Effects of droperidol on cardiovascular adrenoceptors

The influence of droperidol on the pressor effect of noradrenaline was investigated in pithed rats injected with propranolol. Droperidol induced a dose-dependent shift of the noradrenaline dose-response curve to the right, but proved to be 20 times less potent than phentolamine. Droperidol produced a considerably more pronounced inhibition of the effect of tyramine than of that of noradrenaline.--The influence of droperidol on the increase in tension induced by noradrenaline was determined in isolated aortic strips of rats. The drug caused a marked parallel shift of the noradrenaline concentration-response curve to the right (pA2:7.99). In this preparation droperidol and phentolamine were equieffective.--Droperidol did not produce a significant shift of the noradrenaline concentration-response curves obtained for the positive chronotropic and inotropic effects in spontaneously beating right guinea-pig atria and in electrically driven left atria, respectively.--It is concluded that droperidol is a competitive inhibitor of the vascular alpha-adrenoceptors, leaving the beta-adrenoceptors of the heart unaffected, and that it inhibits the neuronal uptake mechanism of noradrenaline.