In vivo lactate production and utilization by Jensen sarcoma and Morris hepatoma 7288CTC

These experiments were designed to determine the characteristics of lactic acid utilization and production in vivo in Jensen sarcoma and Morris hepatoma 7288CTC. Arteriovenous differences for lactic and pyruvic acids, glucose, and the ketone bodies were measured across "tissue-isolated" tumors growing in fed and fasted rats. Lactic acid was utilized (n = 18), produced (n = 24), or neither utilized nor produced (n = 1) by the tumors. Net tumor lactate production or utilization did not depend on the mean rate of glucose utilization which was the same in the lactate-utilizing and -producing tumors. For the lactic acid-utilizing tumors, the mean arterial whole blood lactate concentration entering the tumor was 3.47 +/- 0.39 mM, and the concentration in the tumor venous blood was 2.31 +/- 0.25 mM. For the lactic acid-producing tumors, the mean arterial lactic acid concentration was 1.29 +/- 0.10 mM, and the tumor venous blood concentration was 2.19 +/- 0.19 mM. Thus, both lactate-producing and lactate-utilizing tumors showed identical rates of glucose utilization and identical lactic acid concentrations in the venous blood leaving the tumors. Metabolite levels were also measured in tumors that were freeze clamped in situ immediately following collection of the arterial and tumor venous blood samples. The lactic acid content in the tumor mass (corrected for total tumor water) and the concentration in the tumor venous blood plasma were nearly identical, suggesting that the lactate concentrations in the tumor cells and tumor venous blood are at equilibrium. Transport of lactic acid between arterial plasma and tumor or between tumor and venous plasma was always down a concentration gradient; net lactate uptake and release in these tumors followed the law of mass action. High lactate concentrations were not observed in the Jensen sarcomas or in the venous blood leaving these tumors, and we were unable to confirm earlier studies indicating that Jensen sarcomas are consistently high net lactate producers in vivo.