Plasma and brain amino acids in Walker 256 carcinosarcoma-bearing rats.

that amino acids from tumor protein breakdown may be used as precursors for the synthesis of new protein in tumor cells. Tumor cells have the ability to concentrate amino acids from the plasma amino acid pool more efficiently than do normal cells, thus enabling them to compete successfully with the tissues of their host for available amino acids (17). During times of reduced dietary intake, resulting from anorexia, this com petition may lead to depletion of the host. A similar type of competition exists in the metabolism of carbohydrates and fat, so that a rapidly growing malignant neoplasm may induce in the host a state of combined nitrogen and energy deficiency similar to that seen in malnutrition. If such quantitative changes in free plasma amino acids are superimposed upon tumor related qualitative derangements of the normal plasma amino acid profile, the resulting amino acid pattern of the plasma in malignant disease may be expected to differ from that of malnutrition alone. Reports of plasma amino acid patterns in tumor-bearing humans and animals are largely anecdotal and do not usually include complete amino acid profiles. Furthermore, adequate controls suffering from malnutrition alone have not usually been included. In this study, we report experiments in which tumor-bearing rats have been compared not only with normal rats but also with animals without tumors but with the same degree of malnutrition as that of the tumor-bearing group, a situation achieved by careful pair-feeding. This experimental design was deliberately chosen to allow the effects of the tumor upon amino acid patterns to be distin guished from the effect of malnutrition alone, acknowledging that this would not permit any conclusion to be drawn about the mechanism involved. In addition to studying plasma amino acid profiles, we have measured the concentration of amino acids within the brain. This aspect, which to the best of our knowledge has not been previously studied, was included because of the recent suggestions that changes in brain amino acid concentrations, acting through the agency of altered neu rotransmitter synthesis, might influence feeding behavior (14, 15,21,25).