LEUKAEMOGENIC EFFECT OF WHOLE-BODY ^^CO-y- 

 IRRADIATION COMPARED WITH ^H-THYMIDINE AND 

 3H-CYTIDINE: PRELIMINARY REPORT ON THE 

 DEVELOPMENT OF THYMIC LYMPHOMAS IN C57BL/6J 



MICE! , 



H. COTTIEE, E. P. CRONKITE, E. A. TONNA, and N. 0. NIELSEN 



Medical Research Center, Brookhaven National Laboratory, Upton, New York, 



U.S.A. 



SUMMARY 



Groups of 32 female mice (C57BL/6J) 6 weeks of age were given: 



(1) a total of 480 r whole-body ^"Co-y-irradiation in increments of 160 r at 7 day 

 intervals and at a dose-rate of 22 r/min, or 



(2) three subcutaneous injections of ^H-thymidine (3 X 10 /xc/g body weight; specific 

 activity 1-9 c/m mole) at weekly intervals, or 



(3) three subcutaneous injections of ^H-cytidine (3 X 10 /xc/g body weight; specific 

 activity 1 c/m mole) at weekly intervals, or 



(4) three subcutaneous injections of both ^H-thymidine and ^H-cytidine (dosage as 

 mentioned under (2) and (3)) at weekly intervals, or 



(5) received no treatment. 



The mice have been followed to date for 250 days. Only whole-body *°Co-y-irradiated 

 mice have developed thymic lymphomas. The difference is statistically significant 

 (P<0-01). 



These experiments will be helpful in determinmg the possible hazards involved in the 

 use of these radioactive compounds and also may lead to a better understanding of basic 

 phenomena underlymg radiation leukaemogenesis and carcuiogenesis, smce ^HTDR 

 gives predominantly intranuclear radiation and ^HCR predominantly cytoplasmic 

 irradiation. 



The in vivo application of tritiated thymidine (^HTDR) has been shown to 

 produce morphologically detectable acute radiation damage when sufficient 

 amounts are given (Johnson and Cronkite, 1959; Grisham, 1960; Cronkite et al., 

 1961; Sauer and Walker, 1961; Bateman and Chandley, 1962; Smith et al., 

 1962), The lowest dose reported to cause demonstrable injury is between 1 

 and 5ju,c ^HTDR (specific activity 1-9 c/m mole) per g body weight in: 

 mouse spermatogonia (Johnson and Cronkite, 1959); regenerating rat liver 

 cells (Grisham, 1960); and rat liver cells (Post and Hofman, 1961). No data 

 are available on possible radiation effects of ^H-cytidine (^HCR). 



Radiation dosimetry in an animal injected with ^HTDR is very difficult if 

 not impossible. The /S dose-rate expressed in r per tritium disintegration as 



f Research supported by the U.S. Atomic Energy Commission. 



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