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The role of inducible nitric oxide synthase (iNOS) on cardiovascular function in rats with streptozotocin-induced diabetes Cheng, Xing
Abstract
Cardiovascular complications are leading causes of death in Type 1 and Type 2 diabetes mellitus. Experimental studies and clinical trials have firmly established a link between hyperglycemia and cardiovascular complications. The precise mechanism involved, however, remains elusive. Recently, inducible nitric oxide synthase (iNOS) and oxidative stress have been implicated as factors that initiate cardiovascular complications in diabetes. However, there is a lack of direct evidence that link these biological changes with abnormalities in cardiovascular function. The three primary goals of the present investigation were: 1) to investigate if rats with streptozotocin (STZ, 60 mg/kg i.v.)-induced Type 1 diabetes had functional abnormalities of the cardiovascular system, and if these changes were associated with the activation of iNOS, formation of peroxynitrite, and reduced myocardium antioxidant capacity; 2) to examine if treatment with 1400W (inhibitor of iNOS) improved cardiovascular response to noradrenaline (NA) concurrently with inhibition of the activation of iNOS and formation of peroxynitrite in diabetes; 3) to examine if the chronic treatment of the antioxidant N-acetylcysteine (NAC, antioxidant and inhibitor of iNOS) reduced activation of iNOS, decreased formation of peroxynitrite, increased antioxidative capacity, and improved cardiac contractile function in diabetes. The results show that diabetic and control rats had similar mean arterial pressure (MAP) and total peripheral resistance (TPR) at three weeks after injection of STZ. NA increased in vivo MAP and TPR in both groups; however, the responses were markedly less in the diabetic than control rats. Rats with diabetes, relative to the controls, had reduced potency (increased ED50) for the pressor (2.5-fold of control) and mean circulatory filling pressure (MCFP, an index of venous tone, 4.3-fold of control) response to NA, as well as reduced maximum pressor response (efficacy) to NA. Diabetic rats also had reduced potency (ED50, 5-fold of control) of the pressor response to angiotensin II. Therefore, arterial and venous constrictions are impaired at an early phase of STZ-induced Type I diabetes. The diabetic rats in the present study also had reduced heart rate (HR) and maximal rate of increase as well as decrease of left ventricular pressure (+dP/dt of LV) relative to the controls at three weeks after injection of STZ. In addition, the diabetic rats had reduced inotropic and chronotropic responses to NA and dobutamine (β1-adrenoceptor agonist), exemplified by the decreases in the efficacy (reduced Emax ) and potency (increased EC50) of HR, and left ventricular developed tension as well as contractility (±dP/dt of LV) responses to dobutamine. The activation of iNOS and oxidative stress were confirmed in myocardium at three weeks after injection of STZ, evidenced by 1) detection of RT-PCR products (RNA) of iNOS in the hearts of the diabetic but not control rats; 2) the three-fold increase of activity of iNOS in the hearts of diabetic rats relative to the controls, and inhibition of this increase by 1400W; 3) clear identification of immunostaining (proteins) of iNOS and NT (in vivo marker of peroxynitrite, an oxidant and cytotoxic mediator) in the hearts of the diabetic rats, but not the controls; 4) similar baseline lipid peroxidation (formation of 15-F2t-isoprostane), but decreased tissue antioxidation capacity (increased thiobarbituric acid reactive substances, thiobarbituric acid reactive substance) upon peroxidation challenge. Acute treatment with 1400W (3 mg/kg followed by 3 mg/kg/h, i.v) did not alter baseline hemodynamic variables or responses to NA in the control rats but completely restored the efficacy (Emax) and insignificantly increased the potency (reduced ED50,) of MAP response to NA. This drug also completely restored the TPR response to NA, and increased MCFP response to a high dose of NA. Moreover, treatment with 1400W enhanced the influence of NA on cardiac contractility (LVP, LV ±dP/dt) in the diabetic rats and concurrently reduced the activity of iNOS in the diabetic myocardium. Therefore, an activation of iNOS contributes to depressed cardiovascular contractile response to NA at the acute phase of STZ-induced diabetes. Selective inhibition of iNOS partially restores cardiovascular responses to NA. Chronic treatment with the antioxidant NAC (1.2 g/day/kg) did not affect any measured variables in the control rats but improved cardiac contraction to dobutamine (1-57 μg/min/kg), exemplified by increased efficacy (Emax) and potency (EC50) of HR and left ventricular developed tension (LVP) as well as contractility (±dP/dt of LV) responses to dobutamine. NAC also concurrently reduced immunostaining of iNOS and NT, as well as decreased myocardial level of 15-F2t-isoprostane. Therefore, antioxidant supplementation is beneficial in the management of cardiac contractile dysfunction in diabetes mellitus. To our best knowledge, this is the first study that links cellular activation of iNOS in diabetes to abnormal in vivo adrenoceptor-mediated responses in the heart and blood vessels, and demonstrates the restoration of cardiovascular function after selective inhibition of the activity of iNOS. These results provide direct evidence that link depressed cardiac contractility with the activation of iNOS as well as the production of peroxynitrite and its associated nitration of tyrosine and reduction of antioxidative capacity. These results also provide the first evidence that NAC, an antioxidant/iNOS inhibitor, improved cardiac function concurrently with the reduction of myocardial level of 15-F2t-isoprostane at three week after the induction of diabetes. Our results suggest that antioxidant therapy or inhibition the activity of iNOS is beneficial in the management of cardiac contractile dysfunction at an early phase of diabetes, even when baseline levels of lipid peroxidation products are not yet elevated.
