The oxygen consumption of the placenta and foetal membranes in the sheep

Abstract

SUMMARY1. In anaesthetized sheep near term the 02 uptake of the foetus from the placenta was reduced to zero either by replacing the foetus with a mechanical pump, or by ventilation of the foetus after delivery or in utero. When umbilical arterial and venous Po. were made equal, they were much less than maternal arterial Po2.2. This difference in Po2 was attributed to 02 consumption both within the placental cotyledons and the extra-cotyledonary foetal membranes. 3. The foetal membranes and cord in the sheep are supplied by branches of umbilical blood vessels and constitute an oxygen-consuming by-pass on the foetal side of the placenta.4. The 02 consumption of individual placental cotyledons was measured in vivo.5. The combined 02 consumption of the whole placenta and foetal membranes in vivo was a considerable fraction of foetal 02 consumption.6. The consequences of these observations are discussed in relation to 02 transfer across the placenta.

PO2, PCO2 and pH levels in the umbilical and uterine blood of the mare and ewe

“…Thus foetal hypoxia occurs only after a marked reduction in the maternal arterial blood Po2 and attempts to raise the foetal Po2 have met with little success despite the administration of pure oxygen to the mother (Comline, Silver & Silver, 1965;Kirschbaum, Lucas, De Haven & Assail, 1967; Acheson, Cook & Reynolds, 1967;Parker & Purves, 1967). The Po2 gradient across the placenta is still present even when the foetus is supplied with oxygen by other means (Campbell, Dawes, Fishman, Hyman & James, 1966).…”

The pregnant sheep as a model for human pregnancy

“…In the 1960's, Campbell et al [69] determined that the PO 2 gradient across the placenta remains constant despite decreases in maternal oxygenation and uterine blood flow. The constant oxygen gradient between maternal and fetal circulation sustains fetal oxygen delivery at normal rates.…”

Movement of Oxygen, Glucose, and Lactate across the Uterus of the Awake Near-Term Guinea Pig

“…The fractional distribution ofthe uterine O2 uptake between uteroplacental and fetal tissue can only be determined when the O 2 uptake of one of these two tissues is known. Values reported from in vitro measurements of placental O2 uptake in the sheep, rabbit, rat, mouse, guinea pig, and man range from 100-500 /-tmol.min-'.kg-' (17)(18)(19)(20). However, an in vivo study in the near-term ewe demonstrated the importance of intact uteroplacental and umbilical circulations as well as the absence of anesthesia for normal uteroplacental O2 consumption (12).…”