Chronic ethanol treatment alters the biosynthesis of β -endorphin by the rat neurointermediate lobe

Abstract

Tolerance to ethanol was induced in male Sprague–Dawley rats (225 – 250 g) by chronic feeding with a liquid diet containing 6.5% ethanol (v/v). Control rats were pair-fed with a liquid diet in which the ethanol was replaced by an equicaloric concentration of sucrose. Immediately following sacrifice of the animals the neurointermediate lobes (NIL) were removed and incubated with [3H]phenylalanine. The biosynthesized proopiomelanocortin (POMC), β-lipotropin β-LPH), and β-endorphin (β-EP) were purified by immunoprecipitation with an antiserum to β-EP and analyzed by sodium dodecyl sulfate poly-acrylamide disc gel electrophoresis. Alcohol treatment for 3 days had no effect on the degree of incorporation of [3H]phenylalanine into POMC, β-LPH, and β-EP but treatment for either 15 or 21 days increased the incorporation of [3H]phenylalanine into all three peptides. Ethanol treatment also increased the β-endorphinlike immunoreactivity (β-EPLIR) found in the incubation medium, but no significant change was observed in the β-EPLIR extracted from the NIL either immediately after sacrifice or after 3 h of incubation of the NIL. However, a significant decrease of β-EPLIR was found in the anterior lobes of rats treated with ethanol for 21 days. Furthermore, the β-EPLIR in the serum of alcohol-treated rats was significantly higher than in the serum of their corresponding controls. These results indicate an effect of ethanol on the endorphin system and are consistent with the suggestion that endorphins may be mediators of some of the ethanol effects.