Acute and Long-Term Lipogenic Response to Insulin and Clenbuterol in Bovine Intramuscular and Subcutaneous Adipose Tissues2

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Abstract
The present study was conducted to determine whether insulin and clenbuterol affected either short-term (2-h) incubations or long-term (48-h) tissue cultures of i.m. and s.c. adipose tissue explants. Samples were taken from control steers and steers fed 7 mg·head−1·d−1 clenbuterol for 50 d, after which time the drug was withdrawn from the diet for 90 d prior to slaughter. Neither short-term incubations nor long-term explant cultures contained bovine serum albumin (BSA). Insulin (6.67 × 10−9M) had no effect (P > .05) on lipogenesis in s.c. and i.m. adipose tissue in 2-h tissue incubations of fresh adipose tissue. There was a substantial decrease in activity during the culture period, which was ameliorated somewhat in s.c. adipose tissue by the presence of insulin in the culture media. Clenbuterol exposure for 48 h in vitro decreased the production of lipids from acetate in both adipose tissue depots but had no effect in short-term adipose tissue incubations. Results from the present study confirm that omitting BSA from incubation media does not enhance the responsiveness of bovine s.c. adipose tissue or the less mature i.m. adipose tissue to insulin. Insulin may maintain greater cell viability in 48-h explant cultures.