Noninvasive Measurements of [1‐13C] Glycogen Concentrations and Metabolism in Rat Brain In Vivo

: Using a specific 13C NMR localization method, 13C label incorporation into the glycogen C1 resonance was measured while infusing [1‐13C]glucose in intact rats. The maximal concentration of [1‐13C]glycogen was 5.1 ± 0.6 μmol g‐1 (mean ± SE, n = 8). During the first 60 min of acute hyperglycemia, the rate of 13C label incorporation (synthase flux) was 2.3 ± 0.7 μmol g‐1 h‐1 (mean ± SE, n = 9 rats), which was higher (p 0.05 for correlation). The results implied that net glycogen synthesis of ~3 μmol g‐1 had occurred, similar to previous reports. When infusing unlabeled glucose before [1‐13C]glucose in three studies, the rate of glycogen C1 accumulation was 0.46 ± 0.08 μmol g‐1 h‐1. The results suggest that steady‐state glycogen turnover rates during hyperglycemia are ~1% of glucose consumption.