Dose-dependent effects of nitric oxide synthase inhibition on systemic andrenal hemodynamics in conscious lambs

The present experiments were carried out to determine the role of nitric ox ide in influencing systemic and renal hemodynamics in conscious young sheep . Parameters of cardiovascular function were measured before and for 4 h af ter intravenous injection of either L-NAME (N-G-nitro-L-arginine methyl eat er) or D-NAME (N-G-nitro-D-arginine methyl ester) at doses of 10, 20, or 40 mg/kg in 13 conscious, chronically instrumented young sheep aged 43 +/- 5 days. Blood pressure increased and heart rate decreased in a dose-dependent manner following administration of L-NAME. Renal vascular resistance was i ncreased for 10 min following a dose of 10 mg/kg of L-NAME and for 120 min following a dose of 40 mg/kg of L-NAME. The renal vasodilatory response to close arterial injection of 1 mu g/kg of acetylcholine was attenuated by L- NAME in a dose-dependent manner. These experiments provide the first inform ation that under normal physiological conditions in conscious young animals , nitric oxide influences systemic and renal hemodynamics.