Changes in the DNA labelling index after beta irradiation of the mouse epidermis.

This study looked at the changes in the interfollicular DNA labelling index (LI) with time after strontium-90/yttrium-90 beta irradiation of approximately 100 mm2 of mouse flank skin, after a dose of 100 Gy which produces transitory moist desquamation. Within 24 hr of such a dose the LI of the irradiated area was essentially zero (0.07 +/- 0.03%), whilst those of the side area and of the control area were 15.0 +/- 2.6% and 21.4 +/- 2.7%, respectively. The LI of the side and the control areas then fell within 3-5 days to approximately 4% and approximately 2% respectively, whilst that of the irradiated area rose rapidly to a peak value of 30.2 +/- 1.7% at 10 days post-irradiation. There was a 20% reduction in the diameter of the area with detectable radiation damage within 5 days, and this is primarily due to cell proliferation and migration from the unirradiated margins of the field. In contrast, between days 10 and 20 the major source of repopulation is probably derived from local migration and proliferation of surviving hair follicle basal cells within the irradiated field.