100 



ly used, fluoride is added to inhibit the ATP-ase activity. Addition of the quan- 

 tity of fluoride oridinarily used will decrease enzyme activity by about 50 per 

 cent in both normal and irradiated spleen. However, even in the presence of 

 fluoride, the ATP-ase activity of a phosphorylation system is about twice as 

 high in irradiated as in normal spleen. Therefore, it might appear that oxida- 

 tive phosphorylation was inhibited when actually there might only be increased 

 hydrolysis of the phosphate esters formed. 



The breakdown of 5-adenylic acid is also reversibly increased in the 

 spleens of irradiated animals at doses that are below lethal; after 800 r, there 

 is an irreversible increase in the 5-nucleotidase activity of spleen and thymus. 

 The characteristics of this effect with regard to time of onset, magnitude, and 

 duration are very similar to those that I have just described for ATP. The 

 breakdown of adenylic acid due to increased nucleotidase activity occurs in the 

 spleen and thymus but not in most other tissues of irradiated animals. 



The administration of protective agents will decrease the amount of en- 

 zyme change in tissues of irradiated animals. Para-aminopropiophenone (PAPP) 

 a methemoglobin-forming agent, shown by Storer and Coon (11) to protect ani- 

 mals against lethal doses of radiation, partially prevents radiation-induced in- 

 creases in nucleotidase and adenosine triphosphate activity. For example, when 

 400 r was given to PAPP-treated rats, only a very small increase in the ability 

 of spleen to split adenylic acid was noticed. 



Even though we still have a great deal to do in connection with determi- 

 nation of the exact reason for the increase in enzyme activity, this biochemical 

 change can be used for studying the action of agents which are known to protect 

 against radiation lethality. PAPP does prevent this biochemical change from 

 occurring. This does not mean that the ability of PAPP to prevent mortality is 

 due to its protection against the phosphatase increase but, it does illustrate a 

 method of detecting whether a chemical agent is protecting against radiation- 

 induced damage to the spleen. 



KAMEN: Is there any theory as to how this agent operates? 



DUBOIS: Probably by its ability to produce tissue anoxia, because of 

 methemoglobinemia. 



KAMEN: What concentrations are used? 



DUBOIS: Thirty mg. per kg. 



POTTER: Incidentally, is it ineffective if you give it 30 minutes 

 afterwards? 



DUBOIS: Yes. 



PATT: Does para-aminopropiophenone have any action on isolated 

 tissue or on other in vitro systems? 



DUBOIS: No, insofar as is known. 



KAMEN: How long do you have to wait before it stops being protec- 

 tive? 



DUBOIS: The radiation should be administered within 2 hours at least 

 after the drug is given. 



