Effect of Fasting on 2H-Enrichment Levels of Rat Plasma Glucose as measured by 2H NMR Spectroscopy Following Infusion of 2H2O.

of fasting in rat. These results are consistent with other studies that showed diminished rates of glycogenolysis and glycogen levels after 20-24 hours of fasting in rats (5,6). Our data indicates that the majority of gluconeogenic carbons were derived from PEP with only minor contributions from glycerol. For the 4-6.5-hour fasted group, the H5/H2 enrichment ratio was 0.62 ± 0.08 and the H6S/H2 ratio was 0.45 ± 0.07. From this data, the relative contribution of glycogen was 38 ±8% , glycerol, 17 ±2%a nd PEP 45 ±7% . The contribution of glycogen to hepatic glucose output was significantly higher in comparison to the 24-26.5 hour fasted group (p < 0.001) indicating that glycogenolytic flux was significant after 4-6.5 hours of fasting. The relative contribution of PEP was significantly lower in the 4-6.5 hour compared to 24-26.5 hour fasted group (p < 0.0005) while the contribution from glycerol was not significantly different between the groups. Discussion In conclusion, the relative rates of glycogenolysis and gluconeogenesis in the rat, as measured by 2H NMR spectroscopy of monoacetone glucose, are significantly altered by physiologically-relevant changes in nutritional state. We anticipate that these measurements will also be sensitive to other interventions or disease models that alter hepatic glycogen metabolism in the rat.