324 ADVENTURES IN RADIOISOTOl'E RESEARCH 



P<^) per hour; but, even if this amount of newly formed phosphatides is 

 quantitatively led from the intestine into the liver, it would not suffice 

 to account for the presence of the amount of newly formed phospha- 

 tides found in the latter which corresponds to more than 0.5 mgm 

 phosphatide P per hour. 



An entirely different argument against the intestinal origin of the 

 labelled phosphatides found in the liver is the following. The labelled 

 phosphatides present in the plasma were not found to leave the blood 

 stream at a very fast rate, half of the labelled phosphatides present 

 leaving the plasma in the course of an hour, 30 per cent of these phospha- 

 tides being found in the liver^^) thus, a rapid rush of labelled phosphatides 

 through the plasma does not take place. 



That the labelled phosphatides found in the liver are, at least to a large 

 extent, formed in situ, was also shown in experiments on isolated perfused 

 liver Such investigations were formerly^^) carried out by us on isolated 

 cat livers in which, after the lapse of 2.5 hours, the specific activity of 

 the liver phosphatide P was found to he about 1.5 per cent of that of 

 the liver inorganic P. A further proof that the phosphatides present 

 in the liver were formed there was brought about by Chaikoff and his 

 colleagues(^) who found that, in experiments on rats, the removal of 

 tissues very active in phospholipid turnover, namely the gastrointestinal 

 tract and the kidneys, does not markedly influence the phospholipid 

 Uirnover in the liver. 



Muscle phosphatides 



After discussing the origin of the labelled liver phosphatides we shall 

 put forward similar arguments as to the origin of the labelled muscle 

 phosphatides. The specific activity of the plasma phosphatides is found 

 to be about 3 times higher after the lapse of four hours than that of 

 the muscle phosphatides. Considerations based on the comparison of 

 the specific activity of the plasma phosphatides and the muscle phospha- 



*'' When oil is fed to the rabbit, twice that amount was found to be carried by 

 the intestinal lymph. The feeding of oil raises the rate of turnover in the intestinal 

 mucosa and the liver as well, as shown in experiments on rats (C. Artom, G. 

 Sabzana and E. Segre, Arch. Int. Physiol. 47, 245 (1938); B. A. Fries, S. Ruben, 

 J. Perlman and J. L. Chaikoff, J. Biol. Chem. 123, 587 (1938) and also on isola- 

 ted peifused cat liver, where the turnover rate was fotmd to be about twice as 

 high as in experiments in which non-lipemic (normal) blood was used (L. Hahn 

 and G. Hevesy, Bicchem. J. 32, 342 (1938). 



(2)L. Hahn and G. Hevesy, Nature 164, 72 (1939). 



(3)L. Hahn and G. Hevesy, Biochem. J. 32, 342 (1938). 



(*^ B. A. Fries, S. Ruben, J. Perlman and J.L. C'nMKorF, J. Biol. Chem. 

 123, 567 (1938). 



