Regression of intimal hyperplasia with restoration of endothelium- dependent relaxing factor-mediated relaxation in experimental vein grafts

Background. The reversibility of the morphologic and functional alterations that occur in veins transplanted into the arterial circulation was examined in this study. Methods. Common carotid vein bypass grafts (VG) were performed in 20 male New Zealand White rabbits. Ten VG and jugular veins (CV) were harvested after 14 days, and ten VG were reimplanted as venovenous bypass grafts (REV) and harvested after an additional 14 days. Vessels were taken for structural or isometric tension studies to norepinephrine, serotonin, and bradykinin and to acetylcholine and sodium nitroprusside after precontraction. Results. There was a decrease in the thickness of the intima (p = 0.02) and the media (p = 0.002) in REV compared with VG. In REV, sensitivity to norepinephrine decreased (p = 0.0007) with a reduced maximal tension to norepinephrine (p = 0.02) and to serotonin (p = 0.0001). Bradykinin sensitivity increased in REV (p = 0.003 vs VG) and was greater than in CV. Only the precontracted CV and REV relaxed to acetylcholine. All tissues relaxed to sodium nitroprusside. Conclusions. This study suggests that intimal hyperplasia can be reversed with restoration of endothelium- dependent relaxing factor-mediated relaxation but that only a partial regression of the contractile abnormalities can be achieved.