Development of a two-site solid-phase immunochemiluminescent assay for measurement of dimeric inhibin-A in human serum and other biological fluids.

Inhibin is a heterodimeric glycoprotein that inhibits the secretion of follitropin from the pituitary and has been isolated in two distinct forms composed of a common alpha subunit and either a beta A or beta B subunit. Utilizing paired monoclonal antibodies specific to the alpha and beta A subunit, we have developed an immunochemiluminescent assay for dimeric inhibin-A. The assay is capable of quantifying free and bound inhibin-A in human serum and follicular fluid. The limit of detection is 10 ng/L. Related proteins exhibit little cross-reactivity or interference. Recovery is excellent. Whereas samples from men and postmenopausal women are near the detection limit of the assay, inhibin-A is higher in the luteal than the follicular phase of normally cycling women, 20-fold higher during in vitro fertilization treatment, and approximately 200-fold greater in pregnancy. The assay measures inhibin-A in follicular fluid from a variety of other species.