Plasma levels of dihydroxyphenylalanine, dopamine and norepinephrine in the fetoplacental unit and maternal circulation at delivery.

Dihydroxyphenylalanine (DOPA), dopamine (DA) and norepinephrine (NE) levels were measured in matched samples of maternal plasma (MV), umbilical arterial (UA) and venous (UV) blood of 25 normal infants born following an uncomplicated vaginal delivery. Levels in maternal plasma in the preterm period (36-40 weeks of gestation) and in 20 non-pregnant control subjects were also determined. DOPA and NE concentrations in the maternal vein at delivery were markedly higher than findings in the preterm period. The levels of DOPA and NE in the umbilical artery were significantly higher than those in the maternal vein at delivery. The DOPA levels in umbilical cord plasma showed arteriovenous differences indicating a net distribution of DOPA from the fetus to the mother. These data strongly suggest that the high DOPA levels in cord blood originate mainly from the fetus.