Ovarian and hormonal response of female goats to active immunization against inhibin M S Medan 1,2 , G Watanabe 1,3 , K Sasaki 4 , Y Nagura 5 , H Sakaime 5 , M Fujita 5 , S Sharawy 2 and K Taya 1,3 1 Laboratory of Veterinary Physiology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan 2 Department of Theriogenology, Faculty of Veterinary Medicine, Suez Canal University, Ismailia, Egypt 3 Department of Basic Veterinary Sciences, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan 4 Hitachi Ltd, Central Research Laboratory, Tokyo 185-8601, Japan 5 National Livestock Breeding Centre, Nagano Station, Nagano, Japan (Requests for offprints should be addressed to K Taya; Email: taya@cc.tuat.ac.jp) Abstract This study was conducted to evaluate the effect of active immunization against inhibin on hormonal levels and the ovulation rate in goats. Ten adult Shiba goats (Capra hircus) in two groups were used in this study. The first group was injected with inhibin vaccine (immunized, n =5) and the second group was injected with Freund’s adjuvant (con- trol, n =5) followed by three booster injections at 4-week intervals. After the third booster injection, three consecu- tive periods of oestrus were induced using prostaglandin F 2 at intervals of 11 days. Blood samples were collected at 2–6 h intervals and the ovaries were monitored using B-mode ultrasonography. All inhibin-immunized goats generated antibodies that bound 125 I-labelled bovine inhibin and their FSH concentrations were significantly higher than corresponding values in the control group. Also, inhibin-immunized goats had significantly higher preovulatory oestradiol-17 (P < 0·01) and higher concen- trations of progesterone in the luteal phase (P < 0·05). Immunization of goats against inhibin resulted in a signifi- cant (P < 0·01) increase in ovulation rate (control: 1·7 0·3 vs immunized: 7·6 1·1). These results demonstrate that active immunization against inhibin enhances ovarian follicular development and ovulation rate by promoting an increase in pituitary FSH secretion. Therefore, immunization against inhibin may be a useful alternative to the conventional approach of superovulation in goats. Journal of Endocrinology (2003) 177, 287–294 Introduction In domestic animals, the induction of multiple ovulations is possible by potentiating the stimulatory effects of the endogenous gonadotrophin by administering hormones with follicle-stimulating hormone (FSH)-like activity or by removing the inhibitory action of ovarian hormones on gonadotrophin release by the hypothalamus–pituitary axis. Considerable interest has been placed on inhibin, which by a synergistic action with oestradiol is involved in the negative feedback regulation of FSH at the anterior pituitary (Findlay & Clarke 1987, Findlay et al. 1992, Taya 1993, Taya & Watanabe 1999) thereby controlling ovulation rates. Purification and partial characterization of the inhibin molecule revealed that both inhibin forms (A and B) share a common -subunit, but different -subunits (Ling et al. 1985). Also, the -subunits were found to exist in dimeric forms (activins), often with opposite biological activity to inhibin (Ling et al. 1986, Vale et al. 1986). These observations suggest that the -subunit, but not the -subunit, could be suitable as an immunogen to neutralize the activity of both inhibin forms. Domestic and laboratory animals have been immunized against a variety of inhibin preparations, and increases in ovulation rate have been reported in mares (McCue et al. 1992), sheep (Mizumachi et al. 1990, Wrathall et al. 1990, 1992, Wheaton et al. 1992. Anderson et al. 1998), cattle (Glencross et al. 1994), goats (Dietrich et al. 1995, Hennies et al. 2001) and guinea pigs (Shi et al. 2000). Although most studies revealed that passive immunization against inhibin increased FSH levels (Campbell & Scaramuzzi 1995, Kusina et al. 1995, Akagi et al. 1997, Takedomi et al. 1997, Nambo et al. 1998, Shi et al. 1999), there were conflicting results about the effect of active immunization against inhibin on FSH secretion. The objective of this study was to determine the effect of active immunization against inhibin on gonadotrophins, oestradiol or progesterone secretion and ovulation rate in goats. 287 Journal of Endocrinology (2003) 177, 287–294 0022–0795/03/0177–287  2003 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology.org