EFFECTS OF LOW X-EAY DOSES (0-1-1 r) ON 



HAEMATOPOIESIS SHOWN BY CYTOLOGICAL AND 



HAEMATOLOGICAL STUDY AND ^^Fe INCORPOR- 



ATION-A FOUR MONTHS' SURVEY 



H. MAISIN 



Cliniques Universitaires St. Raphael, Institut du Cancer, Louvain, Belgium 



SUMMARY 



In our strain of rats, total-body irradiation with 0-1 r and 1 r, administered between 

 7 and 84 days before, does not modify the mortality following subsequent sublethal 

 X-ray exposure. Although such a low dose does not affect the chance of survival of the 

 rats from a later lethal dose, the number of cells per mg of marrow and the erythropoiesis 

 as measured by the ^^Fe incorporation in the red cells are, however significantly increased 

 between the 4th and 8th weeks after 1 r. ^^Fe Incorporation in the red cells alone, 4 and 

 6 weeks after 0-1 r is also increased. The number of reticulocytes in the peripheral blood 

 significantly increases during the 2 to 4 weeks after 1 r and 0-1 r; the red and white cells 

 do not change. The significance of these results is discussed. 



Various authors have shown that mice irradiated with sublethal X-rav 

 doses, become radioresistant to a subsequent sublethal, or even lethal, X-ray 

 dose. The phenomenon occurs according to the authors, between 10 and 20 

 days after the administration of the sublethal dose. Thus Betz (1950) has 

 shown that mice irradiated with 500 r {IjD-^q^^q^ in his strain) would become 

 more resistant to 700 r (a LD^qq by the 10th day) administered 15 days later. 

 Paterson et al. (1952) gave the mice one-half of their LDgQ^go^; after 20 days, 

 these mice required 546 r to die in the proportion of 50%. Dacquisto (1959) 

 was able to show in Swiss mice that the LDg^^go) which is 487 r, is increased to 

 560 r if he gave them 50 r WBR 10 days before, and to 617 r if the 50 r are 

 given 17 days before. 



We have tried to confirm these data in our L-strain rats. Thus, we j)lanned 

 (Maisin, 1961) a series of experiments, administering doses of 50 or 400 r — 

 TBio(30) — between 7 and 42 days before a LD^g, LDjq, or LDgo^go), but we 

 did not get enhancement of the resistance of our rats. On the contrary, rats 

 receiving a conditioning, or prior, dose of 400 r died more rapidly and in a 

 much higher proportion than the controls. So, after 450 r (LD^g), the 

 mortality at 30 days varied between 70 and 95% and after 550 r, LDg^, 100% 

 of the rats were dead on the 10th day, half of them by intestinal syndrome 

 when otherwise they die only by medullary syndrome. A conditioning dose of 

 50 r had no influence on a subsequent dose of 450 r but was more or less 

 prejudicial against 500 r, LD^g and 550 r. 



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