Cerebral metabolic changes in profound, insulin-induced hypoglycemia, and in the recovery period following glucose administration.

Abstract

AbstractSevere hypoglycemia was induced by insulin in lightly anaesthetized (70°o N2O) and artificially ventilated rats. Brain tissue was frozen in situ after spontaneous EEG potentials had disappeared for 5. 10. 15 or 30 min and cerebral cortex concentrations of labile organic phosphates, glycolytic metabolites, ammonia and amino acids were determined. In other experiments, recovery was induced by glucose injection at the end of the period of EEG silence.All animals with an isoelectric EEG showed extensive deterioration of the cerebral energy state. and gross perturbation of amino acid concentrations. The latter included a 4‐fold rise in aspartate concentration and reductions in glutamate and glutamine concentrations to 20 and 5oo of control levels respectively. There was an associated rise in ammonia concentration to about 3μmol‐g‐1.Administration of glucose brought about extensive recovery of cerebral energy metabolism. For example, after an isoelectric period of 30 min tissue concentrations of phosphocreatine returned to or above normal, the accumulation of ADP and AMP was reversed, there was extensive resynthesis of glycogen and glutamine and full normalisation of tissue concentrations of pyruvate. α‐ketoglutarate. GABA and ammonia. However, even after 3 h of recovery there was a reduction in the ATP concentration and thereby in adenine nucleotide pool, moderate elevations of lactate content and the lactate pyruvate ratio, and less than complete restoration of the amino acid pool. It is concluded that some cells may have been irreversibly damaged by the hypoglycemia.