POSSIBLE MECHANISMS INVOLVED IN CORONARY VASODILATOR RESPONSE TO DOPAMINE

Abstract

Dopamine increased coronary blood flow in the dog heart pretreated with .alpha.-adrenoceptor blocking agents. The coronary vasodilator response was completely inhibited by indomethacin when pretreated with propranolol in addition to .alpha. blockade. The coronary vasodilation exerted by NaNO2 was potentiated by indomethacin and adrenergic blockade. In coronary arterial strips, dopamine produced a contraction which was abolished by phenoxybenzamine. Dopamine elicited a dose-dependent relaxation in coronary arterial strips contracted previously by KCl after pretreatment with phenoxybenzamine. The relaxation was potentiated by indomethacin; this effect was completely blocked by propranolol. Prostaglandin (PG) E1 produced a relaxing response but reduced the dopamine-induced relaxation. .beta.-Adrenoceptor stimulation and release of PG were involved in the coronary vasodilator response to dopamine. PG released by dopamine may increase coronary blood flow and also reduce .beta.-adrenoceptor stimulation by inhibiting adenylate cyclase.