Figure 7.

Schematic depiction of the TRP metabolic pathways in the rat fetoplacental unit during gestation. Although basal levels of TRP, 5-HT, and KYN in maternal plasma remain stable during gestation, their concentrations change significantly in the placenta and fetal organs. Based on our results and literature research [19,32,33,34,35,36,37] we show that the placental metabolism of TRP to 5-HT is important up to mid-gestation, with a subsequent decline (as the fetus becomes independent of placental sources of 5-HT). On the other hand, the placental production and utilization of KYN increase during pregnancy. Full arrows show metabolic activity or concentration levels, and dotted arrows show the gene or protein expression.