Effects of prolonged vaginal distension and β-aminopropionitrile on urinary continence and urethral structure

Abstract

Objective: To investigate the effects of prolonged vaginal distension and β-aminopropionitrile (BAPN) on the urinary patterns and urethral structure in female virgin rats.

Methods: A total of 21 female virgin rats were randomly divided into 3 groups of 7 rats each. The control group received no intervention; the vaginal distension (VD) group was treated with prolonged VD by balloon inflation; and the VD plus BAPN group was treated with VD plus intraperitoneal injection of 150 mg/kg of BAPN every 3 days. Three weeks later, all the rats underwent conscious cystometric analysis and were then killed for histologic analysis of the urethra.

Results: Conscious cystometry identified 0, 3, and 5 rats in the control, VD, and VD plus BAPN groups with an abnormal voiding pattern, respectively. The urethral collagen content was significantly lower in the VD and VD plus BAPN rats compared with the control rats. The urethral elastic fibers were disorganized and shorter in the VD and VD plus BAPN rats and were fragmented and lacking the intermuscle connections in the VD plus BAPN rats. The urethral striated muscle fibers were shorter and more widely spaced in the VD and VD plus BAPN rats than in the control rats. Additionally, those in the VD plus BAPN group exhibited an abnormal wavy shape suggestive of a lack of architectural support.

Conclusion: Prolonged vaginal distension caused urodynamic changes and histologic abnormalities in the urethra, including reduced collagen content, fragmented elastic fibers, and sparsely arranged and shortened striated muscle fibers. BAPN appears to interfere with the restoration of collagen and elastic fibers.

Figure 1

Changes in urinary patterns. A. Representative cystometric charts of 10 min recording. BP: Bladder Pressure; AP: Abdominal Pressure; pBP: Bladder Pressure without abdominal pressure; V: Voiding; C: Control rats; VD: VD-treated rats; VD+BAPN: VD+BAPN-treated rats. B. Compilation of cystometric analysis results. Each bar represents the average of 7 rats.

Figure 2

Changes in urethral collagen. A. Representative images of trichrome-stained urethral tissues of control (C), VD-treated (VD), and VD+BAPN-treated (VD+BAPN) rats. Urethral lumen is located at the lower right corner of each image. Original magnification is 200×. B. Compilation of quantification data. Each bar represents the average of 7 rats.

Figure 3

Changes in urethral elastic fibers. A. Representative images of urethral tissues stained for elastic fibers (arrowhead) in the striated muscle layer of control (C), VD-treated (VD), and VD+BAPN-treated (VD+BAPN) rats. Original magnification is 1000x. B. Compilation of quantification data. Each bar represents the average of 7 rats.

Figure 4

Changes in urethral muscle. A. Representative images of trichrome-stained urethral tissues of control (C), VD-treated (VD), and VD+BAPN-treated (VD+BAPN) rats. sm: smooth muscle; st: striated muscle (both stained red). B. Representative images of phalloidin-stained urethral tissues. Both smooth (sm) and striated (st) muscles stained green while cell nuclei stained blue with DAPI. Note the striation in the striated muscle fibers in the 1000× magnification. C. Compilation of quantification data. Each bar represents the average of 7 rats.