Aortic walls in atherosclerotic rabbits--mechanical study.

Mechanical properties of the descending thoracic aortae harvested from endothelial cell-denuded and/or cholesterol diet-fed rabbits were studied primarily with their pressure-diameter relationships. Male Japanese white rabbits having 3.1 to 3.5 kg initial body weight were divided into 4 groups. The rabbits in Groups A and C were fed a regular chow, while those in Groups B and D were given 1 percent cholesterol diet; the luminal surfaces of the descending thoracic aortae in the rabbits of Groups C and D were injured by drawing catheter-tip balloons. These animals were sacrificed after keeping for 4, 8, 16 or 32 weeks and, then, their descending thoracic aortae were excised for the studies of pressure-diameter relationships. Stiffness parameter (beta") and incremental elastic modulus (H theta theta were used to quantitatively represent the structural stiffness of the aortic wall and the elastic modulus of the wall material, respectively. Denudation of endothelial cells thickened the aortic walls in Group C, but induced no significant changes in beta" and H theta theta. Shape of the pressure-diameter curve changed gradually with time in Group D, and beta", H theta theta, and thickness to wall radius ratio increased significantly, while those in Group B showed no significant changes with a few exceptions. Averaged percent fraction of the luminal surface area stained with Sudan IV (As) was around 50 percent in Group B and 100 percent in Group D at 32 weeks. Even if As is over 80 percent in Group D, 50 percent (7/14) of the walls gave significantly higher beta"- and H theta theta-values at 100 mm Hg than the others. Significantly increased calcification and intimal hyperplasia were observed in the walls with high beta"- and H theta theta-values.