306 RADIATION BIOLOGY 



Furthermore, blood transfusion from an irradiated rabbit (7500 to 

 10,000 r) to a nonirradiated rabbit also produces in the kidneys of the 

 recipient a definite inhibition of nucleic acid synthesis (Ahlstrom et al., 

 1946). These experiments, which demonstrate the indirect action of 

 ionizing radiations, have been confirmed by Holmes (1949), who found 

 75 per cent inhibition on direct irradiation and 50 per cent on indirect 

 irradiation. These results are in agreement with those of Thoday and 

 Read (1947) who found that the frequency of chromosome aberration of 

 X irradiation of the root tips of Vicia faha is decreased in the absence of 

 oxygen. On the other hand, oxygen has little, if any, influence on the 

 effectiveness of a rays. 



Perhaps the most effective agent for the production of these inhibitions 

 is the hydrogen peroxide produced on X irradiation of aqueous solutions 

 saturated with oxygen, since the ionic yield of H2O2 formation goes down 

 to zero in the absence of oxygen on X irradiation and remains unchanged 

 on a-r&y irradiation. 



Very little has been learned from the in vitro irradiation of tissue slices 

 and the measurement of their metabolism afterwards. The tissues under 

 these conditions are in a closed system, and there is no free and ready 

 circulation of the extracellular fluids which might carry products of 

 irradiation. Radiation of tumor tissues (irradiation with 110 mg of 

 RaBr2-2H20 for 3 to 7 hours) at 37.5°C produces a selective inhibition of 

 respiration in a period during which its glycolysis — aerobic and anaerobic 

 — remains relatively unaffected. Similar irradiation at 10°C inhibits 

 glycolysis, whereas it leaves respiration normal (Crabtree, 1935). There 

 is also increased formation of ammonia (Crabtree, 1936), probably 

 through protein breakdown. The retina irradiated at low temperatures 

 shows inhibition of glycolysis to a greater extent than tumors. Inhibition 

 starts immediately after application of radiation and increases with the 

 time of exposure to a maximum of 70 per cent with 10,000 r. Half- 

 inhibition is obtained with about 2500 r (Crabtree and Gray, 1939). 



The effect of X rays, given in a single dose to rats by body irradiation 

 at doses varying from 900 to 100 r, on the respiration, glycolysis, and rate 

 of oxidation of a number of substrates was studied by Barron (1946a). 

 The measurements were performed on tissue slices of spleen, liver, kidney, 

 thymus, adrenals, testis, submaxillary glands, and small intestine 

 obtained from animals sacrificed at different intervals after irradiation. 

 The respiration of most of these tissues is diminished soon after irradia- 

 tion (Table 5-9). Adrenals are a striking exception; the respiration in 

 this tissue is increased soon after irradiation, and does not decrease until 

 the third day after. Inhibition of the oxygen uptake is increased when 

 measurements are made in the presence of pyruvate, succinate, D-amino 

 acids, and L-glutamate, substrates all requiring sulfhydryl enzymes for 

 their oxidation. Of these substrates pyruvate oxidation is the most 



