Changes in the Localization of Immunoreactive von Willebrand Factor in Microvascular Network of Bovine Ovarian Follicles during Atresia

Abstract

Changes in the localization of von Willebrand factor (vWF) in the follicular microvasculature were examined to determine whether functional modulation of microvasculature occurred in the atretic follicle in cows. Paraffin sections of healthy follicles and various stages of atretic follicles were immunostained with rabbit monoclonal antibody to vWF. The vWF-positive cells were counted in 4 different regions of a follicle from the apical to the basal side. In all types of follicles, immunoreactions for vWF were observed in the endothelial cells of capillaries as well as veins and arteries in the theca interna and externa. In the theca interna, the vWF-positive area was significantly (P<0.05) greater in advanced and late atretic follicles than in healthy and early atretic follicles at all regions except for the apical region of advanced atretic follicles. In the theca externa, vWF-positive area significantly (P<0.05) increased with a progress of atresia only at the apical region of follicles. However, in the late atretic follicles, the theca tissues and blood vessels did not show obvious histological disintegration. These results suggest that the increase of the vWF expression in the endothelial cells occurs before morphological changes of microvasculature appear in the atretic follicles. The functional modulation of microvasculature that is associated with the expression of vWF may be involved in the events of atresia.