# Morphological examination of pelvic floor muscles in a rat model of vaginal delivery

## TL;DR

This study examines how pelvic floor muscles in rats change after simulated vaginal delivery, finding muscle atrophy and composition changes that may explain urinary incontinence.

## Contribution

The study reveals long-term pelvic floor muscle changes after simulated vaginal delivery, even after urethral function recovers.

## Key findings

- Urethral function was significantly reduced one week after simulated vaginal delivery.
- Pelvic floor muscle wet weight and cross-sectional area of Type I fibers were significantly lower in the VD groups.
- Type I muscle fiber composition in both Pcm and Icm was reduced in VD groups, with the lowest in the 2-week group.

## Abstract

This study investigated morphological changes in the composition of the pelvic floor muscles, degree of atrophy, and urethral function in a rat of simulated birth trauma induced by vaginal distension (VD) model.

Female Sprague–Dawley rats were classified into four groups: a sham group, and 1, 2, and 4 weeks post-VD (1 W, 2 W, and 4 W, respectively) groups. We measured the amplitude of urethral response to electrical stimulation (A-URE) to evaluate urethral function. After measuring the muscle wet weight of the pubococcygeus (Pcm) and iliococcygeus (Icm) muscles, histochemical staining was used to classify muscle fibers into Types I, IIa, and IIb, and the occupancy and cross-sectional area of each muscle fiber were determined.

There were 24 Sprague–Dawley rats used. A-URE was significantly lower in the 1 W group versus the other groups. Muscle wet weight was significantly lower in the VD groups versus the sham group for Pcm. The cross-sectional area of Type I Pcm and Icm was significantly lower in the VD groups versus the sham group. Type I muscle fiber composition in Pcm was significantly lower in the VD groups versus the sham groupand lowest in the 2 W group. Type I muscle fiber composition in Icm was significantly lower in the 2 and 4 W groups versus the sham group.

Muscle atrophy and changes in muscle composition in the pelvic floor muscles were observed even after improvements in urethral function. These results may provide insight into the pathogenesis of stress urinary incontinence after VD.