Increased pyruvate flux capacities account for diet-induced increases in gluconeogenesis in vitro

High-fat (HF) and high-sucrose (SU) diets increase gluconeogenesis. The pre sent study was designed to determine the contributions of pyruvate dehydrog enase, pyruvate carboxylase, phosphoenolpyruvate carboxykinase (PEPCK), and pyruvate kinase fluxes to this accelerated gluconeogenesis (GNEO) in the a bsence and presence of fatty acids. Male Sprague-Dawley rats were fed an HF , SU, or starch (ST) diet for 1 wk, and hepatocytes or mitochondria were is olated. In the absence of palmitate, the tracer estimated rates of GNEO (nm ol . min(-1) . mg(-1)) were elevated in hepatocytes isolated from SU (32.3 +/- 1.8) and HF (35.4 +/- 1.8) vs. ST (22.8 +/- 1.5). Pyruvate carboxylase and PEPCK flux rates (nmol . min(-1) . mg(-1)) were increased in the SU (47 .5 +/- 2.2 and 34.8 +/- 1.5) and HF (49.4 +/- 1.8 and 38.2 +/- 1.8) groups compared with the ST group (32.8 +/- 3.2 and 44.3 +/- 2.0). Palmitate (250- 1,000 muM) stimulation of these fluxes was not significantly different amon g groups. Bromopalmitate, an inhibitor of fat oxidation, abolished differen ces in GNEO, pyruvate carboxylase, and PEPCK fluxes in HF and SU vs. ST. In isolated mitochondria, pyruvate carboxylation and palmitoyl carnitine oxid ation were not significantly different among groups. The results of this st udy suggest that the increased gluconeogenic flux observed with HF and SU d iets is associated with an increased pyruvate flux through pyruvate carboxy lase and PEPCK. Moreover, the ability of bromopalmitate to normalize glucon eogenic fluxes suggests that endogenous fatty acids contribute to diet-indu ced increases in GNEO.