Cryopreservation of Unfertilized Mouse Oocytes from Inbred Strains by Ultrarapid Freezing

Abstract

Unfertilized mouse oocytes from inbred strains (BALB/c, C 3 H/He and C 57 BL/6) were frozen ultrarapidly by direct plunging into liquid nitrogen, immediately after exposure to a highly-concentrated solution (DAP 213:2 M dimethyl sulphoxide, 1 M acetamide, and 3 M propylene glycol in PB 1), and were later thawed in a 37.degree.C waterbath. After thawing, 76.8-90.9% of recovered oocytes were morphologically normal. Following fertilization in vitro of cryopreserved oocytes, the proportion of 2-cell embryos of 24 h after insemination ranged from 70.7% to 83.4%. Nearly all 2-cell embryos obtained from cryopreserved oocytes were transferred to the oviducts of pseudopregnant recipients and 31.0-43.0% of 2-cell embryos developed into normal young.