EVIDENCE FOR 100-PERCENT C-13 NMR VISIBILITY OF GLUCOSE IN HUMAN SKELETAL-MUSCLE

The accuracy of the measurement of total muscle glucose by in vivo C-1 3 NMR spectroscopy was tested in five normal volunteers during a eugly cemic [1-C-13]glucose infusion. The NMR visible concentration calibrat ed using an external reference was compared with that calculated from plasma glucose concentration, assuming that glucose remained extracell ular. The NMR measurement always provided higher values than the calcu lation from plasma glucose: 0.51 +/- 0.035 (mean +/- SE) versus 0.38 /- 0.005 mmol/liter of muscle on average. This systematic difference w as interpreted as reflecting the presence of muscle glucose-6-phosphat e, co-resonating with free glucose, Thus, glucose appeared to be virtu ally 100% NMR visible in human skeletal muscle.