title: Hepatic glycogen synthesis from duodenal glucose and alanine. An in situ 13C NMR study.
abstract: An in situ and in vivo surface coil 13C NMR study was performed to study hepatic glycogen synthesis from [3-13C]alanine and [1-13C]glucose administered by intraduodenal infusion in 18-h fasted male Sprague-Dawley rats. Combined, equimolar amounts of alanine and glucose were given. Hepatic appearance and disappearance of substrate and concurrent glycogen synthesis was followed over 150 min, with 5-min time resolution. Active glycogen synthesis from glucose via the direct (glucose----glycogen) and indirect (glucose----lactate----glycogen) pathways and from alanine via gluconeogenesis was observed. The indirect pathway of glycogen synthesis from [1-13C]glucose accounted for 30% (+/- 6 S.E.) of total glycogen formed from labeled glucose. This estimate does not take into account dilution of label in the hepatic oxaloacetate pool and is, therefore, somewhat uncertain. Hepatic levels of [3-13C]alanine achieved were significantly lower than levels of [1-13C]glucose in the liver, and the period of active glycogen synthesis from [3-13C]alanine was longer than from glucose. However, the overall pseudo-first-order rate constant during the period of active glycogen synthesis from [3-13C]alanine (0.075 min-1 +/- 0.026 S.E.) was almost 3 times that from [1-13C]glucose via the direct pathway (0.025 min-1 +/- 0.005 S.E.). The most likely reason for the small rate constant governing direct glycogen formation from duodenally administered glucose compared to that from duodenally administered alanine is a low level of glucose phosphorylating capacity in the liver.
authors.affiliation: Department of Pediatrics, Washington University, St. Louis, Missouri 63110.
authors.forename: R A
authors.initials: RA
authors.lastname: Shalwitz
authors.forename: N V
authors.initials: NV
authors.lastname: Reo
authors.forename: N N
authors.initials: NN
authors.lastname: Becker
authors.forename: A C
authors.initials: AC
authors.lastname: Hill
authors.forename: C S
authors.initials: CS
authors.lastname: Ewy
authors.forename: J J
authors.initials: JJ
authors.lastname: Ackerman
mesh_terms: D000409:Alanine / Q000378:metabolism*; D000818:Animals; D004386:Duodenum / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D007408:Intestinal Absorption; D008099:Liver / Q000378:metabolism*; D008112:Liver Glycogen / Q000096:biosynthesis*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
chemical_list: D008112:Liver Glycogen; D005947:Glucose; D000409:Alanine