Nitrogen movement between host and tumor in mice inoculated with Ehrlich ascitic tumor cells

Tumors function as a nitrogen trap, and they compete with the host for nitrogen compounds. In experiments with whole animals infected with Ehrlich ascitic tumor cells, the glutamine, glutamate, asparagine, and aspartate concentrations were determined for host plasma, ascitic liquid, and tumor cells, throughout the period of tumor growth. Concentration gradients of glutamine or asparagine were created from the host tissues towards the ascitic liquid. The countergradient step from ascitic liquid to tumor cells may be overcome by an active transport process with an apparent Km for glutamine of 3.1 X 10(-4) M. On the other hand, a reverse flux of glutamate and aspartate was seen to take place from cells to plasma. In vitro incubations of tumor cells with near physiological concentrations of glutamine, or asparagine plus glucose, confirmed the host-to-tumor nitrogen movement previously deduced from the relative amino acid concentrations in plasma, ascitic liquid, and tumor cells. The ammonemia detected in tumor-bearing mice at the terminal stage could result from the hydrolysis of glutamine, which was rapidly metabolized by the tumor cells.