Abstract: Objective：To study the effect and mechanism of simvastatin on the quality of vitrified-warmed ovarian tissue after auto-transplantation in mice. Methods：Eighty female ICR mice aged 6 to 8 weeks were used. Fresh ovarian tissues (fresh ovarian tissue group) were collected from 10 mice, and vitrified-warmed ovarian tissues (vitrified-warmed ovarian tissue group) were collected from other 10 mice, whose ovaries were removed and vitrified by two-step vitrification procedures. Ovarian tissues of 60 mice were removed and vitrified for one week. After thawing, ovarian tissues were auto-transplanted to the back muscles. Survival mice were randomly divided into two groups. The mice in simvastatin group (n=30) were administered with simvastatin (5 mg/kg, orally), whereas the mice in saline group (n=30) received normal saline as control. Two treatments lasted for 7 days after auto-transplantation. Mice were sacrificed on the day 3, 7 and 21, five mice were killed in every time point for each group. Ovarian tissues were collected for HE, ki67, CD34 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay (Tunel). Serum was collected for detecting E2 and FSH on the day 3, 7 and 21. Moreover mice were sacrificed on the day 3 and 7，five mice were killed in every time point for each group. Malondialdehyde (MDA) and superoxide dismutase (SOD) were analyzed. Results：Compared with the fresh ovarian tissue, the vitrified-warmed ovarian tissue had lower number of antral follicles and higher number of Tunel positive cells (both P＜0.05). Ki67 in the ovarian tissue was mainly expressed in the granulosa cells and ovarian stroma cells. On the day 3 and 7 after transplantation, the number of primordial follicles in the simvastatin group was higher, and the number of apoptotic follicles was less, than those in the saline group (both P＜0.05). On the day 21, the ovarian tissue grew well and the antral follicles were found in both groups. The number of antral follicles of simvastatin group was higher than saline group. The CD34-positive area in the simvastatin group was increased than that in the saline group (P＜0.05) on the day 3 and 7. The levels of serum E2 was significantly increased after transplantation, and the level of FSH was decreased on the day 21. In the simvastatin group, the level of SOD was increased, and MDA decreased, on the day 3 and 7 (both P＜0.05). Conclusions：Treatment with simvastatin after auto- transplantation of ovarian tissue can prevent the ovarian damage and restore ovarian function through the mechanisms of anti-oxidation and reconstruction of blood vessels.

Key words: Cryopreservation, Ovary, Tissue transplantation, Hydroxymethylglutaryl-CoA reductase inhibitors, Ischemia, Vitrification, Simvastatin