PULSATILE LUTEINIZING-HORMONE SECRETION DURING THE 1ST AND THE 4TH CYCLE ON 2 DIFFERENT ORAL-CONTRACEPTIVES CONTAINING GESTODENE

Oral contraceptives inhibit ovarian follicular growth by suppressing t he release of gonadotropins from the pituitary. We studied basal and g onadotropin-releasing hormone-stimulated gonadotropin release, as well as pulsatile luteinizing hormone (LH) secretion, in ten healthy volun teers who had not used oral contraceptives before. Subjects received e ither a monophasic preparation containing 30 mug of ethinylestradiol a nd 75 mug of gestodene (group 1) or a triphasic formulation containing 30-40 mug of ethinylestradiol and 50, 70 and 100 mug of gestodene (gr oup 2). Blood sampling at 10-min intervals during 6-h periods was perf ormed on days 1, 8, 15 and 21 of both the first and fourth pill cycle. Thirteen healthy volunteers with regular ovulatory cycles served as n ormal controls. Both LH and follicle-stimulating hormone (FSH) were me asured by a sensitive immunoradiometric assay. Pulsatile LH secretion was observed in all oral contraceptive users. Mean serum LH and FSH le vels, number of pulses/6 h and the amplitude of LH pulses on day 1 in both the first and fourth pill cycle did not differ from early follicu lar phase controls in both groups. The FSH levels were suppressed rapi dly in both groups, even in first cycles, while LH serum levels progre ssively declined in all cycles studied. In both groups, amplitudes of LH pulses decreased from day 8 onwards, with a substantial number of l ow-amplitude pulses (< 0.75 U/l) interspersed between large-amplitude pulses. On day 1 of the fourth pill cycle a significant number of puls es were of low amplitude. These results confirm our earlier findings t hat pulsatile secretion of gonadotropins is maintained during oral con traceptive use but is profoundly modified by steroid feedback. There s eems to be no major difference in the suppression of the hypothalamic- pituitary axis in the first cycle on an oral contraceptive as compared to subsequent cycles.