Change in radiosensitivity on the development of sea urchin eggs during the early cleavage stage. II. Protection against x-ray irradiation by cysteamine.

中村 泉:東 京大学理学部動物学教室,東 京都文京区本郷7-3-1,〒113 * Present address : Department of Hygiene, Teikyo University School of Medicine, Tokyo 173 The effect of cysteamine on the fluctuation of X-ray sensitivity during early cleavage stage of sea urchin eggs expressed by pluteus formation rate was examined. Sea urchin eggs were very resistant to radiation immediately after insemination or after S phase of the cleavage. When irradiation was given just prior to S phase or in the phase of cytokinesis, the eggs were very sensitive. In these sensitive stages, existence of cysteamine during X-irradiation appar ently protected eggs against radiation effect. Dose modifying factor increased linearly from 1.8 to 3.4 with increasing dose of cysteamine (25 mM•[75 mM) added.