title: Effects of galactose on direct and indirect pathway estimates of hepatic glycogen synthesis.
abstract: Hepatic glycogen is formed by direct and indirect pathways whose activities reflect altered nutrition or disease. Direct/indirect pathway measurements often involve test meals where ∼ 10% of carbohydrate is galactose, but its effects on direct/indirect pathway estimates are unknown. Therefore, direct/indirect pathway contributions in 24-h fasted rats given 2g/kg 100% glucose (GLU, n=6) or 90% glucose-10% galactose (GLU+GAL, n=6) were measured by [U-(13)C]glucose dilution and by position-5/position-2 glycogen enrichment (H5/H2) from 2H(2)O. For GLU+GAL, galactose glycogenesis was independently measured with [1-(13)C]galactose. Glycogenesis was equivalent in both groups but for GLU+GAL, 23 ± 4% of glycogen was derived from galactose. [U-(13)C]glucose reported a 30 ± 3% direct pathway contribution to glycogenesis for GLU but only 20 ± 3% for GLU+GAL (p=0.012 vs. GLU). H5/H2 yielded identical direct pathway estimates (32 ± 3% GLU, 29 ± 6% GLU+GAL). Thus, galactose glycogenesis was undetected by H5/H2 while [U-(13)C]glucose reported a reduced direct/indirect pathway ratio. With [1-(13)C]galactose also present, correct glycogenic source contributions were obtained.
authors.affiliation: Department of Life Sciences and Center for Neurosciences and Cell Biology, University of Coimbra, Rua dos Estudos, Apartado 3126, 3001-401 Coimbra, Portugal.
authors.forename: Ana F
authors.initials: AF
authors.lastname: Soares
authors.forename: Rui A
authors.initials: RA
authors.lastname: Carvalho
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Veiga
authors.forename: John G
authors.initials: JG
authors.lastname: Jones
mesh_terms: D000818:Animals; D002241:Carbohydrates; D002250:Carbon Radioisotopes; D003903:Deuterium; D004032:Diet; D005690:Galactose / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008112:Liver Glycogen / Q000096:biosynthesis*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002241:Carbohydrates; D002250:Carbon Radioisotopes; D006601:Hexoses; D008112:Liver Glycogen; D003903:Deuterium; D005947:Glucose; D005690:Galactose