EFFECT OF N-OMEGA-NITRO-L-ARGININE METHYL-ESTER ON ARTERIAL-PRESSURE AND ON VASODILATOR AND VASOCONSTRICTOR RESPONSES - INFLUENCE OF INITIAL VASCULAR TONE

Intravenous N(omega)-nitro-L-arginine methyl ester (L-NAME) 0.3, 3 and 30 mg/kg produced a dose-dependent increase of blood pressure in urethane-anesthetized rats. Similar pressure responses occurred in rats after ganglionic or adrenergic blockade, hemorrhage or acetylcholine infusion. L-NAME potentiated the pressor response to phenylephrine in pentolinium-treated rats. L-NAME increased the depressor effect of acetylcholine and sodium nitroprusside and shortened the acetylcholine response. Phenylephrine potentiated the magnitude but not the duration of the acetylcholine response and had no effect on the duration or magnitude of sodium nitroprusside-induced hypotension. L-NAME potentiated the initial fall of blood pressure induced by a 5 min acetylcholine infusion but had no effect on the pressure drop at the end of infusion. These results suggest that basal production of nitric oxide (NO) is not related to vascular tone and do not support the view that acetylcholine releases NO from resistance vessels in vivo.