Blood-brain amino acid transport and content during anoxia and reoxygenation

The isolated dog brain preparation was used to investigate the dynamics of cerebral amino acid metabolism during perfusion with anoxic blood (PO2 less than 10 mmHg). Significant uptake of histidine and lysine, as determined by arteriovenous (A-V) differences in whole blood samples, was observed during 30 min of cerebral anoxia. The A-V differences determined from plasma samples indicated that uptake of histidine and efflux of glutamic acid and proline had occurred. Nitrogen balance in the preparation appeared to be maintained. Thirty minutes of anoxic perfusion resulted in increased tissue concentrations of five essential amino acids (methionine, histidine, leucine, lysine, and valine) and a decreased tissue level of the essential amino acids threonine and phenylalanine. Taurine, gamma-aminobutyric acid, alanine, glycerophosphoethanolamine and phosphoethanolamine also increased, whereas the aspartic acid concentration declined. When aerobic perfusion was resumed, the total pool of essential amino acids continued to increase and was nearly twice normal after 120 min of reperfusion. The combined concentration of asparagine and glutamine, serine, alpha-aminobutyric acid, and cystathionine also increased during postanoxic perfusion. Only taurine and phenylalanine concentrations returned toward normal.