On the Intermediate Metabolism of Carbohydrates in the Brain of Healthy Persons

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Abstract
On 19 healthy subjects distributed in almost all age ranges, glucose, pyruvic acid and lactic acid contents were measured in blood samples taken from the internal jugular vein and the femoral artery, simultaneously with the cerebral hemodynamics by N2O method, to determine the amount of metabolized carbohydrates in unit weight of brain tissue. The cerebral glucose consumption was found to be closely related to cerebral oxygen consumption, suggesting that the blood glucose is the most important source of energy for the brain. Cerebral arterio-venous differences of glucose and cerebral blood flow were in a negative correlation, indicating the constancy of glucose supply as energy source. Pyruvic acid and lactic acid were found to be released from the brain in almost all cases, but the correlation between the outflow of these acids and the cerebral oxygen consumption was obscure. The mean value of cerebral glucose consumption was almost equal to the sum of mean values of the cerebral oxidation of glucose and the amounts of acids transferred out of the brain. Hence, an equilibrium in carbohydrate metabolism of the brain of healthy persons was elucidated. In aged subjects, the derangement of carbohydrate metabolism is evident with a well balanced equilibrium on a lower level, presumably as a physiological senile phenomenon.