Effects of 0.5 mg. of lynestrenol daily on hypothalamic-pituitary-ovarian function.

This study was undertaken to investigate the effect of daily ingestion of 0.5 mg. of lynestrenol on some parameters of the hypothalamic-pituitary-ovarian axis. Daily plasma concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17-beta (estradiol; E2-17beta), and progesterone (P) were determined by specific radioimmunoassays during one control and one treatment cycle of seven normally ovulating women. One of the volunteers was followed throughout 84 days of treatment. The following changes were observed during medication: (1) the midcycle FSH/LH peak was abolished, with a trend toward reduced LH values during the second half of the treatment cycles; (2) progesterone was significantly, though variably, reduced whereas estradiol showed little difference between control and treatment cycles; (3) during prolonged treatment two difference cyclic response patterns were observed in the same individual. It is concluded that daily administration of 0.5 mg. of lynestrenol exerts a profound effect at the central level, which contributes to the satisfactory contraceptive efficacy of this compound. A hypothetic blockade of estradiol receptors at the pituitary and/or hypothalamic level is discussed.