Prostaglandin F2α and conceptus-endometrial interaction during early gestation in the mouse

Pregnant Swiss-Webster mice were treated subcutaneously with 50, 100 or 200 μg PGF_2α on day 4, 5 or 6 postcoitum (p.c.). Twelve hours later, the animals were killed by intracardiac perfusion with Karnovsky's fixative, uteri were removed and a transverse central slice from each implantation site was embedded in Araldite. The conceptus was found by thick sectioning. Thin sections were taken of each implantation site and examined at the electron microscopic level. PGF_2a administered at a dose of 100 μg per animal on day 4 p.c. altered the normal attachment of the blastocyst to the endometrium, as well as formation of the implantation chamber. Cytology of the epiblast and hypoblast was adversely affected by this change. Dosages of 100 or 200 μg PGF_2α per animal adversely affected the apical trophectoderm cell of the blastocyst. Treatment with PGF_2α on day 4 p.c. at a dose of 50 μg per animal reduced the decidual reaction around the implantation chamber while treatment on day 5 p.c. at a dose of 50 or 100 μg per animal was associated with an advanced stage of development. Treatment on day 6 p.c. did not appear to have any influence on implantation or blastocyst development.