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.
Dodd
Stephen L
SL
College of Health and Human Performance, Center for Exercise Science, University of Florida, Gainesville 32611, USA. sdodd@hhp.ufl.edu
Koesterer
Thomas J
TJ
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