Regional Variation in Tissue Composition and Biomechanical Properties of Postmenopausal Ovine and Human Vagina

Abstract

ObjectiveThere are increasing numbers of reports describing human vaginal tissue composition in women with and without pelvic organ prolapse with conflicting results. The aim of this study was to compare ovine and human posterior vaginal tissue in terms of histological and biochemical tissue composition and to assess passive biomechanical properties of ovine vagina to further characterise this animal model for pelvic organ prolapse research.Study DesignVaginal tissue was collected from ovariectomised sheep (n = 6) and from postmenopausal women (n = 7) from the proximal, middle and distal thirds. Tissue histology was analyzed using Masson's Trichrome staining; total collagen was quantified by hydroxyproline assays, collagen III/I+III ratios by delayed reduction SDS PAGE, glycosaminoglycans by dimethylmethylene blue assay, and elastic tissue associated proteins (ETAP) by amino acid analysis. Young's modulus, maximum stress/strain, and permanent strain following cyclic loading were determined in ovine vagina.ResultsBoth sheep and human vaginal tissue showed comparable tissue composition. Ovine vaginal tissue showed significantly higher total collagen and glycosaminoglycan values (p<0.05) nearest the cervix. No significant differences were found along the length of the human vagina for collagen, GAG or ETAP content. The proximal region was the stiffest (Young's modulus, p<0.05), strongest (maximum stress, p<0.05) compared to distal region, and most elastic (permanent strain).ConclusionSheep tissue composition and mechanical properties showed regional differences along the postmenopausal vaginal wall not apparent in human vagina, although the absolute content of proteins were similar. Knowledge of this baseline variation in the composition and mechanical properties of the vaginal wall will assist future studies using sheep as a model for vaginal surgery.

Morphological and Functional Changes in the Vagina following Critical Lifespan Events in the Ewe

“…However, we did not find studies describing physiological changes during the lifespan of asymptomatic women. We came across one study comparing the collagen ratio and total collagen content in the vaginal wall of castrated sheep being compared to that of menopausal women -yet without comparable measurements in premenopausal subjects [12]. This is a comparison we cannot make.…”

“…Non-human primates are closest to humans [7][8][9], however, their use in research has been nearly completely banned in Europe [10]. Sheep may be alternatives as their pelvic floor anatomy and dimensions as well as the microscopic architecture have many similarities to that of humans [11,12]. We and others have recently become interested in sheep for pelvic floor research and experimental surgery [13][14][15].…”

“…We and others have recently become interested in sheep for pelvic floor research and experimental surgery [13][14][15]. For that purpose, we previously compared the pelvic floor anatomy and tissue composition of reproductive, pregnant, and postpartum ewes to that of women [11,12,[16][17][18]. Herein, we further explore the impact of key moments in the lifespan of women on the ovine pelvic floor, using gross anatomical and biomechanical readouts.…”

Ovine multiparity is associated with diminished vaginal muscularis, increased elastic fibres and vaginal wall weakness: implication for pelvic organ prolapse

“…Vaginal tissue is anisotropic1940, thus biaxial testing is currently the most equivalent test available. It is superior to uniaxial biomechanical testing as this only measures properties in one direction, which does not represent the physiologic environment, in which strain is placed on the vaginal wall in all directions182641.…”

“…Due to narrowing of the ewe vagina at the apical end, the 4 cm × 4 cm tissue required for biomechanical testing was taken from the mid-region of the posterior wall. Previous studies have demonstrated similarity in the biochemical and biomechanical properties of the lower-and-mid regions of the ovine vaginal wall41. To avoid the hymnal ring, tissue adjacent to the piece for biomechanical analysis was excised and fixed in 10% formalin, paraffin embedded and 5 μm sections were stained with Haemotoxylin and Eosin (H&E), Masson’s Trichrome and Hart’s elastic fibre stain in the Monash Histology Platform (MHP) facility.…”