Production of activin-binding protein by rat granulosa cells in vitro.

We have developed an assay method for activin-binding protein, which exploits its high affinity for sulfated polysaccharides. We used this method to investigate the production of activin-binding protein by rat ovarian granulosa cells, in vitro. The production of activin-binding protein by granulosa cells was dependent on the cell density; the maximum was observed at 6 x 10(5) cells/ml. Follicle-stimulating hormone (FSH), but not luteinizing hormone (LH), enhanced production significantly. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and ligand blotting analyses of the activin-binding protein secreted by rat granulosa cells demonstrated it was the same protein molecule as that purified from rat ovaries. It is inferred from these results that the granulosa cell is a source of ovarian activin-binding protein and that its secretion is regulated by FSH.