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



effect is annulled by irradiation of cyanide pretreated mice in pure oxygen 

 at 4 atmospheres absolute pressure. A dose of ■ 2 mg NaCN in 1 50-g rats, 

 failed to give significant protection against 1000 r whole-body irradiation. 

 These results are shown in Table 1. 



Table 1. Effect of respired oxygen on radio-protective effect of sodium cyanide in mice 



(1000 r X-rays whole-body irradiation) 



* NaCN administered intraperitoneally 5 minutes preceding irradiation 



However, although cyanide is said to increase oxygen concentration in 

 the blood, due to inhibition of oxygen utilization by tissues, the dose used in 

 mice causes considerable shock and collapse of animals, and it is felt the 

 latter may be sufficient to result in anoxic anoxaemia and slowing of the 

 circulation. This effect in mice was clearly ameliorated when animals were 

 observed in pure oxygen under pressure. In rats, shock and collapse following 

 cyanide in the doses used was much less, although moderate increase in 

 dosage resulted in toxicity and some deaths. 



Ejfect of Cyanide on Chemical Protection in Rats 



Smith et al.^^ have reported that cyanide does not modify the protective 

 action of cysteine in the rat. Our experience is limited to cystamine (10 x 

 10^^ moles) and 5-hydroxytryptamine (0-50x10'^ moles) in rats. The 

 effects of a dose of • 2 mg of NaCN on the protective action of these substances, 

 for 1000 r whole-body irradiation, are shown in Figures 1 and 2. Whilst the 

 protective action of 5-OHT was significantly decreased, no such significant 

 decrease resulted for cystamine although, the difference in dosage of the two 

 protective agents, and the relative degrees of protection afforded must be 

 taken into account. It is quite likely that for lower doses of cystamine, a 

 reduction in the radio-protection observed may be affoi'ded by cyanide. 

 Experiments to test this prediction, are to be conducted. 



Effect of Tetision of Respired Oxygen on Chemical Protection in Rats and Mice 



Cystamine and 5-hydroxytryptamine — The effect of respired pOg on lethality 

 following 1000 r X-rays to whole-body in rats and mice, protected with 

 cystamine (1 x 10~* moles for rats, 3 x 10~^ moles for mice) or 5-OHT 



13 181 



