Cerebral glucose utilization during aerobic metabolism in fetal sheep.

Abstract

Extract: The relative utilization rates of glucose and oxygen by the fetal brain were evaluated by measuring simultaneously arteriovenous differences of glucose (Δ glucose) and oxygen (Δ oxygen) across the cerebral circulation of 10 fetal sheep. The mean ± 1 SEM Δ glucose was 0.197 ± 0.012 mM, and the Δ oxygen was 1.11 ± 0.08 mM. Preductal arterial blood was obtained from the brachiocephalic artery; cerebral venous blood was obtained from the fetal sagittal sinus up to 6 days following surgery. A glucose/oxygen quotient was calculated to determine the fraction of cerebral oxygen consumption required to metabolize the glucose utilized by the brain to CO2 and H2O. This quotient was 1.06 with 95% confidence limits of 1.12 and 1.02. These data indicate that glucose can supply all the aerobic metabolic requirements of the fetal brain. Speculation: Although glucose seems to be the primary substrate of cerebral metabolism, the amount of glucose acquired by the fetal lamb via the umbilical circulation can satisfy, at most, one-half of the total fetal aerobic needs. Thus the fetal brain seems much more dependent on glucose than do other fetal organs, and may be particularly vulnerable to periods of hypoglycemia.