Comparison On The Cryopreservation Method Of Mouse Oocytes Between Conventional Freezing And Vitrification

Background Scholars had done a lot of work for seeding a simple and effective method on cryopreservation of oocytes ,but remains elusive,since the first human pregnancy resulted from cryopreserved oocytes,as reported by Chen in 1986.Ice-crystal would form easily and damnificate the membrane system of oocytes by conventional freezing .Vitrification is performed by suspending the oocytes in a solution containing a high concentration of cryoprotectants and then directly plunging the oocytes into liquid nitrogen.The advantage of this technique is the prevention of ice crystal formation. Recently developed the method of OPS for vitrification of bovine oocytes and reported a favourable capacity for development. The tip of OPS is designed to have a small diameter and thin wall .Oocytes held in OPS with a very small volume(1-2μl) of vitrification solution achieve a faster cooling and warming rate (a theoretical rate of 20 000°C/min) than those in conventional freezing .so far as, vitrification of oocytes has not been widely used for humans .Object This experiment is designed to form the mouse experiment model, comparing on the cryopreservation method of mouse oocytes between conventional freezing and vitrification in OPS, inquirying into the concrete method of cryopreservation of oocytes , providing experiment basis to the clinic.Method Female mice were induced to superovulate.The mature oocytes with the first polar body were collected for the experiments. The oocytes were randomly allocated to four groups including exposure to cryoprotectants without cooling, conventional freezing, vitrification using OPS, and controls without treatment.Observating the survival anddevelopment of cryopreserved mouse oocytes.How the influence of difference incubation time before IVF on fertilization and development of cryopreserved mouse oocytes was.Results There was no statistically difference between Vitrification of oocytes in OPS and conventional freezing on the survival ,fertilization and development of cryopreserved mouse oocytes.but the fronter was slightly higher than the behinder.There was no statistically difference between controls without treatment and exposure to cryoprotectants without cooling on the fertilization and development of cryopreserved mouse oocytes ( P >0.05).but the fronter was slightly higher than the behinder. There was significantly difference between controls without treatment and exposure to cryoprotectants without cooling on 6-8cell embryos rate(P<0.05). There was significantly difference between 2h incubation and 1h incubation on cryopreserved human oocytes(P<0.05).Discussion The result indicated that the OPS vitrification method can cryopreserved mouse oocytes as good as conventional freezing. The result also suggest that the OPS vitrification method is a simple and effective method on cryopreservation of oocytes. The trend of the OPS vitrification method is better than that of conventional freezing.The test of pre-vitrification treatment on mouse oocytes shows that there was negative effect to development of mouse oocytes.The incubation time before IVF is 2 hours at lest. It is essential for the oocytes to recovere their normal spindles.