MATERIALS AND METHODS: Sprague-Dawley rats weighing 250-300 g each were anesthetized with thiopental (50 mg/kg IP). The femoral artery was cannulated and the arterial blood pressure and heart rate were continuously monitored in the anesthetized rats (n=19). ANP was administered into the jugular vein after L-NAME treatment. In vitro experiments were performed on intact and endothelium-denuded isolated thoracic aortic rings (n=51) in the presence of either L-NAME or methylene blue.

RESULTS: Intravenous administration of ANP (5 ug/kg bolus and 0.2 ug/kg/min infusion) caused a decrease in the mean arterial pressure. L-NAME-pretreatment (1 mg/kg) suppressed the depressor response of ANP. In vitro, the ANP caused a dose-dependent relaxation, and the relaxation response to ANP was attenuated by L-NAME (10-4 M). Endothelium removal or methylene blue (10-5 M) also inhibited the ANP-induced vascular relaxation.

CONCLUSION: These results suggest that the hypotensive and the vasorelaxant effect of ANP are, at least in part, NO-dependent.