Effect of clenbuterol on normal and denervated muscle growth and contractility

Abstract

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.

Muscle-Specific Effects of Hindlimb Suspension and Clenbuterol in Mature Male Rats

“…Whether this is the case for ß 2 -AR function remains to be determined. Interestingly, Cb treatment has been shown to prevent atrophy in denervated muscles which, in some cases, respond even more vigorously than do the normal controls [Maltin et al, 1986b;Zeman et al, 1987;Agbenyega and Wareham, 1990]. In these studies, the SOL showed an unusually strong response to Cb treatment, an effect that has been attributed to an increase in protein synthesis [Maltin et al, 1987].…”

“…In young rats, Cb enhances growth and reduces atrophy in unloaded and denervated hindlimb muscles [Maltin et al, 1986a[Maltin et al, , b, 1987Zeman et al, 1987;Agbenyega and Wareham, 1990;Apseloff et al, 1993]. In addition, there is evidence for a drug-induced shift from slow-twitch (type I) toward fast-twitch (type II) fiber types in the slow-fiber-rich soleus muscle [Zeman et al, 1988;Criswell et al, 1996;Dodd et al, 1996].…”

Salbutamol changes the molecular and mechanical properties of canine skeletal muscle.

“…Zeman et al (1988) reported that clenbuterol produced an 11 % increase in time-to-peak tension, and an 18% decrease in half-relaxation time in the rat extensor digitorum longus. The different results may be because mechanical effects were measured in vitro by Zeman et al (1988) and in vivo by Agbenyega & Wareham (1990). In mouse gastrocnemius muscle, Zeman, Zhang & Eltlinger (1994) found that time-to-peak tension remained unchanged and half-relaxation time decreased in response to clenbuterol.…”

“…Zeman et al (1988) found that 12 weeks of exposure of the soleus muscle to clenbuterol decreased time-to-peak tension and half-relaxation times by 34-47 %. In a study of shorter duration (14 days), Agbenyega & Wareham (1990) reported no significant changes in time-to-peak tension and halfrelaxation times in the soleus. Zeman et al (1988) reported that clenbuterol produced an 11 % increase in time-to-peak tension, and an 18% decrease in half-relaxation time in the rat extensor digitorum longus.…”

“…The finding by Zeman et al (1988) that administration of clenbuterol to growing rats decreased time-to-peak tension and half-relaxation times of soleus muscles showed that this drug can produce a soleus muscle with characteristics that resemble a fast-twitch muscle. Agbenyega & Wareham (1990) reported that administration of clenbuterol to growing rats for a shorter period did not affect time-to-peak tension and halfrelaxation times in soleus muscles. Both studies were in growing rats in which twitch times were increasing in the control animals.…”