Immunocytochemical localization of prolactin and relaxin C-peptide in human decidua and placenta.

The production of PRL by the human decidua is generally accepted, but the production of relaxin by this tissue is not. The two hormones were localized in decidual tissue using the avidin-biotin immunoperoxidase procedure with antisera to human PRL and to a synthetic 14-amino acid sequence of the connecting peptide of human relaxin (hCp14). The object of using the hCp14 antiserum was to verify relaxin production by the detection of C-peptide and/or prorelaxin. Cells of the parietal decidua adherent to the fetal membranes stained with both antisera, and immunostaining for both hormones in the same cell was seen. Also, the decidua-like cells of the placental basal plate stained with both antisera. The chorionic cytotrophoblast stained with the antiserum to hCp14, but not the antiserum to human PRL, whereas the placental syncytiotrophoblast stained for PRL and/or human placental lactogen (hPL), but not hCp14. The PRL staining in all tissues was lost when anti-PRL serum absorbed with human placental lactogen (hPL) was used. This finding suggests that the antiserum to PRL could not distinguish between PRL and hPL. It appears, therefore, that the parietal decidua cells and the decidua-like cells of the placental basal plate may be capable of producing both relaxin and PRL, while the syncytiotrophoblast produces hPL and possibly PRL.