Mechanism of emergency contraception with gestrinone: a preliminary investigation

BackgroundA previous investigation showed that among 120 healthy women treated with a single oral dose of gestrinone for emergency contraception (EC), there was only one pregnancy. The effect of a single oral dose of gestrinone given for EC on ovarian function and endometrial development was studied.Study DesignHealthy fertile women were randomly assigned to Group A (n=8) or Group B (n=7). Gestrinone 5 mg was orally administered to each woman before (Group A) or after (Group B) ovulation. The day of ovulation was determined by transvaginal ultrasound and by urinary luteinizing hormone (LH) measured by enzyme immunoassay (One Step LH Ovulation Test). An endometrial biopsy was performed during implantation. Endometrial maturation and expression of markers of endometrial receptivity were analyzed. The tested markers were integrins α1β1, α4β1 and β3. Serum estradiol (E2) and progesterone (P) levels in serum were determined by radioimmunoassay, and estradiol receptors and progesterone receptors (PRs) in the endometrium were assessed by immunohistochemistry.ResultsGestrinone administered during the periovulatory period did not affect follicular development, ovulation, menstrual cycle length and E2 and P levels but decreased the expression of PR in the endometrium. Integrin α4β1 tended to increase after treatment with gestrinone without reaching statistical significance.ConclusionThe mode of action of gestrinone used for EC is probably inhibition of implantation by acting on the endometrium rather than inhibition of ovulation.