Catabolism of xanthine and uracil in tumor-bearing rats.

The urinary excretion of allantoin and uric acid was greatly increased in rats bear ing Walker carcinoma 256. The increase was greater with more advanced tumor growth. A similar increase was also observed in the allantoin concentration of the plasma and liver of these rats. An increase in the RNA and DNA content and a decrease in the RNA/DNA ratio were found in the muscle of the tumor-bearing animals. Liver xanthine oxidase activity was increased in rats bearing Walker 256 and Guerin carcinomas and NovikofT and Morris 3683 hepatomas but was unchanged in rats bearing Jensen sarcoma, Morris 5123, and Morris 3924-A hepatomas, when compared with their re spective controls fed ad libitum. Liver uracil reductase activity showed a decrease in rats bearing Morris 5123 and Morris 3924-A hepatomas but no change in rats bearing Walker carcinoma 256 and Novikoff and Morris 3683 hepatomas. These findings indi cate that the effect of different tumors on a given enzyme in the host system need not be qualitatively uniform. Finally, unlike the other hepatomas tested, Morris 5123 hepatoma was found to possess xanthine oxidase activity approaching that found in a normal liver.