Purification and action sites of a follicle stimulating hormone inhibitor from bovine follicular fluid.

The purification and action sites of a follicle stimulating hormone (FSH) inhibitor obtained from bovine follicular fluid were examined. Bovine follicular fluid was salted out with ammonium sulfate as a concentration of 14.5 to 18.5%, and the salted out fraction was separated into two peaks by Sephadex G-200 column chromatography. The second peak, detectable as a single band by polyacrylamide gel disc electrophoresis, contained all the inhibitory activity to compensatory ovarian hypertrophy in mice. Serum FSH levels of unilaterally ovariectomized mice given injections of the inhibitor were lower than those of unilaterally ovariectomized mice given injections of saline. The inhibitor also suppressed FSH binding to granulosa cells in vitro. These results suggest that this inhibitor has two modes of action: suppression of FSH levels in serum and suppression of FSH binding to granulosa cells.