Endogenous morphine and codeine in mice--effect of muramyl dipeptide.

Administration of morphine exerts many effects on the immune system. On the other hand little attention has been paid to the fact, that endogenous morphine and codeine exists in mammals, including man. This raises the question, whether or not endogenous opiate alkaloids play some role in immunoregulation. In addition muramyl-dipeptide (MDP), product of bacterial cell wall degradation and a potent immunomodulatory agent exhibits a broad spectrum of effects including effects on CNS functions. The present study investigated whether or not the endogenous levels of morphine and codeine are affected by administration of MDP in mice. Marked variation was found in spleen, brain, small intestine and heart in morphine and codeine concentrations. The intraperitoneal administration of MDP produced a significant increase in tissue morphine levels 30 minutes after injection.