Effect of 180 MeV proton or 60 Co gamma radiation on the incorporation of 125 I-iodo-2'-deoxyuridine into intestinal and splenic deoxyribonucleic acid of mice

Effects of low doses of gamma radiation on DNA synthesis in the developing rat brain

Rats of one or ten days of age were irradiated with low doses of gamma radiation, and synthesis of DNA was examined by the incorporation of 3H-thymidine in the cerebellum and the rest of the brain in vivo. DNA synthesis was depressed in both parts of the brain but the effects were larger in cerebellum. A minimum was found about 10 hours after irradiation in the older rats and later (18 h) in the younger ones. The dose response, in 10-day-old rats, was biphasic and showed that cerebellum was more affected. Autoradiographs showed that fewer cells entered the cycle and those synthesizing showed a depressed rate of synthesis. These findings are discussed in relation to induction of cell death.

The effect of 60Co gamma-radiation and hydroxyurea on the in vivo chain growth of DNA in crypt cells of the small intestine of the mouse

DNA chain growth has been studied in small intestinal crypt cells of the mouse in vivo using a sensitive method. The method is designed primarily to study radiation-induced DNA-breaks and their repair; but since there are breaks in DNA at the replicating fork, it is also possible to study DNA chain growth after a 3H-thymidine pulse. We found that DNA chain growth is not depressed by 200 rad of 60Co gamma radiation. This finding supports the hypothesis that irradiation interfers mainly with the initiation of new replicons in mammalian cells affecting DNA chain growth only at higher doses. Hydroxyurea at sufficient dosage, however, depresses or even stops DNA chain growth in mouse crypt cells in vivo.