Action of preoptic injections of β-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, β-endorphin (β-E), naloxone, sodium salicylate, or physiological saline. PO/AH and ear temperature, oxgyen consumption, and evaporative heat loss (EHL) were recorded in free-moving rabbits before and after injection of saline followed with β-E, naloxone, or sodium salicylate at ambient temperatures (T(a)) of 2-31° C. A 5-μg injection of β-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 β-E. The β-E-induced rise in body temperature was directly correlated with T(a). β-E had no effect on oxygen consumption at T(a)'s of 5 and 27° C. When measured 30 min after injection, β-E demonstrated a significant inhibition of EHL at T(a)'s of 27 and 31 but not 5°C. The β-E-induced rise in body temperature was not antagonized with preinjections of sodium salicylate in the PO/AH. These data indicate that β-E promotes a regulated increase in body temperature. The mechanism of activation appears to be distinct from that of an infectious fever.
Rezvani, AH; Gordon, CJ; Heath, JE
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