Prolactin and its receptor in human endometrium.

Synthesis of prolactin (PRL) in human endometrium extends from the late luteal phase of the menstrual cycle throughout the pregnancy. We have studied the hormonal requirements for the sustained production of PRL and its receptor (PRL-R) in a long-term primary cell culture system. Progestin stimulates the production PRL and its receptor when stromal cells transform into decidual cells. The rise in PRL production rate correlates with an increase in steady-state PRL mRNA levels which are caused by increased transcription rate gene. Replacing progestin by the antiprogestin, RU 486, causes a transient superinduction of PRL production followed by reduction to basal level of expression. On the other hand, RU 486 exerts immediate inhibition of PRL-receptor mRNA expression. In addition, relaxin (RLX) enhances PRL synthesis. The transcription of the PRL gene in endometrium is dependent upon the promotor 6-kb upstream of the transcription start site in the pituitary. That biological functions of PRL and its receptor are critical to implantation and the maintenance of pregnancy is suggested by the impaired fertility of PRL and PRL-R knockout mice. PRL enhances endometrial cell growth at low concentrations and inhibits it at high concentrations. This dual action indicates an autocrine action of PRL-R-mediated signaling transduction pathways during reproductive cycles and pregnancy. During gestation, decidual-derived prolactin regulates the volume of amniotic and fetal extracellular fluid and electrolytes.