Implantation and Deciduoma Formation After Administration of Antiestrogenic Compounds

Experiments were done in pregnant rats bearing one sterile cornu to clarify the effect of antiestrogenic compounds on deciduoma formation. Doses of I.C.I. 46474, CN-55945-27, U-11100A, and U-11555A sufficient to prevent implantation completely when given on Day 1 or Day 4 of pregnancy were used. The deciduoma-inducing stimulus was either the intrauterine injection of sesame oil or traumatization of the endometrium on Day 5. Deciduomata were also induced in progesterone-treated ovariectomized pregnant rats which did not receive antiestrogenic compounds. The deciduoma response (DR) in the sterile cornu and the number of implantations in the pregnant cornu were determined on Day 10. In ovariectomized pregnant rats treated with 4 mg of progesterone daily from Days 2 to 9 neither implantation nor an oil-induced DR occurred, but uterine trauma induced a DR; when 1 µg of estrone was added to the progesterone treatment from Day 4 to 9 implantation and an oil-induced DR equivalent to that of intact controls were obtained. The oil-induced, but not the trauma-induced DR, in intact pregnant rats was completely inhibited by all the antiestrogenic compounds when they were given on Day 4, while administration of the same drugs on Day 1 prevented both the oil-induced and the trauma-induced DR. Implantation was uniformly prevented by these compounds after administration on either Day 1 or Day 4. It was concluded that, in the rat, oil instillation is preferable to the use of trauma for deciduoma induction, since it more closely resembles the conditions under which implantation takes place.