title: Studies on the structural prerequisites for the activation of the beta-endorphin receptor on the rat vas deferens.
abstract: The inhibitory activity of a variety of opioid peptides was tested on the electrically stimulated rat vas deferens. Human beta-endorphin (beta h-EP) was the most potent of the opoioid-like peptides; it produced half-maximal inhibition of the neuromuscular twitching at a concentration of about 100 nM. The potency of beta h-EP was greater than that of camel, porcine, ovine or leucine5 beta h-EP, alpha-N-acetyl beta-ovine-EP was inactive. In contrast to beta-endorphin (beta-EP), methionine and leucine-enkephalin, dynorphin-(1-13), morphine and other narcotic analgesics were devoid of opioid-like activity. Fragments of beta-EP with amino acid deletions at the carboxy end of the molecule were considerably less potent than the parent compound. The fragment beta h-EP 1-21 was 70 times less potent than beta h-EP, whereas the segments beta h-EP 1-19 and beta h-EP 1-16 were both completely inactive. Deletions at the amino terminal of beta-EP yielded inactive compounds. The potency of beta h-EP was reduced in a dose-related fashion by applications of nanomolar concentrations of naloxone or N-allylnormetazocine and by micromolar concentrations of levorphanol or morphine. In decided contrast, opioid peptides such as methionine enkephalin, dynorphin-(1-13), beta-casomorphan derivatives or short chain beta h-EP segments such as beta-EP 1-16, beta-EP 1-19, beta-EP 6-31, beta-EP (1-5)-(16-31), methionine enkephalin plus beta-EP 6-31 or the N-acetyl beta-bovine-EP did not antagonize the inhibitory action of beta h-EP. The present results demonstrate that the rat vas deferens contains opioid receptors with considerable selectivity for beta-EP. It is concluded from this structure activity relationship study that the activation of the beta-EP receptor involves at least two sites of recognition on the beta-EP structure.
mesh_terms: D000818:Animals; D004347:Drug Interactions; D004399:Dynorphins; D004558:Electric Stimulation; D004723:Endorphins / Q000378:metabolism* / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects*; D009294:Narcotics / Q000494:pharmacology; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects*; D001615:beta-Endorphin
chemical_list: D004723:Endorphins; D004745:Enkephalins; D009294:Narcotics; D011957:Receptors, Opioid; D001615:beta-Endorphin; D004399:Dynorphins