Some effects of sulfur amino acids upon tumor-host relationship in the rat.

Previous studies have demonstrated that a, semisynthetic diet containing 12 per cent casein is deficient in sulfur amino acids for the growth of tissues in rats (1), supplementation with 0.7 per cent DL-methionine increasing the growth opti mally. A transplanted sarcoma was found to de velop most rapidly in rats fed this sulfur amino acid-deficient diet. Supplementing with 0.7 per cent methionine increased the growth of normal tissues and depressed the development of the tumor (4). Adding more nitrogen in the form of guanidoacetic acid (glycocyamine) or glycine in creased the growth of the normal tissues still fur ther and tended to depress the development of the tumor. The effect of glycine and guanidoacetic acid seemed to be specific and not just the result of adding more nitrogen. The mixture of methionine and guanidoacetic acid was particularly effective in conserving body nitrogen under conditions of stress such as the depleting effect of a large sarco ma or of the chemotherapeutic agent TEPA (3). Further experiments are reported here to deter mine the optimum amounts of methionine for sup plementation in tumor-bearing animals and to compare the supplementing effects of cystine with methionine. Furthermore, the best proportions for ii mixed supplementation of methionine plus guanidoacetic acid were sought. Food efficiencies were used as well as gain in body weight with re spect to tumor weight to determine the effects of simplementation.