The DNA Content of the Small Intestine as a Quantitative Measure of Damage and Recovery after Whole Body Irradiation

Abstract
(1) The total amount of deoxyribonucleic acid (DNA) in the small intestine was used as a measure of cell population in order to follow the course of radiation damage in mice and rats. Changes in total DNA-P were proportionately larger and intrinsically less variable than changes in fresh weight of the intestine. (2) In unirradiated control mice intestinal DNA-P concentration was constant but intestinal weight and total intestinal DNA-P were linearly dependent on body weight. (3) Single doses of whole body irradiation given to mice caused a fall in total intestinal DNA-P which began 12 hours later. Except after 25 000 r which had less effect than 5000 r, the larger the dose of radiation the greater the maximum depression in DNA-P and the later the time at which recovery began. The course of recovery was exponential after 1000 r but not after 750 r. (4) In both rats and mice β-mercaptoethylamine reduced the damaging effect of a dose of radiation but did not modify the course of recovery. (5) Chronic irradiation of mice at levels sufficient to reduce body weight slightly caused a loss in total intestinal DNA-P. The loss was probably, but not certainly, greater than that expected from the loss in body weight alone.