138 II. DIGESTION AND ABSORPTION OF FATS 



hydrolysis of the triglycerides is a necessary prerequisite to fat absorption. 

 This investigator has amassed a great deal of evidence which suggests that 

 unhydrolyzed fat can be absorbed in a finely emulsified form. The forma- 

 tion of di- or monoglycerides is considered merely as an aid to fat absorp- 

 tion in that it provides a medium conducive to the formation of an emulsion 

 of fat droplets sufficiently fine to be capable of absorption. 



Although the initial stage of the lipolysis proceeds rapidly, it comes prac- 

 tically to a stop before 30% of the potential fatty acids are set free. Addi- 

 tion of more lipase will change the extent of the hydrolysis in a given time, 

 although the final percentage is not elevated above the limiting figure. 

 It is not believed that the amount of lipase available is increased markedly 

 as digestion proceeds, since only the initial flow of pancreatic juice contains 

 appreciable amounts of lipase, while the later secretion consists largely of 

 water and salts. 646 When a potent lipase preparation is added to a stand- 

 ard meal, the postabsorptive lipemia is suppressed. This probably indi- 

 cates an increase in the extent of hydrolysis. The natural assumption is 

 that the amount of lipase furnished to the digesting mixture in the intestine 

 is normally small, and that this fact accounts for the partial hydrolysis 

 which occurs. If this quantity of lipase is increased by artificial means, 

 then the whole process of digestion and absorption of the foodstuff pro- 

 ceeds by a different course. 



When pancreatic lipolysis is carried out in vitro under the conditions 

 which obtain in the small intestine, without the introduction of excessive 

 quantities of activators or an abnormal pH level, no free glycerol can be 

 demonstrated over a five-hour period. Control experiments with glycerol 

 demonstrate that this polyhydric alcohol is not destroyed, although it does 

 disappear when the digestion period is prolonged much beyond the five- 

 hour period. Although a considerable proportion of fatty acids is set free 

 during the five-hour period of lipolysis, these originate from the conversion 

 of triglycerides to di- or monoglycerides, rather than from complete cleavage 

 of the fatty acids from the triglyceride molecule. The presence of di- 

 and monoglycerides is inferred from the fact that an increased content of 

 free hydroxyl groups occurs, as is shown by the marked rise in the acetyl 

 value. Since no free glycerol is present, and no hydroxy acids are produced, 

 the increased content of free hydroxyl groups can be attributed only to the 

 di- and monoglycerides. 647 Support for the partial hydrolysis concept is 

 afforded by the isolation of monoglyceride from the intestinal contents 

 obtained from in vivo tests with rats. 647 



646 J. Mellanby, /. Physiol, 60, 85-91 (1925). 



646 A. C. Frazer and H. G. Sammons, Biochem. J., 89, 122-128 (1945). 



