Role of the medium in radiation effects on cells cultivated in vitro

Ionizing radiations suppress the onset of mitosis and affect the synthesis of DNA in cells cultivated in vitro. In order to determine if the culture had any effect on the onset of mitosis and DNA metabolism, a medium containing inorganic salts, lactalbumine hydrolysate, and 5% calf serum was irradiated with a dose of 500 r. Immediately after irradiation, the medium was added to HeLa cells extracted from embryonic calf liver. The inhibitory effect of the irradiated medium on the mitotic index is quite clear. The uptake of H3-thymidine by the nuclei was also strongly inhibited by the irradiated medium. (J.S.R.)