Effect of clenbuterol on normal and denervated muscle growth and contractility.

The reported anabolic action of some beta 2 agonists may have clinical applications in certain muscle wasting states. Administration of clenbuterol (2 mg/kg diet for 14 days) to rats resulted in a limited degree of hypertrophy of normal muscles; the effect was more pronounced on fast-twitch muscles than on slow-twitch muscles. The anabolic effect was greatest in denervated muscles, where it was significantly more effective on the slow-twitch type. Clenbuterol significantly improved the contractile properties of denervated slow-twitch muscle, reverting them toward normal, but had little effect on contractile properties of denervated fast-twitch muscle. Such differential effects of clenbuterol must be taken into consideration in the evaluation of any future human intervention study.