Placental Clearance of Lactate and Bicarbonate in Sheep

Abstract

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.

The effects of metabolic acidosis on renal function of fetal sheep.

“…1 C). These observations confirm the findings of others that bicarbonate and hydrogen ions do not readily cross the sheep placenta (Daniel et al 1975;Kastendieck et al 1979). The fetal renal response to a metabolic acidosis was similar to the adult (Sartorius, Roemmeit & Pitts, 1949) in that initially a natriuresis and chloresis were observed.…”

“…It is often assumed that control of fetal acid-base balance in utero is solely a function of the placenta. Transfer of carbon dioxide across the placental membranes in most mammalian species is rapid (Comline & Silver, 1970;Silver, Steven & Comline, 1973); the transplacental transfer in the sheep of bicarbonate ions (Kastendieck, Kunzel & Kurz, 1979) and hydrogen 6. J. KESBY AND E.R.…”

Plasma free and sulfoconjugated catecholamines during acute asphyxia in the sheep fetus — relation to cardiovascular parameters

“…As a result of total cessation of blood flow to the hindquarters for 5 minutes, metabolic effects on the mother have to be taken into account. However, it seems unlikely that these affects should influence the fetus, since the syndesmochorial placenta of the sheep has a 10 to 20-fold lower permeability for electrolytes, lactate, and bicarbonate as compared to the hemochorial type of placenta [6,18]. Furthermore, there is no evidence for materno-fetal transfer of catecholamines across the placenta [13].…”

Regulation of placental nutrient transport and implications for fetal growth

“…The placentae of other species, including man (Challier et al 1986), are similarly glycolytic. Placental perfusion studies (Kastendieck et al 1979), combined with analysis of the fetoplacental exchanges of radiolabelled glucose and lactate (Bassett, 1986), indicate that the fetomaternal interface of the ovine placenta is highly impermeable to lactate. Thus, little or none of the energetically significant net uptake of lactate by the ovine fetus is derived directly from the maternal circulation or glycolysis in the maternal caruncular tissues.…”