EPIDERMAL MORPHOLOGY, CELL-PROLIFERATION AND REPOPULATION IN MOUSE SKIN DURING DAILY FRACTIONATED-IRRADIATION

In mouse, a 2 cm long field of both legs was irradiated daily with 3 G y,five fractions per week for up to 3 weeks. Epidermal morphology, the circadian variation of the labelling index, and repopulation were det ermined at the end of each week. After a decrease of epidermal cellula rity in the first week, excessive regeneration led to hyperplasia and hypertrophy, which continued throughout the experimental period while the residual tolerance of the epidermis to top-up irradiation decrease d progressively. Although the repopulation rate was accelerated five-f old, it was unable to compensate the effects of more than two-thirds o f the given dose. The hypertrophic and hyperplastic response is attrib uted to pronounced acceleration of abortive proliferation of doomed st em cells.