Distribution of catecholamines between fetal and maternal compartments during human pregnancy with emphasis on L-dopa and dopamine.

This study was undertaken to determine the differential distribution of catecholamines, in particular L-dihydroxyphenylalanine (L-dopa) and dopamine, between the fetal and maternal compartments during human pregnancy. Amniotic fluid and fetal and maternal blood were obtained from two groups of pregnant women with uncomplicated pregnancies. One group was at 15-20 weeks of gestation and the second group was in labor after 36-41 weeks of gestation. Samples were analyzed for L-dopa, dopamine, norepinephrine, and epinephrine by radioenzymatic assays. L-Dopa constituted about 80% of the total circulating fetal catecholamines, and levels were 2- to 3-fold higher in fetal than maternal plasma. Marked increases in norepinephrine, small rises in epinephrine, but no changes in L-dopa or dopamine concentrations occurred in fetal plasma from mid- to late gestation. Maternal plasma catecholamines did not change. Towards the end of gestation, dopamine in the amniotic fluid increased 15-fold, and norepinephrine increased 5- to 6-fold; L-dopa remained high and unchanged. We conclude that L-dopa is the predominant catecholamine in fetal plasma and amniotic fluid during human pregnancy. No significant changes in its concentrations occur in either compartment between mid- and late gestation. In contrast, dopamine levels, which are 30- to 50-fold lower than those of L-dopa in amniotic fluid during midgestation, show a striking elevation toward the time of labor. Neither the sources nor the possible physiological functions of either L-dopa or dopamine during fetal life are known.