Superovulation of ewes immunized against the human recombinant inhibin alpha-subunit associated with increased pre- and postovulatory follicle-stimulating hormone levels.

The efficacy and specificity of human recombinant inhibin alpha-subunit as an immunogen were determined by studying its effect on the ovulation rate and serum gonadotropin levels in ewes. Beginning on July 12 (day 1 of the experiment), 2-yr-old Rambouillet ewes were immunized four times at intervals of 20, 30, and 30 days, respectively, by im injections of the alpha-subunit each time with 100 micrograms. Blood was collected from the jugular vein as required before and after ovulation. Ovulation rates were determined, beginning on day 87, by laparotomy before estrous synchronization by means of vaginal progestagen sponges. After synchronization, ewes were examined again. The ovulation rate before estrous synchronization was over 4 times higher in immunized than control ewes [8.7 +/- (+/- SE) 1.9 vs. 2.0 +/- 0.0]. After estrous synchronization, ovulation rates in the immunized and control ewes were 6.3 +/- 2.4 and 1.3 +/- 0.3, respectively; this increase was accompanied by higher pre- and postovulatory FSH levels, but there was no change in the pattern of circulating LH. Furthermore, the postovulatory FSH surge persisted for longer periods of time in the immunized than control animals. These results demonstrate the potency of the human recombinant alpha-subunit as an immunogen and illustrate its specificity in suppressing the effects of endogenous inhibin. The results also point to inhibin as an important regulatory factor in controlling the ovulation rate by modulating both pre- and postovulatory FSH levels.