LIPOGENESIS FROM LACTATE IN FETAL-RAT BRAIN DURING LATE GESTATION

Much evidence suggests that lactate may play a relevant role as a metabolic substrate for the brain immediately after delivery. In this work, the rate of lactate, glucose, and 3-hydroxybutyrate incorporation into CO2, phospholipids, and sterols was studied in fetal rat brain slices during the last 3 d of gestation. Lactate was the best substrate for the brain during the late gestation, not only as a source of energy, but also as precursor of brain phospholipids and sterols. The rates of oxidation and lipogenesis from glucose and 3-hydroxybutyrate showed a progressive decrease during late gestation (10-15% reduction on d 20.5, p < 0.05, and 22-33% on d 21.5, p < 0.01, for oxidation; 14-18% on d 20.5, p < 0.05, and 20-22% on d 21.5, p < 0.05, for lipogenesis), whereas lactate maintained its rate of utilization in the same circumstances. The main phospholipid synthesized throughout the late gestation was phosphatidylcholine. The synthesis of phosphatidylcholine and phosphatidylethanolamine from lactate, glucose, and 3-hydroxybutyrate decreased during late gestation. Under these circumstances, however, the rate of phosphatidylserine synthesis from glucose was unchanged; it decreased from 3-hydroxybutyrate and increased from lactate. The rate of desmosterol synthesis was about 3- to 4-fold higher than those of cholesterol and lanosterol. Our results suggest that the capacity of fetal brain for lactate utilization remains high during late gestation, but the capacities for the utilization of glucose and 3-hydroxybutyrate decrease until term. This may indicate that lactate is an important substrate for brain development during late gestation.