EFFECT OF THE ANTIPROGESTIN ONAPRISTONE ON FOLLICULAR-GROWTH IN WOMEN

The effects of the antiprogestin onapristone on the menstrual cycle we re assessed in surgically sterilized volunteer women. The steroid was given orally at the dose of 5, 15 or 50 mg/day, from day 5 to day 11 o f the cycle. Ovarian ultrasonography and hormonal determinations in pl asma and urine were used to monitor the pre-treatment, treated and pos t-treatment cycles. Onapristone, given at a dose of 5 mg/day, affected follicular growth inconsistently. The dose of 15 or 50 mg/day arreste d follicular growth and oestradiol increase and delayed gonadotrophin surge, extending the length of the follicular phase in five of seven w omen in each group. After discontinuation of treatment the leading fol licle resumed its growth and ovulation occurred as judged by the eleva tion of plasma progesterone, preceded in most but not all cases by an echographic image of follicular collapse. The ensuing luteal phases we re not significantly altered in length or plasma progesterone concentr ation. Cortisol concentrations were unaffected and no serious side-eff ects were recorded. The antifolliculotrophic effect of onapristone dem onstrated here, together with previous reports of similar activity of mifepristone in women, indicate that this may be a general property of compounds that interfere with progesterone receptor function.