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 stu died primarily with their pressure-diameter relationships. Male Japane se 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, t hen, their decending thoracic aortae were excised for the studies of p ressure-diameter relationships. Stiffness parameter (beta'') and incre mental elastic modulus (H-theta theta were used to quantitatively repr esent the structural stiffness of the aortic wall and the elastic modu lus of the wall material, respectively. Denudation of endothelial cell s thickened the aortic walls in Group C, but the induced no significan t changes in beta'' and H-theta theta. Shape of the pressure-diameter curve changed gradually with time in Group D, and beta'', H-theta thet a and thickness to wall radius ratio increased significantly, while th ose in group B showed no significant changes with a few exceptions. Av eraged 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 a t 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-va lues at 100 mm Hg than the others. Significantly increased calcificati on and intimal hyperplasia were observed in the walls with high beta'' - and H-theta theta-values.