Decidualization and ovum-implantation in spayed mice treated with oestriol

Single injections of oestriol were partially effective in sensitizing the uterus to a decidual stimulus and inducing ovum-implantation in progesterone-treated spayed mice, whereas two injections (6 h apart) were fully effective. It seems that in the progestational uterus, as in the non-progestational organ, oestriol can induce a full oestrogenic response provided that its level in the target organ is maintained. It is also concluded that ovum-implantation is not triggered by some transient early effect of oestrogen, but requires about 12 h of sustained oestrogen action for its successful completion.