Regulation of human gonadotropins. XII. Increase in serum gonadotropins in response to estradiol.

Two potential but very different roles played by estradiol during the normal menstrual cycle were investigated: 1) the ability of estradiol to release pituitary luteinizing hormone; and 2) the possible role of estradiol as an inhibitor of follicular development. In the first study, five regularly cycling women were given estradiol benzoate (5 μg/kg) between days 2 and 6 of their menstrual cycle. Within 12 to 48 hours of the last estradiol injection, all subjects had a 2- to 4-fold elevation in serum LH concentrations but no significant rise in FSH concentration as compared to pretreatment levels. Eleven to fourteen days prior to menstruation there was a second surge of LH and a small FSH surge. Serum progesterone concentrations rose in four of the five subjects after the second but not the first LH surge. The elevation in serum LH concentrations following estradiol administration may have been a direct result of the increased estradiol concentrations or, alternatively, a consequence of the decline of this...