Pituitary-Ovarian Axis Responsivity to Prolonged Gonadotropin-Releasing Hormone Infusion in Normal and Hyperprolactinemic Women*

The integrity of the pituitary-ovarian axis was investigated in seven women with elevated PRL levels and amenorrhea and in four women with normoprolactinemic amenorrhea by infusinggonadotropin-releasing hormone (GnRH) (1μg/min) for 8 h. LH, FSH, and estradiol measurements were obtained serially. The hormonal responses were compared to those observed in five age-matched women with normal menstrual function during days 4–6 of their cycles. The LHresponse was biphasic in all of the women with a normal readily releasable pool (0–1 h). However, the second phase of LHsecretion (1–8 h) was diminished by 30% [hyperprolactinemic women,12,332 ± 1,060 (SE) mIU/ml·7 h,vs. control, 18,051 ± 1,958; P < 0.05] in six of the seven hyperprolactinemic women. The LH responsesin the women with normoprolactinemic amenorrhea were similar to those in control women. Both the pattern and amount of FSH secreted were comparable in all subjects. In the three groups,basalestradiol levels had increased significantly by 6 h and were the same in all groups at the conclusionof the GnRH infusion, representing an increase of 151–226% above the basal level.Thus, the normality in estrogen responses occurred regardless of the pattern of LH reserve. These data indicate that 1) GnRH is a useful tool for determining the integrity of the pituitary-ovarianaxis, 2) hyperprolactinemia reduces LH reserve in the majority of hyperprolactinemic women, and 3)despite diminished LH reserve, estrogen secretion remains normal. We conclude that PRLis not a significant factor in altering ovarian responsiveness to endogenous gonadotropin stimulation.