The mode of action of anabolic agents: the effect of testosterone on muscle protein metabolism in the female rat.

Testosterone (1 mg/kg body-weight per d) given subcutaneously to female rats increased their growth rate and food conversion efficiency but not their food intake compared with that of the placebo-oil controls. A higher dose of testosterone (10 mg/kg body-weight per d) failed to increase the daily weight gain. The increased growth rate of the testosterone-treated rats appeared to occur in the whole body and not specifically in muscle. There were no significant changes in body composition. The fractional synthetic rate of gastrocnemius muscle protein was higher in the hormone-treated rats than in controls. This contrasts with previous results for the anabolic agent trenbolone acetate and reflects differences in the mode of action of these two different steroids, both with androgenic properties.