Stimulation by adrenaline and dopamine but not by noradrenaline of myocardial ?-adrenoceptors mediating positive inotropic effects in human atrial preparations

Abstract

In isolated electrically driven right auricular strips of human hearts (1 Hz at 37°C) the ability of the endogenous catecholamines noradrenaline, adrenaline, and dopamine to mediate positive inotropic effects by stimulation of myocardial α-adrenoceptors was investigated. 1. The concentration-response curve for the positive inotropic effect of noradrenaline was shifted to the right by pindolol, 10⁻⁸M, whereas the additional blockade by phentolamine, 3×10⁻⁶M, was without further effect; therefore, the positive inotropic effect of noradrenaline is mediated by β-adrenoceptors only. 2. In contrast, the positive inotropic effects of adrenaline as well as of dopamine are caused by stimulation of both, β- and α-adrenoceptors. 3. These results are discussed with respect to the possible physiological and pathophysiological function of myocardial α-adrenoceptors.