[3H]-beta-endorphin binding in rat brain.
The binding of [3H]-beta-endorphin to rat brain homogenates is complex. Although Scatchard analysis of saturation studies yields a straight line, detailed competition studies are multiphasic, suggesting that even at low concentrations of the compound, the 3H-ligand is binding to more than one class of site. A portion of [3H]-beta-endorphin binding is sensitive to low concentrations of morphine or D-Ala2-Leu5-enkephalin (less than 5 nM). The inhibition observed with each compound alone (5 nM) is the same as that seen with both together (each at 5 nM). Thus, the binding remaining in the presence of both morphine and the enkephalin does not correspond to either mu or delta sites. The portion of [3H]-beta-endorphin binding that is inhibited under these conditions appears to be equally sensitive to both morphine and the enkephalin and may correspond to mu1 sites. Treating membrane homogenates with naloxonazine, a mu1 selective antagonist, lowers [3H]-beta-endorphin binding to the same degree as morphine and D-Ala2-Leu5-enkephalin alone or together. This possible binding of [3H]-beta-endorphin to mu1 sites is consistent with the role of mu1 sites in beta-endorphin analgesia and catalepsy in vivo.
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D004723:Endorphins / Q000378:metabolism*; D008297:Male; D009270:Naloxone / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014316:Tritium; D001615:beta-Endorphin
D004723:Endorphins; D014316:Tritium; D009270:Naloxone; D001615:beta-Endorphin; C034643:naloxonazine