title: Disposition of [U-2H7]glucose into hepatic glycogen in rat and in seabass.
abstract: The stimulation of hepatic glycogenesis is a ubiquitous response to a glucose challenge and quantifying its contribution to glucose uptake informs its role in restoring euglycemia. Glycogenesis can be quantified with labeled water provided that exchange of glucose-6-phosphate hydrogen 2 (G6P-H2) and body water via glucose-6-phosphate isomerase, and exchange of positions 4, 5 and 6 hydrogens (G6P-H456) via transaldolase, are known. These exchanges were quantified in 24-h fasted rats (Rattus norvegicus; n=6) and 21-day fasted seabass (Dicentrarchus labrax; n=8) by administration of a glucose load (2000mg·kg(-1)) enriched with [U-(2)H7]glucose and by quantifying hepatic glycogen (2)H-enrichments after 2h (rats) and 48h (seabass). Direct pathway contributions of the glucose load to glycogenesis were also estimated. G6P-H2 and body water exchange was 61±1% for rat and 47±3% for seabass. Transaldolase-mediated exchange of G6P-H456 was 5±1% for rat and 10±1% for seabass. Conversion of the glucose load to hepatic glycogen was significant in seabass (249±54mg·kg(-1)) but negligible in rats (12±1mg·kg(-1)). Preload plasma glucose levels were similar for seabass and rats (3.3±0.7 and 4.4±0.1mmol·L(-1), respectively) but post-load plasma glucose was significantly higher in seabass compared to rats (14.6±1.8 versus 5.8±0.3mmol·L(-1), p<0.01). In conclusion, G6P-H2 and body water exchange is incomplete for both species and has to be accounted for in estimating hepatic glycogen synthesis and direct pathway activities with labeled water tracers. Transaldolase-mediated exchange is insignificant. Hepatic direct pathway glycogenesis plays a prominent role in seabass glucose load disposal, but a negligible role in the rat.
authors.affiliation: CNC-Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal.
authors.forename: Fátima O
authors.initials: FO
authors.lastname: Martins
authors.forename: João
authors.initials: J
authors.lastname: Rito
authors.forename: Ivana
authors.initials: I
authors.lastname: Jarak
authors.forename: Ivan
authors.initials: I
authors.lastname: Viegas
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Pardal
authors.forename: M Paula
authors.initials: MP
authors.lastname: Macedo
authors.forename: John G
authors.initials: JG
authors.lastname: Jones
mesh_terms: D000818:Animals; D001492:Bass / Q000378:metabolism*; D001786:Blood Glucose; D005508:Food Deprivation; D005943:Gluconeogenesis; D005947:Glucose / Q000378:metabolism*; D006003:Glycogen / Q000096:biosynthesis*; D008099:Liver / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013045:Species Specificity
chemical_list: D001786:Blood Glucose; D006003:Glycogen; D005947:Glucose
keywords: Direct pathway; Gluconeogenesis; Glycogenesis; Rat; Seabass; Transaldolase