Objective: To introduce a safe and specific approach of (13)C magnetic resonance spectrum ((13)C MRS) spectroscopy and investigate the alterations in hepatic anabolism.
Methods: Relative anaplerotic, pyruvate recycling and gluconeogenic fluxes were measured by (13)C MRS isotopomer analysis of blood glucose from rats with 40% body surface area burn injury, and from rats exposed to sham injury. A short chain fatty acid, [U (13)C] propionate which was avidly extracted by the liver, was infused intravenously to deliver (13)C into the citric acid cycle. Proton-decoupled (13)C MRS of deproteinized plasma or extracts of the freeze-clamped liver were used to determine the distribution of (13)C in blood or hepatic glucose.
Results: There was no difference in the multiplets detected in the glucose carbon-2 anomer from blood or liver after 45 or 60 minutes of the infusion of the propionate, indicating that steady-state isotopic conditions were achieved. Gluconeogenesis relative to citric acid cycle flux was not altered by burn injury; in both sham and burn groups the rate of glucose production was about equal to flux through citrate synthase. In the sham group of animals, the rate of entry of carbon skeletons into the citric acid cycle was about 4 times than that in the burn group. Similarly, flux through pyruvate kinase (again relative to citrate synthase) was significantly increased after the burn injury.
Conclusions: Since results from analysis of the blood glucose are the same as that of the hepatic glucose, (13)C distribution in the glucose and hepatic metabolism can be assessed based on the (13)C MRS analysis of the blood glucose.