Abstract

Pentazocine injected immediately before an injection of vasopressin caused a significantly greater lethality in rats than when either compound was given alone. This effect was not observed in either mice or dogs. There was no alteration of the lethality of pentazocine in mice when injections of vasopressin were given immediately after the narcotic-antagonist analgesic. Vasopressin reduced the magnitude and duration of the behavioral effects of pentazocine in dogs. Oxytocin did not potentiate the lethality of pentazocine in rats. Pentazocine and vasopressin caused cardiac and respiratory depression leading to death in anesthetized rats but not in anesthetized dogs. The synergistic lethality of these compounds in rats was not blocked by prior injections of tripelennamine or atropine. vagotomy did not block the synergistic lethality in the anesthetized rats. Vasopressin significantly increased the level of pentazocine in rat, but not mouse, brain and heart. Oxytocin which did not increase the lethality of pentazocine did not alter the level of pentazocine in rat brain tissue.