Variation in circulating antimüllerian hormone precursor during the periovulatory and acute postovulatory phases of the human ovarian cycle

Objective To determine whether the relative quantity of circulating AMH precursor (proAMH) declines relative to levels of the active form (AMH N,C ) in the periovulatory phase of the ovarian cycle. Design Longitudinal study. Setting Local community. Patient(s) Sixteen women aged between 18 to 30 years with regular menstrual cycles between 25 to 35 days long. Intervention(s) None. Main Outcome Measure(s) Serum concentrations of proAMH and total AMH (proAMH and AMH N,C combined) measured by immunoassay, with relative levels of proAMH expressed as the AMH prohormone index (API = [ProAMH]/[Total AMH] × 100). Result(s) The mean API in the 11 eligible women fell from 20.7 during the luteinizing hormone (LH) surge period to 18.7 during the acute postsurge period. No statistically significant differences in the API were observed among samples taken at single time points in the early follicular, midfollicular, midluteal, and late luteal phases. Conclusion(s) This study suggests that activation of AMH by proteolytic enzymes is largely stable throughout the ovarian cycle. However, there is a subtle but robust decrease in the level of proAMH relative to AMH N,C in the acute postovulatory period. This may indicate that periovulatory increases in prohormone convertases cause increases in proAMH cleavage rates. Alternatively, rapid changes in the hierarchy of follicle developmental stages during ovulation may result in changes in the relative ratios of proAMH and AMH N,C .