Multiple estrogenic action of O,P'-DDT: initiation and maintenance of pregnancy in the rat.

The estrogenic action of O,P'-DDT has been known for many years. The majority of studies have used immature or ovariectomized adult rats to demonstrate estrogenic responses that require interaction with an intranuclear receptor and genic expression. However, evidence is accumulating that not all estrogenic effects are mediated by such a receptor; initiation of implantation being one such effect. The present study examined the ability of O,P'-DDT to initiate embryo implantation in the progesterone-primed uterus of a hypophysectomized adult rat. Not only did O,P'-DDT initiate implantation, it also maintained pregnancy for at least 3 days. However, when administered at the time of mating or early after fertilization, the same dosage caused loss of pre-implantation embryos. The results are consistent with the interpretation that O,P'-DDT has multiple estrogenic actions that may involve more than 1 kind of receptor.