EVIDENCE FOR A CRITICAL PERIOD DURING LATE GESTATION WHEN MATERNAL DIETARY CARBOHYDRATE IS ESSENTIAL FOR SURVIVAL OF NEWBORN RATS

Two experiments were designed to test the hypotheses that 1) maternal dietary carbohydrate is required on d 20-21 of gestation (gd 20-21), when fetal liver glycogen is accumulating, to ensure the postnatal survival of the newborn rat pup and that 2) the lack of maternal dietary carbohydrate during this critical 2-d period will cause high neonatal mortality. Pregnant dams were fed one of two lipid-based, carbohydrate-restricted experimental diets. In experiment 1, the primary energy source was soybean oil; the diets contained no added glucose but contained 4% glucose-equivalents as lipid-glycerol. In experiment 2, the major lipid component was food-grade oleic acid; this diet was supplemented with 4% glucose. A crossover design was used. For gd 0-19, dams were fed either the high carbohydrate diet (62% glucose) or one of the carbohydrate-restricted diets (4% glucose or 4% lipid-glycerol); beginning on gd 19 and through neonatal d 7 (nd 7), the opposite diet was fed. For controls in each experiment, a high carbohydrate diet (62% glucose) and the respective carbohydrate-restricted diets were fed throughout pregnancy. The results showed that restriction to 4% glucose equivalents beginning on gd 20 resulted in high first-day neonatal mortality that was comparable in magnitude to nd-1 mortality rates in dams fed the carbohydrate-restricted diets throughout pregnancy. Repletion with the high carbohydrate, control diet after gd 19 significantly reduced mortality. These experiments demonstrate that maternal dietary carbohydrate beginning in late gestation is essential for the postnatal survival of rat pups.