Abstract

It remains unclear how rapidly progesterone suppresses luteinizing hormone (LH) pulse frequency in women. Previous studies suggested that progesterone markedly increases LH pulse amplitude but does not slow LH pulse frequency within 10 h in estradiol‐pretreated women studied during the late follicular phase. However, this experimental paradigm may be a model of preovulatory physiology, and progesterone may have different effects at other times of the cycle. We studied regularly cycling, nonobese women without hyperandrogenism to assess the acute effect of progesterone during the midfollicular phase and in the absence of estradiol pretreatment. The study involved two admissions in separate cycles (cycle days 5–9). For each admission, either oral micronized progesterone (100 mg) or placebo was administered at 0900 h in a randomized, double‐blind fashion. Frequent blood sampling was performed between 0900 and 1900 h to define 10‐h LH pulsatility. Treatment crossover (placebo exchanged for progesterone and vice versa) occurred in a subsequent cycle. After an interim futility analysis, the study was halted after 7 women completed study. Mean progesterone concentrations after placebo and progesterone administration were 0.5 ± 0.1 (mean ± SD) and 6.7 ± 1.6 ng/mL, respectively. Compared to placebo, progesterone was not associated with a significant difference in 10‐h LH pulse frequency (0.79 ± 0.35 vs. 0.77 ± 0.28 pulses/h, P = 1.0) or amplitude (3.6 ± 2.8 vs. 4.3 ± 2.8 IU/L, P = 0.30). This study suggests that LH pulse frequency is not rapidly influenced by progesterone administration during the midfollicular phase.

Highlights

  • Gonadotropin-releasing hormone (GnRH) stimulates luteinizing hormone (LH) and follicle-stimulating hormone (FSH) synthesis and secretion

  • There was no significant difference in 10-h LH pulse frequency between progesterone and placebo admissions (0.77 Æ 0.28 and 0.79 Æ 0.35 pulses/h, respectively; P = 1.0; Fig. 2A and B)

  • The temporal progression of instantaneous LH pulse frequency over the sampling period did not differ between progesterone and placebo conditions: slopes were À0.0012 Æ 0.0358 (0.0094) and À0.0238 Æ 0.0759 (À0.0010) for the progesterone and placebo admissions, respectively (P = 1.0, Fig. 3)

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Summary

Introduction

Gonadotropin-releasing hormone (GnRH) stimulates luteinizing hormone (LH) and follicle-stimulating hormone (FSH) synthesis and secretion. High GnRH pulse frequencies favor LH secretion and low GnRH pulse frequencies favor FSH secretion (Wildt et al 1981; Gross et al 1987; Spratt et al 1987), and an ability to modulate GnRH pulse frequency appears to be important for the normal cyclic patterns of LH and FSH secretion (Cook et al 1991). Progesterone is the primary modulator of GnRH pulse frequency slowing in women. LH (and by inference GnRH) pulse frequency slows as progesterone increases in the luteal phase Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

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