THE SKIN1FI(A4NCE OF FREE 

 BEOXYRIBONUCLEOTIDES IN RADIATION DAMAGE 



J. SOSKA, L. BENES, V. DRASIL. Z. KARPFEL, E. PALECEK AND 



M. 8KALKA 



Institute of Bkyphijsics, Czechoslovak Academy of Sciences, Brno, 



Czechoslovakia 



SUMMARY 



The authors present a survey of experiments indicating that a part of the radia- 

 tion inhibition of DNA synthesis in animals may be caused by some interference 

 of radiation with the synthesis of DNA precursors. Supplementation of bone- 

 marrow from irradiated guinea-pigs with nucleotide fractions of chick-embryo 

 extract enhanced the synthesis of DNA. Addition of deoxycytidylic acid to 

 irradiated bone-marrow stimulated the incorporation of 32p.phosphate and 

 i-iC-formate into reticular cells. Administration of some, especially pyrimidine, 

 deoxyribonucleotides into irradiated mice increased the mitotic index in their 

 bone-marrow and tended to restore to normal the increased ratio of DNA 

 purines/pyrimidines. The content of free deoxyribosides increased in rat tissue 

 after irradiation, but the increase of deoxyribonucleotides in rat liver, wdiich 

 takes place after partial hepatectomy. was reduced after irradiation. 



In our earlier experiments, we observed that some deoxyniicleotides, 

 esi^ecially deoxycytidylic and thymidylic acids, had a favourable 

 effect on the course of radiation disease, when the dose of radiation was 

 sublethal and that of the nucleotide amounted to 0-1 to 1-0 mg per 

 mouse. A more speedy recovery of the WBC count was observed, par- 

 ticularly in the increase of young leucocyte forms, the rate of sin-vival 

 increased on the average by 20 per cent and the mitotic index of the 

 bone-marrow was also higher as compared with the irradiated control. 

 When deoxycytidylic acid in a concentration of about SO^ug/ml was 

 added to a suspension of bone-marrow from irradiated guinea-pigs 

 surviving in vitro, DNA-synthesis increased in comparison with the 

 irradiated control. In these experiments, we proceeded from delibera- 

 tions based on Jacobson's hypothetical humoral factor of the blood- 

 forming tissue presuming that free deoxyribonucleotides or other com- 

 pounds related to them might be the factor itself; and, further, that the 

 inhibition of DNA synthesis, as observed after irradiation, was of 



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