CRYOPRESERVATION OF KUNMING-MOUSE-OOCYTES USING SLOW COOLING, ULTRARAPID COOLING AND VITRIFICATION PROTOCOLS

The cryopreservation of oocytes has been only marginally successful wi th any of the current protocols, including slow cooling, rapid cooling and vitrification. We wished to test the hypothesis that oocytes from a single mouse strain would freeze successfully by 1 of the 3 mention ed protocols. Unfertilized Kunming mouse oocytes obtained 14 h after P MSG/hCG administration were randomly assigned to be cryopreserved afte r slow cooling, ultra rapid cooling and vitrification. Oocytes were th awed by straws being placed into 37 degrees C water, and their morphol ogical appearance and in vitro fertilization capability were compared with that of oocytes that had not undergone cryopreservation. Survival of oocytes was indicated by the absence of darkened ooplasm or by bro ken membranes or zona pellucida. Functional integrity was evaluated by the formation of a 2-cell embryo after IVF. Survival rate of slow coo led oocytes did not differ from that seen in vitrified oocytes (55.1 v s 65.9%) but was significantly lower in the rapidly cooled oocytes (24 .2%; P<0.01). The results of NF of slow cooled and vitrified oocytes w ere similar to those of the control group (72 and 73 vs 77%; P>0.05). It appears that Kunming mouse oocytes can be successfully cryopreserve d using the slow cooling method with 1,2-propanediol and vitrification , which contains both permeating and nonpermeating cryoprotectants. (C ) 1997 by Elsevier Science Inc.