H. A. S. VAN DEN BRENK 



Selective Toxicity of Indole Amines and Their Radio-protective Action 



The radio-protective action of tryptamine and 5-hydroxytryptamine (5-OHT) 

 has been studied in vivo, and the effects of specific antimetaboHtes and antago- 

 nists of 5-OHT have been determined. A prehminary report has been made.^^ 



Radio-protective action of 5-OHT 



Acute lethality — This substance is a powerful protective agent for radiation- 

 induced acute lethaUty in rats and mice^' ^. Our own resuhs have confirmed 

 this effect. In adult Canberra black stock rats a dose of 0-5 x 10"^ moles 



— X — Controls 



-5, 



■ 5-hydroxytryptamine (0-25 xlO" moles) 

 — • — Cysteamine (7x10"^ moles) 



Figure 1. Protective action of 5-hydroxytryptamine and 

 cysteamine administered 5 minutes preceding irradiation, 

 compared for mortality in Swiss mice due to total body 

 irradiation — Each point represents mean survival for 20 

 animals, at end of 30 days observation period 



5-OHT, given five to seven minutes before whole-body irradiation with 

 1000 r X-rays (250kV) gives 50 to 90 per cent survivors at 30 days. In 

 unprotected similar rats, this dose is uniformly lethal with a mean survival 

 of about seven days. In mice similar results are recorded, and compared 

 with cysteamine. These results are shown in Figure 1. 



Weight loss — Both treated irradiated rats and untreated irradiated controls, 

 lose weight for an initial five days after irradiation, after which controls 

 progressively lose weight until death, whilst protected rats commence to 

 regain weight, and within 20 days after irradiation the original weight has 

 been attained. 



Diarrhoea — There is a 1 00 per cent incidence of diarrhoea amongst irradiated 



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