The central roles of nitric oxide (NO) in regulations of the blood pressure and heart rate were examined in anesthetized rats. Intracerebroventricular (i.c.v.) injection of N(ω)-nitro-L-arginine methyl ester (L-NAME) caused dose-dependent increase in the blood pressure and heart rate. The pressor response of the blood pressure to L-NAME (2 μmol, i.c.v.) was reduced by L-arginine (5 μmol, i.c.v). Pretreatment with a ganglionic blocker, pentolinium (10 mg/kg, i.v.), significantly inhibited both pressor responses induced by L-NAME (2 μmol, i.c.v). The later pressor response of the blood pressure to L-NAME was also inhibited by the angiotensin II AT-1 blocker losartan (10 mg/kg, i.v). These results suggest that the response of the blood pressure to L-NAME is mediated by both the sympathetic nervous system and the renin-angiotensin system.
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