The application of isotopes to the study of lactate metabolism.

The use of 14C as tracer to measure lactate turnover and oxidation and its role in gluconeogenesis are discussed. Lactate is formed as well as utilized in many cells, and most of it in the body is present within cells so that interpretation of 14C data from labelled lactate is more complex and more difficult than that of compounds present largely extracellularly, such as glucose. Apparent uptake of [14C]lactate may occur in the absence of net lactate utilization, and 14CO2 production does not provide a measure of true lactate oxidation. In vivo sites of tracer administration and sampling of blood are of critical significance for evaluation of lactate turnover, lactate space, its incorporation into glucose, and oxidation.