The choice of opiate receptor subtype by neo-endorphins.
The choice of opiate receptor subtype by alpha- and beta-neo-endorphin was studied in isolated preparations. Neo-endorphins had significant inhibitory actions on the electrically evoked contractions of guinea-pig ileum, mouse vas deferens and rabbit ileum as well as on the rabbit vas deferens which had been shown to contain kappa-receptors exclusively. Mr 2266, a relatively specific kappa-receptor antagonist, was more effective than naloxone, a relatively mu-receptor antagonist, to antagonize the agonist actions of neo-endorphins in either the guinea-pig and rabbit ileum or in the rabbit vas deferens. By contrast, in the mouse vas deferens, the effectiveness of Mr 2266 to antagonize the agonist actions of neo-endorphins was low and similar to that of naloxone. The potencies of neo-endorphins relative to that of ethylketocyclazocine, a representative kappa-receptor agonist, in the guinea-pig ileum were similar to those in the rabbit ileum but were significant different from those in the mouse vas deferens. The data indicate that neo-endorphins act as kappa-receptor agonists in either the guinea-pig and rabbit ileum or in the rabbit vas deferens while in the mouse vas deferens they act on opiate receptor subtypes other than kappa- and mu-receptors.
D000818:Animals; D001575:Benzomorphans / Q000031:analogs & derivatives / Q000494:pharmacology; D003496:Cyclazocine / Q000031:analogs & derivatives / Q000494:pharmacology; D004347:Drug Interactions; D004723:Endorphins / Q000494:pharmacology*; D004745:Enkephalins / Q000494:pharmacology*; D016314:Ethylketocyclazocine; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D011498:Protein Precursors / Q000494:pharmacology*; D011817:Rabbits; D011957:Receptors, Opioid / Q000187:drug effects*; D001615:beta-Endorphin / Q000031:analogs & derivatives*
D001575:Benzomorphans; D004723:Endorphins; D004745:Enkephalins; D011498:Protein Precursors; D011957:Receptors, Opioid; D009270:Naloxone; C027247:MR 2266; D016314:Ethylketocyclazocine; D001615:beta-Endorphin; C025681:alpha-neoendorphin; C030719:beta-neo-endorphin; D003496:Cyclazocine