1 



PHOSPHORYLATING ACTIVITY OF MITOCHONDRIA AFTER TOTAL BODY IRRADIATION 



necessary for the biochemical change under discussion to become measur- 

 able do not differ widely if at all. 



TIME-EFFECT 



Since the process of oxidativ^e phosphorylation has thus been found to be 

 highly radiosensitive, it seemed of interest to determine more accurately the 

 earliest time after irradiation at which this lesion becomes discernable. 

 These experiments were performed with rat spleen mitochondria at various 

 times up to 4 hours after total body irradiation with a dose of 700 r. The 

 time-effect curve shown in Figure 4 reveals a latent period of more than 

 1 hour after the irradiation before the oxidative phosphorylation becomes 

 clearly impaired. From most of the tissues used in this series, samples were 

 taken for histological study with the object to investigate whether the dis- 

 turbance of oxidative phosphorylation precedes the morphological changes 

 in the nuclei or otherwise. 



100 



50 



Figure 4. Phosphate uptake of rat spleen 

 mitochondria at various periods after total 

 body irradiation with a dose of 700 r. 

 Abscissae: hours after irradiation, ordinates: 

 percentage of corresponding control value ; 

 white circles with attached vertical lines : 

 mean ± S.E. ; n : number of experiments 



V¥ V2 7 8 V- 



I I I 1 L 



5 3 V^ 5 S 



-"K 



-Tl 



The first definite signs of damage, which consisted mainly of nuclear 

 vacuolization, were found at 1 hour after irradiation, but the number of 

 nuclei affected was very small at this time. At 2 hours after 700 r the 

 degeneration was more pronounced with some pycnotic nuclei in most of 

 the follicles. At this time the picture resembled that found at 4 hours after 

 50-lOOr in the previous series. The slices obtained at 4 hours after 700 r 

 showed a domination of pycnosis and fragmentation in all of the follicles 

 and a number of cells in the pulpa was involved as well. After that period 

 degeneration progresses still further and removal of dead material by 

 macrophages begins. In general this pattern closely resembles the observa- 

 tions made by Trowell^ on lymph nodes after in vivo irradiation. The 

 limited number of our results does not allow a definite conclusion as to the 

 sequence in which the two effects develop after irradiation. It is therefore 

 at present not possible to decide if a causal relationship between the two 

 phenomena exists but the approximately simultaneous appearance of 

 both the cytoplasmic and the nuclear changes seems to warrant further 

 investigation. 



204 



