The reversibility of canine vein-graft arterialization. We assessed the reversibility of functional and morphological changes of arterialized vein segments by returning them to the venous circulation. Thirteen dogs underwent right carotid and femoral veno-arterial grafting. After 12 weeks, veno-arterial grafts were removed for contractility (norepinephrine [NE] and 5-hydroxytryptamine [5-HT]), luminal prostacyclin (PGI2), and morphometric analyses; the remaining segments were used as left jugular and femoral veno-venous grafts. After another 12 weeks, the veno-venous grafts were harvested. To NE, veno-arterial grafts (ED50, 5.4 +/- 0.1 [-log M]) were less sensitive than control veins (ED50, 6.0 +/- 0.2) or veno-venous grafts (ED50, 6.4 +/- 0.2) but were more sensitive than control arteries (ED50, 4.0 +/- 0.1); the maximum tension of veno-arterial grafts (6.2 +/- 0.6 g) was greater than that of veins, less than that of arteries (9.8 +/- 1.0 g), and comparable with that of veno-venous grafts (5.1 +/- 1.1 g). To 5-HT, veno-arterial (ED50, 7.5 +/- 0.1) and veno-venous (ED50, 7.3 +/- 0.2) grafts were more sensitive than arteries (ED50, 6.0 +/- 0.3), while the vein was unresponsive; the maximum tension of veno-arterial grafts (5.0 +/- 0.7 g) was less than that of arteries (6.9 +/- 0.9 g) and greater than that of veno-venous grafts (1.4 +/- 0.3 g). PGI2 production in veins (3.6 +/- 0.8 ng/ml), veno-arterial grafts (3.9 +/- 0.8 ng/ml), and veno-venous grafts (3.3 +/- 0.9 ng/ml) was comparable and less than that of arteries (6.4 +/- 0.9 ng/ml). Veno-arterial graft intimal thickness (127 +/- 8 microns) and intimal area (15.6 +/- 1.8 x 10(3) microns 2) tended to be greater than that in the veno-venous graft (113 +/- 9 microns and 12.4 +/- 1.8 x 10(3) microns 2); also, the veno-arterial graft medial area (103.0 +/- 7.3 x 10(3) microns 2) was greater than that of the veno-venous graft (80.3 +/- 6.9 x 10(3) microns 2), thereby resulting in a similar relative intimal area (13 +/- 1%). Therefore, some changes associated with arterialization, for example, adrenergic sensitivity, maximum tension to 5-HT, medial thickening, and perhaps intimal hyperplasia, reverted toward venous values when replaced in the venous environment, possibly due to variations in pressure, flow, shear stress, and/or graft preparation techniques. Luminal PGI2 was unchanged in the grafts, implying that graft contractility was not modulated by luminal PGI2. 