Role of endothelium in sequestration of lipoprotein and firbrinogen in aortic lesions, thrombi, and graft pseudo-intimas.

In the soft, gelatinous thickenings that appear to be the precursors of fibrous plaques, concentrations of plasma low-density lipoproteins (LP) and fibrinogen were three to four times higher than that in normal intima, but their concentrations of fibrin was not significantly higher. By contrast, in 60% of cholesterol-rich areas from more advanced plaques, fibrin (mean concentration 22.7 mg/100 mg lipid-extracted dry weight) was ten times higher than normal, and this was associated with a twelve-fold increase in a bound LP fraction that was released by incubation with fibrinolytic enzymes. The origin of this fibrin is uncertain, and to test similarity of fibrin in the lesion with that of mural thrombus free and bound LP, fibrinogen, and cholesterol were measured in thrombi and pseudo-intimas from prosthesis grafts. In the pseudo-intimas and the thrombi that were not covered with endothelium the concentrations of all these substances were very low, but in thrombi covered with endothelium the concentrations of free and bound LP were similar to those in intimal lesions. Thus, endothelialisation appears to promote accumulation of LP in mural thrombi.