Abstract:

BACKGROUND: Vitrification is a comparatively new technology which applies high concentration cryoprotectant and rapid refrigeration. By the method, the cells were quickly frozen and to avoid damage by ice crystals inside and outside.
OBJECTIVE: To compare the effect of four cryoprotectants on morphology and function of ovarian tissue in rats after vitrification.
METHODS: The rats were randomly assigned into six groups with 6 rats for each: DMSO + EG, DMSO + EG + sucrose, DMSO + EG + sucrose + acetamide, EG + sucrose + acetamide, ovariectomized, and normal control groups. The ovarian tissues of four freezing groups were treated with the corresponding cryoprotectants, the vitrified ovarian tissues were then resected but not frozen and transplanted; otherwise, tissues were not treated with any treatment in the normal control group. Two weeks after freezing, the tissues were thawed and heterotopic-transplanted into femoribus internus of hind limb. At 30 days after implantation, vaginal epithelial cells and estrus cycle were observed, while after three months, blood were collected to detect the level of estradiol (E2) and the ovarian tissues were reclaimed to analyze their morphological changes.
RESULTS AND CONCLUSION: All ovarian tissues were damaged after cryoprerservation in four freezing groups. The rates of healthy primordial follicles were 67.9%, 71.6%, 80.5%, and 59.4%, respectively, while healthy primary follicles were 41.6%, 52.3%, 55.9%, and 36.7%, respectively. In all freezing groups, the rate of the healthy follicles in DMSO + EG + sucrose + acetamide group was higher than DMSO + EG group and EG + sucrose + acetamide group (P < 0.05). No significant difference was found in the proportion of follicles at different development stages among four groups. The typical secondary follicle was not found in four groups. Damaged ovotid showed oocyte pyknosis and vacuolation in cytoplasmic area. There was not typical cell type of all freezing groups. Ovarian autografting gained visible vascularity from surrounding tissue that connected ovarian tissue to form net. There was a lot of blood capillary in transplanted ovarian tissues and clumped primordial follicles in cortical substance. The rates of primary follicles and secondary follicles were lower than primordial follicles. The level of serum estradiol was obviously decreased compared with normal control group (P < 0.01). There was significant difference between DMSO + EG + sucrose + acetamide group and other three freezing groups (P < 0.05). Four kinds of freezing methods have poor effects on different stages of follicles and the structure of ovarian tissue. DMSO + EG + sucrose + acetamide group is an optimal protocol for cryoprerserving ovarian tissue. Freezing methods still need to explore further because the rats had not appeared disciplinary estrus cycle after ovarian autografting.