Radiation and Ascites Tumour Metabolism 219 



activity (Fig. 1) might be due to a loss of highly active RNA 

 molecules. 



During the first two hours after irradiation, the incorpora- 

 tion of [2-^*C]glycine into both DNA and RNA was depressed 

 to the same degree, averaging about 70 per cent of that of the 

 non-irradiated tumour cells in our experiments. This was 

 established through analyses in which glycine was injected 

 immediately after radiation and the tumour cells were 

 assayed at various times in the interval 0-120 minutes 

 (Forssberg and Klein, 1954). Intraperitoneally injected 

 glycine is very rapidly taken up by the cells. Five minutes 

 after injection, the uptake was found to be the same in irradi- 

 ated and control cells ; the decreased incorporation of glycine 

 in the nucleic acids is therefore not caused by any changes in 

 permeability. 



On comparison of the purely chemical analysis of RNA and 

 DNA with isotope determinations, it appears that total RNA 

 synthesis proceeds roughly linearly with the production of cell 

 mass during the 48-hour period, whereas isotope incorpora- 

 tion, as stated, is reduced to 70 per cent of the normal value 

 during the first two hours. DNA incorporation of ^^C is also 

 reduced to the 70 per cent level as contrasted to the increase 

 in the total amount of DNA which proceeds at an average of 

 33 per cent of that of the unirradiated controls. 



In the amitotic period which follows (time interval 2-20 

 hours), marked changes in the incorporation rate of both 

 RNA and DNA take place and specific activity values equal 

 to or even higher than those of the controls occur. These 

 results were obtained in experiments where i*C-glycine was 

 injected over a period of two hours at different times during 

 the amitotic period. As far as incorpt)ration rate is equivalent 

 to synthesis, this ought to imply that the initial depression of 

 synthesis is followed by a period of increased synthesis. 



In the case of RNA, the increased incorporation rate 

 subsequent to the initial depression shifts the balance, so 

 that the isotope measurement can be made compatible with 

 the finding that the total RNA is synthesized for the most 