Item Metadata
Title |
The role of inducible nitric oxide synthase (iNOS) on cardiovascular function in rats with streptozotocin-induced diabetes
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2004
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Description |
Cardiovascular complications are leading causes of death in Type 1 and Type 2 diabetes
mellitus. Experimental studies and clinical trials have firmly established a link between
hyperglycemia and cardiovascular complications. The precise mechanism involved, however,
remains elusive. Recently, inducible nitric oxide synthase (iNOS) and oxidative stress have
been implicated as factors that initiate cardiovascular complications in diabetes. However, there
is a lack of direct evidence that link these biological changes with abnormalities in
cardiovascular function.
The three primary goals of the present investigation were: 1) to investigate if rats with
streptozotocin (STZ, 60 mg/kg i.v.)-induced Type 1 diabetes had functional abnormalities of the
cardiovascular system, and if these changes were associated with the activation of iNOS,
formation of peroxynitrite, and reduced myocardium antioxidant capacity; 2) to examine if
treatment with 1400W (inhibitor of iNOS) improved cardiovascular response to noradrenaline
(NA) concurrently with inhibition of the activation of iNOS and formation of peroxynitrite in
diabetes; 3) to examine if the chronic treatment of the antioxidant N-acetylcysteine (NAC,
antioxidant and inhibitor of iNOS) reduced activation of iNOS, decreased formation of
peroxynitrite, increased antioxidative capacity, and improved cardiac contractile function in
diabetes.
The results show that diabetic and control rats had similar mean arterial pressure (MAP)
and total peripheral resistance (TPR) at three weeks after injection of STZ. NA increased in
vivo MAP and TPR in both groups; however, the responses were markedly less in the diabetic
than control rats. Rats with diabetes, relative to the controls, had reduced potency (increased
ED50) for the pressor (2.5-fold of control) and mean circulatory filling pressure (MCFP, an
index of venous tone, 4.3-fold of control) response to NA, as well as reduced maximum pressor
response (efficacy) to NA. Diabetic rats also had reduced potency (ED50, 5-fold of control) of
the pressor response to angiotensin II. Therefore, arterial and venous constrictions are impaired
at an early phase of STZ-induced Type I diabetes.
The diabetic rats in the present study also had reduced heart rate (HR) and maximal rate
of increase as well as decrease of left ventricular pressure (+dP/dt of LV) relative to the controls
at three weeks after injection of STZ. In addition, the diabetic rats had reduced inotropic and
chronotropic responses to NA and dobutamine (β1-adrenoceptor agonist), exemplified by the decreases in the efficacy (reduced Emax ) and potency (increased EC50) of HR, and left
ventricular developed tension as well as contractility (±dP/dt of LV) responses to dobutamine.
The activation of iNOS and oxidative stress were confirmed in myocardium at three
weeks after injection of STZ, evidenced by 1) detection of RT-PCR products (RNA) of iNOS in
the hearts of the diabetic but not control rats; 2) the three-fold increase of activity of iNOS in
the hearts of diabetic rats relative to the controls, and inhibition of this increase by 1400W; 3)
clear identification of immunostaining (proteins) of iNOS and NT (in vivo marker of
peroxynitrite, an oxidant and cytotoxic mediator) in the hearts of the diabetic rats, but not the
controls; 4) similar baseline lipid peroxidation (formation of 15-F2t-isoprostane), but decreased
tissue antioxidation capacity (increased thiobarbituric acid reactive substances, thiobarbituric
acid reactive substance) upon peroxidation challenge.
Acute treatment with 1400W (3 mg/kg followed by 3 mg/kg/h, i.v) did not alter baseline
hemodynamic variables or responses to NA in the control rats but completely restored the
efficacy (Emax) and insignificantly increased the potency (reduced ED50,) of MAP response to
NA. This drug also completely restored the TPR response to NA, and increased MCFP
response to a high dose of NA. Moreover, treatment with 1400W enhanced the influence of NA
on cardiac contractility (LVP, LV ±dP/dt) in the diabetic rats and concurrently reduced the
activity of iNOS in the diabetic myocardium. Therefore, an activation of iNOS contributes to
depressed cardiovascular contractile response to NA at the acute phase of STZ-induced
diabetes. Selective inhibition of iNOS partially restores cardiovascular responses to NA.
Chronic treatment with the antioxidant NAC (1.2 g/day/kg) did not affect any measured
variables in the control rats but improved cardiac contraction to dobutamine (1-57 μg/min/kg),
exemplified by increased efficacy (Emax) and potency (EC50) of HR and left ventricular
developed tension (LVP) as well as contractility (±dP/dt of LV) responses to dobutamine. NAC
also concurrently reduced immunostaining of iNOS and NT, as well as decreased myocardial
level of 15-F2t-isoprostane. Therefore, antioxidant supplementation is beneficial in the
management of cardiac contractile dysfunction in diabetes mellitus.
To our best knowledge, this is the first study that links cellular activation of iNOS in
diabetes to abnormal in vivo adrenoceptor-mediated responses in the heart and blood vessels,
and demonstrates the restoration of cardiovascular function after selective inhibition of the
activity of iNOS. These results provide direct evidence that link depressed cardiac contractility
with the activation of iNOS as well as the production of peroxynitrite and its associated nitration of tyrosine and reduction of antioxidative capacity. These results also provide the first evidence
that NAC, an antioxidant/iNOS inhibitor, improved cardiac function concurrently with the
reduction of myocardial level of 15-F2t-isoprostane at three week after the induction of diabetes.
Our results suggest that antioxidant therapy or inhibition the activity of iNOS is beneficial in the
management of cardiac contractile dysfunction at an early phase of diabetes, even when
baseline levels of lipid peroxidation products are not yet elevated.
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Extent |
12468523 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-11-27
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0091749
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2004-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.