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2-agonist treatment
Departments of 1 Exercise and Sport Sciences, 2 Pharmacology, and 3 Physiology, University of Florida, Gainesville, Florida 32611
Aging is associated with a decrease
in diaphragmatic maximal tetanic force production (Po) in
senescent rats. Treatment with the 
2-agonist
clenbuterol (CB) has been shown to increase skeletal muscle mass and
Po in weak locomotor skeletal muscles from dystrophic rodents. It is unknown whether CB can increase diaphragmatic mass and
Po in senescent rats. Therefore, we tested the hypothesis that CB treatment will increase specific Po (i.e., force
per cross-sectional area) and mass in the diaphragm of old rats. Young
(5 mo) and old (23 mo) male Fischer 344 rats were randomly assigned to
one of the following groups (n = 10/group):
1) young CB treated; 2) young control;
3) old CB treated; and 4) old control. Animals were injected daily with either CB (2 mg/kg) or saline for 28 days. CB
increased (P < 0.05) the mass of the costal diaphragm in both young and old animals. CB treatment increased
diaphragmatic-specific Po in old animals (~15%;
P < 0.05) but did not alter (P > 0.05) diaphragmatic-specific Po in young animals.
Biochemical analysis indicated that the improved maximal specific
Po in the diaphragm of CB-treated old animals was not due
to increased myofibrillar protein concentration. Analysis of the myosin
heavy chain (MHC) content of the costal diaphragm revealed a CB-induced
increase (P < 0.05) in type IIb MHC and a decrease in
type I, IIa, and IIx MHC in both young and old animals. These data
support the hypothesis that CB treatment can restore the age-associated
decline in both diaphragmatic-specific Po and muscle mass.
sarcopenia; clenbuterol; myosin heavy chain
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