RADIATION RESPONSE OF MOUSE LIP MUCOSAL EPITHELIUM - A CELL KINETIC-STUDY

Changes in the cell proliferation kinetics of the epithelium of mouse lip mucosa have been assessed after local irradiation with a single do se of 18Gy of Co-60 gamma-rays. By the fifth day after irradiation, tw o distinct sub-populations of epithelial cells could be discerned. The larger of the two populations consisted of cells exhibiting varying d egrees of radiation-induced damage, and the smaller population was com posed of cells of normal size and appearance, intermingled between the radiation-damaged cells. There was a progressive decline in the epith elial cell density with time after irradiation, and focal denudation w as seen after 11 days. Cell colonies were evident in the remnants of t he epithelium by day 7. Degenerate cells could be identified in the ba sal layer of the mucosal epithelium, both before and after irradiation . The proportion of degenerate cells was increased 5 days after irradi ation with the maximum number, approximately 3.6% being counted on day s 7 and 8. In the first 2 days after irradiation, there was a reductio n in the labelling index (LI) of basal cells in the epithelium. This w as followed by recovery to control values on day 3. The LIs of both th e radiation-damaged cells and those with a normal appearance remained relatively constant between days 5 and 11, at approximately 10 and app roximately 60%, respectively. The LI of basal cells in the cell coloni es was very high (approximately 70%). The estimated turnover time (T(T )) for the basal cell population with a normal appearance and for thos e in cell colonies (groups of normal cells with a cord length greater- than-or-equal-to 10 cells), was extremely short < 1 day. There was som e fluctuation in T(T) values for basal cells exhibiting radiation-indu ced damage, with the shortest value (approximately 3 days) at 7 and 8 days after irradiation. It was concluded from the cell kinetic data th at repopulation of the lip mucosal epithelium started between 3 and 5 days after irradiation and the overall reponse of the mucosa to irradi ation was consistent with that predicted by a hierarchical model of ce ll proliferative organization.