Development of a domestic animal model for endometriosis: Surgical induction in the dog, pigs, and sheep

Endometriosis affects one in ten women of reproductive age but it is diagnosed at advanced stages. Our objective was to develop a domestic animal model that would permit sequential assessment of endometriotic changes. Surgical transplantation of endometrial tissue and fat (n = 4 grafts/tissue/animal) was done in dogs (n = 5), pigs (n = 4), and sheep (n = 5). Autologous grafts were sutured to the visceral (urinary bladder in dogs and pigs and uterus in sheep) and parietal peritoneum. Sham surgeries were performed (dogs and sheep n = 5 and pigs n = 3) by placing fat grafts alone. Plasma estrogen and progesterone concentration was performed prior to surgery and weekly following surgery until euthanasia. Animals were euthanized between 80 and 110 days after surgery. Gross and histopathologic features of endometriotic lesions were recorded. A variety of lesions from transplanted endometrial grafts included endometriotic cysts, vesicles, solid lesions, or absence of lesions. The proportion of cysts was greater (p < 0.01) in dogs (18/20 grafts) than in pigs (5/16) and sheep (5/20). The area of endometriotic lesions at the time of euthanasia was greater than at the time of surgery in dogs (0.89 ± 0.11 cm2 vs 0.50 ± 0.09 cm2; p < 0.05), whereas, the size of lesions decreased (p < 0.05) by half or more in pigs and sheep. In dogs, endometrial cysts were characterized by simple cuboidal/columnar epithelium, endometrial glands, stromal tissue with hemorrhage and/or hemosiderin-laden macrophages, and smooth muscle cells. The development of endometriotic cysts was apparent in dogs than in sheep and pigs. Therefore, dog is a better domestic animal model for endometriosis