METABOLIC CHANGES ASSOCIATED WITH ALTERING BLOOD-GLUCOSE LEVELS IN SHORT DURATION FOREBRAIN ISCHEMIA

P-31 nuclear magnetic resonance spectroscopy was used to follow change s in cerebral pH and high-energy phosphate metabolites during forebrai n ischemia in hypo-, normo- and hyperglycemic rats, and during reperfu sion in animals in which the blood glucose level was altered post-isch emia. Pre-ischemia, no differences in the levels of inorganic phosphat e (P(i)) and adenosine triphosphate (ATP) relative to phosphocreatine (PCr) or in tissue pH between blood glucose groups were observed. Duri ng ischemia, the decrease in tissue pH was found to be dependent on th e pre-ischemic blood glucose concentration, being greatest in hypergly cemic and least in hypoglycemic animals. The increase of P(i), a conse quence of the hydrolysis of high-energy phosphate metabolites, also de pended on the blood glucose concentration, being greatest in hypoglyce mic and least in hyperglycemic animals. ATP and PCr decreased more rap idly in hypoglycemic rats compared to normo- or hyperglycemic animals, which showed no differences in the rates of depletion. Post-ischemic hyperglycemia resulted in delayed recovery of tissue pH in all groups and of PCr and ATP in animals hyperglycemic throughout the experiment. Insulin administration immediately following ischemia increased the r ate of recovery of pH, ATP and PCr in hyperglycemic animals. ATP remai ned significantly below pre-ischemia level in all subgroups at 1 h pos t-ischemic, while PCr was lower than it was pre-ischemia only in those subgroups hyperglycemic prior to and/or following ischemia. In animal s maintained severely hypoglycemic throughout the experiment, erratic blood pressure and cerebral energy failure during the reperfusion inte rval were observed.