Abstract
INTRODUCTION: The goal of this study was to define the kinetics of glucose transport from maternal blood to placenta to fetus using real time imaging. METHODS: Positron emission tomography (PET) imaging of the glucose-tracer [(18)F]fluorodeoxyglucose (FDG) was used to temporally and spatially define, in vivo, the kinetics of glucose transport from maternal blood into placentae and fetuses, in the late gestational gravid rat. Computed tomography (CT), with intravenous contrast, co-registered to the PET images allowed anatomic differentiation of placentae from fetal and maternal tissues. RESULTS: FDG was rapidly taken up by placentae and subsequently appeared in fetuses with minimal temporal lag. FDG standardized uptake values in placentae and fetuses approached that of maternal brain. In both anesthetized and awake dams, one quarter of the administered FDG ultimately was accrued in the collective fetuses and placentae. Accordingly, kinetic modeling demonstrated that the placentae had very high avidity for FDG, 2-fold greater than that of the fetus and maternal brain, when accounting for the fact that fetal FDG necessarily must first be taken up by placentae. Consistent with this, placental expression of glucose transporter 1 exceeded that of all other tissues. DISCUSSION: Fetal and placental tissues place a substantial glucose metabolic burden on the mother, owing to very high avidity of placentae for glucose coupled with the large relative mass of fetal and placental tissues. CONCLUSIONS: The placenta has a tremendous capacity to uptake and transport glucose. PET/CT imaging is an ideal means to study metabolite transport kinetics in the fetoplacental unit.