Specific serum binding of morphine, levorphanol and heroin

Effects of repeated subcutaneous pellet implantation of a series of narcotic drugs on the serum binding of [¹⁴C]morphine was studied in rabbits. Three of the compounds, morphine, heroin and levorphanol, elicited production of a morphine-binding globulin in the implanted rabbits. This serum response did not occur with several other compounds tested, including the potent analgesic methadone, and the narcotic antagonist naloxone. The time course of production of this globulin response, as well as the specificity of the binding for the drug that induced the response are both characteristic of an immunological reaction.