Tissue alterations in urethral and vaginal walls related to multiparity in rabbits

In rodents, vaginal distention after delivery or experimental manipulation affects innervations as well as the amount of striated/smooth musculature or collagen in both the urethra and vagina. These changes are associated with modifications in excretory and reproductive processes. Although successive and consecutive vaginal deliveries (multiparity) affect the contractile and functional properties of the female lower urogenital tract (LUT), its impact on LUT morphometry, including persistency, has been barely studied. The caudal urethra (CU) and cranial (V1) and caudal (V2) pelvic vaginal regions were excised from young and adult nulliparous (YN and AN, respectively) and multiparous (YM and AM, respectively) rabbits. Tissues were histologically processed and stained with Masson's trichrome. The thickness of the tissue layers and areas covered by tissue components were measured and compared using two-way ANOVA followed by Student-Newmann-Keuls tests to determine statistical differences (P ≤ 0.05). Compared to YN, YM, and AN tissues showed a reduction in the thickness of the epithelium, as well as in areas covered by striated musculature, collagen, and blood vessels of the LUT. In comparison with YM, only some morphometric changes were recovered in the AM group. Our study shows that multiparity and age can be associated with epithelial and muscular atrophy of urethral and vaginal walls. The morphometry of the LUT between young and adult female rabbits varies with multiparity. These findings may help to better understand the effects of multiparity on young and adult females and its correlation with the development of pelvic dysfunctions.