The initiation of intimal thickening in human arteries

To obtain more detailed information about the relationship of intimal thickening to defects in the elastin structure of the arterial wall, the internal elastic lamina and subsequent elastin formation in the intima was studied by very oblique sectioning of paraffin sections of the arterial wall, and by scanning electron microscopy of formic acid digested preparations. Comparison was made in the same subject between the internal thoracic artery (a vessel showing only slight intimal thickening) and the anterior descending coronary (which usually develops advanced intimal thickening). There was no evidence of penetration of the normal fenestrations of the internal elastic lamina by medial smooth muscle cells. This took place through major defects of this lamina and resulted in a change from transverse to longitudinal orientation of these cells and the accompanying elastin fibers of the intima. A further condensation of elastin (greater for the internal thoracic) occurred in the intima subjacent to the endothelial cells.