Serotonin metabolism in normal and abnormal infants during the perinatal period.

The concentration of serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) in various body fluids was measured during the perinatal period in two groups of infants born with normal and pathological conditions, respectively. Evidence was obtained showing that fetal blood 5-HT level was relatively stable, uninfluenced by maternal or fetal factors, and was about half the value of the maternal blood. High levels of 5-HIAA and evidence of an active decomposition of 5-HT were found in the amniotic fluid. These findings suggest that 5-HT in utero is subjected to a very active metabolic turnover. The origin of the fetal blood 5-HT and the significance of the placenta in the control of intrauterine 5-HT metabolism is discussed. There was no clear evidence of abnormal 5-HT metabolism in toxemic pregnancies, premature babies, and an infant with Down's syndrome in the perinatal period.