SPECIES DIFFERENCES IN ANTAGONISTIC EFFECT OF MORPHINE AGAINST DEPRESSOR RESPONSE TO DOPAMINE

Abstract

Species differences in antagonistic effect of morphine against depressor response to dopamine, determined by the minimum level of blood pressure attained, were observed in dogs, cats and rabbits. A depressor response to dopamine after α-adrenergic blockade was eliminated by morphine in cats, but potentiated in dogs. The response to dopamine after repeated injections of ephedrine was potentiated by morphine both in cats and dogs. Without pretreatment in rabbits, the response to dopamine was diminished by morphine. It thus appears that species difference is considerable regarding antagonism of morphine to dopamine in blood pressure responses.