Enhanced activity of the beta-endorphinergic system in the anterior and neurointermediate lobe of the rat pituitary after chronic treatment with ethanol liquid diet.

Chronic treatment of rats with ethanol liquid diet over a period of two weeks resulted in a pronounced increase in the activity of the beta-endorphinergic system in the anterior and neurointermediate lobe of the pituitary. In the anterior pituitary, the in vitro incorporation of [3H]tyrosine into beta-endorphin and its precursor peptides beta-lipotropin and pro-opiomelanocortin was enhanced by 350, 100 and 135%, respectively. In contrast, the in vitro biosynthesis of total proteins was not altered, indicating that the ethanol-induced stimulatory effects on the beta-endorphinergic system were not due to a nonspecific enhancement of protein synthesis. The in vitro release of beta-endorphin-related peptides from the anterior pituitary was increased; the tissue concentrations, however, remained unchanged. In the neurointermediate pituitary, the in vitro incorporation of [3H]tyrosine into beta-endorphin also was stimulated by more than 50% in response to chronic ethanol treatment, whereas the biosynthesis of total proteins was unaffected. The ethanol-induced stimulation of the beta-endorphin system in the neurointermediate pituitary, however, did not appear to result in an increased formation of beta-endorphin-like peptides with opiate activity, as the concentrations of alpha-N-acetylated forms of beta-endorphin were found to be increased, whereas those of nonacetylated forms were markedly decreased. This is suggestive for an ethanol-induced stimulation of the alpha-N-acetylation of beta-endorphin, a modification that inactivates the peptide in all its opiate-like properties.