Glycogen Metabolism in Neonatal Rat Brain During Anoxia and Recovery

Abstract: Metabolic alterations in glycogen and in glycogen-related metabo lites were studied in neonatal rat brain during controlled anoxia and recovery. One-day postnatal rats were exposed to 100% N, at 37°C for up to 20 min; some rats were allowed to recover in air. Animals were frozen in liquid N, and the brains were prepared for fluorometric analysis of compounds involved in glycogen turnover. During anoxia, glycogen decreased by 29% and 42% at 10 and 20 min, respectively; the free (soluble) and bound (insoluble) components of glycogen decreased in nearly equal proportions. Brain glucose decreased by 72% at 10 min with little further change there after; G-6-P, G-1-P, and UDPG also declined. During recovery from anoxia, glucose and G-6-P increased above control levels for up to 60 min. G-1-P paralleled G-6-P levels, but UDPG remained low. Glycogen returned to control values by 4 h. The findings suggest that although glycogen is mobilized slowly in newborn rat brain, the metabolite contributes at least one-third of the cerebral energy supply during anoxia. Presumably, readily available stores of glycogen combined with low cerebral metabolic requirements underscore the known tolerence of immature animals to hypoxic stress. Glycogen accumulation during recovery appears to be facilitated at the synthetase step, since equilibrium measurements of the phosphoglucomutase and pyrophosphorylase systems indicate that these reactions are not rate-limiting for glycogen synthesis.