Experimental arterial loops and arterial atrophy.

U-shaped arterial loops fashioned in the common carotid artery of rabbits and sheep were studied to determine the chronic effects of the altered blood flow, and results were consistent. Intimal thickening, predominantly of musculoelastic proliferation, was present at the distal aspect of the lesser curvatures of the bends where boundary layer separation might be expected. Lipid was found in the intimal thickening of the four sheep with U-loops. Along the greater curvature of the three bends where blood flow impinges there was considerable fragmentation of the internal elastic lamina with very little intimal thickening. In loops of longer duration considerable atrophy of the media was also observed and in a few specimens there was loss of medial elastica and muscle with slight dilatation. Thus both proliferative and atrophic (nonproliferative) lesions can be induced in the same vessels at anatomical sites similar to those occurring in the carotid siphon in man.