INTERACTION OF PLASMA PHOSPHATE WITH THE PHOSPHOKUS CO.MPOIXDS 487 



even higher (3.3% of the tolal fatty acids) than in the former (2.0%), 

 a still lower content being found in the phosphatide fatty acids secured 

 from the liver. The result obtained as to the turnover of phosphatides 

 in the corpuscles, when using the elaidic acid method, is thus just the 

 opposite of that arrived at when applying iodised fat as an indicator. 

 While these indicators proved to be very useful to show that a rapid 

 turnover of phosphatides actually takes place in som(> of the organs 

 they are less adapted to permit conclusions of a quantitative nature 

 to be drawn. 



By introducing elaidic acid or iodised fat into the phosphatide molecule 

 the properties of the latter are appreciably changed and not only will 

 the different organs utilise the above mentioned substances in the 

 formation of phosphatides only to a restricted extent, but the rate of 

 uptake of these compounds may differ for different organs. In rats 

 provided with large amounts of elaidic acid throughout the entire period 

 of prenatal and postnatal development, the elaidic acid content of the 

 fatty acids in the phosphatides of the brain was found to be only | 

 of that of the liver and muscles. If one finds a slower turnover of elaidic 

 acid in the brain phosphatide than in other organs, this result can be 

 partly due to a slower phosphatide turnover in the brain, and partly 

 to a greater degree of selection in the building up of phosphatides in the 

 Ijrain than in the liver. The rate of the incorporation of elaidic acid into 

 the phosphatide molecules will therefore fail to be a quantitative measure 

 of the rate of phosphatide rejuvenation in the brain tissue, though this 

 method revealed much important information as, for example, that the 

 phosphatide turnover in the muscles is much slower than that of the 

 liver and the intestinal mucosa. In rats, the incorporation of elaidic acid 

 into the liver phosphatides was found to be essentially completed within 

 one day but in the muscle transformation had occurred only after a 

 period of many days. One of the great advantages of the application of 

 isotopic indicators is that the replacement of ^ip by ^ap for example 

 in the phosphatide molecule does not change the chemical character of 

 the substance to any noticeable extent and therefore any possible prefe- 

 rence of an organ for the ^^P phosphatide can be disregarded. A quan- 

 titative comparison of the phosphatide turnover in different organs by 

 using ^^P as an indicator was carried out by different experimentors, 

 a slow turnover being found in the brain and muscles, a fast one in the 

 milk gland, the liver, the kidneys and the intestinal mucosa, while we 

 find a fairly fast rate in tumor tissue. Taking the specific activity of the 

 phosphatide P extracted from the liver of a mouse to be 100, we find 

 for the specific activity of that extracted from the muscles and the graft 

 of the brest tumor 18 and 9% respectively. These figures indicate the 

 relative rate of resynthesis of the phosphatide molecules. They were 

 obtained by extracting and analysing the phosphatides from 1 he organs, 



