The role of the placenta in the supply of essential fatty acids to the fetal sheep: studies of lipid compositions at term.

A study has been made of the comparative distribution and fatty acid compositions of the major lipid fractions of maternal plasma, placenta and fetal plasma of the sheep at approximately 120 days of gestation. Cholesteryl esters and phospholipids constituted the major lipid fractions present in both maternal and fetal plasmas. In the placenta, phospholipids accounted for some 60 per cent of the total lipid present. Within the phospholipids of the maternal and fetal plasmas and placenta, phosphatidylcholine comprised the largest component. Whereas maternal plasma contained high levels of linoleic and arachidonic acids, fetal plasma contained a low proportion only a linoleic acid and high proportions of delta 5,8,11 eicosatrienoic acid and arachidonic acid. In the maternal plasma the arachidonic acid:linoleic acid ratio was only 0.17, but in the fetal plasma the ratio was 3.32. The differences in the lipid and fatty acid compositions between the maternal plasma, fetal plasma and placenta are discussed in relationship to the distinctive polyunsaturated fatty acid metabolism of the fetal and newborn lamb.