POTASSIUM INTERCHANGE IN THE HUMAN BODY 559- 



larger part of the potassium present at any moment in the extracelluhu' 

 space to be excreted through the kidneys in the course of the first 24 

 hours, for example, than of the sodium simultaneously present in Ihe 

 extracellular fluid. Thus, in the urine, a much larger part of "^-K admi- 

 nistered than of 24Na administered should ])e present. This is, however,, 

 not the case. As seen in Table 4, the percentage of daily excreted '^^Na 

 does not much differ from the percentage of daily excreted ^^K. From 

 this result it follows that most potassium ions present in the urine are 

 such as were previously located in the cellular and not in the extra- 

 cellular fluid; a conclusion which is in accordance with the result arrived 

 at in the previous section. 



RESULTS 



Labelled potassium chloride was administered to a human subject 

 and the potassium and the ^^K content of the urine samples collected 

 within 65 hours were determined. After the lapse of 12 minutes, 5x 10^^ 

 part of the ^^K administered was found to be present in the urine. In the 

 course of 48 hours, about 10 per cent were excreted through the kidneys. 



Making the assumption that the ^^K content of 1 mgm potassium 

 present in the urine is about the same as the ^^K content of 1 mgm 

 potassium present in the plasma (extracellular space), from the ^^K 

 content of the urine potassium the ^^K content of the extracellular fluid 

 of the body can be computed. By this method, it was found that a very 

 large part of the ^^K absorbed into the circulation found its way into 

 the tissue cells in the course of 16 hours or less. 



While the accuracy of the method does not suffice to determine whether 

 a full interchange between the potassium of the cells and the potassium 

 of the extracellular fluid took place in the course of the experiment, 

 it is clearly shown that a very substantial part of the labelled potassium 

 and thus of all potassium taken with the food, interchanges with the 

 potassium located in the tissue cells in the course of some hours. 



Labelled sodium was found to leave the body at a similar rate as 

 labelled potassium. 



References 



J. BouRDiLLON (1937) Amer. J. Physiol. 120, 411. 



B. B. Brodie, E. Brand and S. Leshin (1939) J. Biol. Chem. 133, 555. 



I. N. Cuming (1939) Biochem. J. 33, 642. 



W. O. Fenn (1939) Amer. J. Physiol. 127, 356. 



L. Hahn, G. Hevesy and O. Rebbe (1939) 33, 1540. 



G. Hevesy and L. Hahn (1941) Kgl. Danske Vidensk. Selsk. Medd. 16, I. 



