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Effects of dose on effector mechanisms in morphine-induced hyperthermia and poikilothermia

Abstract

The effect of a variety of morphine doses on thermoregulatory effector systems was examined in ambient temperatures of 27.0° C and 4.0° C. Rats were given saline or morphine sulfate (5, 15, or 25 mg/kg); their core temperature, oxygen consumption, and activity were monitored for 4 or 6 h post-injection. The results suggest two distinct actions of morphine, possibly mediated by two opiate receptors. Low doses of morphine produce hyperthermia that is the result of a direct activation of activity and whole body heat production. High doses produce effects dependent on ambient temperature: hypermetabolism and hyperthermia in the 27.0° C environment; hypometabolism, vasodilation, and hypothermia in the 4.0° C environment. The findings suggest limitations in current set-point theories of morphine's thermic actions.

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Correspondence to Timothy B. Baker.

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Jorenby, D.E., Keesey, R.E. & Baker, T.B. Effects of dose on effector mechanisms in morphine-induced hyperthermia and poikilothermia. Psychopharmacology 98, 269–274 (1989). https://doi.org/10.1007/BF00444704

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Key words

  • Morphine
  • Hyperthermia
  • Set-point
  • Oxygen consumption
  • Thermoregulation