ALPHA-1-ADRENOCEPTOR-MEDIATED AND ALPHA-2-ADRENOCEPTOR-MEDIATED PRESSOR-RESPONSES - ARE THEY DIFFERENTIATED BY CALCIUM-ANTAGONISTS OR BY FUNCTIONAL ANTAGONISM

Abstract

We investigated the effect of cardiovascular depression on the pressor responses to the alpha 1-adrenoceptor selective agonist methoxamine, and the alpha 2-adrenoceptor selective agonist B-HT 920 in anesthetized ganglion-blocked rats. The calcium channel blocking drug nifedipine preferentially inhibited the effect of B-HT 920, as has been reported by other authors. Lowering the starting blood pressure by hemorrhage, by nitroprusside infusion, or by additional pentobarbitone also preferentially inhibited the pressor effect of B-HT 920. These selective effects of vascular depression on B-HT 920 are consistent with predicted interactions between functional antagonists and a partial (low-efficac..