Effects of Ethanol Treatment and Withdrawal on Biosynthesis and Processing of Proopiomelanocortin by the Rat Neurointermediate Lobe*

Abstract

Male Sprague Dawley rats were chronically pair-fed with liquid diets containing 6.5% (vol/vol) ethanol, or equicaloric sucrose. After 21 days the ethanol-containing diet was discontinued and both groups were fed the sucrose diet. Groups of animals were killed on day 22 (0 day of ethanol withdrawal) and 1, 3, 8, and 15 days after ethanol withdrawal and the neurointermediate lobes (NILs) were removed and incubated with [3H]phenylalanine for 3 h. Chronic ethanol treatment induced an increase in the biosynthesis and release of beta-endorphin-like peptides by the rat NIL. After ethanol withdrawal the beta-endorphin-like immunoreactivity content in the NIL and the in vitro release of immunoreactive beta-endorphin (beta EP) by the NIL were significantly lower than in the controls on the first day, whereas no significant difference was found on days 3, 8, and 15 after ethanol withdrawal. The in vitro incorporation of [3H]phenylalanine into POMC, beta-lipotropin and beta EP was found to be higher in the ethanol-treated animals than in the controls on days 0, 1, and 3 after ethanol withdrawal, with no significant difference on days 8 and 15 after ethanol withdrawal. Furthermore, in both the ethanol-treated animals and their pair-fed controls the rate of incorporation of [3H]phenylalanine into total proteins, POMC, beta-lipotropin, and beta EP was significantly higher on days 8 and 15 after ethanol withdrawal than on the day of ethanol withdrawal (day 0), suggesting the implication of a nutritional factor. HPLC analysis of the beta EP peptides indicated that the percentage of acetylated forms of beta EP was higher in the NIL of the alcohol-treated animals, especially on days 8 and 15 after ethanol withdrawal. This observation suggests that though the rates of biosynthesis and release of beta EP-related peptides have returned to normal at 15 days after ethanol treatment, the activity of the enzyme responsible for the acetylation of beta EP remained elevated.