Hibernation-induction trigger. I. Opioid-like effects of prairie dog plasma albumin on induced contractility of guinea pig ileum.

Studies have shown that plasma albumin fractions (PAFs) from hibernating mammals can inhibit induced contractility of the guinea pig ileum similarly to morphine. This study examined PAFs from two species of prairie dogs, one that undergoes natural seasonal hibernation (white-tailed, WT) and one that does not but can be induced to hibernate (black-tailed, BT). Dose-response curves of lyophilized PAF yielded IC50 values (mg) of 20.23 for summer WT, 15.53 for hibernating WT, 15.45 for summer BT, and 13.16 for winter-active BT. Winter samples from both species have IC50s lower than samples from summer animals, indicating greater potency of winter PAFs in suppressing guinea pig ileum contractility and therefore the presence of more opioid ligands in winter prairie dog plasma. Studies to elucidate receptor selectivity of PAF continue.

Hibernation-induction trigger. II. In vitro effects of prairie dog plasma albumin on mouse vas deferens contractility.

Involvement of opioid molecules in hibernation is well established, with the delta opioid receptor implicated in hibernation induction. Previous studies have shown that plasma albumin fractions (PAFs) from hibernating mammals contain an uncharacterized ligand called "hibernation-induction trigger" (HIT), which causes inhibition of induced contractility in the guinea pig ileum (GPI). In part I of this study, we described effects of PAF from two species of prairie dogs on induced contractility of the GPI. In the present study (part II), we examine the response of the mouse vas deferens (MVD), which is populated with the delta receptor subtype, to increasing concentrations of PAF from the white-tailed prairie dog (WT) and the black-tailed prairie dog (BT). Dose-response curves of lyophilized PAF yielded IC50 values (mg) (mean dose that inhibits contractility to 50% of control) of 11.0 for summer WT, 10.6 for hibernating WT, 9.4 for summer BT, 12.2 for winter active BT, and 4.7 for winter hibernating BT. These results suggest that delta opioid (HIT) is present in both species throughout the calendar year and that the induction of hibernation may involve not only levels of opioid but also dynamic interactions between endogenous opioid and its receptors.