[Effects of microinjection of L-NNA and SNP into ventrolateral medulla on blood pressure, heart rate and renal sympathetic nerve activity in rats].

The effects of microinjection of a NO synthase inhibitor--N-nitro-L-arginine (L-NNA) and NO donor-sodium nitroprusside (SNP) into ventrolateral medulla on blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were examined in anesthetized rats to define the role of L-arginine: NO pathway in the central regulation of BP and to explore the underlying mechanism. The results obtained were as follows: (1) Following microinjection of L-NNA into rostral ventrolateral medulla (RVLM), both of MAP and RSNA were increased. The effects lasted for more than 30 min and could be reversed by prior intravenous injection of L-arginine. (2) In response to microinjection of SNP into RVLM, MAP and RSNA were decreased, while HR showed no significant change. (3) During microinjection of L-NNA into caudal ventrolateral medulla (CVLM), MAP, HR and RSNA were decreased. (4) Upon injection of SNP into CVLM, MAP and RSNA were increased, but HR showed no significant change. The above-mentioned results indicate that the L-arginine: NO pathway may exhibit a modulatory action on the activity of ventrolateral medulla neurons.