e n y l a l k y l a m i n e c a l c i u m a n t a g o n i s t s on the i n t a c t animal but t h e y have been shown t o d e c r e a s e h e a r t r a t e (Kato e t a l . 1981) w i t h no e f f e c t on the P R - i n t e r v a l (Spedding. 1982). 1.4.2.2 V a s c u l a r smooth muscle. Though c a l c i u m a n t a g o n i s t s d i f f e r WAITE, R.P. 11 i n t h e i r a b i l i t y t o a f f e c t the h e a r t i n v i v o a l l agents t e s t e d were shown t o lower p e r i p h e r a l v a s c u l a r r e s i s t a n c e w h i l e i n c r e a s i n g o r m a i n t a i n i n g c a r d i a c o u t p u t and s t r o k e volume i n c o n s c i o u s r a t s ( F l a i m and Z e l i s 1982; Kanda and F l a i m 1984; D r e x l e r e t a l . 1985), open-chest a n e s t h e t i z e d c a t s (Hof e t a l . 1982; Hof 1983, 1984), a n e s t h e t i z e d r a b b i t s (Hof 1985, 1987, Hof e t a l . 1987), c o n s c i o u s dogs (Gross e t a l . 1979; Ljung 1985), r e n a l h y p e r t e n s i v e r a b b i t s ( B o l t and Saxena 1984), SHR r a t s ( N o r d l a n d e r 1985, F l a i m e t a l . 1986), and i n f a r c t e d r a t s ( D r e x l e r e t a l . 1985c). T h i s i n d i c a t e s t h a t the c a l c i u m a n t a g o n i s t s are a r t e r i a l d i l a t o r s but have minimal e f f e c t s on v e i n s . The e f f e c t o f c a l c i u m a n t a g o n i s t s on the p e r i p h e r a l c i r c u l a t i o n w i l l be d i s c u s s e d i n g r e a t e r d e t a i l i n t h e d i s c u s s i o n s e c t i o n . D i f f e r e n c e s i n the a c t i o n s o f c a l c i u m a n t a g o n i s t s on the myocardium and v a s c u l a r smooth muscle has i m p l i c a t i o n s i n the t r e a t m e n t of d i s e a s e . 1.4.3 A c t i o n s i n e x p e r i m e n t a l and c l i n i c a l c a r d i o v a s c u l a r d i s e a s e 1.4.3.1 A c t i o n s i n e x p e r i m e n t a l c a r d i o v a s c u l a r d i s e a s e . I n d u c t i o n of a r r y t h m i a s i n r a t s by o c c l u s i o n o f t h e l e f t c o r o n a r y a r t e r y i n d u c e s v e n t r i c u l a r a r r y t h m i a s which are s u s c e p t i b l e t o c a l c i u m a n t a g o n i s t t r e a t - ment. The i n c i d e n c e of e c t o p i c b e a t s , v e n t r i c u l a r t a c h y c a r d i a , and v e n t r i - c u l a r f i b r i l l a t i o n were reduced by the c a l c i u m a n t a g o n i s t s v e r a p a m i l , c i n n a r i z i n e , f l u n a r i z i n e and p r e n y l a m i n e (Fagbemi 1984). S t u d i e s i n c o n s c i o u s r a t s i n d i c a t e d t h a t v e r a p a m i l , a n i p a m i l , D-888 a l l p r o t e c t the i s c h e m i c myocardium from v e n t r i c u l a r f i b r i l l a t i o n but the d i h y d r o p y r i d i n e s n i f e d i p i n e and f e l o d i p i n e o n l y p r o t e c t at doses much h i g h e r than t h o s e p r o d u c i n g a maximum h y p o t e n s i v e e f f e c t (Walker 1987). In c o n g e s t i v e h e a r t f a i l u r e t h e a d m i n i s t r a t i o n o f a c a l c i u m a n t a g o n i s t may reduce the a f t e r l o a d o f the h e a r t and thus r e l i e v e f a i l u r e . In r a t models o f h e a r t f a i l u r e the c a l c i u m a n t a g o n i s t d i l t i a z e m was found t o cause a f a v o r a b l e p r o f i l e o f blood f l o w d i s t r i b u t i o n ( D r e x l e r e t a l . 1985b; WAITE, R.P. 12 D r e x l e r e t a l . 1985c) w h i l e i n c r e a s i n g c a r d i a c o u t p u t . E f f e c t i v e doses o f d i l t i a z e m were lower than t h a t needed t o produce a s i g n i f i c a n t n e g a t i v e i n o t r o p i c r e s p o n s e . Treatment o f s p o n t a n e o u s l y h y p e r t e n s i v e r a t s w i t h d i l t i a z e m ( F l a i m e t a l . 1986) and f e l o d i p i n e ( N o r d l a n d e r 1985) lowered MAP by r e d u c i n g the p e r i p h e r a l v a s c u l a r r e s i s t a n c e . Futhermore, long term f e l o d i p i n e a d m i n i - s t r a t i o n ( N o r d l a n d e r 1985) was e f f e c t i v e i n m a i n t a i n i n g a r e d u c t i o n o f MAP and TPR. F e l o d i p i n e , n i c a r d i p i n e , n i m o d i p i n e , n i f e d i p i n e and n i s o l d i p i n e were e f f e c t i v e i n l o w e r i n g the MAP o f r e n a l h y p e r t e n s i v e animals ( B o l t and Saxena 1984; Takato and Kato 1986). T h e r e f o r e , experiments w i t h h y p e r t e n - s i v e animals i n d i c a t e t h a t the v a s c u l a r s e l e c t i v i t y o f the d i h y d r o p y r i d i n e s can be u t i l i z e d i n the t r e a t m e n t o f h y p e r t e n s i o n o f d i f f e r e n t o r i g i n s . D i f f e r e n c e s i n t i s s u e s e l e c t i v i t y o f the c a l c i u m a n t a g o n i s t s has i m p l i c a - t i o n s i n the c l i n i c a l as w e l l as the e x p e r i m e n t a l s e t t i n g . 1.4.3.2 A c t i o n s i n c l i n i c a l c a r d i o v a s c u l a r d i s e a s e . Only t h r e e c a l c i u m a n t a g o n i s t s , v e r a p a m i l , n i f e d i p i n e and d i l t i a z e m , are approved f o r c l i n i c a l use i n the USA. These compounds have found use i n the t r e a t m e n t o f a number of c a r d i o v a s c u l a r d i s o r d e r s such as h y p e r t e n s i o n , s u p r a v e n t r i c u l a r a r r y t h m i a s , a n g i n a p e c t o r i s and P r i n z m e t a l ' s a n g i n a , h y p e r t r o p h i c cardiomyo- pathy and c o n g e s t i v e h e a r t f a i l u r e . In a d d i t i o n , a number of newer c a l c i u m a n t a g o n i s t s are undergoing c l i n i c a l t r i a l s . In the t r e a t m e n t o f h y p e r t e n s i o n the d i h y d r o p y r i d i n e c a l c i u m antagon- i s t s are most used, presumably because o f t h e i r r e l a t i v e s p e c i f i c i t y f o r the v a s c u l a t u r e and r e s u l t i n g l a c k o f n e g a t i v e c h r o n o t r o p i c and i n o t r o p i c e f f e c t s ( T o g g a r t and Z e l i s 1983). N i f e d i p i n e was found t o be e f f e c t i v e i n the l o w e r i n g o f blood p r e s s u r e i n e s s e n t i a l h y p e r t e n s i o n ( B l a u e t a l . 1986 ) w i t h l i t t l e e f f e c t on the myocardium u n l e s s a d m i n i s t e r e d d i r e c t l y i n t o the c o r o n a r y a r t e r y ( T e r r i s e t a l . 1986). The l a c k o f n e g a t i v e c a r d i a c e f f e c t s WAITE, R.P. 13 a l l o w s the p o t e n t i a l c o m b i n a t i o n t h e r a p y o f d i h y d r o p y r i d i n e s w i t h 8 - b l o c k e r s . N i t r e n d i p i n e and p r o p r a n o l o l t o g e t h e r had an a d d i t i v e e f f e c t on blood p r e s s u r e l o w e r i n g w i t h . n o development of t o l e r a n c e o v e r a one y e a r p e r i o d o f study (McMahon 1986). S i m i l a r a d d i t i v i t y was found w i t h n i t r e n d i - p i n e and h y d r o c h l o r t h i a z i d e (Massie e t a l . 1986). Newer d i h y d r o p y r i d i n e s such as i s r a d i p i n e (Hamilton 1987) and f e l o d i p i n e (Muir e t a l . 1985) were shown t o be e f f i c a c i o u s i n the management o f e s s e n t i a l h y p e r t e n s i o n . The use o f verap a m i l i n p a t i e n t s w i t h h y p e r t e n s i o n showed t h a t i t e f f e c t i v e l y lowered b l o o d p r e s s u r e w i t h o u t r a i s i n g plasma n o r a d r e n a l i n e l e v e l s as d i d n i f e d i p i n e ( A g a b i t i - R o s e i e t a l . 1986; E l l i o t t 1987). I t appears t h a t v e r a p a m i l and n i f e d i p i n e are e q u a l l y e f f e c t i v e i n t h e management o f hyper- t e n s i o n ( E l l i o t t 1987). A l l t h r e e o f the c l i n i c a l l y a v a i l a b l e c a l c i u m a n t a g o n i s t s have been found t o be e f f e c t i v e i n the t r e a t m e n t o f P r i n z m e t a l ' s v a r i a n t a n g i n a and angin a p e c t o r i s (Stone e t a l . 1980; S c h r o e d e r 1982; Stone 1987; K r i k l e r 1987). These agents are e s p e c i a l l y e f f e c t i v e i n p r e v e n t i n g t he vasospasm which o c c u r s i n P r i n z m e t a l ' s a n g i n a . Newer d i h y d r o p y r i d i n e s such as i s r a d i - p i n e were r e c e n t l y shown t o be e f f e c t i v e i n r e d u c i n g a n g i n a l a t t a c k r a t e and n i t r a t e consumption ( T a y l o r e t a l . 1987). In t r e a t i n g a r r y t h m i a s , t he drug of c h o i c e i s the more c a r d i o s e l e c t i v e agent v e r a p a m i l . Verapamil i s e f f e c t i v e i n a l l e v i a t i n g paroxysmal s u p r a v e n - t r i c u l a r t a c h y c a r d i a , s u p r a v e n t r i c u l a r t a c h y c a r d i a s a s s o c i a t e d w i t h W o l f f - P a r k i n s o n - W h i t e syndrome and AV j u n c t i o n a l t a c h y c a r d i a s ( K r i k l e r and S p u r r e l l 1974). The e f f e c t o f v e r a p a m i l on v e n t r i c u l a r a r r y t h m i a s i s more q u e s t i o n a b l e , but some s t u d i e s i n d i c a t e t h a t v e r a p a m i l i s o f b e n e f i t i n t r e a t i n g v e n t r i c u l a r a r r y t h m i a s ( S i n g h e t a l . 1983). In c o n g e s t i v e h e a r t f a i l u r e , a d m i n i s t r a t i o n o f the c a l c i u m a n t a g o n i s t n i f e d i p i n e lowered p e r i p h e r a l v a s c u l a r r e s i s t a n c e w h i l e i n c r e a s i n g c a r d i a c WAITE, R.P. 14 o u t p u t , thus improving c i r c u l a t i o n w h i l e not g r e a t l y a f f e c t i n g t he damaged myocardium (Matsui e t a l . 1979, Matsumoto e t a l . 1980). N i t r e n d i p i n e reduced p r e l o a d and i n c r e a s e d s t r o k e volume i n p a t i e n t s w i t h c o n g e s t i v e h e a r t f a i l u r e (Cohn 1985). C a l c i u m a n t a g o n i s t s have been used i n a number o f o t h e r d i s o r d e r s such as t r e a t m e n t o f h y p e r t r o p h i c cardiomyopathy ( C h a t t e r j e e 1987), p r o p h y l a x i s o f m i g r a i n e and t r e a t m e n t o f v e r t i g o (Vanhoutte 1987). A d d i t i o n a l l y , t h e r e are a number o f d i s e a s e s t a t e s i n which c a l c i u m a n t a g o n i s t t r e a t m e n t i s be i n g c o n s i d e r e d . The c a l c i u m a n t a g o n i s t n i m o d i p i n e was found t o be somewhat b e n e f i c i a l i n c e r e b r a l i s c h e m i a due t o s t r o k e (Gelmers 1987). N i f e d i p i n e was shown t o r e l i e v e pulmonary edema ( P o l e s e 1979) but s i m i l a r d e c r e a s e s o f pulmonary v a s c u l a r r e s i s t a n c e d i d not o c c u r upon a d m i n i s t r a t i o n o f d i l t i a z e m ( K l e i n e t a l . 1983). A n t i a t h e r o g e n i c e f f e c t s o f c a l c i u m a n t a g o n i s t s have been r e p o r t e d ( W e i n s t e i n 1987) but o n l y at h i g h doses and the r e l e v a n c e i n the t r e a t m e n t o f t h i s d i s o r d e r has not been a s s e s s e d . There are a number o f c a l c i u m dependent p r o c e s s e s which are not a f f e c t e d by p r e s e n t l y a v a i l a b l e c a l c i u m a n t a g o n i s t s . The study o f t h e s e p r o c e s s e s , and how c a l c i u m i s i n v o l v e d at the m o l e c u l a r l e v e l , may c o n t r i - bute s p e c i f i c and t h e r a p e u t i c a l l y u s e f u l c a l c i u m a n t a g o n i s t s . 1.5 Ca l c i u m a n t a g o n i s t a c t i o n s on c a l c i u m dependent p r o c e s s e s o t h e r than c a r d i a c and smooth muscle c o n t r a c t i o n The a b i l i t y o f c a l c i u m a n t a g o n i s t s t o a f f e c t o t h e r c a l c i u m dependent p r o c e s s e s appears t o be m i n i m a l . Calcium dependent n e u r o t r a n s m i t t e r r e l e a s e from nerve t e r m i n a l s i s not s u s c e p t i b i l e t o c a l c i u m a n t a g o n i s t b l o c k a d e . F u r t h e r m o r e , c a l c i u m a n t a g o n i s t s , at p h a r m a c o l o g i c a l l y r e l e v a n t c o n c e n t r a - t i o n s , have l i t t l e e f f e c t on c a l c i u m dependent p r o d u c t i o n and r e l e a s e o f hormones from t h e a n t e r i o r and p o s t e r i o r p i t u i t a r y , e n d o c r i n e p a n c r e a s , and s t e r o i d e g e n i c organs ( V e l d h u i s 1982). WAITE, R. P. 15 A g g r e g a t i o n o f p l a t e l e t s by c a l c i u m i s w e l l documented but p l a t e l e t s can aggregate w i t h o u t c a l c i u m and a n t i p l a t e l e t a c t i v i t y o f the c u r r e n t l y a v a i l a b l e c a l c i u m a n t a g o n i s t s o c c u r s o n l y at c o n c e n t r a t i o n s 100-1000x t h a t needed f o r i n h i b i t i o n o f smooth o r m y o c a r d i a l muscle c o n t r a c t i l i t y (Rink 1987). R e l e a s e o f v a s o a c t i v e s u b s t a n c e s by mast c e l l s i n a l l e r g i c r e a c t i o n s i s c r i t i c a l l y dependent on the e n t r y o f c a l c i u m i n t o the c e l l . However, c a l c i u m a n t a g o n i s t drugs do not a f f e c t h i s t a m i n e r e l e a s e at c o n c e n t r a t i o n s which b l o c k c a l c i u m c h a n n e l s (Pearce 1987). C a l c i u m a n t a g o n i s t s appear t o i n h i b i t t h e p e r m e a b i l i t y and shape changes o f e n d o t h e l i a l c e l l s i n an acute i n f l a m m a t o r y r e a c t i o n but t h e r e i s no e v i d e n c e t o s u g g e s t t h a t t h e s e drugs modify t h e c a l c i u m c o n t r o l l e d r e g u l a t i o n o f t h e i n v a d i n g immunogens ( N o r t h o v e r 1987).. In r e c e n t y e a r s , i t has become apparent t h a t the e n d o t h e l i u m o f v a s c u l a r smooth muscle r e l e a s e s r e l a x a n t f a c t o r s , e n d o t h e l i u m d e r i v e d r e l a x - ant f a c t o r s (EDRF), i n response t o c h e m i c a l s t i m u l i . R e l a x a t i o n o f i s o l a t e d a r t e r i a l p r e p a r a t i o n s induced by a number o f v a s o a c t i v e s u b s t a n c e s i n c l u d i n g a c e t y l c h o l i n e , s u b s t a n c e P, c a l c i u m ionophore A 23187, ATP, h i s t a m i n e , thrombin and s e r o t o n i n i s dependent on t h e p r e s e n c e of e n d o t h e l i u m and c a l c i u m i o n s ( F u r c h g o t t 1984; Rubanyi 1987). The r e l a t i v e i n ' s e n s i t i v i t y o f EDRF r e l e a s e t o n i f e d i p i n e and v e r a p a m i l i n d i c a t e s t h a t t h e r e l e a s e o f EDRF may be analogous t o o t h e r c a l c i u m dependent r e l e a s e p r o c e s s e s (Peach et a l . 1987; Rubanyi 1987). I n h i b i t i o n o f the c a l c i u m - c a l m o d u l i n i n t e r a c t i o n i s not a major e f f e c t o f c a l c i u m a n t a g o n i s t s . C a l m o d u l i n s e n s i t i v e p h o s p h o d i e s t e r a s e a c t i v i t y of b r a i n i s o l a t e s was not a f f e c t e d by v e r a p a m i l , n i f e d i p i n e , f l u n a r i z i n e , b e p r i d i l o r d i l t i a z e m up t o c o n c e n t r a t i o n s o f 10 M ( D a l y e t a l . 1983, L u g n i e r e t a l . 1984). S i m i l a r l y , f e l o d i p i n e d i d not a f f e c t the myosin l i g h t c h a i n p h o s p h o r y l a t i n g a c t i v i t y i n r a b b i t a o r t a and a t r i a at c o n c e n t r a t i o n s WAITE, R.P. 16 _c below 10 M, a p p r o x i m a t e l y lOOOx g r e a t e r than t h a t n e c e s s a r y f o r i n h i b i - t i o n o f c o n t r a c t i o n ( S i l v e r e t a l . 1984). Though the e f f e c t of c a l c i u m a n t a g o n i s t s on c a l m o d u l i n appear t o be minimal i t demonstrates t h a t t he s p e c i f i c i t y o f t h e s e drugs i s r e l a t i v e and t h a t t h e y have e f f e c t s not r e l a t e d t o c a l c i u m e n t r y i n t o t he c e l l . 1.6 Ca l c i u m a n t a g o n i s t a c t i o n s on no n - c a l c i u m dependent p r o c e s s e s O t h e r p h a r m a c o l o g i c a l e f f e c t s o f the c a l c i u m a n t a g o n i s t s have been i n v e s t i g a t e d such as the bloc k a d e o f a - a d r e n o r e c e p t o r s and m u s c a r i n i c r e c e p t o r s . D-600 i n c o n c e n t r a t i o n s from 10 t o 10 M i n h i b i t e d t h e b i n d i n g o f r a d i o l i g a n d s t o a - a d r e n o c e p t o r s and m u s c a r i n i c r e c e p t o r s i n r a t b r a i n homogenates ( F a i r h u r s t e t a l . 1980) and i s o l a t e d r a t myocardium ( K a r l i n e r e t a l . 1982; N a y l e r e t a l . 1982). Furthermore D-600 was shown t o bin d t o o p i a t e r e c e p t o r s ( F a i r h u r s t e t a l . 1980). Verapamil was shown t o b l o c k a - r e c e p t o r s ( K a r l i n e r e t a l . 1982; N a y l e r e t a l . 1982; Psychoyos e t a l . 1986), r e g a r d l e s s o f subtype ( M o t u l s k y 1983), and m u s c a r i n i c r e c e p - t o r s ( K a r l i n e r e t a l . 1982; N a y l e r e t a l . 1982). D i l t i a z e m and n i f e d i p i n e produced l i t t l e a - a d r e n o c e p t o r b l o c k a d e ( N a y l e r e t a l . 1982; M o t u l s k y 1983) i n d i c a t i n g t h a t t he i n t e r a c t i o n of t h e s e drugs w i t h membrane r e c e p t o r s i s not common f o r a l l c a l c i u m a n t a g o n i s t s . I n h i b i t i o n of the f a s t sodium c u r r e n t , which c a r r i e s t he a c t i o n p o t e n - t i a l i n v e n t r i c u l a r muscle, i s g e n e r a l l y seen at c o n c e n t r a t i o n s g r e a t e r than 10 M by verap a m i l and D-6 00 (Bayer e t a l . 1975). In g e n e r a l , t he c o n c e n - t r a t i o n o f c a l c i u m a n t a g o n i s t n e c e s s a r y f o r b l o c k i n g c a l c i u m e n t r y i n t o c e l l s i s much lower than t h a t needed f o r r e c e p t o r b l o c k a d e o r f a s t channel i n h i b i t i o n . From the p r e c e e d i n g d i s c u s s i o n i t i s apparent t h a t c a l c i u m a n t a g o n i s t s a c t by b l o c k i n g c a l c i u m e n t r y through s p e c i f i c plasma membrane c h a n n e l s . Study o f the s t r u c t u r e and f u n c t i o n of t h e s e c h a n n e l s may g i v e i n d i c a t i o n s WAITE, R.P. 17 as t o why c a l c i u m a n t a g o n i s t s are r e l a t i v e l y t i s s u e s p e c i f i c . 1.7 C a l c i u m e n t r y i n t o the c e l l v i a membrane c h a n n e l s : m o l e c u l a r s i t e o f c a l c i u m a n t a g o n i s t a c t i o n E n t r y o f c a l c i u m i n t o the c y t o p l a s m o f c e l l s i s known t o o c c u r i n t h r e e ways: 1) v i a a leak c u r r e n t , 2) t h r o u g h v o l t a g e o p e r a t e d c h a n n e l s o r 3) t h r o u g h r e c e p t o r o p e r a t e d c h a n n e l s . E n t r y o f c a l c i u m v i a the leak c u r r e n t i s p a r t i a l l y i n h i b i t e d by i n o r g a n i c c a l c i u m a n t a g o n i s t s such as lanthanum, but not by o r g a n i c c a l c i u m a n t a g o n i s t s ( v e r a p a m i l , n i f e d i p i n e e t c . , Cauvin and M a l i k 1984). The amount o f c a l c i u m which can e n t e r the c e l l v i a the leak c u r r e n t i s s u f f i c i e n t t o produce a c o n t r a c t i o n o n l y i f the s e q u e s t e r i n g a b i l i t y o f t h e s a r c o p l a s m i c r e t i c u l u m i s compromised (Johns e t a l . 1987). S e p a r a t i o n o f c a l c i u m i n f l u x e s i n t o t h o s e i n v o l v i n g v o l t a g e dependent c h a n n e l s and r e c e p t o r o p e r a t e d c h a n n e l s was demonstrated by the measurement 45 of c a l c i u m i n f l u x i n t o v a s c u l a r and v i s c e r a l smooth muscle c e l l s . 45 + I n h i b i t i o n o f both Ca uptake and K - i n d u c e d v a s c u l a r smooth muscle c o n t r a c t i o n by c a l c i u m a n t a g o n i s t s was c l o s e l y c o r r e l a t e d (Cauvin e t a l . 1984; Cauvin and M a l i k 1984). N o r a d r e n a l i n e - i n d u c e d c o n t r a c t i o n o f the a o r t a was not accompanied by a change i n membrane p o t e n t i a l and the i n c r e a s e i n c a l c i u m f l u x caused by n o r a d r e n a l i n e and K + were a d d i t i v e . The c a l c i u m 45 channel a g o n i s t Bay K 8644 was a b l e t o i n c r e a s e t h e Ca f l u x i n v e s s e l s c o n t r a c t e d w i t h n o r a d r e n a l i n e but not i n K + d e p o l a r i z e d v e s s e l s ( C a u v i n e t a l . 1984; Cauvin and M a l i k 1984; Yammamoto et a l . 1984). F l u n a r i z i n e 45 i n h i b i t e d both n o r a d r e n a l i n e - i n d u c e d c o n t r a c t i o n and Ca i n f l u x i n r a t a o r t a and m e s e n t e r i c r e s i s t a n c e v e s s e l s ( G o d f r a i n d and Dieu 1981). In r e c e n t y e a r s , e l e c t r o p h y s i o l o g i c a l and b i o c h e m i c a l s t u d y o f the v o l t a g e dependent c a l c i u m c h a n n e l s has y i e l d e d much i n f o r m a t i o n about t h e i r n a t u r e , s t r u c t u r e and pharmacology. Knowledge o f r e c e p t o r o p e r a t e d ' c a l c i u m c h a n n e l s WAITE, R.P. 18 i s l i m i t e d t o f i n d i n g s from p h a r m a c o l o g i c a l e x p e r i m e n t s . 