STUDIES ON RELATIONSHIP BETWEEN UTERINE FLUID COMPONENTS AND DIAPAUSING STATE OF BLASTOCYSTS FROM MAMMALS HAVING DELAYED IMPLANTATION

In the uterine secretions of certain mammals, gross qualitative and quantitative differences in their protein content were observed depending on whether or not the animals exhibited delayed implantation. Diapause blastocysts of the animals representative of those with obligate delayed implantation were stimulated to grow (as measured by total expansion and increased mitotic index) when maintained in vitro in medium containing rabbit “blastokinin” but not in serum‐containing medium. Diapause rat blastocysts taken from animals where a facultative delayed implantation has been produced by heavy lactation, expanded in F10 medium alone or containing serum or the macromolecular components of uterine secretions taken from a 5‐day pregnant animal, but not in rabbit “blastokinin.” The mitotic index, however, was the same under all three conditions and higher than in uncultured controls. Growth of active 5‐day rat blastocysts was stimulated by medium containing the proper concentration of uterine macromolecular components; mitotic activity increased three to four‐fold. We conclude that delayed implantation results from the failure of the mother to provide sufficient protein and/or certain specific proteins as needed for active growth of the blastocysts. In facultative delayed implantation, as exemplified by the lactating rat, there is evidence that, in addition to the protein deficiency, some substance or condition exists in the uterus which inhibits growth of the blastocysts. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company