Affinities of opiate agonists and antagonists for the enkephalin receptors of rat brain.
The binding of 3H-enkephalin (methionine-enkephalin) to membranes of rat brain is inhibited by enkephalin and levorphanol with IC50 values of 5 and 1.6 nM, respectively. Dextrorphan, the optical isomer of levorphanol, is over 6,000 times less effective. Opiate agonists, morphine, dihydromorphine and l-methadone and opiate antagonists, naltrexone and naloxone are less effective inhibitors of 3H-enkephalin than in 3H-dihydromorphine and 3H-naloxone binding. However, opiates without the oxygen bridge as in the structure of morphine, such as levorphanol and the benzomorphans show affinities for the receptors of 3H-enkephalin equal or greater than their affinities for the receptors of 3H-opiates.
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D001921:Brain / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004745:Enkephalins / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008566:Membranes / Q000378:metabolism; D009292:Narcotic Antagonists / Q000378:metabolism* / Q000494:pharmacology; D009294:Narcotics / Q000378:metabolism* / Q000494:pharmacology; D009842:Oligopeptides / Q000378:metabolism*; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*; D013237:Stereoisomerism
D004745:Enkephalins; D009292:Narcotic Antagonists; D009294:Narcotics; D009842:Oligopeptides; D011957:Receptors, Opioid