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Related Experiment Videos

Heat stroke: opioid-mediated mechanisms

A A Romanovsky1, C M Blatteis

  • 1Department of Physiology and Biophysics, University of Tennessee at Memphis 38163, USA.

Journal of Applied Physiology (Bethesda, Md. : 1985)
|December 1, 1996
PubMed
Summary

Opioid agonists contribute to paradoxical responses during heat stroke in guinea pigs, including vasoconstriction and hypothermia. Blocking these opioid pathways with naltrexone prevented these effects and mortality, suggesting therapeutic potential for heat disorders.

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Area of Science:

  • Physiology
  • Thermoregulation
  • Neuroscience

Background:

  • Intraperitoneal heating (IPH) in guinea pigs induces heat stroke with high mortality.
  • Paradoxical phenomena observed include hyperthermia-induced vasoconstriction and post-IPH hypothermia.
  • The role of endogenous opioid agonists in these heat stroke responses was previously uninvestigated.

Purpose of the Study:

  • To test the hypothesis that endogenous opioid agonists mediate hyperthermia-induced vasoconstriction and hypothermia.
  • To investigate the thermoregulatory effects of the opioid antagonist naltrexone (NTX) during IPH-induced heat stroke.

Main Methods:

  • Experiments conducted on 24 unanesthetized guinea pigs with implanted intraperitoneal thermodes and intrahypothalamic thermocouples.
  • IPH induced by perfusing 45°C water through the thermode at a controlled rate and duration.

Related Experiment Videos

  • Thermoregulatory effects of naltrexone (50 μmol/kg sc) were assessed during IPH and under normal conditions at an ambient temperature of ~24°C.

    • Main Results:

    • IPH induced hyperthermia, followed by a significant post-IPH body temperature fall in survivors (50% mortality rate).
    • Naltrexone administration prevented hyperthermia-induced vasoconstriction and attenuated post-IPH hypothermia.
    • NTX-treated animals showed no mortality, and NTX had minor effects on thermoregulation under normal conditions.

    Conclusions:

    • Both hyperthermia-induced vasoconstriction and hypothermia during heat stroke are dependent on endogenous opioid agonists.
    • Opioid-mediated inhibition of metabolism is speculated for hypothermia, and opioid-induced hemodynamic alterations for vasoconstriction.
    • The absence of these phenomena in NTX-treated survivors suggests they are markers of heat stroke severity, and opioid antagonists may offer therapeutic benefits.