THE AGE FACTOR IN THE RESPONSE OF THE RAT TO LEVEL OF DIETARY PROTEIN* By

DURING the past decade much has been written about the deleterious effect of diets rich in protein. Since the kidney is the organ chiefly concerned with the removal of nitrogenous products in the metabolism of protein, attention has naturally been focused on this organ. However, in view of the apparent simplicity of the thesis, the experimental results have been surprisingly variable. It seems, therefore, that any controlled obser vations of the effects of high concentrations of dietary protein will be valu able in helping to clarify a situation which involves a subject of consider able practical importance. Among other confusing statements in the literature are those concerning growth and physiological well-being of experimental animals on rations rich in protein. In some cases poor growth is reported; in others, satisfac tory early growth but failure to reach the usual mature body weight; while normal development is observed in still other studies. In view of the lack of concordance in this respect and in the light of recent accounts (1, 2, 3) of rapid growth of albino rats—the animal most frequently used in these experiments—it seemed desirable to examine anew the influence of dietary protein upon the development of individuals of the same strain of rapidly-growing animals. The increase in body weight in young animals and main tenance in old ones should be a reliable criterion of the adequacy of a diet under conditions where other variables are ruled out. In the present report we have attempted to correlate change in body weight with concentration of dietary protein in white rats of different ages. The observations were made upon a large number of male albino rats from all of which the right kidney had been removed. They were grouped into four different ages and were given complete diets containing three dif ferent amounts of protein (see Table I). At 56 days and 150 days after nephrectomy (the experimental ration was first given on the day of th