Long-term treatment of rats with morphine reduces the activity of messenger ribonucleic acid coding for the beta-endorphin/ACTH precursor in the intermediate pituitary.
Chronic administration of morphine to rats for a period of 4 weeks resulted in a 50-60% decrease in the tissue concentrations of beta-endorphin and in the in vitro release from the neurointermediate pituitary. Incorporation of [3H]phenylalanine into isolated intermediate/posterior pituitaries in vitro revealed a reduction in the amount of label incorporated into the beta-endorphin/ACTH precursor to a similar extent (about 45%), but essentially no effect on the conversion of the precursor into beta-lipotropin and beta-endorphin. Extraction of mRNA from intermediate/posterior pituitaries followed by cell-free translation in a reticulocyte system showed no significant decrease in the total level of translatable mRNA. In contrast, the content of translatable mRNA coding for the beta-endorphin/ACTH precursor was significantly reduced by 50-60%. Thus, long-term treatment with morphine appears to depress beta-endorphin formation in the rat intermediate pituitary at the pretranslational level by markedly decreasing the activity of mRNA coding for the beta-endorphin/ACTH precursor without any alteration in the processing of this precursor.
D000324:Adrenocorticotropic Hormone / Q000235:genetics*; D000818:Animals; D004723:Endorphins / Q000235:genetics*; D007700:Kinetics; D008297:Male; D008970:Molecular Weight; D009020:Morphine / Q000494:pharmacology*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D010908:Pituitary Hormones, Anterior / Q000235:genetics*; D011333:Pro-Opiomelanocortin; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics*; D011817:Rabbits; D051381:Rats; D012156:Reticulocytes / Q000378:metabolism
D004723:Endorphins; D010908:Pituitary Hormones, Anterior; D011498:Protein Precursors; D012333:RNA, Messenger; D011333:Pro-Opiomelanocortin; D009020:Morphine; D000324:Adrenocorticotropic Hormone