Adrenal and Thyroid Interactions of β-Endorphin-Induced Body Temperature Responses of Rats at 24.5°C 1

Abstract

Abstract

The effect of β-endorphin (β-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°C. Relative humidity of 50 ± 0.3% and a 12L:12D photoperiod (L = 0900 to 2100 hr) were maintained. Rectal temperature (T _r )was measured using thermistors. Corticosterone and thyroid hormones were determined by radioimmunoassay. Intracerebroventricular (IVT) administration of varying doses (0.05 to 50.0 μg) of β-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 β-END resulted in little or no T _r response. The β-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 β-END. Adrenalectomized or hypophysectomized rats receiving IVT injections of β-END did not consistently display an increased T _r. β-Endorphin administration had no detectable effect on Serum corticosterone or thyroxine but serum triiodothyronine was decreased. These data suggest the acute hyperthermic action of β-END is mediated centrally through Opiate receptors and does not involve adrenergic receptors.