Spiraled collagen in the major blood vessels.

Vascular spiraled collagen (SC) was investigated by electron microscopic and immunohistochemical means in anatomically corresponding pairs of the major arteries and veins under normal or morbid condition in 45 autopsies. The frequency and extent of SC were marked in the veins, compared with the arteries. SC was particularly noted in the left anterior descending coronary artery beneath a myocardial bridge, which had been free from atherosclerosis, in contrast to those sites in the nonbridged vessel, which is always involved by atherosclerosis. SC was similarly conspicuous in the normal great saphenous vein, when compared with the phlebosclerotic vessel. The diameters of SC increased with the age of the patient. Immunohistochemical examination of matrix metalloproteinases (MMP-1, -2, and -3) revealed significant expression of MMP-1 in smooth muscle cells (SMCs) of vascular wall in which SCs was abundant, whereas tissue inhibitor of MMP-1 was absent in SMCs regardless of the presence of SC. Together with the frequent spatial association of SC with degraded elastic fibers and contractile-type SMCs, the present results indicate that whereas normal collagen fibrils are unilaterally degraded at extracellular spaces by interstitial enzymes and are possibly followed by their assembly to form SC, SMCs remain stationary in cell activities during aging. We conclude that SC is formed preferentially in the normal blood vessels through a physiologic degradation of normal collagen fibrils.