Brain metabolic changes in young vs aged rats during hypoxia.

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Abstract
Brain energy state and glycolytic metabolites were measured in young (6 month) and aged (28 month) male rats under normoxic (70% nitrous oxide, 30% oxygen) or hypoxic (PaO2 = 25 mm Hg) test conditions. Hypoxic ischemia was induced in one cerebral hemisphere by ligation of one carotid artery. Under normoxic test conditions brain energy metabolite concentrations were similar between young and aged rats. Brain tissue glucose, glycogen, glucose-6-phosphate and critic acid cycle intermediate concentrations were decreased in aged rats during normoxia while fructose-6-phosphate and pyruvate were increased. Decreases in brain energy state and increases in lactate/pyruvate ratios were significant in both young and aged rats during hypoxia and were greater in aged animals in hypoxic-ischemic tissues. These results indicate that brain energy state is normal in aged rats under normoxic conditions but that hypoxic-ischemia produces a greater degree of brain energy failure compared to younger animals.