Compartment analysis of cerebral glucose metabolism and in vitro glucose-metabolizing enzyme activities in the rat brain.

To clarify the relationship between cerebral glucose metabolic rate constants and glucose-metabolizing enzyme activities in the cerebral cortex, we evaluated the cerebral metabolic rate of glucose (CMRGlu), metabolic rate constants of [18F]-2-fluoro-2-deoxy-D-glucose (FDG) and related enzyme activities in the frontal cortex under normal and glucose metabolism-suppressed conditions. Applying a three-compartment four-parameter model, metabolic rate constants were obtained by dynamic positron emission tomography with FDG, and CMRGlu was calculated based on these rate constants. The glycolytic enzyme activities were determined by in vitro biochemical assay. Three days after ibotenic acid injection into the basal forebrain, CMRGlu was decreased in the ibotenic acid-treated frontal cortex as well as k3* (phosphorylation), while K1* (plasma to brain) showed no remarkable change. No significant reductions of the enzyme activities except for hexokinase activity were found in the frontal cortex. Regression analysis showed a significant positive correlation between k3* and the hexokinase activity. These results suggested that k3* in the compartment analysis reflects hexokinase activity.