The metabolism of 18∶0 and 18∶2(n−6) by the ovine placenta at 120 and 150 days of gestation

The effects of approach of parturition in the sheep on the incorporation of 18:0 and 18:2(n-6) into the placenta lipids and on the activities of the delta 9- and delta 6-desaturase enzymes of placental tissue have been studied in vitro. The incorporation of 18:0 into the esterified lipids of placental tissue between the 120th and 150th days of gestation declined markedly; the high level of incorporation of 18:2(n-6) into the esterified lipids of the placenta (some 2-fold higher than 18:0) remained constant over the gestational period. While placental delta 9-desaturase activity was the same at 150 days as at 120 days of gestation, the activity of the delta 6-desaturase enzyme increased significantly. These results are discussed in relation to the fetal demand for fatty acids near term and the differences that exist between the mechanisms of maternal-fetal transfer of 18:0 and 18:2(n-6) in the sheep.