1.7.1 V o l t a g e dependent c a l c i u m channel 1.7.1.1 Types o f v o l t a g e dependent c a l c i u m c h a n n e l s . Both biochem- i c a l and e l e c t r o p h y s i o l o g i c a l s t u d i e s have i n d i c a t e d t h a t v o l t a g e dependent c a l c i u m c h a n n e l s are not a homogenous p o p u l a t i o n . E l e c t r o p h y s i o l o g i c a l s t u d i e s on c a l c i u m conductance o f v a r i o u s t i s s u e s r e v e a l e d t h a t t h e r e were t h r e e c a l c i u m channel t y p e s ( L , T and N) and t h a t c e r t a i n t i s s u e s have more than one channel t y p e . V o l t a g e clamp a n a l y s i s o f c a l c i u m c u r r e n t s i n h e a r t c e l l s (Lee and T s i e n 1983; Bean 1985) and v a s c u l a r smooth muscle c e l l s ( S t u r e k and Hermsmeyer 1986), and p a t c h clamp a n a l y s i s o f h e a r t c e l l s ( N i l i u s e t a l . 1985) and v a s c u l a r smooth muscle c e l l s (Worley e t a l . 1986; Bean e t a l . 1986) i n d i c a t e d the p r e s e n c e o f two c a l c i u m c h a n n e l s (L and T ) . The L channel r e q u i r e s s t r o n g d e p o l a r i z a t i o n s f o r a c t i v a t i o n and i n a c t i v a t e s s l o w l y w h i l e the T channel i s a c t i v a t e d by small d e p o l a r i z a t i o n s and i n a c t i v a t e s q u i c k l y . The T channel i s i n a c t i v a t e d at membrane p o t e n t i a l s at o r above -30mV w h i l e the conductance o f the L channel b e g i n s a t t h i s membrane p o t e n t i a l . I t i s l i k e l y t h a t the c o n t r i b u - t i o n t o i n t r a c e l l u l a r c a l c i u m from the T channel i s minimal but may p l a y a r o l e i n the a u t o m a t i c i t y o f the SA node and the c o n d u c t i o n of the a c t i o n p o t e n t i a l at the AV node as inward c u r r e n t s at r e l a t i v e l y n e g a t i v e membrane p o t e n t i a l s are needed. The t h i r d c a l c i u m c h a n n e l , the N c h a n n e l , was d i s c o v e r e d i n c h i c k d o r s a l r o o t g a n g l i o n (Nowycky e t a l . 1985). T h i s channel r e q u i r e s s t r o n g d e p o l a r i z a t i o n s f o r a c t i v a t i o n and s t r o n g l y n e g a t i v e p o t e n t i a l s f o r i n a c t i v a t i o n . I t ' s p r e s e n c e i n nerve c e l l s may e x p l a i n the l a c k of c a l c i u m a n t a g o n i s t e f f e c t on n e u r o t r a n s m i t t e r r e l e a s e even though t h i s i s a c a l c i u m dependent p r o c e s s . I s o l a t i o n of c a l c i u m c h a n n e l s from a number o f s o u r c e s has been a c h i e v e d u s i n g r a d i o l a b e l 1 i n g o r p h o t o a f f i n i t y l a b e l l i n g w i t h s p e c i f i c 1-4 WAITE, R.P. 19 d i h y d r o p y r i d i n e a n a l o g u e s . Treatment o f channel p r e p a r a t i o n s w i t h v a r i o u s agents i n d i c a t e d t h a t c h a n n e l s from h e a r t , b r a i n and s k e l e t a l muscle were d i f f e r e n t i n a t i s s u e , but not s p e c i e s , s p e c i f i c manner (Glossmann e t a l . 1984a, 1985a). S k e l e t a l muscle c h a n n e l s e x h i b i t i n c r e a s e d d i h y d r o p y r i d i n e b i n d i n g w i t h i n c r e a s e d pH but b r a i n c h a n n e l s m a x i m a l l y b i n d d i h y d r o p y r i d i n e s at p h y s i o l o g i c a l pH. Heparin d e c r e a s e d [ H ] - n i m o d i p i n e b i n d i n g i n t h e o r d e r s k e l e t a l muscle > h e a r t = b r a i n and c h e l a t o r s d e c r e a s e d d i h y d r o p y r i - d i n e b i n d i n g i n b r a i n > h e a r t > muscle (Glossmann e t a l . 1984a, Glossmann e t a l . 1985a). I t i s l i k e l y t h a t the crude method o f c a l c i u m channel i s o l a - t i o n and t e s t i n g i s not a b l e t o d e t e c t s u b t l e d i f f e r e n c e s i n channel type but i s i n s t e a d s e p a r a t i n g c h a n n e l s based on t h e i r i n t e r a c t i o n s w i t h o t h e r membrane components. T h e r e f o r e , i t i s s i m p l e s t t o assume t h a t t h e r e are t h r e e t y p e s o f c a l c i u m c h a n n e l s w i t h s i m i l a r s t r u c t u r e s , but not conductance c h a r a c t e r i s t i c s . 1.7.. 1.2 S t r u c t u r e of the v o l t a g e dependent c a l c i u m c h a n n e l . S t r u c t u r e o f t h e v o l t a g e dependent c a l c i u m channel appears t o be s i m i l a r f o r a l l channel p r e p a r a t i o n s t e s t e d . The p r o t e i n n a t u r e o f c a l c i u m c h a n n e l s was demonstrated by heat and t r y p s i n i n a c t i v a t i o n o f d i h y d r o p y r i d i n e s p e c i f i c b i n d i n g (Glossmann e t a l . 1982; Glossmann and F e r r y 1983). Fur t h e r m o r e , the i n t e g r i t y o f v o l t a g e dependent c a l c i u m c h a n n e l s appears t o be c r i t i c a l l y dependent on the p r e s e n c e o f c e r t a i n p h o p h o l i p i d s as a d d i t i o n o f p h o s p h o l i - pases A and C a b o l i s h e d r a d i o l a b e l l e d d i h y d r o p y r i d i n e b i n d i n g (Glossmann e t a l . 1982; Glossmann and F e r r y 1983; Glossmann e t a l . 1985a). The g l y c o p r o t e i n n a t u r e o f d i h y d r o p y r i d i n e b i n d i n g s i t e s ( c a l c i u m c h a n n e l s ) was 'demonstrated by t h e i r a f f i n i t y f o r wheat germ a g g l u t i n i n sepharose columns ( C u r t i s and C a t t e r a l l 1983; Glossmann and F e r r y 1983). D e t e r m i n a t i o n o f m o l e c u l a r weight o f c a l c i u m c h a n n e l s by r a d i a t i o n i n a c t i v a t i o n i n d i c a t e d t h a t the c a l c i u m channel i s a p r o t e i n o f m o l e c u l a r WAITE, R.P. 20 weight 180,000 t o 210,000 kDa f o r r a b b i t s k e l e t a l muscle (Norman e t a l . 1983), g u i n e a p i g b r a i n ( F e r r y e t a l . 1983; Glossmann e t a l . 1985a) and g u i n e a p i g h e a r t (Glossmann e t a l . 1985a). D e t e r m i n a t i o n o f m o l e c u l a r weight f o r the d i h y d r o p y r i d i n e b i n d i n g s i t e i n smooth muscle y i e l d e d a v a l u e o f 278,000kDa ( V e n t e r e t a l . 1983). P h o t o a f f i n i t y l a b e l l i n g o f r a b b i t s k e l e t a l muscle T - t u b u l e membranes w i t h e i t h e r r a d i o l a b e l e d d i h y d r o p y r i - d i n e s o r d i l t i a z e m r e s u l t e d i n i s o l a t i o n o f a p o l y p e p t i d e o f m o l e c u l a r weight 170,00kDa ( G a l i z z i 1985). t h e p r e s e n c e o f d - c i s d i l t i a z e m reduced the m o l e c u l a r weight d e t e r m i n a t i o n o f the d i h y d r o p y r i d i n e b i n d i n g s i t e to a p p r o x i m a t e l y 107,00kDa (Norman e t a l . 1983; F e r r y e t a l . 1983; Glossmann 1985a) w h i l e b i n d i n g o f r a d i o l a b e l l e d desmethoxyverapami1 o r d i l t i a z e m t o g u i n e a p i g s k e l e t a l muscle membranes reduced t h e m o l e c u l a r weight o f the i s o l a t e t o 107 and 131kDa r e s p e c t i v e l y ( G o l l e t a l . 1984). When g u i n e a p i g s k e l e t a l muscle T - t u b u l e membranes are p u r i f i e d and s o l u b i l i z e d i n d i g i t o - n i n , p o l y p e p t i d e s o f 155, 65, and 32kDa were i d e n t i f i a b l e w h i l e p h o t o a f f i n - i t y l a b e l l i n g o f t h e same p r e p a r a t i o n w i t h subsequent i s o l a t i o n o f l a b e l l e d p r o t e i n s under n o n - r e d u c i n g c o n d i t i o n s i n SDS p o l y a c r y l a m i d e gel e l e c t r o - p h o r e s i s r e s u l t e d i n i s o l a t i o n o f one p r o t e i n o f m o l e c u l a r weight 155kDa ( S t r i e s s n i g e t a l . 1986). Added t o the f a c t t h a t t r e a t m e n t o f membrane p r e p a r a t i o n s w i t h s u l f h y d r y l r e a g e n t s r e s u l t s i n a d e c r e a s e i n d i h y d r o p y r i - d i n e b i n d i n g (Glossmann e t a l . 1984a, Glossmann e t a l . 1985a) i t would seem t h a t the c a l c i u m channel i s an o l i g o m e r i c s t r u c t u r e which i s h e l d t o g e t h e r , t o a c e r t a i n degree, by d i s u l f i d e l i n k a g e s . I n t e r r u p t i o n o f the s t r u c t u r e o f t h e channel by b i n d i n g o f c a l c i u m a n t a g o n i s t s o r p e r t u r b a t i o n by e x c e s - s i v e r e d u c i n g agents can d i s r u p t t h i s s t r u c t u r e and r e s u l t i n i s o l a t i o n of v a r i o u s s u b u n i t s o f t h e c h a n n e l . 1.7.1.3 C a l c i u m a n t a g o n i s t a c t i o n s on the v o l t a g e dependent c a l c i u m c h a n n e l . S t u d i e s o f c a l c i u m channel conductance i n the p r e s e n c e o f WAITE, R.P. 21 c a l c i u m a n t a g o n i s t s and b i n d i n g o f r a d i o l a b e l l e d c a l c i u m a n t a g o n i s t s t o channel p r e p a r a t i o n s demonstrates the heterogeneous n a t u r e of c a l c i u m a n t a g o n i s t - c a l c i u m channel i n t e r a c t i o n . A d m i n i s t r a t i o n o f d i h y d r o p y r i d i n e s b l o c k the L channel c u r r e n t but has no e f f e c t on the T channel c u r r e n t o r the N channel c u r r e n t w h i l e the c a l c i u m channel a g o n i s t Bay K 8644 enhances conductance o f the L but not the T o r N channel (Nowycky e t a l . 1985; Bean 1985; Lee and T s i e n 1983; Bean e t a l . 1986 ). D i h y d r o p y r i d i n e c a l c i u m b l o c k a d e was shown to be v o l t a g e dependent u s i n g v o l t a g e clamp a n a l y s i s on c a r d i a c P u r k i n j e f i b e r s ( S a n g u i n e t t i and Kass 1984). Furthermore, i t was p o s t u l a t e d t h a t the use dependance o f ve r a p a m i l and the v o l t a g e dependance o f the d i h y d r o p y r i d i n e s i s r e l a t e d t o the h y d r o p h i 1 i c i t i e s o f the drugs. Verapamil e x i s t s m a i n l y i n the charged form at p h y s i o l o g i c a l pH w h i l e the d i h y d r o p y r i d i n e s are n e u t r a l . I t i s p o s t u l a t e d t h a t v e r a p a m i l must e n t e r the channel i n the open s t a t e t o s t a b i l i z e i t i n the i n a c t i v a t e d s t a t e , analogous t o b l o c k a d e o f the f a s t sodium channel by l i d o c a i n e . D i h y d r o p y r i d i n e s , on the o t h e r hand, b i n d t o t h e i n a c t i v a t e d s t a t e o f the channel t h e r e f o r e the b l o c k i s l a r g e r at more p o s i t i v e membrane p o t e n t i a l s as more c h a n n e l s are i n the i n a c t i v a t e d s t a t e . F u r t h e r s u p p o r t f o r t h i s h y p o t h e s i s was o b t a i n e d when i t was demonstrated t h a t the p a r t i a l l y i o n i z e d d i h y d r o p y r i d i n e , n i c a r d i p i n e , e l i c i t e d some use dependent b l o c k ( S a n g u i n e t t i and Kass 1984) and v e r a p a m i l was i n e f f e c t i v e a t i n c r e a s e d membrane p o t e n t i a l s . V o l t a g e clamp c o n f i r m e d the use dependance o f D-600 and showed t h a t d i l t i a z e m was use dependent i n an i n t e r m e d i a t e way t o D-600 and n i t r e n d i p i n e (Lee and T s i e n 1983). T h i s may e x p l a i n the r e l a t i v e s p e c i f i c i t y o f the d i h y d r o p y r i d i n e s f o r v a s c u l a r smooth muscle as t h i s muscle i s more d e p o l a r i z e d and t h e r e f o r e has a l a r g e r p r o p o r t i o n o f i t s L c h a n n e l s i n the i n a c t i v a t e d s t a t e . B i n d i n g s t u d i e s u s i n g both crude homogenates and s o l u b i l i z e d p u r i f i e d WAITE, R.P. 22 c a l c i u m c h a n n e l s i n d i c a t e t h a t f u n c t i o n a l c a l c i u m c h a n n e l s c o n t a i n t h r e e b i n d i n g s i t e s f o r c a l c i u m a n t a g o n i s t s which i n t e r a c t i n an a l l o s t e r i c f a s h i o n w i t h a d i v a l e n t c a t i o n r e q u i r e m e n t . B i n d i n g o f r a d i o l a b e l e d d i h y d r o p y r i d i n e s t o guinea p i g b r a i n (Glossmann et a l . 1982), bovine h e a r t (Glossmann e t a l . 1983a), gu i n e a p i g h e a r t , s k e l e t a l muscle T - t u b u l e s and b r a i n (Glossmann e t a l . 1984a), c a l f a o r t a , r a b b i t h e a r t and g u i n e a p i g i l e u m (Luchowski 1984) was d e c r e a s e d by c a l c i u m c h e l a t o r s . Furthermore, di h y d r o p y r i d i n e b i n d i n g can be r e c o n s t i t u t e d by a d d i t i o n o f any one o f s e v e r a l d i v a l e n t c a t i o n s (Glossmann e t a l . 1984a, Luchowski e t a l . 1984). B i n d i n g o f r a d i o l a b e l l e d d i h y d r o p y r i d i n e s i s c o m p e t i t i v e l y d i s p l a c e d by o t h e r d i h y d r o p y r i d i n e s . Verapamil and i t s congeners d i s p l a c e d i h y d r o p y - r i d i n e s i n a n e g a t i v e a l l o s t e r i c f a s h i o n and d i l t i a z e m i n c r e a s e s d i h y d r o p y - r i d i n e b i n d i n g i n a p o s i t i v e a l l o s t e r i c f a s h i o n i n a l l membrane p r e p a r a t i o n s t e s t e d (Glossmann e t a l . 1982, Murphy and Snyder 1982, Glossmann et a l . 1984a, Towart and Schramm 1984, Glossmann e t a l . 1985a, T r i g g l e 1986, Vaghy et a l . 1987). B i n d i n g of the p h e n e t h y l a l k y l a m i n e s i t e w i t h the r a d i o l i g a n d [ H]-desmethoxyverapami1 i s a l l o s t e r i c a l l y i n h i b i t e d by the a d d i t i o n o f d - c i s - d i l t i a z e m (Glossmann e t a l . 1985b). These a l l o s t e r i c i n t e r a c t i o n s appear t o be p h a r m a c o l o g i c a l l y s i g n i f i c a n t as c o n t r a c t i o n s o f i s o l a t e d r a t m e s e n t e r i c a r t e r i e s and t a e n i a c o l i induced by d e p o l a r i z a t i o n were i n h i b i t e d by n i f e d i p i n e and d i l t i a z e m t o g e t h e r i n more than an a d d i t i v e manner w h i l e n i f e d i p i n e and D-600 i n h i b i t e d i n an a d d i t i v e manner ( Y o u s i f and T r i g g l e 1985). Furthermore, b i n d i n g o f the r a d i o l i g a n d s i s s t e r e o s p e c i f i c which i s i n agreement with i n v i t r o and i n v i v o p h a r m a c o l o g i c a l e x p e r i m e n t s . (-)-Verapami1 has a h i g h e r a f f i n i t y o f b i n d i n g than ( + ) - v e r a p a m i 1 ( F e r r y and Glossmann 1982), t h e e u d i s m i c r a t i o o f the ( + ) t o t h e (-) isomer of the d i h y d r o p y r i d i n e i s r a d i p i n e i s a p p r o x i m a t e l y 100 (Glossmann et a l . 1983b, Vaghy e t a l . 1987) and the (-) isomer o f n i f e d i p i n e i s more po t e n t than the WAITE, R.P. 23 (+) (Towart e t a l . 1981). The d - c i s enantiomer o f d i l t i a z e m i n c r e a s e s d i h y d r o p y r i d i n e b i n d i n g w h i l e the 1-enantiomer d e c r e a s e s DHP b i n d i n g (Glossmann e t a l . 1983b). T h e r e f o r e , i t appears c a l c i u m a n t a g o n i s t s b i n d t o the v o l t a g e depend- ent c a l c i u m channel at s t e r e o s p e c i f i c s i t e s t h a t are c o n n e c t e d i n an a l l o - s t e r i c manner. A c c e s s t o t h e i r s p e c i f i c s i t e o f a c t i o n depends on the f r e q u e n c y o f channel use, c h e m i c a l n a t u r e o f the drug, membrane p o t e n t i a l and l o c a t i o n o f t h e b i n d i n g s i t e on the c h a n n e l . Use o f the d i p h e n y l a l k y l - amines, such as c i n n a r i z i n e and f l u n a r i z i n e , has not been attempted i n i s o l a t e d channel p r e p a r a t i o n s o r p a t c h clamped c e l l s but smooth muscle experiments i n d i c a t e t h a t t h e s e compounds d i s p l a c e d i h y d r o p y r i d i n e b i n d i n g i n a c o m p e t i t i v e manner w i t h low a f f i n i t y (Spedding 1983). The f u t u r e o f c a l c i u m channel r e s e a r c h would appear t o be p u r i f i c a t i o n and c h a r a c t e r i z a - t i o n of t h e d i f f e r e n t c h a n n e l s t o deduce the i n t e r e l a t i o n s h i p s o f the v a r i o u s s u b u n i t s and how t h e y produce t h e i r conductance c h a r a c t e r i s t i c s . R e c e n t l y s o l u b i l i z e d i s o l a t e d c h a n n e l s from s k e l e t a l muscle have been r e c o n s t i t u t e d i n t o a p h o s p h o l i p i d b i l a y e r and been shown t o r e t a i n L channel c h a r a c t e r i s t i c s i n c l u d i n g c a l c i u m conductance which i s b l o c k e d by D-600 and s t i m u l a t e d by Bay K 8644 ( F l o c k e r z i e t a l . 1986). 1.7.2 R e c e p t o r o p e r a t e d c a l c i u m c h a n n e l s R e c e p t o r a c t i v a t i o n o f smooth muscle i n d u c e s c o n t r a c t i o n s which have a p h a s i c and a t o n i c component. S e r o t o n i n and n o r a d r e n a l i n e induced t o n i c , but not p h a s i c , c o n t r a c t i o n s of i s o l a t e d v a s c u l a r smooth muscle are s u s c e p t - i b l e t o c a l c i u m a n t a g o n i s t b l o c k a d e (Towart 1981; Cauvin and M a l i k 1984; Cauvin e t a l . 1984, Wong e t a l . 1986). L i d o f l a z i n e d e c r e a s e d the c o n t r a c - t i l e response o f g u i n e a p i g i l e u m t o a n g i o t e n s i n II i n a n o n c o m p e t i t i v e manner ( G o d f r a i n d e t a l . 1966). C i n n a r i z i n e and i t s d e r i v a t i v e f l u n a r i z i n e i n h i b i t e d n o r a d r e n a l i n e induced v a s o c o n s t r i c t i o n o f the p e r f u s e d h i n d l i m b o f WAITE, R.P. 24 th e dog (van Neuten and Janssen ,1971; van Neuten and Janssen 1973) as w e l l as t he c o n t r a c t i o n of i s o l a t e d i l e u m by h i s t a m i n e , b r a d y k i n i n , a n g i o t e n s i n II and m e t h a c h o l i n e (Van Neut i n and Janssen 1973) i n a n o n c o m p e t i t i v e manner. In t he i n t a c t a n i m a l , c a l c i u m a n t a g o n i s t s have been shown t o modify t h e v a s o c o n s t r i c t i n g a c t i v i t i e s o f s e v e r a l a g o n i s t s . N i t r e n d i p i n e b l o c k e d the v a s o c o n s t r i c t o r i n f u e n c e o f n o r a d r e n a l i n e , a n g i o t e n s i n II and v a s o p r e s - s i n i n a n a e s t h e t i z e d r a t s ( P e d r i n e l l i and T a r a z i 1985). C o n s t r i c t i o n o f v a r i o u s v a s c u l a r beds i n the a n e s t h e t i z e d c a t by n o r a d r e n a l i n e (Hof e t a l . 1985), and the a n e s t h e t i z e d c a t and r a b b i t by a n g i o t e n s i n II and v a s o p r e s s i n (Hof 1984, 1985) was a t t e n u a t e d by d a r o d i p i n e . Ouabain induced v a s o c o n - s t r i c t i o n i n the a n e s t h e t i z e d c a t was a l s o a t t e n u a t e d by the c a l c i u m a n t ago- n i s t d a r o d i p i n e (Hof and Hof 1985). I t appears t h a t t he a g o n i s t r e c e p t o r i n t e r a c t i o n i n some way s t i m u - l a t e s t h e e n t r y o f c a l c i u m i n t o t he c e l l ( t o n i c component) as w e l l as the r e l e a s e o f s a r c o p l a s m i c r e t i c u l u m c a l c i u m ( p h a s i c component). R e c e p t o r s t i m u l a t e d e n t r y o f c a l c i u m i n t o t he c e l l i s s u s c e p t i b l e t o c a l c i u m antagon- i s t b l o c k a d e . V o l t a g e clamp a n a l y s i s o f i s o l a t e d m y o c a r d i a l c e l l s has i n d i c a t e d t h a t t he conductance o f the v o l t a g e o p e r a t e d c a l c i u m channel can be modulated by c y c l i c - A M P . I n j e c t i o n o f cAMP analogues i n c r e a s e s t he c a l c i u m conductance ( C a c h e l i n e t a l . 1982) as does i n j e c t i o n o f the c a t a l y - t i c s u b u n i t o f cAMP dependent p r o t e i n k i n a s e ( O s t e r r e i d e r 1982) o r a p p l i c a - t i o n o f t h e e - a d r e n o r e c e p t o r a g o n i s t i s o p r e n a l i n e (Bean e t a l . 1984) an agent known t o i n c r e a s e i n t r a c e l l u l a r cAMP. T h i s r a i s e s t he q u e s t i o n , does r e c e p t o r o p e r a t e d m o d u l a t i o n o f the v o l t a g e dependent c a l c i u m channel account f o r the i n c r e a s e i n c a l c i u m i n f l u x upon a g o n i s t - r e c e p t o r i n t e r a c t i o n o r i s t h e r e a s e p a r a t e c a l c i u m channel which i s opened by the r e c e p t o r a c t i v a t i o n ? A t t h e p r e s e n t time i t i s not p o s s i b l e t o d i s t i n g u i s h between t h e s e p o s s i b i l i t i e s . R e c e n t l y i t has been suggested t h a t t he a g o n i s t WAITE, R.P. 25 receptor in teract ion may cause release of sarcoplasmic reticulum calcium by way of the second messenger inos i to l triphosphate (IP3) (Johns 1987). Furthermore the agonist receptor in teract ion would appear to sens i t i ze the con t rac t i l e apparatus such that less calcium is needed to sustain contrac- t ion (Morgan 1987). Differences in second messenger production or d i f f e r - ences of c e l l u l a r machinery for in terpret ing the second messenger may explain why some t issues stimulated by an agonist are susceptible to calcium antagonist blockade and some are not. In recent years there has been a growing controversy whether al adrenoceptors, a2 adrenoceptors, or both, st imulate calcium entry into vascular smooth muscle c e l l s and are thus suscept ible to calcium antagon- ism. It has been hypothesized that a2-adrenoceptor st imulat ion causes an in f lux of calcium and i s therefore suscept ible to blockade by calcium antagonists while al-adrenoceptor st imulat ion does not cause an in f lux of calcium. Evidence indicates that the suscep t i b i l i t y of a-adrenoceptor stimulated ef fects to calcium antagonists i s dependent on species (van Meel et a l . 