EFFECTS OF RALOXIFENE IN A GUINEA-PIG MODEL FOR LEIOMYOMAS

OBJECTIVE: Chronic exposure of oophorectomized guinea pigs to 17 beta- estradiol causes leiomyoma formation. Our aims were to determine wheth er these leiomyomas can become estradiol independent after exposure to estradiol and ii raloxifene inhibits leiomyoma growth when given conc omitantly with estradiol. STUDY DESIGN: To induce leiomyoma developmen t, 6 oophorectomized animals received two estradiol implants for 140 d ays. Next, the estradiol implants were replaced with empty implants in 3 animals, whereas the other 3 received 2 new estradiol implants and raloxifene given per os 10 mg/kg per day for 60 days. Tumor size was m onitored biweekly by ultrasonography. RESULTS: On estradiol removal, a bdominal wall leiomyomas regressed within 15 to 30 days; when estradio l implants were reintroduced, leiomyomas redeveloped. Within 30 days o n raloxifene, all abdominal leiomyomas (n = 9) regressed as determined by ultrasonography and verified at laparotomy. Serum raloxifene and e stradiol levels were 432 +/- 46 pg/mL and 78 +/- 13 pg/mL (mean +/- SE M, n = 3), respectively, after 60 days of treatment. CONCLUSIONS: Leio myomas did not become estradiol independent, even after long exposure to estradiol; ultrasonography allowed frequent, noninvasive assessment of leiomyoma site, and raloxifene rapidly regressed leiomyomas in thi s animal model.