Adrenal and thyroid interactions of beta-endorphin-induced body temperature responses of rats at 24.5 degrees C

The effect of beta-endorphin (beta-END) and the role of the adrenal and thyroid glands on body temperature were examined in male rats in a controlled environment room at 24.5 +/- 0.1 degrees C. Relative humidity of 50 +/- 0.3% and a 12L:12D photoperiod (L = 0900 to 2100 hr) were maintained. Rectal temperature (Tr) was measured using thermistors. Corticosterone and thyroid hormones were determined by radioimmunoassay. Intracerebroventricular (IVT) administration of varying doses (0.05 to 50.0 micrograms) of beta-END resulted in a hyperthermia that began 30 min post-IVT injection and continued for an additional hour. Intravenous injections of the same doses of beta-END resulted in little or no Tr response. The beta-END-induced hyperthermia was antagonized by intraperitoneal injection of naloxone. Pretreatment with propranolol, phenotolamine, or both drugs in combination did not block the hyperthermia caused by beta-END. Adrenalectomized or hypophysectomized rats receiving IVT injections of beta-END did not consistently display an increased Tr. beta-Endorphin administration had no detectable effect on serum corticosterone or thyroxine but serum triiodothyronine was decreased. These data suggest the acute hyperthermic action of beta-END is mediated centrally through opiate receptors and does not involve adrenergic receptors.