Nitric oxide modulates arteriolar responses to increased sympathetic nerve activity

Area of Science:

• Physiology
• Vascular Biology
• Neuroscience

Background:

• Sympathetic nerve activity regulates blood flow through vasoconstriction.
• Nitric oxide (NO) is a key mediator of vascular tone.
• The role of endogenous NO in modulating sympathetic neurogenic vasoconstriction in the intestinal microvasculature remains unclear.

Purpose of the Study:

• To investigate whether endogenous nitric oxide limits arteriolar responses to increased sympathetic nerve activity in the rat small intestine.

Main Methods:

• Utilized intravital microscopy to measure diameter changes in rat intestinal small feed arteries (SFA), first-order arterioles (1A), and second-order arterioles (2A).
• Applied perivascular sympathetic nerve stimulation at varying frequencies.
• Administered alpha-adrenoceptor antagonist phentolamine and nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) to assess the role of NO.

Main Results:

• Sympathetic nerve stimulation induced frequency-dependent constriction in all studied vessels.
• Phentolamine completely abolished the sympathetic-induced constriction.
• Inhibition of nitric oxide synthase with L-NMMA significantly enhanced sympathetic neurogenic constriction in SFA and 1A.
• The enhanced constriction in the presence of L-NMMA was reversed by L-arginine.

Conclusions:

• Endogenous nitric oxide production attenuates sympathetic neurogenic constriction in the intestinal microvasculature.
• These findings highlight a regulatory mechanism involving NO in controlling sympathetic vasoconstriction within the gut.