RADIO-PRCriECTIVE ACTION OF CERTAIN AMINES 



results suggest that the protective action /// vivn lor rats and mice is oxygen 

 dependent, Inil liu- results do not suggest that the protector acts solely by 

 causing anoxic anoxaemia. For the oxidized substance cystaniine (-S-S-), 

 partial pressures of respired oxygen from 0-2 to 4 atiuosphcres absolute 

 cause very little reduction in the radio-protection afforded in rats. This 

 differs from the findings of Salerno el aiy' with the reduced substance cyste- 

 amine (-SH). Direct measurements of vena caval blood oxygen concentra- 

 tions for different partial pressures of respired oxygen after administration of 

 protective agents is required, but this is difTicult in practice. We hope to make 

 some measurements of oxidation- reduction potentials and oxygen tensions 

 using platinum electrodes after tlie technique of Cater el al.^ to obtain more 

 direct information of the conditions which prevail, but inspection of the 

 protected animals respiring 2 to 4 atmospheres pure oxygen, does not reveal 

 the cyanosis, i-espiratory difficulty, or collapse, seen under similar circum- 

 stances in air at 1 atmosphere absolute. 



^20r 



o 



I 10 



c 



o. 



00-2 12 3 4 



p02 (atmosphere absolute) 

 -•Control • •Methylene blue 



o oNaCN + [-Methylene + NaCN 



Figure 5. Effect of respired oxygen tension on acute 

 radiation-induced lethality in mice (830 r X-rays), 

 following pretreatment with sodium cyanide (0- 1 mg), 

 methylene blue (2-0 mg), or combinations of these 

 substances 



Hislamine and Adrenalin — A few experiments have been conducted with 

 rats, using histamine phosphate (10 mg) or adrenalin («-methyl-«o;-adrenalin 

 hydrochloride 0-01 mg) as protective agents. In our experience, these 

 substances are very weak protective agents in the rat. Increasing the respired 

 pOg beyond 1 atmosphere absolute, annulled the protective action of these 

 substances — one (histamine), a bronchoconstrictor and vasodilator, the 

 other (adrenalin), a bronchodilator and vasoconstrictor. Again we have no 

 direct knowledge of the various oxygen concentrations which prevailed under 

 these circumstances, but an oxygen effect seems important in the protective 

 action. 



184 