1981a, 1981b; Timmermans et a l . 1983a, 1983b; Saeed et a l . 1983; Llenas and Massingham 1983; Kalkman 1984; Morita et a l . 1985), vessel type (Mul ler-Schweini tzer 1983; Cavero et a l . 1983; Medgett and Rajanayagam 1984; Toda 1986; van Brummelen et a l . 1987), presence of cardiovascular ref lexes (DeJonge et a l . 1981), receptor reserve (Bou and Massingham 1984; Jim et a l . 1986; Pedr ine l l i and Taraza 1986; Bou and Massingham 1986) and type of a l-agonist (Beckeringh 1984; Matthews et a l . 1985; Bou and Massingham 1986). In general, e f fects caused by a2-adrenoceptor st imulat ion are suscept ible to inh ib i t i on by calcium antagonists while al-adrenoceptor stimulated ef fects vary in the i r suscep t i b i l i t y to calcium antagonists. Obviously a greater understanding of agonist stimulated calcium channel opening i s needed at the biochemical and e lect rophys io log ica l l e v e l . WAITE, R.P. 26 The above i n t r o d u c t i o n has o u t l i n e d t h e e f f e c t s o f c a l c i u m a n t a g o n i s t s on i n t a c t a n i m a l s , i s o l a t e d t i s s u e s and c a l c i u m c h a n n e l s . Though a l a r g e amount o f r e s e a r c h has been done on the c a l c i u m a n t a g o n i s t s , few comparative s t u d i e s o f t h e i r a c t i o n s on i n t a c t animals have been performed. Thus e x p e r - iments were d e s i g n e d t o e v a l u a t e t h e v a l i d i t y o f Spedding's c l a s s i f i c a t i o n of c a l c i u m a n t a g o n i s t s w i t h r e g a r d t o t h e i r e f f e c t on the i n t a c t r a t . 1.8 E x p e r i m e n t a l Aims The purpose o f the experiments conducted were t o 1) determine and compare t h e e f f e c t o f r e p r e s e n t a t i v e drugs from Spedding's c a l c i u m antagon- i s t subgroups on s y s t e m i c hemodynamics and b l o o d f l o w d i s t r i b u t i o n and 2) i n v e s t i g a t e the e f f e c t s o f t h e s e drugs on c a p a c i t a n c e v e s s e l s . 1.8.1 C a l c i u m a n t a g o n i s t e f f e c t s on s y s t e m i c hemodynamics and blood f l o w d i s t r i b u t i o n o f the 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 r a t The i n i t i a l s e r i e s o f experiments were d e s i g n e d t o determine the e f f e c t s o f t h r e e c a l c i u m a n t a g o n i s t s , v e r a p a m i l , n i f e d i p i n e and f l u n a r i z i n e , on s y s t e m i c hemodynamics, ECG and blood f l o w d i s t r i b u t i o n o f the 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 r a t u s i n g t h e r a d i o l a b e l e d m i c r o s p h e r e t e c h n i - que. Though s e v e r a l s t u d i e s have been undertaken t o determine the e f f e c t s o f v a r i o u s c a l c i u m a n t a g o n i s t s on s y s t e m i c hemodynamics and b l o o d f l o w d i s t r i b u t i o n i n c o n s c i o u s r a t s ( F l a i m and Z e l i s 1982; Kanda and F l a i m 1984; D r e x l e r e t a l . 1985; F l a i m e t a l . 1986), a n e s t h e t i z e d r a t s ( G u l a t i et a l . 1983), open-chest a n e s t h e t i z e d c a t s (Hof e t a l . 1982; Hof 1983; Hof 1984; Hof e t a l . 1985) and a n e s t h e t i z e d r a b b i t s (Hof 1985), no s t u d y has y e t compared the c a r d i o v a s c u l a r e f f e c t s o f r e p r e s e n t a t i v e drugs from the t h r e e s u b c l a s s e s i n the same p r e p a r a t i o n . Spedding.(1982) used r e p r e s e n t a - t i v e drugs from the t h r e e s u b c l a s s e s t o determine t h e i r e l e c t r o c a r d i o g r a p h i c e f f e c t s i n the p i t h e d r a t p r e p a r a t i o n . The e f f e c t s o f a h i g h and a low dose o f n i f e d i p i n e ( c l a s s I ) , v e r a p a m i l ( c l a s s I I ) and f l u n a r i z i n e ( c l a s s I I I ) on WAITE, R.P. 27 mean a r t e r i a l p r e s s u r e (MAP), h e a r t r a t e (HR), l e f t v e n t r i c u l a r s y s t o l i c p r e s s u r e (LVP), c a r d i a c c o n t r a c t i l i t y ( d P / d t ) , ECG, c a r d i a c o u t p u t (CO) and blood f l o w d i s t r i b u t i o n were i n v e s t i g a t e d i n 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 r a t s . C a r d i a c o u t p u t and the d i s t r i b u t i o n o f blood f l o w were determined by the m i c r o s p h e r e t e c h n i q u e (Pang 1983a; Pang 1983b). 1.8.2 Cal c i u m a n t a g o n i s t a c t i o n s on venous tone o f the c o n s c i o u s r a t C a r d i a c o u t p u t i s c o n t r o l l e d by c a r d i a c and v a s c u l a r f a c t o r s i n c l u d i n g h e a r t r a t e , c a r d i a c c o n t r a c t i l i t y , b l o od volume, v a s c u l a r c ompliances and v a s c u l a r r e s i s t a n c e s (Greenway 1982). An i n c r e a s e o f venous tone alone can i n c r e a s e venous r e t u r n and t h e r e b y i n c r e a s e c a r d i a c o u t p u t . V a r i o u s i n v e s t - i g a t o r s have determined t h a t c a r d i a c o u t p u t i s i n c r e a s e d o r m a i n t a i n e d f o l l o w i n g c a l c i u m a n t a g o n i s t a d m i n i s t r a t i o n i n p a t i e n t s , w i t h h y p e r t e n s i o n ( E l l i o t t 1987), c o n g e s t i v e h e a r t f a i l u r e (Matsumoto et a l . 1980) and angina p e c t o r i s (Soward e t a l . 1985). In c o n s c i o u s r a t s ( F l a i m and Z e l i s 1982; Kanda and F l a i m 1984; D r e x l e r e t a l . 1985a), open c h e s t a n e s t h e t i z e d c a t s (Hof e t a l . 1982; Hof 1983; Hof 1984), a n e s t h e t i z e d r a b b i t s (Hof 1985) and c o n s c i o u s dogs (Gross e t a l . 1979) c a l c i u m a n t a g o n i s t s induce s i m i l a r i n c r e a s e s i n c a r d i a c o u t p u t . Furthermore, c a l c i u m a n t a g o n i s t s w i t h i n v i v o c a r d i o d e p r e s s i v e a c t i o n s , e.g. ve r a p a m i l and d i l t i a z e m , have been shown t o i n c r e a s e c a r d i a c output (Hof 1983). The purpose o f t h i s s t u d y was t h e r e f o r e t o determine t he e f f e c t o f n i f e d i p i n e , v e r a p a m i l and f l u n a r i z i n e on t o t a l body venous tone i n the c o n s c i o u s r a t . Venous tone was measured u s i n g mean c i r c u l a t o r y f i l l i n g p r e s s u r e (MCFP) (Yammamoto e t a l . 1980; Pang and T a b r i z c h i 1985). MCFP i s the p r e s s u r e t h a t would o c c u r t h r o u g h o u t t he c i r c u l a t i o n i f the c i r c u l a t i o n was i n s t a n t a n e o u s l y a r r e s t e d and a l l p r e s - s u r e s were brought t o an e q u i l i b r i u m (Guyton 1973). T h i s measure was shown to be r e l a t e d t o c a r d i a c o u t p u t (Guyton 1955; Guyton 1973) and p r o v i d i n g t h a t t he bl o o d volume remains c o n s t a n t an i n c r e a s e i n MCFP i n d i c a t e s an WAITE, R.P. 28 i n c r e a s e i n t h e t o t a l body venous tone ( G r o d i n s 1959). The r o l e o f the autonomic nervous system i n the e f f e c t of v e r a p a m i l on MCFP was a l s o determined by use o f the g a n g l i o n b l o c k e r hexamethonium. WAITE, R.P. 29 2. MATERIALS AND METHODS The a c t i o n s of the c a l c i u m a n t a g o n i s t s on s y s t e m i c hemodynamics, ECG and b l o o d f l o w d i s t r i b u t i o n were i n v e s t i g a t e d i n the 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 r a t p r e p a r a t i o n u s i n g r a d i o a c t i v e l y l a b e l l e d m i c r o s p h e r e s w h i l e t h e i r e f f e c t on venous tone was determined i n the c o n s c i o u s r a t p r e p a r a t i o n . The s u r g i c a l p r e p a r a t i o n s and e x p e r i m e n t a l d e s i g n s used i n the two s t u d i e s were as f o l l o w s . 2.1 S u r g i c a l p r e p a r a t i o n s 2.1.1 M i c r o s p h e r e s t u d i e s Male Sprague-Dawley r a t s (260-410 g, C h a r l e s R i v e r Canada) were anes- t h e t i z e d w i t h sodium p e n t o b a r b i t a l (60 mg/kg) and s u b j e c t e d to c a n n u l a t i o n s (PE 50) o f the r i g h t i l i a c a r t e r y , f o r the measurement o f MAP (Grass P o l y - graph, Model 79D, Mass.) by a p r e s s u r e t r a n s d u c e r (P231D, Gould. Statham, C a l i f . ) , t he r i g h t f emoral v e i n f o r the i n f u s i o n o f drug and the l e f t i l i a c a r t e r y f o r t h e removal o f the r e f e r e n c e blood sample. Cannulae (PE 50) f i l l e d w i t h h e p a r i n i z e d s a l i n e (25 IU/ml) were i n s e r t e d i n t o the l e f t v e n t r i c l e v i a the r i g h t common c a r o t i d a r t e r y f o r the i n j e c t i o n o f m i c r o - spheres and measurement o f LVP. HR was determined e l e c t r o n i c a l l y from the u p s t r o k e o f t h e a r t e r i a l p u l s e p r e s s u r e u s i n g a tachograph ( G r a s s , Model 7DAG). DP/dt was determined e l e c t r o n i c a l l y from the LVP u s i n g a p o l y g r a p h d i f f e r e n t i a t e r ( G r a s s , Model 7P20C). An ECG t r a c e was o b t a i n e d u s i n g Grass EB2 subdermal e l e c t r o d e s p l a c e d on the r i g h t and l e f t f o r e l i m b s and the r i g h t h i n d l e g (Lead I) and r e c o r d e d on a Grass p o l y g r a p h (Model 79D). From the ECG r e c o r d i n g s , P-R and QRS i n t e r v a l s were measured a c c o r d i n g t o the method of Budden e t a l . (1980). 2.1.2 Mean c i r c u l a t o r y f i l l i n g p r e s s u r e (MCFP) s t u d i e s MCFP i n c o n s c i o u s r a t s was determined by the method of Yamamoto et a l . WAITE, R.P. 30 (1980). Male Sprague-Dawley r a t s (300-400 g, C h a r l e s R i v e r , Canada) were a n e s t h e t i z e d w i t h h a l o t h a n e ( 5 % f o r i n d u c t i o n , 1.5% f o r maintenance) and s u b j e c t e d t o c a n n u l a t i o n s o f the i l i a c a r t e r y f o r the measurement o f a r t e r - i a T p r e s s u r e by a p r e s s u r e t r a n s d u c e r (P23D8, Gould Statham, CA, USA), t h e femoral v e i n f o r the i n f u s i o n o f drugs and the i n f e r i o r vena cava v i a t h e femoral v e i n f o r the measurement o f c e n t r a l venous p r e s s u r e by a p r e s s u r e t r a n s d u c e r (P23DB, Gould Statham, CA). A s a l i n e - f i l l e d b a l l o o n - t i p p e d c a t h e t e r was i n s e r t e d i n t o the r i g h t a t r i u m through the r i g h t e x t e r n a l j u g u l a r v e i n . The p r o p e r p o s i t i o n o f t h e b a l l o o n was t e s t e d by the i n f l a - t i o n of t h e b a l l o o n t o s t o p the c i r c u l a t i o n c o m p l e t e l y , which caused a s i m u l t a n e o u s d e c r e a s e i n mean a r t e r i a l p r e s s u r e (MAP), t o l e s s than 25 mmHg, and an i n c r e a s e i n venous p r e s s u r e . A l l c a n n u l a e were f i l l e d w i t h h e p a r i n - i z e d s a l i n e (25 IU/ml) and t u n n e l e d s u b c u t a n e o u s l y t o t h e back o f the neck, e x t e r i o r i z e d and s e c u r e d . The r a t s were all o w e d at l e a s t 12 hr t o r e c o v e r from s u r g e r y b e f o r e f u r t h e r use. Heart r a t e (HR) was determined e l e c t r o n i - c a l l y from the u p s t r o k e o f the a r t e r i a l p u l s e p r e s s u r e u s i n g a t a c h o g r a p h ( G r a s s , Model 7P20C). 2.2 M i c r o s p h e r e s used i n the blood f l o w d i s t r i b u t i o n s t u d i e s CO and the d i s t r i b u t i o n of blood f l o w were determined by the r e f e r e n c e sample method ( M a l i k e t a l . 1976 ) u s i n g r a d i o a c t i v e m i c r o s p h e r e s , l a b e l l e d w i t h e i t h e r 5 7 C o o r 1 1 3 S n (15 m diameter, New England N u c l e a r ) . Blood was withdrawn at 0.35 ml/min w i t h a withdrawal pump (Harvard Apparatus) from the i l i a c a r t e r i a l c a n n u l a i n t o a h e p a r i n i z e d s y r i n g e f o r 1.5 min. Ten sec a f t e r t h e s t a r t o f blood w i t h d r a w a l , a 150 u l sample o f a v i g o r o u s l y - v o r - texed p r e c o u n t e d m i c r o s p h e r e s u s p e n s i o n [ c o n t a i n i n g 20,000-30,000 m i c r o s - pheres i n F i c o l l 70 (10%) and Tween 80 (0.05%) was i n j e c t e d and f l u s h e d (150 y l s a l i n e ) o v e r 10 sec i n t o the l e f t v e n t r i c l e . To a v o i d v a r i a t i o n s i n the WAITE, R.P. 31 d i s t r i b u t i o n o f the m i c r o s p h e r e s l a b e l l e d w i t h e i t h e r ^ C o o r ** 3Sn h a l f 57 o f t he experiments i n each group were f i r s t i n j e c t e d . w i t h C o - l a b e l l e d 113 f o l l o w e d by S n - l a b e l l e d m i c r o s p h e r e s and the o r d e r of the i n j e c t i o n was r e v e r s e d i n t h e second h a l f o f the experiment. Where measurement o f blood f l o w i n the l e f t and r i g h t k i d n e y s d i f f e r e d by more than 20%, i t was assumed t h a t t he m i c r o s p h e r e s were i n a d e q u a t e l y mixed and the experiment was r e j e c t e d . Experiments were a l s o r e j e c t e d i f the c a l c u l a t e d c a r d i a c o u t p u t s f o r t h e two m i c r o s p h e r e a d m i n i s t r a t i o n s were v e r y d i f f e r e n t , as i t was assumed t h a t c l o t f o r m a t i o n i n the i l i a c a r t e r i a l c a n n u l a had i m p a i r e d the withdrawal o f t h e r e f e r e n c e sample. Whole o r g a n s , e x c e p t f o r muscle and s k i n (30 g e a c h ) , were e x c i s e d , weighed and loaded i n t o v i a l s f o r c o u n t i n g . Blood samples, t i s s u e samples, t e s t tubes and s y r i n g e s used f o r the i n j e c - t i o n of m i c r o s p h e r e s and the c o l l e c t i o n o f blood were counted f o r r a d i o a c t - i v i t y by a S e a r l e 1185 s e r i e s dual channel a u t o m a t i c gamma c o u n t e r w i t h a 3 i n c h Nal c r y s t a l at energy s e t t i n g s o f 80-160 kev and 330-480 kev f o r Co and Sn, r e s p e c t i v e l y . At t h e s e energy s e t t i n g s the s p i l l o v e r o f 5 7 C o i n t o t h e ** 3Sn channel was n e g l i g i b l e (0.03%) and t h e r e f o r e no s p i l l o v e r c o r r e c t i o n was made. The s p i l l o v e r o f "^ 3Sn i n t o t h e 5 7 C o 57 chan n e l was 16%. C o r r e c t i o n o f Co counts was done by s u b t r a c t i n g ^ 3 S n s p i l l o v e r from ^ C o c o u n t s . 2.3 E x p e r i m e n t a l p r o t o c o l 2.3.1 E f f e c t o f v e r a p a m i l , n i f e d i p i n e and f l u n a r i z i n e on hemodynamics and blood f l o w d i s t r i b u t i o n of the 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 r a t Experiments were performed a c c o r d i n g t o d o u b l e - b l i n d and random d e s i g n s . P r e l i m i n a r y experiments were conducted t o s e l e c t a low and high dose o f each drug c a p a b l e o f c a u s i n g d e c r e a s e s i n MAP by 10 and 20 mm Hg, as compared t o c o n t r o l animals t r e a t e d w i t h t h e v e h i c l e . A l l drugs were d i s - s o l v e d i n the same v e h i c l e ( 3 0 % e t h a n o l , 0.014% t a r t a r i c a c i d ; i n d i s t i l l e d WAITE, R.P. 32 water) so t h a t o n l y one c o n t r o l group was n e c e s s a r y and t o s i m p l i f y t h e b l i n d and random d e s i g n . Drug groups were d e s i g n a t e d , A = v e h i c l e , B = v e r a p a m i l 43 ug/kg/min, C = ve r a p a m i l 83 ug/kg/min, D = n i f e d i p i n e 12 ug/kg/min, E = n i f e d i p i n e 36 ug/kg/min, F = f l u n a r i z i n e 174 ug/kg/min, G = f l u n a r i z i n e 275 ug/kg/min, and randomized by l i n e i n an e i g h t by seven b l o c k which was c o n c e a l e d from t he person p e r f o r m i n g the ex p e r i m e n t s . Stock s o l u t i o n s o f drug s , SI = v e h i c l e , S2 = ve r a p a m i l 1 mg/ml, S3 = n i f e d i p i n e 0.3 mg/ml, S4 = f l u n a r i z i n e 2 mg/ml, were made up and p r o t e c t e d from l i g h t at a l l t i m e s . S o l u t i o n s were drawn up i n t o s y r i n g e s p r o t e c t e d from t he l i g h t by aluminum f o i l . A l l ca n n u l a e t h r o u g h which t he drug was t o pass were p a i n t e d b l a c k t o p r o t e c t t he drug from t he l i g h t . A f t e r s u r g i c a l p r e p a r a t i o n s , t he r a t s were a l l o w e d 30 min t o e q u i l i b r a t e b e f o r e drug i n f u s i o n was commenced. A f t e r i n j e c t i o n s o f the f i r s t s e t o f m i c r o s p h e r e s , drugs o r v e h i c l e were i n f u s e d a t 0.07 ml/min f o r 12 min. At t h e end o f the i n f u s i o n s , t h e second s e t o f m i c r o s p h e r e s was g i v e n . A f t e r w a r d s , t he r a t s were k i l l e d by an i n j e c t i o n of KCL i . v . 2.3.2 E f f e c t o f v e r a p a m i l , n i f e d i p i n e and f l u n a r i z i n e on MCFP o f the c o n s c i o u s r a t MCFP measurements were made a f t e r t e m p o r a r i l y s t o p p i n g the c i r c u l a t i o n by means o f i n f l a t i n g t h e b a l l o o n p r e v i o u s l y i n s e r t e d i n t o t h e r i g h t a t r i u m . W i t h i n 5 s f o l l o w i n g i n f l a t i o n o f the b a l l o o n w i t h s a l i n e , MAP de c r e a s e d and c e n t r a l venous p r e s s u r e i n c r e a s e d s i m u l t a n e o u s l y t o a p l a t e a u . C e n t r a l venous p r e s s u r e measured w i t h i n 5 s o f c i r c u l a t i o n a r r e s t was r e f e r r e d t o as venous p l a t e a u p r e s s u r e (VPP). MAP, HR and VPP were measured a t the onset o f the experiment and a t the p l a t e a u phase o f response t o each dose o f d r u g . I n d i v i d u a l dose-response c u r v e s (MAP, HR, MCFP) f o r n i f e d i p i n e , v e r a p a m i l and f l u n a r i z i n e were c o n s t r u c t e d and compared t o t h e i r r e s p e c t i v e v e h i c l e c o n t r o l s . Rats were d i v i d e d i n t o seven groups w i t h n = 6 WAITE, R.P. 33 i n each group: e t h a n o l , n i f e d i p i n e , s a l i n e , v e r a p a m i l , t a r t a r i c a c i d , _o f l u n a r i z i n e and a time c o n t r o l group. Verapamil (5.8 x 10 t o -7 -3 - 2 8.5 x 10 mol/kg/min) and s a l i n e (2 x 10 t o 3 x 10 ml/min) were i n f u s e d f o r 10 minutes, w h i l e n i f e d i p i n e (1.1 x 10~° t o 4.6 x 10"' mol/kg/min), e t h a n o l (30% e t h a n o l i n d i s t i l l e d water, 8 x 10"^ t o -2 ' -7 -6 3 x 10 ml/min), f l u n a r i z i n e (1.6 x 10 t o 1.3 x 10 mol/kg/min) and t a r t a r i c a c i d (0.02% i n d i s t i l l e d water, 9 x 1 0 - 3 t o 7 x 1 0 - 2 ml/min) were i n f u s e d f o r 15 minutes. N i f e d i p i n e was p r o t e c t e d from t h e l i g h t at a l l times d u r i n g d i s s o l u t i o n and was drawn up i n t o a s y r i n g e wrapped i n aluminum f o i l . A l l ca n n u l a e used f o r t h e i n f u s i o n o f n i f e d i p i n e were p a i n t e d b l a c k . MCFP measurements were made a t t h e end o f each i n f u s i o n p e r i o d . I n f u s i o n s were stopped f o r 15 min between doses t o a l l o w MAP t o r e c o v e r t o pr e d r u g l e v e l s . In the time c o n t r o l group, MCFP measurements were made at time i n t e r v a l s c o r r e s p o n d i n g w i t h t h o s e made f o r t h e drug groups ( o n s e t o f experiment, 15 min a f t e r o n s e t and e v e r y 30min t h e r e a f t e r f o r 2.5 hr) t o a s s e s s t he a f f e c t o f time on the MCFP o f t h e c o n s c i o u s r a t . 2.3.3 R o l e o f the autonomic nervous system on MCFP d u r i n g v e r a p a m i l a d m i n i s t r a t i o n The r o l e of the autonomic nervous system i n the maintenance o f MCFP i n r a t s t r e a t e d w i t h v e r a p a m i l was a s c e r t a i n e d by the use o f two a d d i t i o n a l groups of r a t s (n = 6 i n each g r o u p ) : hexamethonium; hexamethonium + v e r a p a m i l . In both groups, hexamethonium was c o n t i n u o u s l y i n f u s e d v i a the c e n t r a l venous c a n n u l a at 0.15 mg/kg/min f o r t h e d u r a t i o n o f the experiment at an i n f u s i o n r a t e o f 0.05 ml/hr. The i n f u s i o n o f hexamethonium was t e m p o r a r i l y stopped d u r i n g t he measurement o f c e n t r a l venous p r e s s u r e . Verapamil was i n f u s e d at the same dose-regimen as p r e v i o u s l y d e s c r i b e d , a f t e r s u f f i c i e n t b l o c k a d e o f g a n g l i o n i c t r a n s m i s s i o n had been o b t a i n e d , one hr f o l l o w i n g t h e s t a r t o f t h e hexamethonium i n f u s i o n . MCFP was determined WAITE, R.P. 34 p r i o r t o hexamethonium a d m i n i s t r a t i o n , a f t e r 1 hr e q u i l i b r a t i o n w i t h hexa- methonium and at time i n t e r v a l s d u r i n g t he i n f u s i o n o f ve r a p a m i l o r hexa- methonium as d e s c r i b e d . In each r a t o f the hexamethonium c o n t r o l group, r e f l e x HR resp o n s e s t o the a d m i n i s t r a t i o n of a b o l u s i . v . dose o f a c e t y l c h o - l i n e (2 ug) was used t o i n d i c a t e t h e e f f e c t i v e n e s s o f g a n g l i o n i c b l o c k a d e . In a l l c a s e s r e f l e x t a c h y c a r d i a was reduced by at l e a s t 50.