60 II. BIOSYNTHESIS 



ation in which a constancy in synthesis between phospholipid P and nucleo - 

 protein P was absent was in the case of rats which were receiving a 25% 

 casein diet supplemented with 1% of thiourea. ^^' 



b. The Effect of Ingested Cholesterol. It has long been known that 

 an antagonism exists between cholesterol and phospholipid metabolism. 

 Thus, when fatty livers are produced by cholesterol, ^^^~^" the excess fat 

 deposition in the liver can be prevented by choline. ^^^-^^^ Perlman and 

 Chaikoff-^^ found that an inverse relation exists between the rate of fat 

 deposition in the liver and the speed of phospholipid exchange, following 

 the administration of choline. In a later study, these workers^^^ found 

 that cholesterol depressed the phospholipid exchange in rat livers. The 

 effect was observed as early as thirty hours after the feeding of cholesterol 

 was initiated. Choline stimulated the rate of phospholipid turnover in 

 cholesterol-fed rats. In fact, the acceleration of phospholipid production 

 induced by choline was more pronounced in the cholesterol-fed rat than in 

 the fat-fed animal. These results were confirmed by C16ment and co- 

 workers. ^^^ When rats received a high cholesterol diet for ten months, a 

 significant decrease in turnover occurred. When they were again given a 

 normal diet, fatty livers disappeared, but the phospholipid turnover did 

 not return to normal. 



c. The Effect of the Adrenal Glands. Verzar and Laszt'^"" suggested 

 that the reason why adrenalectomy interferes with fat absorption is be- 

 cause the adrenal glands are concerned with phosphorylation. However, 

 most investigations have failed to support this hypothesis. Thus, Still- 

 man, as cited by Chaikoff,^^^ found no difference in the rate at which P^- 

 was incorporated into the phospholipids of the liver and small intestine of 

 rats, irrespective of whether or not both adrenal glands had been excised. 

 Moreover, Barnes and collaborators'"^- '"^ showed that the rate at which 

 tagged fatty acids were incorporated into phospholipids was not influenced 

 by adrenalectomy. These results indicate that the synthesis of phospho- 

 lipids occurs normally after the removal of the adrenal glands, not only as 



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