Comparative studies of the ethynyl estrogens used in oral contraceptives. III. Effect on plasma gonadotropins.

Twenty-one-day treatment cycles of ethynylestradiol or mestranol at dosages of 50 to 100 mug per day were administered to 191 normal volunteer women from six cycles, followed by six cycles of this estrogen treatment combined with 2.5 mg. of norethindrone acetate, 2 mg. of megestrol acetate, or 0.5 mg. of norgestrel. The drugs were prepared to insure uniform bioavailabiltiy. Plasma FSH and LH were determined by radioimmunoasay during the last week of medication intake in each cycle. In another study, a large number of blood samples were obtained at various times during the menstrual cycle from women using IUD's (as a control population) and from women who had been taking oral contraceptives regularly for 5 to 12 years. With the various estrogen treatments, the median FSH level showed no change at any estrogen dose at the end of the first cycle. From the second cycle on, a stable, dose-related fall was obtained with the 80 or 100 mug per day doses. The addition of any of the three progestins caused a prompt, stable, further fall in FSH level. By contrast, the median LH level rose in the first cycle with all estrogen regimens, and then fell progressively in a dose-related fashion in cycles 2 to 6. The addition of a progestational agent also caused a further prompt and stable fall in LH during cycles 7 to 12. Except for a minimal indication of greater LH suppression by ethynylestradiol as compared to mestranol at 50 mug per day, all other indices and dosages showed ethynylestradiol and mestranol to be essentially equipoten under these experimental conditions. Long-term administration of oral contraceptives produced a comparable degree of gonadotropin suppression. There was a suggestion of slightly less FSH suppression with agents using 50 to 75 mug per day of estrogen than from those with 100 mug per day. Both in normal controls (IUD cycles) and in cycles under chronic treatment with oral contraceptives, pulses of both FSH and LH were seen with some frequency, at times distant from the "periovulatory" period. The significance and origin of these random FSH and LH pulses is unknown.