Human Relaxin in the Amnion, Chorion, Decidua Parietalis, Basal Plate, and Placental Trophoblast by Immunocytochemistry and Northern Analysis*

Abstract

Immunocytochemistry and Northern analysis were used to show that relaxin is a product of intrauterine tissues of pregnancy. In addition, tissues from a patient without ovaries had similar results on both immunocytochemistry and Northern analysis as tissues from intact patients. The parietal decidua was clearly the major source of relaxin within the uterus and the relaxin mRNA (1.2 kilobases) from this tissue was detected with a 48-mer oligonucleotide probe designed to hybridize with both H1 and H2 relaxin gene transcripts. The mRNA isolated from the placental trophoblast was slightly smaller (1.1 kilobases), and the placental basal plate which has both maternal and fetal cells contained relaxin mRNAs of both sizes. Two monoclonal antibodies (Mabs) raised to synthetic human relaxin (H2) gave different patterns of localization in the fetal membranes, decidua and placenta. One Mab (RLX8) stained the chorionic cytotrophoblast in the fetal membranes and all of the cells in the placental basal plate. The other Mab (RLX6) stained the chorionic cytotrophoblast in some instances and selectively stained the decidua-like cells of the placental syncytiotrophoblast, whereas Mab RLX8 failed to detect this relaxin. Tissues obtained after spontaneous labor and delivery contained significantly less relaxin mRNA than tissues obtained at elective ceasarean section without labor, but their hormone contents, as judged by immunocytochemistry, were not different. We conclude that the relaxin gene (H2) is expressed in intrauterine tissues, but that expression and hormone synthesis are not ubiquitous. Whether the relaxin gene H1 is expressed has not been determined.