% t h r o u g h o u t t he c o u r s e o f the experiment. 2.4 Drugs A l l s t o c k drug s o l u t i o n s f o r the m i c r o s p h e r e s t u d i e s were made up f r e s h weekly. On the day o f the experiment, a p p r o p r i a t e drug d i l u t i o n s from the s t o c k s o l u t i o n s were made up by a person t h a t wasn't p e r f o r m i n g t he ex p e r i m e n t s . Verapamil HCl ( K n o l l Ag., Ludwigshafen, Germany), n i f e d i p i n e (Bayer, L e v e r k u s e n , Germany) and f l u n a r i z i n e d i HCl (Sigma Chemical Co., S t . L o u i s ) were d i s s o l v e d i n 0.014% t a r t a r i c a c i d and 30% e t h a n o l . M i c r o s p h e r e s were suspended i n F i c o l l (Pharmacia F i n e Chemicals AB,. Sweden) and Tween 80. F o r the MCFP ex p e r i m e n t s , drug s o l u t i o n s were p r e p a r e d d a i l y . Verapamil HCl ( K n o l l Ag., Ludwigshafen, Germany), hexamethonium (K K L a b o r a t o r i e s Inc., P l a i n v i e w N.Y.) and a c e t y l c h o l i n e (Sigma Chemical Co., S t . L o u i s ) were d i s s o l v e d i n normal s a l i n e , f l u n a r i z i n e d i HCl (Sigma Chemical Co., S t . L o u i s ) was d i s s o l v e d i n t a r t a r i c a c i d ( 0 . 0 2 % i n d i s t i l l e d water) and n i f e d i p i n e (Bayer, Leverkusen, Germany) was d i s s o l v e d i n e t h a n o l (30% i n d i s t i l l e d w a t e r ) . 2.5 C a l c u l a t i o n s T o t a l p e r i p h e r a l r e s i s t a n c e (TPR) was c a l c u l a t e d by d i v i d i n g MAP (mmHg) by CO (ml/min). CO and BF were c a l c u l a t e d as f o l l o w s : CO (ml/min) = Rate of withdrawal o f b l o o d (ml/min) x t o t a l i n j e c t e d cpm cpm i n withdrawn b l o o d WAITE, R.P. 35 T i s s u e BF (ml/min) = Rate o f withdrawal o f b l o o d (ml/min) x t i s s u e cpm cpm i n withdrawn b l o o d T o t a l amount o f r a d i o a c t i v i t y (cpm) i n j e c t e d was o b t a i n e d by s u b t r a c t i n g t h e amount o f r a d i o a c t i v i t y l e f t i n 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 s y r i n g e from the amount o f r a d i o a c t i v i t y o r i g i n a l l y p r e s e n t i n t h e t u b e . R a d i o a c t i v i t y (cpm) i n b l o o d was o b t a i n e d by adding the amount of r a d i o a c t i v i t y i n the b l o o d sample t o t h a t i n the c a n n u l a and s y r i n g e used f o r c o l l e c t i n g b l o o d . T i s s u e conductance was c a l c u l a t e d by d i v i d i n g b l o o d f l o w by MAP. S t r o k e volume (SV) was determined by d i v i d i n g CO by HR. MCFP was c a l c u l a t e d u s i n g t h e e q u a t i o n o f Samar and Coleman (1978) and a v a l u e o f 1/60 f o r the a r t e r i a l - t o - v e n o u s c o m p l i a n c e r a t i o ( 1 8 ) . MCFP = VPP + 1/60 (FAP - VPP) FAP r e p r e s e n t s the f i n a l a r t e r i a l p r e s s u r e (mmHg) o b t a i n e d w i t h i n 5 s f o l l o w i n g c i r c u l a t o r y a r r e s t . 2.6 S t a t i s t i c a l a n a l y s i s 2.6.1 M i c r o s p h e r e S t u d i e s A n a l y s i s o f v a r i a n c e (ANOVA) w i t h r e p e a t e d measures was used t o compare hemodynamic, ECG and blood f l o w d a t a o b t a i n e d d u r i n g the f i r s t and second i n j e c t i o n s o f the m i c r o s p h e r e s w h i l e ANOVA, complete random d e s i g n , was used t o compare d a t a between d i f f e r e n t groups o f r a t s . To o b t a i n homo- g e n e i t y o f v a r i a n c e s , d a t a o f b l o o d f l o w and conductance changes were l o g a r i t h m i c a l l y - t r a n s f o r m e d p r i o r t o a n a l y s i s . Duncan's m u l t i p l e range t e s t was used t o compare group means. In a l l c a s e s , a p r o b a b i l i t y o f e r r o r o f l e s s than 0.05 was p r e s e l e c t e d 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 ce. R e s u l t s are p r e s e n t e d as means * SEM. WAITE, R.P. 36 2.6.2 MCFP S t u d i e s Data were a n a l y z e d by a n a l y s i s o f v a n a n c e / c o v a r i a n c e . For m u l t i p l e comparisons o f d a t a , Duncan's m u l t i p l e range t e s t was used t o compare group means. In a l l c a s e s a p r o b a b i l i t y o f e r r o r o f l e s s than 0.05 was p r e s e l e c t e d 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 . WAITE, R.P. 37 3. RESULTS R e s u l t s o b t a i n e d from the m i c r o s p h e r e s t u d i e s i n c l u d e the e f f e c t s o f c a l c i u m a n t a g o n i s t s on s y s t e m i c hemodynamics and ECG, blood f l o w d i s t r i b u - t i o n and t i s s u e conductance. MCFP s t u d i e s determined the e f f e c t of v e r a p a - m i l , n i f e d i p i n e and f l u n a r i z i n e on venous tone o f t h e r a t as w e l l as the r o l e of the autonomic nervous system i n t h e venous response t o v e r a p a m i l . 3.1 C a l c i u m a n t a g o n i s t e f f e c t s on s y s t e m i c hemodynamics and ECG T a b l e 2 g i v e s the p r e t r e a t m e n t v a l u e s f o r s y s t e m i c hemodynamic and ECG measurements. E f f e c t s o f t h e v e h i c l e and c a l c i u m a n t a g o n i s t s on t h e s e v a r i - a b l e s are p r e s e n t e d as p e r c e n t change from p r e t r e a t m e n t v a l u e s i n F i g . 1. I n f u s i o n s o f t h e v e h i c l e and a l l doses of the c a l c i u m a n t a g o n i s t s caused s i g n i f i c a n t d e c r e a s e s o f MAP compared w i t h p r e t r e a t m e n t v a l u e s . The d e c r e a s e s i n MAP produced by both doses o f v e r a p a m i l and the h i g h doses o f n i f e d i p i n e and f l u n a r i z i n e were s i g n i f i c a n t l y g r e a t e r than t h a t by the v e h i c l e . CO was s l i g h t l y i n c r e a s e d by t h e v e h i c l e and a l l doses o f the c a l c i u m a n t a g o n i s t s but the i n c r e a s e was o n l y s a t i s t i c a l l y s i g n i f i c a n t f o r t h e low doses o f n i f e d i p i n e and f l u n a r i z i n e compared w i t h p r e t r e a t m e n t v a l u e s . The i n c r e a s e i n CO by the low doses o f n i f e d i p i n e and f l u n a r i z i n e were not d i f f e r e n t from t h a t o f v e h i c l e - t r e a t e d r a t s . TPR was s i g n i f i c a n t l y d e c r e a s e d by a l l doses of c a l c i u m a n t a g o n i s t s but not the v e h i c l e . However, the d e c r e a s e s of TPR of r a t s t r e a t e d w i t h a l l doses o f the c a l c i u m antagon- i s t s were not s t a t i s t i c a l l y s i g n i f i c a n t when compared w i t h the v e h i c l e - t r e a t e d r a t s . The v e h i c l e and a l l doses o f c a l c i u m a n t a g o n i s t s s i g n i f i c a n t - l y d e c r e a s e d LVP. The d e c r e a s e i n LVP induced by both doses o f v e r a p a m i l and the h i g h dose o f n i f e d i p i n e were s i g n i f i c a n t l y g r e a t e r than t h a t induced by v e h i c l e . DP/dt was s i g n i f i c a n t l y d e c r e a s e d by a l l doses o f the c a l c i u m a n t a g o n i s t s compared w i t h p r e t r e a t m e n t v a l u e s , but not the v e h i c l e . WAITE, R.P. 38 TABLE 2. P r e t r e a t m e n t v a l u e s of s y s t e m i c hemodynamic and ECG v a r i a b l e s f o r al1 r a t groups A B C D E F G MAP 116*6 113*6 110*3 118*5 121*4 124*6 114*2 CO 79*4 77*6 90*5 81*5 102*14 92*10 89*8 TPR 1.5*0.1 1.5*0.1 1.3*0.1 1.5*0.1 1.3*.02 1.4*0.1 1.4*0.1 LVP 149*6 138*7 144*7 148*6 153*4 154*7 146*4 dP/dt 8530*580 7560*480 8000*400 7880*280 8530*390 8470*610 7880*340 HR 371*17 344*17 366*11 351*17 389*22 401*21 388*12 SV 0.22*0.02 0.23*0.02 0.25*0.01 0.23*0.01 0.27*0.04 0.23*0.02 0.23*0.02 PR i n t . 49*2 49*2 46*2 51*2 46*1 47*2 49*1 , QRS i n t . 34*1 34*1 36*1 38*1 33*1 34*1 33*. 9 MAP = mean a r t e r i a l p r e s s u r e (mmHg); CO = c a r d i a c o u t p u t (ml/min.); TPR = t o t a l p e r i p h e r a l r e s i s t a n c e (mmHg/ml/min); LVP = l e f t v e n t r i c u l a r p r e s s u r e (mmHg); dP/dt = c o n t r a c t i l i t y (mmHg/sec); HR = h e a r t r a t e ( b e a t s / m i n . ) ; SV = s t r o k e volume ( m l / b e a t ) ; PR i n t e r v a l (msec); QRS i n t e r v a l (msec); A = v e h i c l e c o n t r o l ; B = v e r a p a m i l , 43 ug/kg/min; C = v e r a p a m i l , 83 ug/kg/min; D = n i f e d i p i n e , 12 ug/kg/min; E = n i f e d i p i n e , 36 ug/kg/min; F = f l u n a r i z i n e , 174 ug/kg/min; G = f l u n a r i z i n e , 275 ug/kg/min. A l l v a l u e s r e p r e s e n t t he mean * SEM; n = 8. WAITE, R.P. -40 % Change from Pretreatment -20 0 20 40 MAP CO TPR LVP P S •dP/dt HR SV PR-Interval . . V N *5 F C V & N F FIG 1. E f f e c t s o f a low dose ( c r o s s e d column) and a hi g h dose ( s o l i d column) o f v e r a p a m i l ( V ) , n i f e d i p i n e (N), f l u n a r i z i n e (F) and v e h i c l e (C, open column) on hemodynamics and ECG i n 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 r a t s . Each column r e p r e s e n t s t h e mean ± SEM; n = 3. See Tab l e 1 f o r a b b r e v i a t i o n s and u n i t s . Denotes drug e f f e c t s which are s t a t i s t i c a l l y s i g n i f i c a n t from v e h i c l e . WAITE, R.P. 40 Both doses o f v e r a p a m i l and the h i g h dose o f n i f e d i p i n e caused s i g n i f i c a n t l y g r e a t e r d e c r e a s e s of dP/dt than d i d the v e h i c l e . HR was d e c r e a s e d i n a dose-dependent manner by both v e r a p a m i l and f l u n a r i z i n e , i n c r e a s e d by the low dose o f n i f e d i p i n e , and not changed by v e h i c l e o r t h e h i g h dose o f n i f e d i p i n e compared w i t h p r e t r e a t m e n t v a l u e s . The changes i n HR i n r a t s t r e a t e d w i t h verapamil and f l u n a r i z i n e were s i g n i - f i c a n t l y d i f f e r e n t from v e h i c l e - t r e a t e d r a t s . SV was i n c r e a s e d by t h e low doses o f v e r a p a m i l and f l u n a r i z i n e and s l i g h t l y i n c r e a s e d by v e h i c l e and o t h e r doses o f t h e c a l c i u m a n t a g o n i s t s . None o f the i n c r e a s e s of p r e t r e a t - ment SV by the c a l c i u m a n t a g o n i s t s were s i g n i f i c a n t l y d i f f e r e n t from t h a t i n v e h i c l e - t r e a t e d r a t s . The P-R i n t e r v a l was i n c r e a s e d by the h i g h dose o f v e r a p a m i l but not by t h e v e h i c l e o r o t h e r doses o f the c a l c i u m a n t a g o n i s t s . The i n c r e a s e of P-R i n t e r v a l by the h i g h dose of v e r a p a m i l was s t a t i s t i c a l l y s i g n i f i c a n t compared w i t h v e h i c l e - t r e a t e d r a t s . N e i t h e r t h e v e h i c l e nor any doses o f the c a l c i u m a n t a g o n i s t s s i g n i f i c a n t l y a l t e r e d the QRS i n t e r v a l . 3.2 C a l c i u m a n t a g o n i s t e f f e c t s on b l o o d f l o w d i s t r i b u t i o n T a b l e 3 g i v e s p r e t r e a t m e n t v a l u e s of blood f l o w t o v a r i o u s organs i n the d i f f e r e n t groups o f r a t s . The e f f e c t s o f t h e d r u g s , and v e h i c l e , on b l o o d f l o w are shown as p e r c e n t change from p r e t r e a t m e n t blood f l o w i n F i g s . 2 and 3. A l l t h r e e a n t a g o n i s t s caused s i m i l a r changes i n the d i s t r i - b u t i o n o f blood f l o w . Changes i n blood f l o w t o the lungs was i n c r e a s e d by a l l doses o f the c a l c i u m a n t a g o n i s t s compared w i t h v e h i c l e - t r e a t e d r a t s . The v e h i c l e and a l l doses o f c a l c i u m a n t a g o n i s t s produced s i m i l a r i n c r e a s e s i n blood f l o w t o the h e a r t . A l l drugs i n c r e a s e d b l o o d f l o w t o the l i v e r , however, t h e s e changes were s t a t i s t i c a l l y s i g n i f i c a n t o n l y f o r both doses o f n i f e d i p i n e and t h e low dose o f f l u n a r i z i n e . A l l the drugs tended to d e c r e a s e b l o o d f l o w t o the i n t e s t i n e , k i d n e y s , s k i n , s p l e e n and b r a i n . The WAITE, R.P. 41 TABLE 3. P r e t r e a t m e n t v a l u e s o f organ b l o o d f l o w (ml/min) f o r a l l r a t - g r o u p s A B - C D E F G Lungs 1.5±0.3 1.3*0.3 2.1*0.5 1.4*0.3 1.8*0.5 1.5*0.2 1.1*0.2 Heart 4.0*0.4 4.6*0.5 5.2*0.5 4.7*0.5 4.4*0.6 4.7*0.5 4.7*0.3 L i v e r 1.7*0.4 1.9*0.3 2.4*0.3 1.9*0.5 1.9*0.5 2.5*0.3 2.7*0.5 Stomach 1.0*0.1 1.0*0.1 1.2*0.2 1.2*0.2 1.5*0.2 1.5*0.3 1.3*0.2 I n t e s t i n e 10.7*1.1 10.1*1.0 10.9*1.0 10.8*0.6 13.8*1.2 13.1*2.8 11.2*0.8 Cae Col 3.9*0.5 4.3*0.9 4.1*0.4 4.1*0.3 5.1*0.9 4.3*0.5 4.1*0.5 Kidn e y s 15.6*1.2 15.3*1.2 18.5*1.2 15.3*1.0 20.9*2.3 18.2*2.2 19.0*1.9 S p l e e n 1.4*0.3 1.3*0.2 1.6*0.3 1.1*0.1 1.6*0.2 1.4*0.2 1.9*0.4 Muscle 1.5*0.3 1.6*0.1 1.9*0.2 1.6*0.1 1.9*0.3 1.9*0.4 1.8*0.2 S k i n 2.2*0.5 2.2*0.3 2.6*0.4 2.5*0.3 3.3*0.8 2.6*0.5 2.4*0.4 T e s t i s 1.3*0.1 1.3*0.1 1.3*0.1 1.4*0.1 1.6*0.1 1.3*0.2 1.4*0.1 B r a i n 1.3*0.2 1.5*0.2 1.7*0.2 1.4*0.1 1.7*0.2 1.3*0.2 1.5*0.2 A = v e h i c l e c o n t r o l ; B = v e r a p a m i l , 43 yg/kg/min; C = v e r a p a m i l , 83 yg/kg/min; D = n i f e d i p i n e , 12 yg/kg/min; E = n i f e d i p i n e , 36 yg/kg/min; F = f l u n a r i z i n e , 174 yg/kg/min; G = f l u n a r i z i n e , 275 yg/kg/min; Cae Col = caecum + c o l o n . A l l b l o o d f l o w s are c a l c u l a t e d f o r whole organs, except f o r s k i n and muscle which are 30 g each. A l l v a l u e s r e p r e s e n t the mean * SEM; n = 8. WAITE, R.P. % Change from Pretreatment -80 -40 0 40 80 120 160 Lungs Heart Liver Skin Muscle Brain FIG 2. E f f e c t s o f a low dose ( c r o s s e d column) and a hi g h dose ( s o l i d column) o f ve r a p a m i l ( V ) , n i f e d i p i n e (N), f l u n a r i z i n e (F) and v e h i c l e (C, open column) on organ blood f l o w i n 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 r a t s . Each column r e p r e s e n t s blood f l o w (mean ± SFM; n = 8) t o whole o r g a n s , except f o r s k i n (30 g) and muscle (30 g ) . Denotes drug e f f e c t s which are s t a t i s t i c a l l y s i g n i f i c a n t from v e h i c l e . WAITE, R.P. 43 % Change from P r e t r e a t m e n t -40 0 40 80 Stomach I n t e s t i n e Caecum + Colon Kidneys Spleen T e s t i s FIG 3 . E f f e c t s o f a low dose ( c r o s s e d column) and a h i g h dose ( s o l i d column) o f v e r a p a m i l ( V ) , n i f e d i p i n e (N), f l u n a r i z i n e (F) and v e h i c l e (C, open column) on organ b l o o d f l o w i n 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 r a t s . Each column r e p r e s e n t s b l o o d f l o w (mean ± SEM; n = 8 ) t o whole organs. Senotes drug e f f e c t s which are s t a t i s t i c a l l y s i g n i f i c a n t from v e h i c l e . WAITE, R.P. 44 d e c r e a s e s i n blood f l o w to the i n t e s t i n e and s p l e e n were s t a t i s t i c a l l y s i g n i f i c a n t f o r the h i g h doses of v e r a p a m i l and n i f e d i p i n e , and both doses o f f l u n a r i z i n e compared w i t h v e h i c l e - t r e a t e d r a t s . Renal blood f l o w was d e c r e a s e d by h i g h doses o f a l l c a l c i u m a n t a g o n i s t s , s k i n blood f l o w was s i g n i f i c a n t l y d e c r e a s e d by both doses of v e r a p a m i l and the h i g h dose of n i f e d i p i n e and f l u n a r i z i n e , b r a i n b l ood f l o w was d e c r e a s e d by both doses o f v e r a p a m i l and t h e high dose o f f l u n a r i z i n e when compared w i t h the changes i n v e h i c l e - t r e a t e d r a t s . Change i n b l o o d f l o w t o the o t h e r organs were not a f f e c t e d by any drug compared w i t h t h e v e h i c l e . 3.3 C a l c i u m a n t a g o n i s t e f f e c t s on t i s s u e conductance T a b l e 4 g i v e s the p r e t r e a t m e n t v a l u e s of conductance f o r the v a r i o u s organs w h i l e e f f e c t s o f drugs and v e h i c l e are shown i n F i g s . 4 and 5 as p e r c e n t change from p r e t r e a t m e n t conductance. Conductance i n the lungs was i n c r e a s e d by a l l c a l c i u m a n t a g o n i s t s as compared w i t h the v e h i c l e . Conductances i n the l i v e r were s i g n i f i c a n t l y i n c r e a s e d by a l l drugs compared w i t h t h e v e h i c l e except f o r the h i g h dose o f f l u n a r i z i n e . V e h i c l e and c a l c i u m a n t a g o n i s t s caused s i m i l a r i n c r e a s e s i n conductances i n the h e a r t , stomach, muscle, caecum and c o l o n . Heart and muscle conductance i n c r e a s e s tended t o be g r e a t e r f o r the h i g h doses o f the c a l c i u m a n t a g o n i s t s than f o r t h e v e h i c l e . Conductances i n a l l o t h e r organs were not s i g n i f i c a n t l y a f f e c t e d by the c a l c i u m a n t a g o n i s t s , as compared w i t h the v e h i c l e , a l t h o u g h conductances i n t h e i n t e s t i n e , k i d n e y s and s k i n d i d show a tendency to d e c r e a s e compared w i t h the v e h i c l e c o n t r o l . 3.4 C a l c i u m a n t a g o n i s t e f f e c t s on MAP, HR and MCFP Ta b l e 5 g i v e s the c o n t r o l v a l u e s of MAP, HR and MCFP f o r the 9 t r e a t - ment groups. R e s u l t s of the d o s e - r e s p o n s e c u r v e s t u d i e s f o r the c a l c i u m a n t a g o n i s t s and v e h i c l e are p r e s e n t e d as p e r c e n t o f p r e t r e a t m e n t v a l u e s i n F i g s . 6-8. N i f e d i p i n e ( F i g . 6) was found t o d e c r e a s e MAP and i n c r e a s e HR i n WAITE, R.P. 45 TABLE 4. P r e t r e a t m e n t - v a l u e s o f organ conductances (ml/min/mmHg x-1Q~^) f o r a l l r a t - g r o u p s A. B C D E F G. Lungs 1.4±0.3 1.1*0.3 1.9*0.5 1.2*0.2 1.5*0.4 1.1*0.2 0.9*0.2 Heart 3.4*0.2 4.2*0.3 4.8*0.1 4.0*0.4 3.6*0.5 3.7*0.3 4.2*0.3 L i v e r 1.5*0.3 1.7*0.3 2.2*0.4 1.6*0.3 1.6*0.4 2.0*0.2 2.4*0.5 Stomach 0.8*0.1 0.9*0.1 1.1*0.1 1.0*0.1 1.2*0.2 1.2*0.2 1.1*0.2 I n t e s t i n e 9.2*0.9 9.2*1.2 10.1*1.0 9.3*0.6 11.6*1.2 10.5*1.8 9.9*0.8 Cae Col 3.5*0.5 3.8*0.7 3.7*0.3 3.6*0.3 4.2*0.7 3.4*0.3 3.7*0.5 Kidneys 13.6*1.1 13.8*1.2 16.8*1.0 13.2*0.9 17.4*1.8 14.7*1.3 16.8*1.7 Sp l e e n 1.3*0.3 1.0*0.2 1.5*0.3 0.9*0.1 1.3*0.2 1.2*0.1 ' ' 1.7*0.4 Muscle 1.3*0.2 1.5*0.2 1.8*0.2 1.3*0.1 1.6*0.3 1.5*0.3 1.6*0.2 S k i n 1.9*0.4 2.0*0.3 2.4*0.3 2.1*0.2 2.7*0.6 2.0*0.3 2.1*0.2 T e s t i s 1.1*0.1 1.2*0.1 1.2*0.1 1.2*0.1 1.3*0.1 1.0*0.1 1.2*0.1 B r a i n 1.2*0.2 1.3*0.2 1.6*0.1 1.2*0.2 1.4*0.2 1.1*0.2 1.4*0.2 A = v e h i c l e c o n t r o l ; B = v e r a p a m i l , 43 ug/kg/min; C = v e r a p a m i l , 83 ug/kg/min; D = n i f e d i p i n e , 12 ug/kg/min; E = n i f e d i p i n e , 36 ug/kg/min; F = f l u n a r i z i n e , 174 ug/kg/min; G = f l u n a r i z i n e , 275 ug/kg/min; Cae C o l . '= caecum + c o l o n . A l l c o nductances are c a l c u l a t e d f o r whole organs, except f o r s k i n and muscle which are c a l c u l a t e d f o r 30 g o f t i s s u e . A l l v a l u e s are the mean * SEM; n = 8. WAITE, R.P. Lungs Heart L ive r Skin Muscle Brain % Change from Pretreatment •TOO 0 TOO 200 V N F C V N F C V N F ^ V C V N F C V ^ N F TTfTir-1 300 FIG 4. E f f e c t s of a low dose (crossed column) and a high dose ( s o l i d column) of verapamil (V), n i f ed ip ine (N), f l u n a r i z i n e (F) and veh ic le (C, open column) on a r t e r i a l conductance in pentobarb i ta l -anesthet ized r a t s . Each column represents conductance (mean * SEM; n = 8) to whole organs, except for skin (30 g) and muscle (30 g ) . Denotes drug e f f e c t s which are s t a t i s t i c a l l y s i g n i f i c a n t from v e h i c l e . WAITE, R.P % Change from Pretreatment • TOO 0 100 200 Stomach Intesti ne Caecum + Colon Kidneys Spleen Testis C V N F C V N F C V N F C V C V N F F fir FIG 5. Effects of a low dose (crossed column) and a high dose (so l id column) of verapamil (V), n i fedip ine (N), f lunar iz ine ( F ) and vehic le (C, open column) on a r te r i a l conductance in pentobarbital-anesthetized r a t s . Each column represents conductance (mean ± SEM; n = 8) to whole organs. *Denotes drug ef fects which are s t a t i s t i c a l l y s ign i f i can t from veh ic le . WAITE, R.P. TABLE 5 . Basel ine-values of MAP;-HR and-MCFP-for-al l rat-groups .Control values Group MAP HR MCFP I) Ethanol 115 ± 5 387 ± 9 6.1 ± 0.2 II) Nifedipine 109 4 376 ± 17 6.1 ± 0.1 I I I) Sal ine 104 ± 3 373 ± 20 5.5 ± 0.2 IV) Verapami1 105 ± 2 366 ± 12 5.9 ± 0.2 V) Tar tar ic acid 113 ± 4 383 ± 13 5.8 ± 0.2 vi) Flunar iz ine 108 ± 6 393 ± 7 5.9 ± 0.2 VII) Before hexamethonium 114 ± 5 378 ± 13 5.9 0.1 After hexamethonium 103 3 374 ± 11 4.9 ± 0.1 VIII) Before hexamethonium 113 ± 5 388 ± 3 5.7 ± 0.1 After hexamethonium 104 ± 2 383 ± 10 5.1 ± 0.2 MAP (mmHG) = baseline values for mean a r te r ia l pressure; HR (beats/min) = heart r a te ; MCFP (mmHG) = mean c i rcu la to ry f i l l i n g pressure for a l l rat groups. Each group represents the mean ± SEM; n = 6. WAITE, R . P . 