In this study, we analyzed the effect of ovariectomy and gonadal hormone replacement on the cross-sectional area of pubococcygeus (Pcm) fibers. It was found that in comparison to intact animals, ovariectomized animals [for 2 or 6 weeks] had an increased cross-sectional area average in Pcm fibers. Ovariectomy also reduced the percentage of fibers with smaller cross-sectional area. In ovariectomized animals after 4 weeks of hormone replacement with an empty Silastic capsule or filled with testosterone propionate or dihydrotestosterone, significantly increased the cross-sectional area average and the percentage of fibers with larger size. However, 17β-estradiol but not estradiol benzoate treatment reduced the cross-sectional area average and increased the percentage of Pcm fibers with smaller size. Progesterone did not have an effect on the cross-sectional area of this muscle. We conclude that Pcm fibers of female rats are sensitive to gonadal hormones, and contrary to male castration, ovariectomy promotes an increase in their cross-sectional area. Also, we discuss according to other studies that an external mechanism which lies within the neuromuscular periphery could also participate in the modulatory hormonal effect on mass or muscle fiber size. Furthermore, in this process, estradiol is likely to regulate the fiber cross-sectional area growing produced by androgens.
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