THE EFFECT OF 6-MERCAPTOPURINE ON THE TURNOVER OF I¹³¹-GAMMA GLOBULIN AND I¹²⁵-ALBUMIN IN RABBITS

¹ Clinical Physiology Section, Laboratory of Clinical Investigations, National Institute of Allergy and Infectious Diseases, and Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland

Increased catabolism, redistribution and decreased synthesis are all possible explanations for the decrease in circulating gamma globulin noted after the administration of 6-mercaptopurine (6-MP). Gamma globulin and albumin labeled with I¹³¹ and I¹³⁵, respectively, were administered to rabbits, and the turnover and distribution of these proteins during 6-MP therapy were studied. Circulating levels of gamma globulin were significantly lower in the treated animals. The turnover and distribution of the albumin were not altered in the drug-treated group, suggesting that 6-MP may selectively affect the cells governing immunoglobulin production prior to altering the production of other proteins. Since there was no evidence of increased catabolism or redistribution of gamma globulin, decreased production is suggested as the mechanism for suppression of gamma globulin levels in 6-MP-treated rabbits.