Abstract
Twenty-three male Fisher-344 rats were used to investigate the effects of low levels of clenbuterol on retention of muscle mass, work capacity, and muscle twitch contractile properties after a 3-week hindlimb suspension. Groups consisted of normal control (XX), n = 6; suspension control (SX), n = 6; suspension placebo (SP), n = 7; and suspension clenbuterol (SC), n = 6. Clenbuterol was administered I.P., 20 μg/kg/d for 6 days, then 10μg/kg/d thereafter. After 3 weeks of hindlimb suspension, body weight (BW) was significantly less in SX (232 ± 7.6 g) and SP (257.3 ± 17.1 g) than XX (314.8 ± 12 g). There was no significant BW change in SC. Soleus muscles (SOL) of SX, SP, and SC atrophied significantly (XX: 136.1± 4.25 mg, SX:72.3 ± 2.3 mg, SP:82.7 ± 8.9 mg, and SC:85.4 ± 9.6 mg). Normalized SOL (mg SOL/g BW) significantly decreased in SX, SP, and SC (XX:44 ± 0.8%, SX:31 ± 0.8%, SP:32 ± 2% and SC:33 ± 2%). Treadmill running time to exhaustion did not change after suspension in any group. Time to peak twitch tension of SOL was less in SP and SC (XX: 61 ± 11 ms, SP:35 ± 3 ms, and SC:35 ± 5 ms). Twitch one-half relaxation time of SOL was shorter in SP and SC (XX: 109± 7 ms, SP:77 ± 3 ms, and SC:67 ± 10 ms). These results suggest that clenbuterol retards body weight loss but does not improve aerobic work capacity in response to suspension. Suspended muscles have faster twitch properties but contractile properties were not altered by clenbuterol.
Published Version
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