Inhibition of implantation in the golden hamster by zona-precipitating antibody.

Antisera prepared against saline extracts of hamster ovary, and made specific to ovary by absorption with small intestine, precipitated the zona pellucida of provulatory hamster ova and all early embryonic stages examined, including the pronuclear, 2-, 4-, 8-, and 16-cell, morula, and blastocyst stages; this indicates that (1) the zona antigen is present during oocyte maturation and early embryonic development and (2) the antigen does not change its ability to react with zonaprecipitating antibody. Embryos in the morula and blastocyst stages, treated in vitro with zona-precipitating antibody, pre-immunization rabbit serum, or control media were transferred into synchronized pseudopregnant recipients. Precipitation of zonae by specific antibody inhibited implantation by blocking the process known as zona shedding, and thereby prevented the embryo from making contact with the uterus.