Studies on the rate of protein synthesis and the size of the nitrogen pool in both the rat and the human (1, 2) have provided the research worker with technical procedures and mathematical treatment by which it is possible to assess directly nutritional and endocrine effects on the regulation of amino acid and protein metabolism. Sprinson and Rittenberg (2) have shown that the empirical equation A& = bA(l -e--Bt) describes the excretion of labeled glycine nitrogen in both the rat and the human

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... nd have developed the relationship of the constants A and B to the size of the metabolic nitrogen pool and the rate of protein synthesis. The recently published studies of Hoberman (3-5), in which rate-process constants for the protein e amino acid equilibrium and for the catabolism of amino acids to urine nitrogen are derived and tabulated, include a number of observations (3) which are of considerable interest in connection with the present experiments and preceding ones (6). Hypophysectomy of the rat was found to result in an increase in the rate-process constant for the catabolism of amino acids, and treatment of the hypophysectomized animal with growth hormone returned the constant to normal. Synthesis of protein from amino acids was shown to be only slightly affected by hypophysectomy, but definitely accelerated in the hypophysectomized animal treated with growth hormone. Doubt concerning the production of continuous growth with growth hormone has largely been dispelled since the demonstration by Evans et al. (7) that repeated injection of this hormone into normal adult female rats resulted in continuous growth for a period of 437 days. Parallel studies of the chemical composition of the body (8) showed that growth hormone produced a rise in protein and water content and a lowering of the fat content of the body. Since changes such as these are characteristic