Cimaterol-induced growth in rats: growth pattern and biochemical characteristics.

Sixty Sprague-Dawley female rats weighing 170 g were used to investigate the effect of cimaterol on the growth pattern and biochemical characteristics of skeletal muscles. Cimaterol (CIM) was mixed in a powdered rat chow at 10 ppm. A significant (P less than .01) improvement in the weight gain of CIM group was observed during the first 8 days of the 49-day trial period, followed by no significant improvement thereafter. When CIM was withdrawn from the diet, treated rats lost weight, eventually regressing to the same weight as control rats after 28 days. CIM-fed rats showed 28.6% (P less than .01) and 12.9% (P less than .05) increases in plantaris muscle weight over the control at 8 and 14 d, respectively. DNA concentration significantly (P less than .05) decreased, whereas RNA concentration increased at 3 d (31%) and 8 d (12.7%), but decreased at 14 d compared to the control. The increase in RNA concentration preceded the significant improvement of muscle weight in the CIM group. In the soleus muscle, there was no significant difference in muscle weight or DNA concentration between the control and CIM groups. Cimaterol-feeding significantly (P less than .05) increased the size of both type I and II fibers. The size increase of type II fibers in plantaris was twice that of type I fibers in soleus (34.2% vs 17.5%). This may explain why the plantaris muscle (type II predominant) showed a greater weight increase than the soleus muscle (type I predominant).