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and1 Department of Anatomy, University of South Florida, Tampa, Florida 33612; and 2 Division of Exercise Physiology, School of Medicine, West Virginia University, Morgantown, West Virginia 26506-9227
Supraphysiological
levels of clenbuterol (CL) reduce muscle degradation in both young and
old animals; however, these pharmacological levels induce side effects
that are unacceptable in the elderly. In this study, we tested the
hypothesis that a "physiological" dose of CL (10 µg · kg
1 · day
1) would attenuate the loss
of in situ isometric force and mass in muscles of senescent rats during
hindlimb suspension (HS). Adult (3 mo) and senescent (38 mo) Fischer
344 × Brown Norway rats received CL or a placebo during 21 days
of normal-weight-bearing or HS conditions (8 rats/age group). HS
reduced soleus muscle weight-to-body weight ratio by 31%, muscle
cross-sectional area by 37%, and maximal isometric tetanic force
(Po) by 76% in senescent rats. CL attenuated the
loss of Po and muscle weight by 17 and 8%, respectively,
in the soleus of senescent rats relative to HS+placebo conditions, but
it did not improve muscle weight normalized for body weight. CL did not
reduce the decrease in soleus Po or mass after HS in adult
rats. CL failed to reduce the loss of plantaris weight (
20%) and
Po (
46%) in senescent rats after HS. Our data support
the conclusion that physiological levels of CL do not improve fast
muscle atrophy and only modestly reduce slow muscle atrophy, and,
therefore, it is largely an ineffective countermeasure for preventing
muscle wasting from HS in senescent rats.
aging; disuse;
-agonist; muscle strength; isometric contraction; hypokinesia; myosin heavy chain; sarcopenia
Deceased 2 June 1998.
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