Size and spatial orientation of uterine tissue transplants on the peritoneum crucially determine the growth and cyst formation of endometriosis-like lesions in mice.

BACKGROUND In many studies in rodents, intraperitoneal endometriosis-like lesions are surgically induced by syngeneic or autologous transplantation of uterine tissue samples, which are sutured to the abdominal wall. However, until now the surgical techniques have not been standardized, and we address this issue here. METHODS Uterine tissue samples were transplanted to the peritoneum of C57BL/6 mice (four study groups, n = 7 each). Using non-invasive high-resolution ultrasound imaging over a period of 4 weeks, we analyzed growth characteristics and cyst formation of the endometriosis-like lesions which developed, in relation to mode of transplantation (syngeneic versus autologous), type of tissue fixed adjacent to the peritoneum (endometrium versus perimetrium), and size of tissue transplanted (2 versus 3 mm). Immunohistochemical analysis was also performed. RESULTS When the perimetrium, with underlying myometrium, was sutured next to the host peritoneum the endometriosis-like lesions which developed exhibited a higher growth rate (P< 0.05 versus endometrium), and contained more proliferating cell nuclear antigen (PCNA)-positive cells and an increased microvessel density (both P< 0.05 versus endometrium). In the group with 3 mm uterine tissue grafts, lesion growth was significantly decreased when compared with 2 mm samples (P< 0.05). However, the larger grafts developed more cysts throughout the observation period than the smaller ones. There was no difference between syngeneic and autologous endometriosis-like lesions. CONCLUSIONS Our study demonstrates that size and spatial orientation of peritoneally fixed uterine tissue samples crucially determine growth and cyst formation of endometriotic lesions in mice. These findings should improve the standardization and reliability of future studies, performed in the frequently used mouse model of surgically induced endometriosis.