Cytokinetics of Regeneration in β-Irradiated Guinea-Pig Epidermis

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Abstract
Depopulation and repopulation of epidermal cells in guinea-pig skin after .beta. irradiation from a 90Sr-90Y sealed source was studied. Immediately after clipping, 1 site on each flank was locally irradiated with 1000, 2200, 3000 or 5000 rad (6 sites/animal). The changes in number of basal cells, labeling index (LI) and the appearance of clusters of 3H-thymidine-labeled basal cells (2 or more pulse-labeled cells in direct contact) were observed. Maximum cell loss of recognizable basal cells of 20% on day 8, 60% on day 12 and 75% on day 15 occurred after irradiation with 1000, 2200 and 3000 rad, respectively. The data for 5000 rad was similar to that in 3000 rad-irradiated epidermis. Repopulation (as evidenced by increase in LI and clusters of labeled cells) at all doses began on about the day of maximal cell loss. Regeneration occurred from survivors within the irradiated area after 1000 and 2200 rad and was completed in 5 days (i.e., on days 13 and 17, respectively). Reepithelization from the radiation margins occurred after 3000 and 5000 rad .beta. irradiation beginning on about day 15 and was completed in about 7 days. Labeled cells in clusters were rarely seen in nonirradiated epidermis. In irradiated tissue clusters paralleled the rise in LI and reached peaks at about the time of maximal cell loss and then returned to control level at days 23 and 27 after 1000 and 2200 rad. They remained somewhat above the control level to the 33rd day after 3000 rad (3 clusters/mm). There was no hyperplasia after 1000 rad, but a long-lived hyperplastic epidermis resulted after higher doses.

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