Baroreceptor dysfunction induced by nitric oxide synthase inhibition in humans

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Regulation
• Endothelial Function

Background:

• The sympathetic nervous system and endothelium-derived substances are critical for cardiovascular homeostasis.
• Interactions between the sympathetic nervous system and nitric oxide (NO) in cardiovascular regulation are not well understood.

Purpose of the Study:

• To investigate how inhibiting nitric oxide (NO) synthesis affects baroreceptor regulation of sympathetic nerve activity and hemodynamics.
• To elucidate the specific role of NO in autonomic cardiovascular control.

Main Methods:

• Healthy volunteers underwent microneurography to record muscle sympathetic nerve activity (MSA).
• Central hemodynamics were measured under varying central venous pressures induced by lower body negative pressure.
• Nitric oxide synthase was inhibited using NG-monomethyl-L-arginine (L-NMMA).

Main Results:

• Inhibition of NO synthesis increased systolic and diastolic blood pressure and decreased stroke volume index.
• L-NMMA administration blunted the compensatory heart rate increase during orthostatic stress but did not affect MSA.
• Altered heart rate response was not attributed to elevated blood pressure, as phenylephrine infusion had no similar effect on heart rate.

Conclusions:

• Nitric oxide (NO) synthesis inhibition specifically alters baroreceptor-mediated heart rate regulation, leaving muscle sympathetic activity unaffected in healthy individuals.
• These findings underscore a significant role for NO in human reflex-mediated heart rate control.