Effect of immunization against the alpha N (alphaN) and alpha C (alphaC) peptides of the alpha43 subunit of inhibin on antral follicular growth and atresia and the patterns of gonadotrophin secretion in ewes.

The aims of this study were to investigate the role of inhibin in the distribution of healthy and atretic antral follicles and the secretion patterns of gonadotrophins. Ewes were actively immunized against either aN or αC of the inhibin a subunit with a primary injection and three booster injections. The control ewes received adjuvant only. The ovaries were removed either before or at 24 h after hCG administration in a synchronized follicular phase 48 h after removal of intravaginal progesterone pessaries. Morphological observations were made on every fifth section of the complete ovary (one per ewe) stained with haematoxylin and eosin. The mean number of corpora lutea observed per ewe with corpora lutea was not significantly different in ewes immunized against αN (2.4; aN-immunized ewes) or aC (2.6; aC-immunized ewes), and control (2.4) ewes, although some corpora lutea appeared cystic in the immunized ovaries. Compared with luteal phase concentrations, mean basal FSH concentrations in the early follicular phase were significantly increased in the aC-immunized ewes, similar in aN-immunized ewes and reduced in control ewes. No differences were observed in any of the LH parameters. Before hCG treatment, healthy antral follicles > 1 mm in diameter were not observed in any of the 52 follicles in the aC-immunized ewes and were observed in one of 37 follicles from aN-immunized ewes compared with 19 of 28 follicles in control ewes (P 6 mm in diameter) were observed in αN- and aC-immunized ewes either before or 24 h after hCG administration. Two newly formed corpora lutea from aC-immunized ovaries contained retained oocytes compared with none in control and αN-immunized ovaries. In conclusion, immunization against aN and aC may result in disruption of the normal processes of antral follicular growth and maturation independent of the concentrations of FSH and LH.