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

Abstract

The integrity of the pituitary-ovarian axis was investigated in 7 women with elevated PRL [prolactin] levels and amenorrhea and in 4 women with normoprolactinemic amenorrhea by infusing gonadotropin-releasing hormone (gonadoliberin, GnRH) (1 .mu.g/min) for 8 h. LH [lutropin], FSH [follitropin] and estradiol measurements were obtained serially. The hormonal responses were compared to those observed in 5 age-matched women with normal menstrual function during days 4-6 of their cycles. The LH response was biphasic in all of the women with a normal readily releasable pool (0-1 h). The 2nd phase of LH secretion (1-8 h) was diminished by 30% [hyperprolactinemic women, 12,332 .+-. 1060 (SE) mIU/ml per 7 h, vs. control, 18,051 .+-. 1958; P < 0.05] in 6 of the 7 hyperprolactinemic women. The LH responses in 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 3 groups, basal estradiol levels had increased significantly by 6 h and were the same in all groups at the conclusion of 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. GnRH apparently is a useful tool for determining the integrity of the pituitary-ovarian axis; hyperprolactinemia reduces LH reserve in the majority of hyperprolactinemic women and despite diminished LH reserve, estrogen secretion remains normal. PRL apparently is not a significant factor in altering ovarian responsiveness to endogenous gonadotropin stimulation.