Immunologic effects of morphine in rodents, rabbits, monkeys, and cats

The effects of prolonged morphine administration on immunologic reactivity against morphine was studied in a number of animal species: rabbit, monkey, guinea pig, rat, and cat. Some evidence for increased serum binding of 14C-labeled morphine was noted after morphine treatment in all test species, with the rabbit the best responder and the cat showing little or no response. In addition to measurements on serum binding of 14C-labeled morphine, other methods (measurement of serum binding of 14C-labeled codeine and methadone, competitive inhibition tests, radial immunodiffusion, and passive hemagglutination) were used for one or more of the species. Overall, results with these test methods have shown that prolonged morphine administration can result in immunologic responsiveness to morphine in animals.