Collagen remodeling and suburethral inflammation might account for preserved anti-incontinence effects of cut polypropylene sling in rat model

Abstract

Objectives: To determine whether the inflammatory responses or collagen remodeling in suburethral tissue could have contributed to the preserved anti-incontinence effects of a cut polypropylene sling.

Methods: Stress urinary incontinence was created in 60 age-matched female Sprague-Dawley rats that were subsequently randomized into 3 equal-size groups according to surgical procedure: placement of a vaginal suburethral sling, placement of a vaginal suburethral sling in which the suburethral portion of the sling was immediately cut, and sham surgery without placement of the sling. In a previous study, the leak point pressure measurements were obtained on these rats 6 weeks after surgery. The rats were then killed, the urethrovaginal tissue was harvested (cross-section of the entire urethra and anterior vagina) from 30 animals (10 from each experimental group), and the tissue was stained with hematoxylin-eosin and Masson's trichrome for histopathologic studies and picrosirius red for collagen fibers.

Results: As previously published, the median leak point pressures were similarly and significantly increased in the rats in the intact and cut sling groups compared with those in the sham surgery group. The inflammatory mediators and interstitial edema were similarly increased in the intact and cut sling specimens compared with the sham surgery specimens. Under polarized light, picrosirius red-stained specimens from the sham surgery animals appeared to be composed of collagen that predominately birefringed red to yellow (typical of type I collagen). The picrosirius red-stained cut and intact sling specimens appeared to contain collagen fibers that predominately birefringed green (typical of type III collagen).

Conclusions: Histologic changes, including inflammation, localized edema, and differential collagen remodeling, might contribute to the preserved anti-incontinence mechanisms of cut or intact polypropylene slings observed clinically.

Figure 1

Hematoxylin-eosin stained urethrovaginal specimens from rats with (A) cut sling, (B) intact sling, and (C) sham surgery. (D) Vacuoles that resulted from fragmented polypropylene sling fibers in cut sling specimen surrounded by fibrosis (arrowhead) and lymphocytes (arrow). Similar vacuoles seen in specimens from rats with intact slings. V, vacuoles from fragmented sling fibers; U, urethra. Fig. A–C, bar > 500 µm; Fig. D, bar > 80 µm.

Figure 2

Masson’s trichrome stained urethrovaginal specimens from rats with (A) cut sling, (B) intact sling, and (C) sham surgery. Smooth muscle and collagen stained light pink and blue, respectively. V, vacuoles from fragmented sling fibers; U, urethra. Bar > 500 µm.

Figure 3

Picrosirius red-stained specimens from different treatment groups viewed with polarized light. Images from rats with (A) cut sling, (B) intact sling, and (C) sham surgery. Suburethral area, bordered superiorly and laterally by striated urethral muscles and inferiorly by vaginal epithelium, was analyzed (outlined in white). Collagen type I birefringes yellow to red. Collagen type III birefringes green. V, vacuoles from fragmented sling fibers; U, urethra. Bar > 500 µm.