Previous studies in adult animals have shown that nitric oxide synthetase(NOS) is present in afferent baroreceptor neurons (Wang, J Comp Neurol 336:419, 1993) and that NO inhibits carotid baroreceptor activity(BRA) (Matsuda, Circ Res 76:426, 1995). Since NOS containing neurons have been found in the carotid sinus of newborn animals (Tanaka,Microscopy Research and Technique, 29:90, 1994), the present study was designed to test the hypothesis that NO modulates BRA early in life and that this modulation is developmentally regulated. Using an isolated carotid sinus preparation, we assessed BRA in anesthetized newborn (1 to 7 days, n=6) and 2 month old lambs (n=4). First, NOS-inhibitor L-NMMA (10-4 M) did not modify BRA during progressive increase in carotid sinus pressure (CSP). Second, the NO donor S-nitrosocysteine (CysNO) in the presence of L-NMMA(5×10-4 M) did not change the BRA response to progressive rises in CSP in either age group. We conclude that, in contrast to the adult where NO decreases BRA, there is no significant effect of NO on BRA in newborn and young (2 month old) sheep.

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