Does "blastocyst estrogen" initiate implantation?

Fertilized eggs were incubated for 2 hours in a medium containing estradiol-17beta and then transferred into the uteri of day 5 pseudopregnant rats. These eggs, but not estrogen-free control eggs, induced a local increase in capillary permeability. We suggest that the blastocyst factor which induces the local increase in capillary permeability during early pregnancy is estrogen synthesized by the blastocyst.