title: Substrate utilization and dose response to insulin by subcutaneous adipose tissue of Angus steers fed corn- or hay-based diets.
abstract: We hypothesized that, at a common age endpoint, adipose tissue from corn-fed steers would be less sensitive to insulin than adipose tissue from hay-fed steers. Angus steers were assigned to either a corn-based diet (n = 6) or hay-based diet (n = 6) and fed to common days on feed. Steers fed the corn-based diet had 2.44 cm of fat thickness over the 12th thoracic rib, whereas hay-fed steers had 1.04 cm of fat thickness. At slaughter, subcutaneous adipose samples were collected and portions of subcutaneous adipose tissue were incubated with [U-(14)C]acetate to quantify fatty acid synthesis or with [U-(14)C]glucose to assess glucose utilization in the presence of 0, 100, or 500 ng/mL of insulin. Additional subcutaneous samples were used to evaluate glycolytic intermediate concentrations as indicators of glycolytic flux. Data were analyzed as a split-plot with diet in the main plot and insulin concentration and its interaction with diet in the sub-plot. Within diet, linear and quadratic contrasts of insulin concentration were tested. Diet had no effect (P > or = 0.31) on glucose metabolism or acetate carbon incorporation into total lipids (P = 0.32). Insulin had no effect (P > 0.21) on glucose conversion to CO(2), lactate, or total lipids, nor did it affect (P = 0.28) acetate conversion to total lipids. No diet x insulin interaction (P > 0.36) was observed for any measure of subcutaneous metabolism in vitro. Steers fed the corn-based diet exhibited neither a linear (P > 0.22) nor a quadratic (P > 0.24) effect to increasing insulin concentration. However, when steers were fed the hay-based diet, there was a positive linear (P = 0.06) effect for glucose oxidation. These results suggest that subcutaneous adipose tissue may become resistant to stimulation by insulin in steers fed to a fat thickness above the average feedlot steer, but this is independent of diet.
authors.affiliation: Department of Animal Science, Texas A&M University, College Station, TX 77843, USA.
authors.forename: R D
authors.initials: RD
authors.lastname: Rhoades
authors.forename: J E
authors.initials: JE
authors.lastname: Sawyer
authors.forename: C H
authors.initials: CH
authors.lastname: Ponce
authors.forename: D K
authors.initials: DK
authors.lastname: Lunt
authors.forename: S B
authors.initials: SB
authors.lastname: Smith
mesh_terms: D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism; D000273:Adipose Tissue / Q000187:drug effects* / Q000378:metabolism*; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001786:Blood Glucose; D001823:Body Composition / Q000502:physiology; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D019344:Lactic Acid / Q000378:metabolism; D050356:Lipid Metabolism / Q000187:drug effects; D008297:Male; D006109:Poaceae; D003313:Zea mays
chemical_list: D001786:Blood Glucose; D007328:Insulin; D019344:Lactic Acid; D005947:Glucose