48 II. DIGESTION AND ABSORPTION OF FATS 



were initially present in higher concentration in this tissue than in brain. 26 

 This result is diametrically opposed to that of Risley and Davies, 270 who 

 noted a constant increase from birth to a maximum at four weeks. This 

 was followed by a steady decrease to a value, in the adult, of one-half that 

 at birth and one-third of the maximal level. 



The cholinesterase content of rat skeletal muscle obtained from the leg 

 has been shown to reach a maximum seven days after birth. A slight 

 decrease in activity then ensues. The level in the adult rat decreases 

 to only 10% or less of that observed in the muscle during the first week of 

 life. During the first week of life, the muscle is able to hydrolyze propionyl- 

 choline much more rapidly than acetylcholine. It was also reported that 

 the cholinesterase activity of the kidney decreases in the rat with increas- 

 ing age. 



Species is another factor which can result in variations in blood cholin- 

 esterase. Thus, variations in the cholinesterase of the colostrum, related 

 to species, 265 have already been described. Moreover, guinea pigs, in con- 

 tradistinction to other newborn, did not exhibit the rapid increase in cholin- 

 esterase shortly after birth. 265 Galehr and Plattner 181 found that the rate of 

 destruction of acetylcholine (and hence the activity of cholinesterases) in 

 blood obtained from different species decreased in the following order: 

 man, pig, cattle, horse, rabbit, and cat. Davies et aZ. 271 noted that the ac- 

 tivity of sheep tissues against acetylcholine was much lower than that of 

 rat tissues. The ratios of activity of sheep tissues are considerably less 

 constant than in the rat. Thus, the relative activity toward propionyl- 

 choline : butyrylcholine varies only from 1.4 to 2.0 in the rat, but the values 

 recorded for sheep are from 0.4 to 3.0. The ratios of activity of butyryl- 

 choline : benzoylcholine and of propionylcholine : benzoylcholine are irregu- 

 lar in the ruminant, in contrast to their relative regularity in the case of the 

 rat. Few sheep tissues except kidney were found to hydrolyze butyryl- 

 choline. 271 



Sex is another factor which may alter cholinesterase content. Although 

 Davies and Rutland 272 and Harrison and Brown 273 were unable to demon- 

 strate a sex difference in the content of s-cholinesterase, in man, and the 

 findings were the same for the dog, 273,274 the situation is entirety different 

 in the rat. Sawyer and Everett 276 reported higher levels of the enzyme in 

 the livers and gonads of female rats than was the case in males. Although 



271 D. R. Davies, J. E. Risley, and J. P. Rutland, Biochem. J., 68, xv (1953). 



272 D. R. Davies and J. P. Rutland, Biochem. J., 47, xxi-xxii (1950). 



273 M. F. Harrison and L. M. Brown, Biochem. J., 48, 151-154 (1951). 



274 R. W. Brauer and M. A. Root, Am. J. Physiol., 149, 611-625 (1947). 



275 C. H. Sawyer and J. W. Everett, Am, J. Physiol, 148, 675-683 (1947). 



