Nucleic Acid Changes in the Rat after Total-Body X-Irradiation

Abstract

Among the observations made by the early investigators who studied cellular changes after X-irradiation was the effect on the chromosomes of the nucleus (1). These chromosome aberrations were subsequently related to the genetic mutations which frequently result from exposure to ionizing radiations. The more recently developed ideas of the close relationship and possible identity of deoxypentosenucleic acid (DNA) and genetic structure (2-6) and the general interest in the possible relation of ribonucleic acid (RNA) and DNA have stimulated investigations into the effect of radiation on the synthesis and breakdown of nucleic acids in a wide variety of organisms. A great deal of this work has been concerned with changes in the incorporation into RNA and DNA of isotopic tracers such as p32 and C14 in the form of simple nucleic acid precursors. Although some of this work is controversial, there is considerable agreement that subsequent to whole-body irradiation there is reduction in the synthesis of DNA, first demonstrated by Hevesy and co-workers (7) and later confirmed by many others (8-13). This is true even in mammalian liver (9), which is generally regarded as being radioresistant, at least with respect to histological alterations (14). Pelc and Howard (15) have recently suggested that the observed inhibition of DNA synthesis can be explained to a large extent on the basis of the arrest of mitosis in those cells which at the time of irradiation are in early interphase. One facet which has been largely overlooked in favor of isotope incorporation is the possibility of changes in the composition, and therefore possibly the structure, of the nucleic acids. With this in mind an investigation was undertaken to study the effect in vivo of X-rays on the composition of rat tissue nucleic acids. Shortly after this work was begun, a report appeared by Paigen and Kaufman (16), who studied