Metabolic, respiratory, vasomotor and body temperature responses to beta-endorphin and morphine in rabbits.
1. The effects of beta-endorphin and morphine on thermoregulatory responses of unanaesthetized rabbits to different ambient temperatures (Ta) of 2, 22 and 32 degrees C were assessed. 2. Intraventricular administration of either beta-endorphin or morphine produced dose-dependent hypothermia at 2 and 22 degrees C Ta. At 2 degrees C Ta the hypothermia was brought about solely by a decrease in metabolic heat production. At 22 degrees C Ta the hypothermia was due to a decrease in metabolism and an increase in peripheral blood flow. However, at 32 degrees C Ta, there were no changes in rectal temperature in response to either beta-endorphin or morphine application. 3. Hypothermic effects of the administration of beta-endorphin or morphine were greatly antagonized by pretreatment of animals with either an opiate antagonist naloxone or a serotonin depletor 5,6-dihydroxytryptamine. 4. These findings indicate that the hypothermic responses to beta-endorphin or morphine in rabbits may be mediated through central serotonergic mechanisms. The hypothermia was due to a decrease in heat production and/or an increase in heat loss.
D015115:5,6-Dihydroxytryptamine / Q000494:pharmacology; D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects*; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D004431:Ear, External / Q000098:blood supply; D004723:Endorphins / Q000494:pharmacology*; D007276:Injections, Intraventricular; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D011817:Rabbits; D012039:Regional Blood Flow / Q000187:drug effects; D012119:Respiration / Q000187:drug effects
D004723:Endorphins; D009270:Naloxone; D009020:Morphine; D015115:5,6-Dihydroxytryptamine