Changes in energy state and acid-base parameters of the rat brain during complete compression ischemia

Abstract

Carbohydrate substrates, organic phosphates, amino acids and ammonia were studied in the rat brain during complete ischemia of 1–15 min duration utilising an ischemic model with increase of the intracranial CSF pressure. Depletion of glucose occurred in 1 min and accumulation of lactate was maximal at 3 min. Measurements of phosphocreatine, ATP, ADP and AMP and calculations of energy use showed that no useful energy remained after 5 min of ischemia. The results indicate that tissue P co 2 increased to over 100 mm Hg and that cell pH fell by 0.5 units. Depletion of α-ketoglutarate occurred in 1 min and there was no pyruvate left with prolonged ischemia. Since decreases were observed also in citrate, malate and oxaloacetate the results either suggest that citric acid cycle intermediates in general were diverted towards amino acid formation, or that ischemia is associated with a redistribution of carbon atoms within the cycle with accumulation of other (unmeasured) intermediates. With 1 min of ischemia, ammonia increased although the adenine nucleotide sum remained constant. Prolonged ischemia was associated with unchanged levels of glutamate and aspartate but there was a moderate fall in glutamine.