Enhanced degradation of collagen within apical vs. basal wall of ovulatory ovine follicle.

Electron microscopic examination of ovulatory ovine follicles indicated that dissolution of thecal collagen was enhanced along the follicular circumference adjacent to the ovarian serosa. Concentrations of hydroxyproline were correspondingly lower within apical than basal tissues. Collagenolytic activity of tissue homogenates and extracts was assessed by monitoring radioactive peptide release from cocultured collagen fibrils. Collagenase inhibitors were separated from enzyme by sequential extraction of follicular homogenates with detergent and heating. Enzymatic activities of homogenates and heat extracts of apical and basal tissues increased toward ovulation. A distinction between apex and base was not attributed to significant differences in homogenates; however, collagenolytic activity of heat extracts of apical tissue was selectively elevated (i.e., extraction was evidently required to effectively dissociate collagenase from thecal fibrils, making more enzyme available for substrate digestion). Activity of detergent extracts was restored by dithiothreitol and iodoacetamide (which inactivate tissue inhibitors of metalloproteinases), and collagenolysis induced by heat extracts was augmented by aminophenylmercuric acetate (a stimulator of latent collagenases). Nonetheless, variations between apex and base invoked by these compounds were relative. It therefore appears that active collagenase is more tightly bound within the extracellular matrix of the follicular apex than enzyme associated with basal tissue. This phenomenon might serve to preferentially favor enzymatic catabolism of collagen in that region, thereby dictating the ovarian site of follicular rupture.