Cerebral metabolism of doubly labeled glucose in humans in vivo

¹ Research Facility, Rockland State Hospital, Orangeburg, New York

With glucose-3-C¹⁴ as injected substrate, the production of C¹⁴O₂ almost kept pace with the net uptake of C¹⁴ by brain. Brain C¹⁴O₂ specific activities practically coincided with venous blood glucose specific activities. This rapid production of C¹⁴O₂ with little or no dilution of C¹⁴ led to the derivation of theoretical curves for glucose-2-, glucose-1-, or glucose-6-C¹⁴ experiments. The dissimilarity between theoretical and experimental values suggested that there is a significant dilution of C¹⁴ in traversing the Krebs cycle. Equations derived from hypothetical metabolic pathways which included a pool of substrate, x, were employed to match theoretical with average experimental values. In experiments with doubly labeled glucose-C¹⁴-T, brain TOH (tritiated water) specific activities were used to derive brain C¹⁴O₂ specific activity values which closely approximated actual results. A scheme for human cerebral metabolism of glucose in vivo, which includes a small, metabolically active pool of glutamate, -aminobutyrate, and succinic semialdehyde, is proposed.

Submitted on February 3, 1964

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