Measurement of lactate production by tracer techniques

Tracer methodology is developed for use in the study of lactate metabolism. A one-compartment model introduces the inference of lactate flux from specific activity. Two compartments distinguish between blood and tissue, and give an estimate of tissue specific activity from measurements in blood. The two-compartment model is applied directly to the problem of flux between lactate and pyruvate in a single tissue. It is shown that equilibration between lactate and pyruvate pools does not invalidate the use of tracer methodology to study lactate metabolism. Application of the two-compartment model to a perfused muscle preparation shows that both lactate and pyruvate fluxes can be measured by using tracer techniques. A three-compartment formalism is presented to resolve the controversy regarding sampling and infusion sites, with special attention given to anatomical identity of the sites. Future directions include measurement of tracer transients during tracee steady state, measurement of distribution of blood flow, and further study of isolated organ preparations.