Arterial remodeling following mechanical injury. The role and nature of smooth muscle cells.

The main feature of an atherosclerotic plaque is the formation of a new tissue in the arteries. In this respect atherosclerosis is similar to other conditions where non-neoplastic tissue formation occurs like in embryogenesis, in healing or in repair processes. A progressive intimal thickening occurs in the early phase of human atherosclerotic lesions and also in certain experimental models. Long-standing aortic intimal thickening could be induced by mechanical injury to the inner surface of the aorta with a microsurgical instrument, which causes controlled endothelial denudation. The injury is followed by an arterial remodeling. The latter process is caused by the development of an intimal plaque which consists of two main components: the smooth muscle cell (SMC) and the intercellular matrix. The matrix components are mostly synthetized by the SMC. Two distinct SMC populations could be distinguished by morphological means in the intimal proliferation: the synthetizing type and the proliferating type. Their role will be discussed and their morphological appearance will be compared with SMC present in other lesions.