Nitric oxide mediation of cardiac receptor reflex responses in the pregnant rat.

Abstract

Our purpose was to determine the contribution of centrally released nitric oxide to baseline sympathetic tone and reflex cardiovascular responses to cardiac stretch in the pregnant rat. Baseline blood pressure and renal sympathetic nerve activity and reflex changes in these variables in response to intraatrial saline solution injections were measured in anesthetized pregnant (n = 24) and virgin (n = 27) rats before and after bilateral microinjection of L-nitroarginine methyl ester (0.01 to 1 micromol) into the dorsal medulla. Data were analyzed with use of nonparametric analysis of variance. L-Nitroarginine methyl ester microinjection altered basal blood pressure and sympathetic nerve activity (p < 0.05) in virgin but not pregnant rats. L-Nitroarginine methyl ester significantly and equivalently attenuated the reflex sympathoinhibitory and depressor responses to cardiac stretch for 40 minutes in pregnant and virgin animals. Central nitric oxide does not modulate basal sympathetic tone in the pregnant rat but is released in the medulla in response to cardiac stretch and plays a role in reflex cardiovascular responses similar to that in virgin rats.