Effect of peritoneal fluid from endometriosis patients on endometrial stromal cell proliferation in vitro

Late proliferative phase endometrial stromal cells grown in short-term culture were used as a model for the stromal component of endometriotic implants. Cells were grown in medium alone and in medium supplemented by 5, 10, and 20% concentrations of the cell-free fractions of peritoneal fluid obtained from patients with and without endometriosis. Nine fluid-sample pairs were matched based on the presence or absence of endometriosis at laparoscopy and the similarity of peritoneal fluid estradiol concentrations. Stromal cell proliferation as reflected by 3H-thymidine incorporation during sequential cell harvests over 72 hours was greater for cells exposed to endometriosis peritoneal fluid than for those exposed to non-endometriosis peritoneal fluid. This reached statistical significance with exposure to peritoneal fluid concentrations of 10 and 20% (P less than .05). A linear dose-response relationship between 3H-thymidine incorporation and peritoneal fluid concentration could be derived only for stromal cells exposed to fluid samples obtained from endometriosis patients (r = 0.51; P less than .001). In addition, proliferation over 72 hours was significantly greater for cells grown in 20% endometriosis peritoneal fluid than for those grown in nutrient medium alone (P less than .001). These data imply that factor(s) secreted into the peritoneal fluid of endometriosis patients may play a role in the proliferation or maintenance of disease implants.