A regional difference in endothelium-dependent relaxation responses to acetylcholine in the canine venous system

Endothelium-dependent relaxations of canine veins isolated from 15 different sites were examined. Acetylcholine (ACh, 10(-10)-10(-6) M) caused marked endothelium-dependent relaxations in the external jugular vein, superior vena cava, brachiocephalic vein, segment A (supradiaphragmatic portion) and D (infrarenal portion) of the inferior vena cava. However, only contractile responses were induced by ACh in the portal, mesenteric veins and the segment C of the inferior vena cava (between liver and renal veins) with or without endothelium. The other 7 veins showed only small endothelium-dependent relaxations (10-20%). These results indicated that the endothelium-dependent responses of canine veins to ACh are regionally different.