Evidence for the solubilization of multiple opioid binding sites from mammalian brain

Good yields of 3H-opioid agonist binding in solution have been obtained following fractionation of brain membrane extracts on sucrose density gradients. The presence of multiple opioid binding sites was demonstrated for extracts from rat and guinea pig brain. Fractionation of solubilized material from guinea pig brain resulted in the separation of the peak of 3H-bremazocine binding (in the presence of DAGO and DADL) from the peaks of binding of tritiated mu and delta agonists. These results suggest that the kappa binding site may represent a separate molecular species from mu and delta opioid binding sites.