Androgen sensitivity of skeletal muscle: nondependence on the motor nerve in the frog forearm

The effects of castration and of subsequent androgen administration on fiber size were investigated in several frog skeletal muscles. Four months after castration, cross-sectional cell area decreased by 70% and 14%, respectively, in the flexor carpi radialis and flexor carpi centralis muscles of the forearm and only by 2% in the ileo fibularis muscle of the thigh. Injection of testosterone propionate induced a hypertrophic response that reversed the effects of androgen deprivation; after 6 weeks, complete recovery to the control value was observed in all muscles selected. This sensitivity to the exogenous androgen was not altered by denervation; a similar hypertrophic evolution was seen in the denervated right muscles and in the homologous intact left muscles of the forearms. Using the myosin ATPase reaction, the muscle histochemical patterns were unchanged in all conditions tested. These results suggest that (i) a gradient of sensitivity to androgens exists in different frog muscles; (ii) androgens control the myofiber size but not the nerve-muscle organization as can be seen from the myofibrillar ATPase pattern; and (iii) the androgen sensitivity is not dependent on the motor nerve.