MODERATE HYPERGLYCEMIA AFFECTS ISCHEMIC BRAIN ATP LEVELS BUT NOT INTRACELLULAR PH

We used P-31 nuclear magnetic resonance (NMR) spectroscopy to study th e effect of moderate hyperglycemia on brain ATP and intracellular pH i n a model of severe incomplete forebrain ischemia. Plasma glucose in t he hyperglycemic rats was 277 +/- 9 mg/100 ml compared with 115 +/- 10 mg/100 ml in the normoglycemic rats at the onset of ischemia. After 1 5 min of ischemia, brain ATP levels decreased to 31 +/- 8% in normogly cemic rats vs. 63 +/- 11% in hyperglycemic rats (P < 0.05). Phosphocre atine levels were 31 +/- 9 and 55 +/- 8% for normoglycemic and hypergl ycemic rats, respectively. Intracellular pH decreased to the same leve l (similar to 6.5) in both normoglycemic and hyperglycemic animals aft er 15 min of ischemia. In summary, we found that moderate hyperglycemi a during severe incomplete forebrain ischemia significantly increases ischemic brain ATP levels but does not have a significant effect on in tracellular pH. These results support the hypothesis that alterations in brain ATP and adenosine concentrations may be important in the path ogenesis of ischemic tissue injury under moderate hyperglycemic condit ions, whereas alterations in tissue pH may be less important.