H. A. S. VAN DEN BRENK AND RUTH MOORE 



reduced by increasing the partial pressure of respired oxygen during irradi- 

 ation, but even at 4 atmospheres pure oxygen (respired gases), substantial 

 radio-protection exists for both rats and mice. In rats, oxygen reduces the 



2 3 4 



p02 (atmospheres absolute) 



Control 



r5 



o o Cystamine(3x10" moles) 



X X 5- OHT (0-25 X 10"^ moles) 



Figure 3. Effect of respired oxygen tension on the radio- 

 protective actions of cystamine and 5-hydroxytryptamine 

 against acute radiation-induced lethality in mice (830 r) 



protective action of 5-OHT considerably more than that of cystamine, whilst 

 the reverse holds for mice, although doses of the amines used must be taken 



• — • Controls 



X X 5-OHT (0 5x10'* moles) 



30 



in 

 n 



Q 



20 



> 



Z3 

 ifl 



c 

 ft) 



10 



1 2 3 A 



p02 (atmospheres absolute) 



Figure 4. Effect of respired oxygen tension on 

 the radio-protective actions of cystamine and 

 5-hydroxytryptamine against acute radiation- 

 induced lethality in rats (1000 r) 



into consideration. Before any firm conclusions are reached, experiments 

 being conducted using the amines in various doses for various partial pres- 

 sures of respired oxygen will need to be evaluated. However, these preliminary 



183 



