1004 



ADVEJ^TURES IX RADIOISOTOPE RESEARCH 



In normal human per kgm weight 0.35 — 0.65 mgm/kgm iron leaves the 

 plasma in the course of 24 hours or in a 70 kgm subject 24—45 mgm. and 

 is replaced to a very large extent by endogenous iron finding its way 

 into the circulation as the uptake from the intestinal tract makes out 

 only 1 — 2 mgm daily. The bulk of the plasma iron finds its way into the 

 marrow and is utilized in haemoglobin formation. If haemopoiesis is 

 impaired it will reflect itself in a change in the amount of iron leaving 

 the plasma and incorporated into the red corpuscles. Interference with 



0,50 1,00 



P.C. "Fe in hemoglobin 



Fig. 3. — ^^Fe content of haemoglobin 2 hours after intravenous 

 injection of ^^Fe labelled plasma plotted against the reticulocyte 



content of human blood. 



normal haemopoiesis will reflect itself in a change in the haemoglobin 

 content of the circulation as well. However it takes days before a notice- 

 able change in the haemoglobin content can be ascertained, while 

 a few hours only, or even less, after such a disturbance has set in it will 

 reflect itself already in a change of the amount of iron leaving the circu- 

 lation, which can be determined only by labelling the plasma iron and 

 measuring the disappearance rate of ^^Fe from the plasma and the iron 

 content of the latter. The ^^Fe incorporation into haemoglobin some hours 

 only after labelling the plasma iron has to be interpreted very cautiously 

 as the ^''Fe absorbed at that very early date in the circulating haemog- 

 lobin is not due to, or not mainly due to, incorporation of ^^Fe into 

 haemoglobin in the marrow but into circulating reticulocytes and is a 

 measure of the number of the latter as seen in Fig. 3, taken from a 

 paper of m.y collaborator Dal Santo^i^). 



