Low dose formoterol administration improves muscle function in dystrophic mdx mice without increasing fatigue.
The beta(2)-adrenoceptor agonist (beta(2)-agonist), formoterol, has been shown to cause muscle hypertrophy in rats even when administered at the micromolar dose of 25 micro g/kg/day. We investigated whether a similar low dose of formoterol could improve muscle function in the dystrophic mdx mouse. Ten-week-old male mdx and wild-type (C57BL/10) mice were administered formoterol (25 micro g/kg/day, i.p.) for 4 weeks. Formoterol treatment increased extensor digitorum longus (EDL) and soleus muscle mass, increased median muscle fibre size in diaphragm, EDL, and soleus muscles, and increased maximum force producing capacity in skeletal muscles of both wild-type and mdx mice. In contrast to other studies where beta(2)-agonists have been administered to mice and rats, generally at higher doses, low dose formoterol treatment did not increase the fatiguability of EDL, soleus or diaphragm muscles. Although others have found formoterol can decrease ubiquitin mRNA and proteasome activity when administered to tumour bearing rats at high doses (2mg/kg/day), in the present study low dose formoterol treatment did not alter ubiquitin or the E1 and E3 ubiquitin ligases in diaphragm muscles of wild-type or mdx mice, but it did reduce the level of ubiquitinated proteins in diaphragm of wild-type mice. The findings indicate that formoterol has considerably more powerful anabolic effects on skeletal muscle than older generation beta(2)-agonists (like clenbuterol and albuterol), and has considerable therapeutic potential for muscular dystrophies and other neuromuscular disorders where muscle wasting is indicated.