

PHOSPHORYLATING ACTIVITY OF MITOCHONDRIA AFTER TOTAL BODY IRRADIATION 



can only be expected to throw some light on the mechanism of initial radia- 

 tion injury, if performed within a few hours after exposure. After a larger 

 interval, especially when relatively large doses of radiation are being 

 employed, the structural changes in the tissue are so radical that a change in 

 tissue composition rather than in cellular function is most likely to be 

 reflected in the results. 



Therefore our experiments are usually performed at 4 hours or less after 

 total body irradiation, when changes in organ weight are not yet apparent. 



INFLUENCE OF DOSE 



After the effect of large doses of total body irradiation had been established, 

 we have attempted to assess the sensitivity of oxidative phosphorylation to 

 this type of injury. Furthermore our studies have been extended to mito- 

 chondria isolated from rat thymus. The methods employed with spleen 



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Figure 1. Oxidative phosphorylation of rat spleen mitochondria at 4 hours 



after various doses of total body irradiation. Black bars : phosphate 



uptake in [j.moI/mgN ; white bars : oxygen uptake in [i,atoms/mgN. 



Each experiment consists of 4 groups including a control. 



mitochondria have been described previously (van Bekkum et al^) and were 

 applied with minor modifications to the study of mitochondria from 

 thymus. Mitochondria were prepared from the pooled tissues of at least 

 2 rats in case of spleen and of 4 rats in case of thymus. Oxidative phos- 

 phorylation of these preparations was estimated in duplicate. Variation of 

 activity between and to a less extent within batches of normal rats necessitated 

 the inclusion of control animals in every experiment. Some of the results 

 are depicted in Figures 1-3. 



It is apparent that in the case of spleen mitochondria, oxygen uptake is 

 usually much less affected than phosphorylation, while in the case of mito- 

 chondria from thymus this difference is not so outspoken, although P/O 

 ratios are depressed after irradiation in most experiments. The minimal 

 dose of radiation which was capable of inducing a decrease of mitochondrial 

 phosphorylation was found to be between 50 r and lOOr for both tissues. 



Microscopical examination of the tissues used in these experiments revealed 

 extensive cellular destruction at 4 hours after doses of 300 r and more. In 



202 



