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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2008-1365v1 87/7/2338    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Rhoades, R. D. Articles by Smith, S. B. PubMed PubMed Citation Articles by Rhoades, R. D. Articles by Smith, S. B.

Substrate utilization and dose response to insulin by subcutaneous adipose tissue of Angus steers fed corn- or hay-based diets

R. D. Rhoades^*, J. E. Sawyer^*,,1, C. H. Ponce^*, D. K. Lunt^*, and S. B. Smith^*

^* Department of Animal Science, Texas A&M University, College Station 77843; and Texas AgriLife Research-McGregor Center, McGregor, TX 76657

¹ Corresponding author: j-sawyer{at}tamu.edu

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-¹⁴C]acetate to quantify fatty acid synthesis or with [U-¹⁴C]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 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 CO₂, 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.

Key Words: acetate • adipose tissue • cattle • glucose • insulin