Subendothelial layer of pseudointima of polytetrafluoroethylene graft is formed by transformation of fibroblasts migrated from extravascular space

Abstract

A well organised pseudointima is formed in polytetrafluoroethylene (PTFE) grafts within 4 weeks after implantation into inferior vena cava (IVC) of rabbits. To investigate the process of the subendothelial organisation of pseudointima, an animal experiment was conducted. The outer wall of PTFE graft (30 microns fibril length, 3 mm inner diameter, 3 cm long) was coated with 10 um silicon film in the following ways to prevent cellular ingrowth from the extravascular space: non-coating; full-length coating; half-length coating; and full-length coating excluding 5 mm midportion. These grafts were implanted into rabbit IVC and were harvested 4 weeks later. All the grafts were patent but the lumen of the non-coated area was narrowed by pseudointimal hyperplasia. The degree of the hyperplasia estimated by dried tissue deposit was inversely proportional to the length of the coating. The coverage of the luminal surface with endothelial-like cells was noted at anastomotic areas and also at the surface corresponding to the non-coated area. Light microscopy and immunostaining studies on the non-coated midportion revealed the presence of fibroblasts in the interstices of PTFE and smooth muscle cells and myofibroblasts in the pseudointima. Transmission electron microscopy confirmed the presence of myofibroblasts in the midportion of the non-coated area. No transmural capillary ingrowth was observed in the midportion by histological and immunohistochemical analysis. These observations suggest that the subendothelial layer of pseudointima in PTFE grafts is formed by proliferation and transformation of fibroblasts migrating from the extravascular space and that endothelial-like cells may also be derived from such transformation.