Endogenous Gluconeogenic Sources Account for the Majority of Hepatic Glycogen Synthesis After an Oral Glucose Load in 24-Hour Fasted Rats

Ana Francisca Soares^1,2, John Griffith Jones¹, Francisco Veiga², Rui Albuquerque Carvalho¹

Hepatic glycogen fluxes were characterized in 24-hour fasted rats following an oral tracer-enriched load. Combination of ¹³C isotopomer analysis with ²H-enrichment from ²H₂O, resolved load contribution from that of endogenous gluconeogenesis to hepatic glycogen. The latter accounted for 66 13 % of the glycogen synthesized during the experiment whereas less than one third originated in the oral load following direct and indirect pathways at similar extents: 18 3 % and 16 2 %, respectively. Thus hepatic glycogen synthesis contributes to normoglygemia mostly by diverting gluconeogenic carbons from hepatic glucose production rather than through net uptake of glucose.