Evidence against involvement of β-endorphin in thermoregulation in the cat

Wesley G. Clark, Iok Hou Pang, Gary L. Bernardini

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In the cat naloxone has little, if any, effect on temperature under usual laboratory conditions and does not reduce febrile responses to leukocytic pyrogen. Hence, endogenous opioid peptides that are antagonized by naloxone are not essential for induction of fever or for maintenance for normal temperature in the absence of appreciable thermal stress. The purpose of this study was to assess the contribution of such endogenous opioids to thermoregulation in cats exposed to more severe thermal and non-thermal stresses. Changes in temperature of unanesthetized cats were determined after third cerebral ventricular injections of large doses (100, 250 μg) of naloxone or saline vehicle. Naloxone had no appreciable effect on the temperature of cats acutely exposed to hot (34°C) or cold (4°C)environments, either before or after tolerance to morphine had been induced by progressively greater daily or twice-daily intraventricular doses of 10-70 μg morphine sulfate. Naloxone also did not significantly affect the temperature of cats subjected to neck-restraint or forced to stand on a small platform if they were to avoid contact with ice water. These results provide no indication that an endogenous opioid peptide, such as β-endorphin, that is antagonized by naloxone contributes appreciably to thermoregulation in cats. They do not rule out the possibility that endogenous opioids, such as Met-enkephalin, that are not readily antagonized by naloxone are important for normal thermoregulation.

Original languageEnglish
Pages (from-to)741-745
Number of pages5
JournalPharmacology, Biochemistry and Behavior
Issue number5
StatePublished - May 1983


  • Cat
  • Endogenous opioid peptides
  • Morphine tolerance
  • Naloxone
  • Restraint
  • Thermal stress
  • Thermoregulation


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