Studies on the effect of X-rays on the biochemistry and cellular composition of ascites tumors: II. Changes in the pattern of glycine-2- 14C incorporationduring the first two hours after irradiation in vivo

Abstract

Summary o 1. The Ehrlich mouse ascites tumor was irradiated in vivo with 1250 rX-rays. The incorporation of 14C-glycine into various cellular components was studied during the period between 35 and 150 minutes after irradiation and was compared to unirradiated controls. Determinations were made of the total activity of tumor cells and ascites serum per unit weight, and of the spec. act. of ATP-ADP, PNA, DNA, proteins, total lipids and the Ba-soluble and Ba-insoluble fractions of trichloroacetic acid (TCA)-extracts. 2. Irradiation produced pronounced changes in the incorporation rate of14C into ATP-ADP, the nucleic acids, proteins, lipids, and a complex carbohydrate fraction. These changes were dependent upon the time that elapsed between the injection of the isotope (which took place immediately after irradiation) and the killing of the animals. There was a strong depression of activity levels of the nucleic acids, proteins, and lipids 35 minutes after irradiation. This was followed by a temporary increase between 35 and 80 minutes in case of the nucleic acids and lipids. 3. Irradiation did not change the permeability of the tumor cells to the isotope. The low activities found in various compounds 35 minutes after irradiation were thus not due to alteration of cellular permeability. 4. The cellular concentration of the ATP-ADP fraction, consisting predominantlyof ATP, was increased 35 minutes after irradiation by about 25 per cent. It is suggested that the consumption of ATP is inhibited soon after irradiation. This might lead to a delay of precursor formation for nucleic acid, protein and lipid synthesis, resulting in their decreased spec. act. During the interval between 35 and 100 minutes after irradiation, an increased consumption of ATP occurs concomitantly with a rise of spec. act. in the highmolecular compounds. The low spec. act. of ATP at 35 minutes can be interpreted as “isotope dilution”, while the subsequent increase of activity during the time interval 35–100 minutes indicates that ATP-synthesis is not impaired. It appears that X-ray effects on ATP-utilization may possibly determine initial biochemical changes after irradiation. 5. Irradiation was followed by a decreased 14C-incorporation into both PNA and DNA to about 75 per cent of the control value. The similar X-ray effect on both nucleic acids might be related to the fact that the incorporation rate of labeled glycine into both compounds is quantitatively similar in the control material. Since total DNA-synthesis in irradiated cells is only 33 per cent of the controls, there is a surplus incorporation of 14C into DNA which is not accounted for by a net increase of DNA-molecules. 6. There was a good agreement between the relative growth rate of tumorcells with varying physiological age and the rate of 14C-incorporation into the protein fraction.