Increased cell proliferation in experimentally induced endometriosis in rabbits

Objective: To characterize the pattern of cell proliferation and apoptosis of eutopic and ectopic endometrium in rabbits after endometrium implantation for the experimental induction of endometriosis. Design: Animal experimental study. Setting: Sector of experimental surgery. Animal(s): Twenty-female New Zealand rabbits. Intervention(s): All animals underwent laparotomy for endometriosis induction by resection of one uterine horn, isolation of the endometrium, and fixation of tissue segment to the pelvic peritoneum. Two groups of 10 animals were sacrificed 4 and 8 weeks after endometriosis induction. The lesion was excised together with the opposite uterine horn for endometrial gland and stroma determination. Main Outcome Measure(s): Cell proliferation and apoptosis were determined in the eutopic and ectopic endometrium, and the cell proliferation index (CPI) and apoptotic index (AI) were calculated as the number of labeled cells per 1,000 cells. The tissue homeostasis index was the CPI/AI ratio. Glands and stroma were analyzed separately. Result(s): The CPI for ectopic tissue was increased compared with eutopic tissue, but there was no difference in the ectopic lesions between 4 and 8 weeks of induction. Considering only the AI, eutopic and ectopic endometrium did not differ after 4 weeks, but differed significantly in glandular tissue after 8 weeks. The tissue homeostasis index revealed cell proliferation in these tissues, with a CPI/AI more than 1. Conclusion(s): Ectopic lesions seem to have a higher CPI than eutopic endometrium, with uncontrolled tissue growth occurring in induced endometriotic lesions. (Fertil Steril (R) 2010;93:1637-42. (C)2010 by American Society for Reproductive Medicine.)