Abstract: 46

FOLLICLE SELECTION IN GUINEA PIGS WITH ACTIVE IMMUNIZATION AGAINST INHIBIN -SUBUNIT IN OVULATION RATE.

F-X. Shi¹ , G. Watanabe¹ , A.L. Trewin² , R.J. Hutz² , C.G. Tsonis³ , K. Taya¹
Laboratory of Veterinary Physiology, Tokyo University of Agriculture and Technology, Japan. ¹
Department of Biological Sciences, University of Wisconsin-Milwaukee, U.S.A. ²
Biotech Australia. Pty Ltd, Australia. ³

In the guinea pig, only 2 to 4 follicles are ovulated in a typical estrous cycle. It is reported that inhibin is a important factor in the selection of dominant follicles. Our experiments were conducted to investigate the cellular localization of inhibin subunits in ovaries and to determine whether neutralizing endogenous inhibin would affect follicular development and ovulation rate in guinea pigs. The immunoreactivity of inhibin , A and B subunits was localized in the granulosa cells of some of healthy large follicles in each ovary throughout the cycle, and the number of stained follicles was in accordance with the number of offspring. The immunoreactivity of B was also localized in the granulosa cells of small antral follicles after ovulation. There were strongly and weakly stained follicles for inhibin , A and B subunits on Day 12. These results suggested that only dominant follicles were positively stained with inhibin and A subunits and confirmed the hypothesis that the follicular development of guinea pigs shows two waves. Eighteen female guinea pigs were given the subcutaneous injection of 1 ml placebo, 25 µg or 50 µg inhibin vaccine for 3 times at 4 week intervals. The results showed that inhibin vaccine increased the ovulation rate in a dose-dependent manner (placebo: 4.2±0.4; 25 µg inhibin vaccine: 6.2±0.9 (P<0.05); 50 µg inhibin vaccine: 9.8±0.9(P<0.01) without any effects on duration of the estrous cycle. The present study for the first time shows that the active immunization against inhibin may be a useful method to induce multiple ovulation in guinea pigs.

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