Standardized method to develop an endometriosis model in Sprague-Dawley rats: A step-by-step description

To establish a standardized and reproducible rat model of endometriosis by refining the classic Vivian technique, with the aim of minimizing methodological variability and replicating key features of human disease.

Sixty female Sprague-Dawley rats (6 weeks old) were evaluated for estrous-cycle phase using vaginal cytology, and only animals in proestrus or estrus were selected. Under ketamine-xylazine anesthesia, a 1-cm segment of the uterine horn was excised, opened longitudinally, and sutured to the peritoneal wall with the endometrial surface facing the peritoneum. Protocol refinements included strict graft orientation, fixation with four interrupted sutures, and perioperative ceftriaxone prophylaxis. A second laparotomy was performed one month later to assess lesion development, followed by histological confirmation.

All animals (100%) developed macroscopically visible lesions. These lesions presented as cystic, fluid-filled masses with hyperemic surfaces and neovascularization; adhesions to the bowel or omentum were also observed. Lesion size was quantified using digital imaging software. Histological analysis confirmed the presence of endometrial-like tissue composed of cuboidal epithelium, glandular structures, and stromal elements. No perioperative mortality occurred.

This standardized rat model reliably reproduces hallmark features of human endometriosis, including angiogenesis and adhesion formation. The protocol refinements address common sources of variability in rodent models and provide a stepwise, reproducible framework for mechanistic investigation and preclinical evaluation of novel therapies.