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

Abstract

Background/Aims: The ewe is increasingly being used as an animal model for pelvic floor disorders. The aim was to further characterize changes in the vaginal properties during its entire lifespan. Methods: Vaginal tissues were collected at different stages of reproductive life (neonatal, prepubescence, nulliparous, primiparous, multiparous, and menopausal; ≥6 ewes/group). Vaginal size, as well as active and passive biomechanics, was measured. Microscopy included thickness of glycogen, epithelium, lamina propria and muscularis thickness, densities of collagen, elastin, smooth muscle, and nerves. Results: Vaginal dimensions increase during adolescence, peak at reproductive levels, and decrease sharply after ovariectomy. One year after first delivery, the distal vagina gets more compliant, yet this is reversed later in life. The thickness of glycogen staining epithelial layers changed with puberty and menopause. The epithelium was markedly thicker after multiple deliveries. The thickness of lamina propria and muscularis increased in puberty and in nulliparous. Semi-quantitative collagen assessment demonstrated a lower collagen and higher elastin content after first and multiple deliveries. Conclusion: The changes in the ovine vaginal wall during representative moments of her lifespan parallel those observed in women.

Animal models for pelvic organ prolapse: systematic review

“…Its etiology is not well described. Several authors describe signs of milder forms of mid-and lower-vaginal descent following pregnancy and delivery [27,[30][31][32][33][34][35][36][37].…”

“…Changes induced by ovariectomy (OVX) in rats, rabbits and sheep were described in 11 studies [36,[75][76][77][78][79][80][81][82][83][84] (Supplementary Table 4). The effects depend on the age when OVX is done and the interval to measurement.…”

“…"Yes" refers to low bias with low risk; "No" refers to high bias with high risk; "Unclear" means the degree of risk is uncertain. For easier orientation, answers at each domain are represented by color dots as follows: [27,36,61] and decrease tensile strength [61] Ambiguous No difference [36] Decrease to KCl (distal vagina) [27] Decreased [27,36] _ _ I n c r e a s e d [ 27,36] D e c r e a s e [ 27] Spontaneous vaginal birth (multiparous)…”

“…No difference [36]; decrease [35,37,34]or increase [30] __ Ambiguous Decrease [30]or increase [34][35][36] Ambiguous No effect [30]; Increase [37]or decrease [ [68,73] Iatrogenic menopause…”

“…Primiparous ewes have an increased vaginal compliance and lower tensile strength. Also, this seems to be the case for multiparous females, except in two studies [36,37]. One of these studies [33] is interesting, because it introduces a quantitative POP system by measuring spontaneous displacement of a point 3 cm above the introitus, both anterior and posterior in the vagina, as well as a point above the urethra.…”