LACTATE-PYRUVATE INTERCONVERSION IN BLOOD - IMPLICATIONS FOR IN-VIVO TRACER STUDIES

We have evaluated lactate and pyruvate kinetics in whole blood or plas ma by the addition of [1-C-13]lactate (n = 5) or [1-C-13]pyruvate (n = 5) and application of compartmental modeling to the resulting data. P yruvate and lactate concentrations and tracer-to-tracee ratios were me asured at frequent intervals for 45 min. Pyruvate and lactate tracer-t o-tracee ratios equilibrated almost completely within 3-4 min in whole blood, whereas there was no isotopic exchange in plasma. The average rate of interconversion between unlabeled lactate and pyruvate was fou r to five times (pyruvate to lactate) and three to four times (lactate to pyruvate) the net production rate of lactate. We conclude that the re is a very rapid interconversion between lactate and pyruvate in blo od that has to be considered in the interpretation of in vivo tracer s tudies.