A comparison of brain glucose metabolism in diabetes as measured by positron emission tomography or by arteriovenous techniques.

[U-11-C]-glucose and positron emission tomography was used to evaluate transport and oxidative metabolism of glucose in the brain of non-diabetic and insulin dependent diabetic (IDDM) subjects. These results were compared with results obtained by the Fick principle. Blood glucose was regulated by a Biostator controlled glucose infusion during a constant insulin infusion. [U-11-C]-glucose was injected during normoglycemia as well as during moderate hypoglycemia. The tracer data were analysed using a three compartment model with a fixed correction for [11-C]-CO2 egress. During normoglycemia the influx rate constant (k1) and blood brain glucose flux of the two groups were similar. During hypoglycemia k1 increased significantly and to the same extent in both groups. During normoglycemia the tracer calculated metabolism of glucose was higher in the brain of non-diabetic than of diabetic subjects. When measured by the Fick principle the net uptake of glucose was broadly the same for the groups. During normoglycemia the molar ratio of O2 to glucose uptake was, however, lower in IDDM than in non-diabetic subjects (4.67 vs 5.50, P less than 0.05, Wilcoxon test). A significant release of lactate and pyruvate was seen in IDDM but not in non-diabetic subjects. The results imply that a larger fraction of glucose is non-oxidatively metabolized in IDDM than in non-diabetic subjects.