Abstract
It is recognised that ovarian factors, including steroid and protein hormones, are critical in the feedback regulation of pituitary gonadotropins; however, their individual contributions are less defined. The aim of this study was to explore the reciprocal relationships between ovarian and pituitary hormones across the normal ovulatory menstrual cycle as women age. FSH, LH, oestradiol, progesterone, inhibin A, inhibin B and anti-mullerian hormone (AMH) were measured in serum collected every 1-3 days across one interovulatory interval (IOI) from 26 healthy women aged 18-50 years. The antral follicle count (AFC) for follicles 2-5 mm, >6 mm and 2-10 mm were tabulated across the IOI. Independent associations between ovarian hormones/AFC vs pituitary follicle-stimulating hormone (FSH) and luteinising hormone (LH) were investigated using multivariate regression analysis. The data were sub-grouped based on the presence or absence luteal phase-dominant follicles (LPDF). Serum oestradiol and AMH were inversely correlated with FSH in both follicular and luteal phases. Inhibin B correlated inversely with FSH and LH in the late follicular phase and directly in the luteal phase. AFC, inhibin A and progesterone were not key predictors of either FSH or LH. The strong association between AMH and FSH with age implies that AMH, as well as oestradiol and inhibin B are important regulators of FSH. The change in feedback response of inhibin B with both FSH and LH across the cycle suggests two phases of the negative feedback.