Detection of [1,6‐13C2]‐glucose metabolism in rat brain by in vivo 1H‐[13C]‐NMR spectroscopy

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Abstract
Localized, water‐suppressed 1H‐[13C]‐NMR spectroscopy was used to detect 13C‐label accumulation in cerebral metabolites following the intravenous infusion of [1,6‐13C2]‐glucose (Glc). The 1H‐[13C]‐NMR method, based on adiabatic RF pulses, 3D image‐selected in vivo spectroscopy (ISIS) localization, and optimal shimming, yielded high‐quality 1H‐[13C]‐NMR spectra with optimal NMR sensitivity. As a result, the 13C labeling of [4‐13C]‐glutamate (Glu) and [4‐13C]‐glutamine (Gln) could be detected from relatively small volumes (100 μL) with a high temporal resolution. The formation of [n‐13C]‐Glu, [n‐13C]‐Gln (n = 2 or 3), [2‐13C]‐aspartate (Asp), [3‐13C]‐Asp, [3‐13C]‐alanine (Ala), and [3‐13C]‐lactate (Lac) was also observed to be reproducible. The 13C‐label incorporation curves of [4‐13C]‐Glu and [4‐13C]‐Gln provided direct information on metabolic pathways. Using a two‐compartment metabolic model, the tricarboxylic acid (TCA) cycle flux was determined as 0.52 ± 0.04 μmol/min/g, while the glutamatergic neurotransmitter flux equaled 0.25 ± 0.05 μmol/min/g, in good correspondence with previously determined values. Magn Reson Med 49:37–46, 2003.