Evidence of differential control of FSH and LH responses to GnRH by ovarian steroids in the luteal phase of the cycle
BACKGROUND: It is known that during the follicular phase of the cycle, estradiol sensitizes the pituitary to GnRH. The aim of this study was to determine the role of ovarian steroids in the control of GnRH-induced gonadotrophin secretion in the luteal phase of the cycle. METHODS: Eighteen normally cycling women were studied during the week following bilateral ovariectomy plus hysterectomy performed in early to mid-luteal phase. Six of the women received no hormonal treatment post-operatively (group 1, control), six received estradiol through skin patches (group 2) and the remaining six received estradiol plus progesterone (group 3). In all women the response at 30 min of LH (DeltaLH) and FSH (DeltaFSH) to GnRH (10 mug i.v.) was investigated on a daily basis. RESULTS: In group 1, serum FSH, LH and DeltaFSH values increased progressively following ovariectomy, while in groups 2 and 3 this increase was postponed or abolished. In contrast to DeltaFSH, DeltaLH values showed the same pattern of changes in all three groups with a significant decline up to post-operative day 4 and a gradual increase thereafter. CONCLUSIONS: These results demonstrate, for the first time, that in the early to mid-luteal phase of the cycle, estradiol and progesterone participate in the control of GnRH-induced FSH, but not LH, secretion. It is possible that in the luteal phase, the response of LH to GnRH is partly regulated by gonadotrophin surge attenuating factor.