Regional comparison of prolactin gene expression in the human decidualized endometrium in early and term pregnancy

Prolactin (PRL) is known to be expressed in the decidualized human endometrium and secreted into amniotic fluid. Although the site of synthesis of endometrial PRL is known to be the decidual cells, the difference in PRL gene expression within each area of decidua, i.e. decidua basalis, decidua parietalis and decidua capsularis, during pregnancy is not clear. We have applied an in situ hybridization histochemistry technique using a radiolabeled RNA probe to compare the difference in expression of PRL gene within each area of the decidualized endometrium. Specific hybridization signals were distributed over the decidual cells in early and term pregnancy. More intense hybridization signals were always detected in the tissues of early pregnancy than in those of term pregnancy. In the decidua capsularis of early pregnancy, labeled cells were concentrated close to the amniotic cavity, whereas cells were concentrated close to the maternal surface of the fetal membrane in term pregnancy. In the decidua parietalis, almost all decidual cells were labeled, but no specific labeling was seen in the endometrial glands or capillary endothelium in both groups. In the decidua basalis, most decidual cells showed hybridization signals whereas no hybridization signal was seen over the trophoblast cells. These results show that there are regional and periodic differences in PRL gene expression in the decidual cells during pregnancy.