Delta 9- and delta 6-desaturase activities of the ovine placenta and their role in the supply of fatty acids to the fetus.

Although the fatty acid compositions of the total lipids of the sheep placenta and fetal plasma were shown to be broadly similar, they differed significantly from the fatty acid composition of the maternal plasma unesterified fatty acids, the plasma lipid component from which the fetus derives almost all of its requirements for pre-formed fatty acids. In particular, the placental and fetal plasma lipids displayed a 3-fold higher oleic acid/stearic acid ratio and contained a significantly higher proportion of arachidonic acid than the maternal unesterified fatty acids. These differences correlated well with the high delta 9- and delta 6-desaturase activities, respectively, shown to be present in sheep placental tissue in vitro. The levels of these enzymes in placental tissue contrasted with the relatively low desaturase activities found to be present in adult and neonatal sheep liver and in the placentas of other, non-ruminant, species. The possible role of such high levels of desaturase activity in the sheep placenta is discussed in relation to the particularly poor essential fatty acid status imposed upon the fetal ruminant.