AN ULTRASTRUCTURAL-STUDY OF LIPOPROTEIN ACCUMULATION IN CARDIAC VALVES OF THE RABBIT

Heart valves are composed chiefly of extracellular matrix surrounded b y 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 streak s similar to those seen in the aorta. In this study we demonstrate tha t the heart valves (atrioventricular and aortic) can be isolated and u sed as an in vitro preparation to control and follow low-density lipop rotein (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 topo graphy. This association of LDL with collagen may be a key step in lip id aggregation in the intima.