Hypertrophy of cultured bovine aortic endothelium following irradiation.

The vascular endothelium is a vital multifunctional tissue which covers the entire luminal surface of the circulatory system. Loss of continuity of the endothelial lining normally results in cell migration and proliferation to make up for cell loss and to ensure that exposure of the thrombogenic subendothelium to platelets and clotting factors is minimized. We showed that ionizing radiation (400-3000 cGy) causes dose-dependent cell loss from confluent monolayer cultures of bovine aortic endothelium, which cannot immediately be compensated by cell proliferation. Within 24 h, the remaining attached cells undergo substantial somatic hypertrophy (evidenced by increased protein content, cell volume, and attachment area) but remain diploid. If cell loss is not excessive, monolayer continuity is restored within several days. Although reduced protein degradation may contribute, most of the protein accumulation is due to synthesis of new protein. Unlike endothelium, irradiation of smooth muscle cultures causes neither cell loss nor increased protein synthesis. Hypertrophy of irradiated endothelial cells appears to be a consequence of a proliferative stimulus (cell loss) in a population of cells which is unable to divide. It can be modulated by replating irradiated cells at different densities. We suggest that endothelial hypertrophy is an early vascular homeostatic response before clonal proliferation of surviving cells or repopulation by cells from outside of the irradiated field can compensate for cell loss.