Phospholipids from rat, human, and canine gastric mucosa. Composition and metabolism of molecular classes of phosphatidylcholine. To validate a recent proposal that a phospholipid lining with a high content of dipalmitoylphosphatidylcholine may protect gastric mucosa against luminal acid, it was decided to study composition and metabolism of phospholipids in the gastric mucosa. Phospholipids were analyzed in rat, human, and dog gastric mucosal surface tissue and in a chloroform/methanol-lavage of rat and canine stomach. Phosphatidylcholine and phosphatidylethanolamine were the main components. Saturated fatty acids were almost exclusively esterified at the sn-1 position of the glycerol moiety of phosphatidylcholine, and unsaturated fatty acids mainly at the sn-2 position. The disaturated class of phosphatidylcholine comprised 2%-6% of total phosphatidylcholine. Precursors of phosphatidylcholine, i.e., [32P]orthophosphate and [methyl-14C]choline, were preferentially incorporated into the disaturated molecular class 0.5-6 hours after IV administration. It can be speculated that disaturated phosphatidylcholine, although quantitatively a minor component, is specifically triggered in mucosal renewal processes. 