ABSORPTION AND TRANSPORT OF FATS 161 



racic lymph is increased during fat absorption, 717,763 the fatty acids in the 

 phospholipids account for only a fraction of the total absorbed. This does 

 not rule out a continued turnover of phospholipid within the intestinal cell 

 or the transfer of extra phospholipid to the liver in the portal blood. How- 

 ever, more recent studies render these explanations questionable. 



A number of reports are available which demonstrate an increase in the 

 specific activity of intestinal phospholipid phosphorus, during fat absorp- 

 tion, after the injection of P 32 into rats. The recent findings of Schmidt- 

 Nielsen 764 and of Zilversmit et al. 717 indicate that this augmentation of the 

 specific activity of phospholipid phosphorus is too small to account for the 

 conversion of the absorbed fat to phospholipid unless the phosphorylation 

 process is limited to the epithelial cells. In the case of the tests on dogs, no 

 increase whatsoever was noted in the relative specific activities of the phos- 

 pholipids in the villi during fat absorption. 717 Another experimental 

 finding which supports this thesis is that of Artom and Cornatzer, 765 who 

 noted that fat absorption proceeded without an increase in phospholipid 

 formation in the intestine in choline-deficient rats. All of these results are 

 interpreted by Zilversmit and collaborators 717 as indicating that phospholip- 

 ids are not obligatory intermediates in the passage of absorbed fat through 

 the intestinal wall. 



(6) Functions of Phospholipids Other Than in Fat Synthesis. Even if 

 phospholipids are not obligatory intermediates in the resynthesis of fats in 

 the intestinal mucosa, there are a number of reasons why the synthesis of 

 phospholipids may assist in fat utilization. The phospholipids are conven- 

 ient forms for the transportation of fat, and they may be more suitable than 

 the triglycerides for metabolic transformations. The most important func- 

 tion of the phospholipids is as an essential component in stabilizing the 

 film on the circulating fat droplets in the blood. Without a stabilizer, 

 negatively charged fat droplets flocculate in the presence of plasma proteins 

 and 1% sodium chloride 645 - 730 at a pH of 7.5. Soap will not prevent the 

 flocculation under the above-mentioned conditions. The protective film 

 on these chylomicrons contains phospholipid, as can be shown by its in- 

 stability to the lecithinase D produced by Clostridium welchii (gas bacillus). 

 Frazer 645 suggests that the phospholipid may be added to the fat particles 

 in the intestinal cell, where it may be formed in situ at the oil/ water inter- 

 face. Another possibility is that the monoglyceride absorbed may serve as 



763 E. V. Flock, W. C. Cain, J. H. Grindlay, and J. L. Bollman, Federation Proc, 6, 252 

 (1947). 



764 K. Schmidt-Nielsen, Acta physiot. Scand., 12, suppl., 37, 3-83 (1946). 

 76 » C. Artom and W. E. Cornatzer, J. Biol. Chem., 165, 393-394 (1946). 



