Umbilical and Uterine Venous PO₂ in Different Species during Late Gestation and Parturition

Abstract

A large PO₂ difference (l7–21mmHg) between uterine and umbilical venous blood is found in the cotyledonary placenta of ruminants, whereas in the equine placenta the corresponding vein-to-vein difference is only 2–4mmHg (Silver, Steven & Comline, 1973). The pig is another species with a diffuse placenta like that of the mare but without the specialised microcotyledons of the latter; simple vascular networks are found on either side of the pig placenta (Tsutsumi, 1962). Preliminary experiments have now been carried out in this species to determine the transplacental blood gas gradients and the changes which occur when maternal arterial levels are altered. In acute experiments under sodium pentobarbitone anaesthesia, vinyl catheters were inserted into uterine and umbilical vessels without disturbance of the fetus. The umbilical vessels were catheterised through small branches which were only a short distance from the cord. Because each fetus was small even near term, repeated observations were made on different fetuses rather than on a single individual.