36 II. DIGESTION AND ABSORPTION OF FATS 



number of bile salts (cholic, desoxycholic, glycocholic, dehydrocholic, and 

 dehydrodesoxycholic acids as their sodium salts) on the activity of cholin- 

 esterase. This inhibiting action may explain the fact that cholinesterase is 

 absent from swine bile. 217 Ammon 166 likewise confirmed the partial block- 

 ing of the cholinesterase activity of human, horse, and snail sera by bile 

 acids. The results obtained with human serum are supported by the 

 demonstration of Antopol, Schifrin, and Tuchman 218 that the cholinesterase 

 effect is decreased in jaundice. 



At least one hormone has been shown to be important as an inhibitor. 

 Benson 219 reported that adrenalin inhibited the ability of lyophilized prepa- 

 rations of e- and s-types of cholinesterase to bring about the hydrolysis of 

 acetylcholine. It was later shown by Benson and Meek 220 that adrenalin 

 in concentrations of 0.00015 to 0.006 M inhibits the ability of cholinesterase 

 to hydrolyze choline esters in a concentration of 0.003 M. Both the e- 

 and s-type are inhibited to the same extent. When methylcholine is used 

 as the substrate for the specific esterase, the degree of inhibition by adrena- 

 lin is comparatively high, while the hydrolysis of benzoylcholine by the 

 non-specific cholinesterase (s) is inhibited to only a slight extent. 



The inhibition of cholinesterases possesses some degree of specificity. 

 This can, in some cases, be used as a method for the differentiation of the 

 type of cholinesterase. 221 - 222 Zeller reported that, in the case of unpuri- 

 fied enzymes, the degree of inhibition varied according to the tissue and 

 species from which the cholinesterase was obtained. Thus, human serum 

 cholinesterase was more sensitive to 4-isopropyl-antipyrine than was that 

 prepared from the human central nervous system. 194 On the other hand, 

 the cholinesterases of the human brain and erythrocytes were found to 

 be inhibited to a similarly slight degree, while that prepared from serum 

 presented a markedly different behavior, in that it was strongly inhibited. 18 -" 



Table 4 gives data as to the inhibition of several preparations of cholin- 

 esterases by certain common drugs, while Table 5 compares the action 

 of a variety of chemical inhibitors on the two types of cholinesterases. 



(b') Comparative Mechanism of Inhibition. — The inhibitors function 

 differently in counteracting the several types of cholinesterases. Thus 

 the alkaloids inhibit human plasma cholinesterase by competing with 



217 D. Glick, A. Lewin, aud W. Antopol, Proc. Soc. Exptl. Biol. Med., 40, 28-32 (1939). 



218 W. Antopol, A. Schifrin, and L. Tuchman, Proc. Soc. Exptl. Biol. Med., 88, 363-366 

 (1938). 



219 W. M. Benson, Proc. Soc. Exptl. Biol. Med., 68, 598-601 (1948). 



220 W. M. Benson and W. J. Meek, Am. J. Physiol., 158, 327-331 (1949). 

 - 2) E. A. Zeller, Hclv. Chim. Acta, 25, 216-229 (1942). 



222 E. A. Zeller, Verhandl. Ver. schweiz. Physiol, 19, 35-36 (1941); 20, 51-52 (1912). 



