Comparison of the effects of morphine, pethidine and pentazocine in rabbits pretreated with a monoamine oxidase inhibitor.

1. Rabbits were premedicated with pargyline and the changes in rectal temperature measured after the intravenous infusion of morphine, pentazocine and pethidine.2. Pethidine produced pronounced rises in rectal temperature which were dose dependent. One out of the four rabbits given 1 mg/kg died in hyperthermia. Four out of the four rabbits given 5 mg/kg died in hyperthermia. Doses of 10 mg/kg of pethidine caused no significant change in the rectal temperature of rabbits not pretreated with pargyline.3. Morphine and pentazocine in doses of 1 mg and 10 mg/kg did not significantly alter the rectal temperature of rabbits pretreated with pargyline except for one rabbit which developed a delayed hyperthermia following the injection of morphine 1 mg/kg.