642 



ADVENTURES IN RADIOISOTOPE RESEARCH 



cable since a considerable part of the injected iron is transported into 

 the organs, before it has the opportunity to be incorporated in the 

 transferrin, and may complicate the experimental results by its presence 

 in them . Even when the very small amount of 2 jugm of iron is injected 



as citrate or chloride into a rabbit, 

 i.e. one-hundredth of the amount 

 which the still available transferrin 

 can combine with, this iron does not 

 combine completely with the plas- 

 ma transferrin, but a part of it leaves 

 the plasma before having an oppor- 

 tunity to combine with the protein. 

 It is evident in Fig. 2, w^hich is ta- 

 ken from a study performed in our 

 laboratory by Giuliano, that this 

 process is concluded after a period 

 of only 4—5 min and that ^^Fe still 

 present then disappears from the 

 plasma of the rabbit with a half- 

 life of about 2 hr, which is charac- 

 teristic of the metabolism of physio - 



7000 



6300 - 



5600 - 



4900 



4200 



3500 



- 2800 



2100 



1400 



700 



Konfroile 



Noch Adrenolm-Injektion 



■ • 



. 0--0 



10 20 



30 



mm 



40 50 60 



Fig. 3. The effect of adre- 

 nalin on the rate of escape 

 of labelled phosphate from 



the plasma. 

 KontroUe = control test; 

 Nach Adrenahn-Injektion 

 = after injecting adrenalin; 

 Aktivitat in 1 ml Plasma 

 = activity per ml plasma. 



logical plasma iron. 



Vahlquist and co-workers have 

 already observed the very rapid 

 disappearance of 0.5 to 2.0 mgm iron, 

 after injection into a rabbit, from 

 the plasma^28)^ j^^t the radioactive 

 method makes it possible also to fol- 

 low the course of very small 

 amounts of iron, 1 /ugm or less, 



and to measure both the unilateral loss of iron and the renewal rate of 



plasma iron. 



By making use of the ready accessibility of the radioisotopes of sodium, 

 potassium, etc. it was shown at an early date that the rate of replacement 

 of these ions may be extraordinarily high^is)^ j^ the course of 2 min about 

 half of the sodium ions present at the beginning of the experiment in 

 the plasma of a rabbit is replaced by extra vascular sodium ions. 

 A rapid disappearance of injected iron salts such as that indicated in 

 Fig. 2 is therefore not very surprising. The iron combined in the trans- 

 ferrin, on the contrary, escapes relatively slowly with a half-life of from 

 70 to 120 min from the human circulatory system and still more slowly 

 from the rabbit. Experiments with transferrin labelled with i^ij showed 

 that this compound leaves the blood fluid with a half-life of a few days^i^). 

 Iron to a very large extent escapes from the plasma not in a form com- 



