The role of mode of delivery on elastic fiber architecture and vaginal vault elasticity: A rodent model study

Abstract

We report on an experimental study of the role of mode of delivery and pregnancy on the architecture of vaginal elastic fibers and vaginal vault elasticity in female Sprague-Dawley rats. In primiparous rats submitted to spontaneous or Cesarean delivery and virgin rats submitted to simulated delivery, the tortuosity of elastic fibers (defined as the ratio of length to end-to-end distance) was observed to decrease when measured two days to two weeks postpartum. In addition, the measured tortuosity of elastic fibers in multiparous rats was greater than that of virgin rats. The tortuosity of elastic fibers of all rats measured at two days postpartum were found to be similar to that of multiparous rats. At two weeks postpartum the measured tortuosity of vaginal elastic fibers was indistinguishable from virgin rats, regardless of the delivery method. Borrowing from the field of polymer physics, a model is suggested that connects elastic fiber tortuosity to the resulting tension under an applied stress; fibers having high tortuosity are expected to provide less structural support than more linear, low tortuosity fibers. To probe the macroscopic effects in elasticity due to architectural changes observed in elastic fibers, we have measured the stiffness of the vaginal vault in each cohort using a pressure-infusion system. The vaginal vault stiffness of all primiparous rats measured two weeks postpartum was greater than that measured two days postpartum. In addition, the vaginal vault of virgin rats was stiffer than that of multiparous rats. These observations confirmed that vaginal vault elastic fibers undergo significant remodeling due to pregnancy and parturition, and that the complex remodeling may be a significant contributor to tissue elasticity. Remarkably, regardless of the mode of delivery or simulated tissue trauma, elastic fiber tortuosity is observed to decrease from two days to two weeks postpartum indicating the onset of repair and recovery of tissue stiffness.

Mechanical Properties of Female Reproductive Organs and Supporting Connective Tissues: A Review of the Current State of Knowledge

“…The vaginal vault of virgin rats was found to be stiffer than that of multiparous rats. These results, in conjunction with the measured tortuosity results, confirmed that the elastin fibers in the vaginal vault may significantly remodel due to pregnancy and parturition, contributing to tissue elasticity [64].…”

“…Several studies have shown that the onset of pregnancy, prolapse, and menopause can alter the structure of vaginal tissue [59,[61][62][63][64]. A study conducted by Downing et al [64] on the influence of pregnancy and mode of delivery on the elastic fiber architecture and vaginal vault elasticity in rats showed that the tortuosity of elastin fibers decreased when measured at 2 days postpartum compared to virgin vaginal tissue. After 2 weeks postpartum, the measured tortuosity was similar to virgin vaginal tissue, suggesting that the vaginal tissue undergoes structural remodeling to allow for events such as pregnancy and then returns to its prior state [64].…”

“…A study conducted by Downing et al [64] on the influence of pregnancy and mode of delivery on the elastic fiber architecture and vaginal vault elasticity in rats showed that the tortuosity of elastin fibers decreased when measured at 2 days postpartum compared to virgin vaginal tissue. After 2 weeks postpartum, the measured tortuosity was similar to virgin vaginal tissue, suggesting that the vaginal tissue undergoes structural remodeling to allow for events such as pregnancy and then returns to its prior state [64]. While studying the effect that parity has on the collagen structure in vaginal tissues of rhesus macaque monkeys, Feola et al [63] found a decrease in collagen alignment with parity.…”

“…In addition to measuring the tortuosity of the elastin fibers in the vaginal wall, Downing et al [64] used a pressure infusion system to measure the stiffness of the vaginal vault of female rats. The goal of the study was to determine the architectural changes in the vagina that lead to changes in the elasticity of the vaginal tissue.…”

Transforming Growth Factor β1 and Extracellular Matrix Protease Expression in the Uterosacral Ligaments of Patients With and Without Pelvic Organ Prolapse

“…In this study, we evaluated MMP-9 as one downstream effector of TGF-β1, although other factors such as elastin may play a role in POP. We believe that optimal evaluation of elastin requires specialized approaches that could be done in future studies [23]. …”