Autocrine/paracrine regulation of prolactin release from human decidual cells.

Studies from this laboratory indicate that the synthesis and release of prolactin from human decidual cells are regulated by factors released by the placenta, decidua and fetal membranes. A 23.5 kD protein (decidual prolactin-releasing factor, PRL-RF) has been purified to homogeneity from human placental tissue and placental conditioned medium. The releasing factor stimulates an acute release of prolactin that occurs within the first few minutes of exposure and a prolonged release, secondary to new hormone synthesis, that begins about 6-8 hours later. In addition, the synthesis and release of decidual prolactin are stimulated by IGF-I, insulin and relaxin, each acting through distinct plasma membrane receptors. In contrast, the synthesis and release of decidual prolactin are inhibited by arachidonic acid, lipocortin I and a 35-45 kD decidual protein (prolactin-releasing inhibitory factor) that has been partially purified from decidual conditioned medium. Studies of the second messengers involved in the regulation of decidual prolactin release strongly suggest that decidual prolactin release may be mediated, at least in part, by activation of phosphoinositide metabolism and stimulation of adenylate cyclase. The demonstration that the synthesis and release of decidual prolactin are regulated by PRL-RF, IGF-I, insulin, relaxin, arachidonic acid, PRL-IF and lipocortin I strongly suggests that there is novel autocrine/paracrine feedback regulation between the placenta, fetal membranes, and decidua in the regulation of decidual prolactin.