Echographical Assessment of the Early Stage of Experimental Atherosclerosis of the Descending Aorta in Rabbits

To assess the early stage of atherosclerosis of the thoracic descending aorta, we evaluated morphological atheromatous lesions (atherosis) and the stiffness parameter of the artery (beta; sclerosis) in 24 male rabbits using echography. Male Japanese white rabbits weighing 2.5-3.0 kg were fed a diet containing 1% cholesterol for 7 (n = 8) or 14 weeks (n = 8). Rabbits fed a normal diet were used as controls (n = 8). Atheromatous lesions were evaluated with intravascular ultrasound (IVUS: Aloka, 20 MHz, 6F). We also calculated beta using M-mode echography (7.5 or 10 MHz) and direct aortic pressure measurement. Thickening of the intima-media complex was clearly observed with IVUS in the 14-week group but was not detected in the others. Histologically, only a thin layer of foamy cells on the intima (thickness < 20 microns) was observed in the 7-week group. The value of beta was significantly increased in both the 7-week (4.7 +/- 2.2) and 14-week groups (4.5 +/- 0.8) compared with controls (1.7 +/- 0.9, both p < 0.01). These results suggest that the development of atherosis might be preceded by vascular sclerosis during the early stage of atherosclerosis when the serum cholesterol level is high: at a time when the thin layer of foamy cells could not be detected by conventional IVUS.