Endogenous opioid peptides and regulation of drinking and feeding.

Considerable work across the last 10 yr has implicated the endogenous opioid peptides in the regulation of ingestion. The opioid antagonists, such as naloxone and naltrexone, reduce intake of water, flavored water, and food. Naloxone's effects are pharmacologically specific, ie, its effects are dose-related and stereoselective. Further, a variety of antagonists produce similar effects. A primary site of action of naloxone, with respect to intake, is in the central nervous system. Naloxone's effects are also behaviorally specific, ie, its effects seem particularly related to palatability functions. The effects of opioid agonists, in small doses, enhance intake of some nutrients, but these effects are not opposite those of the antagonists. Benzodiazepines enhance drinking and eating and apparently interact with opioid systems. These observations combine with those directly measuring features of the endogenous opioid peptides to support a conclusion that opioid peptides are part of a system for regulating ingestion.