Glucose transport and metabolism in the brain.

A model is proposed for the uptake and metabolism of cold and radiotracer glucose that takes into account the concentration profiles of the cold and tracer glucose as they pass through the capillary bed of the brain. The model incorporates capillary blood flow, nonlinear transport between blood and brain, and Michaelis-Menten kinetics for incorporation of glucose into the brain metabolic pool. Analytical equations are derived for the conditions of normoglycemia and hypoglycemia. In normoglycemia, cold glucose uptake is determined solely by metabolic demand and is relatively independent of fluctuations in plasma glucose levels. At lower glucose levels, transport of glucose across the blood-brain barrier becomes a progressively more important factor in determining uptake. Uptake of radiotracer glucose depends primarily on transport parameters. Functional heterogeneity of the capillary bed is considered both in relation to glucose uptake and parameter estimation.