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Effects of aging and voluntary exercise
on the function of dystrophic muscle from mdx mice.
Wineinger MA, Abresch RT, Walsh SA, Carter GT.
Department of Rehabilitation Medicine, University of Washington
School of Medicine, Seattle, USA.
To understand how exercise affects the contractile function
of dystrophic muscle, we examined the effect of long-term
voluntary exercise on mdx mice and related these effects to
our findings in sedentary aging mice. Although the mdx mouse
is the genetic homolog for Duchenne muscular dystrophy, it
does not demonstrate the same progression in limb muscle dysfunction
as Duchenne muscular dystrophy as it ages. We postulated that
the sedentary lifestyle of this animal plays an important
role in its minimal phenotypic expression. To examine the
effect of exercise, eight C57BL/10 (C57) and eight mdx mice
were allowed to run ad libitum for one year. Forty sedentary
mdx mice and 40 sedentary C57 from one month to 18 months
of age were used as controls. Contractile characteristics
of the extensor digitorum longus and soleus muscles and morphometric
characteristics of the mice were examined. The mdx mice ran
approximately 45% fewer kilometers per day than C57 mice.
Long-term voluntary running had beneficial training effects
on both the old mdx mice and their C57 controls. The exercise
ameliorated the age-associated loss in tension production
that was observed in the soleus of sedentary mdx and sedentary
C57 mice. There was a 9% reduction in the fatigability of
the extensor digitorum longus muscle of the old mdx mice after
the exercise. Despite these improvements, the old mdx mice
exhibited significant functional deficits compared with their
C57 controls. Our hypothesis, that long-term voluntary exercise
would have a beneficial training effect on control mice and
a deleterious effect on mdx mice as they aged, was not supported
by this study. This study shows that dystrophin-less muscles
from sedentary mice display significant signs of muscle damage,
yet can respond beneficially to low-level voluntary running
in a manner similar to that of the C57 control.
PMID: 9482375 [PubMed - indexed for MEDLINE]
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