Development of whole-body and skeletal muscle insulin resistance after one day of hindlimb suspension.
Hindlimb suspension (HS) of rats is a model of simulated weightlessness and induces dynamic alterations in insulin action. In the present study, the effect of acute (1-day) HS on whole-body glucose tolerance and insulin action on skeletal muscle glucose transport was assessed in juvenile, female Sprague-Dawley rats. Compared to weight-bearing control rats, 1-day HS animals displayed significantly decreased glucose tolerance and diminished whole-body insulin sensitivity. Glucose transport activity in the 1-day unweighted soleus muscle was significantly decreased (P <.05) compared to weight-bearing control muscles both in the absence and presence of insulin (2 mU/mL). Insulin-mediated glucose transport activity in the extensor digitorum longus (EDL) muscles also tended (P =.09) to be lower. There was no change in the protein expression of insulin receptor beta-subunit (IR-beta), insulin receptor substrate-1 (IRS-1), IRS-2, the p85 subunit of phosphatidylinositol-3 kinase (PI3-kinase), Akt, and glucose transporter protein 4 (GLUT-4). The activities of these proteins were also unchanged, as insulin-stimulated IR-beta tyrosine phosphorylation, IRS-1 tyrosine phosphorylation, IRS-1-associated p85, and Akt serine phosphorylation were similar to controls. However, basal Akt phosphorylation was significantly depressed (P <.05) in the 1-day HS soleus. In addition, the protein expression and basal phosphorylation of the stress-activated p38 mitogen-activated protein kinase (p38 MAPK) were significantly elevated (P <.05) in the 1-day unweighted soleus. These results indicate that the development of insulin resistance in the 1-day unweighted soleus is not due to impaired functionality of elements involved in the IR/IRS-1/PI3-kinase/Akt signaling pathway. However, activation of p38 MAPK may play a role in this response.
O'keefe
Matthew P
MP
Department of Physiology, University of Arizona College of Medicine, Tucson, AZ 85721, USA.
Perez
Felipe R
FR
Kinnick
Tyson R
TR
Tischler
Marc E
ME
Henriksen
Erik J
EJ
D000818:Animals; D005260:Female; D005947:Glucose / Q000378:metabolism; D005951:Glucose Tolerance Test; D051275:Glucose Transporter Type 4; D019417:Hindlimb Suspension / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins / Q000096:biosynthesis / Q000378:metabolism; D018482:Muscle, Skeletal / Q000502:physiology*; D051058:Oncogene Protein v-akt; D009929:Organ Size / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism; D015398:Signal Transduction; D014280:Triglycerides / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
D051275:Glucose Transporter Type 4; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D010750:Phosphoproteins; D015682:Retroviridae Proteins, Oncogenic; C495694:Slc2a4 protein, rat; D014280:Triglycerides; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D051058:Oncogene Protein v-akt; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D005947:Glucose