Abstract: BACKGROUND: Currently, there are many modeling methods for pelvic organ prolapse animal models, and the commonly used methods are vaginal balloon dilatation, oophorectomy and the combination of the two. There is no study comparing the three modeling methods in detail.
OBJECTIVE: To construct and validate a rat animal model of pelvic organ prolapse using three different methods and to identify the advantages and disadvantages of various models.
METHODS: Seventy-two 8-week SPF-grade female Sprague-Dawley rats were selected and randomly divided into four groups, namely, vaginal balloon dilatation group, ovariectomy group, ovariectomy combined with vaginal balloon dilatation group (the combined group), and the sham-operated group (no ovariectomy and no vaginal dilatation). The vaginal wall tissues of rats were collected at 4, 8 and 12 weeks after the operation for hematoxylin-eosin staining, Masson staining, EVG staining and immunohistochemical staining of α-smooth muscle actin, Vimentin and matrix metalloproteinase 9 detection, and the pelvic floor muscle tissues were taken at 4, 8 and 12 weeks after the operation for hematoxylin-eosin staining, Masson staining and EVG staining.
RESULTS AND CONCLUSION: (1) Hematoxylin-eosi staining showed that there was no significant difference in the decrease of vaginal epithelial layer thickness in the vaginal balloon dilatation group compared with the sham-operated group,  (P > 0.05), while the thickness of the vaginal epithelial layer was significantly reduced in the ovariectomy group and the ovariectomy combined with vaginal balloon dilation group (P < 0.001), and the reduction was more significant in the ovariectomy combined with vaginal balloon dilation group, remained stable at 8 weeks after surgery and lasted until 12 weeks.  (2) The changes in the content of collagen fibers and elastic fibers in the vaginal wall stained by Masson and EVG staining were the same as the changes in the thickness of the vaginal epithelial layer stained by hematoxylin-eosin, and there were no changes in collagen fibers and elastic fibers in the pelvic floor muscle tissues of the treatment groups. (3) At 4, 8 and 12 weeks after treatment, there was no significant difference in the expression levels of α-smooth muscle actin, Vimentin and matrix metalloproteinase 9 in the vaginal wall tissue of the balloon dilation group compared with the control group (P > 0.05), whereas the expression levels of α-smooth muscle actin and Vimentin were significantly decreased in the ovariectomy group and ovariectomy combined with vaginal balloon dilation group (P < 0.01) and the expression of matrix metalloproteinase 9 showed a significant increase (P < 0.01), with a more pronounced increase in the ovariectomy combined with vaginal balloon dilation group, and the increase reached a stable state at 8 weeks after surgery and could persist up to 12 weeks. To conclude, vaginal balloon dilatation could not maintain the degeneration of pelvic organ prolapse formed by the vaginal wall for a long period, and both ovariectomy and the combined method can be used. Ovariectomy combined with vaginal balloon dilatation can significantly accelerate and aggravate the formation of typical histological features of pelvic organ prolapse in vaginal wall tissues, effectively shorten the experimental period, and improve the efficiency. These effects reach a stable state at 8 weeks after surgery and can be sustained up to 12 weeks, which is practical and convenient for the study of pelvic organ prolapse animal models. 

Key words: pelvic organ prolapse, animal model, ovariectomy, vaginal balloon dilatation, rat