α-adrenoceptor-mediated positive inotropic effect of phenylephrine in isolated human ventricular myocardium

Abstract In isolated human ventricular myocardium the α-adrenoceptor agonist phenylephrine had a positive inotropic effect in preparations from 9 of 14 patients. This effect was seen in the presence of the β-adrenoceptor-bloking agent propronolol but was nearly abolished by the α-adrenoceptor blocking agent prazosin. In contrast to the β-adrenoceptor-mediated positive inotropic effect, the effect of phenylephrine was accompanied by a prolongation of the isometric contraction. The results suggest that α-adrenoceptors exist in human ventricular myocardium.