Developmental regulation of the human relaxin genes in the decidua and placenta: overexpression in the preterm premature rupture of the fetal membranes.

The decidua and placenta synthesize the human relaxins, termed H1 and H2, believed to be involved in collagen remodeling in the amnion and chorion in an autocrine/paracrine manner. The developmental regulation of the relaxin genes was quantitated in normal pregnancy by in situ hybridization histochemistry with six 48-mer oligonucleotide probes that detect both relaxin genes. A significant increase in relaxin expression occurred in both decidua (p < 0.01) and placenta (p < 0.05) at 12.5-14.4 wk gestation, with the mean peak value in the placenta more than double that of the decidua, suggesting a coordinate regulation of the relaxin genes. At term after spontaneous labor and delivery, a marginal increase in both decidual and placental relaxin gene expression occurred. Given these normal data, three abnormal preterm situations were investigated: 1) premature uterine contractions without prior rupture of the membranes, 2) premature rupture of the fetal membranes (PPROM), 3) cesarean section for medical reasons with intact membranes and no uterine contractions. Tissues showing intrauterine infection were eliminated. Significantly more relaxin was expressed in the preterm decidua from patients with PPROM when compared to patients in group 1 (p < 0.02) or group 3 (p < 0.008). These data were confirmed by Northern analysis with a relaxin cRNA probe. The placental tissues after PPROM also had a significantly higher and a uniform overexpression of relaxin in the placental syncytiotrophoblast. Tissues collected at term, in comparison, showed no such increases in decidua or placenta.