Effect of chronic morphine treatment on beta-endorphin biosynthesis by the rat neurointermediate lobe.
The effect of chronic morphine treatment on the in vitro biosynthesis of beta-endorphin by rat pars intermedia was investigated. Tolerance and physical dependence were induced in 200 g rats by the subcutaneous implantation of 75 mg morphine pellets for either 3 days or 15 days. Immediately following sacrifice of the animals the neurointermediate lobes were removed and incubated with [3H] phenylalanine. The protein extracts of the lobes were analyzed for the incorporation of the labelled amino acid into total protein, pro-opiomelanocortin, beta-lipotropin (beta-LPH) and beta-endorphin. the biosynthesized products were purified by immunoprecipitation with an antiserum to beta-endorphin. The identity and purity of beta-endorphin were verified by polyacrylamide disc gel electrophoresis with sodium dodecyl sulfate, and microsequencing. The identity of pro-opiomelanocortin (POMC) was verified by peptide mapping of its tryptic digestion products. The results showed that morphine treatment induced a decrease in the incorporation of the radioactive amino acid into total protein, pro-opiomelanocortin, beta-LPH and beta-endorphin. The decrease was more pronounced for the incorporation into beta-LPH and beta-endorphin than into pro-opiomelanocortin and total proteins, suggesting an effect of morphine treatment on the processing of the pro-opiomelanocortin to its final maturation products.
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D004361:Drug Tolerance; D004591:Electrophoresis, Polyacrylamide Gel; D004723:Endorphins / Q000096:biosynthesis*; D006801:Humans; D007031:Hypothalamus / Q000378:metabolism*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009021:Morphine Dependence / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D001615:beta-Endorphin
D000596:Amino Acids; D004723:Endorphins; D009419:Nerve Tissue Proteins; D001615:beta-Endorphin; D009020:Morphine