Gonadectomy and reduced physical activity: Effects on skeletal muscle

Objectives: To examine the effects of testosterone (TST) loss on skeletal muscle contractile function and the potential interactive effects of TST loss and physical inactivity. Design: Randomized control trial. Animals: Forty-eight male rats (age, 6mo) were placed into control (Con) or gonadectomized (Orx) groups. Intervention: Two weeks after Orx or sham surgery, half the Con and On; rats were hind-limb unloaded (HLU) to reduce muscle activity for 2 weeks. Subsequently, in situ contractile function tests were performed on the soleus (SOL), plantaris (PLAN), peroneus longus (PER), and extensor digitorum longus (EDL). These 4 muscles and gastrocnemius (GAST) then were removed( weighed, sectioned, and stained with adenosine triphosphatase for fiber typing and fiber area measures. Main Outcome Measures: Peak tetanic tension (P-o), time to peak twitch contraction (TPT), half relaxation time (RT1/2), muscle mass, fiber area, and specific tension (ratio of P-o/muscle mass). Results: Body weight and muscle mass were similar in the Con and Orx groups. The ratio of P-o to muscle mass was significantly (p <.05) reduced with Orx in SOL (20%), PLAN (18%), PER (28%), and EDL (20%). TPT and RT1/2 were significantly faster after Or. in PLAN, PER, and EDL. HLU significantly reduced muscle mass in SOL, PLAN, and CAST in Orx and intact groups. HLU also caused a significant decline in SOL and PLAN P-o. The loss in P-o in the Orx-HLU rats was no greater than the decline in P-o with HLU alone. Conclusions: Gonadectomy results in a loss of P-o regardless of muscle fiber type or function, it is likely to speed up TPT and RT1/2, and it does not exacerbate HLU-related atrophy and P-o loss. Findings may have implications for men with reduced TST levels, as in aging, for instance.