Muscle-specific effects of hindlimb suspension and clenbuterol in mature male rats.
Anabolic agents are useful tools for probing the mechanisms by which muscle fibers perceive and respond to disuse. beta(2)-Adrenergic agonists exert protective, and/or reparative, effects on atrophying muscle tissue. The effects of one such agent, clenbuterol (Cb), were examined on muscle mass, total protein content, and myofibrillar protein content in selected hindlimb muscles [adductor longus (ADL), extensor digitorum longus (EDL), plantaris (PLAN), soleus (SOL)] of mature male rats, under different loading conditions. Pair-fed rats were divided into four experimental groups: vehicle- and Cb-treated nonsuspended, vehicle- and Cb-treated hindlimb suspended (HLS). Experiments lasted 14 days, during which the rats received subcutaneous injections of 1 mg/kg Cb or 1 ml/kg vehicle. HLS induced significant atrophy in all muscles, except the EDL, in a generally fiber type-related pattern. However, myofibrillar protein content was affected in a more regional pattern. Cb treatment of nonsuspended rats induced hypertrophy in all muscles, in a generally uniform pattern. However, myofibrillar protein content was affected in a more fiber type-related pattern. Cb treatment of HLS rats reduced or eliminated HLS-induced atrophy in all muscles, in a muscle-specific pattern. Overall, the ADL and SOL were most susceptible to HLS-induced atrophy. The PLAN had the greatest magnitude of Cb-induced sparing of atrophy. The results show that, in mature male rats, Cb exerts anabolic effects that are load-dependent and muscle-specific. Responses to this drug cannot be reliably predicted by fiber-type composition alone.
Wineski
Lawrence E
LE
Space Medicine and Life Sciences Research Center, Morehouse School of Medicine, Atlanta, Ga 30310-1495, USA. wineski@msm.edu
von Deutsch
Daniel A
DA
Abukhalaf
Imad K
IK
Pitts
Sidney A
SA
Potter
David E
DE
Paulsen
Douglas F
DF
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002976:Clenbuterol / Q000494:pharmacology*; D019417:Hindlimb Suspension; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D009133:Muscular Atrophy / Q000503:physiopathology; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000378:metabolism
D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D002976:Clenbuterol