O-2 CONSUMPTION IN THE IN-VITRO FETAL SIDE HUMAN PLACENTA

The relative dependence of placental O-2 consumption (M(O2)) on O-2 su pply (SupO(2)) parameters, and the fraction of aerobic O-2 utilization , was studied by in-vitro perfusion of the fetal side of term human pl acental lobes. Placental (M(O2), was a function of the combined effect of SupO(2) parameters (P-O2), perfusate flow rate, perfusate effectiv e O-2 solubility) and not of each separately. At SupO(2) greater than 800 mu l(min . lobe), M(O2) saturated at 260 mu l/(min . lobe). No acc umulation of O-2 debt could be detected even after 2 h anoxia. Adding CN- or CO to perfusate did not abolish M(O2), and a residual M(O2) Of 31-37% of control M(O2) was measured. In its M(O2), the placenta is a typical conformer tissue. This conformity enables conservation of O-2 transfer to the embryo even when placental SupO(2) is radically reduce d. Only about 60-70% of placental M(O2) is utilized in the aerobic res piratory pathway, while about 30-40% of the oxygen is used in other pa thways.