866 



ADVENTURES IN RADIOISOTOPE RESEARCH 



haemins of guinea pigs, rats and rabbits exposed to 500 r, and in some 

 cases up to 1400 r, and killed 5 to 66 hours after the injection of radio- 

 iron (Hevesy and Bonnichsen, 1955; Bonnichsen and Hevesy, 1955). 

 The results of these experiments are seen in Fig. 10. ^^Fe incorporation 

 into haemoglobin and myoglobin alone is interfered with by exposure 



400r 



2 3 4 5 



Time after injecfion (days) 



Fig. 9. Uptake of ^®Fe in circulating blood of rats ("August" strain) 



injected subcutaneously with ferric chloride in citrate buffer 48 



hours after irradiation wich various doses of 250 kVp X-rays. 



to radiation. Incorporation of ^^Fe into all other haemins investigated 

 is not depressed; it is even enhanced. As after irradiation the number 

 of marrow cells, the chief competitors for ^^Fe, get strongly reduced, 

 more ^^Fe takes its way into the cells of the liver and other organs. 



Doses up to 100 r do not disturb clearance of ^^Fe in man (Loeffler, 

 Collins and Hyman, 1953), but a dose of 800 r was found to decrease 

 markedly the clearance of ^^Fe in the rabbit (Hevesy and Dal Santo, 

 1954). 



The above findings suggest the explanation that interference with 

 haemoglobin formation is due to the radiation sensitivity of marrow 

 cells. Radiation produces mitotic arrest in the latter, new-formation of 

 erythropoietic cells is interfered with and, if larger doses are applied, 

 cell destruction independent of mitotic processes may take place as well. 



