Regional hemodynamic effects of atrial natriuretic peptide or captopril in Brattleboro rats.

The regional hemodynamic effects of rat atrial natriuretic peptide (ANP) (1 and 10 nmol) were measured in the same conscious Brattleboro rats in water-replete and in water-deprived states (14 h). In the latter condition, the effects of ANP were compared with those of captopril (3.2 mumol). In rats in the water-replete state, the low dose of ANP had no significant effects on mean arterial pressure (MAP) or renal, superior mesenteric, or hindquarter vascular resistances, although heart rate (HR) showed a transient increase. The high dose of ANP caused a fall in MAP and an increase in HR. Renal and hindquarter vascular beds showed dilatation followed by constriction; there was a mesenteric vasoconstriction only. In rats in the water-deprived state, the low dose of ANP caused a marked fall in MAP but only a transient increase in HR; there was marked hindquarters vasodilation. The high dose of ANP caused dramatic hypotension and bradyarrhythmia; an initial hindquarter vasodilation gave way to vasoconstriction; renal and mesenteric vasoconstrictions also occurred. The initial effects of captopril on MAP were similar to those of the high dose of ANP, but the regional hemodynamic effects of captopril indicated a potent inhibition of both primary and secondary vasoconstrictor mechanisms.