Influence of anabolic agents on protein synthesis and degradation in muscle cells grown in culture.

Muscle cell culture (L6) studies were conducted to determine whether anabolic agents have a direct effect on the muscle cell. The effects of zeranol, testosterone propionate, estradiol benzoate, progesterone, dexamethasone and anabolic agent-dexamethasone combinations on protein synthesis and degradation were measured. Myoblast and myotube cultures were pretreated with 1 microM compounds for 12, 24 and 48 h before a 6-h synthesis or degradation measuring period. Protein synthesis was determined as cpm of [3H] leucine incorporated per mg cell protein. Protein degradation was measured by a pulse-chase procedure using [3H] leucine and expressed as the percentage labeled protein degraded in 6 h. Progesterone slightly increased (P less than .05) protein synthesis in myoblast cultures. Testosterone propionate had no effect on synthesis. Protein synthesis was decreased by estradiol benzoate (P less than .01) in myotube cultures. Protein degradation was not altered appreciably by anabolic agents. Protein synthesis was initially inhibited in myotubes (P less than .05) by dexamethasone, but increased (P less than .01) in myoblasts and myotubes in the extended incubation time. Dexamethasone also consistently increased protein degradation, but this required several hours to be expressed. Anabolic agents did not interfere with dexamethasone-induced increases in protein synthesis and degradation. The magnitude of response and sensitivity were similar for both the myoblast and the more fully differentiated myotube for all compounds tested. These results indicate that anabolic agents at the 1 microM level do not have a direct anabolic effect on muscle or alter glucocorticoid-induced catabolic response in muscle.