The effect of endotoxin shock on the aortic endothelium of young rats

Aortic endothelium of normal and endotoxin treated rats (endotoxin shock) was investigated in "Häutchen" preparations by light microscopy, autoradiography, and DNA cytophotometry. In the edothelium of control animals two cell populations were found: 1. endothelial cells which were subdivided into four groups according to their different nuclear morphology and DNA contents, 2. monocytoid cells which were taken for monocytes. In the endothelium of treated animals distinct damages of endothelial cells occurred during the period of 7 hours and 2 days after endotoxin application. Small groups of leukocytes were found in the surroundings of the damaged cells. A great number of monocytoid cells was found in the endothelial layer between the second and third day after endotoxin treatment. The monocytoid cells increased the total number of cells/mm2 on the aortic surface by one third. At the same time the maximum of DNA-synthesis of endothelial cells and monocytoid cells was reached (31-fold compared with controls). This cell proliferation is attributed to the following mechanisms: 1. repair process at sites of cell injury, 2. mitogenic effect of endotoxin. In the period between the 13th and 23rd day after endotoxin treatment all changes in the aortic endothelium returned to normal.