Gluconeogenesis in hepatocytes determined with [2-13C]acetate and quantitative 13C NMR spectroscopy

1. In the present study the major metabolic pathways of glucose metabolism were determined in isolated liver cells using [2-13C]acetate and 13C magnetic resonance spectroscopy. 2. The relative reaction rates of glucose synthesis to the TCA cycle were determined from the 13C distribution in glucose where the overall 13C enrichment of glucose was 6.41 +/- 1.94% (mean +/- SD; n = 6) and the mean 13C enrichment of C1, C2, C5, C6 to C3, C4 was 2.63 +/- 0.30. 3. Since the distribution of tracer in glucose is a function of the relative entry rates of pyruvate to acetyl-CoA into the oxaloacetate pool this was calculated to be 0.32 +/- 0.15 and the factor for carbon exchange (1/P) between the gluconeogenic pathway and the TCA cycle was calculated to be 1.03 +/- 0.20. 4. With this carbon exchange factor and the approximated 13C enrichment of acetyl-CoA the intramitochondrial 13C enrichment of phosphoenolpyruvate was calculated and the "true" rate of hepatic gluconeogenesis from phosphoenolpyruvate estimated. 5. Since acetate was metabolized solely in liver cells the 13C enrichment of acetyl-CoA could be approximated from that of 3-hydroxybutyrate. 6. The carbon 13 enrichment of 3-hydroxybutyrate and phosphoenolpyruvate was 5.89 +/- 0.90% and 5.96 +/- 1.67%, respectively. 7. The per cent gluconeogenesis from phosphoenolpyruvate calculated as the ratio of the 13C enrichment of glucose to that of 3-hydroxybutyrate times 1/P was 107 +/- 8%.(ABSTRACT TRUNCATED AT 250 WORDS)