366 ' GENERAL DISCUSSION 



which the protective substances reduce the possibiHty of the formation 

 of radicals at the instant of the action of X- and y-rays. This notion of 

 the mechanism of the action of the protective substances has a direct 

 Hnk with the oxygen effect. 



It would, of course, be a mistake to connect the mechanism of the 

 protective action of diverse compounds only with those of other 

 variations of the oxygen concentration in the medium or the sub- 

 strate. It is important, however, to emphasize that for all the means 

 of chemical protection studied in experiments on mammals we suc- 

 ceeded in establishing the link with the oxygen effect. 



This link was expressed to a greater or lesser extent for the protective 

 substances belonghig to the various classes of chemical compound. 

 Of course, the alteration in the free oxygen concentration in different 

 tissues was effected by means of various biochemical and physiological 

 mechanisms. 



For protective substances belonging to the group of cyanide com- 

 pounds or to the nitriles or azides, the connection with the oxygen 

 effect emerges in more open form. For amines which do not contain 

 an - SH group and for aminothiols this connection with the oxygen 

 effect frequently emerges in veiled form. 



In technically exquisite experiments van Muir and van Bekkum have 

 recently shown convincingly with the help of an oxygen electrode that 

 the so-called biogenic amines — histamine, tryptamine, phenylethyl- 

 amine, j8-epinephrine — ^clearly reduce the concentration of oxygen in 

 the spleen. There is a good positive correlation between the tissue 

 hypoxia produced in the spleen and the prophylactic action of these 

 amines. 



In our experiments carried out with aminothiols we discovered that, 

 when introducing such aminothiols as |S-mercaptoethylmine, ^- 

 mercaptopropylamine, AET(aminoethylisothiouronium bromide), rats 

 begin to consume a reduced amount of oxygen and the irradiation of 

 the animals proceeds against the background of a general reduction 

 in the intensity of oxidation-reduction processes. By making use of 

 the polarographic method we have succeeded in showing that after 

 introducing ^S-mercaptopropylamine in rabbits, the concentration of 

 the free oxygen in the cortex of the brain is distinctly reduced. 



Thus, one may regard as established the role of the oxygen effect 

 in the mechanism of the action of aminothiols and biogenic amines in 

 mammals. 



One of the possible release mechanisms for radiation damage is the 

 chain reaction evidently induced by various compounds, for example 

 by organic peroxides in the lipid fraction. This concept has been 



