Determination of follicle regulatory protein levels in urine during the normal menstrual cycle using an enzyme-linked immunosorbant assay

A protein from follicular fluid [referred to as follicle regulatory protein (FRP)] which inhibits aromatase activity in granulosa cells was recently isolated and partially characterized. The purified FRP was used to produce a monoclonal antibody which was used to develop an enzyme-linked immunosorbant assay suitable for quantitation of FRP in urine. Twelve normal premenopausal women underwent daily collection of blood and first morning urine samples, beginning on the 1st day of menses, as well as daily ultrasonographic evaluation of follicular diameter, beginning on the 10th day of the menstrual cycle, until the onset of the next menses. Serum estradiol, progesterone, LH, and FSH levels were determined by RIA. Urinary FRP levels increased in the midfollicular phase, reached their zenith in the midluteal phase [mean, 0.38 ± 0.03 (±se) immunoreactive units; 1 immunoreactive unit = ∼1 ng FRP/mL·mg creatinine], and then declined to reach their nadir (not detectable) during the early follicular phase. Immunohistochemical evaluation of ovarian tissue demonstrated that anti-FRP localized to mural granulosa cells in viable follicles, to all follicular epithelial cells in atretic follicles, and to the large cells of the corpus luteum. These findings indicate that immunoreactive FRP levels in urine change during the menstrual cycle and suggest a relationship among FRP, follicular maturation, and corpus luteum formation.