title: Stress-induced release of brain and pituitary beta-endorphin: major role of endorphins in generation of hyperthermia, not analgesia.
abstract: The present paper examines the conjectured causal relationship between the alterations in brain, pituitary and plasma levels of endorphins and the antinociception (analgesia) and hyperthermia elicited by acute stress. A 5-min foot-shock instigated a significant depression in the levels of beta-endorphin immunoreactivity (beta-EI) in both the hypothalamus and periventricular beta-endorphinergic fibre-containing tissue. A large elevation in plasma levels of beta-EI, consisting of about 70% beta-endorphin (beta-EP), and 30% beta-lipotropin (beta-LPH) was associated with a significant reduction in the beta-EI content of both the anterior (AL) and neurointermediate (NIL) lobes of the pituitary. No concomitant changes in the levels of Met-enkephalin immunoreactivity (M-EI) in discrete areas of brain and pituitary were detectable. Application of a high (10 mg/kg) but not a low (1 mg/kg) dose of naloxone, prior to foot-shock, slightly reduced the increase in tail-flick latency evoked by this stress. In contrast, both of these doses strongly and dose-dependently attenuated the accompanying rise in core temperature (Tc). Chronic (approximately 30 day) morphine treatment resulted in a 45% decrease in the NIL content of beta-EI and a clear depression in its basal plasma levels, although a substantial post-stress rise in plasma beta-EI was still found: stress-induced analgesia (SIA) was enhanced, but the concurrent stress-induced hyperthermia (SIH), reduced in morphinized animals. These data demonstrate that stress produces a generalized mobilization of both central and pituitary pools of beta-EI, and indicate that endorphins may play a more important role in the mediation of changes in Tc than in the generation of the concomitant increase in nociceptive threshold, upon activation by stress.
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects; D004597:Electroshock; D004723:Endorphins / Q000502:physiology*; D004744:Enkephalin, Methionine; D004745:Enkephalins / Q000502:physiology; D007031:Hypothalamus / Q000502:physiology*; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D010902:Pituitary Gland / Q000502:physiology*; D051381:Rats; D013312:Stress, Physiological / Q000503:physiopathology; D001615:beta-Endorphin
chemical_list: D004723:Endorphins; D004745:Enkephalins; D009270:Naloxone; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; D009020:Morphine