title: The evolution of insulin resistance in muscle of the glucose infused rat.
abstract: Glucose infusion into rats causes skeletal muscle insulin resistance that initially occurs without changes in insulin signaling. The aim of the current study was to prolong glucose infusion and evaluate other events associated with the transition to muscle insulin resistance. Hyperglycemia was produced in rats by glucose infusion for 3, 5 and 8 h. The rate of infusion required to maintain hyperglycemia was reduced at 5 and 8 h. Glucose uptake into red quadriceps (RQ) and its incorporation into glycogen decreased between 3 and 5 h, further decreasing at 8 h. The earliest observed change in RQ was decreased AMPKα2 activity associated with large increases in muscle glycogen content at 3 h. Activation of the mTOR pathway occurred at 5 h. Akt phosphorylation (Ser(473)) was decreased at 8 h compared to 3 and 5, although no decrease in phosphorylation of downstream GSK-3β (Ser(9)) and AS160 (Thr(642)) was observed. White quadriceps showed a similar but delayed pattern, with insulin resistance developing by 8 h and decreased AMPKα2 activity at 5 h. These results indicate that, in the presence of a nutrient overload, alterations in muscle insulin signaling occur, but after insulin resistance develops and appropriate changes in energy/nutrient sensing pathways occur.
authors.affiliation: Diabetes and Obesity Program, Garvan Institute of Medical Research, Darlinghurst, NSW 2010, Australia. a.brandon@garvan.org.au
authors.forename: Amanda E
authors.initials: AE
authors.lastname: Brandon
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Hoy
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Wright
authors.forename: Nigel
authors.initials: N
authors.lastname: Turner
authors.forename: Bronwyn D
authors.initials: BD
authors.lastname: Hegarty
authors.forename: Tristan J
authors.initials: TJ
authors.lastname: Iseli
authors.forename: X
authors.initials: X
authors.lastname: Julia Xu
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Cooney
authors.forename: Asish K
authors.initials: AK
authors.lastname: Saha
authors.forename: Neil B
authors.initials: NB
authors.lastname: Ruderman
authors.forename: Edward W
authors.initials: EW
authors.lastname: Kraegen
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000818:Animals; D020690:GTPase-Activating Proteins / Q000378:metabolism; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D007333:Insulin Resistance; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D020690:GTPase-Activating Proteins; C533101:TBC1D4 protein, rat; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D055372:AMP-Activated Protein Kinases; D005947:Glucose