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

Abstract

In the isolated, perfused guinea pig placenta, glucose seemed to be a major nutrient of energy metabolism, because the excreted amounts of CO2 and lactate were explained solely by the catabolism of glucose. In steady-state experiments, H ions, ammonia, lactate and CO2 dioxide were excreted for at least 90 min in rather constant amounts. The production of lactate showed no significant dependence on the glucose concentration in the perfusion fluid. The guinea pig placenta seemed to cover its energy requirement mainly by means of anaerobic glycolysis. Of the utilized glucose, 76% was metabolized anaerobically. The placenta produced significant quantities of lactate, although it was well oxygenated. A reduction of the O2 tension in the perfusion fluid did not result in an increase of the production of lactate. Of the H ions excreted, nearly 50% were excreted as ammonia. Although the excreted amounts were small compared with the known transfer rates, they were taken into consideration when studying transplacental transfers of these metabolites.