Effects of dietary corticosterone and trilostane on growth and skeletal muscle protein turnover in broiler cockerels.

1. The effects of dietary corticosterone and trilostane, an inhibitor of glucocorticoid synthesis, on: growth, rates of synthesis and breakdown of skeletal muscle protein, and content of abdominal fat were studied in broiler chickens. 2. Dietary corticosterone (5, 10 or 20 mg/kg) depressed body weight gain and increased abdominal fat content in a dose-dependent manner while dietary trilostane (1.4 or 7.0 mg/kg) had no effect. 3. The rate of protein breakdown in skeletal muscle estimated from N tau-methylhistidine excretion was increased in a dose-dependent manner by dietary corticosterone but it was decreased by trilostane. 4. The rate of skeletal muscle protein synthesis was not affected by corticosterone although it was decreased by trilostane. 5. Plasma corticosterone concentration was increased in a dose-dependent manner by dietary corticosterone and decreased by treatment with 7 mg trilostane/kg diet. 6. The results indicate that higher concentrations of plasma corticosterone increase protein breakdown in skeletal muscle but do not affect muscle protein synthesis while both the rates of synthesis and breakdown are decreased when plasma corticosterone concentration is reduced.