Shear stress regulates smooth muscle proliferation and neointimal thickening in porous polytetrafluoroethylene grafts.

High shear stress appears to decrease wall thickening in diseased arteries and vascular grafts. To determine if increased shear stress diminishes smooth muscle (SMC) proliferation, we studied the effect of increased blood flow on neointimal thickening in porous polytetrafluoroethylene grafts implanted in baboons. An aorto-aortic 5-mm graft was placed in tandem with a pair of aorto-iliac 5-mm grafts, so that the proximal graft supplied all flow to both distal grafts. At 12 weeks, calculated luminal shear stress in proximal grafts was twice that in distal grafts (24 +/- 8 versus 11 +/- 5 dynes/cm2; p less than 0.05). All grafts were completely endothelialized. The neointimal cross-sectional area in proximal grafts was about half as large as in distal grafts (3.36 +/- 1.61 versus 5.93 +/- 0.61 mm2; p less than 0.05). Proximal grafts also had significantly less SMC proliferation (0.14 +/- 0.05% versus 0.24 +/- 0.10%; p less than 0.05) and SMC volume (6.1 +/- 4.0 versus 12.4 +/- 2.6 mm3/cm graft; p less than 0.01) when compared with distal grafts. We conclude that the elevation in shear stress in the proximal graft, which remained within the physiological range, inhibits SMC proliferation and neointimal thickening in these grafts.