Abstract
The objective of the present investigation was to perform a 14-day time-course study of treatment with salbutamol, a beta2 adrenoceptor agonist, on rat soleus muscle in order to assess fiber type selectivity in the hypertrophic response and fiber type composition. Male Wistar rats were divided into four groups: control (N = 10), treated with salbutamol (N = 30), denervated (N = 30), and treated with salbutamol after denervation (N = 30). Salbutamol was injected intraperitoneally in the rats of the 2nd and 4th groups at a concentration of 0.3 mg/kg twice a day for 2 weeks. The muscles were denervated using the crush method with pean. The animals were sacrificed 3, 6, 9, 12, and 14 days after treatment. Frozen cross-sections of soleus muscle were stained for myosin ATPase, pH 9.4. Cross-sectional area and percent of muscle fibers were analyzed morphometrically by computerized image analysis. Treatment with salbutamol induced hypertrophy of all fiber types and a higher percentage of type II fibers (21%) in the healthy rat soleus muscle. Denervation caused marked atrophy of all fibers and conversion from type I to type II muscle fibers. Denervated muscles treated with salbutamol showed a significantly larger cross-sectional area of type I muscle fibers, 28.2% compared to the denervated untreated muscle. Moreover, the number of type I fibers was increased. These results indicate that administration of salbutamol is able to induce changes in cross-sectional area and fiber type distribution in the early phase of treatment. Since denervation-induced atrophy and conversion from type I to type II fibers were improved by salbutamol treatment we propose that salbutamol, like other beta2 adrenoceptor agonists, may have a therapeutic potential in improving the condition of skeletal muscle after denervation.
Highlights
Salbutamol is a ß2 adrenoceptor agonist (BAA) known to induce bronchiolar relaxation, higher vascularization of skeletal muscle, as well as muscle hypertrophy [1]
The number of type I fibers was increased. These results indicate that administration of salbutamol is able to induce changes in cross-sectional area and fiber type distribution in the early phase of treatment
Since denervation-induced atrophy and conversion from type I to type II fibers were improved by salbutamol treatment we propose that salbutamol, like other ß2 adrenoceptor agonists, may have a therapeutic potential in improving the condition of skeletal muscle after denervation
Summary
Salbutamol is a ß2 adrenoceptor agonist (BAA) known to induce bronchiolar relaxation, higher vascularization of skeletal muscle, as well as muscle hypertrophy [1]. Data reported by Maltin et al [6] indicate that clenbuterol inhibits and partially reverses denervation-induced atrophy of rat soleus muscle. This was evident from measurements of both muscle protein content and fiber cross-sectional areas. Some studies have demonstrated that the cross-sectional area of slow twitch oxidative fibers is not changed by chronic administration of BAA [8,10,11] while others have shown that all fiber types are affected [12,13]. 2) to explore the changes in fiber type distribution in slow rat skeletal muscle, both in the presence and in the absence of the nerve
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