An ultrastructural study of endotoxin induced damage in rabbit mesenteric arteries.

Mesenteric arteries from control and endotoxin-treated rabbits were studied by electron microscopy. Animals were injected intracardially with an LD dose of endotoxin or saline 3 and 24 hr before being killed. Vessels were perfused with buffered glutaraldehyde before removal. In control arteries endothelial cells were thin except in the nuclear region. Vesicles and caveolae were abundant in the cytoplasm. Few mitochondria, scanty endoplasmic reticulum and Golgi apparatus, free ribosomes, and glycogen granules were scattered in the cytoplasm. The endothelial cells rested on a basement membrane which was closely apposed to the internal elastic lamina. The medial smooth muscle layer contained many collagen fibres. Endothelial cells from endotoxin-treated animals revealed extensive degeneration of subcellular organelles with only the vesicles and caveolae remaining intact. Ruptured mitochondria, areas of cytolysis and large vacuoles were prominent. The nucleus was often spindle shaped or tortuous in outline and sometimes exhibited vacuolization. Swelling and protrusion of endothelial cells into the lumen, the detachment of these cells from the internal elastic lamina, and the marked thickening of the internal elastic lamina were also prominent. Vascular endothelium reacts to histamine, serotonin, epinephrine and norepinephrine in a similar manner, suggesting that the effects observed after the administration of endotoxin may be due to the release of such chemical mediators. This study cannot differentiate between direct and indirect damage; however, it shows that bacterial endotoxin induces severe damage to continuous endothelium and internal elastic lamina.