Possible mechanisms implicated on the hypothermic effect induced by morphine in guinea-pig

Morphine 50 mg/kg i.p. produced a hypothermic effect in unrestrained guinea-pigs and this effect was potentiated when animals were restrained. The morphine-induced hypothermia was antagonized by dexamethasone treatment (1 mg/kg 24 hr and 0.5 mg/kg i.p. 2 hr before morphine). Treatment with the inhibitor of peptide biosynthesis cycloheximide (10 mg/kg i.p. 24 and 2 hr before morphine) also inhibited the hypothermic effect of morphine. ACTH injected intracerebroventricular produced no changes in body temperature. These results are consistent with the hypothesis that anterior pituitary peptide beta-endorphin may play a role in the hypothermic effect produced by morphine in the guinea-pig.