Measurement of gluconeogenesis and pyruvate recycling in the rat liver: A simple analysis of glucose and glutamate isotopomers during metabolism of [1,2,3-¹³C₃]propionate

Simple equations that relate glucose and glutamate ¹³C-NMR multiplet areas to gluconeogenesis and pyruvate recycling during metabolism of [1,2,3-¹³C₃]propionate are presented. In isolated rat livers, gluconeogenic flux was 1.2 times TCA cycle flux and about 40% of the oxaloacetate pool underwent recycling to pyruvate prior to formation of glucose. The ¹³C spectra of glucose collected from rats after gastric versus intravenous administration of [1,2,3-¹³C₃]propionate indicated that pyruvate recycling was slightly higher in vivo (49%) while glucose production was unchanged. This indicates that a direct measure of gluconeogenesis and pyruvate recycling may be obtained from a single ¹³C-NMR spectrum of blood collected after oral administration of enriched propionate.