Comparison of response to injury in organ culture of human saphenous vein and internal mammary artery.

Autologous saphenous vein grafts, unlike internal mammary artery grafts, suffer many late occlusions as a result of excessive proliferation of vascular smooth muscle cells and the superimposition of atheroma on the resulting thickened intima. We investigated the possible basis of this difference using organ cultures. Internal mammary artery segments and freshly isolated and surgically prepared saphenous vein segments were obtained from patients undergoing coronary artery bypass grafting. Internal mammary artery and freshly isolated vein segments showed a high degree of endothelial coverage and medial cell viability that were maintained during culture. Surgically prepared veins showed partial endothelial denudation and medial cell injury, both of which tended to be reversed during culture. Neointimal thickening was greater in surgically prepared vein (72 +/- 13 microns; n = 11) than in freshly isolated vein (44 +/- 8 microns; n = 10) or internal mammary artery (34 +/- 4 microns; n = 13) segments. The occurrence of proliferating cells in the medial layer was also significantly greater in surgically prepared vein (2.8 +/- 1.0/mm; n = 11) than in freshly isolated vein (0.8 +/- 0.3/mm; n = 9) or internal mammary artery (0.6 +/- 0.3/mm; n = 10) segments. The data show that although the smooth muscle proliferation was similar in undamaged saphenous vein and internal mammary artery, it was significantly greater in damaged vein. This implies that the greater intimal proliferation seen in saphenous vein grafts may arise not from intrinsic differences in arterial and venous smooth muscle cells but from a greater susceptibility to injury.