[1-13C]glucose metabolism in the tumoral and nontumoral cerebral tissue of a glioma-bearing rat

C6 cells were used to establish a glioma-bearing rat model by stereotaxic injection in the left caudate nucleus. The tumor status was evaluated by magnetic resonance imaging and conventional histology. The glioma-bearing rats were infused for 1 h with a [1-C-13]glucose solution. Perchloric acid extracts of the tumor and the ipsilateral and contralateral hemispheres were analyzed by C-13-NMR spectroscopy. The C-13-labeling patterns in compounds, mainly amino acids, indicated no drastic modification of carbon metabolism in both ipsilateral and contralateral hemispheres, as compared with control rats, whereas profound metabolic differences between brain tissue and tumor were observed. Glutamine C4 enrichment was lower in the glioma than in the brain [mean +/- SD values, 5.4 +/- 2.3 (n = 5) and 15.0 +/- 0.8% (n = 10), respectively] and also lower than the glutamate C4 enrichment in the glioma (mean +/- SD value, 22.6 +/- 4.2%; n = 5), indicating that tumor glutamine was neither synthesized inside the glioma nor taken up from the surrounding brain. The glutamine C4 enrichment in the serum (6.7 +/- 0.5%; n = 10) suggested that the glioma imported glutamine from the blood, a process probably connected with angiogenesis.