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Effect of Acute and Recurrent Hypoglycemia on Changes in Brain Glycogen Concentration

Department of Internal Medicine (R.I.H., O.C., E.C.M., R.S.S.), Section of Endocrinology, and Yale Center for Clinical Investigation (S.Y., J.D.), Yale University School of Medicine, New Haven, Connecticut 06520

Address all correspondence and requests for reprints to: Robert S. Sherwin, M.D., Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, P.O. Box 208020, New Haven, Connecticut 06520. E-mail: robert.sherwin{at}yale.edu.

Our objective was to evaluate whether excessive brain glycogen deposition might follow episodes of acute hypoglycemia (AH) and thus play a role in the hypoglycemia-associated autonomic failure seen in diabetic patients receiving intensive insulin treatment. We determined brain glucose and glycogen recovery kinetics after AH and recurrent hypoglycemia (RH), an established animal model of counterregulatory failure. A single bout of insulin-induced AH or RH for 3 consecutive days was used to deplete brain glucose and glycogen stores in rats. After microwave fixation and glycogen extraction, regional recovery kinetics in the brain was determined using a biochemical assay. Both AH and RH treatments reduced glycogen levels in the cerebellum, cortex, and hypothalamus from control levels of 7.78 ± 0.55, 5.4 ± 0.38, and 4.45 ± 0.37 µmol/g, respectively, to approximately 50% corresponding to a net glycogen utilization rate between 0.6 and 1.2 µmol/g·h. After hypoglycemia, glycogen levels returned to baseline within 6 h in both the AH and the RH group. However, recovery of brain glycogen tended to be faster in rats exposed to RH. This effect followed more rapid recovery of brain glucose levels in the RH group, despite similar blood glucose levels in both groups. There was no statistically significant increase above baseline glycogen levels in either group. In particular, brain glycogen was not increased 24 h after the last of recurrent episodes of hypoglycemia, when a significant counterregulatory defect could be documented during a hyperinsulinemic hypoglycemic clamp study. We conclude that glycogen supercompensation is not a major contributory factor to the pathogenesis of hypoglycemia-associated autonomic failure.

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