The effect of trenbolone acetate with time on the various responses of protein synthesis of the rat.

1. The anabolic agent trenbolone acetate (3-oxo-17beta-hydroxy-4,9,11-oestratriene acetate; TBA) given subcutaneously to female rats increased their growth rate compared with that of the placebo-treated controls. 2. The increased growth rate of the TBA-treated rats was not a consequence of an increased water retention. The TBA-treated rats had a significantly higher (P less than 0.01) total carcass nitrogen content but the total carcass fat content decreased by a non-significant (P greater than 0.05) 8.3%. 3. There was evidence of a time-lag in the response of the fractional synthetic rate of certain individual tissues to TBA. The fractional synthetic rates of the uterus and skeletal muscle mixed tissue proteins were significantly reduced in the TBA-treated rats. 4. The measured reduction in fractional synthetic rates was concluded to reflect true changes in the synthetic rate rather than a result of an alteration in the specific activity of the tyrosine pool used for protein synthesis.