4.5. Endometriosis Induction

Endometriosis was induced in adult female recipient rats using a protocol based on the menstruating mouse model of Greaves et al. [9]. Briefly, menstrual endometrial tissue from the donor’s decidualized horns (cultivated via the MRM) was separated from the myometrium and finely minced using scissors (size of the pieces < 18 G). Any individual variability was minimized by pooling the tissue together in saline, before dividing the tissue into different syringes. In general, a single uterine horn was used to induce endometriosis in one recipient rat. Approximately 400 mg wet weight tissue/0.6 mL saline was injected i.p. in each recipient rat using a 16 G catheter. Note that the recipient rats were given high estradiol-17β (500 ng/100 µL peanut oil) two consecutive days beforehand to synchronize the estrus cycle (Figure 3A). Twelve weeks after the inoculation, recipient rats were sacrificed and the presence of endometriosis was assessed. Lesions were fixed in 4% PFA for histologic analysis. SHAM animals received an i.p. injection of 0.6 mL saline.