Observations on Cerebral Carbohydrate Metabolism in Man

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Abstract
Measurements of normal human cerebral metabolism indicate total brain glucose consumption to be about 95 mg. glucose per minute and that cerebral glucose consumption represents about 70% of the total glucose output of the resting liver. In vivo and in vitro observations denote that glucose is the normal fuel for cerebral O2 consumption, and that cerebral respiratory quotient is close to 1.0. Glucose deprivation is consistent with longer survival of brain tissue than is anoxia, because the brain metabolizes its own available oxidizable stores. The role of carbohydrate metabolism in central nervous system function is manifold. It produces energy for normal cellular processes, including fat and protein synthesis. Interconversion between cerebral lipids and carbohydrates probably occurs through acetyl-coenzyme A. Glutamine and aspartic and glutamic acids are produced from oxalacetate and a-ketoglutarate, both of which are intermediary steps in oxidative glucose metabolism. Cerebral glycolysis results in production of pyruvate or lactate which in the presence of O2 then enter the aerobic phase of metabolism, which is productive of most of the energy required for the complex function of the cell. Cellular energy maintains the cell''s internal environment by transport of electrolytes and solutes across the cell membrane and is also essential for the resynthesis of acetylcholine after impulse transmission. Finally, the 6 moles of CO2 produced by each mole of glucose are vital to the maintenance of the cellular milieu by regulation of pH, and are important in the intrinsic regulation of cerebral vascular tone.