Induction of aneurysms in the rat by a stenosing cotton ligature around the inter-renal aorta.

Aortic aneurysms have been induced in the rat by combining the chemotactic property of cotton for inflammatory cells and the resulting granuloma formation with the mechanical and haemodynamic stress of aortic coarctation. A stenosing cotton ligature was placed around the aorta, between the renal arteries, in male Wistar rats under standardized conditions. Three months later, 7 out of 12 rats (58%) had developed saccular aneurysms of the inter-renal aorta. The aneurysmal wall consisted of a collagenous shell with a few newly formed elastic fibrils on its luminal side. Detailed histological studies of the inter-renal aorta at different times after placing stenosing or non-stenosing cotton or nylon ligatures between the renal arteries, together with studies using anti-hypertensive therapy (cilazapril) and immunohistochemical studies using an anti-macrophage antibody (ED1) were performed to try to establish cellular events involved in this aneurysmal remodelling. We conclude that in this model aneurysm formation requires (i) deep mechanical injury to the aortic wall, (ii) the presence of hypertension upstream to the stenosis and (iii) an inflammatory response to the cotton ligature. The early inflammatory reaction was less in the case of nylon and although macrophages were present in both cases the most striking difference was the greater incidence of PMNs in the case of cotton.