Evaluation of a surgical model to induce endometriosis in female rats

The endometriosis is a chronic disease related with the proliferation of viable endometrial cells out of the uterus and it has high relevance in human health because it can causes infertility. Animals with estrous cycle don’t develop endometriosis spontaneously, but the disease can be induced by ectopic transplant of endometrial tissue. Rodents can be an alternative model to the study of the disease, so this work searched to establish and to validate a surgical protocol to the induction of endometriosis in female rats. The study was conducted according to the Ethical Committee for Animal Research of the Univ Estadual Paulista (UNESP), (protocol 824-CEUA). Adult Wistar female rats (70 days) were maintained under conditions with controlled temperature and luminosity with ad libitum access to commercial diet and water in isolated boxes. The animals (n=20) were equitably distributed in a group of rats with surgical induction of endometriosis (G1) and a control group (G2). After anesthesia, it was done opening of the abdominal cavity by longitudinal incision in Alba line (about 2cm) to identify the right uterine horn. In G1 animals, 1/3 of the median portion of the uterine horn was separated and immersed in saline. Three transverse segments were inverted with surgical tweezers to expose the endometrium. The pieces were fixed in inner muscles wall of the abdominal cavity with catgut. After these procedures, the abdominal cavity wall and skin of the G1 and G2 animals were sutured and it was made post surgical clinical accompaniment. After 20 days the animals were killed and the implants (G1) or the uterine horn segments were processed in histopathological routine. The implants were identified adhered to the abdominal muscle layer and adhered to the intestinal loops in G1 group. Histologically the implants showed glandular arrangement internally covered by simple cubic epithelium and some had luminal leukocytes. These arrangements were inserted in the stroma with typical endometrial characteristics. Aspects of granulomatous chronic inflammatory answer and hemosiderin deposition were frequently observed. Occasionally it was also observed accumulation of xanthomatous cells. The morphological findings show lesions compatible with that expected to endometriosis, suggesting success in the procedure. Animal models allow controlled studies of the disease, minimizing or eliminating variations like age, menstrual cycle phases, diet, use of medication and environmental influence. The surgical induction in female rat is a fast and cheap procedure compared with primates or rabbits.