Endothelium modifies the altered metabolism of the injured aortic wall

Results of previous experiments in this laboratory indicate that lipids, especially cholesterol and cholesteryl ester, preferentially accumulate in re-endothelialized, as compared with de-endothelialized, areas of aorta (Am J Pathol 1980, 99:81-104). In the experiments reported here, the hypothesis that this lipid accumulation results from alterations in arterial wall metabolism induced by injury and modified by endothelium was tested. Activities of the two cholesterol-ester-metabolizing enzymes acyl CoA: cholesterol acyltransferase and acid cholesteryl esterase were assayed in uninjured aortas and in de-endothelialized and re-endothelialized areas of balloon-catheter-injured aortas from normocholesterolemic and hypercholesterolemic rabbits. Activities of marker enzymes for major cell organelles were also assayed. Our results indicate that acyl CoA: cholesterol acyltransferase activity was similarly increased in re-endothelialized and de-endothelialized areas of injured aortas. Activity of acid cholesteryl esterase was also increased; however, it was significantly less in re-endothelialized as compared with de-endothelialized areas. Activities of several marker enzymes were changed in injured aortas, particularly in de-endothelialized as compared with re-endothelialized areas. These findings suggest that 1) injury predisposes to general metabolic changes in the aorta that are modified by endothelium and 2) increased cholesteryl ester accumulation in re-endothelialized aortas occurs at least in part from increased synthesis and decreased hydrolysis.