POTENTIATION OF MORPHINE ANALGESIA BY COCAINE IN MICE

The interaction between morphine and cocaine in producing analgesia in mice has been studied. To investigate the mechanism of this interaction, some other local anaesthetics and amphetamine and imipramine were tested in combination with morphine. The effect of pretreatment with reserpine, or of treatment with the antiadrenaline drug phentolamine, was examined. The potency of each local anaesthetic in potentiating noradrenaline was assessed. Cocaine potentiated morphine analgesia. Procaine and lignocaine, though less potent, were also effective, but cinchocaine was not. Hence, ability to potentiate morphine was not related to local anaesthetic activity. Involvement of the sympathomimetic action of cocaine was indicated because (1) the potencies of cocaine, procaine and lignocaine in potentiating morphine were related to their potencies in potentiating noradrenaline, (2) reserpine antagonized the actions of morphine and morphine-cocaine combinations and (3) amphetamine potentiated morphine. However imipramine did not increase and phentolamine did not reduce the action of morphine. © 1993.