SELECTIVE CHANGES IN MUSCLE FIBER SIZE FOLLOWING BONE FRACTURE IN AGED RATS

Abstract

PURPOSE The purpose of this study was to investigate the effect of bone fracture-induced muscle atrophy on the histochemical property of muscle fibers in aged rats. METHODS All experimental procedures were approved by the institutional Animal Care and Use Committee at Kyoto University. Ten male and female Wistar Kyoto rats (aged:88.7 □} 3.2 wk) were subdivided into four groups based upon gender and the presence of fractures or non-fractures of the metatarsal bone of the right hindlimb paw: …3) male fractur ed (M-FR, n=5); …) non-fractur ed (M-NFR, n=5); … μ) female fractured (F-FR, n=5); …¶) non-fractured (F-NFR, n=5). The soleus muscles were dissected from both hindlimbs and analyzed for histochemical properties. Myofibrillar adenosine triphosphatase (ATPase) histochemical staining procedure was used to determine muscle fiber type and calculate the percentage distribution and cross-sectional area (CSA) of each fiber type. RESULTS The wet weight of the soleus muscles of the leg with the fractured paw decreased by 9.6% in M-FR and decreased by 10.0% in F-FR compared to M-NFR and F-NFR, respectively (p > 0.05). However, the wet weight of the soleus muscle of the contralateral, nonfractured site of both M-FR and F-FR groups displayed a hypertrophic compensation and was increased by 12% in M-FR and increased by 3.3% in F-FR (p > 0.05). The CSA of the fast-twitch oxidative glycolytic (FOG) fibers hypertrophied by 40% (p < 0.05) in the soleus muscles of the leg with the fractured paw in the M-FR compared with M-NFR group. In contrast, there was no change in CSA of the FOG of soleus muscle between the female groups. CONCLUSION The data suggest that stress-induced increases in male androgen hormones upregulated the synthesis of contractile proteins of the fast twitch oxidative and glycolytic fibers.