Cerebral metabolic responses of hyperglycemic immature rats to hypoxia-ischemia.

Unlike adult rats, glucose supplementation of immature rats does not lead to accentuated hypoxic-ischemic brain damage. To explore the reason for this age-specific paradox, we subjected 7-day postnatal rats to unilateral common carotid artery occlusion followed by a subcutaneous injection of either 0.1 ml 50% glucose or normal saline. They were then exposed to hypoxia with 8% oxygen, during which they received 2.5 microCi 2-[14C]-glucose or were quick-frozen for brain metabolite analysis. During hypoxia-ischemia, glucose transport into the ipsilateral cerebral hemisphere of the hyperglycemic rats was greater (+100-150%) than in normoglycemic animals. However, glucose consumption was similar in the two groups. Glucose concentrations in brain were lower during hypoxia-ischemia in the normoglycemic animals, whereas lactate increased to similar levels in the two groups. The high-energy phosphate reserves, ATP and phosphocreatine, were depleted to a similar extent. Thus, hyperglycemia combined with hypoxia-ischemia, although associated with increased glucose transport into brain, does not lead to enhanced glucose utilization or lactate accumulation by brain over that of hypoxia-ischemia alone.