Effect of immunization against the alpha N (alpha N) and alpha C (alpha C)peptides of the alpha(43) 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 distr ibution of healthy and atretic antral follicles and the secretion patterns of gonadotrophins. Ewes were actively immunized against either alphaN or al phaC of the inhibin cu subunit with a primary injection and three booster i njections. The control ewes received adjuvant only. The ovaries were remove d either before or at 24 h after hCG administration in a synchronized folli cular phase 48 h after removal of intravaginal progesterone pessaries. Morp hological observations were made on every fifth section of the complete ova ry (one per ewe) stained with haematoxylin and eosin. The mean number of co rpora lutea observed per ewe with corpora lutea was not significantly diffe rent in ewes immunized against alphaN (2.4; alphaN-immunized ewes) or alpha C (2.6; alphaC-immunized ewes), and control (2.4) ewes, although some corpo ra lutea appeared cystic in the immunized ovaries. Compared with luteal pha se concentrations, mean basal FSH concentrations in the early follicular ph ase were significantly increased in the alphaC-immunized ewes, similar in a lphaN-immunized ewes and reduced in control ewes. No differences were obser ved in any of the LH parameters. Before hCG treatment, healthy antral folli cles > 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 alphaN-imm unized ewes compared with 19 of 28 follicles in control ewes (P < 0.0001). For healthy antral follicles < 1 mm in diameter, there were 72 of 85 follic les in the <alpha>C-immunized ewes, 79 of 81 follicles in the alphaN-immuni zed ewes and 81 of 82 follicles in the control ewes. Similar results were o btained in healthy antral follicles < 1 mm in diameter at 24 h after hCG ad ministration. In contrast to the control ewes, no healthy preovulatory foll icles (> 6 mm in diameter) were observed in alphaN- and alphaC-immunized ew es either before or 24 h after hCG administration. Two newly formed corpora lutea from alphaC-immunized ovaries contained retained oocytes compared wi th none in control and alphaN-immunized ovaries. In conclusion, immunizatio n against alphaN and alphaC may result in disruption of the normal processe s of antral follicular growth and maturation independent of the concentrati ons of FSH and LH.