EFFECT OF IMMUNIZATION AGAINST THE AMINO-TERMINAL PEPTIDE (ALPHA-N) OF THE ALPHA(43)-SUBUNIT OF INHIBIN ON FOLLICULAR ATRESIA AND EXPRESSION OF TISSUE INHIBITOR OF MATRIX METALLOPROTEINASE (TIMP-1) IN OVARIAN FOLLICLES OF SHEEP

Ewes actively immunized against alpha N, the N-terminal peptide of inh ibin a,precursor, have lowered fertility associated with ovulation fai lure, restricted tissue remodelling and reduced matrix metalloproteina se-2 activity in the follicular fluid at the time of expected ovulatio n. This could be due to altered ratios of matrix metalloproteinase-2 a nd tissue inhibitor of matrix metalloproteinase (TIMP-1), or to the on set of atresia in antral follicles destined to ovulate. The objectives of the present study were to investigate the effects of immunization against aN on the localization of TIMP-1 in ovine follicles, and on fo llicular growth and atresia in the follicular phase. Ewes were either immunized against aN or remained as controls and the ovaries were remo ved before (0, n = 4) and at 12 h (n = 4) and 24 h (n = 4) after hCG a dministration in a synchronized follicular phase, 48 h after removal o f intravaginal pessaries. Observations were made on a single section t aken through the largest follicle present in the ovaries of each ewe. There were no healthy antral follicles > 1 mm in immunized ovaries (0/ 29) compared with controls (16/31) (P < 0.001), whereas the proportion of healthy antral follicles < 1 mm was the same in each group (9/19 v ersus 5/12). TIMP-1 immunoactivity was localized in large luteal cells , smooth muscle and endothelial cells, and in all antral follicles, in cluding oocytes. At the time of hCG administration, no TIMP-1 immunore activity was detected in the apical region of the follicular wall of l arge follicles (> 6 mm) compared with the rest of the follicle wall, b ut staining appeared in the apical granulosa layer 24h later. In newly formed corpora lutea, TIMP-1 expression was found along the invaginat ing vascular layer. There was no effect of immunization on the pattern s of TIMP-1 immunoreactivity, suggesting that changes in TIMP-1 are no t involved in the effects of aN. These data are consistent with a para crine role for aN in the selection and atresia of antral follicles, an d for TIMP-1 in tissue reorganization and steroidogenesis at the time of ovulation.