170 II. DIGESTION AND ABSORPTION OF PATS 



bacterial degradation, and that they could not be recovered in appreciable 

 amounts from the lymph. However, it was later shown by Kiyasu 

 and co-workers 804 that the ratio of C 14 -labeled fatty acids in portal blood to 

 that in the inferior vena cava was high after tagged decanoic acid was fed, 

 in contrast to a 1 : 1 ratio following the administration of C 14 -palmitic acid. 

 Frazer 645 has accepted as part of his theory the absorption of the short- 

 chain triglycerides after hydrolysis via the portal circulation. 



In addition to the transport of the water-soluble fatty acids by the portal 

 route, it is probable that other water-soluble hydrolysis products of lipids 

 may also be absorbed in this manner. On the other hand, de la Huerga 

 and Popper 805 reported that choline is changed by bacteria, in the intestinal 

 tract, into trimethylamine; this is absorbed as such and excreted in the 

 urine, mainly as the oxide. No significant amounts of choline were found 

 to be present in the stools. In another study, 806 these workers noted that 

 about two-thirds of the ingested choline appeared in the urine as tri- 

 methylamine and trimethylamine oxide. No choline is normally present 

 in urine. Although the transformation of choline to trimethylamine can 

 be largely ascribed to intestinal bacteria, the liver also plays a role. In 

 liver disease the elimination of trimethylamine in the urine after the ad- 

 ministration of choline was found to be delayed or decreased. 



According to Rohse and Searle, 807 choline is transported from the intestine 

 via the portal vein rather than via the intestinal lymphatics, in the case of 

 the dog. 



One fact which is not explained in the Frazer Theory is the site of the 

 resynthesis of fatty acids to neutral fat. Most workers agree that the free 

 fatty acid content of the blood and lymph is low. If free fatty acids which 

 are absorbed from the intestine pass through the intestinal cells as such, 

 then one would expect the synthesis into triglyceride to take place in the 

 liver. 



c. The Route of Distribution of Fats vs. Fatty Acids. One of the unique 

 methods of approach to the question of fat absorption has been a study of 

 the ultimate fate of the absorbed fat when given as fatty acid or as triglycer- 

 ide. A comparison of the differences in behavior of these two types of fat 

 according to the Lipolytic and Partition Theories is summarized in Table 20. 



According to the Lipolytic Theory, one should observe no differences in 

 the disposal of the fat, irrespective of whether the substances fed were 



804 J. Y. Kiyasu, B. Bloom, and I. L. Chaikoff, J. Biol. Chem., 199, 415-419 (1952). 



805 J. de la Huerga and H. Popper, J. Clin. Invest., 31, 598-603 (1952). 



806 J. de la Huerga and H. Popper, /. Clin. Invest., 30, 463-470 (1951). 



807 W. G. Rohse and G. W. Searle, Federation Proc, 12, 118 (1953). 



