Oxygen, glucose, and lactate uptake by fetus and placenta during prolonged hypoxemia

Our aim was to compare the effects of short (4 h) and prolonged (24 h) periods of reduced uterine blood flow (RUBF) on fetal and placental uptake of O₂, glucose, and lactate. In pregnant sheep, uterine and umbilical blood flows were measured under normal conditions and after 4 and 24 h of RUBF. A 50% reduction in uterine blood flow caused a 56% reduction in fetal arterial O₂ saturation (Sa(O₂)). Umbilical blood flow increased from 325 ± 33 to 378 ± 32 ml · min^-1 · kg^-1 (P < 0.05) after 4 h but was not different from pre-RUBF values after 24 h. O₂ uptake by the gravid uterus was not altered by RUBF, due to an increase (84%) in uterine O₂ extraction. Similarly, uteroplacental and fetal O₂ consumptions and fetal glucose uptake were not affected by RUBF, whereas uteroplacental glucose uptake was significantly reduced after 4 h (by 42%) and 24 h (by 58%) of RUBF. Fetal lactate uptake was greatly reduced from 78.7 ± 15.5 to -167 ± 57 μmol · min^-1 · kg^-1 after 4 h and to -198 ± 80 μmol · min^-1 · kg^-1 after 24 h of RUBF; negative values indicate placental lactate uptake from the fetal circulation. Thus, although RUBF significantly reduced fetal Sa(O₂), fetal and uteroplacental O₂ consumptions did not change. In addition, although fetal glucose uptake was not altered by RUBF, during RUBF the placenta became a major site of lactate clearance from the fetal circulation.