The effect of phosphatidylcholine and lysophosphatidylcholine on the absorption and mucosal metabolism of oleic acid and cholesterol in vitro.

The absorption and mucosal metabolism of [14C]oleic acid and [3H]cholesterol were studied using everted sacs of rat jejunum in an in vitro incubation system. The labeled compounds were present in the incubation mixture either singly or together as mixed micelles with bile salt and monoacylglycerol and in the presence or absence of phosphatidylcholine or lysophosphatidylcholine. The presence of cholesterol or phosphatidylcholine markedly suppressed oleic acid absorption. We suggest that both compounds interacted with the micelles causing changes in micellar mass, charge or configuration leading to possible interference with access of the fatty acid to the cell membrane. Lysophosphatidylcholine enhanced oleic acid absorption and stimulated incorporation of the fatty into mucosal triacylglycerol. When the incubation temperature was lowered to suppress metabolism lysophosphatidylcholine had no effect. The results suggest that the increased absorption occurring at the higher temperature was secondary to enhanced glycerol acylation. Lysophosphatidylcholine had only a minimal effect on cholesterol absorption and no effect on cholesterol acylation. Evidence is presented showing that lysophosphatidylcholine is itself well absorbed and variously metabolized. We conclude that phosphatidylcholine and lysophosphatidylcholine have quite divergent effects on lipid absorption but the full elucidation of their mechanisms of action must await further study.