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Oral contraceptives inhibit ovarian follicular growth by suppressing the release of gonadotropins from the pituitary. We studied basal and gonadotropin-releasing hormone-stimulated gonadotropin release, as well as pulsatile luteinizing hormone (LH) secretion, in ten healthy volunteers who had not used oral contraceptives before. Subjects received either a monophasic preparation containing 30 micrograms of ethinylestradiol and 75 micrograms of gestodene (group 1) or a triphasic formulation containing 30-40 micrograms of ethinylestradiol and 50, 70 and 100 micrograms of gestodene (group 2). Blood sampling at 10-min intervals during 6-h periods was performed on days 1, 8, 15 and 21 of both the first and fourth pill cycle. Thirteen healthy volunteers with regular ovulatory cycles served as normal controls. Both LH and follicle-stimulating hormone (FSH) were measured by a sensitive immunoradiometric assay. Pulsatile LH secretion was observed in all oral contraceptive users. Mean serum LH and FSH levels, 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 follicular phase controls in both groups. The FSH levels were suppressed rapidly in both groups, even in first cycles, while LH serum levels progressively declined in all cycles studied. In both groups, amplitudes of LH pulses decreased from day 8 onwards, with a substantial number of low-amplitude pulses (< 0.75 U/l) interspersed between large-amplitude pulses. On day 1 of the fourth pill cycle a significant number of pulses were of low amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)