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2-agonist clenbuterol on
respiratory and limb muscles of weaning rats
2 Institute of Human Physiology and 3 Department of Physiological and Pharmacological Sciences, University of Pavia, 27100 Pavia; 1 Hospital San Biagio, 15100 Alessandria; and 4 Department of Anatomy and Physiology, University of Padova, 35131 Padova, Italy
The aim of this study was to
analyze the effects of chronic administration of the
2-agonist clenbuterol (1.5 mg · kg
1 · day
1 for 4 wk in
the drinking water) on respiratory (diaphragm and parasternal
intercostal) and hindlimb (tibialis and soleus) muscles in young rats
during postnatal development (21 to 49 postnatal days).
The treatment resulted in very little stimulation of muscle growth. Significant slow-to-fast transitions in the expression of myosin heavy chain isoforms and significant increases in the myofibrillar ATPase activity were found in the diaphragm and soleus, whereas tibialis anterior and intercostal muscles did not show any significant fiber-type alteration. Decrease of oxidative enzyme activities and increase of glycolytic enzyme activities were also observed.
It is concluded that whereas the growth stimulation is age dependent and only detectable in adult rats, the fiber-type transformation is also present in weaning rats and particularly evident in the soleus and diaphragm. The fiber-type transformation caused by clenbuterol might lead to an enhancement of contractile performance and also to a reduced resistance to fatigue.
muscle; myosin isoforms; muscle metabolism;
-adrenoreceptors; muscle development
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