Suppression of ovine plasma FSH by bovine follicular fluid: neutralization by plasma from ewes immunized against an inhibin-enriched preparation from bovine follicular fluid.

Adult Merino ewes were immunized against an inhibin-enriched preparation (bFFI) obtained by affinity chromatography of bovine follicular fluid (bFF). Plasma was obtained in early luteal phase from these ewes and from control ewes immunized against bovine serum albumin. Ten months after ovariectomy the plasma concentration of FSH, but not LH, in control ewes was decreased by four s.c. injections of 8 ml bFFI (17,500 units inhibin/injection). There was no decrease in plasma concentrations of FSH or LH in immunized ewes with the same dose of bFFI. In a second study with long-term ovariectomized ewes, four injections of 20 ml plasma from the immunized ewes significantly reduced the decrease in FSH concentration caused by four injections of steroid-free bFF (2500 units inhibin/injection) in comparison with similar ewes injected with plasma from control ewes. These results show that the plasma of ewes immunized against bFFI contains substances, presumably antibodies, which neutralize the FSH-suppressive effects of bFF and bFFI in ovariectomized ewes.