A study of free amino acids and of glutamine synthesis in tumor-bearing rats.

The concentrations of some eight free amino acids in the plasma, liver, and muscle have been determined in male rats bearing tumors of different sizes (Walker car cinoma 256) and in their pair-fed controls. No change in the concentrations of free amino acids was found in the plasma or tissues when tumors were of small size. As the tumors grew larger, the concentrations of most free amino acids determined were in creased in the plasma and liver and decreased in the muscle. Glutamine was the only compound studied whose concentration was consistently decreased in the plasma, liver, and muscle. Increased excretion of the nonprotein-bound form of all amino acids determined was observed in the urine of tumor-bearing rats. The excretion of free amino acids could be shown to be increased also, if the quantities excreted daily were expressed as a function of carcass weight rather than total body weight (carcass plus tumor). Both glutamine synthetase and glutamyltransferase activities in the liver of tumor bearing rats were decreased when the tumors were still very small, and no further de crease was noted as the tumors grew larger. However, the ratio of the synthetase activity to the transferase activity was less in the tumor-bearing rat than in the con trol rat.