PROLIFERATION STUDIES OF THE ENDOTHELIAL AND SMOOTH MUSCLE CELLS OF THE MOUSE MESENTERY AFTER IRRADIATION

Abstract

To investigate the effects of external .beta.-radiation on the proliferation of endothelial cells and smooth muscle cells in the mesenteric arterioles of mice, a continuous labeling technique was used. Labeled and non-labeled cells of either type were determined by autoradiographic techniques in control animals and at different times (3, 12 and 48 wk) after single doses of 20 and 45 Gy [gray] (2000 and 4500 rad). The fraction of cells labeled, even after 7 days of repeated injections, was very low in all instances. Very long turnover times for the 2 cell populations in control animals (> 2 yr for endothelium and > 3 yr for smooth muscle) existed. After 20 and 45 Gy, no significant increase in endothelial proliferation was seen except at 3 wk. No significant increase in labeling was observed in smooth muscle at any time after irradiation. These labeling data were compared with the pattern of cell depletion of the irradiated endothelium. The depletion apparently was much earlier than expected for a slowly proliferating tissue, if all the cells were cycling very slowly. Such an early depletion is consistent with cell death resulting from a small proportion of the cells having a short cell cycle. The recovery of the endothelial cell numbers between 9-12 mo. was not accompanied by a rise in the fraction of labeled cells. Repopulation may occur from outside the treated area.