Alterations in wall tension and shear stress modulate tyrosine kinase signaling and wall remodeling in experimental vein grafts

Purpose: Hemodynamic alterations have been implicated as major stimuli for the development of intimal hyperplasia in vein grafts that are implanted in the arterial circulation. Tyrosine kinase is known to mediate cell signaling. However, its role with in vivo mechanotransduction is not yet well defined. We used a novel bioprosthetic collagen tube to provide an external support: to vein grafts and examined the subsequent changes in hemodynamics, tyrosine kinase signaling, wall remodeling, and vasomotor function. Methods: Carotid interposition bypass grafting was performed with the reversed jugular vein in New Zealand white rabbits. In the experimental group (n = 15), after the completion of the proximal anastomosis, the vein was passed through a 4-mm collagen tubs and the distal anastomosis was performed. The tube support was fashioned to completely co,er die vein grafts. The control animals (n = 14) had no tube support, After surgery; the blood pressure and flow rate were measured and the wall tension and shear stress were calculated in the vein grafts on day 3 or day 28 (n = 5 per group). Tyrosine phosphorylation was assessed with the Western blot test in vein grafts at day 3 (n = 4 per group). The intimal and medial dimensions of the vein grafts were assessed with videomorphometry on day 28 (n = 5 per group). The cumulative dose response curves of the vein grafts to contractile and relaxant agonists were determined in isometric tension studies on day 28 (n = 5 per group). Results: The use of tube support reduced wall tension 1.7-fold (P < .01) and increased shear stress 4.8-fold (P < .001) without altering the flow rate or blood pressure. The tyrosine kinase activity was reduced 15-fold(P<.001) in the tube-supported vein grafts. The intimal thickness was reduced by 45% in the tube-supported vein grafts as compared with the control grafts (46 +/- 2 mu m vs 84 +/- 5 mu m, respectively; P<.0001), and the media thickness was reduced by 20% (63 +/- 8 mu m vs 79 +/- 4 mu m, respectively; P < .05). Isometric tension studies showed preservation of contractile function and modulation of endothelial-dependent dysfunctional relaxation in tube-supported vein grafts. Conclusion: These results show that reduced n all tension and increased shear stress with an external tube support can effectively modulate the signaling, functional, and hyperplastic responses in vein grafts. We conclude that this simple strategy deserves further study and clinical consideration.