Relative Higher Hematocrit Attenuates the Cerebral Excitatory Amino Acid Elevation Induced by Deep Hypothermic Circulatory Arrest in Rats.

Hemodilution is a commonly used technique in cardiopulmonary bypass (CPB) and deep hypothermic circulation arrest (DHCA). Our previous study showed that lower hematocrit aggravated the brain injury after DCHA. Because the excitatory amino acids are critical pathways of ischemic neuronal damage, the purpose of the present study was to investigate the effects of different degrees of hemodilution on the excitatory amino acid content in different brain areas after DHCA Adult Sprague-Dawley rats were randomly divided into four groups: group I hematocrit (Hct) 10% (H1), group II Hct 20% (H2), group III Hct 30% (H3), and control group (C). All animals except those in the control group underwent DHCA at 18°C for 90 minutes. Different degrees of hemodilution were accomplished by changing the composition and volume of the priming solution used in CPB. High-performance liquid chromatography was used to determine the concentration of glutamate (Glu), aspartate (Asp), glycine (Gly), gamma-aminobutyric acid (GABA), and taurine (Tau) in the cerebral cortex, hippocampus, and thalamus. We found that the concentration of these five amino acids in the hippocampus and cortex were all increased after DHCA. Glu, Asp, and Gly in the hippocampus and cortex were significantly lower in the Hct 30% group than in the other two groups (p<0.05). There was no significant difference in the GABA and Tau concentrations among the three groups. In summary, excitatory amino acids increased significantly after DHCA, and relative higher hematocrit attenuates this response.