Action of preoptic injections of beta-endorphin on temperature regulation in rabbits.
Male New Zealand White rabbits, Oryctolagus cuniculus, were stereotaxically implanted with a guide tube above the preoptic/anterior hypothalamus area (PO/AH) for the injection of the opioid peptide, beta-endorphin (beta-E), naloxone, sodium salicylate, or physiological saline. PO/AH and ear temperature, oxygen consumption, and evaporative heat loss (EHL) were recorded in free-moving rabbits before and after injection of saline followed with beta-E, naloxone, or sodium salicylate at ambient temperatures (Ta) of 2-31 degrees C. A 5-micrograms injection of beta-E promoted a rapid reduction in ear temperature followed by a prolonged rise in PO/AH (body) temperature. Preinjection with an isovolumetric amount of the opiate antagonist, naloxone, inhibited the thermoregulatory effects of beta-E. The beta-E-induced rise in body temperature was directly correlated with Ta. beta-E had no effect on oxygen consumption at Ta's of 5 and 27 degrees C. When measured 30 min after injection, beta-E demonstrated a significant inhibition of EHL at Ta's of 27 and 31 but not 5 degrees C. The beta-E-induced rise in body temperature was not antagonized with preinjections of sodium salicylate in the PO/AH. These data indicate that beta-E promotes a regulated increase in body temperature. The mechanism of activation appears to be distinct from that of an infectious fever.
D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D001833:Body Temperature Regulation / Q000187:drug effects*; D004423:Ear; D004723:Endorphins / Q000494:pharmacology*; D007031:Hypothalamus / Q000502:physiology*; D007700:Kinetics; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D011301:Preoptic Area / Q000187:drug effects / Q000502:physiology*; D011817:Rabbits; D014661:Vasoconstriction / Q000187:drug effects; D001615:beta-Endorphin
D004723:Endorphins; D009270:Naloxone; D001615:beta-Endorphin