Stress-related changes of opiate sensitivity in thermoregulation.

Body temperature reactions to morphine were tested in freely-moving adult rats reared without any previous experience to human handling. These animals reacted to 8 mg/kg morphine s.c. with a biphasic hypo-hyperthermic response. When the rats had been handled for six days, the same dose of morphine induced a monophasic hyperthermic reaction. The results are regarded as evidence that stress-related factors interfere with the thermoregulatory effects of morphine.