Estrogen administration during superovulation increases oocyte quality and expressions of vascular endothelial growth factor and nitric oxide synthase in the ovary

Aims: This study investigated whether estrogen administration during superovulation enhances oocyte quality using a mice model. We also investigated whether this estrogen treatment regulates the expressions of angiogenic factors, such as vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS), in the ovary. Method: Female mice were co‐injected with various doses of estrogen (1 µM, 10 µM and 100 µM) and pregnant mare serum gonadotrophin during superovulation, followed by human chorionic gonadotrophin injection 48 hours later. Then they were mated with individual males. After 18 hours, zygotes were flushed and cultured to blastocyst. The expression of VEGF and eNOS in the ovary was examined using Western blot and immunohistochemistry. The control group was superovulated without estrogen. Results: Both numbers of ovulated zygotes and the rate of embryo development to blastocyst were significantly increased in the 1‐µM estrogen dose compared to the control group. VEGF and eNOS expressions were stimulated by estrogen treatment. In particular, VEGF expression was significantly increased at 1‐µM estrogen concentration, whereas, eNOS expression was significantly increased in all estrogen concentrations compared to controls. Conclusions: The study showed that estrogen co‐injection during superovulation increased the ovarian response, embryo developmental competence and expressions of VEGF and eNOS in the ovary.