Effect on Placental Transfer of Exogenous Lipid Administered to the Pregnant Rabbit

The transfer of lipids across the placenta was measured after infusion of an emulsion of triacylglycerol and phospholipid (intralipid) into 10 anesthetized rabbits. Maternal and umbilical venous and arterial samples were collected at 10-min intervals. All samples were analyzed for concentration and fatty acid composition of FFA, triacylglycerol, and phospholipid fractions. At the end of the infusion period of intralipid, there was a significant increase in the maternal concentrations of total triacylglycerol (p 0.05). Maternal plasma triacylglycerol and phospholipid altered in composition to match that of the infused Intralipid by the end of the infusion. Despite the significant rise in maternal triacylglycerol and phospholipid concentrations, the umbilical vein-artery difference for these lipid fractions remained unchanged and very low. In contrast, the umbilical vein-artery difference for FFA (p < 0.02) rose gradually throughout the experiments. There was no significant change in the fatty acid composition of the maternal FFA, but the fatty acid composition of the umbilical vein-artery difference for FFA changed to reflect the composition of Intralipid. These experiments show that exogenous triacylglycerol and phospholipid dramatically alter the lipid fractions presented to the placenta in the maternal plasma but do not cross the placenta intact. However, the composition of the FFA crossing the placenta is modulated to become more similar to that of the exogenous lipid.