790 VII. LIPID DISTRIBUTION IN SPECIFIC TISSUES 



gut; ordinarily these substances are rather rapidly transferred to the lac- 

 teals for transport to the liver and other tissues. The interval during which 

 the elevated lipid concentration would be expected would depend upon 

 the amount of lipid fed. In general, it would not be prolonged for more 

 than three to six hours. Although considerable amounts of plasmalogens 

 were indicated in the 0.27% of phosphatides found in pig intestine, prac- 

 tically no pure material could be separated, and these compounds were 

 probably not present in appreciable amounts. 40 



The cholesterol content of intestinal mucosa varies according to the 

 portion of the intestine from which it is obtained. Thus, in samples of 

 human intestine, material from the upper portion was shown to have a 

 cholesterol concentration of 0.37%, 457 while that from the sigmoid had a 

 concentration of 0.65%, based upon dry weight. 457 On the other hand, the 

 cholesterol content of the large intestine was 0.65% (dry weight). 458 

 This sterol was present largely in the mucosa, as is shown by the fact that 

 the concentration in the latter case was 0.82%. Bloor 49 calculates that the 

 total mucosa of the large intestine of man would contain only 78 mg., 

 which is less than the amount excreted daily on a cholesterol-free diet. 

 Variations in cholesterol content may be related to the fact that it can be 

 synthesized from acetate in the wall of the gut. 7 This fact would empha- 

 size the mobile nature of the cholesterol stores in the mucosa. 



The presence of phospholipids in intestinal mucosa has been repeatedly 

 demonstrated. For example, Sinclair 459 reported an average of 10.4% of 

 phospholipid (based upon dry weight) in the intestinal mucosa of the fasted 

 cat. No change in the amount of phospholipid could be demonstrated 

 after fats were fed ; however, marked variations occurring in the composi- 

 tion of the phospholipid fatty acids were referable to diet. This led Sin- 

 clair to postulate that fatty acids are transformed into phospholipids 

 within the intestinal mucosa as an essential step in the resynthesis of fat. 

 In a recent study, Morehouse 460 demonstrated that only 66% of the total 

 fatty acids absorbed pass through the phospholipid stage in the intestinal 

 wall. Moreover, Zilversmit et al. 461 and Flock and associates 462 found that 

 the phospholipid turnover in the intestinal wall is too slow to allow all 



467 M. Burger and H. D. Oeter, Z. physiol. Chern., 182, 141-147 (1929). 



458 M. Burger and H. D. Oeter, Z. physiol. Chern., 184, 258-260 (1929). 



459 R. G. Sinclair, J. Biol. Chern., 82, 117-136 (1929). 



460 M. G. Morehouse, unpublished observations, 1953. 



461 D. B. Zilversmit, I. L. Chaikoff, and C. Entenman, /. Biol. Chern., 172, 637-650 

 (1948). 



462 E. V. Flock, J. C. Cain, J. H. Grindlay, and J. L. Bollman, Federation Proc, 6, 

 252 (1947). 



