CIRCANNUAL VARIATIONS IN BEAR PLASMA-ALBUMIN AND ITS OPIOID-LIKE EFFECTS ON GUINEA-PIG ILEUM

Previous studies suggest that hibernation is controlled by an opioid s ystem. In this study we examined the effect of plasma albumin fraction s drawn from black bears at timed intervals while in hibernation or du ring the awake state in fall and winter, on induced contractility of t he guinea pig ileum. Four hundred nM morphine produced typical suppres sion of contractility and 400 or 1000 nM naloxone (an opiate antagonis t) restored it. Twenty mg of lyophilized albumin fraction from the win ter hibernating bear caused similar suppression, the effect being grea ter than that of either summer bear or winter-active bear plasma album in. Naloxone reversed the suppression in all cases. Strong suppression of contractility was also demonstrated with 2.5 nM [D-Pen(2,5)]-enkep halin (DPDPE), a delta agonist, but only minor suppression with 2.5 nM dynorphin A, a kappa agonist. Results support the opioid nature of th e albumin-bound hibernation-induction trigger substance, that it binds to the delta opiate receptor, and that delta agonist opioid productio n may increase during the hibernation season.