Oxidation of (14)C-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 (14)C-labeled compounds into the interstitial fluid of adult rat brain and by collecting the brain-generated (14)CO(2) from the dialysis eluate. All compounds were readily oxidized. The recovery of (14)CO(2) 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, (14)C-glutamate and (14)C-glutamine, was stimulated by the addition of nonradioactive acetate and pyruvate. alpha-Cyano-4-hydroxycinnamate decreased (14)C-lactate and (14)C-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.