IMMUNIZATION AGAINST THE N-TERMINAL PEPTIDE OF THE INHIBIN ALPHA-43-SUBUNIT (ALPHA-N) DISRUPTS TISSUE REMODELING AND THE INCREASE IN MATRIXMETALLOPROTEINASE-2 DURING OVULATION

Immunization of ewes against the N-terminal peptide of inhibin alpha 4 3 (alpha N) reduces fertility; this is thought to be due to impaired o ocyte release at ovulation. This study further investigates the effect of alpha N immunoneutralization on the ovulatory process. Light micro scopy was used to examine the effects of alpha N immunization on the t issue-remodeling process during ovulation and formation of the corpus luteum (CL) structure. Changes in follicular levels of matrix metallop roteinase-2 (MMP-2) with approaching ovulation were also investigated in normal and alpha N-immunized ewes. Differences in structure of 2-da y-old CL were observed between control and alpha N-immunized ewes. Con trol 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 a ntra, giving them a cystic appearance; luteal tissue remained a thin 1 0- to 15-cell layer lining the wall surrounding the antrum. Infolding of the surrounding tissue was incomplete, and thecal/vascular invagina tions were rare and failed to penetrate into the luteal tissue. Morpho logically normal rupture stigma were seen at the apex of both control and alpha N-immunized CL. Gelatin-digesting activity in follicular flu id collected 0, 12, and 24 h after hCG administration in control ewes increased significantly as the time of ovulation approached (827 +/- 1 82, 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 ti me 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 sig nificant at 24 h in Exp 1 and at all times in Exp 2. Gelatin zymograph y of follicular fluid revealed bands of gelatinase of 72/67 kilodalton s, consistent with latent and active MMP-2. The area digested by both latent and active MMP-2 increased with approaching time of ovulation a nd was reduced by alpha N immunization. These data suggest that MMP-2 has a role in the tissue-remodeling processes of ovulation and CL form ation in the ewe and that immunization against alpha N, which impairs fertility, effects the preovulatory cascade of intrafollicular proteol ytic activity, reducing MMP-2 levels and disrupting normal CL formatio n.