Vascularity and expression of angiogenic factors in bovine dominant follicles of the first follicular wave1

Abstract

To determine the relationships among vascularity, expression of angiogenic factors, and selected intrafollicular factors in dominant and nondominant follicles of the first follicular wave, ovaries were obtained on d 3 of the estrous cycle from mature cross-bred beef heifers (n = 8) after a synchronized estrus. Follicular fluid (FF) was collected from all follicles > or = 3 mm for determination of estradiol-17beta (E), progesterone (P4), vascular endothelial growth factor (VEGF), and IGFBP concentrations. The ovaries were then perfusion-fixed and used for histochemical detection of lectin BS-1 (a marker of endothelial cells and thus vascularization) binding, and immunolocalization of VEGF, endothelial nitric oxide synthase (eNOS), and proliferating cell nuclear antigen, followed by image analysis of selected follicles. Follicles were classified, based on E and P4 concentrations in FF, as dominant, estrogen-active (EA; E:P4 > or = 1) or nondominant, estrogen-inactive (EI; E:P4 <1). Concentrations of E and VEGF in FF, the area of positive staining for lectin BS-1, VEGF, and eNOS, and the labeling index (an index of the percentage of cells proliferating) in granulosa and theca layers were greater (P < 0.05) in the EA than in the EI follicles, but concentrations of P4 and IGFBP in FF were less (P < 0.05) in EA than in EI follicles. In addition, vascularity was positively correlated (P < 0.05) with VEGF and eNOS protein expression, and tended (P < 0.1) to be positively correlated with the E:P4 ratio in FF but tended (P < 0.1) to be negatively correlated with IGFBP and P4 concentrations in FF. These data highlight the importance of vascularity, angiogenic factors, and IGFBP in the health of the dominant follicle in heifers, and indicate that the FF concentrations of E, VEGF, IGFBP, and P4, and the E:P4 ratio can be used as markers of dominant follicles.