To analyze the potential mediator(s) involved in flow-induced endothelium-dependent vasodilation, we measured the wall tension of intraluminally perfused canine femoral artery segments and compared the content of 6-ketoprostaglandin F1 alpha (determined by radioimmunoassay) and the relaxing activity of the effluent (determined by bioassay on canine coronary artery rings). During perfusion at a steady flow of 2 ml/min the effluent contained 6-keto-prostaglandin F1 alpha and relaxed the bioassay rings. Sudden increase in steady flow rate to 4 ml/min, or the introduction of pulsatile flow, increased the release of 6-keto-prostaglandin F1 alpha and induced further relaxations of the bioassay ring. No relaxations were observed with the effluent passing through a femoral artery segment without endothelium. Indomethacin significantly depressed the release of 6-keto-prostaglandin F1 alpha during increases in flow but had no significant effect on the relaxing activity of the effluent. In the presence of indomethacin, increases in flow produced significant relaxation in the perfused femoral artery segments with endothelium. Superoxide dismutase restored the relaxing activity of the effluent during increases in flow at a transit time of 30 seconds. These data demonstrate that in addition to prostacyclin, flow triggers the release of another relaxing substance (or substances) from vascular endothelial cells that has characteristics similar to the endothelium-derived relaxing factor released by acetylcholine.

Experiments were designed to determine the effects of oxygen-derived free radicals on the production and biological activity of endothelium-derived relaxing factor or factors released by acetylcholine. Rings of canine coronary arteries without endothelium (bioassay rings) were superfused with solution passing through a canine femoral artery with endothelium. Superoxide dismutase caused maximal relaxation of the bioassay ring when infused upstream, but not downstream, of the femoral artery; this effect of superoxide dismutase was inhibited by catalase. Infusion of acetylcholine relaxed the bioassay rings because it released a labile relaxing factor (or factors) from the endothelium. When infused below the femoral artery, superoxide dismutase and, to a lesser extent, catalase augmented the relaxations to acetylcholine. Superoxide dismutase, but not catalase, doubled the half-life of the endothelium-derived relaxing factor(s). This protective effect of the enzyme was augmented fivefold by lowering the oxygen content of the perfusate from 95 to 10%. These data demonstrate that: superoxide anions inactivate the relaxing factor(s) released by acetylcholine from endothelial cells and hyperoxia favors the inactivation of endothelium-derived relaxing factor(s).

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Abstract-Most previous studies of atherosclerosis in hyperlipidemic mouse models have focused their investigations on lesions within the aorta or aortic sinus in young animals. None of these studies has demonstrated clinically significant advanced lesions. We previously mapped the distribution of lesions throughout the arterial tree of apolipoprotein E knockout (apoE Ϫ/Ϫ ) mice between the ages of 24 and 60 weeks. We found that the innominate artery, a small vessel connecting the aortic arch to the right subclavian and right carotid artery, exhibits a highly consistent rate of lesion progression and develops a narrowed vessel characterized by atrophic media and perivascular inflammation. The present study reports the characteristics of advanced lesions in the innominate artery of apoE Ϫ/Ϫ mice aged 42 to 60 weeks. In animals aged 42 to 54 weeks, there is a very high frequency of intraplaque hemorrhage and a fibrotic conversion of necrotic zones accompanied by loss of the fibrous cap. By 60 weeks of age, the lesions are characterized by the presence of collagen-rich fibrofatty nodules often flanked by lateral xanthomas. The processes underlying these changes in the innominate artery of older apoE Ϫ/Ϫ mice could well be a model for the critical processes leading to the breakdown and healing of the human atherosclerotic plaque. Key Words: atherosclerosis Ⅲ apoE knockout mice Ⅲ hemorrhage Ⅲ fibrosis G enetically modified hyperlipidemic mice have helped to delineate the processes regulating fatty streak formation. The fatty streak, a xanthoma formed in the intima of hyperlipidemic animals and often called the early atherosclerotic lesion, is composed of fat-filled macrophages focally situated in the arterial intima. 1 These mouse models have demonstrated that formation of the intimal xanthoma can be accelerated or retarded by a variety of different manipulations, including the following: alterations of apolipoprotein production and/or structure, changes in lipoprotein lipid composition, and additions or deletions of lipoprotein receptors. [2][3][4][5][6][7][8][9][10][11][12][13][14] Furthermore, transgenic and knockout mouse models, which interfere with monocyte adherence and chemotaxis [15][16][17][18][19][20] or macrophage differentiation and foam cell development, [21][22][23] in most cases inhibit formation of these xanthomata, whereas models that increase macrophage involvement stimulate the formation of xanthomata. 4 See page 2503In spite of this success in modeling early lesion formation, there has been limited use of these mice in modeling the progression of lesions to more complex advanced stages, as occur in humans. Murine lesions that are usually described as "advanced" typically contain an imperfectly formed fibrous cap overlying a central fatty mass that has undergone extensive necrosis. Even in the rare cases in which mouse lesions have progressed to occlusion, the morphology suggests obstruction of the lumen by formation of a very large xanthoma, 24 a pattern rarely seen in humans. 1 Thus, whereas mous...