49 W A I T E , R.P FIG. 6. D o s e - r e s p o n s e c u r v e s f o r t h e e f f e c t o f n i f e d i p i n e ( • ) a n d a l c o h o l v e h i c l e ( • ) o n mean a r t e r i a l p r e s s u r e ( M A P ) , H e a r t r a t e (HR) a n d mean c i r c u l a t o r y f i l l i n g p r e s s u r e ( M C F P ) r e p r e s e n t e d a s % o f c o n t r o l v a l u e s . E a c h p o i n t r e p r e s e n t s t h e mean ± SEM; n = 6. D a t a i s p l o t t e d t o m a t c h t h e d o s e o f d r u g g i v e n w i t h i t s c o r r e s p o n d i n g v e h i c l e i n f u s i o n r a t e . WAITE, R.P. 51 - 7 . 0 - 6 . 5 -6 .0 Log Dose (mol/Kg/min) WAITE, R.P. FIG. 7. Dose-response c u r v e s f o r . the e f f e c t o f v e r a p a m i l ( • ) and s a l i n e ( • ) on mean a r t e r i a l p r e s s u r e (MAP), h e a r t Rate (HR) and mean c i r c u l a t o r y f i l l i n g p r e s s u r e (MCFP) r e p r e s e n t e d as % o f c o n t r o l v a l u e s . Each p o i n t r e p r e s e n t s the mean ± SEM; n = 6. Data i s p l o t t e d t o match the dose o f drug g i v e n w i t h i t s c o r r e s p o n d i n g v e h i c l e i n f u s i o n r a t e . WAITE, R.P. 53 110 l Log Dose (mol/Kg/min) WAITE, R.P. FIG. 8. Dose response c u r v e s f o r the e f f e c t o f f l u n a r i z i n e ( • ) and t a r t a r i c a c i d ( • ) on mean a r t e r i a l p r e s s u r e (MAP), h e a r t r a t e (HR) and mean c i r c u l a t o r y f i l l i n g p r e s s u r e (MCFP) r e p r e s e n t e d as % o f c o n t r o l v a l u e s . Each p o i n t r e p r e s e n t s t he mean ± SEM; n = 6. Data i s p l o t t e d t o match the dose o f drug g i v e n w i t h i t s c o r r e s p o n d i n g v e h i c l e i n f u s i o n r a t e . WAITE, R.P. 55 a s t a t i s t i c a l l y s i g n i f i c a n t manner compared w i t h e t h a n o l - t r e a t e d r a t s . MCFP was s i g n i f i c a n t l y i n c r e a s e d by n i f e d i p i n e compared w i t h c o n t r o l r a t s . Verapamil ( F i g . 7) was found t o d e c r e a s e both MAP and HR i n a dose dependent manner and i n c r e a s e MCFP compared w i t h t he v e h i c l e c o n t r o l . F l u n a r i z i n e s i g n i f i c a n t l y d e c r e a s e d MAP and HR and i n c r e a s e d MCFP compared w i t h t a r t a r i c a c i d - t r e a t e d r a t s ( F i g . 8 ) . F i g . 9 i l l u s t r a t e s t h e e f f e c t o f time on the MAP, HR and MCFP o f the c o n s c i o u s r a t . HR remains t he same f o r the time c o u r s e o f the experiment w h i l e MAP d e c r e a s e s s l i g h t l y a f t e r 100 min. MCFP was s i g n i f i c a n t l y d e c r e a s e d a f t e r 75 min. The r e d u c t i o n i n MCFP caused by th e v e h i c l e s and i n the time c o n t r o l as a f u n c t i o n o f time a re compared i n F i g . 10. In a l l c a s e s , MCFP i s s i g n i f i c a n t l y reduced a f t e r 75 min. 3.5 Role o f the autonomic nervous system on MCFP d u r i n g v e r a p a m i l a d m i n i s t r a t i o n MAP and MCFP were s i g n i f i c a n t l y d e c r e a s e d by hexamethonium i n both t h e hexamethonium and hexamethonium + ve r a p a m i l groups ( T a b l e 5 ) . These d e c r e a s e s were m a i n t a i n e d f o r the d u r a t i o n o f the expe r i m e n t . HR was not a f f e c t e d by hexamethonium t h r o u g h o u t the c o u r s e o f the experiment. Responses t o ve r a p a m i l o r hexamethonium are p r e s e n t e d as p e r c e n t o f t h e p o s t - e q u i l i b r a t i o n v a l u e w i t h hexamethonium ( F i g . 11). MAP and HR were s i g n i f i c a n t l y d e c r e a s e d by v e r a p a m i l compared w i t h hexamethonium-treated c o n t r o l r a t s . MCFP was not s i g n i f i c a n t l y a l t e r e d by ver a p a m i l compared w i t h t h e hexamethonium-treated r a t s but t h e h i g h e s t dose o f v e r a p a m i l d i d s i g n i f i c a n t l y lower t h e MCFP compared w i t h i t s c o r r e s p o n d - i n g c o n t r o l measurement. WAITE, R.P. o S-+J c o u 4-o 110 -1 100 90 -\ J ° 110 100 -J 90 J J 110 o 100 - u - I 1 1 1 -1 1 1 0 60 120 180 Time (min) FIG. 9. The e f f e c t o f time on mean a r t e r i a l p r e s s u r e (MAP), heart r a t e (HR) and mean c i r c u l a t o r y f i l l i n g p r e s s u r e (MCFP) r e p r e s e n t e d as % o f c o n t r o l v a l u e s . Each p o i n t r e p r e s e n t s the mean * SEM; n = 6. WAITE, R.P. 0 60 120 180 Time (min) FIG. 10. The e f f e c t o f e t h a n o l ( • ), s a l i n e ( • ), t a r t a r i c a c i d ( O ), hexamethonium ( v ) and time ( • ) on mean c i r c u l a t o r y f i l l i n g p r e s s u r e as a f u n c t i o n o f t i m e . Each p o i n t r e p r e s e n t s t he mean ± SEM; n = 6. WAITE, R.P. 58 110 1 -7.0 -6.5 -6.0 Log dose (mol/Kg/min) WAITE, R.P. FIG. 11. Dose r e s p o n s e c u r v e s f o r the e f f e c t o f hexamethonium + v e r a p a m i l ( • ) and hexamethonium ( • ) on t h e mean a r t e r i a l p r e s s u r e (MAP), h e a r t r a t e (HR) and mean c i r c u l a t o r y f i l l i n g p r e s s u r e (MCFP) r e p r e s e n t e d as % o f c o n t r o l v a l u e s a f t e r e q u i l i b r a t i o n w i t h hexamethonium. Each p o i n t r e p r e s e n t s the.mean'* SEM; n = 6. Data i s p l o t t e d t o match the dose o f drug g i v e n w i t h i t s c o r r e s p o n d i n g v e h i c l e i n f u s i o n r a t e . WAITE, R.P. 60 4. DISCUSSION These s t u d i e s were performed t o e v a l u a t e the v a l i d i t y o f Spedding*s c l a s s i f i c a t i o n o f c a l c i u m a n t a g o n i s t s w i t h r e s p e c t to t h e i r e f f e c t on the c a r d i o v a s c u l a r system o f the i n t a c t r a t . My f i n d i n g s w i l l be d i s c u s s e d i n r e l a t i o n t o Spedding's c l a s s i f i c a t i o n scheme and p r e v i o u s s t u d i e s o f c a l c i u m a n t a g o n i s t a c t i o n s . The p r o f i l e o f s y s t e m i c and r e g i o n a l hemodynamic a c t i o n s were s i m i l a r f o r the t h r e e c a l c i u m a n t a g o n i s t s w i t h n i f e d i p i n e b e i n g t h e most p o t e n t , on a weight b a s i s , and f l u n a r i z i n e the l e a s t . D i f f e r e n c e s i n t h e i r p r o f i l e s were most marked i n terms o f t h e i r e f f e c t s on the h e a r t . C a r d i a c c o n t r a c t - i l i t y , as measured by dP/dt, was s l i g h t l y but not s i g n i f i c a n t l y d e c r e a s e d by n i f e d i p i n e and f l u n a r i z i n e and s i g n i f i c a n t l y d e c r e a s e d by v e r a p a m i l . HR was reduced by v e r a p a m i l and f l u n a r i z i n e but i n c r e a s e d by n i f e d i p i n e . S i m i l a r - l y , n i f e d i p i n e and f l u n a r i z i n e had no e f f e c t on the P-R i n t e r v a l w h i l e v e r a - pamil lengthened the P-R i n t e r v a l at the h i g h dose. Thus, at the doses g i v e n , f l u n a r i z i n e had more d e p r e s s a n t e f f e c t on t h e SA than on t h e AV node, ve r a p a m i l a f f e c t e d both w h i l e n i f e d i p i n e a f f e c t e d n e i t h e r . . These e f f e c t s on t h e h e a r t c l e a r l y d i f f e r e n t i a t e t h e t h r e e s u b c l a s s e s o f c a l c i u m a n t a g o n i s t s proposed by Spedding (1985) and a l s o i n d i c a t e t h a t n i f e d i p i n e and f l u n a r i - z i n e are more v a s c u l a r s e l e c t i v e than v e r a p a m i l . S i m i l a r ECG r e s u l t s t o ours were o b t a i n e d i n the p i t h e d r a t p r e p a r a - t i o n u s i n g v e r a p a m i l , d i l t i a z e m , n i f e d i p i n e and c i n n a r i z i n e as r e p r e s e n t a - t i v e drugs from the v a r i o u s s u b c l a s s e s o f c a l c i u m a n t a g o n i s t s (Spedding 1982). O t h e r i n v e s t i g a t o r s have shown t h a t d i h y d r o p y r i d i n e s i n c r e a s e d HR and d e c r e a s e d LVP i n the c o n s c i o u s r a t p r e p a r a t i o n (Kanda and F l a i m 1984; D r e x l e r e t a l . 1985a) w h i l e d i l t i a z e m , a proposed c l a s s 2 compound, dose- d e p e n d e n t l y d e c r e a s e d both HR and LVP ( F l a i m and Z e l i s 1982). F l u n a r i z i n e WAITE, R.P. 61 was shown t o be i n e f f e c t i v e at i n h i b i t i n g the c o n t r a c t i l e f o r c e o f i s o l a t e d c a t p a p i l l a r y muscle (van Neuten et a l . 1978). T h i s i s i n agreement w i t h our i n v i v o r e s u l t s which i n d i c a t e t h a t f l u n a r a z i n e had l i t t l e e f f e c t on m y o c a r d i a l c o n t r a c t i l i t y . In s p i t e of a d e c r e a s e i n c a r d i a c c o n t r a c t i l i t y , as measured by dP/dt, CO and SV were s l i g h t l y i n c r e a s e d by a l l agents a l t h o u g h the i n c r e a s e s were not s t a t i s t i c a l l y s i g n i f i c a n t compared w i t h v e h i c l e - t r e a t e d r a t s . T h i s f i n d i n g i s i n agreement w i t h r e s u l t s u s i n g c o n s c i o u s r a t s which showed t h a t CO and SV were not a l t e r e d s i g n i f i c a n t l y by n i s o l d i p i n e ( D r e x l e r e t a l . 1985a), n i f e d i p i n e (Kanda and F l a i m 1984) o r d i l t i a z e m ( F l a i m and Z e l i s 1982) . There was a tendency f o r CO t o be i n c r e a s e d i n c h l o r a l o s e - a n e s t h e - t i z e d o pen-chest c a t s by PY 108-068, n i c a r d i p i n e , v e r a p a m i l , d i l t i a z e m (Hof 1983) and n i f e d i p i n e (Hof et a l . 1982). In c o n t r a s t t o s y s t e m i c hemodynamics, the t h r e e c a l c i u m a n t a g o n i s t s caused s i m i l a r d i s t r i b u t i o n o f b l o o d f l o w , and a l t e r a t i o n s of v a s c u l a r c o n d u c t a n c e s . Blood f l o w was i n c r e a s e d t o the l u n g s , h e a r t and l i v e r but d e c r e a s e d t o the i n t e s t i n e , k i d n e y s , s k i n , s p l e e n and b r a i n . The i n c r e a s e i n h e p a t i c a r t e r i a l f l o w may be a r e g u l a t o r y phenomenon secondary to a d e c r e a s e of p o r t a l venous f l o w . I t has been shown t h a t a d e c r e a s e i n p o r t a l venous f l o w l e a d s t o an i n c r e a s e i n h e p a t i c a r t e r i a l f l o w such t h a t t o t a l h e p a t i c b l o o d f l o w remains c o n s t a n t ( L a u t t 1980). S i m i l a r i n c r e a s e s i n l i v e r b l o od f l o w have been r e p o r t e d i n c o n s c i o u s r a t s t r e a t e d w i t h n i f e d i - p i n e (Kanda and F l a i m 1984). Blood f l o w t o the h e a r t was i n c r e a s e d , but the i n c r e a s e was not s i g n i f i c a n t l y g r e a t e r than t h a t seen i n the v e h i c l e - t r e a t e d r a t s p o s s i b l y because the l a r g e c o r o n a r y v a s o d i l a t e r e f f e c t of the v e h i c l e had almost m a x i m a l l y d i l a t e d t h e c o r o n a r y a r t e r i e s . O t h e r i n v e s t i g a t o r s have shown t h a t c a l c i u m a n t a g o n i s t s cause an i n c r e a s e i n c o r o n a r y blood f l o w ( F l a i m and Z e l i s 1982; Hof e t a l . 1982; Hof 1983; Hof 1984; Kanda and WAITE, R.P. 62 F l a i m 1984; D r e x l e r e t a l . 1985a; Hof e t a l . 1985). V a r i o u s c a l c i u m a n t a g o n i s t s were found t o have no e f f e c t on r e n a l b l o o d f l o w i n open-chest c h l o r a l o s e - u r e t h a n e - a n e s t h e t i z e d c a t s (Hof e t a l . 1982; Hof 1983) and c o n s c i o u s r a t s ( F l a i m and Z e l i s 1982; Kanda and F l a i m 1984; D r e x l e r e t a l . 1985a). In c o n t r a s t , r e n a l b l o o d f l o w was d e c r e a s e d by the c a l c i u m a n t a g o n i s t PY 108-068 i n 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 r a b b i t s (Hof 1985), by f l u n a r i z i n e i n 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 r a t s ( G u l a t i e t a l . 1983) and by n i m o d i p i n e i n p e n t o b a r b i t o n e - a n e s t h e t i z e d p i g s (Duncker e t a l . 1986). Thus, r e n a l blood f l o w was not a f f e c t e d by the c a l c i u m a n t a g o n i s t s i n c h l o r a l o s e - u r e t h a n e a n e s t h e t i z e d o r c o n s c i o u s a n i m a l s but was d e c r e a s e d i n t h e p r e s e n t s t u d y and i n o t h e r b a r b i t u r a t e a n e s t h e t i z e d a n i m a l s . P o s s i b l y a c o m b i n a t i o n of b a r b i t u r a t e a n e s t h e s i a and c a l c i u m a n t a g o n i s t s h i n d e r t h e a b i l i t y o f the k i d n e y t o a u t o r e g u l a t e i t s blood f l o w . Renal blood f l o w a u t o r e g u l a t i o n i n a n e s t h e t i z e d dogs has been shown t o be reduced by d i l t i a z e m (Ogawa and Ono 1986a), and by v e r a p a m i l (Ogawa and Ono 1986b) at a dose s i m i l a r t o the h i g h dose used i n t h i s e x p e r i m e n t . Furthermore i n v i t r o e x p e r i m e n t s have shown t h a t b a r b i t u r a t e a n e s t h e s i a has d e p r e s s a n t e f f e c t s on c o n t r a c t i l e f u n c t i o n o f v a s c u l a r smooth muscle, p o s s i b l y due t o i t s a c t i o n s on movement o r t r a n s l o c a t i o n o f c a l c i u m ( A l t u r a and A l t u r a 1975a, b). The r e d u c t i o n o f b l o o d f l o w t o the b r a i n upon a d m i n i s t r a t i o n o f t h e c a l c i u m a n t a g o n i s t s i n the p r e s e n t e x periments may a l s o have been due t o i n t e r f e r e n c e w i t h a u t o r e g u l a t i o n . I t i s w e l l known t h a t the r e n a l and c e r e b r a l c i r c u l a t i o n s show the most pronounced a u t o r e g u l a t i o n (Shepherd and Vanhoutte 1979). R e d u c t i o n o f blood f l o w t o t h e s k i n and s p l e e n i s i n agreement w i t h p r e v i o u s f i n d i n g s u s i n g t h e c o n s c i o u s r a t p r e p a r a t i o n (Kanda and F l a i m 1984; D r e x l e r e t a l . 1985). At t h e h i g h doses o f the c a l c i u m a n t a g o n i s t s b l o o d f l o w t o the g a s t r o i n t e s t i n a l organs was d e c r e a s e d p r o b a b l y due t o WAITE, R. P. 6 3 r e f l e x v a s o c o n s t r i c t i o n . T h i s was not seen i n p r e v i o u s experiments u s i n g the c o n s c i o u s r a t p r e p a r a t i o n (Kanda and F l a i m 1984) though the doses o f n i f e d i p i n e used d i d not lower t h e MAP t o as g r e a t an e x t e n t as t h e h i g h dose used i n the p r e s e n t experiment. The d i s t r i b u t i o n of blood f l o w caused by t h e h i g h dose of v e r a p a m i l , n i f e d i p i n e and f l u n a r i z i n e was s i m i l a r to t h a t caused by n i m o d i p i n e i n i n a c t i n - a n e s t h e t i z e d r a t s (McCann e t a l . 1986). Verapamil and f l u n a r i z i n e , on t h e o t h e r hand, had l i t t l e e f f e c t on blood f l o w d i s t r i b u t i o n i n i n a c t i n - a n e s t h e t i z e d r a t s . - However, n i m o d i p i n e lowered MAP f a r more than f l u n a r i - z i n e o r v e r a p a m i l . O b v i o u s l y , c a l c i u m a n t a g o n i s t induced changes i n blood f l o w d i s t r i b u t i o n are dependent on the degree o f h y p o t e n s i o n caused by the d r u g . Conductance more a c c u r a t e l y r e f l e c t s the a c t i v e changes i n v a s c u l a r t o n e . When our blood f l o w r e s u l t s were c o r r e c t e d f o r changes i n MAP, i t was found t h a t conductance i n l u n g s , l i v e r , h e a r t and s k e l e t a l muscle were a l l i n c r e a s e d by t h e t h r e e d r u g s , a l t h o u g h t h e changes were o n l y s i g n i f i c a n t f o r the lungs and l i v e r . Though conductances t o the s k i n , i n t e s t i n e , s p l e e n and k i d n e y s were not s i g n i f i c a n t l y changed by t h e c a l c i u m a n t a g o n i s t s , a l l showed a tendency t o d e c r e a s e i n a dose-dependent manner p o s s i b l y as a r e s u l t o f the r e l e a s e o f v a s o c o n s t r i c t o r agents f o l l o w i n g a d e c r e a s e o f MAP. Decreases i n blood p r e s s u r e have been shown to cause r e f l e x a c t i v a t i o n o f v a s o p r e s s o r systems i n c l u d i n g the s y m p a t h e t i c nervous, r e n i n - a n g i o t e n s i n (Keeton and Campbell 1981) and v a s o p r e s s i n (Share 1976) systems. Verapamil i n f u s i o n i n c o n s c i o u s sheep ( M z a i l and Noble 1986)' and n i f e d i p i n e i n f u s i o n i n t o the r e n a l a r t e r y o f a n a e s t h e t i z e d dogs (Imagawa e t a l . 1986) has been shown t o i n c r e a s e plasma r e n i n a c t i v i t y . In a n e s t h e t i z e d r a t s , endogenously r e l e a s e d v a s o p r e s s i n had a prominent v a s o c o n s t r i c t o r i n f l u e n c e i n s k i n and stomach w h i l e a n g i o t e n s i n II caused the g r e a t e s t v a s o c o n s t r i c t o r i n f l u e n c e WAITE, R.P. 64 i n s k i n and k i d n e y s (Pang 198.3b). The sy m p a t h e t i c nervous system, on t h e o t h e r hand, had the g r e a t e s t v a s o c o n s t r i c t o r i n f l u e n c e i n lungs and s k e l e t a l muscle ( T a b r i z c h i and Pang 1987). Thus blood f l o w d i s t r i b u t i o n f o l l o w i n g a d m i n i s t r a t i o n o f c a l c i u m a n t a g o n i s t s would appear t o be a consequence o f d i r e c t l y - i n d u c e d v a s o d i l a t a t i o n and r e f l e x v a s o c o n s t r i c t i o n , mediated by v a r i o u s v a s o c o n s t r i c t o r agents r e l e a s e d as a r e s u l t o f t h e r e d u c t i o n i n MAP. V a r i a t i o n i n the dose o f dru g , s p e c i e s o f animal used, t h e p r e s e n c e o f an a n e s t h e t i c agent and the c o n d i t i o n o f t h e animal may a l l a f f e c t t he v a s c u l a r response t o a c a l c i u m a n t a g o n i s t . C a l c i u m a n t a g o n i s t a d m i n i s t r a t i o n i n c r e a s e d t h e CO o f 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 r a t s ( F i g . 1), a n e s t h e t i z e d c a t s (Hof e t a l . 1982), a n e s t h e - t i z e d r a b b i t s (Hof 1985), a n e s t h e t i z e d dogs (Gross e t a l . 1979) and c o n s c i o u s r a t s ( F l a i m and Z e l i s 1982). CO o f p a t i e n t s w i t h h y p e r t e n s i o n ( E l l i o t t 1987), angi n a p e c t o r i s (Soward e t a l . 1986) and c o n g e s t i v e h e a r t f a i l u r e (Matsumoto e t a l . 1980) was a l s o i n c r e a s e d by c a l c i u m a n t a g o n i s t s . I t i s b e l i e v e d t h a t the i n c r e a s e d CO i s due t o t h e c a l c i u m a n t a g o n i s t induced d e c r e a s e i n a f t e r l o a d o f the h e a r t . However, verap a m i l d e c r e a s e s the c o n t r a c t i l i t y o f the h e a r t as w e l l as t h e p e r i p h e r a l r e s i s t a n c e y e t CO i s s t i l l i n c r e a s e d . P o s s i b l y a r e f l e x i n c r e a s e i n venous r e t u r n c o n t r i b u t e s t o t he c a l c i u m a n t a g o n i s t induced i n c r e a s e i n CO. Experiments were thus d e s i g n e d t o e v a l u a t e c a l c i u m a n t a g o n i s t a c t i o n s on t h e venous s i d e o f t h e c i r c u l a t i o n i n c o n s c i o u s r a t s . The c o n c e p t o f venous r e t u r n b e i n g an i m p o r t a n t d e t e r m i n a n t i n the maintenance o f c a r d i a c o u t p u t was f i r s t p o s t u l a t e d by S t a r l i n g (1897). Of pri m a r y importance i n the c o n t r o l o f venous r e t u r n i s t h e mean c i r c u l a t o r y f i l l i n g p r e s s u r e (MCFP), an e q u i l i b r i u m p r e s s u r e t h a t would o c c u r t h r o u g h o u t the c i r c u l a t i o n i f the c i r c u l a t i o n i s a r r e s t e d and a l l t h e p r e s s u r e s i n the c i r c u l a t o r y system are r a p i d l y made t o e q u i l i b r a t e (Guyton 1955). T h e o r e t i - WAITE, R.P. 65 c a l l y MCFP has been shown t o be a measure o f the r a t i o o f b l o o d volume t o the o v e r a l l c o m p l i a n c e o f the c i r c u l a t o r y system ( G r o d i n s 1959). S i n c e venous compliance i s many times g r e a t e r than a r t e r i a l c ompliance (Guyton 1973; Samar and Coleman 1978; Yammamoto e t a'1. 