Arachidonic acid incorporation into lipids of term human amnion

There were no differences in the rate or amount of (1-14C)-labeled arachidonic acid incorporated into triacylglycerides, diacylglycerides, or any phospholipid species of freshly dispersed term human amnion cells obtained before or after labor. Both phosphatidylcholine and phosphatidylethanolamine incorporated 14C-arachidonic acid in proportion to their molar percent of total amnion phospholipids, but phosphatidylinositol incorporated three times as much 14C-arachidonic acid, suggesting either a rapid turnover in this specific phospholipid pool or a greater specificity for the transfer of arachidonoyl-coenzyme A to lysophosphatidylinositol. No or little competition of 14C-arachidonic acid incorporation into triacylglycerides or phospholipids occurred with palmitic acid, linoleic acid, or gamma-linolenic acid. However, dihomo-gamma-linolenic acid, eicosapentaenoic acid, and unlabeled arachidonic acid were effective inhibitors. We conclude that the term amnion has high acyl transferase activity, that no change in the basal activity of this enzyme occurs with the onset of labor, and that a specific acyl transferase exists for 20-carbon polyunsaturated fatty acids.