Estrogen-induced surface coat and enzyme changes in the implanting mouse blastocyst.

Blastocysts from estrogen-stimulated mice tend to be very sticky, a characteristic which can be correlated with estrogen-induced enzyme activation and changes in the surface coat of the trophoblast cells. The blastocyst surface coat was investigated using colloidal ironPrussian blue stain. In addition, the activity of tyrosine aminotransferase was assayed histochemically in preimplantation blastocysts. The surface and enzyme changes were correlated with the presence of estrogen by investigations in normal blastocysts from intact mice before and after the endogenous estrogen surge and in delayed-implantation blastocysts from ovariectomized mice preceding and following estrogen treatment. Colloidal iron stains the surface coat of the blastocyst after, but not before, the endogenous estrogen surge and the exogenous estrogen treatment. Tyrosine aminotransferase activity also is increased considerably after estrogen induction.