Chemical Protection of Rat Thymocytes Irradiatedin Vitro

Abstract

The effect of chemical compounds on the survival of rat thymocytes irradiated in vitro was studied. The oxygen-concentration of the treated and untreated cell-suspension was also determined. The addition of cysteine, l-dimethylcysteine, isocysteine, cysteamine and S-2 aminoethyl-isothiuronium bromide hydrobromide (AET) to the suspensions appreciably retarded the death-rate of the irradiated cells, but did not reduce the oxygen-content of the suspensions to a level which could be expected to affect their radiosensitivity. It was concluded that these compounds protect by reacting with radiosensitive sites in the cell and not by causing anoxia in cells or radiosensitive organs. Cystamine, β-homocysteine, adrenaline and histamine were ineffective with regard to the death-rate and depleting the cell-suspension of oxygen. Since these compounds are radioprotective in vivo it is proposed that they have a pharmacological mode of action and therefore do not protect by reacting with the radiosensitive sites in the cells. The different effect of cystamine in vivo and in vitro may also be explained by its conversion to cysteamine, which may occur in vivo but not in vitro. Noradrenaline, diethyldithiocarbamate, d- and dl-dimethyl-cysteine, α-homocysteine and glutathione were found to interfere with the eosin-staining technique employed to determine the number of non-viable cells, but have been classified as non-protectors at the cellular level.