Nandrolone Decanoate Reduces Changes Induced by Hindlimb Suspension in Voltage-Dependent Tension of Rat Soleus Muscle

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The effect of 8 weeks of nandrolone decanoate treatment (15 mg kg−1/week, 5 weeks under normal conditions followed by 3 weeks of unloading) was tested for the voltage-dependence of activation and steady-state inactivation of contraction in isolated small bundles (2–4 cells) of intact slow-twitch skeletal muscle in rats. Twenty-four male rats were divided into three groups (8 rats/group, weight matched) for 8 weeks: (1) control, (2) unloaded, and (3) unloaded-treated. Compared with age-matched control values (unloaded vs. control), suspension induced a shift in the isometric tension characteristics toward fast-twitch types in the soleus muscle. In contrast, nandrolone decanoate treatment of suspended animals reduced unweighting-induced atrophy in the muscle and maintained: (1) the relative amplitude of twitch tension to the maximal Ca2+ activated in saponin-treated fibers (control: 3.6 ± 0.4%, unloaded: 6.9 ± 1.1% and unloaded-treated: 4.6 ± 0.2%), (2) the time to peak tension (control: 130 ± 18 ms, unloaded: 85 ± 12 ms and unloaded-treated: 110 ± 11 ms), (3) the time constant of relaxation (control: 320 ± 12 ms, unloaded: 120 ± 13 ms and unloaded-treated: 349 ± 20 ms), (4) the relative amplitude of K+ contracture tension to the maximal Ca2+ activated in saponin-treated fibers (control: 82.9 ± 3.1%, unloaded: 65.1 ± 2.8%, and unloaded-treated: 91.7 ± 1.9%), (5) the potential at 50% of the activation curve (control: −40.4 ± 1.2 mV, unloaded: −35.5 ± 1.6 mV, and unloaded-treated: −48.4 ± 1.2 mV), and (6) the potential at 50% of the inactivation curve (control: 42.2 ± 1.9 mV, unloaded: −34.5 ± 1.1 mV, and unloaded-treated: −37.9 ± 1.1 mV). This study clearly shows that treatment with anabolic-androgenic steroids can prevent atrophy and functional changes induced by 3 weeks of unweighting in rat skeletal muscles.<br>

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