The role of blood in early endometrial–peritoneal interactions in a syngeneic mouse model of endometriosis

Purpose The aim of this study was to clarify the role of blood in the early stage of development of endometriotic lesions by developing a syngeneic transplantation model using immunocompetent mice. Methods Endometriotic lesions were induced in C57BL/6 mice by an intraperitoneal injection of endometrial fragments plus saline or endometrial fragments plus blood. Some endometrial fragments plus blood were injected with heparin, hirudin or tissue plasminogen activator (tPA). Endometriotic lesions on days 1, 3 and 5 were evaluated by gross and microscopic findings. Results The areas of endometriotic lesions in the blood group (6.4 ± 1.7 mm 2 ) were significantly larger than those in the saline group (0.5 ± 0.3 mm 2 ). The areas of endometriotic lesions were significantly reduced by the addition of heparin, hirudin or tPA. On day 1, endometriotic lesions in the blood group were observed on the peritoneum in five of the six mice. Endometriotic lesions on days 3 and 5 were significantly larger than those on day 1. On day 5, endometriotic lesions appeared cystic in all the mice. Conclusions Blood accelerates the early stage of development of endometriotic lesions when endometrial fragments plus blood are injected. Blood property might be involved in early endometrial–peritoneal interactions.