Development of Mouse and Rat Zygotes Following Transfer to Non-Synchronized Rat and Mouse Oviducts

It has repeatedly been observed that transfer of zygotes, two-cell stages or blastocysts to the oviduct of a recently mated mouse leads to implantation and subsequent pregnancy (Bittner & Little, 1937; Tarkowski, 1959; Zeilmaker, 1968). Studies in vitro have shown that the development of the mouse zygote to the blastocyst stage is frequently hampered by a failure to pass the two-cell stage (Whittingham, 1966). For this critical phase in the development, the ampullar region of the mouse oviduct must be present, either in vivo (Whittingham, 1968a; Cross & Brinster, 1970) or in vitro (Biggers, Gwatkin & Brinster, 1962; Whittingham, 1968b, c). The question arises whether the critical contribution of the oviduct is dependent on the hormonal conditions prevailing after oestrus, since Whittingham (1968c) demonstrated, in explantation studies with oviducts containing zygotes, that the cycle stage at which the oviducts were explanted influenced egg development. The present study is concerned with