ABSTRACT
Hibernation is characterized by a drastic decrease in metabolic rate and associated decreases in body temperature, heart rate and respiratory rate. As a general depression in autonomic functions is characteristic of entry into hibernation and during the hibernation state, it is quite possible that an increase in endogenous opioid activity could facilitate hibernation. Several studies have implicated that endogenous opioids may participate in the entrance and/or the maintenance of hibernation. As endogenous opioids and their receptors are shown to exist in pancreas, intestine, and adrenal gland, it is possible that peripheral opioids may also contribute to the regulation of hibernation. Rather than being an opioid peptide, recent evidence indicates that substance(s) which regulates the hibernation process may initiate its effect indirectly by modulating endogenous opioid activity. The thermogenic effect of this peptide can be antagonized by naloxone, indicating the involvement of endogenous opioid in this peptide's biological effect.
