EFFECTS OF ESTROGEN, PROGESTERONE, AND METHOXYCHLOR ON SURGICALLY INDUCED ENDOMETRIOSIS IN RATS

Endometriosis is a disease of women where endometrial tissue is found growing at ectopic sites. While evidence suggesting a role for the ova rian hormones in endometriosis exists, no complete studies of the role s of estrogen and progesterone have heretofore been performed. Also, i f estrogen has a role in the growth and/or maintenance of endometriosi s, it is likely that the proestrogenic pesticide, methoxychlor (MXC), might also have such an effect. Sixty rats underwent surgery on Day 0 to induce endometriosis. On Day 21, all rats were ovariectomized. Duri ng surgery, the diameters of all endometriotic implants (which were fu lly developed) were measured. Starting on Day 21, groups of rats were treated daily, for 3 weeks, with (a) vehicle; (b) estrone, 1 mu g/rat, E; (c) progesterone, 2 mg/rat, P; (d) E + P, 1 mu g + 2 mg; (e) MXC, 250 mg/kg; or (f) MXC + P, 250 mg/kg + 2 mg/rat. On Day 42, all rats w ere killed, and the diameters of all endometriotic sites were measured . While no differences in diameter were found across groups prior to o variectomy, ovariectomy plus treatment altered the growth of endometri otic tissue. Progesterone and vehicle treatments produced results that were identical: regression of endometriotic sites. Both estrogen and MXC treatments maintained endometriotic site size at a level greater t han that in the vehicle-treated group. The combination of progesterone with either estrone or MXC did not alter the effect of either chemica l. We conclude that while estrogen promotes the growth of endometriosi s, progesterone either produces regression or fails to maintain the si tes. MXC, at a relatively high dose, supports the development of endom etriosis. Concurrent progesterone treatment does not modulate the effe cts of estrone or MXC. These results suggest that exposure of women to high doses of MXC may exacerbate the development of endometriosis or contribute to its recurrence. (C) 1995 Society of Toxicology