A Radiation Effect from Low Doses of Tritiated Thymidine or X-Rays

When the number of millimoles of3 H-labeled thymidine administered to mice is kept constant, but the quantity of radioactivity is increased from 1 μCi/mouse to 10, 25, and 88 μCi/mouse, a radiation effect is produced in proliferative tissues (intestine and testis). The radiation effect causes acceleration of the removal of the long-term nonvolatile tissue activity which probably is mainly in DNA. Low exposures to x-rays (25 R), which are too low to cause significant levels of cell killing can produce a similar radiation effect. The radiation effect may be related to the repair of cellular sublethal damage.