ENZYMES CONCERNED WITH DIGESTION OF LIPIDS 47 



cholinesterase activity in puppies was found to rise to 25 times the level at 

 birth within three days. Although proteinaceous materials such as en- 

 zymes are generally considered to be destroyed in the gastrointestinal tract, 

 and one would not expect orally ingested enzymes to reach the blood serum, 

 it is recognized that a considerable amount of unaltered proteins can be 

 absorbed from the colostrum during the early days of life. Schafer and 

 Maier 266 also conclude that the cholinesterase content of the blood de- 

 pends upon age; these workers state that the minimal level is reached at 

 30 years. 



Age, also, has been found to have a profound effect on the cholinesterase 

 activity of several tissues. Thus, Bayliss and Todrick 267 reported that the 

 activity of true cholinesterase increased in the whole brain from the third 

 to the twentieth day at a rate of slightly more than 300 units per day, 

 after which a decrease in rate occurred. On the other hand, the concen- 

 tration of pseudocholinesterase was found to remain constant at 150 to 

 160 units per unit weight from the third to the tenth day. An increase 

 followed, which continued to the twenty-fourth day, when a level of 300 

 units was reached. The period of rapid change in the cholinesterase con- 

 tent of the brain coincides with the rapid increase in the number of capil- 

 laries. Craigie 268 reported that the differences between the capillary con- 

 tent in the newborn and adult rat brain become established between the 

 tenth and the twenty-first day. Since Koelle, 269 on the basis of histochemi- 

 cal evidence, suggested that the pseudocholinesterase of the rat brain is 

 located principally in the walls of the capillaries, in the muscle fibers of the 

 arterioles and venules, and in some gliocytes, there would seem to be some 

 justification for associating the rise in capillary content of the brain with 

 an increase in pseudocholinesterase. Risley and Davies 270 likewise noted 

 that the cholinesterase content is four times as high in adult brain as in 

 this organ of the newborn rat. Similar changes were noted in the hydro- 

 lytic action of brain on acetyl-/3-methylcholine, benzoylcholine, propionyl- 

 choline, and butyrylcholine. 



In the case of spinal cord, no significant change per unit weight was found 

 to occur between the eighth and the twenty-second days, but both enzymes 



266 H. Schafer and E. Maier, Biochem, Z., 819, 420-438 (1949). 



267 B. J. Bayliss and A. Todrick, Biochem, J., 54, xxix (1953). 



268 H. E. Craigie, in The Circulation of the Brain and Spinal Cord, Research Pubis. 

 Assoc, Research Nervous Mental Disease, 18, Chap. I. "The Comparative Anatomy 

 and Embryology of the Capillary Bed of the Central Nervous System," pp. 3-28, 

 Williams and Wilkins, Baltimore, 1938, p. 23. 



269 G. B. Koelle, /. Pharmacol. Exptl. Therap., 106, 401 (1952). 



270 J. E. Risley and D. R. Davies, Biochem. J., 54, xxx (1953). 



