The placental transfer of lactate and bicarbonate in the guinea-pig

In order to study the lactic acid transfer in a hemochorial placenta, the placenta of the guinea-pig was perfused in situ through the umbilical circulation with a colloidal solution containing L(+)-lactate and bicarbonate in various concentrations. It was found that the transfer rates of lactate and bicarbonate were proportional to the respective materno-fetal arterial concentration differences. When the concentration gradients for lactate and bicarbonate were opposite to each other, an exchange of lactate for bicarbonate occurred which is equivalent to a lactic acid transfer. The placental permeability for lactate was found to be 25 micronmol(h - micronmol/ml) per g of placental weight (S.E. = 2). A similar value was obtained for bicarbonate (23 micronmol/(h - micronmol/ml) per g; S.E. = 1.3). It is calculated that fetal concentrations of lactate and bicarbonate follow maternal concentration changes with a half time of 23 min.