MP03-06 VAGINAL DELIVERY ALTERS THE MUSCLE FIBER COMPOSITION OF THE PELVIC FLOOR MUSCLES
Abstract
INTRODUCTION AND OBJECTIVE:
It is well known that transvaginal childbirth weakens the pelvic floor muscles (PFM) and pelvic nerves, leading to stress urinary incontinence (SUI). PFM training is recommended as Grade A conservative therapy for SUI. Thus, PFM play important roles in lower urinary tract functions. In our previous study, we reported that the distribution of fiber types in the PFM is altered beginning 1 to 4 weeks post vaginal distension (VD), leading to muscle atrophy. SUI after vaginal delivery is known to persist in approximately 2% of patients who have had a vaginal delivery, even after 2 months postpartum. Therefore, we hypothesized that the long-term SUI that occurs after vaginal delivery may be influenced by the fiber-type distribution of PFM. The purpose of this study was to examine the long-term histological changes in PFM in a rat model of VD.
METHODS:
Eighteen female Sprague-Dawley rats (248-335 g) were used in this study. They were divided into 3 groups: a sham group, 1 (1M) and 3 months (3M) post VD. Urethral pressure was measured as urethral baseline pressure (UBP) and amplitude of urethral response (A-URE) (cmH2O). Right side pubococcygeus muscle (Pcm) was sampled and wet weight to body weight was measured. Pcm frozen sections 10 mm thick were prepared and stained using succinate dehydrogenase (SDH) activity. Stained images were imported into a personal computer to identify muscle fiber type (Ⅰ, Ⅱa and Ⅱb) distribution. In addition, the cross-sectional area (CSA) (μm2) of each muscle fiber type was determined. One-way analysis of variance was performed to compare the data among 3 groups. P value of less than 0.05 was regarded to be statistically significant. The present study was conducted after being approved by Animal Study Facility Ethics Committee.
RESULTS:
UBP was not significantly different among the 3 groups. In A-URE, 1M group was significantly lower than in the sham (p < 0.05). The Pcm wet weight was significantly lower in the 1M and 3M groups compared to the sham group (p<0.05). The CSA of type Ⅰ fibers in the Pcm was significantly lower in the 1M group than in the 3M group (p<0.05). The CSA of Type Ⅱa and Ⅱb fibers was not significantly different among the 3 groups. The ratio of typeⅠ fibers was significantly lower in the 1M and 3M groups compared to the sham group. The ratio of type Ⅱa fibers was not significantly different among the 3 groups. The ratio of type Ⅱb fibers was significantly higher in the 1M and 3M groups than in the sham group (p<0.05).
CONCLUSIONS:
In the present study, at 3 months post VD, the urethral function improved, but there was a decrease in muscle wet weight of the Pcm and a change in muscle fiber composition (leading to a decrease in slow-twitch muscle response). This may be due to decreased muscle function due to atrophy of the PFM and changes in muscle composition when SUI occurs beyond 3 months after vaginal delivery.
Source of Funding:
none
