Oxidation of 14C-labeled compounds perfused by microdialysis in the brains of free-moving rats

The oxidative capacity of the brain for alternate substrates, glucose, lactate, pyruvate, acetate, glutamate, and glutamine was determined by using microdialysis to infuse C-14-labeled compounds into the interstitial fluid of adult rat brain and by collecting the brain-generated (CO2)-C-14 from the dialysis eluate. All compounds were readily oxidized. The recovery of (CO2)-C-14 was enhanced for those compounds metabolically close to entry into the TCA cycle or known to have a low interstitial concentration. Two compounds, pyruvate and lactate, demonstrated reciprocal competition when added as nonradioactive competitors. Oxidation of two amino acids, C-14-glutamate and C-14-glutamine, was stimulated by the addition of nonradioactive acetate and pyruvate. alpha-Cyano-4-hydroxycinnamate decreased C-14-lactate and C-14-pyruvate oxidation, consistent with the transport of both compounds via a monocarboxylate transporter. The results of this in vivo study support the results of previous in vitro studies that showed that a wide range of compounds formed from glucose in the brain are also oxidized in the brain for energy production. (c) 2007 Wiley-Liss, Inc.