Changes in the cell kinetics of pig epidermis after single doses of X rays

Changes in the cell kinetics of pig epidermis have been investigated after irradiation with single doses of 15 Gy and 20 Gy of X rays. The epidermis exhibited an initial degenerative phase when the rate of cell depletion was independent of radiation dose. Changes consistent with repopulation were evident between the 14th and 18th day after irradiation. The severity of cell depletion and the rate of recovery of the epidermis were dose dependent. The regenerative phase was characterized by an increased cell proliferation; values for the labelling index (LI) were greater than those in the non-irradiated epidermis, from 14 days after 15 Gy and from 18 days after 20 Gy. The LI was still elevated at the end of the observation period, i.e. Day 56. No change in the time for DNA synthesis was found. Eighteen days after 15 Gy and 22 days after 20 Gy, islands of cells (colonies), with an appearance similar to the cells in the normal epidermis, were seen. The minimum turnover time (TT) for the proliferating cells of the basal layer of the epidermis in radiation-damaged skin was 61-68 h as compared with 125 h in unirradiated skin. For the basal cells in the colonies, TT was 16-22 h.