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 Orx 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(0)), time to peak twitch contraction (TPT), half relaxation time (RT(1/2)), muscle mass, fiber area, and specific tension (ratio of P(0)/muscle mass).
RESULTS: Body weight and muscle mass were similar in the Con and Orx groups. The ratio of P(0) to muscle mass was significantly (p <.05) reduced with Orx in SOL (20%), PLAN (18%), PER (28%), and EDL (20%). TPT and RT(1/2) were significantly faster after Orx in PLAN, PER, and EDL. HLU significantly reduced muscle mass in SOL, PLAN, and GAST in Orx and intact groups. HLU also caused a significant decline in SOL and PLAN P(0). The loss in P(0) in the Orx-HLU rats was no greater than the decline in P(0) with HLU alone.
CONCLUSIONS: Gonadectomy results in a loss of P(0) regardless of muscle fiber type or function, it is likely to speed up TPT and RT(1/2), and it does not exacerbate HLU-related atrophy and P(0) loss. Findings may have implications for men with reduced TST levels, as in aging, for instance.

RCT Entities:   Population Interventions Outcomes