Effects of vaginal trauma and oophorectomy on the continence mechanism in rats

PURPOSE: To establish an animal model for studying the effects of vaginal trauma and oophorectomy on the continence mechanism in rats. METHODS: Ninety-six female rats were used in the experiments. The rats were divided into 8 groups that received either no treatment (control), or single vaginal trauma at 0 day and 4 weeks, multiple vaginal traumas, oophorectomy at 4 and 12 weeks, and combined oophorectomy and single vaginal trauma or multiple vaginal traumas at 4 weeks. In vivo experiments were performed to determine abdominal leak point pressure (ALPP) by recording the intravesical pressure obtained during compression of the lower abdomen. In vitro urethral contractility experiments were then performed using isolated urethra and electrical field stimulation, acetylcholine, and norepinephrine. Finally, histological study of the urethral muscles and paraurethral structures was performed. RESULTS: Single or multiple vaginal traumas resulted in a significant reduction of ALPP. The reduced ALPP recovered at 4 weeks after single vaginal trauma. Oophorectomy did not significantly affect ALPP compared to controls; however, when oophorectomy was combined with multiple vaginal traumas, a significant reduction in ALPP occurred. Urethral contractility was reduced after multiple vaginal traumas but was not significantly different from the control after oophorectomy. Histological studies revealed disruption of the ventral part of striated muscles after single or multiple vaginal traumas. Degenerative and hyalinization changes were noted in submucosal and muscle layers after oophorectomy combined with multiple vaginal traumas. CONCLUSIONS: Vaginal trauma can injure the urethral muscles and nerves. Single or multiple vaginal traumas can induce denervation of periurethral muscles and reduce ALPP. With a period of recovery, the urethral resistance increases and ALPP returns. Oophorectomy mainly affected the intrinsic urethral closure mechanism and resulted in a nonsignificantly reduced ALPP; however, a significant reduction of ALPP developed when oophorectomy was combined with multiple vaginal traumas.