HUMAN SAPHENOUS-VEIN GRAFTS EXPLANTED FROM THE ARTERIAL CIRCULATION DEMONSTRATE ALTERED SMOOTH-MUSCLE AND ENDOTHELIAL RESPONSES

Purpose: Animal models have been used to assess the function of vascul ar smooth muscle and endothelium of veins grafted into arterial circul ation. The primary model consists of grafting the external jugular vei n into the carotid artery of the rabbit. These studies suggest a selec tive increase in the responsiveness of the grafted veins to serotonin. However, in both human cardiac and peripheral vascular operations, th e saphenous, not the jugular, is the vein most frequently used. Thus t he propriety of the rabbit model is unknown. Methods: Human saphenous veins and vein grafts were obtained from patients undergoing leg vein bypass graft revisions (n = 8). The reversed vein grafts were placed i nto arterial circulation for periods ranging from 4 to 26 months befor e removal (mean 16 months). All vessels were immediately cut into ring s and suspended in organ chambers for recording isometric contractions to norepinephrine and serotonin. Results: The maximal contractions el icited by both norepinephrine and serotonin were reduced in human vein grafts in comparison to the results in human saphenous vein (maximal response to norepinephrine 1.42 +/- 0.34 gm [vein graft] vs 4.59 +/- 1 .13 gm [saphenous vein],p = 0.031; maximal response to serotonin 2.68 +/- 0.58 gm [vein graft] vs 4.72 +/- 1.11 gm [saphenous vein], p = 0.0 42). Human vein grafts were less responsive to norepinephrine than was saphenous vein (negative log of concentration that caused 50% of the maximal response -5.91 +/- 0.10 and -6.84 +/- 0.22, respectively; p < 0.009). After precontraction with norepinephrine (to 30% of the maxima l response), saphenous vein, but not vein grafts, demonstrated endothe lium-dependent relaxation to acetylcholine (maximum relaxation 27.4% /- 6.8%; p = 0.001). Conclusion: Human saphenous veins grafted into ar terial circulation exhibit loss of endothelium-dependent relaxation to acetylcholine and diminished contractions to agonists (norepinephrine and serotonin). In contrast to rabbit data, serotonin elicits dose-de pendent contractions in both human saphenous vein and human vein graft s. Since the vascular wall contractility varies widely across species, the relevance of rabbit vein graft data to human bypass grafts is unc ertain.