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Abstract:
The regional influx of glucose across the blood-brain barrier and regional blood flow were studied simultaneously in conscious and restrained rats using the single pass bolus injection of [14C]butanol and [3H]D-glucose method. Glucose extraction by the cerebellum was about twice that of other brain regions. Thus, despite the lower cerebellar blood flow, the influx of glucose into the cerebellum was equivalent to that of the cerebral cortex and higher than that of the hippocampus over a wide range of plasma glucose concentrations. Because the local metabolic rate for glucose is higher in the cerebral cortex than in the cerebellum, the equal influx of glucose in these two regions means a relative oversupply of glucose to the cerebellum. In vivo analysis of blood to brain glucose transport kinetics showed similar plasma glucose concentrations at half-maximal transport (Kt) in brain regions that were studied. The values for Kt ranged between 4.4 and 5.1 mM. Maximal transport capability (Tmax), on the other hand, was similar in the cerebral cortex and cerebellum but significantly lower in the hippocampus (P less than 0.05). The higher ratio of glucose influx to glucose utilization in the cerebellum may explain the clinical and experimental findings of relative resistance of the cerebellum to hypoglycemia while the lower Tmax in the hippocampus may be the mechanism underlying its selective vulnerability during pathophysiologic conditions associated with marked increments in brain oxidative metabolism, such as status epilepticus.