Modification of morphine withdrawal: Effect of tuftsin, [Lys4]-tuftsinyltuftsin, tetrapeptide fragment (1-4) of substance P and its amide

Abstract Withdrawal behavior in morphine-dependent rats precipitated by naloxone was attenuated after pretreatment with the tetrapeptide tuftsin and to some extent by its synthetic derivated [Lys 4 ]-tuftsinyltuftsin. The tetrapeptide fragment ( 1–4 ) of Substance P was ineffective in suppressing morphine-withdrawal behavior, whereas its C-amide exerted only weak action. Possible involvement of an immunological mechanism is discussed.