Glycolysis versus TCA cycle in the primate brain as measured by combining 18F-FDG PET and 13C-NMR

The glycolytic flux (cerebral metabolic rate of glucose CMRglc) and the TCA cycle flux (VTCA) were measured in the same monkeys by F-18-fluorodeoxyglucose (F-18-FDG) positron emission tomography (PET) and C-13 NMR spectroscopy, respectively. Registration of nuclear magnetic resonance (NMR) and PET data were used for comparison of CMRglc and VTCA in the exact same area of the brain. Both fluxes were in good agreement with literature values (CMRglc = 0.23 +/- 0.03 mu mol/g min, V-TCA = 0.53 +/- 0.13 mu mol/g min). The resulting [CMRglclV(TCA)] ratio was 0.46 +/- 0.12 (n = 5, mean +/- s.d.), not significantly different from the 0.5 expected when glucose is the sole fuel that is completely oxidized. Our results provide a cross-validation of both techniques. Comparison of CMRglc with V-TCA is in agreement with a metabolic coupling between the TCA cycle and glycolysis under normal physiologic conditions.