Time-dependent effects of endotoxin on the ultrastructure of aortic endothelium

The aortic endothelium from control and Escherichia coli (E. coli) endotoxin-treated rats and rabbits was examined by transmission and scanning electron microscopy. Following the intravenous injection of endotoxin, the animals were sacrificed at intervals ranging from 1 min to 4 hr. As early as 1 min after endotoxin, there was a widening of the subendothelial space (SES) and an increase in tortuosity of the internal elastic lamina (IEL). At 5 min, the tortuosity of the IEL increased to a peak value, and the SES showed an increase in the amount of smooth muscle cells (SMC). Initial endothelial damage occurred 5 min after endotoxin: SEM showed some spindle-shaped endothelial cells starting to peel from the underlying SES, and TEM showed some endothelial cells protruding or arching into the lumen. The new findings in this study are that endotoxin injection a) has a very rapid (less than 15 min) effect on rat and rabbit aortic endothelium, including localized endothelial injuries in the intima, and b) induces ultrastructural alterations also in the SES, IEL and portions of the tunica media. These effects were largely reversed within 1 hr after endotoxin administration, thus indicating that the endothelium and other components of the arterial wall can recover with great speeds.