Dynamic mechanical properties of atherosclerotic aorta A correlation between the cholesterol ester content and the viscoelastic properties of atherosclerotic aorta

Abstract

The effect of cholesterol and cholesterol ester content of aortas on the dynamic mechanical properties of these tissues was studied in rabbits during development of atherosclerosis. The disease was induced by feeding a 1.5% cholesterol diet for six weeks. At two week intervals, an equal number of control and experimental animals were sacrificed and their aortas were collected. After grading the aortas for lesions, one-half of each aorta was used for the determination of cholesterol and cholesterol ester content while the other half was used for the determination of viscoelastic properties. The viscoelastic properties were determined in both the longitudinal and the tangential direction of the aortas. The results showed that cholesterol feeding had no effect on the longitudinal dynamic Young's modulus of the aortas. On the other hand, the tangential dynamic Young's modulus of the aortas was found to be very much influenced by the cholesterol diet. After the first two weeks of cholesterol feeding, the tangential dynamic Young's modulus was found to be increased markedly with time. At the end of the 6-week period, the average value of the tangential Young's moduli was 4.0 × 10 6 dynes/cm 2 in the cholesterol-fed group while in the control group it remained 2.7 × 10 6 dynes/cm 2. This increase in the tangential Young's moduli showed a remarkable correlation with the increase in the cholesterol ester content of the aortas. The cholesterol ester content of aortas, like the tangential Young's modulus, remained unaffected during the first two weeks of cholesterol feeding. But after the first two weeks, a rapid increase in the cholesterol ester content was observed which coincided with an almost identical increase in the tangential Young's modulus values. It is concluded that during the early stages of atherosclerosis, the cholesterol ester content of aortas exerts a significant influence on the tangential dynamic Young's modulus of aortas. The serum levels of cholesterol and cholesterol ester, although increased steadily with the cholesterol feeding, did not show any direct correlation with the viscoelastic properties of the aortas.