Assessment of human muscle glycogen synthesis and total glucose content byin vivo C-13 MRS

Background Obesity is often accompanied by a decreased ability of insulin t o stimulate glucose uptake and glycogenesis in skeletal muscle. The aim of this study was to investigate the rare of glycogen formation and of muscula r glucose content in relation to insulin sensitivity under euglycemic condi tions. Materials and methods We applied a hyperinsulinemic (430 pmol m(-2) min(-1) ) euglycemic clamp with infusion of 20% glucose (30% enriched with C-13-1-g lucose) to 8 subjects with a wide range of insulin sensitivities. Glycogen and glucose levels were monitored simultaneously by in vivo C-13 MRS of the calf muscle on a clinical MR system at 1.5T field strength. Results and conclusions Glycogen synthesis rate showed a strong correlation with whole body glucose uptake during the clamp (r = 0.93, P < 0.01). With the use of C-13 MRS, total muscular glucose content could be determined in vivo, and showed a positive, linear correlation with glycogen synthesis ra te (r = 0.85, P < 0.01). C-13 MRS provides important information regarding in vivo insulin action. Preliminary results indicate that the glycogen synt hesis rate improves after treatment with troglitazone.