Vascular endothelial growth factor expression correlated with microvessel density in the antral follicle of sheep ovary

Vascular Endothelial Growth Factor (VEGF) promotes the proliferation and angiogenesis of endothelial cells and plays important physiological roles in the follicular development and oocyte maturation. However, the role of VEGF in endothelial cells is only partly understood in the angiogenesis of the sheep ovary. Our study analyzed the protein expression of VEGF and its correlation with microvessel density (MVD) in the sheep ovary from 0 to 15 d after the synchronization of estrus. The results showed that VEGF was expressed at increasingly higher levels from the primordial follicle to the secondary follicle (P<0.05). In Graafian follicles VEGF expression was increased from 0 to 5 d followed by a significant decline (P<0.05), and it was markedly increased again at 15 d (P<0.05). Capillaries began to appear around the follicular theca of the primary follicle. MVD significantly increased around the secondary follicle and in Graafian follicles from 0 to 5 d and 12 to 15 d (P<0.05). Pearson correlation analysis showed a highly positive correlation between VEGF expression level and MVD in the primordial follicle, primary follicle and secondary follicle (r=0.81, p=0.01). These data indicate that VEGF has a close relationship with vascular regeneration of sheep ovary.