Pregnancy-associated plasma protein-A and placental protein 5 in human ovarian follicular fluid

By sensitive and specific radioimmunoassays PAPP-A and PP5 were detected in follicular aspirates obtained from women undergoing ovarian hyperstimulation for oocyte harvest prior to in vitro fertilization and embryo transfer. Follicular and pregnancy-derived PAPP-A were immunologically and physicochemically indistinguishable. Similarly, pregnancy- and nonpregnancy-derived PP5 were immunologically indistinguishable. However, in addition to the 18- and 36-K species, a larger species having a molecular size greater than 140K was found in the follicular fluid. Mean follicular PAPP-A and PP5 concentrations were 727 mIU/L and 1376 mAU/L, respectively, with no significant correlation between follicular PAPP-A, PP5, and steroid concentrations. There was, however, a significant but negative relationship with follicular volume. Preliminary in vitro studies indicated that both proteins were synthesized by granulosa cells in preparation for follicular rupture. Follicular PP5, like antithrombin III, interacted reversibly with heparin and thrombin affinity matrices, suggesting a potential biological role as a follicular anticoagulant, whereas PAPP-A, a specific and potent inhibitor of leukocyte elastase, contributes to the maintenance of proteolytic homeostasis and the protection of spermatozoa and embryo against proteolytic attack originating from the maternal leukocytes.