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Effect of exogenous nitric oxide on baroreflex function in humans.
N Hogan1, A Kardos, D J Paterson
1Department of Cardiovascular Medicine, John Radcliffe Hospital, Oxford OX3 9UD, United Kingdom.
The American Journal of Physiology
|July 17, 1999
Summary
Exogenous nitric oxide (NO) did not affect baroreflex sensitivity in humans but reduced blood pressure variability, suggesting decreased sympathetic control. NO donors also directly increased heart rate.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Regulation
- Nitric Oxide Signaling
Background:
- Nitric oxide (NO) donors are known to inhibit sympathetic neurotransmission and baroreceptor activity in vitro.
- Previous research suggests NO may directly stimulate heart rate.
Purpose of the Study:
- To investigate the effects of exogenous nitric oxide (NO) on cardiovascular autonomic control in humans.
- To assess the impact of NO on baroreflex sensitivity and heart rate variability.
Main Methods:
- Infusion of sodium nitroprusside (SNP), a NO donor, or glucose in 16 healthy subjects.
- Phenylephrine (PE) was used to prevent SNP-induced hypotension.
- Baroreflex sensitivity (BRS) and blood pressure (BP) and heart rate (HR) variability were measured.
Main Results:
- SNP + PE infusion did not alter BRS or HR variability.
- A significant reduction in low-frequency power of diastolic and systolic BP was observed.
- A sustained 12% increase in HR occurred without changes in brachial or aortic BP.
Conclusions:
- Exogenous NO does not affect the cardiac-vagal baroreflex in humans.
- SNP reduced BP low-frequency power, indicating decreased baroreflex/sympathetic control of peripheral resistance.
- NO donors exert a direct positive chronotropic effect on heart rate.