Abstract: Objective：To study the effect of miR-200b on the expression of VEGF in PCOS rat model, and to explore the role of miR-200b and target gene VEGF in the pathogenesis of PCOS. Methods: Sixty female SD rats of six weeks age were randomly divided into three groups (20 rats for each group): experiment group and experiment control group，blank control group. Set up an animal model by using Letrozole. The estrus cycles changes and histologic changes in ovaries and serum hormone levels were examined. The miR-200b and VEGF in serum was detected by real-time quantitative PCR. Results: The estrus cycles of PCOS group become irregular, which indicated that the rats had no ovulation. Serum testosterone and LH levels were elevated, while FSH，progestone and estradiol levels were reduced (both P＜0.01). Real-time-PCR results showed that the expression of miR-200b in the serum of PCOS rats decreased significantly (P＜0.01). The expression of target gene VEGF in the serum of PCOS rats increased significantly (P＜0.01)． Conclusions: The level of miR-200b in serum of PCOS rats was reduced and it may play an important role in the development of PCOS by regulating its target gene VEGF. We hypothesized that circulating miR-200b may be a new non-invasive diagnostic marker for PCOS diagnosis．

Key words: Polycystic ovary syndrome, Letrozole, Disease models, animal, Circulating miR-200b, Vascular endothelial growth factors