Vasoreactivity of 11 coronary artery vein bypass grafts and 13 human saphenous veins was examined. Isometric tension studies were performed in response to potassium chloride (110 mmol/l), noradrenaline (10-9-10-4 mol/l), serotonin (10-9-10-4 mol/l) and histamine (10-8-10-2 mol/l). After precontraction with noradrenaline (10-5 mol/l), the response to acetylcholine (10-8-10-4 mol/l) and the calcium ionophore A23187 (10-8-10-4 mol/l) was also assessed. Results are given as mean (s.e.m.). Compared with saphenous veins, vein grafts showed decreased sensitivity to noradrenaline (1.7 (0.5) versus 0.4 (0.1 μmol/l, P=0.01), no change in sensitivity to serotonin (55 (18) versus 37 (15) μmol/l, P>0.05) and supersensitivity to histamine (3.2 (0.9) versus 30.1 (13.2) μmol/l, P=0.01). Vein grafts had a decreased maximal contraction to potassium chloride (1.1 (0.3) versus 5.5 (0.8) g, P=0.0001), noradrenaline (1.2 (0.3) versus 4.1 (0.8) g, P=0.005), histamine (1.2 (0.3) versus 4.5 (0.8) g, P= 0.003) and serotonin (0.7 (0.2) versus 5.7 (0.6) g, P=0.0002) compared with saphenous vein. Precontracted vein grafts did not relax in response to acetylcholine; in contrast, saphenous vein relaxed in a dose-dependent manner to a maximal relaxation of 22 (3) per cent. Both saphenous vein and vein graft relaxed in response to A23187. Vein graft intimal thickness was approximately fourfold greater than that of saphenous vein (540 (110)) versus 136 (30) μm). Scanning electron microscopy of vein and vein graft revealed an intact endothelium. Coronary artery vein grafts are capable of responding to various contractile agonists; these responses are notably different from those of saphenous vein and there is a loss of endothelium-dependent relaxation. Even at a late stage vein grafts are not inert but are functional conduits with an abnormally responsive endothelium and a less potent, but significantly altered, smooth muscle contractile profile.
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