Interactions of codeine-7,8-oxide (codeine-epoxide), as a new metabolite of codeine, with multiple opiate receptors

Interactions of codeine-epoxide, a new metabolite of codeine, with multiple opiate receptors were studied using radioligand binding assay. The ability of codeine-epoxide to displace [3H]dihydromorphine binding was the most effective among three labeled ligands, that is, [3H]dihydromorphine, [3H]-D-Ala2-D-Leu5-enkephalin and [3H]ethylketocyclazocine, suggesting that codeine-epoxide had a selectively high affinity to mu-receptors, despite the fact the affinities of codeine-epoxide to opiate receptors were slightly less potent than its parent compound, codeine. Since "sodium ratio" and "GTP ratio" on codeine-epoxide binding lay between those of codeine and naloxone, the interaction of codeine-epoxide with opiate receptors may be slightly different from that of codeine.