Localization and developmental change of indoleamine 2,3-dioxygenase activity in the human placenta.

Previously, we pointed out the importance of the kynurenine metabolism in fetuses and neonates. We examined localization and developmental change of indoleamine 2,3-dioxygenase activity in human placenta. The indoleamine 2,3-dioxygenase was found localized in syncytiotrophoblast in the placenta. The indoleamine 2,3-dioxygenase activity was not detected in placenta in the early stage of gestation. It was first detected at around 14 weeks of gestation, increased rapidly thereafter and was maintained at high levels till near term. The indoleamine 2,3-dioxygenase activity was significantly lower in placenta with retarded intrauterine development. These results suggest the importance of placental indoleamine 2,3-dioxygenase during fetal development.