Estimating gluconeogenesis by NMR isotopomer distribution analysis of [13C]bicarbonate and [1-13C]lactate

The gluconeogenic contribution to glucose production in livers isolated from rats fasted for 24h was determined by C-13-NMR isotopomer distribution analysis of secreted glucose enriched from 99% [C-13]bicarbonate (n = 4) and 99% [1-C-13] lactate (n = 4). Experiments with 3% (H2O)-H-2 were also performed, allowing the gluconeogenic contribution to be measured by the relative H-2 enrichments at positions 5 and 2 of glucose. From C-13-NMR analyses, the contribution of gluconeogenesis to glucose output was estimated to be 93 +/- 3% for [C-13]bicarbonate perfusion and 91 +/- 3% for [1-C-13] lactate perfusion, in good agreement with the H-2-NMR analysis of the gluconeogenic contribution to glucose production (100 +/- 1% and 99 +/- 1%, respectively) and consistent with the expected negligible contribution from glycogenolysis. These results indicate that C-13-NMR analysis of glucose C-13-isotopomer distribution from either [C-13] bicarbonate or [1-C-13]lactate precursor provides realistic estimates of the gluconeogenic contribution to hepatic glucose output. Copyright (C) 2007 John Wiley & Sons, Ltd.