This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The luteal phase of the menstrual cycle is marked by high estradiol (E2) and progesterone (P) levels and a slow luteinizing hormone (LH) pulse frequency. E2 and P levels fall during the luteal-follicular transition, which allows dramatic increases in LH pulse frequency. Studies suggest that P is the principal effector of LH pulse frequency slowing. However, a previous study showed that maintaining E2 levels for 3 weeks after withdrawal of P results in a delayed and prolonged recovery of LH pulse frequency, consistent with E2 enhancing inhibition by low levels of P. We hypothesize that the P antagonist mifepristone, given immediately after P withdrawal, will result in rapid and dramatic increases in LH pulse frequency despite maintenance of E2 levels. Studies will be performed in normal volunteers with regular cycles.
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