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To determine the placental clearance of lactate and bicarbonate in sheep, the fetal side of an isolated cotyledon and the umbilical circulation of the total placenta were artificially perfused. The release and uptake of lactate and bicarbonate by the perfusion fluid and the fetomaternal concentration differences of these substances were measured. From these data, the clearance of lactate and bicarbonate was determined to be 0.9 (SE = 0.2) ml/h/g of placental tissue. The production of lactate by the placenta was calculated to be about 30 µmol/min, the placental permeability of lactate was evaluated to be about 1.3 ml/h/g of placental tissue. These results indicate that fetal concentration changes of lactate and bicarbonate due to placental transfer occur with a half time of about 4 h. It is concluded that the lactate and bicarbonate permeability of the syndesmochorial placenta of the sheep is about 20 times smaller than the placental permeability of the hemochorial placenta of the guinea pig. It seems unjustified to draw any conclusions from experimental data obtained in the sheep placenta for the transplacental acid-base balance between mother and fetus in human beings.

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The cardiovascular and metabolic responses during acute fetal hypoxia were studied in 7 pregnant sheep near term. Complete reduction of uterine flow (UBF) for 180 s was performed in 13 experiments by inflating a balloon positioned in the maternal aorta. Fetal heart rate (FHR), systolic and diastolic blood pressure (BP) and fetal arterial oxygen saturation (SO₂) were measured continuously. Blood samples were taken at short intervals and analyzed for pH, PO₂, PO₂ SO₂ base excess and lactate. Following the reduction of UBF, FHR began to rise after 4.7 ± 14.4 (SD) s and fell after 31.3 s paralleled by the rise of the BP after 23.2 ± 8.2 (SD) s. The fall of FHR was not related to the SO₂ at control, but to the decline of the SO₂ by 10–15%. There was no critical limit of SO₂ at which the FHR started to fall and the BP began to rise. The rise of the FHR after UBF had been released was significantly correlated to the rise of SO₂.Lactate production during hypoxia was related to the slope of the SO₂ decline, i.e., to the fetal O₂ consumption. The total metabolic response during hypoxia and recovery given by the pH area was correlated to the SO₂ at control. No correlation between dip area of FHR and PH area could be established.