Alterations in Deoxyribonucleic Acid from Regenerating Rat Liver after X-radiation in vivo

Abstract

WHILE it is thought that X-radiation in vivo does not produce any changes in the properties of deoxyribonucleic acid (DNA) which are associated with H bonding¹, alterations in its structure are suggested from differences in fractionation pattern on ECTEOLA^2,3 and from the diminished capacity of nuclei isolated after irradiation in vivo to act as templates for DNA synthesis⁴. The validity of the chromatographical evidence has been questioned for normal animals by Kondo and Osawa⁵ and after irradiation^6,7, due to our ignorance of the means by which fractionation on ECTEOLA is attained and because of the possibility that the differences found between DNA from control and irradiated animals could be due to the action of DNases which are known to be activated in thymus after X-radiation. In view of these uncertainties, it was decided to extend our earlier observations on thymus DNA to regenerating rat liver. This tissue is advantageous since it is possible to irradiate at a known period in the mitotic cycle, and because in normal rat liver activation of DNases post-irradiation is much less marked than in thymus⁸. DNA was isolated by Kirby's method⁹, which would reduce to a minimum DNase action during the isolation.