STORAGE OF MAMMALIAN OOCYTES AND EMBRYOS: A REVIEW

Abstract

This article reviews the literature on storage of mammalian oocytes and embryos. Preimplantation embryos have been stored in vitro, in ligated oviducts and uteri of donor females, or in ligated oviducts of heterogenous females, and developed to term following transfer to suitable recipients. Embryo viability declined markedly after 48 h in storage anywhere other than in the reproductive tracts of species in which delayed implantation occurs naturally. Embryos stored at 0–37 C retained viability for 120 h; thereafter viability decreased. Storing oocytes in vitro at 10 C prolonged fertilizability for up to 3 days, but none developed to term if fertilized after 31 h storage. For successful storage, both cleavage and metabolism of embryos must be inhibited completely. This inhibition was accomplished with mouse and rabbit embryos by using dimethyl sulfoxide (DMSO) as the cryoprotective agent, slow rates of cooling (0.3–2 C/min) and warming (3–25 C/min), and a stepwise dilution of DMSO immediately after thawing. Neonates have resulted from the transfer of embryos previously frozen for 222 days.