1980), MCFP i s i n v e r s e l y r e l a t e d t o venous c o m p l i a n c e . Thus, i f t h e volume o f t h e system remains c o n s t a n t , MCFP r e f l e c t s p r e d o m i n a n t l y venous t o n e . I t has been shown e x p e r i m e n t a l l y t h a t MCFP i s the d r i v i n g f o r c e f o r r e t u r n i n g blood t o the he a r t and, the d i f f e r e n c e between MCFP and r i g h t a t r i a l p r e s s u r e i s p r o p o r - t i o n a l t o c a r d i a c output (Guyton 1955). The c o n s c i o u s r a t p r e p a r a t i o n o f Yamamoto (1980) was used t o determine MCFP. T h i s p r e p a r a t i o n has the advantage o f c o n c u r r e n t l y i n v e s t i g a t i n g t he e f f e c t o f drugs on MAP and t o t a l body venous tone i n the absence o f anaes- t h e s i a and s u r g e r y . P e n t o b a r b i t a l - a n a e s t h e s i a has been shown t o lower MCFP i n dogs (Hirakawa 1975). The c a l c i u m a n t a g o n i s t s t e s t e d a l l i n c r e a s e d MCFP when compared w i t h t h e i r r e s p e c t i v e v e h i c l e c o n t r o l s . By the i n t e r p o l a t i o n o f t he dose-res p o n s e c u r v e s f o r the v a r i o u s drugs, i t was found t h a t MCFP was i n c r e a s e d t o 128%, 110% and 107 % o f p r e t r e a t m e n t v a l u e s by doses o f f l u n a r i z i n e , v e r a p a m i l and n i f e d i p i n e , r e s p e c t i v e l y , which caused a 2 7 % d e c r e a s e i n c o n t r o l MAP. S i n c e c a l c i u m a n t a g o n i s t s g e n e r a l l y r e l a x v a s c u l a r smooth muscle, t h e i n c r e a s e i n MCFP induced by t h e s e drugs was l i k e l y a r e s u l t o f r e f l e x a c t i v a t i o n o f t h e sy m p a t h e t i c nervous system. N i f e d i p i n e was shown t o cause an i n c r e a s e i n CO i n a n e s t h e t i z e d c a t s accom- pa n i e d by h e p a t i c v e n o c o n s t r i c t i o n and a d e c r e a s e i n h e p a t i c b l o o d volume due t o r e f l e x mechanisms (Seaman and Greenway 1983; S e g s t r o e t a l . 1986). In c o n t r a s t t o our r e s u l t s , a s i n g l e dose o f v e r a p a m i l , n i f e d i p i n e and n i c a r d i p i n e had l i t t l e e f f e c t on the MCFP of a n e s t h e t i z e d open-chest dogs whereas d i l t i a z e m was found t o d e c r e a s e MCFP ( I t o 1984). However, the e x p e r i m e n t a l c o n d i t i o n s i n the study by I t o and Hirakawa were c l e a r l y v e r y WAITE, R. P. 66 d i f f e r e n t from o u r s . Edema i s one o f the f r e q u e n t s i d e e f f e c t s f o l l o w i n g t he a d m i n i s t r a t i o n of c a l c i u m a n t a g o n i s t s t o p a t i e n t s ( E l l i o t t 1987). I n c r e a s e d f l u i d t r a n s u d - a t i o n and edema f o r m a t i o n suggest t h a t c a l c i u m a n t a g o n i s t s d e c r e a s e t he r a t i o o f pre t o p o s t - c a p i l l a r y r e s i s t a n c e . T h i s i s c o n s i s t e n t w i t h our r e s u l t s o f d e c r e a s e d a r t e r i o l a r tone but i n c r e a s e d venous tone f o l l o w i n g the a d m i n i s t r a t i o n o f c a l c i u m a n t a g o n i s t s . In t h i s s t u d y , HR was found t o be de c r e a s e d by f l u n a r i z i n e and v e r a p a - m i l but i n c r e a s e d by n i f e d i p i n e . Our r e s u l t s on HR w i t h r e p r e s e n t a t i v e drugs from v a r i o u s s u b c l a s s e s of c a l c i u m a n t a g o n i s t s are c o n s i s t e n t w i t h r e s u l t s i n p i t h e d r a t s (Spedding 1982) and 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 r a t s ( F i g . 1). Verapamil was found t o d o s e - d e p e n d e n t l y d e c r e a s e HR and induce p a r t i a l AV b l o c k at high doses as shown by t h e sudden d e c r e a s e s i n HR ( F i g . 2 ) . F l u n a r i z i n e appeared t o have a major e f f e c t on the SA node as HR was reduced d o s e - d e p e n d e n t l y w i t h o u t s i g n s of AV-block. N i f e d i p i n e , on the o t h e r hand, caused a dose-dependent i n c r e a s e i n HR which had u s u a l l y abated by t h e time MCFP measurements were made 15 min. a f t e r commencing t h e i n f u s i o n of t h i s drug. N i f e d i p i n e was found t o cause a r e f l e x i n c r e a s e i n h e a r t r a t e i n a n e s t h e t i z e d dogs (Gross e t a l . 1979) and r a t s ( N o r d l a n d e r 1985) which s u b s e q u e n t l y abated a f t e r a d m i n i s t r a t i o n f o r more than 20 min. The e f f e c t o f time on MCFP was determined as a l l v e h i c l e s caused a s i g n i f i c a n t r e d u c t i o n i n MCFP a f t e r 75 min. F i g . 9 shows MAP and HR do not change o v e r t h e time c o u r s e o f t h e experiment but MCFP i s s i g n i f i c a n t l y reduced a f t e r 75 min. Thus, r e d u c t i o n o f MCFP by a l l v e h i c l e s would appear to be due t o a time e f f e c t . R e d u c t i o n o f MCFP was not seen i n p r e v i o u s s t u d i e s w i t h r e s p e c t t o time (Yamamoto et a l . 1980) o r i n f u s i o n o f s a l i n e ( T a b r i z c h i and Pang 1985) o v e r a time p e r i o d of 100 min though i t was WAITE, R.P. 67 reduced w i t h a s a l i n e i n f u s i o n a f t e r 120 min. ( T a b r i z c h i and Pang 1986). P o s s i b l y , because MCFP was measured much more f r e q u e n t l y i n t h e s e e x p e r i - ments, a h i g h e r l e v e l o f s y m p a t h e t i c nerve a c t i v i t y r e s u l t e d and m a i n t a i n e d the MCFP at a h i g h e r l e v e l . T h i s e x p l a n a t i o n i s su p p o r t e d by the o b s e r v a - t i o n t h a t MCFP was lowered by time and v e h i c l e s , e x c e p t e t h a n o l , t o t h e same l e v e l as the hexamethonium c o n t r o l ( p o s t - e q u i l i b r a t i o n , F i g . 10). T h i s l e v e l o f MCFP was m a i n t a i n e d i n hexamethonium c o n t r o l r a t s f o r the d u r a t i o n o f t h e experiment (3 h r ) . The e t h a n o l c o n t r o l caused a r e d u c t i o n i n MAP, p o s s i b l y r e s u l t i n g i n t h e r e f l e x i n c r e a s e i n venous tone which m a i n t a i n e d MCFP at a h i g h e r l e v e l than t he o t h e r v e h i c l e s . F u r t h e r experiments were conducted t o i n v e s t i g a t e whether the i n c r e a s e i n MCFP induced by ve r a p a m i l was due t o r e f l e x a c t i v a t i o n o f the autonomic nervous system. The a d m i n i s t r a t i o n o f hexamethonium was found t o d e c r e a s e MAP by 10% and MCFP by 15%, but had no e f f e c t on HR. F o l l o w i n g g a n g l i o n i c b l o c k a d e , t he h i g h e s t two doses o f verap a m i l caused a g r e a t e r d e c r e a s e i n MAP compared t o r a t s not s u b j e c t e d t o t r e a t m e n t w i t h hexamethonium. HR was de c r e a s e d by t h e lowest dose o f ve r a p a m i l by 10% and m a i n t a i n e d at t h i s l e v e l u n t i l a dose o f 4.7 x 10 -^ mol/kg/min when HR was d e c r e a s e d r a p i d l y , p r o b a b l y as a r e s u l t o f de p r e s s e d AV c o n d u c t i o n . MCFP was s i g n i f i c a n t l y d e c r e a s e d at the h i g h e s t dose o f verap a m i l i n the pr e s e n c e o f hexamethonium as opposed t o the i n c r e a s e seen when no g a n g l i o n b l o c k e r was p r e s e n t . Our r e s u l t s i n d i c a t e t h a t r e f l e x a c t i v a t i o n o f t h e autonomic nervous system d i d p l a y a r o l e i n maintenance o f MCFP i n c o n s c i o u s a n i m a l s f o l l o w i n g a d m i n i - s t r a t i o n o f the c a l c i u m a n t a g o n i s t v e r a p a m i l . 4.1 Summary We have found t h a t t he c a l c i u m a n t a g o n i s t s v e r a p a m i l , n i f e d i p i n e and f l u n a r i z i n e do e x h i b i t d i f f e r e n t i a l e f f e c t s on c h r o n o t r o p y , i n o t r o p y and dromotropy o f t h e 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 r a t . Verapamil reduced t h e WAITE, R.P. 68 c o n t r a c t i l i t y and HR w h i l e l e n g t h e n i n g t he P R - i n t e r v a l . N i f e d i p i n e i n c r e a s e d HR, had no e f f e c t on P R - i n t e r v a l and caused a d e c r e a s e i n c o n t r a c t i l i t y o n l y at h i g h doses. F l u n a r i z i n e d e c r e a s e d HR w i t h no e f f e c t on t he o t h e r two parameters. Thus, S p e d d i n g 1 s c l a s s i f i c a t i o n o f c a l c i u m a n t a g o n i s t s appears t o be v a l i d w i t h r e s p e c t t o t h e i r a c t i o n s on t h e h e a r t . However, t h e i r e f f e c t on a r t e r i a l smooth muscle are s i m i l a r . Blood f l o w t o t h e h e a r t , l u n g s and l i v e r i n c r e a s e d w h i l e f l o w t o the Gl organs, k i d n e y s , s k i n , s p l e e n and b r a i n d e c r e a s e d . H e a r t , l u n g , l i v e r and s k e l e t a l muscle conductances i n c r e a s e d w h i l e t i s s u e conductance i n t h e k i d n e y s , s p l e e n , s k i n and Gl organs d e c r e a s e d upon a d m i n i s t r a t i o n o f the c a l c i u m a n t a g o n i s t s . T h i s demonstrated 1) t h a t t he c a l c i u m a n t a g o n i s t s a re not g e n e r a l a r t e r i o l a r d i l a t o r s and 2) doses of the c a l c i u m a n t a g o n i s t s which lower MAP t o t h e same e x t e n t s i m i l a r l y a f f e c t t he d i s t r i b u t i o n o f blood f l o w . R e s u l t s from c o n s c i o u s r a t experiments c o n f i r m e d t h a t v e r a p a m i l , n i f e d i p i n e and f l u n a r i z i n e produced d i f f e r e n t e f f e c t s on h e a r t r a t e . A l l t h r e e drugs i n c r e a s e d t he t o t a l body venous tone o f t h e c o n s c i o u s r a t , as measured by MCFP, i n d i c a t i n g t h a t t he i n c r e a s e o f CO seen upon a d m i n i s t r a - t i o n o f a c a l c i u m a n t a g o n i s t may be due t o an i n c r e a s e i n venous tone o f the animal w i t h subsequent i n c r e a s e i n venous r e t u r n . A d m i n i s t r a t i o n o f hexa- methonium t o b l o c k t h e autonomic nervous system i n d i c a t e d t h a t t he i n c r e a s e i n venous tone e l i c i t e d by verap a m i l was due t o r e f l e x a c t i v a t i o n o f t h e autonomic nervous system. WAITE, R.P. 6 9 5. REFERENCES A d e l s t e i n , R.S., J.R. S e l l e r s . E f f e c t s o f c a l c i u m on v a s c u l a r smooth muscle c o n t r a c t i o n . Am. J . C a r d i o l . 59: 4B-10B, 1987. A g a b i t i - R o s e i , E., M.L. Muiesan, G. R o m a n e l l i , M. C a s t e l l a n o , M. B e s c h i , L. Corea, G. Muiesan. S i m i l a r i t i e s and d i f f e r e n c e s i n t h e a n t i h y p e r t e n - s i v e e f f e c t o f two c a l c i u m a n t a g o n i s t drugs, v e r a p a m i l and n i f e d i - p i n e . J . Am. C o l l . C a r d i o l . 7 ( 4 ) : 916-924, 1986. A l t u r a , B.T., B.M. A l t u r a . B a r b i t u r a t e s and a o r t i c and venous smooth-muscle f u n c t i o n . A n e s t h e s i o l o g y 43: 432-44, 1975. A l t u r a , B.T., B.M. A l t u r a . P e n t o b a r b i t a l and the c o n t r a c t i o n of v a s c u l a r smooth muscle. Am. J . P h y s i o l . 229: 1635-40, 1975. Bayer, R., D. K a l u s c h e , R. Kaufmann, R. Mannhold. I n o t r o p i c and e l e c t r o p h y s i o l o g i c a l a c t i o n s o f verapamil and D-600 i n mammalian myocardium. I I I . E f f e c t s o f the o p t i c a l isomers on transmembrane a c t i o n p o t e n t i a l s . Nauyn-Schmiedebergs A r c h . Pharmacol. 290: 81-97, 1975. Bayer, R., T. Ehara. C o m p a r i t i v e s t u d i e s on c a l c i u m a n t a g o n i s t s . P r o g r . Pharmacol. 2 ( 1 ) : 30-37, 1978. Bean, B.P. Two k i n d s of c a l c i u m c h a n n e l s i n c a n i n e a t r i a l c e l l s . J . Gen. P h y s i o l . 86: 1-30, 1985. Bean, B.P., M.C. Nowycky, R.W. T s i e n . e - a d r e n e r g i c m o d u l a t i o n o f c a l c i u m c h a n n e l s i n f r o g v e n t r i c u l a r h e a r t c e l l s . Nature 307: 371-375, 1984. Bean, B.P., M. S t u r e k , A. Puga, K. Hermsmeyer. Ca l c i u m c h a n n e l s i n muscle c e l l s i s o l a t e d from r a t m e s e n t e r i c a r t e r i e s : m o d u l a t i o n by d i h y d r o - p y r i d i n e drugs. C i r c . Res. 59_: 229-235, 1986. B e c k e r i n g h , J.J.,.M. Thoolen, A. deJonge, B. W i l f f e r t , P.B.M.W.M. Timmermans, P.A. van Zwieten. D i f f e r e n t i a l e f f e c t s o f the c a l c i u m e n t r y b l o c k e r D-600 on c o n t r a c t i o n s o f r a t and g u i n e a - p i g a o r t a s , e l i c i t e d by v a r i o u s alpha-1 a d r e n o c e p t o r a g o n i s t s . J . Pharmacol. Exp. Ther. 229: 515-521, 1984. B l a u , A., A. B a t t l e r , M. E l d a r , S. Rath, H.N. N e u f e l d , S. K a p u l a r , A. I a i n a , D. Cohen, H.E. E l i a h o u . Hemodynamic e f f e c t s o f n i f e d i p i n e i n hyper- t e n s i o n i n the presence o f e l e v a t e d a n g i o t e n s i n - I I and 8 - a d r e n e r g i c b l o c k a d e . J . C l i n . H y pertens. 2: 13-20, 1986. B o l t , G.R., P.R. Saxena. Acute s y s t e m i c and r e g i o n a l hemodynamic e f f e c t s o f f e l o d i p i n e , a new c a l c i u m a n t a g o n i s t , i n c o n s c i o u s r e n a l h y p e r t e n s i v e r a b b i t s . J . C a r d i o v a s c . Pharmacol. 6_: 707-712, 1984. Bou, J . , R. Massingham. Phenoxybenzamine induced i n h i b i t i o n o f c i r a z o l i n e p r e s s o r responses i n p i t h e d r a t s p r e t r e a t e d w i t h o r g a n i c o r i n o r g a n i c c a l c i u m e n t r y b l o c k i n g d r u g s . Eur. J . Pharmacol. 102: 535-539, 1984. WAITE, R.P. 70 Bou, J . , R. Massingham. E f f e c t o f d i l t i a z e m upon c o n t r a c t i l e r e s p o n s e s t o p h e n y l e p h e r i n e , c i r a z o l i n e , Sgd 101/75, St 587 and BHT 920 i n r a b b i t a o r t a and dog saphenous v e i n p r e p a r a t i o n s . Eur. J . Pharmacol. 121: 319-325, 1986. Budden R, Buschmann G, Kuhl UG. The r a t ECG i n acute pharmacology and t o x i c o l o g y . In: Budden R, D e t w e i l e r DK, Zbinden G eds. The Rat E l e c t r o c a r d i o g r a m i n Pharmacology T o x i c o l o g y . O x f o r d : Pergamon P r e s s , 1980: 41-81. C a c h e l i n , A.B., J . E . de Peyer, S. Kokubun. Calcium channel m o d u l a t i o n by 8 - b r o m o c y c l i c AMP i n c u l t u r e d h e a r t c e l l s . Nature 304: 462-464, 1983. Cauv i n , C , S. Lukeman, J . Cameron, 0. Hwang, K. M e i s h e r i , H. Yamamoto, C. van Breeman. T h e o r e t i c a l bases f o r v a s c u l a r s e l e c t i v i t y o f c a l c i u m a n t a g o n i s t s . J . C a r d i o v a s c . Pharmacol. 6_: S630-S638; 1984. Cauvin, C , S. M a l i k . I n d u c t i o n o f c a l c i u m i n f l u x and i n t r a c e l l u l a r c a l c i u m r e l e a s e i n i s o l a t e d r a t a o r t a and m e s e n t e r i c r e s i s t a n c e v e s s e l s by n o r e p i n e p h e r i n e a c t i v a t i o n o f alpha-1 r e c e p t o r s . J . Pharmacol. Exp. Ther. 230: 413-418, 1984. Cavero, I . , N. Shepperson, F. L e f e v r e - B o r g , S.Z. Langer. D i f f e r e n t i a l i n h i b i t i o n o f v a s c u l a r smooth muscle responses t o a l - and a2-adreno-c e p t o r a g o n i s t s by d i l t i a z e m and v e r a p a m i l . C i r c . Res. 52 (s u p p l I ) : 69-76, 1983. — C h a t t e r j e e , K. Ca l c i u m a n t a g o n i s t agents i n h y p e r t r o p h i c cardiomyopathy. Am. J . C a r d i o l . 59: 146B-152B, 1987. Cohn, J.N. Calcium a n t a g o n i s t s and l e f t v e n t r i c u l a r f u n c t i o n : E f f e c t s o f n i t r e n d i p i n e i n c o n g e s t i v e h e a r t f a i l u r e . Am. J . C a r d i o l . 58: 27D-30D, 1986. C u r t i s , B.M., W.A. C a t t e r a l l . S o l u b i l i z a t i o n o f the c a l c i u m a n t a g o n i s t . r e c e p t o r from r a t b r a i n . J . B i o l . Chem. 258: 7280-7283, 1983. Da l y , M.J., S.E. P e r r y , W.G. N a y l e r . E f f e c t s o f n i f e d i p i n e , v e r a p a m i l , and d i l t i a z e m on c a l m o d u l i n mediated, c a l c i u m s t i m u l a t i o n o f p h o s p h o d i - e s t e r a s e a c t i v i t y . J . Mol. C e l l . C a r d i o l . _15 ( s u p p l . 1 ) : 231, 1983. Dangman, K.H., B.F. Hoffman. E f f e c t s o f n i f e d i p i n e on e l e c t r i c a l a c t i v i t y o f c a r d i a c c e l l s . Am. J . C a r d i o l . 46: 1059-1067, 1980. DeJonge, A., B. W i l f f e r t , H.0. Kalkman, J.C.A. van Meel, M. Thoolen, P.B.M.W.M. Timmermans, P.A. van Zwieten. C a p t o p r i l i m p a i r s t he v a s c u l a r smooth muscle c o n t r a c t i o n mediated by p o s t s y n a p t i c a2-adreno-r e c e p t o r s i n the p i t h e d r a t . Eur. J . Pharmacol. 74: 385-386, 1981. D r e x l e r , H., S.F. F l a i m , R.H. F i e l d s , R. Z e l i s . E f f e c t s of n i s o l d i p i n e on c a r d i o c i r c u l a t o r y dynamics and c a r d i a c o u t p u t d i s t r i b u t i o n i n c o n s c i o u s r a t s at r e s t and d u r i n g t r e a d m i l l e x e r c i s e . J . Pharmacol. Exp. Ther. 232: 376-378, 1985a. WAITE, R.P. 71 D r e x l e r , H., A.G. Truog, H. J u s t , R. Z e l i s . D ie b e e i n f l u s s u n g d e r o r g a n p e r f u s i o n durch k a l z i u m b l o c k e r und c o n v e r t i n g - e n z y m i n h i b i t o r an d e r h e r z i n s u f f i z i e n t e n , wachen r a t t e . K l i n . Wochenschr. 63: 262-267, 1985b. ~ D r e x l e r , H., J.W. Depenbusch, A.G. Truog, R. Z e l i s , S.F. F l a i m . E f f e c t s o f d i l t i a z e m on c a r d i a c f u n c t i o n and r e g i o n a l blood f l o w at r e s t and d u r i n g e x e r c i s e i n a c o n s c i o u s r a t p r e p a r a t i o n o f c h r o n i c h e a r t f a i l u r e ( m y o c a r d i a l i n f a r c t i o n ) . C i r c u l a t i o n 71: 1262-1270, 1985c. Duncker, D.J., J . H e i l i g e r s , E . J . Mylecharane, P.R. Saxena, P.D. Verdouw. Nimodipine induced changes i n t h e d i s t r i b u t i o n o f c a r o t i d blood f l o w and c a r d i a c o u t p u t i n p e n t o b a r b i t o n e - a n a e s t h e t i z e d p i g s . B r i t . J . Pharmac. 89: 35-46, 1986. E l l i o t t , H. The r o l e of c a l c i u m a n t a g o n i s t s i n the t r e a t m e n t of e s s e n t i a l h y p e r t e n s i o n . In Calcium a n t a g o n i s t s ; an i n t e r n a t i o n a l seminar on the c u r r e n t and p o t e n t i a l t h e r a p e u t i c i n d i c a t i o n s f o r drugs a f f e c t i n g c a l c i u m . 1987. Endo, M. Ca l c i u m r e l e a s e from the s a r c o p l a s m i c r e t i c u l u m . P h y s i o l . Rev. 57: 71-108,. 1977. Fagbemi, 0., K.A. Kane, F.M. McDonald, J.R. P a r r a t t , A.L. R o t h a u l . The e f f e c t s o f v e r a p a m i l , p r e n y l a m i n e , f l u n a r i z i n e and c i n n a r i z i n e on c o r o n a r y a r t e r y o c c l u s i o n - i n d u c e d a r r y t h m i a s i n a n a e s t h e t i z e d r a t s . Br. J . Pharmac. 83: 299-304, 1984. F a i r h u r s t , A.S., M.L. W h i t t a k e r , F . J . E h l e r t . I n t e r a c t i o n s o f D-600 (methoxyverapami1) and l o c a l a n e s t h e t i c s w i t h r a t b r a i n a - a d r e n e r g i c and m u s c a r i n i c r e c e p t o r s . Biochem. Pharmacol. ^ 9 : 155-162, 1980. F e r r y , D.R., H. Glossmann. Evidence f o r m u l t i p l e r e c e p t o r s i t e s w i t h i n t h e p u t a t i v e c a l c i u m c h a n n e l . Nauyn Schmeidebergs A r c h . Pharmacol. 321: 80-83, 1982. F e r r y , D.R., A. G o l l , H. Glossmann. P u t a t i v e c a l c i u m channel m o l e c u l a r weight d e t e r m i n a t i o n by t a r g e t s i z e a n a l y s i s . Nauyn Schmeidebergs A r c h . Pharmacol. 323: 292-297, 1983. F l a i m , S.F., R. Z e l i s . E f f e c t s o f d i l t i a z e m on t o t a l c a r d i a c o u t p u t d i s t r i b u t i o n i n c o n s c i o u s r a t s . J . Pharmacol. Exp. Ther. 222: 359-66, 1982. F l a i m , S.F., Newman ED, A n n i b a l i JA. E f f e c t s of i n t r a v e n o u s d i l t i a z e m on c a r d i o c i r c u l a t o r y dynamics and c a r d i a c o u t p u t d i s t r i b u t i o n i n c o n s c i o u s s p o n t a n e o u s l y h y p e r t e n s i v e r a t s . J . C a r d i o v a s c . Pharmacol. 8: 241-51, 1986. F l e c k e n s t e i n , A. Die Bedeutung der e n e r g i e r e i c h e n Phosphate f u r K o n t r a k t i l i t a t und Tonus des Myokards. Verh. D t s c h . Ges. Inn. Med. 70: 81-99, 1964 WAITE, R.P. 72 F l e c k e n s t e i n , A. S p e c i f i c pharmacology o f c a l c i u m i n myocardium, c a r d i a c pacemakers, and v a s c u l a r smooth muscle. Ann. Rev. Pharmacol. T o x i c o l . 17: 149-166, 1977. F l e c k e n s t e i n , A. C a l c i u m Antagonism i n Heart and Smooth Muscle, E x p e r i m e n t a l F a c t s and T h e r a p e u t i c P r o s p e c t s . New York: John W i l e y and Sons, 1983. F l e c k e n s t e i n , A., H. Kammermeier, H.J. D o r i n g , H.J. Freund. Zum Wirkungsmechanismus n e u a r t i g e r K o r o n a r d i l a t i t o r e n mit g l e i c h z e i t i g S a u e r s t o f f - e i n s p a r e n d e n M y o k a r d - E f f e k t e n , Prenylamin und I p r o v e r a t r i 1 . Z. K r e i s l . - F o r s c h . 56 : 716 -7 4 4, 196 7. F l e c k e n s t e i n , A., H. T r i t t h a r t , B. F l e c k e n s t e i n , A. H e r b s t , G. Grun. A new group o f c o m p e t i t i v e c a l c i u m a n t a g o n i s t s ( I p r o v e r a t r i 1, D-600, P r e n y l - amine) w i t h h i g h l y p o t e n t i n h i b i t o r y e f f e c t s on e x c i t a t i o n - c o n t r a c t i o n c o u p l i n g i n mammalian myocardium. P f l u e g e r s A r c h . 307: R25, 1969. F l e c k e n s t e i n , A., H. T r i t t h a r t , H.J. D o r i n g , Y.K. Byon. Bay a 1040- e i n h o c h a k t i v e r Ca - a n t a g o n i s t i s c h e r i n h i b i t o r der e l e k t r o - m e c h a n i s c h e n k o p p e l u n g s p r o z e s s e im warmbluter-myokard. A r z n e i m i t t e l f o r s c h . 