Clenbuterol attenuates muscle atrophy and dysfunction in hindlimb-suspended rats.
BACKGROUND
Muscle wasting and dysfunction is a significant problem in prolonged exposure to microgravity.


OBJECTIVE
This study tested the hypothesis that a beta-adrenergic agonist (clenbuterol) could attenuate the effects of 14 d of unweighting on mixed fiber type skeletal muscle.


METHODS
Female, Sprague-Dawley rats were maintained in cages as: 1. controls (C; n = 12); 2. hindlimb suspended via tail casting (HLU; n = 12); 3. clenbuterol injected daily (3 mg x kg(-1)) (CL; n = 10); or 4. hindlimb suspended and injected with clenbuterol daily (3 mg x kg(-1)) (HLU + CL; n = 12).


RESULTS
At the end of the study, both CL and HLU + CL had higher body weights compared with HLU (p < 0.05). Gastrocnemius mass (wet weight and muscle weight/body weight) and maximal tetanic force were significantly decreased during HLU (p < 0.05) (mean +/- SE; mass: C = 1.6 +/- 0.04 g, HLU = 1.2 +/- 0.05 g force: C = 3483 +/- 113 g, HLU = 2765 +/- 52 g). Clenbuterol attenuated the decrease in both mass and force generation (mass: HLU + CL = 1.4 +/- 0.04 g; force: HLU + CL = 3162 +/- 135). Twitch tension during HLU (1057 +/- 72 g) was significantly less (p < 0.05) than during C (1362 +/- 61 g), and clenbuterol did not attenuate this loss. HLU caused a decrease (p < 0.05) in force at 30 Hz and decreased one-half relaxation time (1/2 RT) (p < 0.05) from 30 +/- 2 to 25 +/- 2 ms. Clenbuterol caused further decreases (p < 0.05) in both force (20 and 30 Hz) and 1/2 RT.


CONCLUSIONS
These data suggest that a beta-adrenergic agonist may be of benefit in attenuating wasting and the reduced maximal force seen during periods of unweighting in mixed fiber type muscle.
College of Health and Human Performance, Center for Exercise Science, University of Florida, Gainesville 32611, USA. sdodd@hhp.ufl.edu
Stephen L
SL
Dodd
Thomas J
TJ
Koesterer
D000318:Adrenergic beta-Agonists / Q000494:pharmacology / Q000627:therapeutic use*; D000818:Animals; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000502:physiology; D002976:Clenbuterol / Q000494:pharmacology / Q000627:therapeutic use*; D004195:Disease Models, Animal; D004353:Drug Evaluation, Preclinical; D005260:Female; D019417:Hindlimb Suspension / Q000009:adverse effects*; D007273:Injections, Intramuscular; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology; D009133:Muscular Atrophy / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D009929:Organ Size / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
D000318:Adrenergic beta-Agonists; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002976:Clenbuterol