The potentiating effect of naloxone upon apomorphine-induced hyperthermia

Intravenous or intracerebroventricular pretreatment with the narcotic antagonist naloxone in rabbits significantly enhanced the magnitude of the hyperthermic response to the dopaminergic agonist apomorphine. Naloxone did not potentiate the hyperthermic action of either amphetamine or lysergic acid diethylamide. Apomorphine-in induced hyperthermia was sensitive to antagonism by haloperidol, cyproheptadine and p-chlorophenylalanine. However in rabbits pretreated with any of the above antagonists, administration of naloxone five minutes prior to apomorphine challenge restored the hyperthermic effect of apomorphine. Increasing the dose of the apomorphine challenge likewise surmounted the antagonism. It was concluded from these data that naloxone exerts a potentiating influence upon apomorphine drug effect in naive rabbits as well as rabbits pretreated with antagonists of apomorphine-induced hyperthermia.