Introduction and aim of the study: Vaginal childbirth is, next to age, an important risk factors for the development of pelvic floor disorders. Several animal models are being used to study the pathogenesis and develop preventive or therapeutic strategies. In a rat model we aimed to determine the effect of simulated vaginal delivery (SVD) on the urethral sphincter and vaginal smooth muscle layer. Because leak point pressure, a proxy for urethral resistance, is operator-dependent, and because electromyography of the urethral sphincter is invasive, we developed a technique using micro-ultrasound to assess urethral function. We use contractility testing of the vaginal smooth muscle as a proxy for vaginal function. This outcome measure has not yet been determined in the rat SVD injury model.
Materials and methods: 81 virgin Sprague-Dawley female rats (250–300 g) underwent either sham injury or vaginal distension (VD) and bilateral pudendal nerve crush (PNC) to establish simulated vaginal birth injury. Seven, 14, 21 or 42 days post-injury, micro-ultrasound was used to record high frequency oscillations (HFOs) during voiding were recorded. Another group of rats was euthanized at 7, 14, 21 or 42 days post-injury and full thickness circumferential strips of the middle rat vagina were assessed in organ bath experiments.
Results: Ultrasound of the urethral sphincter showed absence of HFOs in the rats at 7 days post-injury, yet with partial recovery at later time points. The half maximal effective concentration (EC50) for carbachol induced contraction was significantly different at 14, 21 and 42 days.
Interpretation of results: Simulated vaginal birth injury causes, next to other well characterised other effects, dysfunction of the urethral sphincter and increases the sensitivity of the vaginal smooth muscle layer to carbachol.
Conclusions: Simulated vaginal birth injury causes dysfunction of the urethral sphincter and increases the sensitivity of the vaginal smooth muscle layer to carbachol.
© 2017 Published by Elsevier Inc.