Glucose production, gluconeogenesis, and hepatic tricarboxylic acid cycle fluxes measured by nuclear magnetic resonance analysis of a single glucose derivative

Abstract

A triple-tracer method was developed to provide absolute fluxes contributing to endogenous glucose production and hepatic tricarboxylic acid (TCA) cycle fluxes in 24-h-fasted rats by 2H and 13C nuclear magnetic resonance (NMR) analysis of a single glucose derivative. A primed, intravenous [3,4-13C2]glucose infusion was used to measure endogenous glucose production; intraperitoneal 2H2O (to enrich total body water) was used to quantify sources of glucose (TCA cycle, glycerol, and glycogen), and intraperitoneal [U-13C3] propionate was used to quantify hepatic anaplerosis, pyruvate cycling, and TCA cycle flux. Plasma glucose was converted to monoacetone glucose (MAG), and a single 2H and 13C NMR spectrum of MAG provided the following metabolic data (all in units of [mu]mol/kg/min; n=6): endogenous glucose production (40.4 ± 2.9), gluconeogenesis from glycerol (11.5 ± 3.5), gluconeogenesis from the TCA cycle (67.3 ± 5.6), glycogenolysis (1.0 ± 0.8), pyruvate cycling (154.4 ± 43.4), PEPCK flux (221.7 ± 47.6), and TCA cycle flux (49.1 ± 16.8). In a separate group of rats, glucose production was not different in the absence of 2H2O and [U-13C]propionate, demonstrating that these tracers do not alter the measurement of glucose turnover.