Influence of labor on fetoplacental adrenomedullin concentrations

OBJECTIVE: Circulating adrenomedullin is increased in pregnancy, and placen tal and fetal membranes participate significantly in its secretion. Recent studies have suggested a potential role for this peptide in the regulation of fetoplacental circulation and placental hormonal secretion. Because adre nomedullin acts also as a uterorelaxant in rats, this study was designed to investigate whether fetoplacental adrenomedullin production changes with h uman labor, either at term or preterm. STUDY DESIGN: Eighty pregnant women grouped according to gestational age an d presence of labor were studied. Adrenomedullin concentrations in plasma, amniotic fluid, and placental tissue extracts were measured by means of rad ioimmunoassay and immunohistochemistry. In addition, the ability of amnion and chorion-decidua to secrete adrenomedullin was investigated in vitro. RESULTS: Adrenomedullin concentrations in amniotic fluid were higher in pre term labor, whereas no differences were found in adrenomedullin expression or concentrations in tissues or in maternal and fetal plasma between vagina l delivery or elective cesarean section, both at term and preterm. During t erm labor (8 patients), maternal plasma adrenomedullin concentration decrea sed with advancing cervical dilatation, being 173 pg/mL at the beginning of the active stage of labor and 57 pg/mL at the time of delivery. Adrenomedu llin concentration in the medium of amnion- and chorion-decidua-cultured ce lls was higher after vaginal delivery. CONCLUSION: These results suggest that a decrease in adrenomedullin product ion is not involved in the onset of labor in human subjects but rather that it may play a role other than that of a myometrial relaxant in human partu rition.