Further evidence for enhanced phospholipid synthesis by rat jejunal villus cells during fat absorption.

The effect of fat absorption on the phospholipid turnover of rat intestinal mucosa was determined in animals receiving single fatty meals by stomach tube or multiple meals in the form of corn-oil-soaked laboratory chow diet. The specific activity and relative specific activity of the total phospholipids and of individual phospholipid classes were measured in the isolated jejunal villus cells of fasting and fat-fed animals following an injection of radioactive inorganic phosphate 0.5-31 h prior to sacrifice, which was scheduled to coincide with the peak of fat absorption (2.5-3 h after the last meal). It was shown that the relative specific activity of the fat-absorbing cells increased by about 33% when the samples were taken 0.5 h after intravenous injection of radioactive phosphate. Samples taken 11 and 31 h after the introduction of the radioactive phosphate showed about 16% decrease in the relative specific activity of the phospholipids of the fat-absorbing cells when compared with the fasting controls. These changes in the relative specific activity of the total phospholipids included all phospholipid classes and corresponded to the recently described expansion of the cellular phospholipid pool owing partly to increased de novo synthesis of the membrane phospholipids. The present results are consistent with the known biochemical and physiological changes taking place in the mucosal cells during fat absorption and transport and find support in various less direct biochemical and morphometric measurements.