Oxidative metabolism in fetal rat kidney during late gestation

Slices of fetal rat kidney were incubated for 90 min at 37 degrees C in Krebs phosphate buffer containing [14C]glucose. Glucose uptake did not change significantly with age, but the 14CO2 evolved from [14C]-glucose dropped, and the lactate concentration at the end of incubation rose. The increasing development of the medulla during gestation was believed to be responsible for this. Higher glucose uptake and lower [14C]glucose incorporation into CO2 was observed in whole fetal slices compared to cortical slices from adult kidney, incubated following the same procedure. These results might be due to the smaller number of functionally differentiated nephrons present in fetal compared to adult kidney. Competition between glucose and lactate, normally found at high concentrations in fetal blood, and between glucose and beta-hydroxybutyrate, known to increase in circumstances such as starvation in the mother, showed a decrease in the 14CO2 evolved from [14C]glucose. This suggests that both these substrates might be oxidized by fetal kidney. This was confirmed by experiments in which lactate or beta-hydroxybutyrate replaced glucose in the incubation medium. Further, both these substrates seemed to be preferential fuels for oxidation compared to glucose, and their possible role in saving glucose is discussed.