title: Metabolic impairment precedes insulin resistance in skeletal muscle during high-fat feeding in rats.
abstract: To examine whether impairment of intracellular glucose metabolism precedes insulin resistance, we determined the time courses of changes in insulin-stimulated glucose uptake, glycolysis, and glycogen synthesis during high-fat feeding in rats. Animals were fed with a high-fat (66.5%) diet ad libitum for 0, 2, 4, 7, or 14 days (n = 10-11 in each group) after 5 days of a low-fat (12.5%) diet. Submaximal and maximal insulin-stimulated glucose fluxes were estimated in whole body and individual skeletal muscles using the glucose clamp technique combined with D-[3-3H]glucose infusion and 2-[1-14C]deoxyglucose injection. Both submaximal and maximal insulin-stimulated glucose uptake in whole body decreased gradually with high-fat feeding. However, the decreases were minimal and not statistically significant during the initial few days (i.e., 2 and 4 days) of high-fat feeding (P > 0.05). In contrast, insulin-stimulated whole-body glycolysis (both maximal and submaximal) significantly decreased by approximately 30% with 2 days of high-fat feeding and remained suppressed thereafter (P < 0.05). Similar patterns of changes in insulin-stimulated glucose uptake and glycolysis were also observed in skeletal muscle. Insulin-stimulated glycogen synthesis and glucose-6-phosphate (G-6-P) concentrations in skeletal muscle increased significantly during the initial few days of high-fat feeding and gradually returned to control levels by day 14, suggesting that increased G-6-P concentrations were responsible for increased glycogen synthesis. Thus, suppression of insulin-stimulated glycolysis and a compensatory increase in glycogen synthesis (presumably arising from the glucose-fatty acid cycle) preceded decreases in insulin-stimulated glucose uptake in skeletal muscle during high-fat feeding. These findings suggest that the insulin resistance may develop as a secondary response to impaired intracellular glucose metabolism.
authors.affiliation: Department of Physiology and Biophysics, University of Southern California, School of Medicine, Los Angeles 90033, USA.
authors.forename: J K
authors.initials: JK
authors.lastname: Kim
authors.forename: J K
authors.initials: JK
authors.lastname: Wi
authors.forename: J H
authors.initials: JH
authors.lastname: Youn
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003847:Deoxyglucose / Q000378:metabolism; D018752:Diet, Fat-Restricted; D004041:Dietary Fats; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005947:Glucose / Q000378:metabolism*; D015309:Glucose Clamp Technique; D006003:Glycogen / Q000096:biosynthesis; D006019:Glycolysis / Q000187:drug effects; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology; D007333:Insulin Resistance; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014316:Tritium
chemical_list: D001786:Blood Glucose; D004041:Dietary Fats; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D014316:Tritium; D006003:Glycogen; D003847:Deoxyglucose; D005947:Glucose