Changes in collagen fibril morphology in experimental aneurysms and arteriovenous fistulae in sheep.

To investigate the effect of haemodynamic stress on collagen fibril morphology, the ultrastructure of intimal and adventitial collagen in the walls of experimental saccular aneurysms and in the veins of arteriovenous fistulae in sheep was compared with that of adventitial collagen from control veins. Ultrastructurally the collagen fibril is usually described as having a regular round profile in cross-section and a diameter dependent on collagen function and location in the blood vessel wall. The collagen fibrils in the intimal proliferation from both experimental models showed increased variation in shape and size when compared with adventitial collagen. These abnormally shaped collagen fibrils resemble those seen in inherited connective tissue disorders and in blood vessels from aged animals, suggesting that the collagen changes can be acquired and can be produced experimentally in blood vessels subjected to augmented haemodynamic stress.