Cerebral blood flow and metabolic rate of oxygen, glucose, lactate, pyruvate, ketone bodies and amino acids.

The cerebral blood flow (CBF) and cerebral metabolic rate (CMR) of oxygen, glucose, lactate, pyruvate, ketone bodies, and 24 amino acids were examined in 10 healthy subjects, five 21-24 and five 55-65 years old. The subjects were free from drugs. The results of psychometric and neurological examinations were negative. CBF was determined with the nitrous oxide method on the subjects who were awake and normocapnic and had fasted overnight. No differences were found between the young and the old groups except in arterial levels of four amino acids, viz. aspartic acid, methionine, lysine, and tryptophan. In the whole group of 10 subjects, a significant cerebral net uptake (expressed as median values in mumol X kg-1 X min-1) was found not only for oxygen (1719) and glucose (248), but also for acetoacetate (4.3), D-beta-hydroxybutyrate (6.2), arginine (2.0), leucine (5.2), and isoleucine (1.2). There was a significant net release of lactate (-28). CBF was positively correlated to the CMR of oxygen and D-beta-hydroxybutyrate. Arterial concentrations and CMR were positively correlated for ketone bodies, glutamic acid, proline and taurine. It is of particular interest that the whole group of healthy subjects showed a significant cerebral uptake of branched-chain and dibasic amino acids.