22: 22-33, 1972. F l o c k e r z i , V., H.J. Oeken, F. Hofmann, D. P e l z e r , A. C a v a l i e , W. T r a u t w e i n . P u r i f i e d d i h y d r o p y r i d i n e b i n d i n g s i t e s from s k e l e t a l muscle t - t u b u l e s i s a f u n c t i o n a l c a l c i u m c h a n n e l . Nature 323: 66-68, 1986. Franckowiak, G., M. Bechem, M. Schramm, G. Thomas. The o p t i c a l isomers o f t h e 1,4 d i h y d r o p y r i d i n e Bay K 8644 show o p p o s i t e e f f e c t s on c a l c i u m c h a n n e l s . Eur. J . Pharmacol. 114: 223-226, 1985. F u r c h g o t t , R.F. The r o l e of e n d o t h e l i u m i n the responses o f v a s c u l a r smooth muscle t o d r u g s . Ann. Rev. Pharmacol. T o x i c o l . 24: 175-197, 1984. G a l i z z i , J.P., M. B o r s o t t o , J . B a r h a n i n , M. F o s s e t , M. L a z d u n s k i . C h a r a c t e r i z a t i o n and p h o t o a f f i n i t y l a b e l l i n g o f r e c e p t o r s i t e s f o r t h e c a l c i u m channel i n h i b i t o r s d - c i s d i l t i a z e m , (*)- b e p r i d i l , desmethoxy- v e r a p a m i l , and (+)-PN 200-110 i n s k e l e t a l muscle t r a n s v e r s e t u b u l e membranes. J . B i o l . Chem. 261: 1393-1397, 1986. Gelmers, H.J. E f f e c t of c a l c i u m a n t a g o n i s t s on the c e r e b r a l c i r c u l a t i o n . Am. J . C a r d i o l . 59: 173B-176B, 1987. Glossmann, H., D.R.( F e r r y . S o l u b i l i z a t i o n and p a r t i a l p u r i f i c a t i o n o f p u t a t i v e c a l c i u m c h a n n e l s l a b e l l e d w i t h [ 3 H ] - n i m o d i p i n e . Nauyn Schmiedebergs-Arch. Pharmacol. 323: 279-291, 1983. Glossmann, H., D.R. F e r r y , F. Lubbecke, R. Mewes, F. Hofmann. Calcium c h a n n e l s : d i r e c t i d e n t i f i c a t i o n w i t h r a d i o l i g a n d b i n d i n g s t u d i e s . Trends i n Pharmacol. S c i . 431-437, 1982. Glossmann, H., D.R. F e r r y , F. Lubbecke, R. Mewes, F. Hofmann. I d e n t i f i c a t i o n o f v o l t a g e o p e r a t e d c a l c i u m c h a n n e l s by b i n d i n g s t u d i e s : d i f f e r e n t i a t i o n o f s u b c l a s s e s o f c a l c i u m a n t a g o n i s t drugs w i t h [ H ] - n i m o d i p i n e r a d i o l i g a n d b i n d i n g . J . Rec. Res. 3: 177-190, 1983a. WAITE, R.P. 73 Glossmann, H., D.R. F e r r y , C B . Boschek. P u r i f i c a t i o n o f the p u t a t i v e c a l c i u m channel from s k e l e t a l muscle w i t h t h e a i d o f [ 3 H ] - n i m o d i p i n e b i n d i n g . Nauyn Schmiedebergs A r c h . Pharmacol. 323: 1-11, 1983b. Glossmann, H., D.R. F e r r y , A. G o l l , M. Rombusch. M o l e c u l a r pharmacology o f t h e c a l c i u m c h a n n e l : e v i d e n c e f o r subt y p e s , m u l t i p l e drug r e c e p t o r s i t e s , channel s u b u n i t s and the development o f a r a d i o i o d i n a t e d 1,4 d i h y d r o p y r i d i n e c a l c i u m c h a n n e l l a b e l , [ I ] I o d i p i n e . J . C a r d i v a s c . Pharmacol. 6_: S608-S5 21, 1984. Glossmann, H., D.R. F e r r y , A. G o l l , J . S t r i e s s n i g , G. Z e r n i g . C a l c i u m c h a n n e l s and c a l c i u m channel drugs: r e c e n t b i o c h e m i c a l and b i o p h y s i - c a l f i n d i n g s . A r z n e i m - F o r s c h . 35(11): 1917-1935, 1985a. Glossmann, H., D.R. F e r r y , A. G o l l , J . S t r i e s s n i g , M. Schober. C a l c i u m c h a n n e l s : b a s i c p r o p e r t i e s as r e v e a l e d by r a d i o l i g a n d b i n d i n g s t u d i e s . J . C a r d i o v a s c . Pharmacol. _7(Suppl. 6 ) : S20-S30, 1985b. Glossmann, H.-, D.R. F e r r y , J . S t r i e s s n i g , A. G o l l , K. Moosburger. R e s o l v i n g t h e s t r u c t u r e of the c a l c i u m channel by p h o t o a f f i n i t y l a b e l l i n g . Trends i n Pharmacol. S c i . 8: 95-100, 1987. G o d f r a i n d , T. C l a s s i f i c a t i o n o f c a l c i u m a n t a g o n i s t s . Am. J . C a r d i o l . 5 9 : 11B-23B, 1987. "~~ G o d f r a i n d T., A. Kaba. A c t i o n s phas'ique e t t o n i q u e de T a d r e n a l i n e s u r un muscle l i s s e v a s c u l a i r e e t l e u r i n h i b i t i o n p a r des agents pharmacolog- i q u e s . A r c h . I n t . Pharmacodyn. Ther. 178: 488-491, 1969b. G o d f r a i n d T., A. Kaba. Blockade o r r e v e r s a l o f the c o n t r a c t i o n induced by c a l c i u m and a d r e n a l i n e i n d e p o l a r i z e d a r t e r i a l smooth muscle. Br. J . Pharmacol. 36 : 549-56 0, 196 9a. G o d f r a i n d , T., D. Dieu. The i n h i b i t i o n by f l u n a r i z i n e o f the n o r e p i n e p h e r i n e - e v o k e d c o n t r a c t i o n and c a l c i u m i n f l u x i n r a t a o r t a and m e s e n t e r i c a r t e r i e s . J . Pharmacol. Exp. Ther. 217: 510-515, 1981. G o d f r a i n d , T., R.C. M i l l e r . S p e c i f i c i t y o f a c t i o n of c a l c i u m e n t r y b l o c k e r s : A comparison o f t h e i r a c t i o n s i n r a t a r t e r i e s and i n human c o r o n a r y a r t e r i e s . C i r c . Res. 52 (su p p l I ) : 81-91, 1983. G o d f r a i n d , T., A. Kaba, P. P o l s t e r . S p e c i f i c antagonism t o the d i r e c t and i n d i r e c t a c t i o n o f a n g i o t e n s i n on i s o l a t e d g u i n e a - p i g i l e u m . Br. J . Pharmac. 28: 93-104, 1966. G o d f r a i n d , T., A. Kaba, P. P o l s t e r . D i f f e r e n c e s i n s e n s i t i v i t y o f a r t e r i a l smooth muscles t o i n h i b i t i o n o f t h e i r c o n t r a c t i l e response to d e p o l a r -i z a t i o n by p o t a s s i u m . A r c h . I n t . Pharmacodyn. Ther. 172: 235-239, 196 8. G o d f r a i n d , T., M. F i n e t , J.S. Lima, R.C. M i l l e r . C o n t r a c t i l e a c t i v i t y o f human c o r o n a r y a r t e r i e s and human myocardium i n v i t r o and t h e i r s e n s i t i v i t y t o c a l c i u m e n t r y b l o c k a d e by n i f e d i p i n e . 37 Pharmacol. Exp. Ther. 230: 514-518. 1984. WAITE, R.P. 74 G o l l , A., H. Glossman, R. Mannhold. C o r r e l a t i o n between the n e g a t i v e i n o t r o p i c potency and b i n d i n g parameters o f 'l, 4-d i hyd ropy r i d i n e and p h e n y l a l k y l a m i n e s c a l c i u m channel b l o c k e r s i n c a t h e a r t . Nauyn Schmiedebergs A r c h . Pharmacol. 334: 303-312, 1986. Greenway, C.V. Mechanisma and q u a n t i t a t i v e a s s e s s m i n t o f drug e f f e c t s on c a r d i a c o u t p u t e i t h a new model o f the c i r c u l a t i o n . Pharmacol. Rev. 33: 213-51, 1982. G r e i g , M., D. O s t e r l i n . U.B.C. Anova Computing Centre P u b l i c a t i o n s , The U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, 1977. G r o d i n s , F.S. I n t e g r a t i v e c a r d i o v a s c u l a r p h y s i o l o g y : a mathematical s y n t h e s i s o f c a r d i a c and blood v e s s e l hemodynamics. Q. Rev. B i o l . 34: 93-116, 1959. Gross, R., H. K i r c h h e i m , K. von Olshausen. E f f e c t s o f n i f e d i p i n e on c o r o n a r y and s y s t e m i c hemodynamics i n the c o n s c i o u s dog. Arzn e i m -F o r s c h . 2 9 ( 1 1 ) : 1361-6 8, 1979. G u l a t i , N., H. Huggel, O.P. G u l a t i . Pharmacodynamic s t u d i e s w i t h f l u n a r i z i n e , a c a l c i u m i n f l u x b l o c k e r . A r c h . I n t . Pharmacodyn. 263: 17-27, 1983. Guyton, A.C. D e t e r m i n a t i o n o f c a r d i a c o u t p u t by e q u a t i n g venous r e t u r n c u r v e s w i t h c a r d i a c response c u r v e s . Am. J . P h y s i o l . 35: 123-29, 1955. — Guyton, A.C. Mean c i r c u l a t o r y p r e s s u r e , mean s y s t e m i c p r e s s u r e , and mean pulmonary p r e s s u r e and t h e i r e f f e c t on venous r e t u r n . In: Ci r c u l a t o r y  P h y s i o l o g y : C a r d i a c Output and I t s R e g u l a t i o n . P h i l a d e l p h i a : baunders, L9/3, pp 205-221. Haas, H., G. H a r t f e l d e r . a - i s o p r o p y l - a ( N - m e t h y l h o m o v e r a t r y l - y - a m i n o p r o p y l ) - 3 , 4 - d i m e t h o x y - p h e n y l a c e t o n i t r i 1 , e i n e substanz mit c o r o n -a r g e f a b e r v e i t e r d e n e i g e n s c h a t f e n . Arzneim. F o r s c h . 12_: 5 4 9 -5 58, 196 2. Hamilton, B.P. Treatment o f e s s e n t i a l h y p e r t e n s i o n w i t h PN 200-110 ( i s r a d i p i n e ) . Am. J . C a r d i o l . 59: 141B-145B, 1987. Hirakawa, S., H. I t o , Y. Kondo, I. Watanabe, K. H i e i , S. Banno, S. Hayase. The mean c i r c u l a t o r y p r e s s u r e , r e p r o d u c i b i l i t y o f i t s measurements and th e e f f e c t o f p h e n y l e p h e r i n e w i t h a note on t h e e f f e c t o f p e n t o b a r b i -t a l . Jap. C i r c . J . 39: 403-9, 1975. Hirakawa, S., H. I t o , Y. Kondo, I. Wantanabe, K. H i e i , S. Banno, S. Hayase. Coronary c i r c u l a t i o n , s y s t e m i c r e s i s t a n c e and c a p a c i t a n c e blood v e s -s e l s o f dogs as a f f e c t e d by bay a 1040. A r z n e i m - F o r s c h . 22: 344-349, 1972. — Hof, R.P. Cal c i u m a n t a g o n i s t and the p e r i p h e r a l c i r c u l a t i o n : d i f f e r e n c e s and s i m i l a r i t i e s between PY 108-068, n i c a r d i p i n e , v e r a p a m i l and d i l t i a z e m . Br. J . Pharmacol. 78: 375-94, 1983. WAITE, R.P. 75 Hof, R.P. The c a l c i u m a n t a g o n i s t s PY 108-058 and v e r a p a m i l d i m i n i s h t h e e f f e c t s o f a n g i o t e n s i n I I : s i t e s o f i n t e r a c t i o n i n the p e r i p h e r a l c i r c u l a t i o n o f a n a e s t h e t i z e d c a t s . Br. J . Pharmacol. 82: 51-60, 1984. Hof, R.P. M o d i f i c a t i o n of v a s o p r e s s i n and a n g i o t e n s i n II induced changes by c a l c i u m a n t a g o n i s t s i n t h e p e r i p h e r a l c i r c u l a t i o n o f a n a e s t h e t i z e d r a b b i t s . Br. J . Pharmacol 85: 75-87, 1985. Hof, R.P. Comparison o f c a r d i o d e p r e s s a n t and v a s o d i l a t o r e f f e c t s o f PN 200-110 ( I s r a d i p i n e ) , n i f e d i p i n e and d i l t i a z e m i n a n e s t h e t i z e d r a b b i t s . Am. J . C a r d i o l . 59: 37B-42B, 1987. Hof, R.P., A. Hof. PY 108-068, a d i h y d r o p y r i d i n e d e r i v a t i v e , and v e r a p a m i l i n t e r a c t d i f f e r e n t l y w i t h t he ouabain e f f e c t s on the h e a r t and the p e r i p h e r a l c i r c u l a t i o n . B a s i c . Res. C a r d i o l . 80: 66-75, 1985. Hof, R.P., A. Hof, P. Neumann. E f f e c t s o f PY 108-068, a new c a l c i u m a n t a g o n i s t , on g e n e r a l hemadynamics and r e g i o n a l blood f l o w i n a n e s t h e t i z e d c a t s : a comparison w i t h n i f e d i p i n e . J . C a r d i o v a s c . Pharmacol. 4: 352-62, 1982. Hof, R.P., A. Hof, H.0. Kalkman. M o d i f i c a t i o n of the v a s o c o n s t r i c t o r e f f e c t s o f n o r a d r e n a l i n e and s e r o t o n i n b'y the s e l e c t i v e c a l c i u m a n t a g o n i s t PY 108-068 i n the p e r i p h e r a l c i r c u l a t i o n o f a n e s t h e t i z e d c a t s . J . C a r d i o v a s c . Pharmacol. ]_ ( s u p p l . 6 ) : S53-S60, 1985. Hof, R.P., R. Salzman, H. S i e g l . S e l e c t i v e e f f e c t s of PN 200-110 ( I s r a d i p i n e ) on the p e r i p h e r a l c i r c u l a t i o n and t h e h e a r t . Am. J . C a r d i o l . 59: 30B-36B, 1987. Hof, R.P., U.T. Ruegg, A. Hof, A. V o g e l . S t e r e o s e l e c t i v i t y a t the c a l c i u m c h a n n e l : o p p o s i t e a c t i o n of t h e enantiomers o f a 1,4 d i h y d r o p y r i - d i n e . J . C a r d i o v a s c . Pharmacol. _7_: 689-693, 1985. Imagawa, J . , H. Kurasawa, S. Satoh. E f f e c t s o f n i f e d i p i n e on r e n i n r e l e a s e and r e n a l f u n c t i o n i n a n a s t h e t i z e d dogs. J . C a r d i o v a s c . Pharmacol. 8: 6 36-40, 1986. I t o , H., S. Hirakawa. E f f e c t s o f v a s o d i l a t o r s on the s y s t e m i c c a p a c i t a n c e v e s s e l s , a s t u d y w i t h t h e measurement o f t h e mean c i r c u l a t o r y p r e s s u r e i n dogs. Jap. C i r c . J . 48: 388-404, 1984. Jim, K.F., R.A. Macia, W.D. Matthews. Role o f r e c e p t o r r e s e r v e i n t h e i n h i b i t i o n o f alpha-1 a d r e n o c e p t o r - m e d i a t e d p r e s s o r responses by c a l c i u m a n t a g o n i s t s i n the p i t h e d r a t . J . Pharmacol. Exp. Ther. 238: 89-94, 1986. Johns, A., P. L e i j t e n , H. Yamamoto, K. Hwang, C. van Breeman. Ca l c i u m r e g u l a t i o n i n v a s c u l a r smooth muscle c o n t r a c t i l i t y . Am. J . C a r d i o l . 59: 18A-23A, 1987. Kalkman, H.0., M. Thoolen, P.B.M.W.M. Timmermans, P.A. van Zwieten. The i n f l u e n c e o f a l - and a 2-adrenoceptor a g o n i s t s on c a r d i a c o u t p u t i n r a t s and c a t s . J . Pharm. Pharmacol. 36: 265-268, 1984. WAITE, R.P. 76 Kanda, K., S.F. F l a i m . E f f e c t s o f n i f e d i p i n e on t o t a l c a r d i a c output d i s t r i b u t i o n i n c o n s c i o u s r a t . J . Pharmacol. Exp. Ther. 228: 711-18, 1984. K a r l i n e r , J.S., H.J. M o t u l s k y , J . Dunlap, J.H. Brown, P.A. I n s e l . Verapamil c o m p e t i t i v e l y i n h i b i t s a l - a d r e n e r g i c and m u s c a r i n i c but not e-adrener- g i c r e c e p t o r s i n r a t myocardium. J . C a r d i o v a s c . Pharmacol. 4: 515-520, 1982. Kato, H., J . K u r i h a r a , K. I s h i i , Y. Kasuya. V a s o d i l a t i n g e f f e c t o f f l u n a r i z i n e i n a n e s t h e t i z e d dogs. Arch. I n t . Pharmacodyn. Ther. 249: 257-26 3, 1981. Keeton, T.K., W.B. Campbell. The p h a r m a c o l o g i c a l t e r a t i o n of r e n i n r e l e a s e . Pharmacol. Rev. 31: 81-227, 1981. K l e i n , W., D. Brandt, K. Vrecko, M. H a r r i n g e r . Role o f c a l c i u m a n t a g o n i s t s i n the t r e a t m e n t o f e s s e n t i a l h y p e r t e n s i o n . C i r c . Res. 52 ( s u p p l . 1 ) : 174-181, 1983. — Knoch, G., M. Sc h l e p p e r , E. W i t z l e b . I s o p t i n - A c l i n i c a l s t u d y u s i n g normal s u b j e c t s and p a t i e n t s w i t h c o r o n a r y d i s e a s e . Med. K l i n . 58: 1485-1491, 196 3. ~ K r i k l e r , D.M. Calcium a n t a g o n i s t s f o r c h r o n i c s t a b l e angina p e c t o r i s . Am. J. C a r d i o l . 59: 95B-100B, 1987. K r i k l e r , D.M., R.A.J. S p u r r e l l . Verapamil i n the t r e a t m e n t o f paroxysmal s u p r a v e n t r i c u l a r t a c h y c a r d i a . P o s t g r a d . Med. J . 50: 447-453, 1974. L a u t t , W.W. C o n t r o l o f h e p a t i c a r t e r i a l b l o od f l o w : independance from l i v e r m e t a b o l i c a c t i v i t y . Am. J . P h y s i o l . 239: H559-H564, 1980. Lee, K.S., R.W. T s i e n . Mechanism o f c a l c i u m channel b l o c k a d e by v e r a p a m i l , D600, d i l t i a z e m and n i t r e n d i p i n e i n s i n g l e d i a l y s e d h e a r t c e l l s . Nature 302: 790-794, 1983. L j u n g , B. V a s c u l a r s e l e c t i v i t y o f f e l o d i p i n e . Drugs 29 ( s u p p l . 2): 46-58, 1985. L l e n a s , J . , R. Massingham. A compaison of the e f f e c t s o f v e r a p a m i l and c i n n a r i z i n e upon responses e l i c i t e d by s e l e c t i v e a l - and a2-adrenocep-t o r a g o n i s t s i n the a u t o p e r f u s e d c a n i n e h i n d l i m b . Eur. J . Pharmacol. 87: 53-59, 1983. Loev, B., M.M. Goodman, K. M. Snader, R. T e d e s c h i , E. Macko. "Hantzsch t y p e " d i h y d r o p y r i d i n e h y p o t e n s i v e a g e n t s . J . Med. Chem. 17: 956-965, 1974. ~ Luchowski, E.M., F. Y o u s i f , D.J. T r i g g l e , S.C. Maurer, J.G. Sarmiento, R.A. Jam's. E f f e c t s o f metal c a t i o n s and c a l m o d u l i n a n t a g o n i s t s on [»] n i t r e n d i p i n e b i n d i n g i n smooth and c a r d i a c muscle. J . Pharmacol. Exp. Ther. 230: 607-613, 1984. WAITE, R.P. 77 L u g n i e r , C , A. F o l l e n i u s , D. G e r a r d , J.C. S t o c l e t . B e p r i d i l and f l u n a r i z i n e as c a l m o d u l i n i n h i b i t o r s . Eur. J . Pharmacol. 98: 157-158, 1984. ~~ M a l i k , A.B., J . E . Kaplan, T.M. Saba. R e f e r e n c e sample method f o r c a r d i a c o u t p u t and r e g i o n a l blood f l o w d e t e r m i n a t i o n s i n the r a t . J . A p p l . P h y s i o l . 40: 472-475, 1976. Mannhold, R., R. S t e i n e r , W. Haas, R. Kaufmann. I n v e s t i g a t i o n s on the s t r u c t u r e a c t i v i t y r e l a t i o n s h i p s o f v e r a p a m i l . Nauyn Schmiedebergs A r c h . Pharmacol. 302: 217-226, 1978. M a s s i e , B.M., J.F. Tubau, J . S z l a c h c i c , C. V o l l m e r . Comparison and a d d i t i v i t y o f n i t r e n d i p i n e and h y d r o c h l o r o t h i a z i d e i n s y s t e m i c h yper- t e n s i o n . Am. J . C a r d i o l . 58: 16D-19D, 1986. M a t s i u , S., E. Murakami, N. T a k e k o s h i , Y. Hiramaru, H. Murakami, E. Kitan.o, K. Masuya, T. Saga, M. Nomura, S. F u j i t a , S. T s u j i . Hemodynamic e f f e c t s o f s u b l i n g u a l n i f e d i p i n e i n c o n g e s t i v e h e a r t f a i l u r e . Jap. C i r c . J . 43: 1081-1088, 1979. Matsumoto, S., T. I t o , T. Sada. Hemodynamic e f f e c t s o f n i f e d i p i n e i n c o n g e s t i v e h e a r t f a i l u r e . Am. J . C a r d i o l . 46: 476-80, 1980. Matthews, W.D., R.A. Macia, J . J . B e c k e r i n g h , R.M. d e M a r i n i s , A. deJonge, M. Thoolen, B. W i l f f e r t , P.B.M.W.M. Timmermans, P.A. van Z w i e t e n . C a l c i u m u t i l i z a t i o n i n the v a s o c o n s t r i c t i o n t o e n a n t i o m e r s o f SK F 89748-A. J . Pharmacol. Exp. Ther. 232: 330-336, 1985. McCann, E., C. Lundberg, B. G e r d i n , K.E. A r f o r s . S e l e c t i v e a c t i o n s of c a l c i u m a n t a g o n i s t i c drugs on the heamodynamic and r e g i o n a l organ blood f l o w i n r a t s . I n t . J . T i s s . 8 ( 3 ) : 205-212, 1986. McMahon, F.G. Comparison o f n i t r e n d i p i n e w i t h p r o p r a n o l o l and i t s use i n combined c a r d i o v a s c u l a r t h e r a p y . Am. J . C a r d i o l . 58: 8D-11D, 1986. Medgett, I.C., M.A.S. Rajanayagam. E f f e c t s o f reduced c a l c i u m i o n c o n c e n t r a t i o n and o f d i l t i a z e m on v a s o c o n s t r i c t o r responses t o n o r a d r e n a l i n e and s y m p a t h e t i c nerve s t i m u l a t i o n i n r a t i s o l a t e d t a i l a r t e r y . Br. J . Pharmac. 83: 889-898, 1984. M e l v i l l e , K.I., B.G. Benfey. Coronary v a s o d i l a t o r y and c a r d i a c a d r e n e r g i c b l o c k i n g e f f e c t s o f I p r o v e r a t r i 1 . Can. J . P h y s i o l . Pharmacol. 43: 339-342, 196 5. — M i l l a r d , R.W., G. Grupp, I.L. Grupp, J . D i S a l v o , A. OePover, A. Schwartz. C h r o n o t r o p i c , i n o t r o p i c , and v a s o d i l a t o r a c t i o n s o f d i l t i a z e m , n i f e d i -p i n e , and v e r a p a m i l . C i r c . Res. 52 ( s u p p l . 1 ) : 29-39, 1983. Morgan, K.G. R o l e o f c a l c i u m i o n i n maintenance o f v a s c u l a r smooth muscle t o n e . Am. J . C a r d i o l . 59: 24A-28A, 1987. WAITE, R.P. 78 M o r i t a , T., T. Maniwa, K. Satoh, N. T a i r a . U n d i f f e r e n t i a t e d e f f e c t s o f c a l c i u m a n t a g o n i s t s on p r e s s o r responses t o s e l e c t i v e alpha-1 and alpha-2 a d r e n o c e p t o r a g o n i s t s i n a n e s t h e t i z e d , s p i n a l dogs. J . Pharmacol. Exp. Ther. _234: 728-734, 1985. Mot u l s k y , H.J., M.D. Sn a v e l y , R.J. Hughes, P.A. I n s e l . I n t e r a c t i o n o f ver a p a m i l and o t h e r c a l c i u m channel b l o c k e r s w i t h o.l- and ( ^ - a d r e n e r - g i c r e c e p t o r s . C i r c . Res. 52 : 226 -231, 1983. Muir, A.L., C G . Wathen, W.J. Hannan. E f f e c t s o f f e l o d i p i n e on r e s i s t a n c e and c a p a c i t a n c e v e s s e l s i n p a t i e n t s w i t h e s s e n t i a l h y p e r t e n s i o n . Drugs 29 ( s u p p l . 2 ) : 59-65, 1985. M u l l e r - S c h w e i n i t z e r , E. T i s s u e s p e c i f i c s u s c e p t i b i l i t y o f a l p h a a d r e n o c e p t o r mediated v a s l c o n s t r i c t i o n t o n i f e d i p i n e . Nauyn-Schmiede- bergs A r c h . Pharmacol. 324: 64-6 9, 1983. Murphy, K.M.M., S.H. Snyder. Calcium a n t a g o n i s t r e c e p t o r b i n d i n g s i t e s l a b e l l e d w i t h [ 3H] n i t r e n d i p i n e . Eur. J . Pharmacol. 77: 201-202, 1982. — Murphy, K.M.M., R.J. Gould, B.L. L a r g e n t , S.H. Snyder. A u n i t a r y mechanism o f c a l c i u m a n t a g o n i s t drug a c t i o n . Proc. N a t l . Acad. S c i . 80: 860-864, 1983. ~ M z a i l , A.H.K., A.R. Noble. Verapamil induced s e c r e t i o n o f a c t i v e and i n a c t i v e r e n i n i n c o n s c i o u s sheep. C l i n . Exp. Pharmacol. P h y s i o l . 