ObjectiveTo observe the effect of nitric oxide(NO）on cardiovascular activities in the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM), so as to understand the role of central NO in cardiovascular regulation. MethodsThe changes of blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were observed following treatments with increased or decreased NO in the NTS and RVLM of anaesthetized SD rats.ResultsMicroinjection of the NO precusor L-arginine (L-Arg, 2 nmol in 50 nl) into the NTS, a key relay of cardiovascular reflex transmission, produced significant decreases in BP, HR, and RSNA (P<0.05), and injection of NO synthase inhibitor NG-nitro-L-arginine methyl ester(L-NAME,10 nmol in 50 nl) into the NTS produced significant increases in these cardiovascular parameters (P<0.05). However, injection of L-Arg (2 nmol in 100 nl) into the RVLM, a key region controlling sympathetic outflow, significantly increased basal BP, HR, and RSNA (P<0.05), and injection of L-NAME (10 nmol in 100 nl) into the RVLM showed a cardiovascular inhibition effect (P<0.05).ConclusionNO exhibits different effects in different cardiovascular centers, suggesting that it plays a special role in maintaining the basal cardiovascular activity.