THE ANTIPROGESTIN RU486 DELAYS THE MIDCYCLE GONADOTROPIN SURGE AND OVULATION IN GONADOTROPIN-RELEASING HORMONE-INDUCED CYCLES

Objective: To investigate whether the antiprogestin RU486 acts primari ly on the hypothalamus to delay the midcycle gonadotropin surge and th us gain insight into the site(s) of action of P in the control of ovul ation. Design: Prospective, crossover, single-blinded clinical study. Setting: Outpatient clinic in an academic research environment. Patien ts: Women with hypothalamic amenorrhea. Interventions: RU486 or a plac ebo was given orally at a low dose of 1 mg/d for 5 days, starting when the dominant follicle reached 14 to 16 mm, to women with hypothalamic amenorrhea undergoing ovulation induction with GnRH pulses of unvaryi ng frequency and dose. Blood samples and ovarian ultrasounds were obta ined daily in the late follicular phase and every 3 to 4 days in the r emainder of the cycle.