Glucose, lactate and oxygen metabolism in the fetal pig during late gestation

Using [U-C-14]glucose tracer, rates of umbilical uptake, utilization and production of glucose, and of CO2 production from glucose carbon, were measured in seven chronically catheterized fetal pigs, when the sow was in the fed state, between 100 and 113 days of gestation (term, 114 +/- 2 days). At the same time, rates of umbilical O-2 and lactate uptake were determined in all seven fetuses by the Fick principle. The mean fetal rates of umbilical glucose uptake, glucose utilization and CO2 production from glucose carbon were 38.4 +/- 4.2, 41.3 +/- 5.2 and 126.9 +/- 12.6 mu mol min(-1) (kg fetal body weight)(-1), respectively (n = 7). No glucose production was therefore detected in the fetuses. Production of CO2 from glucose carbon accounted for 37.3 +/- 34% (n = 7) of the umbilical O-2 uptake, which averaged 340 +/- 13 mu mol min(-1) kg(-1) (n = 7). There was also significant umbilical lactate uptake in the fetal piglets when the sow was in the fed stale (32.6 +/- 10.4 mu mol min(-1) kg(-1), n = 7, P < 0.05). No significant changes in fetal glucose, O-2 or lactate metabolism were observed with increasing age towards term. The fetal rates of glucose metabolism and of umbilical uptake of O-2 and lactate were not correlated with the fetal blood glucose level. Hence, glucose is used for both oxidative and non-oxidative metabolism in utero and is an important, although not the sole, source of carbon for metabolic processes in the fetal pig during late gestation.