Studies on the mechanism by which exogenous glucose is converted into liver glycogen in the rat. A direct or an indirect pathway

摘要: To quantify the extent to which exogenous glucose is used directly or indirectly for hepatic glycogen synthesis, fasted rats were given [U-14C,3-3H] intragastrically, intravenously, as a component of solid diet eaten ad libitum. In all cases liver was deposited at high linear rates over 3-h period. Portal vein levels seldom exceeded 8 mM. At time when specific activities 3H and 14C in circulating identical with those administered material their values newly synthesized reduced by 72-88% 50-65%, respectively. An intragastric load unlabeled sufficient suppress completely output greatly stimulated incorporation intravenously infused [14C]bicarbonate, [14C]lactate, [14C]alanine, [14C] glutamine into glycogen. Using an improved assay ability homogenates phosphorylate concentrations 5-10 mM found be far short what would needed if support synthesis vivo. These data notion that rat major fraction response carbohydrate formed pathway involving leads C3 unit glycogen, although site initial steps sequence not yet known. The limited capacity utilize intact might reside its sugar physiological concentrations.