SOME FACTORS CONTROLLING THE 



HAEMATOPOIETIC REGENERATION IN WHOLE 



BODY IRRADIATED RATS* 



E. H. Betz 



Department of Pathology, University of Liege, Belgium, National Foundation for Scientific 



Research 



Many papers in the field of radiobiology have shown that there is a close 

 relationship between the survival rate of whole body irradiated animals and 

 their ability to regenerate the destroyed haematopoietic tissues. During 

 the last yeai^s, it has been shown that different chemicals are able to protect 

 animals against a lethal dose of X-rays. Whereas animals submitted to a 

 lethal whole body irradiation do not show any regeneration of their haemato- 

 poietic tissues, there is an extensive regeneration of bone marrow, spleen, 

 lymph nodes and thymus in the animals receiving a protective agent before 

 the lethal irradiation. Qiiite similar results have been described in animals 

 protected with potassium cyanide (Betz^ ; Betz and Fruhling^), gluta- 

 thione (Cronkite et al^), thiourea (Mole^), cysteine (Lorenz^). An 

 identical stimulation of haematopoiesis is observed in animals protected by 

 spleen or bone marrow homogenates injected after X-irradiation (Jacob- 

 son et al^, Lorenz et aP). 



In earlier experiments, we have shown that, in animals submitted to a 

 lethal dose of X-rays, there is an inhibition of haematopoiesis which is 

 independent of the tissular lesions themselves. It is possible, indeed, by 

 grafting the spleen of an irradiated mouse to a normal one to induce an 

 extensive regeneration of myeloid and lymphoid tissues within the graft. 

 Such a regeneration would never have taken place if the splenic tissue had 

 remained within the radiated body till death. From these observations, 

 we may conclude that the regeneration of the haematopoietic tissues depends 

 not only on tissular lesions, but also on the humoral conditions within the 

 body where such tissues are living. These observations led us to investigate 

 different factors which could possibly control the haemopoietic regeneration 

 of irradiated rats (Betz^). 



The first factor we started to investigate was the influence of the adrenal 

 cortex. It is well known that whole body irradiation stimulates the activity 

 of the adrenal cortex (Patt et aP). The increased production of adreno- 

 cortical hormones could influence the haematopoietic regeneration ; Baker 

 and Ingle^" have observed indeed an atrophy of bone marrow in rats 

 treated with large doses of cortisone and AGTH. Therefore, the hyper- 

 corticism existing in whole body irradiated rats, could possibly explain the 

 inhibition of the haematopoiesis observed in such animals. 



* A more detailed paper on this subject has been published in Revue d'Hemaiologie, 1953, 

 8 489. 



292 



