Correction for metabolic exchange in the calculation of the rate of gluconeogenesis in rats.

The degree by which the rate of gluconeogenesis is underestimated when calculated from the transfer of 14C atoms from circulating precursors to plasma glucose was estimated from the ratio of the specific activity of plasma glucose and blood acetoacetate during the infusion of [2-14C]acetate in rats fasted for 3 days. The specific activity of blood acetoacetate was taken to be equal to that of its only precursor, the acetyl C atoms of hepatocellular AcCoA. These latter are assumed not to be available for the net synthesis of glucose and may be incorporated into the molecule by "metabolic exchange" in the hepatic oxalo-acetate pool only. By this approach 25% of the C atoms of plasma glucose have been estimated to arise from AcCoA. Multiplication by a correction factor H = 1.33 +/- 0.03 is being suggested to compensate for the metabolic exchange of 14C for 12C atoms when the rate of gluconeogenesis is calculated from the transfer of 14C atoms from labeled precursors to glucose.