13: 187-94, 1986. Nakajima, H., M. Hoshiyama, K. Yamashita, A. Kiyomoto. E f f e c t o f d i l t i a z e m on e l e c t r i c a l and mechanical a c t i v i t y o f i s o l a t e d c a r d i a c v e n t r i c u l a r muscle o f guin e a p i g . Japan. J . Pharmacol. ,25: 383-392, 1975. N a y l e r , W.G., I. Mclnnes, J.B. Swann, J.M. P r i c e , V. Carson, D. Race, T.E. Lowe. Some e f f e c t s o f I p r o v e r a t r i l ( I s o p t i n ) on the a r d i o v a s c u l a r system. J . Pharmacol. Exp. Ther. 161: 247 -261, 196 8. N a y l e r , W.G., J.E. Thompson, B. J a r r o t t . The i n t e r a c t i o n of c a l c i u m a n t a g o n i s t s (slow channel b l o c k e r s ) w i t h m y o c a r d i a l a l p h a a d r e n o r e c e p - t o r s . J . Mol. C e l l . C a r d i o l . JL4: 185-188, 1982. N i l i u s , B., P. Hess, J.B. Lansman, R.W. T s i e n . A novel t y p e o f c a r d i a c c a l c i u n channel i n v e n t r i c u l a r c e l l s . Nature 316: 443-446, 1985. Nor d l a n d e r , M. A n t i h y p e r t e n s i v e haemadynamic e f f e c t s o f f e l o d i p i n e . Drugs 29 ( s u p p l . 2 ) : 90-101, 1985. Norman, R.I., M. B o r s o t t o , M. F o s s e t , M. L a z d u n s k i . D e t e r m i n a t i o n of the m o l e c u l a r s i z e o f the n i t r e n d i p i n e s e n s i t i v e c a l c i u m channel by r a d i a -t i o n i n a c t i v a t i o n . Biochem. Bio p h y s . Res. Comm. I l l : 878-883, 1983. North o v e r , B.J. Calcium a n t a g o n i s t s as a n t i - i n f l a m m a t o r y a g e n t s . In Calcium a n t a g o n i s t s ; an i n t e r n a t i o n a l seminar on the c u r r e n t and p o t e n t i a l t h e r a p e u t i c i n d i c a t i o n s f o r drugs a f f e c t i n g c a l c i u m . 19877 WAITE, R.P. 79 Nowycky, M.C, A.P. Fox, R.W. T s i e n . Three t y p e s o f neuronal c a l c i u m channel w i t h d i f f e r e n t c a l c i u m a g o n i s t s e n s i t i v i t y . Nature 316: 440-443, 1985. Ogawa, N., H. Ono. D i f f e r e n t e f f e c t s o f v a r i o u s v a s o d i l a t o r s on a u t o r e g u l a t i o n o f r e n a l blood f l o w i n a n e s t h e t i z e d dogs. Jap. J . Pharmacol. 41: 299-306, 1986a. Ogawa, N., H. Ono. D i f f e r e n t e f f e c t s o f n o r a d r e n a l i n e , a n g i o t e n s i n II and Bay K 8644 on the a b o l i t i o n o f a u t o r e g u l a t i o n o f r e n a l blood f l o w by v e r a p a m i l . Nauyn Schmiedebergs A r c h . Pharmacol. 333: 445-49, 1986b. O g i l v i e , R.I. Comparative e f f e c t s o f v a s o d i l a t o r drugs on f l o w d i s t r i b u t i o n and venous r e t u r n . Can. J . P h y s i o l . Pharmacol. 63: 1345-55, 1985. O s t e r r e i d e r , W., G. Brum, J . H e s c h l e r , W. T r a u t w e i n , V. F l o c k e r z i , F. Hofmann. I n j e c t i o n of s u b u n i t s o f c y c l i c AMP-dependent p r o t e i n k i n a s e i n t o c a r d i a c myocytes modulates c a l c i u m c u r r e n t . Nature 298: 576-578, 1982. Pang, C.C.Y. E f f e c t o f v a s o p r e s s i n a n t a g o n i s t and s a r a l a s i n on r e g i o n a l bk)od f l o w f o l l o w i n g hemorrhage. Am. J . P h y s i o l . 245: H749-H755, Pang, C.C.Y. V a s o p r e s s i n and a n g i o t e n s i n i n the c o n t r o l o f a r t e r i a l p r e s s u r e and r e g i o n a l blood f l o w i n a n a e s t h e t i z e d , s u r g i c a l l y s t r e s s e d r a t s . Can. J . P h y s i o l . Pharmacol. 61: 1494-1500, 1983b. Pang, C.C.Y., R. T a b r i z c h i . The e f f e c t s o f n o r a d r e n a l i n e , B-HT 920, methoximine, a n g i o t e n s i n II and v a s o p r e s s i n on mean c i r c u l a t o r y f i l l i n g p r e s s u r e i n c o n s c i o u s r a t s . Br. J . Pharmacol. 89: 389-94, 1986. ~~ Patmore, L., R.L. W h i t i n g . Calcium e n t r y b l o c k i n g p r o p e r t i e s of Tanshinone 11—A S u l p h o n a t e , an a c t i v e p r i n c i p a l o f the a n t i a n g i n a l e x t r a c t , Dan Shen. Br. J . Pharmacol. 75: 149P, 1982. Peach, M.J., H.A. S i n g e r , N.J. Izzo, A.L. Loeb. R o l e o f c a l c i u m i n endothelium-dependent r e l a x a t i o n o f a r t e r i a l smooth muscle. Am. J . C a r d i o l . 59: 35A-43A, 1987. Pearce, F.L. C a l c i u m as a t a r g e t f o r a n t i a l l e r g i c drugs. In C a l c i u m a n t a g o n i s t s ; an i n t e r n a t i o n a l seminar on the c u r r e n t and p o t e n t i a l  t h e r a p e u t i c i n d i c a t i o n s f o r drugs a f f e c t i n g c a l c i u m . 198/. P e d r i n e l l i , R., R.C. T a r a z i . Calcium e n t r y blockade by n i t r e n d i p i n e and a l p h a a d r e n e r g i c r e s p o n s i v e n e s s i n v i v o : Comparison w i t h n o n c a l c i u m e n t r y b l o c k e r v a s o d i l a t o r s i n absence and p r e s e n c e o f phenoxybenzamine p r e t r e a t m e n t . J . Pharmacol. Exp. Ther. 233: 636-642, 1985. P e r r y , V., R.J.A. Grand. Mechanisms o f c o n t r a c t i o n and the s p e c i a l i z e d p r o t e i n components o f smooth muscle. B r i t . Med. B u l l . 35(No. 3 ) : 227-234, 1979. WAITE, R.P. 80 Pol e s e , A., C. F i o r e n t i n i , M.T. O l i v a r i , M.D. G u a z z i . C l i n i c a l useof a c a l c i u m a n t a g o n i s t i c agent ( n i f e d i p i n e ) i n acute pulmonary edema. Am. J . Med. 56: 825-830, 1979. Pshychoyos, S., M. Bax, C. A t k i n s . D i f f e r e n c e s i n c a l c i u m e n t r y b l o c k e r s r e v e a l e d by e f f e c t s qn adenosine and a d r e n e r g i c r e c e p t o r s and c y c l i c AMP l e v e l s o f [2- H ] - a d e n i n e - p r e l a b e l l e d v e s i c l e s p r e p a r e d from g u i n e a p i g b r a i n . Biochem. Pharmacol. 35 (No. 10): 1639-1646, 1986. Rink, T . J . C a l c i u m and the p l a t e l e t . A p o t e n t i a l t a r g e t f o r novel a n t i t h r o m b o t i c d r u g s . In C a l c i u m a n t a g o n i s t s ; an i n t e r n a t i o n a l seminar on the c u r r e n t and p o t e n t i a l t h e r a p e u t i c i n d i c a t i o n s f o r drugs a f f e c t i n g c a l c i u m . 1987. R o d e n k i r c h e n , R.* R. Bayer, R. Mannhold. I I . S p e c i f i c and n o n - s p e c i f i c c a l c i u m a n t a g o n i s t s . A s t r u c t u r e - a c t i v i t y a n a l y s i s o f c a r d i o d e p r e s s i v e drugs. Prog. Pharmacol. J>(1): 9-23, 1982. R o d e n k i r c h e n , R., R. Bayer, R. S t e i n e r , F. B o s s e r t , H. Meyer, E. M o l l e r . S t r u c t u r e a c t i v i t y s t u d i e s on n i f e d i p i n e i n i s o l a t e d c a r d i a c muscle. Nauyn Schmiedebergs A r c h . Pharmacol. 310: 69-78, 1979. Roy, F., D. Pruneau. Comparison of the e f f e c t s o f n i f e d i p i n e , d i l t i a z e m and v e r a p a m i l on the mechanical a c t i v i t y o f r a b b i t p a p i l l a r y muscles induced by barium c h l o r i d e . Pharmacology 33: 69-75, 1986. Rubanyi, G.M. R o l e o f c a l c i u m i n t h e r e l e a s e o f e n d o t h e l i u m - d e r i v e d r e l a x i n g f a c t o r s . In C a l c i u m a n t a g o n i s t s ; an i n t e r n a t i o n a l seminar on the c u r r e n t and p o t e n t i a l t h e r a p e u t i c i n d i c a t i o n s f o r drugs a f f e c t i n g  c a l c i u m , 1987. Saeed, M., J . H o l t z , D. E i s n e r , E. Bassenge. A t t e n u a t i o n o f s y m p a t h e t i c v a s o c o n s t r i c t i o n by n i f e d i p i n e : The r o l e o f v a s c u l a r (^-adrenocep-t o r s . Eur. J . Pharmacol. 94: 149-153, 1983. Samar, R.E., T.G. Coleman. Measurement o f mean c i r c u l a t o r y f i l l i n g p r e s s u r e and v a s c u l a r c a p a c i t a n c e i n the r a t . Am. J . P h y s i o l . 234: H94-H100, 1978. S a n g u i n e t t i , M.C, R.S. Kass. V o l t a g e dependent b l o c k o f c a l c i u m channel c u r r e n t i n t h e c a l f c a r d i a c p u r k i n j e f i b e r by d i h y d r o p y r i d i n e c a l c i u m channel a n t a g o n i s t s . C i r c . Res. 55: 336-348, 1984. Schramm, M., G. Thomas, R. Towart, G. Franckowiak. Novel d i h y d r o p y r i d i n e s w i t h p o s i t i v e i n o t r o p i c a c t i o n t h r o u g h a c t i v a t i o n o f c a l c i u m chan- n e l s . Nature 303: 535-537, 1983. S c h r o e d e r , J.S. Treatment o f ' c o r o n a r y spasm w i t h c a l c i u m b l o c k e r s v a r i a n t a n g i n a and u n s t a b l e a n g i n a . I n " C a l c i u m b l o c k e r s , Mechanisms of a c t i o n and c l i n i c a l a p p l i c a t i o n s . Eds. S.F. F l a i m and R. Z e l i s , Urban and Schwarzenberg, B a l t i m o r e - M u n i c h , (1982), pp. 219-230. Seaman, K.L., C V . Greenway. H e p a t i c v e n o c o n s t r i c t o r e f f e c t s o f i s o p r o t e r e n o l and n i f e d i p i n e i n a n e s t h e t i z e d c a t s . Can. J . P h y s i o l . Pharmacol. 62: 665-672, 1983. WAITE, R.P. 81 S e g a s t r o , R., K.L. Seaman, I.R. Innes, C.V. Greenway. E f f e c t s o f n i f e d i p i n e on h e p a t i c blood volume i n c a t s : i n d i r e c t v e n o c o n s t r i c t i o n and absence o f i n h i b i t i o n o f p o s t s y n a p t i c a 2 - a d r e n o c e p t o r r e s p o n s e s . Can. J . P h y s i o l . Pharmacol. 64: 615-620, 1985. Share, L. ,Role o f c a r d i o c a s c u l a r r e c e p t o r s i n c o n t r o l o f ADH r e l e a s e . C a r d i o l o g y 61 ( s u p p l . 1 ) : 51-64, 1976. Shepherd, J.T., P.M. Vanhoutte. In The Human C a r d i o v a s c u l a r System F a c t s and Concepts. New York: Raven p r e s s , 1979. S i l v e r , P.J., J.M. Ambrose, R.J. M i c h a l a k , J . Dachiw. E f f e c t s o f f e l o d i p i n e and W-7 on a r t e r i a l myosin p h o s p h o r y l a t i o n , a c t i n - m y o s i n i n t e r a c t i o n and c o n t r a c t i o n . Eur. J . Pharmacol. 102: 417-424, 1984. Sing h , B.N., E.M. Vaughan W i l l i a m s . A f o u r t h c l a s s o f a n t i d y s r h y t h m i c a c t i o n . E f f e c t o f verap a m i l on ouabain t o x i c i t y , on a t r i a l and v e n t r i c u l a r i n t r a c e l l u l a r p o t e n t i a l s , and on o t h e r f e a t u r e s o f c a r d i a c f u n c t i o n . C a r d i o v a s c . Res. 6: 109-119, 1972. Si n g h , B.N., K. Nademanee, G. F e l d . C a l c i u m b l o c k e r s i n the tr e a t m e n t o f c a r d i a c a r r y t h m i a s . In Calcium b l o c k e r s , Mechanisms o f a c t i o n and  c l i n i c a l a p p l i c a t i o n s . Eds. S.F. FTaTm ancl W. Z e l i s , Urban and" Schwarzenberg, B a l t i m o r e - M u n i c h , (1982), pp. 245-264. Soward A.L., F r a c p , De F e y t e r PJ, Hugenholtz PG, S e r r u y s PW. Coronary and s y s t e m i c hemodynamic e f f e c t s o f i n t r a v e n o u s n i s o l d i p i n e . Am. J . ' C a r d i o l . 58: 1199-1203, 1986. Spedding, M. D i f f e r e n c e s between the e f f e c t s o f c a l c i u m a n t a g o n i s t s i n the p i t h e d r a t p r e p a r a t i o n . J . C a r d i o v a s c . Pharmacol. 4̂ : 973-79, 1982. Spedding, M. F u n c t i o n a l i n t e r a c t i o n s o f c a l c i u m a n t a g o n i s t s i n K + d e p o l a r i z e d smooth muscle. Br. J . Pharmac. 80: 485-488, 1983. Spedding, M. Changing s u r f a c e charge w i t h t h e s a l i c y l a t e d i f f e r e n t i a t e s between subgroups of c a l c i u m - a n t a g o n i s t s . Br. J . Pharmacol. 83: 211-20, 1984. — Spedding, M. Calcium a n t a g o n i s t subgroups. Trends i n Pharmacol. S c i . 3: 109-14, 1985. Spedding, M., C. Berg. I n t e r a c t i o n s between a " c a l c i u m channel a g o n i s t " , Bay K 8644, and c a l c i u m a n t a g o n i s t s d i f f e r e n t i a t e c a l c i u m a n t a g o n i s t subgroups i n K - d e p o l a r i z e d smooth muscle. Nauyn Schmiedebergs A r c h . Pharmacol. 328: 69-75, 1984. S t a r l i n g , E.H. Some p o i n t s i n the p a t h o l o g y of h e a r t d i s e a s e . Lancet I: 652, 1897. Stone, P.H. Cal c i u m a n t a g o n i s t s f o r P r i n z m e t a l ' s v a r i a n t a n g i n a , u n s t a b l e a n g i n a and s i l e n t m y o c a r d i a l i s c h e m i a : T h e r a p e u t i c t o o l and probe f o r i d e n t i f i c a t i o n of p a t h o p h y s i o l o g i c mechanisms. Am. J . C a r d i o l . 59_: 101B-115B, 1987. WAITE, R.P. 82 Stone, P.H., E.M. Antman, J.E. M u l l e r , E. Braunwald. Calcium channel b l o c k i n g agents i n the tre a t m e n t o f c a r d i o v a s c u l a r d i s o r d e r s . P a r t I I : Hemodynamic e f f e c t s and c l i n i c a l a p p l i c a t i o n s . Ann. I n t . Med. 93 : 886 -904, 198 0. S t r i e s s n i g , J . , K. Moosburger, A. G o l l , D.R. F e r r y , H. Glossmann. S t e r e o s e l e c t i v e p h o t o a f f i n i t y l a b e l l i n g of th e p u r i f i e d 1,4 d i h y d r o p y - r i d i n e r e c e p t o r o f the v o l t a g e dependent c a l c i u m c h a n n e l . Eur. J . Biochem. 161: 6 03-609, 1986. St u r e k , M., K. Hermsmeyer. Ca l c i u m and sodium c h a n n e l s i n s p o n t a n e o u s l y c o n t r a c t i n g v a s c u l a r muscle c e l l s . S c i e n c e 233: 475-478, 1986. T a b r i z c h i , R., C.C.Y. Pang. Comparative e f f e c t s of r a u w o l s c i n e , p r a z o s i n and p hentolamine on blood p r e s s u r e and c a r d i a c o u t p u t i n a n e s t h e t i z e d r a t s . Can. J . P h y s i o l . Pharmacol, ( i n p r e s s ) , 1987. T a i r a , N. D i f f e r e n c e s i n c a r d i o v a s c u l a r p f o f i l e among c a l c i u m a n t a g o n i s t s . Am. J . C a r d i o l . 59: 24B-29B, 1987. T a i r a , N., Y. Imai, M. H i w a t a r i . D i f f e r i n t i a l e f f e c t s o f n i t r o g l y c e r i n , t r i m e t a z i d i n e , v e r a p a m i l and SK F 24260 on venous r e t u r n as r e v e a l e d by t h e open-loop method i n the dog. Jap. J . Pharmacol. 30: 449-61, 1980. T a k a t a , Y., H. Kato. Comparative s t u d y on acute a n t i h y p e r t e n s i v e e f f e c t s and p h a r m a c o k i n e t i c s o f n i s o l d i p i n e , n i f e d i p i n e , n i m o d i p i n e and n i c a r -d i p i n e a d m i n i s t e r e d o r a l l y t o c o n s c i o u s r e n a l h y p e r t e n s i v e dogs. Arzneim-Forschung. 36( I I ) N o . 10: 1464-1471, 1986. T a y l o r , S.H., N.C. Jackson, J . A l l e n , P.E. P o o l . E f f i c a c y o f a new c a l c i u m a n t a g o n i s t PN 200-110 ( i s r a d i p i n e ) i n an g i n a p e c t o r i s . Am. J . C a r d i o l . 59: 123B-129B, 1987. T e r r i s , S., P.D. B o u r d i l l o n , D.T. Cheng, B. P i t t . D i r e c t c a r d i a c and p e r i p h e r a l v a s c u l a r e f f e c t s o f i n t r a c o r o n a r y and i n t r a v e n o u s n i f e d i - p i n e . Am. J . C a r d i o l . 58: 25-30, 1986. Timmermans, P.B.M.W.M., A. deJonge, J.C.A. van Meel, M.J. Mathy, P. van Zwie t e n . I n f l u e n c e o f n i f e d i p i n e on f u n c t i o n a l responses i n v i v o i n i t i a t e d a t a 2-adrenoceptors. J . C a r d i o v a s c . Pharmacol. 5: 1-11, 1983a. Timmermans, P.B.M.W.M., M. Thoolen, M. Mathy, B. W i l f f e r t , A. deJonge, P.A. van Z w i e t e n . SGD 101/75 i s d i s t i n g u i s h e d from o t h e r s e l e c t i v e a l - a d r e n o c e p t o r a g o n i s t s by the i n h i b i t i o n o f i t s p r e s s o r responses by c a l c i u m e n t r y blockade and v a s o d i l a t a t i o n i n p i t h e d r a t s and c a t s . Eur. J . Pharmacol. 96_: 187-192, 1983b. Toda, N. a - a d r e n o c e p t o r subtypes and d i l t i a z e m a c t i o n s i n i s o l a t e d human c o r o n a r y a r t e r i e s . Am. J . P h y s i o l . 250: H718-H724, 1986. Tog g a r t , E . J . , R. Z e l i s . The r o l e o f c a l c i u m b l o c k e r s i n the t r e a t m e n t of o t h e r c a r d i o v a s c u l a r d i s o r d e r s . In Ca l c i u m b l o c k e r s , Mechanisms of a c t i o n and c l i n i c a l a p p l i c a t i o n s . Eds. S.F. F l a i m and R. Z e l i s , Urban and Schwarzenberg, B a l t i m o r e - M u n i c h (1982), pp. 265-283. WAITE, R.P. 83 Towart, R. The s e l e c t i v e i n h i b i t i o n o f s e r o t o n i n induced c o n t r a c t i o n s o f r a b b i t c e r e b r a l v a s c u l a r smooth muscle by c a l c i u m a n t a g o n i s t i c d i h y d r o p y r i d i n e s : An i n v e s t i g a t i o n o f the mechanism o f a c t i o n o f ni m o d i p i n e . C i r c . Res. 48: 650-6 57, 1981. Towart, R., E. Wehinger, H. Meyer. E f f e c t s o f unsymmetrical e s t e r s u b s t i t u t e d 1,4 d i h y d r o p y r i d i n e d e r i v a t i v e s and t h e i r o p t i c a l isomers on c o n t r a c t i o n o f smooth muscle. Nauyn Schmeidebergs A r c h . Pharmacol. 317: 183-185, 1981. Towart, R., M. Schramm. Recent advamces i n the pharmacology o f the c a l c i u m c h a n n e l . Trends i n Pharmacol. S c i . 111-113; 1984. T r i g g l e , D.J. A n t i h y p e r t e n s i v e mechanism of a c t i o n and b i n d i n g s i t e s o f n i t r e n d i p i n e . Am. J . C a r d i o l . 58: 35D-38D, 1986. Tschirdewahz, B., H. K l e p z i g . C l i n i c a l s t u d i e s on the e f f e c t o f I s o p t i n and I s o p t i n S i n p a t i e n t s w i t h c o r o n a r y i n s u f f i c i e n c y . Deut. Med. Wochensch. 88: 1702-1710, 1963. Vaghy, P.L., J.S. W i l l i a m s , A. Schwartz. R e c e p t o r pharmacology o f c a l c i u m e n t r y b l o c k i n g agents. Am. J . C a r d i o l . 59: 9A-17A, 1987. Van Brummelen, K.J.P., P. Vermey, P.B.M.W.M. Timmermans, P.A. van Zwi e t e n . I n f l u e n c e o f c a l c i u m e n t r y -blockade on a l - and a2- a d r e n o c e p t o r mediated v a s o c o n s t r i c t i o n i n the for e a r m o f h y p e r t e n s i v e p a t i e n t s . Eur. J . C l i n . Pharmacol. 32: 115-120, 1987. Vanhoutte, P.M. The e x p e r t committe o f the world h e a l t h o r g a n i z a t i o n on c l a s s i f i c a t i o n o f c a l c i u m a n t a g o n i s t s : The v i e w p o i n t o f the r a p o r t e u r . Am. J . C a r d i o l . 59: 3A-8A, 1987. van Meel, J.C.A., A. deJonge, H . o / K a l k m a n , B. W i l f f e r t , P.B.M.W.M. Timmermans, P.A. van Zwieten . O r g a n i c and i n o r g a n i c c a l c i u m antagon- i s t s reduce v a s o c o n s t r i c t i o n i n v i v o mediated by p o s t s y n a p t i c a 2 - a d r e n o r e c e p t o r s . Nauyn Schmiedebergs A r c h . Pharmacol. 316: 288-293, 1981a. van Meel, J.C.A., A. deJonge, H.O. Kalkman, B. W i l f f e r t , P.B.M.W.M. Timmermans, P. van Zwi e t e n . V a s c u l a r smooth muscle c o n t r a c t i o n i n i t i a t e d by p o s t s y n a p t i c a 2 - a d r e n o r e c e p t o r a c t i v a t i o n i s induced by an i n f l u x o f e x t r a c e l l u l a r c a l c i u m . Eur. J Pharmacol. 69: 205-208, 1981b. van Neuten, J.M. Comparative b i o a s s a y o f v a s o a c t i v e drugs u s i n g i s o l a t e d p e r f u s e d r a b b i t a r t e r i e s . Eur. J . Pharmacol. 6_: 286 -2 9 3, 196 9. van Neuten, J.M., P.A-.J. Janssen. E f f e c t o f c i n n a r i z i n e on p e r i p h e r a l c i r c u l a t i o n i n dogs. Eur. J . Pharmacol. 17: 103-106, 1972. van Neuten, J.M., P.A.J. Janssen. Comparative s t u d y of the e f f e c t s of f l u n a r i z i n e and c i n n a r i z i n e on smooth muscles and c a r d i a c t i s s u e s . Arch. I n t . Pharmacodyn. 204: 37-55, 1973. WAITE, R.P. 84 van Neuten, J.M., J . van Beek, P.A.J. Janssen. E f f e c t o f f l u n a r i z i n e on c a l c i u m - i n d u c e d responses o f p e r i p h e r a l v a s c u l a r smooth muscle. A r c h . I n t . Pharmacodyn. 232: 42-52, 1978. V e l d h u i s , J.D. Calcium a c t i o n s i n e n d o c r i n e c e l l s . In Ca l c i u m b l o c k e r s . Mechanisms o f a c t i o n and c l i n i c a l a p p l i c a t i o n s . Eds. S.F. F l a i m and R. Z e l i s , Urban and Schwarzenberg, B a l t i m o r e - M u n i c h , (1982), pp. 107-120. Ve n t e r , J.C., C M . F r a s e r , J.S. Schaber, C Y . Jung, G. B o l g e r , D.J. T r i g g l e . M o l e c u l a r p r o p e r t i e s o f the slow inward c a l c i u m c h a n n e l . J . B i o l . Chem. 258: 9344-9348, 1983. Walker; M.J.A. Calcium a n t a g o n i s t s and c a r d i a c a r r y t h m i a s . In Cal c i u m a n t a g o n i s t s ; an i n t e r n a t i o n a l seminar on the c u r r e n t and p o t e n t i a l t h e r a p e u t i c i n d i c a t i o n s f o r drugs a f f e c t i n g c a l c i u m , 1987. W e i n s t e i n , D.B., J.G. H e i d e r . A n t i a t h e r o g e n i c p r o p e r t i e s o f c a l c i u m a n t a g o n i s t s . Am. J . C a r d i o l . 59: 163B-172B, 1987. Wong, P . C , C J . K e i r a n s , P. Timmermans. Heterogenous e f f e c t s o f c a l c i u m e n t r y b l o c k e r s on b i p h a s i c c o n s t r i c t i o n o f the r a b b i t e a r a r t e r y . Eur. J . Pharmacol. 131: 307-310, 1986. Worley, J.F., J.W. Deitmer, M.T. Nelson. S i n g l e n i s o l d i p i n e s e n s i t i v e c a l c i u m c h a n n e l s i n smooth n u s c l e c e l l s i s o l a t e d from r a b b i t mesent-e r i c a r t e r y . Proc. N a t l . Acad. S c i . 83: 5746-5750, 1986. Yamamoto,- J . , N.C. Tr i p p o d o , S. I s h i s e , D. F r o h l i c h . T o t a l v a s c u l a r pressure-volume r e l a t i o n s h i p i n t h e c o n s c i o u s r a t . Am. J . P h y s i o l . 238: H823-H828, 1980. Yammamoto, H., 0. Hwang, C. van Home. Bay K 8644 d i f f e r e n t i a t e s between p o t e n t i a l and r e c e p t o r o p e r a t e d c a l c i u m c h a n n e l s . Eur. J . Pharmacol. 102: 555-557, 1984. Y o u s i f , F., D.J. T r i g g l e . F u n c t i o n a l i n t e r a c t i o n s between o r g a n i c c a l c i u m channel a n t a g o n i s t s i n smooth muscle. Can. J . P h y s i o l . Pharmacol 63: 193-195, 1984. ~

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