Modulation of arteriolar sympathetic constriction by local nitric oxide: Onset during rapid juvenile growth

The goal of this study was to determine if the endogenous activity of nitri c oxide (NO) and/or prostanoids can limit arteriolar responses to increased sympathetic nerve activity in striated muscle, and to explore possible cha nges in these influences during rapid juvenile growth. Using intravital mic roscopy, arteriolar responses to 2-16 Hz sympathetic nerve stimulation were studied in the superfused spinotrapezius muscle of weanling (4-5 weeks old ) and juvenile (7-8 weeks old) rats. Nerve stimulation elicited frequency-d ependent arteriolar constrictions that were abolished in both age groups by the fast Naf-channel blocker tetrodotoxin or the alpha-antagonist phentola mine. Diameter and now responses to 2-8 Hz stimulation were greater in juve nile rats than in weanling rats. In juvenile rats but not in weanling rats, the NO synthase inhibitor N-G-monomethyl-L-arginine (L-NMMA) reduced arter iolar diameters and blood now at rest and enhanced the arteriolar diameter and now responses to sympathetic nerve stimulation. The cyclooxygenase inhi bitor meclofenamate reduced resting arteriolar diameters in both age groups , but had no effect on responses to sympathetic nerve stimulation in either group. These results suggest that juvenile growth is accompanied by an ove rall increase in arteriolar responsiveness to sympathetic nerve activity, a nd by the onset of local NO activity that limits this increased responsiven ess. (C) 1998 Academic Press.