Endometriosis: role of ovarian steroids in initiation, maintenance, and suppression

Although endometriosis is commonly associated with infertility, the hormonal requirements for its spontaneous initiation and maintenance remain unknown. Since endometriosis occurs in the monkey, these primates are useful for examining the hormonal dependencies of endometrial plaques. Sequential estradiol and progesterone in Silastic capsules were placed subcutaneously into long-term castrated monkeys (N = 26). Blood samples obtained biweekly were assayed for progesterone and estradiol by radioimmunoassay. Three weeks later, endometriectomies were performed and the minced endometrium was "seeded" into the peritoneal cavity. Thereafter, monkeys were divided into four groups: (1) control, received no therapy; (2) received only estradiol capsules; (3) received only progesterone capsules; and (4) received both estradiol and progesterone capsules. All monkeys underwent laparotomy 4, 12, and 16 weeks after endometrial transplantation to determine whether viable endometrial plaques were present. After 4 weeks, endometriosis was found in all groups, including the controls. At 12 and 16 weeks, monkeys treated with both estradiol and/or progesterone contained viable endometrial plaques, whereas monkeys without steroid supplementation contained only "burnt out" plaques, that is, nonviable endometrial tissue. In conclusion, endometrial tissue transplanted into the peritoneum required no steroid supplementation for initiation. However, once implanted, either estradiol or progesterone, alone or in combination, was required for maintenance. These findings suggest that successful treatment of endometriosis may require both the eradication of existing endometrial plaques and the prevention of reseeding over the peritoneum resulting from retrograde menstruation.