Influence of bilateral oophorectomy and estrogen substitution on the striated anal sphincter in adult female rats.

A quantitative histologic analysis of the striated anal sphincter of 24-month-old virgin female rats was performed to evaluate the effect of oophorectomy and estrogen substitution. The oophorectomized rats had a 21% (11-31%, 95% confidence limits) reduction in the cross-sectional area of the striated muscle tissue compared with controls. This was due to a reduction in the mean cross-sectional area of the muscle fiber, whereas the number of fibers was unchanged. Although the relative amount of stromal tissue was increased in the oophorectomized rats, the total stromal tissue was unchanged. No difference in the cross-sectional area of muscle tissue was found between the estrogen-substituted, oophorectomized rats and controls. This indicates that the estrogen depletion in the oophorectomized rats has induced the reduction in muscle tissue in the striated anal sphincter.