Vein to artery grafts. An experimental study of reinnervation of the graft wall

Iliolumbar vein to iliac artery grafts were placed in 21 rats by microsurgical techniques. Graft innervation was examined at five time intervals between 1 and 32 weeks after surgery. Nerve fibers were demonstrated microscopically by formaldehyde-induced fluorescence of catecholamines. The morphology and degree of graft innervation were assessed, semiquantitatively, relative to the contralateral iliac artery (control) within each animal. Nerves were seen in the graft region as early as 2 weeks, but it was not until 4 weeks that they were present along its length (5 mm). The formation of a nerve plexus in the adventitia surrounding the graft was evident at 8 weeks. By 16 weeks the degree of innervation in the graft had increased to a level that was greater than the control iliac artery in three of four animals examined. Grafts at 32 weeks were also hyperinnervated. However, the morphology of this innervation was different from the control arteries; nerve fibers were finer, not varicosed, and were located at a greater distance from the outer layer of smooth muscle cells. The origin of the nerves appeared to be collateral sprouts from nerves supplying the adjacent iliac vein and also from invading vasa vasorum. The host iliac artery nerve plexus did not contribute to graft innervation.