Immunoreactive adrenomedullin in human fetoplacental tissues

OBJECTIVE: Adrenomedullin is increased in maternal plasma in pregnancy and has been found in very high concentrations in amniotic fluid and umbilical plasma. To identify adrenomedullin-producing tissue in pregnancy we measured adrenomedullin concentration and distribution in fetoplacental tissues. STUDY DESIGN: By use of a specific radioimmunoassay we determined the concentrations of adrenomedullin and, by immunohistochemical studies, its localization and distribution in fetal membranes and placentas collected at elective cesarean section from 11 healthy pregnant women at term. RESULTS: The content of adrenomedullin in placentas (117.7 ± 7.8 pg/mg wet tissue) and fetal membranes (168.7 ± 2.3 pg/mg wet tissue) was similar to the adrenomedullin concentration in adrenal medulla (157.3 ± 4.4 pg/mg wet tissue). Adrenomedullin staining appears to be greater in fetal membranes than in placentas and was localized in amnion and trophoblast cells. In term placentas positive staining was detected predominantly in extravillous trophoblast cells, although a few syncytiotrophoblast cells and endothelial cells of primary villi stained for adrenomedullin. CONCLUSION: This study provides evidence that is consistent with fetoplacental tissues as a site of synthesis or action of adrenomedullin during pregnancy.