title: Mechanisms limiting glycogen storage in muscle during prolonged insulin stimulation.
abstract: The extent to which muscle glycogen concentrations can be increased during exposure to maximal insulin concentrations and abundant glucose was investigated in the isolated perfused rat hindquarter preparation. Perfusion for 7 h in the presence of 20,000 microU/ml insulin and 11-13 mM glucose increased muscle glycogen concentrations to maximal values 2, 3, and 3.5 times above normal fed levels in fast-twitch white, slow-twitch red, and fast-twitch red fibers, respectively. Glucose uptake decreased (mean +/- SE) from 34.9 +/- 1.2 mumol.g-1.h-1 at 0 h to 7.5 +/- 0.7 after 7 h of perfusion. During the perfusion muscle glycogen synthase activity decreased and free intracellular glucose and glucose 6-phosphate increased indicating that glucose disposal was impaired. However, glucose transport as measured by the uptake of 3-O-[14C]methyl-D-glucose was also markedly decreased after 5 and 7 h of perfusion compared with initial values. Total muscle water concentration decreased during glycogen loading of the muscles. Mechanisms limiting glycogen storage under maximal insulin stimulation include impaired insulin-stimulated membrane transport of glucose as well as impaired intracellular glucose disposal.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D005947:Glucose / Q000378:metabolism; D005958:Glucosephosphates / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D006006:Glycogen Synthase / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013268:Stimulation, Chemical; D013997:Time Factors; D014867:Water / Q000378:metabolism
chemical_list: D005958:Glucosephosphates; D007328:Insulin; D010725:Phosphocreatine; D014867:Water; D000255:Adenosine Triphosphate; D006003:Glycogen; D006006:Glycogen Synthase; D005947:Glucose