Nitric oxide mediates sympathetic vasoconstriction at supraspinal, spinal, and synaptic levels

Area of Science:

• Physiology
• Neuroscience
• Pharmacology

Background:

• Nitric oxide (NO) plays a crucial role in regulating vascular tone.
• The precise level of the sympathetic nervous system where NO mediates regional vasoconstriction is not fully understood.
• Neural mechanisms contributing to vasoconstriction following NO inhibition require further investigation.

Purpose of the Study:

• To determine the spinal level at which NO modulates sympathetic vasoconstriction in regional circulations.
• To elucidate the involvement of neural pathways in vasoconstriction after NO inhibition.
• To differentiate the regulatory mechanisms of NO on mesenteric, renal, and hindquarter vascular beds.

Main Methods:

• Utilized ganglionic blockade (hexamethonium) and alpha1-receptor blockade (prazosin) in conscious rats.
• Investigated sympathetic nervous system involvement via spinal sectioning at T1.
• Blocked NO synthesis using Nomega-nitro-L-arginine methyl ester (L-NAME).
• Monitored regional blood flow in mesenteric arteries, renal arteries, and terminal aorta using electromagnetic flowmetry.

Main Results:

• L-NAME administration increased arterial pressure and peripheral resistance.
• Ganglionic blockade attenuated L-NAME-induced resistance increases in the mesentery and kidney, irrespective of spinal integrity.
• Ganglionic blockade reduced hindquarter resistance in intact rats but not in spinal-sectioned rats.
• Prazosin significantly decreased hindquarter resistance, indicating alpha1-adrenergic mediation.

Conclusions:

• NO suppresses sympathetic vasoconstriction in the mesenteric and renal circulations at the spinal level.
• Hindquarter vascular tone is regulated by supraspinal and synaptic neural mechanisms.
• These findings highlight distinct NO-mediated regulatory pathways in different vascular beds.