title: Exercise training improves muscle insulin resistance but not insulin receptor signaling in obese Zucker rats.
abstract: Exercise training improves skeletal muscle insulin sensitivity in the obese Zucker rat. The purpose of this study was to investigate whether the improvement in insulin action in response to exercise training is associated with enhanced insulin receptor signaling. Obese Zucker rats were trained for 7 wk and studied by using the hindlimb-perfusion technique 24 h, 96 h, or 7 days after their last exercise training bout. Insulin-stimulated glucose uptake (traced with 2-deoxyglucose) was significantly reduced in untrained obese Zucker rats compared with lean controls (2.2 +/- 0.17 vs. 5.4 +/- 0.46 micromol x g(-1) x h(-1)). Glucose uptake was normalized 24 h after the last exercise bout (4.9 +/- 0.41 micromol x g(-1) x h(-1)) and remained significantly elevated above the untrained obese Zucker rats for 7 days. However, exercise training did not increase insulin receptor or insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation, phosphatidylinositol 3-kinase (PI3-kinase) activity associated with IRS-1 or tyrosine phosphorylated immunoprecipitates, or Akt serine phosphorylation. These results are consistent with the hypothesis that, in obese Zucker rats, adaptations occur during training that lead to improved insulin-stimulated muscle glucose uptake without affecting insulin receptor signaling through the PI3-kinase pathway.
authors.affiliation: Department of Physiology, University of Texas Health Sciences Center, San Antonio, Texas 78712, USA.
authors.forename: Christine Y
authors.initials: CY
authors.lastname: Christ
authors.forename: Desmond
authors.initials: D
authors.lastname: Hunt
authors.forename: Joe
authors.initials: J
authors.lastname: Hancock
authors.forename: Rebeca
authors.initials: R
authors.lastname: Garcia-Macedo
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Mandarino
authors.forename: John L
authors.initials: JL
authors.lastname: Ivy
mesh_terms: D000818:Animals; D003847:Deoxyglucose / Q000493:pharmacokinetics; D051275:Glucose Transporter Type 4; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009765:Obesity / Q000503:physiopathology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010805:Physical Conditioning, Animal; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D011924:Rats, Zucker / Q000502:physiology*; D011972:Receptor, Insulin / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D003847:Deoxyglucose; D051275:Glucose Transporter Type 4; D055504:Insulin Receptor Substrate Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; C526296:Irs1 protein, rat; C495694:Slc2a4 protein, rat; C494920:Akt1 protein, rat