[The effects of dopamine agonist (bromocriptine) on the secretion of pituitary gonadotropins and ovarian sex steroids in normally cycling women].

To investigate the effects of bromocriptine on the secretion mechanism of pituitary gonadotropins and ovarian sex steroids, 5 mg of bromocriptine was administered to four normally cycling women in the follicular, pre-ovulatory, mid-luteal or menstrual phase, respectively. Blood samplings were taken from two hours before until six hours after the administration every 15 min. by an intravenous indwelling catheter. Serum FSH, LH, prolactin, estradiol and progesterone were determined by RIA, and the changes of basal levels and the pulsatile patterns of these hormones were analysed in each of the four phases. Serum prolactin levels decreased significantly (p less than 0.005) from two hours after the administration of bromocriptine and remained in a very low range in all phases of the cycles until the end of the experiments. The basal levels of FSH showed a significant decrease in the pre-ovulatory and mid-luteal phases two to six hours after the administration (p less than 0.025 approximately p less than 0.005). Also the basal levels of LH showed a significant decrease in the follicular, pre-ovulatory and mid-luteal phases two to six hours after the administration (p less than 0.05 approximately p less than 0.005). However, no significant change was observed in the amplitude or the frequency of the pulsatile patterns of FSH and LH in all phases of the menstrual cycles. The serum levels of estradiol did not show marked changes by the administration of bromocriptine, but the serum levels of progesterone were significantly decreased in the mid-luteal phase two to six hours after the administration (p less than 0.005). These facts suggest that bromocriptine acts mainly on the pituitary rather than the hypothalamus to decrease the serum levels of gonadotropins, and also may have some role in the steroidogenesis of the ovary.