Patterns of Serum LH and FSH in Response to 4-Hour Infusions of Luteinizing Hormone Releasing Hormone in Normal Women during Menstrual Cycle, on Oral Contraceptives, and in Postmenopausal State*†

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Abstract
Infusions of 1 µg/min of LHRH for 4 h were administered to 17 normal premenopausal women at various phases of the menstrual cycle, to 4 women on oral contraceptive tablets, and to 3 normal postmenopausal women. A biphasic response of serum LH was observed in the follicular and luteal phases although the response was much larger in the latter. The initial LH peak occurred 15–45 min after the start of the infusion following which LH levels plateaued or declined, rising subsequently for the remainder of the infusion. In all 9 women studied during the periovulatory phase, the largest response of LH was observed, which in some women was not biphasic and could not be maintained despite continuation of the infusion of LHRH; in others, an augmented biphasic pattern was present whereas in the two women with the highest progesterone levels studied in the periovulatory phase, the response was indistinguishable from the mid-luteal phase response. Women on combined oral contraceptive medication studied between days 11–14 of their cycle showed a biphasic response intermediate in magnitude between follicular and luteal phases with some blunting of the initial phase of secretion. The response of serum FSH was not clearly biphasic but was greatest in the periovulatory phase, intermediate in the luteal phase, and least in the follicular phase. In the periovulatory phase, the FSH response closely patterned that seen for LH. In postmenopausal women, the total output of LH by the pituitary gland was similar to the luteal phase and the output of FSH was equivalent to that seen at mid-cycle. The results support the concept that the biphasic response to LH to the prolonged infusion of LHRH is present in women and that its magnitude and characteristics are probably modulated by the levels of estradiol and progesterone. (J Clin Endocrinol Metab46: 227, 1978)

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