O2 consumption in the in-vitro fetal side human placenta

The relative dependence of placental O2 consumption (MO2) on O2 supply (SupO2) parameters, and the fraction of aerobic O2 utilization, was studied by in-vitro perfusion of the fetal side of term human placental lobes. Placental MO2 was a function of the combined effect of SupO2 parameters (PO2, perfusate flow rate, perfusate effective O2 solubility) and not of each separately. At SupO2 greater than 800 microliters/(min.lobe), MO2 saturated at 260 microliters/(min.lobe). No accumulation of O2 debt could be detected even after 2 h anoxia. Adding CN- or CO to perfusate did not abolish MO2, and a residual MO2 of 31-37% of control MO2 was measured. In its MO2, the placenta is a typical conformer tissue. This conformity enables conservation of O2 transfer to the embryo even when placental SupO2 is radically reduced. Only about 60-70% of placental MO2 is utilized in the aerobic respiratory pathway, while about 30-40% of the oxygen is used in other pathways.