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Calcium suppresses central angiotensin II pressor response less in SHR
1Second Department of Medicine, Kyoto Prefectural University of Medicine, Japan.
Insights
Central nervous system calcium injections lower blood pressure and heart rate in rats. This effect is modulated by calcium channel blockers and angiotensin II, with differences observed in spontaneously hypertensive rats.
Area of Science:
- Cardiovascular Physiology
- Neuropharmacology
- Hypertension Research
Background:
- Central cardiovascular regulation is complex and influenced by various ions and neurotransmitters.
- Calcium's role in central cardiovascular control remains incompletely understood.
- Spontaneously hypertensive rats (SHR) exhibit altered central regulatory mechanisms compared to normotensive controls.
Purpose of the Study:
- To investigate the effects of intracerebroventricular (ICV) calcium administration on central cardiovascular regulation in conscious rats.
- To explore the interaction between central calcium and angiotensin II.
- To compare responses in Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR).
Main Methods:
- Cardiovascular parameters (mean arterial pressure, heart rate) were monitored in conscious rats following ICV calcium injection.
- Calcium channel blocker (diltiazem) pretreatment was used to assess the role of calcium channels.
- Plasma norepinephrine levels were measured to evaluate sympatho-inhibition.
- Responses to ICV angiotensin II were assessed before and after calcium administration.
Main Results:
- ICV calcium induced dose-dependent decreases in mean arterial pressure and heart rate.
- Diltiazem attenuated the cardiovascular effects of calcium.
- Calcium administration led to decreased plasma norepinephrine, suggesting sympatho-inhibition.
- Central calcium modulated pressor responses to angiotensin II, with differential effects observed between WKY and SHR.
Conclusions:
- Calcium exerts significant effects on central cardiovascular regulation, including vasodilation and sympatho-inhibition.
- A pharmacological interaction exists between central calcium and angiotensin II.
- Altered central calcium-angiotensin II interaction in SHR may contribute to the maintenance of hypertension.
Abstract:
To determine whether calcium alters central cardiovascular regulation, cardiovascular responses to intracerebroventricular (ICV) injection of calcium were recorded in conscious Wistar rats. Calcium injection consistently produced dose-dependent decreases in mean parterial pressure and heart rate. Pretreatment with a calcium channel blocker, diltiazem, attenuated cardiovascular responses to calcium. Decreases in plasma norepinephrine indicated the contribution of sympatho-inhibition to vasodepression by calcium. Preceding calcium injection reduced pressor responses to ICV-injected angiotensin II. These findings suggest that there is a pharmacological interaction between calcium and angiotensin II in the central nervous system. In spontaneously hypertensive rats (SHR), cardiovascular responses to calcium was larger than Wistar Kyoto rats (WKY). By contrast, calcium reduced pressor responses to angiotensin II only in WKY but not in SHR. Because the central interaction between calcium and angiotensin II has been different in SHR, our results imply that this difference may be related to the maintenance of high blood pressure in SHR.