Estradiol replacement reverses ovariectomy-induced muscle contractile and myosin dysfunction in mature female mice.

Skeletal muscle contractility and myosin function decline following ovariectomy in mature female mice. In the present study we tested the hypothesis that estradiol replacement can reverse those declines. Four-month-old female C57BL/6 mice (n = 69) were ovariectomized (OVX) or sham operated. Some mice were treated immediately with placebo or 17beta-estradiol (OVX + E(2)) while other mice were treated 30 days postsurgery. Thirty or sixty days postsurgery, soleus muscles were assessed in vitro for contractile function and susceptibility to eccentric contraction-induced injury. Myosin structural dynamics was analyzed in extensor digitorum longus (EDL) muscles by electron paramagnetic resonance spectroscopy. Maximal isometric tetanic force was affected by estradiol status (P < 0.001) being approximately 10% less in soleus muscles from OVX compared with sham-operated mice [168 mN (SD 16.7) vs. 180 mN (SD 14.4)] and was restored in OVX + E(2) mice [187 mN (SD 17.6)]. The fraction of strong-binding myosin during contraction was also affected (P = 0.045) and was approximately 15% lower in EDL muscles from OVX compared with OVX + E(2) mice [0.263 (SD 0.034) vs. 0.311 (SD 0.022)]. Plasma estradiol levels were correlated with maximal isometric tetanic force (r = 0.458; P < 0.001) and active stiffness (r = 0.329; P = 0.044), indicating that circulating estradiol influenced muscle and myosin function. Estradiol was not effective in protecting muscle against an acute eccentric contraction-induced injury (P >or= 0.401) but did restore ovariectomy-induced increases in muscle wet mass caused by fluid accumulation. Collectively, estradiol had a beneficial effect on female mouse skeletal muscle.