Journal of Applied Physiology, Vol 39, Issue 5 728-734, Copyright © 1975 by American Physiological Society
Physiological evidence consistent with the presence of a specific O2 carrier in the placenta
G. Gurtner and B. Burns
In 30 experiments we perfused the fetal side of the sheep placenta with
fluids which had different solubilities for argon, N2, and O2 (dextran,
blood, and fluorocarbon emulsions). In some of the experiments we partially
exchange-transfused the ewe with the fluorocarbon emulsion. By these
procedures we were able to change the physical solubility of argon and N2
severalfold in the fetal perfusion fluid and maternal blood. We found that
the diffusing capacity for argon and N2 did not increase with increases in
physical solubility in the fetal perfusion medium or in maternal blood.
This indicated that the rate-limiting step in the placental transfer of
these gases is the small diffusing capacity of the placenta. In contrast,
O2 diffusing capacity increased markedly with increased solubility in the
fetal perfusion medium. Also the Po2 was frequently the same in the venous
blood leaving both sides of the placenta. This indicates that O2 may reach
equilibrium between maternal and fetal capillaries in one pass through the
placenta. The results are compatible with the presence of specific O2
carrier in the placenta.
