Rat gastric hydrophobic barrier: modulation of phosphatidylcholine molecular species by dietary lipids.

Phospholipids protect the gastric mucosa by forming a proton-repellent hydrophobic layer on its luminal surface. We have recently shown that two molecular species of phosphatidylcholine (PC), PC16:0/18:1, and PC16:0/18:2, but not PC16:0/16:0, are predominantly released into gastric mucus. We investigated whether these molecular species in mucus are modified by dietary fat. Rats were fed (for three weeks) a diet supplemented with either 10% cod liver, palm, or sunflower oil, or 10% corn starch as a control. In tissue, cod liver oil decreased PC16:0/20:4 and PC18:0/20:4. Cod liver oil and palm oil increased PC16:0/18:1, whereas sunflower oil decreased PC16:0/18:1. Palm oil additionally decreased PC16:0/18:2, whereas the other diets had no effect on PC16:0/18:2. In mucus, however, PC16:0/18:1 and PC16:0/18:2 were not significantly altered by any diet. They were increased over tissue values and comprised 37.6 +/- 3.3 and 33.1 +/- 1.4 mol% in controls. PC16:0/16:0 was lower in mucus than in mucosa and even decreased by cod liver oil (1.2 +/- 0.2 vs. 2.7 +/- 0.3 mol%; P < 0.01). We conclude that PC16:0/18:1 and PC16:0/18:2 are modified by dietary fat in tissue. In gastric secretions, however, PC16:0/18:1 and PC16:0/18:2 are kept constant and together comprise 70 mol% of the released PC species, whereas PC16:0/16:0 does not play a role for the gastric hydrophobic barrier under any dietary treatment. Additionally, cod liver oil decreases the content of PC16:0/20:4 and PC18:0/20:4 in gastric mucosa, thereby possibly decreasing the formation of eicosanoids.