ISOTOPIC INDICATORS IN HAEIVIATOLOGY 



641 



of 150 /igm % is already indicative of a pathological state. Knowledge 

 of the combining capacity of the plasma for iron is therefore of great 

 interest in such cases. 



METABOLISM OF PLASMA IRON 



0) 



a 



E 



27- Fe ais Fed, 



injiziert 



The two important quantities, the iron content and the combining 

 capacity of the plasma for iron, can be determined analytically; the 

 metabolic rate of the plasma iron, a quantity no less important than 

 these, cannot be so determined. The ascertainment of the metabolic 

 rate of the iron is made possible by using radioactive iron as an indi- 

 cator. By labelling the iron of the /^^ globulin and tracing how the radio- 

 activity of the plasma decreases with time, and also how the iron fraction 

 in the organs and in the red corpuscles increases with time, it is possible 

 to trace the path of these iron 

 atoms which were present at the 

 beginning of the experiment in 

 the blood fluid(9>. 



At the present time ^sFe is used 

 almost exclusively for labelling 

 iron; it has a half-life of 45.1 

 days and emits both easily mea- 

 surable ^- (from 0.26 to 0.46 

 MeV) and y-radiation (1.1 to 1.3 



MeV). 



Labelling of the plasma trans- 

 ferrin is accomplished by incu- 

 bating a plasma sample in the 

 presence of ^sFe, e.g. as the cit- 

 rate, at the body temperature for 

 20 min. If an amount of radio- 

 active iron not exceeding 1 f^gm is 

 added to 1 ml of plasma it w^U 

 be combined quantitatively in 



transferrin. If the labelled plasma is now re-injected into the subject, 

 the whole of his transferrin iron in the plasma will thereby be labelled. 

 In animal experiments iron may also be added to a donor, possibly even 

 in larger quantities and, e.g. labelled plasma may then be transferred 

 from the donor to the acceptor after 1 hr has elapsed. 



Flexner and his co-workers^^^ were the first to label the plasma trans- 

 ferrin of guinea-pigs by the injection of radioactive iron and to determine 

 the rate at which the iron escapes from the blood fluid. Labelling the 

 transferrin iron by injecting iron into the subject is frequently inapplic- 



240 



min 



Fig. 2. Loss of labelled iron 

 from rabbit plasma after in- 

 travenous injection of 2 /^gm 

 of iron. 2 yMgm Fe injected as 

 FeClg (caption on the graph). 



41 Hevesy 



