Creatine Metabolism after X-irradiation of Rats

1. Creatine-2-14C was injected into rats at different times after x- or sham-irradiation. 2. Muscle creatine and phosphocreatine, as well as creatine from blood, kidney and urine, were isolated and their respective specific activities determined. Urinary creatinine was also isolated and its 14C-activity determined. 3. Coincident with the maximal excretion of creatine, the specific activities of muscle creatine and phosphocreatine decreased after x-irradiation. 4. Immediately after injecting the x-irradiated rats with creatine-2-14C, the specific activity of urinary creatine increased, whereas that of creatinine decreased, but at a somewhat later time. 5. It is postulated that defective utilization of creatine by muscle constitutes the cause of radiation-induced creatinuria.