Effects of Combined Stretching and Clenbuterol on Disuse Atrophy in Rat Soleus Muscle

Abstract

ABSTRACT. Background and Purpose: Clinically, disuse muscle atrophy is often seen among patients who are severely debilited and are on prolonged bed rest. Common physical therapy interventions are not successful in preventing disuse muscle atrophy early in the medical treatment of critically ill patients. In situations such as this, the use of a 2-adrenergic agonist such as clenbuterol (Cb) may be of benefit in preventing atrophy. Also, recent studies have suggested that stretching is possible in preventing disuse muscle atrophy and the decline in muscle strength. The objective of this study was to evaluate the effects of Cb medication combined with stretching (ST) on rat soleus muscle (SOL) during the progression of disuse muscle atrophy. Subjects: Thirty-five male Wistar rats were used in this study. Methods: The rats were divided into five groups: control (CON), hindlimb-unweighting (HU) only, HU+ST, HU+Cb medication, and HU+ST+Cb groups. The right SOL in stretching groups was maintained a stretched position for one hour daily by passively dorsiflexing the ankle joint under non-anesthesia. The experimental period was 2 weeks. Results: In the ST group, peak twitch tension per cross-sectional area in soleus muscle was significantly larger than in the Cb group, while there was no significant difference between the CON and ST groups. The conversion of type I to type II fibers that was observed in the Cb group was not recognized in the combined ST and Cb group. Discussion and Conclusion: Distinct effect of combined stretching and Cb medication was not recognized statistically. The results indicate that Cb affects muscle morphological characteristics while stretching affects contractile properties. These data suggest that a combined ST and Cb intervention considered the type-specificity of muscle fiber may be need more consideration for preventing disuse muscle atrophy and the decline in muscle strength. Key words: stretching, clenbuterol, disuse muscle atrophy, rat, atrophy prevention (J Jpn Phys Ther Assoc 12: 13-19, 2009) Disuse muscle atrophy has a substantial effect on activities of daily living (ADL) such as standing and walking 1,2) . Clinically, disuse muscle atrophy is often seen among patients who are severely debilitated and have been on prolonged bed rest in an acute care setting. Early initiation of weight-bearing activities such as ambulation in the clinical course of a patient's critical illness has been advocated to prevent disuse atrophy of lower extremity muscles. However, due to underlying illness, early weightbearing exercises are often contraindicated. While hindlimb unweighting (HU) has been used as a model for spaceflight, it is also used as a model for decreased muscle use. On the basis of the results from a study in rats, Brown et al. 3) reported that one hour of weightbearing per day, during two weeks of HU, is useful in suppressing the progression of disuse atrophy in soleus muscle (SOL). We have also been exploring effective means of preventing atrophy by using a clinically applicable ...