Immunization against the N-terminal peptide of the inhibin alpha 43-subunit (alpha N) disrupts tissue remodeling and the increase in matrix metalloproteinase-2 during ovulation.

Immunization of ewes against the N-terminal peptide of inhibin alpha 43 (alpha N) reduces fertility; this is thought to be due to impaired oocyte release at ovulation. This study further investigates the effect of alpha N immunoneutralization on the ovulatory process. Light microscopy was used to examine the effects of alpha N immunization of the tissue-remodeling process during ovulation and formation of the corpus luteum (CL) structure. Changes in follicular levels of matrix metalloproteinase-2 (MMP-2) with approaching ovulation were also investigated in normal and alpha N-immunized ewes. Differences in structure of 2-day-old CL were observed between control and alpha N-immunized ewes. Control CL had confluent luteal tissue throughout the internal structure and invaginations of theca and vasculature were common and penetrated deep into the luteal tissue. Immunized ewe CL had large fluid-filled antra, giving them a cystic appearance; luteal tissue remained a thin 10- to 15-cell layer lining the wall surrounding the antrum. Infolding of the surrounding tissue was incomplete, and thecal/vascular invaginations were rare and failed to penetrate into the luteal tissue. Morphologically normal rupture stigma were seen at the apex of both control and alpha N-immunized CL. Gelatin-digesting activity in follicular fluid collected 0, 12, and 24 h after hCG administration in control ewes increased significantly as the time of ovulation approached (827 +/- 182, 842 +/- 159, and 1230 +/- 89 mU/ml, respectively, in Exp 1; 743 +/- 32, 1182 +/- 98, and 1306 +/- 91 mU/ml at the same times in Exp 2). alpha N immunization reduced follicular gelatinase activity at each time in Exp 1 (533 +/- 132, 740 +/- 67, and 809 +/- 147 mU/ml) and Exp 2 (587 +/- 21, 768 +/- 27, and 891 +/- 53 mU/ml); the reduction was significant at 24 h in Exp 1 and at all times in Exp 2. Gelatin zymography of follicular fluid revealed bands of gelatinase of 72/67 kilodaltons, consistent with latent and active MMP-2. The area digested by both latent and active MMP-2 increased with approaching time of ovulation and was reduced by alpha N immunization. These data suggest that MMP-2 has a role in the tissue-remodeling processes of ovulation and CL formation in the ewe and that immunization against alpha N, which impairs fertility, effects the preovulatory cascade of intrafollicular proteolytic activity, reducing MMP-2 levels and disrupting normal CL formation.