Collagens in the human ovary and their changes in the perifollicular stroma during ovulation

Background. Remodeling of the collagens around the follicle is a major event in ovulation. The aim of the present study was to investigate the distribution of collagen I, III, and IV in the human ovary. Methods. Biopsies of the perifollicular stroma were obtained at sterilization during the preovulatory phase (follicle size > 14 mm) or at any of three intervals (12-18 h after human chorionic gonadotrophin: early ovulatory phase; > 18-24 h: late ovulatory phase; 44-77 h: postovulatory phase) after human chorionic gonadotrophin. Excised dominant follicles and whole ovarian sections were also obtained. Immunohistochemistry using antibodies against collagen I, III, IV, vimentin, and CD 45 was performed. Results and conclusions. Collagens I and III were distributed in concentric layers in the capsular stroma with bundles of collagens connecting these layers to form a mesh. Collagen I was present in larger quantities in the outer layers and collagen III showed the inverse distribution. In the theca, collagen I was present in the externa and collagen III in the entire layer. The staining intensity of collagens I and III in the perifollicular stroma decreased from the preovulatory stage. Collagen IV was present in the basal lamina separating granulosa and theca cells. This study shows that collagen I and III are abundant in and around the ovulating human follicle with typical patterns of distribution. Collagen IV is present in the basal membrane that separates the granulosa from the theca cells. Taking into account the abundance of collagens in the follicular wall and their specific localization, major site-directed degradation of collagens seems to be necessary for follicular rupture to occur.