Beta-endorphin-(1-27) is a naturally occurring antagonist to etorphine-induced analgesia.
The potent opioid peptide beta-endorphin is found in the brain and pituitary with two related fragments, beta-endorphin-(1-27) and beta-endorphin-(1-26). The fragments retain substantial opioid-receptor binding activity but are virtually inactive analgesically. beta-Endorphin-(1-27) inhibits beta-endorphin-induced and etorphine-induced analgesia when coinjected intracerebroventricularly into mice. Antagonism by competition at the same site(s) is suggested from parallel shifts of the dose-response curves of etorphine or beta-endorphin in the presence of beta-endorphin-(1-27). Its potency is 4-5 times greater than that of the opiate antagonist naloxone. beta-Endorphin-(1-26) does not antagonize the antinociceptive action of etorphine or beta-endorphin in doses up to 500 pmol per animal.
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D000818:Animals; D001667:Binding, Competitive; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000378:metabolism / Q000494:pharmacology*; D005048:Etorphine / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008297:Male; D051379:Mice; D009019:Morphinans / Q000037:antagonists & inhibitors*; D009270:Naloxone / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology*; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000378:metabolism; D001615:beta-Endorphin
D004723:Endorphins; D009019:Morphinans; D010446:Peptide Fragments; D011957:Receptors, Opioid; D009270:Naloxone; D005048:Etorphine; D001615:beta-Endorphin; C035581:beta-endorphin (1-27)