An immunohistochemical study of the vascularization of the human Graafian follicle

The wall of the largest Graafian follicle or corpus luteum was biopsied in 22 patients at laparoscopy. Both granulosa and theca cells were contained in 18 samples. These samples were classified as pre-luteinizing hormone (LH) surge (n = 3), LH surge (n = 3), early luteal (n = 3), mid-luteal (n = 4), late luteal (n = 3) and menstrual (n = 2). A double-staining immunohistochemical protocol was used to demonstrate proliferating endothelial cells: mouse-anti-rat-proliferating cell nuclear antigen, for proliferating cells; mouse-anti-human-CD34 antibody for endothelial cells. The percentage of endothelial cells proliferating (proliferation index) and the area of tissue occupied by endothelial cells (areal fraction) were determined for granulosa and theca layers. Intra- and inter-slide coefficients of variation were < 15%. The granulosa layer was avascular until the LH surge subsided. Maximum vascularization was achieved by the mid-luteal phase. The theca endothelial cell proliferation index was constant from pre-LH surge to mid-luteal phases. The mean theca endothelial cell proliferation index for these phases was significantly greater than for the late luteal and menstrual phases. From first appearance in the granulosa layer, endothelial cells had the same proliferation index as the theca endothelial cells, the proliferation index decreasing significantly in both after the mid-luteal phase (P = 0.018). It is concluded that endothelial cell proliferation is unchanged throughout the follicular, early and mid-luteal phases, decreasing significantly in the late luteal phase. By contrast, endothelial cell invasion of the membrane granulosa, presumably in response to a chemotactic stimulus, occurs after the LH surge has subsided.