ABSTRACT
In this study, we used a new computerized analytical method for the measurement of the endothelial function in sequential ultrasound images and compared it with histological studies, using the abdominal aorta in normal and atherosclerotic rabbits. Six rabbits received a standard rabbit chow as the normal group and the other 6 rabbits were fed a high cholesterol diet for four weeks as the atherosclerotic group. B-mode images of the abdominal aorta with 46 frames per second were saved over three cardiac cycles at baseline and during acetylcholine or nitroglycerin drug infusion in the normal and atherosclerotic rabbits. In order to evaluate endothelial-dependent relaxation, acetylcholine-mediated dilation [AMD] was measured during the infusion of acetylcholine at a rate of 0.5 microg/kg/min and endothelial-independent relaxation was evaluated by measuring nitroglycerine-mediated dilation [NMD] during the infusion of nitroglycerin at a rate of 5 microg/kg/min. In addition, the ultrasonic evaluation was confirmed by histopathological evaluation of the abdominal aorta. Significant differences in AMD were detected between the normal and the four-week cholesterol-fed rabbits [p value < 0.05], whereas there were no significant differences in NMD between the two groups [p value > 0.05]. No microscopic intimal lesions were seen in the normal rabbits, but intimal thickening was observed in the histological studies in the four week cholesterol-fed rabbits. Additionally, the total cholesterol, triglycerides, low-density lipoprotein cholesterol, and high density lipoprotein cholesterol levels were remarkably increased in the sera of the four-week cholesterol-fed rabbits [p value < 0.05]. A new automatic method can help accurately evaluate the endothelial function in normal and hypercholesterolemic rabbits.
ABSTRACT
A precise understanding of the mechanism of human neointimal stenoses and atherosclerotic fibrous plaques, which give rise to thromboses in vital arteries, requires a suitable animal model that would mimic the same characteristics well. We developed a rabbit model of neointimal stenosis and fibrotic plaque rupture in the carotid artery to visualize the lesion progress and to characterize the lesion types according to the American Heart Association classification. Twenty-eight healthy male New Zealand white rabbits were randomly divided into two groups: The rabbits in group A [n = 14] consumed a standard chow diet, and those in group B [n = 14] were injured via perivascular cold injury using liquid nitrogen at the right common carotid artery before being fed a high cholesterol diet [1.5%] for eight weeks. Plasma lipid evaluation was performed before the sacrificing of the rabbits. At the end of every week, at least 1 rabbit from group B was sacrificed for an analysis of lesion histopathology and calculation of the area ratios of the intima to media. The plasma lipid level in group B was significantly higher than that in group A [p value < 0.05]. The histopathological results revealed atherosclerosis characteristics such as endothelial layer destruction, fatty streaks and lipid-containing macrophages [foam cells] formation in the intima and media layers, extracellular lipid collections, smooth muscle cells proliferation and migration, neointima formation, intima thickening and deformation, fibrotic plaque formation, and finally plaque rupture. Statistical analysis revealed a significant increase in the intima-to-media ratio at the end of the eighth week [6.41 +/- 0.27, p value < 0.05]. We successfully developed a rabbit model of neointimal stenosis and atherosclerotic fibrous connective tissue plaque rupture, which is not only quickly and easily reproducible and inexpensive but also without mortality. The merits of our model render the evaluation of neointimal stenoses and fibrotic plaques and their treatment strategies more feasible in humans