766 ADVENTURES IX RADIOISOTOPE RESEARCH 



ratio of 1.2 was found^i\ That in the experiments described in this note, 

 the specific activity of the plasma P amounts on the average to about 

 \/2 of the specific activity of the liver P is due to the fact, that in contra- 

 distinction to the above mentioned experiments, the labelled free phos- 

 phate penetrates from the liver into the plasma. 



As soon as the free phosphate reaches the plasma it interchanges with 

 the phosphate of the various organs; with some at a remarkable rate. 

 This interchange leads to very marked lowering of the level of the 

 plasma activity. 



From the above considerations it follows that an appreciable part of 

 the free ^'^P split off from the labelled nucleic acid in the liver is taken 

 up by other organs and the percentage ^^p split off from labelled nucleic 

 acid in the liver is even appreciably larger than indicated by the ratio 



total acid-souble ^sp 



present in the liver, recorded in Table 5. 



total 32p ^ 



Some phosphate of the labelled nucleic acid introduced into the 



circulation is also split off in the plasma. 



Intrusion of ^-P into the Liver Nuclei 



Liver nuclei contain several phosphorus compounds, desoxyribo- 

 nucleic acid, ribonucleic acid, phosphatides and acide-soluble phosphorus 

 compounds(2). jj;^ ^j^g nuclei of regenerating liver tissue of rats weighing 

 50 gm Marsh AK and Walker^^) found 3 hours after intra veneous injection 

 of labelled sodium phosphate an appreciable percentage of the ^-P 

 administered (L54 per cent per gmuclei) to be present. 



When instead of labelled phosphate labelled chromatin was adminis- 

 tered a much higher ^-P content of the nuclei (5.08 per cent) was found. 

 The result was interpreted as demonstrating the incorporation either 

 of the whole chromatin or parts of it into the nuclei. 



While the possibility of some chromatin or some nucleoprotein present 

 in the chromatin entering into the nucleus cannot be excluded, in view 

 of the results obtained in this investigation it is more probable that 

 not labelled nucleoproteids but labelled phosphate split off in the liver 

 and is mainly or exclusively incorporated into the nuclei. 



The liver takes up a large part of the plasma-foreign labelled phospho- 

 lus compounds introduced into the circulation and splits off phosphate 



^1^ H. EuLER and G. Hevesy, So. Vet. Akad. Arkiv f. Kemi, A 17, Nr. 30 

 (1944). 



^2^ Most of the acid-soluble P of the nuclei is removed during the separation 

 of the nuclei which takes place in an acid solution. 



(3> A. Marshak and A. C Walker, Amer.J. Physiol. 143, 235 (1945). 



