ANALGESIC EFFECTS IN MONKEYS OF MORPHINE, NALORPHINE, AND A BENZOMORPHAN NARCOTIC ANTAGONIST

¹ Department of Pharmacology and Experimental Therapeutics and Department of Medicine (Division of Clinical Pharmacology), The Johns Hopkins University School of Medicine, Baltimore, Maryland

The comparative analgesic actions of morphine, nalorphine, and a benzomorphan narcotic antagonist (Win 20,740) were assessed in monkeys by means of a titration schedule. This schedule permits a continuous recording of the subject's aversive threshold to a painful electrical stimulus. Both morphine and Win 20,740 increased the level at which the monkeys kept the stimulus. Nalorphine, even at extremely high dose levels, had no reliable analgesic effect. It was able to antagonize the threshold-raising actions of morphine, however, which the benzomorphan compound could not reliably do.