Age-related changes in the striated anal sphincter in female rats. A quantitative morphometric study.

A quantitative histologic analysis of the striated anal sphincter of virgin female rats aged 2 months and 24 months was performed to evaluate age-related changes. A 27% (8% to 46%, 95% confidence limits) increase in the cross-sectional area of the muscle in the older rats was observed compared with the young. This was due to an increase in both muscle and connective tissue. There was hypertrophy of both the small and large muscle fibres without change in the number with age. No evidence of age-related degenerative changes in this muscle in the virgin female rat was found.