488 ADVENTURES IN RADIOISOTOPE RESEARCH 



4 hours after the administration of labelled sodium phosphate. These 

 figures, however, fail to inform us as to the percentage of the phosphatide 

 molecules which were renewed within the last 4 hours. Most of the active 

 phosphate ions will exchange with bone and other tissue phosphate and 

 will thus be prevented from taking part in the synthesis of phosphatide 

 molecules. Knowledge relative to the percentage of, for example the liver 

 phosphatides, renewed within 4 hours can be obtained, as already dis- 

 cussed on p. 485, by administering the sodium phosphate solution drop 

 by drop and thus keeping the active phosphate concentration of the 

 blood at an approximately constant level, or in perfusion experiments 

 carried out on the isolated liver. In the latter case, active sodium phos- 

 phate is added to the blood circulating through an isolated liver and, 

 after the lapse of a few hours, the specific activity of the plasma inorganic 

 P and that of the phophatide P extracted from the liver are compared. 

 Through the kindness of Prof. Lundsgaard we were able to carry 

 out such a determination from which it was concluded that, in the course 

 of 2iA hours, about 2% of the phosphatides in the cat liver are renewed*-^^ 

 In the same time, when blood is shaken with active sodium phosphate, 

 only a very slight amount of active phosphatide was formed. From these 

 experiments it may be concluded that less than 0.1% of the phosphatide 

 molecules present in the isolated blood was renewed in the course of 

 2y, hours. In experiments on goats, 4 hours after injecting labelled 

 sodium phosphate, less and probably much less than 1% of the blood 

 phosphatide molecules were labelled. We have therefore to conclude that 

 the phosphatide molecules present in the blood can only get rejuvenated 

 by an influx of molecules from the organs like the liver in which they 

 were synthesized. As a possible source of formation of the blood phos- 

 phatides the liver is first to be considered in view of the fast phosphatide 

 turnover found in the liver and the large amounts of phosphatides 

 stored in it. In this connection the results obtained by Nedswedsky*^-* 

 should be recalled according to which blood leaving the liver contains 

 23% more phosphatide than that entering the liver from the portal 

 vein. 



Laying hens are especially well suited to the study of phosphatide 

 metabolism. A hen laying daily incorporates into the yolk 1 — 2 gm 

 of phosphatides corresponding to about 60 mgm of P. We found that 

 these phosphatides were not produced in the ovary but were carried 

 by the plasma in the main from the liver. To what extent phosphatides 

 are carried into the circulation through the lymph from the intestinal 

 mucosa is not yet settled. In the above mentioned experiment the specific 

 activity of the phosphatide P extracted from the hens' intestinal mucosa 



(1) L. A. Hahn and G. C Hevesy, Biochem. J. 32, 342 (1938). 



(1) S. W. Nedswedsky and K. Alexandry, Z. pftys^o/. Chem. 119, 619 (1928). 



