Mode of action of dl-norgestrel and ethinylestradiol combination in postcoital contraception. III. Effect of preovulatory administration following the luteinizing hormone surge on ovarian steroidogenesis

A combination of 1.0mg dl-norgestrel and 0.1mg ethinylestradiol was administered orally at 18 hours after the detection of luteinizing hormone rise and again at 30 hours in five healthy volunteers with normal menstrual cycles. The effects on ovarian function were studied by comparing the daily serum levels of progesterone (P), 17α-hydroxyprogesterone, and estradiol (E2) measured in a control (placebo) cycle with those in two consecutive treatment cycles. Treatment did not alter the steroid levels in one subject. P was suppressed in one or both treatment cycles of four subjects. E2 was suppressed in both treatment cycles of one subject and produced widely fluctuating patterns in another. The hormonal patterns in the two consecutive treatment cycles of the same individual were similar in all but one instance, where only the P level in the second treatment cycle was diminished. These results showed that this treatment can elicit steroidogenic responses of varying degrees and duration. The contraceptive action may lie in the altered P and/or E2 level at certain points in the menstrual cycle.