Purpose: Immunoreactive inhibin (i-inhibin) has been reported to be present in the peritoneal fluid of women. The radioimmunoassay employed measures free, biologically inactive alpha-subunits(s) equally as well as dimeric, biologically active inhibin. The present study was designed to determine if biologically active, dimeric inhibin is present in the peritoneal fluid of women.
Methods: Peritoneal fluid of four women was assayed by radioimmunoassay, a sheep pituitary bioassay, and two ELISA procedures which utilized specific monoclonal antibodies for the "capture" of the alpha-subunit (ELISA-A) or the beta-subunit (ELISA-B) of inhibin and subsequent quantification of dimeric inhibin-A.
Results: There was a good correlation between the values obtained by radioimmunoassay, bioassay, and both ELISAs; two samples (from the late follicular phase) with relatively high i-inhibin concentrations were positive in all four assays, whereas two samples (from the early follicular phase) with very low i-inhibin concentrations were negative in the bioassay and ELISAs.
Conclusion: A significant portion of the immunoreactive inhibin in the peritoneal fluid obtained during the late follicular phase of women is dimeric, biologically active inhibin. We speculate that this may have potential implications for oocyte maturation and early embryogenesis within the oviduct.