Pulsatile luteinizing hormone secretion during the first and the fourth cycle on two different oral contraceptives containing gestodene.

Oral contraceptives (OCs) inhibit ovarian follicular growth by suppressing the release of gonadotropins from the pituitary. The authors studied basal and gonadotropin-releasing hormone-stimulated gonadotropin release as well as pulsatile luteinizing hormone (LH) secretion in 10 healthy volunteers who had not used OCs before. Subjects received either a monophasic preparation containing 30 mcg of ethinyl estradiol and 75 mcg of gestodene (group 1) or a triphasic formulation containing 30-40 mcg of ethinyl estradiol and 50 70 and 100 mcg of gestodene (group 2). Blood sampling at 10-minute intervals during 6-hour periods was performed on days 1 8 15 and 21 of both the first and fourth pill cycle. 13 healthy volunteers with regulatory 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 OC users. Mean serum LH and FSH levels number of pulses/6 hours 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. These results confirm our earlier findings that pulsatile secretion of gonadotropins is maintained during OC use but is profoundly modified by steroid feedback. There seems to be no major difference in the suppression of the hypothalamic-pituitary axis in the first cycle on an OC as compared to subsequent cycles. (authors)