Effect of Pretreatment with Cysteine on Survival of Mice Exposed to External and Internal Irradiation.

Abstract

CFW and dba mice were pretreated with small (125 and 250 mg./kg.) doses of cysteine (pH 1.0 or 6.5) before irradiation with lethal doses of X-rays (600 r). It was found that 10 to 14 days after irradiation the percentage of surviving animals was consistently higher in cysteine-pretreated group than in irradiated, not pretreated controls. These results illustrate "protective" effect of cysteine against radiation. In new mice prepared with high doses (more than 800 mg./kg.) of cysteine the X-ray treatment was followed immediately by death or agony. In mice treated by one of these factors alone, the condition was affected only after several days. Thus, the rapid lethal effect of combined treatment with cysteine (high doses) and X-rays is interpreted as potentiation of one factor by the other. This effect of high doses of cysteine was absent in X-ray-treated mice possessing copious peritoneal exudate due to the growth of free S-37 cells in the peritoneal fluid. This failure of cysteine is attributed to inactivation (oxidation) of cysteine by some factor of the peritoneal fluid. In these mice with exudate pretreated with small doses of cysteine, the decrease in the cell number (in the exudate) induced by irradiation was followed by a steady increase, while in irradiated controls the decrease continued until their death. Pretreatment with small doses of cysteine (intraven.) had unfavorable effect on survival of mice injd. intraperiton. with radioactive colloidal gold. An explanation of the above phenomenon as manifestation of cysteine penetration from blood stream into tissues after increase of blood vessels permeability by high doses of irradiation is offered.