On the relative constancy of the free amino acids of lymphatic tissues.

The free amino acids are present in tissues of animals in the postabsorptive st,ate at 3 to 9 times their concentration in the blood (1). Aspartic acid, glutamic acid, glutamine, proline, alanine, glycine, taurine, and ethanolamine phosphate contribute over two-thirds of the total free amino acid nitrogen of rat tissues (l-3). The pattern of these amino acids is, however, highly characteristic for each tissue (4). In a recent study of free amino acids of rodent lymphosarcomas and of the homologous normal tissues, patterns were found to be very similar for the tumors, but to differ from those of the homologous normal tissues (5). After an L-amino acid was administered intravenously to rats, the concentration of the injected amino acid rapidly rose in the tissues (6). In liver, some increases of related amino acids were also noted owing to transamination and other transformations. However, the resting level was rapidly restored. Because of these observations, the interpretation was made that the free amino acid pattern of tissues reflects the enzymatic pattern of the tissue in question. To evaluate further the significance of the observed differences between the tumors and normal tissues, it was deemed of interest to ascertain the extent to which the normal pattern would be held constant in spite of altered physiological states. Rat thymus and spleen, tissues which had previously been compared with lymphosarcomas, were chosen for study of the effects of hyperplasia in normal tissues, of fasting, and of metabolic poisons. Bilateral adrenalectomies were performed on one group of rats, since thymus and spleen enlarge after this operation. Secondly, animals which had been fasted for 16 hours or 4 days were compared with controls. Thirdly, the effect of malonate or fluoroacetate poisoning was examined. The mechanism of action of these poisons is fairly well understood, and one may infer that they alter the enzymatic pattern of the cell by reducing the activity of certain enzymes. Under these conditions, secondary changes of the free amino acid