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First delivery and ovariectomy affect biomechanical and structural properties of the vagina in the ovine model

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Abstract

Introduction and hypothesis

Animal models are useful for investigating the genesis of pelvic floor dysfunction and for developing novel therapies for its treatment. There is a need for an alternative large-animal model to the nonhuman primate. Therefore we studied the effects of the first vaginal delivery, ovariectomy and systemic hormonal replacement therapy (HRT) on the biomechanical and structural properties of the ovine vagina.

Methods

We examined the gross anatomical properties of nulliparous, primiparous, ovariectomized multiparous, and ovariectomized hormone-replaced multiparous sheep (six animals per group). We also harvested mid-vaginal and distal vaginal tissue to determine smooth muscle contractility and passive biomechanical properties, for morphometric assessment of the vaginal wall layers, to determine collagen and elastin content, and for immunostaining for α-smooth muscle actin and estrogen receptor-α.

Results

There were no regional differences in the nulliparous vagina. One year after the first vaginal delivery, stiffness and contractility of the distal vagina were decreased, whereas the elastin content increased. The mid-vagina of ovariectomized sheep was stiff, and its epithelium was thin and lacked glycogen. HRT decreased the stiffness of the mid-vagina by 45% but had no measurable effect on contractility or elastin content, and increased epithelial thickness and glycogen content. HRT also increased the epithelial thickness and glycogen content of the distal vagina. At this location, there were no changes in morphology or stiffness.

Conclusion

In sheep, life events including delivery and ovariectomy affect the biomechanical properties of the vagina in a region-specific way. Vaginal delivery mainly affects the distal region by decreasing stiffness and contractility. HRT can reverse the increase in stiffness of the mid-vagina observed after surgical induction of menopause. These observations are in line with scanty biomechanical measurements in comparable clinical specimens.

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Acknowledgments

We thank Ivan Laermans, Rosita Kinart and Ann Lissens (Centre for Surgical Technologies, KU Leuven, Leuven, Belgium), and Godelieve Verbist and Rita van Bree (Department of Development and Regeneration, KU Leuven, Leuven, Belgium) for their technical support during the experiments. We thank Leen Mortier for help with data and manuscript management.

Funding

Our research program on the ovine model was supported by an unconditional grant from Medri and Blasingame, Burch, Garrard and Ashley (Atlanta GA, USA). Agreements were handled via the Leuven Research and Development Transfer office. The sponsors did not interfere with the planning, execution or reporting of this study, nor do they own the results. A.F. and L.H. are recipients of a grant from the European Community in the FP7 framework (Bip-Upy project; NMP3-LA-2012-310,389). A.F. was supported by a grant from the European Community in the Industry-Academic Partnership program 251,356.

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Correspondence to Jan Deprest.

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Ethical approval

The study was approved by the Ethics Committee for Animal Experimentation of the Faculty of Medicine of the K.U. Leuven. All applicable international, national and institutional guidelines for the housing, care and use of animals were followed. Procedures performed in this study were in accordance with the ethical standards of the institution at which they were conducted.

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Urbankova, I., Callewaert, G., Blacher, S. et al. First delivery and ovariectomy affect biomechanical and structural properties of the vagina in the ovine model. Int Urogynecol J 30, 455–464 (2019). https://doi.org/10.1007/s00192-017-3535-9

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