FETAL LIPOPROTEINS AND PLACENTAL RELEASE OF ESTERIFIED LIPIDS

An in vitro incubation technique was used to examine the release of li pids from the rabbit placenta. Free fatty acid, but not phospholipid o r triacylglycerol, was released into the incubation media. In a second series of experiments, the addition of lipids to the umbilical circul ation was studied in situ in the placenta of anaesthetized rabbits at late gestation. Each placenta was perfused from the fetal side in turn with two different perfusate solutions, either 4% bovine albumin solu tion or rabbit plasma. The rabbit plasma contained the appropriate car riers (lipoproteins) for esterified lipids, whereas the 4% albumin sol ution did not. The effluent perfusates were remarkably similar in free fatty acid concentration and composition, which closely matched the m aternal free fatty acid profiles. The concentrations and fatty acid co mposition of the perfusate triacylglycerol and phospholipid fractions were unchanged by passage through the placenta, whether perfused with 4% albumin or with rabbit plasma. With this system, no evidence could be found for the addition of esterified lipids to the umbilical circul ation in the rabbit despite the provision of appropriate carriers on t he fetal side of the placenta.