Effect of plasma glucose on infarct size in focal cerebral ischemia-reperfusion

Although hyperglycemia has been shown to consistently exacerbate ischemia brain injury following global or diffuse cerebral ischemia, the effect of hyperglycemia in unilateral focal cerebral ischemia remains controversial. Recent advances in thrombolytic therapy have enhanced the clinical significance of postischemic reperfusion. We studied the effect of plasma glucose on ischemic brain injury in a newly developed focal cerebral ischemia-reperfusion model. Rats allowed free access to food until ischemic insult developed intra- and postischemic hyperglycemia and cortical infarction. Rats fasted for 24 hours had blunted hyperglycemic responses. Infarct volumes were correspondingly smaller. The protective effect of fasting was partially abolished by glucose loading during ischemia to induce intra-ischemic hyperglycemia. Glucose loading immediately or 3 hours after focal cerebral ischemia did not significantly alter the protective effect of fasting. Insulin treatment in fed rats before ischemia also reduced hyperglycemic responses and infarct volume. Timing of insulin treatment was also critical in the reduction of ischemic injury. These findings indicate that plasma glucose during the period of ischemia is an important determinant of brain injury in focal cerebral ischemia-reperfusion and there is a therapeutic window for normalization of plasma glucose to be efficacious.