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Effect of hypoglycemia on brain glycogen metabolism in vivo

Authors

  • In-Young Choi,

    1. Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota
    Current affiliation:
    1. Nathan Kline Institute, Medical Physics, 140 Old Orangeburg Road, Orangeburg, NY 10962
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  • Elizabeth R. Seaquist,

    1. Department of Medicine, University of Minnesota Medical School, Minneapolis, Minnesota
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  • Rolf Gruetter

    Corresponding author
    1. Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota
    2. Department of Neuroscience, University of Minnesota Medical School, Minneapolis, Minnesota
    • Center for Magnetic Resonance Research, 2021 6th Street SE, Minneapolis, MN 55455
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Abstract

The brain contains a small but significant amount of glycogen, which has long been considered to play an insignificant role in the brain. In this study, brain glycogen metabolism was measured using 13C NMR spectroscopy at 9.4 T. Brain glycogen metabolism was modulated by hyperinsulinemia resulting in a net accumulation. The role of glycogen in maintaining brain function is unknown; one possibility is that it may serve as an endogenous glucose reservoir to protect the brain against severe hypoglycemia. To address this possibility, rats were subjected to insulin-induced moderate hypoglycemia and when the level of brain glucose approached zero, brain glycogen content began to decrease gradually, demonstrating utilization of this glucose reservoir. The brain glycogen signal never became undetectable, however, even during 2 hr of hypoglycemia. When plasma and brain glucose concentrations were restored, glycogen increased and the concentration exceeded the pre-hypoglycemic level by several-fold. The data suggest that brain glycogen can provide fuel for extended periods of time when glucose supply is inadequate. Furthermore, brain glycogen can rebound (super-compensate) after a single episode of hypoglycemia. We postulate that brain glycogen serves as an energy store during hypoglycemia and that it may participate in the creation of reduced physiological responses to hypoglycemia that are involved in a symptom often observed in patients with diabetes, hypoglycemia unawareness. © 2003 Wiley-Liss, Inc.

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