Bidirectional Placental Transfer of Glucose and Its Turnover in Fetal and Maternal Sheep

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Abstract
SUMMARY: Glucose biokinetics were assessed simultaneously in the pregnant ewe and its fetus by a primed constant infusion of 2-1H glucose and U-1 C glucose. Late in gestation fetal glucose turnover was 27.3 ± 3.7 mg/min; expressed in terms of fetal weight this is 6 to 10 mg/kg/min. In the fed state the results indicated that all of the fetal glucose turnover was derived from the mother via placental transfer and there was no evidence that the fetus was capable of glucose production. Maternal glucose turnover was 145.6 ± 9.3 mg/min (2.8 mg/kg/min). There was a significant amount of glucose (16.3 ± 2.3 mg/min) transferred from the fetus to the mother. This feto-maternal transfer of glucose accounted for 11% of the maternal glucose turnover and approximately 50% of the total glucose coming to the fetus from the mother. This study provides the first in vivo simultaneous quantification of the bidirectional glucose transfer across the placenta. Speculation: In the fed state all the fetal glucose is derived from the mother, and the fetus does not produce glucose. A large portion of the glucose coming from the mother to the fetus is returned to the mother, despite glucose concentrations that are threefold higher in the mother than fetus. Thus, the transplacental passage of glucose is bidirectional, this bidirectionality may be responsible for maintaining the concentration gradient that always keeps fetal glucose ooncentration at a lower level than that of the mother, and thereby facilitates fetal glucose supply.

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