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Objective: To introduce a safe and specific approachof 13C magnetic resonance spectrum (13C MRS )spectroscopy and investigate the alterations in hepaticanabolism.Methods: Relative anaplerotic, pyruvate recyclingand gluconeogenic fluxes were measured by 13C MRSisotopomer analysis of blood glucose from rats with 40%body surface area burn injury, and from rats exposed tosham injury. A short chain fatty acid, [U-13C] propionatewhich was avidly extracted by the liver, was infusedintravenously to deliver 13C into the citric acid cycle.Proton-decoupled 13C MRS of deproteinized plasma orextracts of the freeze-clamped liver were used to determinethe distribution of 13C in blood or hepatic glucose.Results: There was no difference in the multipletsdetected in the glucose carbon-2 anomer from blood or liverafter 45 or 60 minutes of the infusion of the propionate,indicating that steady-state isotopic conditions wereachieved. Gluconeogenesis relative to citric acid cycle fluxwas not altered by burn injury; in both sham and burngroups the rate of glucose production was about equal toflux through citrate synthase. In the sham group ofanimals, the rate of entry of carbon skeletons into the citricacid cycle was about 4 times than that in the burn group.Similarly, flux through pyruvate kinase (again relative tocitrate synthase) was significantly increased after the burninjury.Conclusions: Since results from analysis of the bloodglucose are the same as that of the hepatic glucose, 13Cdistribution in the glucose and hepatic metabolism can beassessed based on the 13C MRS analysis of the bloodglucose.
