The purpose of this study was to investigate the effect of exogenous nitric oxide (NO) on rabbit carotid sinus (CS) baroreceptor (BR) activity in vitro, especially in regard to determining whether the effect might be mediated by cGMP. The carotid sinus nerve (CSN) basal discharge could be divided into two groups: low-amplitude (LA) and high-amplitude (HA) ones. It was found that the HA discharge depended on superfusing-rate, but was not affected by several types of chemoreceptor stimuli, hence indicating a baroreceptive origin of the HA. Secondly, L-arginine (L-arg, 4.6-5.7 mmol/L) and nitroglycerin (NG, 0.07-0.88 mmol/L), precursor or donor of NO, excitated BR in a dose-dependent manner (P < 0.01). Lastly, inhibition of soluble guanylate cyclase (GC) with methylene blue (MB) affected neither the basal discharge of BR nor the response of BR to L-arg or nitroglycerin (NG).