Ds. Bruce et al., CIRCANNUAL VARIATIONS IN BEAR PLASMA-ALBUMIN AND ITS OPIOID-LIKE EFFECTS ON GUINEA-PIG ILEUM, Pharmacology, biochemistry and behavior, 53(4), 1996, pp. 885-889
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.