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

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