The Maintenance of Muscle Mass Is Independent of Testosterone in Adult Male Mice

Testosterone is considered a potent anabolic agent in skeletal muscle with a well-established role in adolescent growth and development in males. However, alterations in the role of testosterone in the regulation of skeletal muscle mass and function throughout the lifespan has yet to be established. While some studies suggest that testosterone is important for the maintenance of skeletal muscle mass, an understanding of the role this hormone plays in young, adult, and old males with normal and low serum testosterone levels is lacking. We investigated the role testosterone plays in the maintenance of muscle mass by examining the effect of orchiectomy-induced testosterone depletion in C57Bl6 male mice at ages ranging from early postnatal through old age; the age groups we used included 1.5-, 5-, 12-, and 24-month old mice. Following 28 days of testosterone depletion, we assessed mass and fiber cross-sectional-area (CSA) of the tibialis anterior, gastrocnemius, and quadriceps muscles. In addition, we measured global rates of protein synthesis and degradation using the SuNSET method, western blots, and enzyme activity assays. 28 days of testosterone depletion resulted in smaller muscle mass in the two youngest cohorts but had no effect in the two older ones. Mean CSA decreased only in the youngest cohort and only in the tibialis anterior muscle. Testosterone depletion resulted in a general increase in proteasome activity at all ages. We did not detect changes in protein synthesis at the terminal time point. This data suggest that within physiological serum concentrations, testosterone is not important for the maintenance of muscle mass in mature male mice; however, in young mice testosterone is crucial for normal growth.