Tumor-host relationships. II. Tolerance to injection of amino acids.

Summary 1.Time curves of free amino acid concentrations of liver, muscle, and plasma were determined following the intraperitoneal injection of massive doses of selected amino acids into normal and tumor-bearing rats. 2.Significant alterations in concentrations were produced by the injected amino acids (glycine, serine, threonine, and proline) on the other amino acids with which they are metabolically interrelated. 3.The data suggest an increased rate of metabolism of several of the amino acids, particularly glycine, in the tumor-bearing animal. 4.An altered threonine dehydrase level was demonstrated in the livers of tumor-bearing rats; serine dehydrase levels remained unaltered. Such data suggest that assay of tissue enzyme levels might be a more sensitive method for the detection of a derangement in amino acid metabolism in the tumor-bearing host.