Vein grafts for arterial repair: an experimental study of the histological development of the intima.

Vein grafts were studied in rats using the incompatible DA and Lewis inbred strains. Allografts were performed in the Lewis-to-DA and DA-to-Lewis combinations with Lewis-to-Lewis isografts serving as controls. A 5 mm segment of iliolumbar vein was placed into a defect in the iliac artery, using micro-surgical techniques. Histological studies of the grafts at 1 hour, 1, 2, 4, 10 and 18 weeks after insertion showed that there was no evidence of rejection in any of the allografts and the tissue changes which occurred were indistinguishable from those of isografts. At the time of grafting, the vein wall consisted of a thin layer of collagen (50 microns thick) with a fine elastic lamina and no endothelium. By 1 week, most of this tissue was necrotic. By 2 weeks an endothelial layer was present and the wall was made of connective tissue, which increased in density by 4 weeks. At 10 weeks, a thick new intima had formed which doubled in thickness by 18 weeks. Electron micrographs revealed that this 'regenerated' intima was composed of smooth muscle cells surrounded by dense collagen and elastin. Sclerotic plaques were evident in some 18 week grafts.