Influence of dietary protein level on growth: effect of clenbuterol.

1. The influence has been studied of a beta-agonist, clenbuterol, on body weight increase, feed efficiency and muscular tissue growth in Wistar rats of two different weights (70 and 200 g) fed with a diet of differing protein levels (4, 10 and 15%). 2. Treatment with clenbuterol had a negative influence on body growth and feed efficiency when the animals were fed with low protein diets (4%). 3. With a higher protein content (10 and 15%), the situation changed completely, and these indices increased, with a relationship appearing between these changes, the agonist dose and the animal's age. 4. In all the experiments clenbuterol improved muscle/body ratio significantly (P less than 0.001). The favourable effect of clenbuterol on muscle growth is due to a specific increase in protein deposition and not to changes in the water content of muscular tissue, even though these changes may be produced.