Melatonin is as effective as testosterone in the prevention of soleus muscle atrophy induced by castration in rats.

The purpose of this experiment was to compare the weight, insulin-like growth factor-I (IGF-I) expression, and ultrastructure of the soleus muscle in growing castrated rats treated with testosterone or melatonin. In this study, adult male Wistar albino rats were used. The groups were arranged as sham, castrated, and testosterone- or melatonin-injected groups after castration. The soleus muscle samples were fixed in Bouin's solution for immunohistochemistry, and in 2.5% gluteraldehyde in 0.1 M phosphate buffer (pH 7.4). Whereas castration reduced the soleus weight and fiber diameter, testosterone and melatonin administration increased them. IGF-I immunostaining observed in the satellite cells and periphery of the myofibers was least intense in the castrated group. Strong staining of IGF-I was observed in the testosterone- and melatonin-administered groups. The ultrastructure of the soleus muscle in castrated animals showed the important ultrastructural modifications related to degeneration. In these groups, degenerative mitochondria, glycogen clusters under the sarcolemma, irregular Z lines, and loss of lamina externa were observed. The ultrastructure of myofibrils in the testosterone- and melatonin-injected groups was similar to that in sham groups in view of structure. In conclusion, we suggest that melatonin is as effective as testosterone in the prevention of atrophy induced by castration through the IGF-I axis.