Hypotensive effects of N,N-din-n-propylodopamine in the anesthetized dog: comparison with sodium nitroprusside

N,N-Din-n-propyldopamine (DPDA), a dopamine (DA) vascular agonist without beta 1-adrenergic activity, was compared with mitroprusside in pentobarbital-anesthetized dogs. DPDA was infused intravenously at 20, 40, and 80 microgram/kg/min. DPDA caused dose-related reductions in mean arterial pressure when infused at 20 and 40 microgram/kg/min; no further decrease occurred at 80 microgram/kg/min. Sodium nitroprusside, 1-6 microgram/kg/min, approximately equaled the hypotension produced by 40 microgram/kg/min of DPDA. DPDA differed from sodium nitroprusside in causing a more rapid fall in mean arterial pressure and a more rapid recovery upon discontinuation. DPDA had no effect on pulmonary arterial pressure, but sodium nitroprusside reduced it. DPDA reduced heart rate; sodium nitroprusside increased heart rate. Hexamethonium. 10 mg/kg, significantly reduced the hypotension produced by DPDA. The DA antagonist, sulpiride, completely eliminated the reduction in blood pressure caused by DPDA. Neither hexamethonium nor sulpiride affected the hypotension produced by sodium nitroprusside. These studies suggest that DPDA reduces blood pressure in part by inhibiting the sympathetic nervous system and in part by vasodilation secondary to action on DA vascular receptors.