PROGRESS OF THE ISOTOPIC METHODOLOGY 1 003 



REPLACEMENT RATE OF THE IRON ATOMS OF THE PLASMA 



Splitting the dynamic equilibrium, which the plasma iron content 

 represents into its components, illustrates the wealth of biological and 

 clinical information which can bo obtained by applying a radioactive 

 tracer, and by this way only. 



As already mentioned the first application of ^^Fe was that of Hahn — 

 Whipple and their associates. They compared among others the incor- 

 poration of labelled iron into the erythrocytes of non-bled and bled 

 dogs and found very much more ^^Fe in the latter than in the former. 

 Since most of the absorbed iron is in time incorporated into the erythro- 

 cytes the activity of the latter is a measure of the iron absorbed from 

 the intestinal tract. The determination of the extent of iron absorption, 

 formerly a very tedious process, is immensely facilited by following the 

 incorporation of administered labelled iron into the red corpuscles. 

 By using this method among others Chodos and assoc.^^^ demonstrated 

 recently that the quantity of inorganic iron administered to a fasting 

 subject concomitantly with ascorbic acid is 2 to 100 times larger than 

 that of food iron. In these experiments labelled eggs and vegetables were 

 fed which contained comparable quantities of iron with those of the 

 inorganic compounds (FeSO^ or FeClg). 



An important advance was due to the study of FLEXNERandassoc.^^^ 

 who injected labelled FeClg into the circulation of the guniea pig and 

 observed that a fraction of ^^Fe left the plasma exceedingly rapidly, 

 while an other fraction left at a very appreciably slower rate. The last 

 mentioned fraction, which could be found from Holmberg andLAURELL's 

 and ScHADE and Caroline's results, was ^^Fe bound to the /^^ -globulin 

 fraction of the plasma. Only a fraction of the latter is combined with 

 iron under physiological conditions, thus small amounts of iron added 

 to the plasma sample have opportunity to combine with this protein. 



Huff and his associates'^'') were the first to incubate plasma with 

 minute amounts of labelled iron, reinject the plasma sample and follow 

 the rate at which the ^^Fe leaves the circulation. The reinjected labelled 

 plasma sample is distributed within a few minutes all over the plasma 

 and thus the disappearance of the ^^Fe from the plasma indicates the 

 disappearance rate of the circulating plasma iron. This method was 

 widely applied in very numerous investigations. By following the rate 

 <^)f disappearance of the iron atoms of the plasma, the iron concentration 

 remaining constant during the experiment, we determine the rate of 

 intrusion of iron atoms into the plasma as well. The mgm plasma iron 

 replaced per hour = 



0.693 {fig Fe/ml) x plasma volume (ml) 

 time of half-disappearance of plasma ^^Fe (in hours) x 1000 



