An Apparent Stress-Induced Release of Arginine Vasopressin by Human Neonates*

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Abstract
The condition (s) that results in elevated concentrations of arginine vasopressin (AVP) in umbilical cord plasma of human neonates was investigated, and we sought to ascertain if a correlation exists between the plasma concentration of AVP and fetal stress. The concentration of AVP in arterial cord plasma was consistently greater than that in venous cord plasma regardless of the status of the neonate or whether it was delivered vaginally or by cesarean section. This umbilical arteriovenous difference is suggestive of fetal secretion of AVP and clearance of circulating AVP by the placenta. The concentration of AVP in fetal plasma was greater than that in maternal plasma at the time of vaginal delivery. We found appreciably higher concentrations of AVP in cord plasma from infants who were believed to have been subjected to stress during pregnancy, labor, and⁄or delivery than in cord plasma from infants believed not to have been stressed. The concentration of AVP in arterial cord plasma from vaginally delivered stressed neonates was greater than that in nonstressed neonates [150 ± 15 vs. 11.8 ± 1.0 µU/ml (mean ± SE); P < 0.001] a similar relationship was seen in venous cord plasma from these neonates (62.5 ± 15 vs. 4.7 ± 0.7 µU/ml; P < 0.01). In infants delivered by cesarean section during labor, the concentration of AVP in arterial cord plasma from stressed neonates was greater than that in nonstressed neonates (93 ± 28 vs. 10 ± 1.8 µU⁄ml; P < 0.01). In infants delivered by cesarean section before labor, the concentration of AVP in arterial cord plasma from stressed neonates was greater than that from nonstressed neonates (64 ± 12 vs. 4.3 ± 1.1 µU⁄ml; P < 0.001); a similar relationship was seen in venous cord plasma from these neonates (30 ± 9 vs. 2.6 ± 0.9 µU/ml; P < 0.01).The presence of meconium in amniotic fluid was usually associated with high concentrations of AVP in cord plasma. It is concluded that the concentration of AVP in umbilical cord plasma from the human newborn is a sensitive indicator of fetal stress, and the passage of meconium into the amniotic fluid may be related to the release of AVP during stressful conditions.