Metabolism of amniotic fluid dopamine by fetal membranes

The concentrations of L-dopa, three catecholamines and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured both in the amniotic fluid and the fetal urine obtained at term elective cesarean section, using high performance liquid chromatography with electrochemical detection. Dopamine was the major compound in the fetal urine, while DOPAC predominated in the amniotic fluid. Monoamine oxidase (MAO) activity was detected in the fetal membranes by the method of Wurthman and Axelrod. MAO activities in the amnion, chorion and decidua were 0.023 +/- 0.003, 0.180 +/- 0.05 and 2.69 +/- 0.66 nmol/mg protein/min (mean +/- SE), respectively. Incubation experiments, using fetal membranes with human amniotic fluid, demonstrated that dopamine in amniotic fluid was metabolized to DOPAC by fetal membranes. Additional incubation experiments with pargyline, a MAO inhibitor, showed that it strongly inhibited the conversion of dopamine into DOPAC. These results suggest that the dopamine in amniotic fluid was metabolized to DOPAC by MAO in the fetal membranes. This mechanism may regulate the dopamine concentration in amniotic fluid.