Effects of testosterone replacement therapy on skeletal muscle after spinal cord injury

Study design: Randomized control. Objective: To examine the effects of testosterone replacement therapy (TRT) on skeletal muscle 11 weeks after complete SCI. Setting: Athens, Georgia USA. Methods: Soleus (SOL), gastrocnemius (GA), tibialis anterior (TA), vastus lateralis (VL) and triceps brachii (TRI) muscles were taken from twelve young male Charles River rats I I weeks after complete SCI (T-9 transection, n = 8) or sham surgery (n = 4). Rats received either TRT (two 5 cm capsules, n = 4) or empty capsules (n = 8) implanted at surgery. Muscle samples were sectioned and fibers analyzed qualitatively for myosin ATPase and quantitatively for succinate dehydrogenase (SDH), alpha-glycerol-phosphate dehydrogenase (GPDH) and actomyosin ATPase (qATPase) activities using standard techniques. Results: SCI decreased average fiber size (49+/-4%) in affected muscles and the percentage of slow fibers in SOL (93+/-3% to 17+/-2%). In addition, there was a decrease in SDH and an increase in GPDH and qATPase activities across the four hind-limb muscles of the SCI animals. Fiber size in the TRI was increased (31+/-2%) by SCI while enzyme activities were not altered. Average fiber size across the four hind limb muscles was decreased by only 30% in TRT SCI animals and their SOL contained 39+/-2% slow fibers. TRT also attenuated changes in enzyme activities. There was no effect of TRT on the TRI relative to SCI. Conclusions: TRT was effective in attenuating alterations in myofibrillar proteins during 11 weeks of SCI in affected skelatal muscles. Sponsorship: Supported by a grant from The National Institutes of Health (HD-33738) and HD-37645 to KV, and HD-39676 to GAD.