OPEN PULLED STRAW (OPS) VITRIFICATION - A NEW WAY TO REDUCE CRYOINJURIES OF BOVINE OVA AND EMBRYOS

Although cryopreservation of certain mammalian embryos is now a routin e procedure, considerable differences of efficiency exist depending on stage, species and origin tin vivo or in vitro produced). Factors tha t are suspected to cause most of these differences are the amount of t he intracellular lipid droplets and the different microtubular structu re leading to chilling injury as well as the volume/surface ratio infl uencing the penetration of cryoprotectants. A new approach, the Open P ulled Straw (OPS) method, which renders very high cooling and warming rates lover 20,000 degrees C/min) and short contact with concentrated cryoprotective additives (less than 30 sec over -180 degrees C) offers a possibility to circumvent chilling injury and to decrease toxic and osmotic damage. In this paper we report the vitrification by the OPS method of in vitro produced bovine embryos at various stages of develo pment. Embryos cryopreserved from Day 3 to Day 7 (Day 0 = day of ferti lization) exhibited development into blastocysts at rates equivalent t o those of control embryos; even those cryopreserved on Day 1 or 2 exh ibited only somewhat reduced survival. Eighty one percent of Day 8 hat ched blastocysts also survived the procedure. The method was also succ essfully used for bovine oocytes; of 184 vitrified oocytes, 25% develo ped into blastocysts after fertilization and culture for 7 days. Pregn ancies were achieved following trans fer after vitrification at both t he oocyte and blastocyst stage. The OPS vitrification offers a new way to solve basic problems of reproductive cryobiology and may have prac tical impact on animal biotechnology and human assisted reproduction. Mel. Reprod. Dev. 51:53-58, 1998. (C) 1998 Wiley-Liss, Inc.