Metabolic Balance of the Ovine Fetus during the Fed and Fasted States

The present study was performed in order to quantitate the uptake and excretion of a number of metabolic substrates by the sheep uterus as well as the fetus during the fed and fasted states within the same animals. 5 dated Suffolk sheep were studied initially at least 7 days after surgical placement of catheters in the fetal umbilical artery and vein, as well as the uterine veins and maternal artery. During the fed state and after 5 days of complete maternal fasting, measurements were made of uterine and umbilical blood flow by the steady-state antipyrine method, and the concentrations of whole blood glucose, oxygen, ammonia, 23 amino acids and plasma urea nitrogen were assessed. The results indicate that free amino acids and glucose comprise the major substrates required by the fetal lamb during both the fed and fasted states. While a number of amino acids changed in concentration in both the maternal and fetal circulations, few amino acids demonstrated a significant change in uptake in either the umbilical or uterine circulations. Similarly, no changes were observed in the uptake of oxygen by either the fetus or the uterus, while glucose consumption by the fetus decreased substantially with a concomitant increase in urea production. Consumption of both glucose and oxygen by the uteroplacenta remained unchanged during fasting. Leucine is one of several amino acids which is metabolized to a significant extent within the uteroplacenta, and theoretically may play a role in modulating glucose metabolism within the placenta and fetus.