Effects of clenbuterol, ICI118551 and sotalol on the growth of cardiac and skeletal muscle and on beta 2-adrenoceptor density in female rats.

The aim of the present study was to determine whether the anabolic effects of clenbuterol in rat skeletal muscle are mediated by beta 2-adrenoceptor stimulation. Female rats were treated with clenbuterol, alone or in combination with either the nonselective beta 1/beta 2-adrenoceptor antagonist sotalol, or the beta 2-adrenoceptor-selective antagonist ICI118551. Clenbuterol caused an increase in muscle growth, accompanied by a reduction in beta 2-adrenoceptor density in the rat hind-limb. Both actions were attenuated by sotalol. However, at the dose tested ICI118551 was the more effective antagonist of the muscle growth response, and when given alone, ICI118551 caused significant muscle atrophy. An increase in the weight of the heart was also observed in clenbuterol-treated rats, and again while this effect was attenuated by sotalol, it was reversed by ICI118551. It is concluded that beta 2-adrenoceptors mediate the anabolic effects of clenbuterol in cardiac and skeletal muscle, and that they play an important physiological role in the growth and maintenance of muscle mass in the rat hind-limb.