Newborn humans and rats malnourished in utero: free plasma L-tryptophan, neutral amino acids and brain serotonin synthesis.

In the present study we report results concerning 5-hydroxytryptamine (5-HT) metabolism in two groups of small for date (SFD) human babies (gestational age 36 and 3 weeks), who suffered intrauterine nutritional restriction. A complementary study in the brain of rat fetuses with two types of intrauterine deprivation, in which brain L-tryptophan (L-Trp), tryptophan-5-hydroxylase (T5-H) activity and 5-HT content were determined on days 17, 19 and 21 of gestation. The same parameters studied prenatally were followed in both species during the immediate postnatal period. In the SFD babies the results were: (a) the free fraction of plasma L-Trp was significantly elevated; (b) plasma neutral amino acids were not substantially modified; (c) the bound fraction of L-Trp and plasma proteins were significantly low, as compared to controls. In the fetal brain of intrauterine malnourished rats, L-Trp, activity of T5-H and 5-HT content, were significantly elevated, since day 17, as related to normal littermates. These alterations in 5-HT metabolism persisted during the early postnatal period in both species. Elevation of the free fraction of plasma L-Trp in early malnourished SFD human babies suggest an increased transport of this amino acid to the brain with a possible enhancement of serotonin synthesis, during a critical period of brain differentiation.