Low affinity inhibition of opioid receptor binding by FMRFamide.
The ability of the molluscan neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) to inhibit the binding of opioid-receptor radioligands to mammalian neural tissue was examined. Rabbit brain membrane preparations were exposed to tritiated dihydromorphine and ethylketocyclazocine in the presence of various concentrations of FMRFamide. FMRFamide inhibited the specific binding of both ligands in a dose-related manner, suggesting that the neuropeptide can inhibit binding to at least two subtypes of opioid receptors (mu and kappa). These data are consistent with the recent proposal that FMRFamide, or the immunoreactive FMRFamide-like material in mammalian brain, spinal cord, and gastrointestinal tract, can act as an endogenous opioid antagonist. However, the low binding affinity of FMRFamide might suggest an alternative mechanism for FMRFamide antagonism of opioid action in vivo.
D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D019835:FMRFamide; D007700:Kinetics; D008297:Male; D009419:Nerve Tissue Proteins / Q000494:pharmacology*; D011817:Rabbits; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*; D014316:Tritium
D009419:Nerve Tissue Proteins; D011957:Receptors, Opioid; D014316:Tritium; D019835:FMRFamide