An Autoradiogaphic and Biochemical Study of the Effects of Radiation on Deoxyribonucleic Acid Synthesis in the Intact Animal

This is part of a continuing study of the effects of localized radiation on mammalian cells in the intact animal. Exploration of the immediate effects of radiation, as well as recovery and long-term survival of somatic cells, is in progress (1, 2). Previous studies have shown that one specific dose (3000 r) decreased the rate of deoxyribonucleic acid (DNA) synthesis to 40 % of the control values. Combined autoradiographic and cytochemical studies on individual cells demonstrated that these cells continued to synthesize DNA at a slower rate than the paired controls. The mean time for DNA replication in the irradiated cells was 13 hours, and the mean time for replication in the controls was 8 hours (1). Regenerating rat liver was used in this study of the effects of irradiation on DNA synthesis. Since regenerating rat liver is a semisynchronous system it is possible to confine the studies to the DNA synthetic period and separate them from other cell functions such as mitosis. The studies were made at the beginning, near the midpoint, and at the end of the 8-hour period of DNA replication of the first cycle of hepatocytes. Quantitative autoradiographic methods have been utilized to assess radiation effects on individual cells. Biochemical methods have been utilized to assess radiation effects on the total population of cells. Chromatographic separation of labeled precursors has been made in order to study changes in the biosynthetic pathways of DNA synthesis after irradiation. Local irradiation to the liver has permitted the study of the dose range from 750 r to 40,000 r.