Endothelial changes induced by arterial spasm.

Prolonged arterial constriction can cause damage to the artery itself. The purpose of this study was to define the intimal changes. Two muscular arteries of the rat were studied by electron microscopy 15 minutes to 7 days after L-norepinephrine had been dripped over the vessels. Endothelial damage was caused by the tight folding of the internal elastic lamina, which mechanically squeezed the cells. As the artery relaxed, the endothelium showed gaps, patches of thinned cytoplasm, and many adhesions between cells on opposite sides of intimal folds. The adhesions involved whole cells of cytoplasmic bridges stretched across the intimal "valleys." They were present up to one day; later they seemed to snap and disappear without causing further cellular damage. A survey of the literature shows that such adhesions can also develop in collapsed arteries postmortem. They explain the endothelial "bridges" previously described by others as a normal intimal structure.