The reciprocal pool model for the measurement of gluconeogenesis by use of[U-C-13]glucose

To improve upon the [U-C-13]glucose method to estimate "gluconeogenesis" as described by J. Katz and J. A. Tayek (Am. J. Physiol. Endocrinol. Metab. 2 72: E476-E484, 1997, and 275: E537-E542, 1998), we describe the reciprocal pool model by using only the isotopomer data of plasma glucose during infus ion of [U-C-13]glucose. The glucose pool serves as both precursor and produ ct for the calculation of the fraction of molecules generated by gluconeoge nesis and to correct for exchange and loss of labeled carbon at the level o f the tricarboxylic acid cycle. We have applied this model to both our own data and those of other investigators using [U-C-13]glucose and have demons trated excellent agreement between the Katz and Tayek model and our recipro cal pool model. When we compare the results of the reciprocal pool model wi th those of Hellerstein ([2-C-13]glycerol) and Landau (2H(2)O-glucose-C-5), the results are similar in short- and long-term fasted adult humans. Final ly, when we apply the reciprocal pool model to our data from premature infa nts, it is clear that we account for the inflow of unlabeled glycerol and p resumably amino acids. This is not surprising, because the vast majority of gluconeogenesis is the result of recycling of glucose and pyruvate carbon.