The metabolism of the isolated artificially perfused guinea pig placenta. I. Excretion of hydrogen ions, ammonia, carbon dioxide and lactate, and the consumption of oxygen and glucose.

In the isolated, perfused guinea pig placenta glucose seems to be a major nutrient of energy metabolism, because the excreted amounts of carbon dioxide and lactate can be explained solely by the catabolism of glucose. In steady state experiments hydrogen ions, ammonia, lactate and carbon dioxide are excreted for at least 90 minutes in rather constant amounts. The production of lactate shows no significant dependence on the glucose concentration in the perfusion fluid. The guinea pig placenta seems to cover its energy requirement mainly by means of anaerobic glycolysis. Of the utilized glucose 76% are metabolized anaerobically. The placenta produces significant quantities of lactate, although it is well oxygenated. A reduction of the oxygen tension in the perfusion fluid does not result in an increase of the production of lactate. Of the hydrogen ions excreted nearly 50% are excreted as ammonia. Although the excreted amounts are small compared with the known transfer rates, they have to be taken into consideration, when studying transplacental transfers of these metabolites.