Potential roles of decidual prolactin in early pregnancy.

Successful establishment of pregnancy is dependent on uterine receptivity at the time of trophoblast invasion and implantation. The endometrium undergoes morphological and functional differentiation during the mid- to late secretory phase of the menstrual cycle in preparation for such an event. These changes are orchestrated by ovarian steroid hormones. However, local autocrine-paracrine signalling at the deciduo-placental interface is crucial for successful establishment of pregnancy. One key cytokine that may regulate many functions in implantation is prolactin. Prolactin is secreted by the decidualized endometrium at the time of predicted conception and, in the event of pregnancy, local expression and secretion of prolactin persists until term. Prolactin mediates its effect on target cells through interaction with single-pass transmembrane receptors. Localization of the sites of expression of the prolactin receptor indicates that the cytokine may regulate an array of functions in the pregnant uterus that are crucial in im-plantation and early pregnancy.