SYNTHESIS OF DEOXYGLUCOSE-1-PHOSPHATE, DEOXYGLUCOSE-1,6-BISPHOSPHATE,AND OTHER METABOLITES OF 2-DEOXY-D-[C-14]GLUCOSE IN RAT-BRAIN INVIVO - INFLUENCE OF TIME AND TISSUE GLUCOSE LEVEL

When the kinetics of interconversion of deoxy[C-14]glucose ([C-14]DG) and [C-14]DG-6-phosphate ([C-14]DG-6-P) in brain in vivo are estimated by direct chemical measurement of precursor and products in acid extr acts of brain, the predicted rate of product formation exceeds the exp erimentally measured rate. This discrepancy is due, in part, to the fa ct that acid extraction regenerates [C-14]DG from unidentified labeled metabolites in vitro. In the present study, we have attempted to iden tify the C-14-labeled compounds in ethanol extracts of brains of rats given [C-14]DG. SiX C-14-labeled metabolites. in addition to [C-14]DG- 6-P, were detected and separated. The major acid-labile derivatives, D G-1-phosphate (DG-1-P) and DG-1,6-bisphosphate (DG- 1,6-P2), COMPrised approximately 5 and approximately 10-15%, respectively, of the total C-14 in the brain 45 min after a pulse or square-wave infusion of [C-1 4] DG, and their levels were influenced by tissue glucose concentratio n. Both of these acid-labile compounds could be synthesized from DG-6- P by phosphoglucomutase in vitro. DG-6-P, DG-1-P, DG-1,6-P2, and ethan ol-insoluble compounds were rapidly labeled after a pulse of [C-14]DG, whereas there was a 10-30-min lag before there was significant labeli ng of minor labeled derivatives. During the time when there was net lo ss of [C-14]DG-6-P from the brain (i.e., between 60 and 180 min after the pulse), there was also further metabolism of [C-14]DG-6-P into oth er ethanol-soluble and ethanol-insoluble C-14-labeled compounds. These results demonstrate that DG is more extensively metabolized in rat br ain than commonly recognized and that hydrolysis of [C-14] DG-1-P can explain the overestimation of the [C-14]DG content and underestimation of the metabolite pools of acid extracts of brain. Further metabolism of DG does not interfere with the autoradiographic DG method.