The initial step in the development of atherosclerotic lesions is suggested to be the retention of low-density lipoprotein. This suggestion would seem to imply that some interval of time ought to intervene between the initial retention of interstitial lipid and subsequent influx of fatty streak cellular elements. Yet no evidence for such a waiting interval has been offered.
To describe findings from application to coronary arteries from forensic autopsy specimens of a new method for staining lipids in paraffin sections.
Isolated interstitial lipid (IIL) (extracellular lipid pools accompanied by no perceptible intracellular lipid or other fatty streak elements at the affected sites) was identified in various intimal compartments, and smooth muscle cell (SMC) numbers were counted at these sites.
Isolated interstitial lipid was a surprisingly frequent finding after age 35 years, seen in 87 (84%) of 104 cases. The number of SMCs per unit area of sectioned intima was high in specimens lacking IIL (15.5 SMCs/[100 microm]2), lowest at sites displaying IIL (8.3 SMCs/[100 microm]2), and intermediate at sites lacking IIL in specimens that do contain IIL at some other location (12.6 SMCs/[100 microm]2).
These findings plus other evidence support the proposal that retention of lipid most often happens, in aging arteries, at sites where the architecture was previously altered by diluting of constant SMC numbers by expanding collagenous matrix, thereby lowering SMC densities.