An ultrastructural study of lipoprotein accumulation in cardiac valves of the rabbit

Heart valves are composed chiefly of extracellular matrix surrounded by an endothelial cell monolayer and as a result are an excellent model of the intima. Heart valves from rabbits fed a high-cholesterol diet accumulate lipids within the matrix and over time develop fatty streaks similar to those seen in the aorta. In this study we demonstrate that the heart valves (atrioventricular and aortic) can be isolated and used as an in vitro preparation to control and follow low-density lipoprotein (LDL) uptake and deposition. Using thin-section and freeze-etch microscopy we found that LDL rapidly associates with collagen within the extracellular matrix. As it accumulates along the collagen fibers the LDL appears to undergo structural changes in size and surface topography. This association of LDL with collagen may be a key step in lipid aggregation in the intima.