Carbon-14 tracer studies in rat-liver perfusion experiments under conditions of gluconeogenesis from lactate and pyruvate.

The intracellular events in the metabolic pathway of gluconeogenesis from lactate and pyruvate in liver tissue were assumed to be understood. Nevertheless the results of several 14C-tracer experiments gave rise to the postulation of still unknown intracellular interactions under this condition. We have tried to contribute to the solution of this problem by using different 14C labeled tracers such as [1-14C]lactate or pyruvate and [2-14C]lactate or pyruvate, [14C]bicarbonate and [1-14C]octanoate in perfusion experiments with livers from rats under conditions of gluconeogenesis from lactate and pyruvate. The 14C labeling patterns of intracellular metabolites as malate, citrate, phosphoenolpyruvate, phosphoglycerate and newly synthesized glucose were analysed under different conditions. A comparison with values calculated by using metabolic models, based on the generally accepted concepts of intracellular interactions, showed some fundamental discrepancies, which justify the postulation of still unknown intracellular interactions in the pathway of gluconeogenesis from lactate and pyruvate.