Influence of oral contraceptives on integrated secretion of gonadotropins

The mechanism of action of various oral contraceptives has not yet been satisfactorily resolved, as to how gonadotropins affect ovarian function. Alterations of the pulsatile release of LH might be a common denominator. As methodological difficulties for the evaluation of LH pulse pattern with low basal levels exist, we elected to determine the area under the curve (AUC) for LH and FSH for 6 hours before and during treatment with oral contraceptives. LH and FSH were determined every 15 min for 6 hours on day 4 and day 20 of a control cycle and a treatment cycle in 22 women with ovulatory cycles. They received either a combined preparation containing 150 micrograms desogestrel and 30 micrograms ethinyl estradiol, a sequential preparation containing 50 micrograms of ethinyl estradiol and 125 g of desogestrel or only 125 micrograms desogestrel. There was no difference between the sum of LH pulses on day 4 and day 20 of the control cycle. The AUC for FSH was lower on day 20. When the combined preparation was taken, FSH was suppressed on day 4, and FSH and LH on day 20 of treatment. The degree of suppression was even more pronounced when the sequential OC was taken. Ethinyl estradiol alone was as effective as the combination with desogestrel. Desogestrel alone inhibited ovulation without affecting serum LH and FSH in a comparable manner, suggesting a direct effect on the ovary. The determination of the AUC seems to be a sensitive tool for the evaluation of OC-induced changes in gonadotropin output.