A vast literature indicates that prolactin also functions as an immunomodulatory protein, but it is difficult to relate prolactin’s immune effects to the maintenance of pregnancy. Prolactin is widely regarded as a hormone of immunocompetence that facilitates the rejection of foreign antigens. However, it has been suggested that the local tissue concentrations of prolactin may influence its actions whereby prolactin is immunostimulatory at low doses but inhibitory at high doses. In addition, the prolactin receptor is down-regulated by its cognate ligand, which may explain how high levels of prolactin can inhibit immune responses. asthma inhalers
Progesterone, relaxin, insulin, and insulin-like growth factor-1 as well as the placental protein, PRL-RF (prolactin-releasing factor), all produce a marked increase in prolactin synthesis and release by decidual explants or stromal cells in vitro. The production of decidual prolactin is inhibited in vitro by the antiprogestin RU-486 and by a partially purified extract of human decidua designated decidual prolactin release-inhibitory factor.