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 cesarean 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.

Changes in Circulating Relaxin Levels during Pregnancy and Early Lactation in Japanese Monkeys (Macaca fuscata fuscata).

“…In support of our findings, previous studies reported that high concentrations of relaxin were observed in extracts of corpus luteum, and the removal of luteal tissue resulted in a rapid fall in circulating relaxin concentrations in the macaque monkey [12]. It is possible that relaxin comes from a source other than the corpus luteum, as it is known that the human endometrium [33] and decidua [34] produce relaxin. However, it has been reported that circulating relaxin was not detectable in women with premature ovarian failure after embryo transfer and treatment with progesterone [44], which suggests that endometrial relaxin does not enter circulation in detectable amounts.…”

Serum relaxin levels are reduced in pregnant women with a history of recurrent miscarriage, and correlate with maternal uterine artery Doppler indices in first trimester

“…(26). It is unlikely that the serum RLX that we measured originated from non-gestational tissues as gestational relaxin is only expressed in placental syncytiotrophoblast, decidua, and corpus luteum.…”

Analysis of the 5'-upstream regions of the human relaxin H1 and H2 genes and their chromosomal localization on chromosome 9p24.1 by radiation hybrid and breakpoint mapping

“…The systemic relaxin acting in this way is the H2 form and the only relaxin produced by the human corpus luteum (Hudson et al 1984). It has been shown, however, that relaxins are also autocrine/paracrine hormones in a number of other tissues such as prostate (Hansell et al 1991), placenta (Sakbun et al 1990), endometrium, decidua (Bryant-Greenwood et al 1993) and mammary gland (Tashima et al 1994). When relaxins are produced and act locally in this manner, both relaxin genes are expressed (Bryant-Greenwood & Schwabe 1994).…”