Effects of Excess Dietary d/-Methionine and/or /-Arginine on Rats ∗

Summary

When excess /-arginine is added to casein, the nitrogen balance index is reduced slightly. An excess of d/-methionine on the other hand reduces the nitrogen balance index markedly and the excretion of creatinine is increased. When both /-arginine and d/-methionine are added to casein the nitrogen balance index is not reduced as much as it is in the presence of casein plus methionine, but the creatinine excretion is increased. The animals receiving 12% casein and pair-fed with the group receiving 12% casein plus 4.8% d/-methionine lose weight slightly over a 20-day period. Those receiving 12% casein plus 4.8% methionine lose weight markedly, a loss which is overcome in part by adding 1.7% /-arginine to the methionine diet. The decrease in weight in the presence of a large excess of methionine is associated with a loss in body nitrogen and fat. The addition of d/-methionine increases the amount of nitrogen in the liver and reduces the amount of fat. Feeding d/-methionine plus casein increases the size of the kidney, an effect which is antagonized by /-arginine.