Digestion and absorption of carbohydrates by the fetal lamb in utero.

Intestinal digestive function was studied in 12 chronically catheterized third trimester fetal lambs by instilling glucose, fructose, lactose, maltose, and sucrose into their duodenums. Glucose was absorbed rapidly with the peak circulating glucose concentration reached within 1 hr. Fructose was absorbed well, but in contrast to glucose, blood fructose concentration did not peak; it continued to climb for 4 hr. Intraduodenal lactose administration resulted in a rapid rise in blood glucose with the maximum value reached in 1 hr. After receiving either glucose or lactose fetuses older than 130 days showed a faster rise in blood glucose, a greater total increase in glucose and a more rapid return to control levels than the younger fetuses. No change in blood glucose occurred with either maltose or sucrose administration. An increase in lactate concentration and a rise in fetal [H+] were noted after glucose and lactose administration, the only studies in which an increase in blood glucose concentration occurred.

Fetal umbilical venous-arterial differences of citrate in the chronically catheterised sheep.

Whole blood citrate concentration was measured simultaneously in the umbilical vein, fetal femoral artery and maternal artery in seven chronically catheterised pregnant ewes and their fetuses. The mean citrate concentration was 0-321 mmoles/litre in the umbilical vein, 0-297 mmoles/litre in the fetal femoral artery and 0-095 mmoles/litre in the maternal artery. The mean concentration difference for citrate across the fetal placental circulation was 0-024 mmoles/litre but this was not statistically significant (P less than 0-1).

Glucose and oxygen metabolism in normally oxygenated and spontaneously hypoxemic fetal lambs.

Whole blood glucose and oxygen concentration were measured in chronically catheterized fetal lambs, some of whom had implanted common umbilical artery flow transducers. Ten of the fetuses were well oxygenated (femoral arterial PaO2 less than 18 torr) and 13 fetuses had evidence of chronic hypoxemia (femoral arterial PaO2 less than 18 torr). The mean glucose uptake (54.0 +/- 7.6 S.E.M. mM. per kilogram per day), umbilical blood flow (230 +/- 13 S.E.M. ml. per kilogram per minute), and glucose/oxygen ratio (0.503) were the same in both fetal groups. The oxygenated fetuses had higher glucose levels at ang given maternal glucose concentration than the hypoxemic animals (p less than 0.001y and showed a correlation between glucose again across the placental circulation and the transplacental driving force for glucose (p less than 0.002). The hypoxemic fetuses, who had a higher per kilogram oxygen consumption than the oxygenated fetuses (p less than 0.05), showed no correlation between the amount of glucose taken up and the transplacental glucose concentration gradient.

Lactate and pyruvate as fetal metabolic substrates.

Lactate and pyruvate concentration differences across the fetal umbilical circulation and the maternal uterine circulation were measured in a chronic sheep preparation. Significant gains in lactate in both the fetal and maternal circulations were observed. The lactate taken up by the fetus would account for 32% of fetal oxygen consumption if oxidized. There was no significant change in pyruvate concentration across the fetal umbilical circulation; however, pyruvate was gained by maternal uterine blood.

Acetate as a metabolic substrate in the fetal lamb.

Fetal acetate metabolsim was studied in chronically catheterized fetal lambs of 110-141 days' gestation. Acetate concentration was measured enzymatically in whole blood drawn simultaneously from maternal and fetal pre- and postplacental vessels. The oxygen content of the fetal blood samples was also measured. Fetal umbilical venous acetate concentration was found to be proportional to the maternal arterial acetate concentration and had a mean value of 0.366 mM. Fetal blood acetate increased significantly, by a mean of 0.081 mM, during circulation through the placenta. This increase was proportional to both the maternal acetate concentration and the concentration gradient of acetate across the placenta. The mean maternal arterial acetate concentration was 1.153 mM. Maternal blood lost significant amounts of acetate, 0.112 mM, during circulation through the uterus and appeared to be the source of the acetate being gained by the fetus. It is estimated that a total of 23 mmol of acetate/kg of fetal weight is being taken up by the fetus each day, providing it with 0.560 g of carbon/kg. Comparisons of acetate uptake with fetal oxygen uptake indicate 10% of the daily fetal oxygen consumption would be required to completely oxidize the acetate being gained by the fetus.