Epidermal growth factor (EGF) replaces estradiol for the initiation of embryo implantation in the hypophysectomized rat.

Several studies have provided evidence that epidermal growth factor (EGF) or transforming growth factor alpha (TGF alpha) mediate some of the physiological effects of estrogen. The object of the present study was to determine whether exogenous EGF could initiate embryo implantation in the rat, a response known to depend upon the action of estrogen in a progesterone-primed uterus. Immunocytochemical examination showed the presence of immunoreactive EGF, TGF alpha and the EGF receptor in luminal glandular epithelium of uteri on days 4,5 and 6 of pregnancy. EGF receptor was also present in the implanting embryo and in decidual cells of the uterine stroma. Attempts to initiate implantation by intravenous injection of murine EGF into ovariectomized or hypophysectomized delayed-implanting rats maintained with progesterone were unsuccessful. Implantation sites were found, however, in 24 of 33 (73 per cent) hypophysectomized progesterone-primed rats given 100 micrograms EGF immediately after intrauterine transfer of blastocysts from hypophysectomized delayed implanting animals. Although EGF is capable of initiating implantation in the delayed implanting rat model it remains to be determined whether this growth factor is responsible for the implantation inducing action of estrogen in vivo.