Single monthly administration of the anti-progestagen Org 31710 in users of the 75 mu g desogestrel progestagen-only pill: effects on pituitary-ovarian activity

Endocrine and ultrasound effects were studied of an intermittent (every 28 days) oral administration of 150 mg of the anti-progestagen Org 31710 durin g the continued daily use of 75 mu g desogestrel (DSG) for progestagen-only contraception. A randomized, double-blind, placebo-controlled two-centre s tudy was conducted in 50 healthy volunteers. Serum luteinizing hormone (LH) , follicle stimulating hormone (FSH), oestradiol and progesterone concentra tions, and follicle number and size were studied, as well as endometrial th ickness, which was assessed by transvaginal sonography at least twice weekl y during a single medication cycle (cycle 3-5), Forty-eight women were eval uated (Org 31710, n = 25; placebo, n = 23), Seven ovulations were observed in the treated group versus none in the placebo group. LH concentrations we re higher on days 9 and 11 and oestradiol concentrations lower on day 3 in the treated group, irrespective of whether ovulation occurred, No parameter could predict ovulation, Endometrial thickness was greater on cycle days 7 -13 and 19 in the treated group, However,within the Org 31710 group, no sig nificant differences were found in volunteers who did or did not ovulate, O bserved differences may be attributed to a competitive effect of Org 31710 with progestagen-induced suppression of the pituitary-ovarian axis, altered oestradiol feedback mechanisms, and/or altered receptor availability.