796 ADVENTURES IN RADIOISOTOPE RESEARCH 



these objections seemed not justified or to a minor extent only so, — in 

 the growing Jensen sarcoma the rate of additional formation of desoxy- 

 ribo nucleic acid does not lag much behind the rate of formation 

 of desoxyribo nucleic acid ^ap _ they induced us to study the effect 

 of irradiation on the incorporation of ^^C with the purines of desoxyribo 

 nucleic acid. 



In experiments previously described^^) acetate labelled in the carboxyl 

 group was injected to suckling rats irradiated with 880 r and to control 

 suckling rats. The silver purines were secured from the desoxyribo 

 nucleic acid of various organs 4 to 7 hours after injection and their 

 activity was compared. Incorporation of ^^c into the purines of the 

 irradiated rats was found to be depressed by 20 to 70 per cent. For the 

 liver fractions the mean values seen in Table 1 were obtained. 



The results obtained indicate an arrest caused by irradiation in the 

 formation of purine moiety of desoxyribo nucleic acid as well. 



Abrams^^) investigated recently the effect of irradiation on the incor- 

 poration of ^^C with purines of the nucleic acids of the rat intestine 

 using glycine — 1 — ^"*C as source of ^^C. He found ^"^C incorporation 

 with DNA inhibited by 80% and with RNA by 49 %, while the percen- 

 tage incorporation into proteins was hardly affected. 



Urethane is known to interfere with mitotic processes and we can 

 thus expect large doses of urethane to depress nucleic acid formation. 

 In a recent investigation Skipper^^) administered large doses of urethane 

 (1800 mgm/kg)ra and then ^^C labelled formate to mice and investigated 

 the incorporation of ^^C into the viscera nucleic acids and into the total 

 tissue of various organs. Incorporation of i'*C into the viscera nucleic 

 acids was found to be depressed under the effect of urethane to about one 

 half of the value found in controls, thus to a similar extent as the incor- 

 poration of acetate i*C into nucleic acid was observed to be reduced 

 under the effect of X-rays (cf. Table 1). Total tissue took up, however, 

 in the urethane injected mice more formate carbon than in the controls. 

 The latter effect is presumably due to a decrease in the sensisivity of the 

 radioactive indicator (higher i*C level) and was formerly observed'*) in 

 experiments in which following administration of labelled acetate the 

 i*C uptake by tissue w^as compared in the urethane injected mice and in 

 controls. 



The precursor of the nucleic acid ^HJ may also have a higher activity 

 level in the urethane injected mice than in the controls, but in spite 



(i) G. Hevesy, Nature 163, 809 (1949). 

 (2)R. Abbams, Arch. Biochem. 30, 90 (1951). 

 (2)H. E. Skipper, Texas Rep. Biol, and Med. 8, 543 (1950). 

 (4)g. Hevesy, Nature 164, 1007 (1949); G. Hevesy, R. Ruyssen and H. L. 

 Beeckmans, Experientia 7, 144 (1951). 



