Expression of delta opioids in heart and other tissues from summer‐active and hibernating woodchucks

Abstract

In response to the severe environmental challenges of reduced temperature and limited food, mammalian hibernators enter into an extraordinarily protective state of decreased activity, temperature, and metabolism. Cardioprotection is transferred to hearts from non‐hibernators by treatment with plasma and plasma fractions from hibernating animals, and this protection is blocked by delta opioid receptor antagonists. To further elucidate the role of opioids in hibernation, we measured proenkephalin (PENK), the precursor protein for endogenous delta opioids, the delta opioid receptor (DOR), and plasma enkephalin levels in woodchuck tissues and blood. PENK and DOR were widely distributed in woodchuck tissues, including heart and skeletal muscle, and circulating levels of enkephalins were relatively high (> 300 pM). Additional studies are underway to compare levels of these proteins in samples from summer‐active and hibernating animals. The overall goal of these studies is to gain additional insight into the mechanism(s) by which hibernation and enkephalins increase cardiac ischemic tolerance. This insight in turn may contribute to future therapeutic approaches that mimic these naturally, and sometimes profound, protective processes to improve prevention and treatment of ischemic disease. Funding for these studies was provided by the University of Iowa Department of Emergency Medicine.