The endogenous opioids, which include β-endorphins, are proteins that bind to the opioid receptors. Alcohol is believed to stimulate the release of certain opioid peptides, which could interact with opioid receptors in regions of the brain associated with reward and positive reinforcement.105 Increased activity of brain β-endorphin (enkephalin) opioid peptide systems may be important for initiating and maintaining high levels of alcohol consumption.105 Subjects with a family history of alcoholism presented with lower concentrations of plasma β-enodorphin in the early morning hours and a more pronounced increase in pituitary β-endorphin release after ingestion of moderate doses of alcohol.106,107 When examining the heritability of hormonal responses, a twin study found that β-endorphin response to alcohol was heritable.108 Decreased β-endorphin has been noted in the cerebrospinal fluid (CSF) of abstinent alcoholics.109 Opioid antagonists, such as naltrexone, have been shown to decrease the self-administration of alcohol in animals and humans.110-112 This effect has been attributed to blunting the stimulatory effect of alcohol, enhancing the sedative effect, and/or decreased levels of reinforcement from alcohol.
