The early and late responses of the arterial wall to graft placement

The relationship between the early smooth muscle cell proliferative response (SMC-PR) to injury and the later development of myointimal hyperplasia (MIH) complicating arterial bypass grafts remains unclear. In the present study, the early SMC-PR and the later MIH induced by a 2-mm-diameter PTFE graft placed in a rabbit carotid were compared with the response induced by an autogenous artery (AA) graft in the contralateral carotid. The early SMC-PR was measured in the proximal and distal arterial segments 5 days after graft placement by in vivo labeling with [3H]thymidine to determine the DNA specific activity (DNA-SA). The later anastomotic MIH was measured 16 and 32 weeks postgrafting by calculating the intimal/medial ratio. There was a marked and similar increase in the early SMC-PR noted with both the AA and the polytetrafluoroethylene (PTFE) grafts. The distal segments demonstrated a significantly higher DNA-SA when compared to the proximal in both AA- and PTFE-grafted arteries. There was a moderate degree of anastomotic MIH noted in chronic grafts; however, a regression in intimal thickening was observed over time in the AA-grafted arteries, while the distal anastomosis of the PTFE-grafted vessels demonstrated a continuous progression of the MIH process. The early SMC-PR may abate in arteries grafted with autogenous grafts, but there is a persistent proliferative response at the distal anastomosis associated with synthetic grafts.