Birth stress increases adrenomedullin in the newborn

Adrenomedullin is a peptide that induces pulmonary vasodilation in experimental animals. Adrenomedullin was measured in blood samples from cord artery and vein from 41 term newborns. In 23 of the newborns delivered vaginally, levels of adrenomedullin in the cord artery, 71.8 +/- 45.8 pg ml(-1) (mean +/- SD), and vein, 75.6 +/- 45.2 pg ml(-1), were significantly higher than in 18 newborns delivered by elective Caesarean section (40.7 +/- 14.6 pg ml(-1) and 32.4 +/- 10.3 pg ml(-1), respectively; both p < 0.01). A significant correlation existed between the concentration of adrenomedullin and pH in the cord artery (r = -0.545, p = 0.002). The fetus responds to birth stress by secreting high concentrations of adrenomedullin. As a potent vasodilator, the peptide may play a role in postnatal cardiovascular adaptation.