THE DIGESTION OF FATS 137 



Thus, if the hydrolysis of triglycerides were a random reaction, one might 

 expect that the intestinal contents, during the early stages of digestion of a 

 mixed triglyceride, would include not only undigested triglyceride, but also 

 mixtures of at least two diglycerides, at least two monoglycerides, glycerol, 

 and the several fatty acids composing the mixed triglyceride molecule. 

 However, according to Mattson et aZ., 640 the action of the pancreatic lipase 

 is not a random one but proceeds according to pathway A. 



If the medium is alkaline, one may anticipate finding that the soaps re- 

 place the fatty acids; if soluble calcium compounds are available, the soaps 

 will tend to consist largely of the calcium salts. In the absence of calcium, 

 sodium and potassium soaps predominate. However, most evidence points 

 to the fact that the reaction in the intestine is such that fatty acids rather 

 than soaps are present in the small intestine. For example, Kostyal, 641 in a 

 study of the pH in the intestines of rats, dogs, guinea pigs, and pigeons, 

 found that it was almost never above 7.0, and was usually on the acid side 

 of neutrality. Robinson 642 also reported a pH of 6.5 in the duodenum of 

 dogs and rats, and a value of 7.5 to 8.0 at the ileocecal valve. Schulte 643 

 noted that the glycerides formed from fatty acids produced synthetically 

 by oxidation of hydrocarbons were acted upon by pig pancreatic lipase. 

 Cleavage occurred in the same manner as in the case of the regular dietary 

 fats. 



b. The Extent of Hydrolysis of Fats. There is a difference of opinion 

 as to how completely the triglycerides are hydrolyzed in the small intestine. 

 Verzar and McDougall, 554 and Bloor 35 ' 644 believe that a complete hydrolysis 

 to glycerol and fatty acids is a prerequisite for fat absorption. Since it is 

 known that fats are largely digestible, if one accepts the Lipolytic Theory, 

 one must postulate that an equally complete hydrolysis of the triglycerides 

 must have obtained prior to absorption. The fact that glycerol and fatty 

 acids (or soaps) are rapidly removed from the medium by absorption will 

 permit the hydrolysis of the triglyceride to continue, without inhibition 

 due to the accumulation of end-products, until the splitting reaction has 

 proceeded to completion. 



On the other hand, Frazer 645 questioned whether or not the complete 



640 F. H. Mattson, J. H. Benedict, J. B. Martin, and L. W. Beck, /. Nutrition, 48, 335- 

 344 (1952). 



641 L. Kostyal, Magyar Orvosi Archivum, 27, 276-281 (1926); Chem. Abst., 21, 126 

 (1927). 



642 C. S. Robinson, /. Biol. Chem., 108, 403-408 (1935). 



643 K. E. Schulte, Biochem. Z., 818, 220-226 (1948). 



644 W. R. Bloor, Physiol. Revs., 2, 92-115 (1922). 

 846 A. C. Frazer, Physiol. Revs., 26, 103-119 (1946). 



