The role of the endothelium in the control of venous tone: studies on isolated human veins.

The role of the endothelium in the vasomotor control of veins was investigated in 14 isolated ring preparations of presumably normal saphenous veins obtained from vein grafts in connection with vascular surgery. The investigations were performed with the specimens mounted for recording isometric tension in organ baths. Paired rings were used, one normal and the other de-endothelialized by gentle rubbing. The responses to noradrenaline (10(-8)-2 X 10(-5) M), acetylcholine (10(-6) M) and 120 mM KCl solution were tested. After precontraction with 10(-7) M noradrenaline, acetylcholine at 10(-6) M did not induce cholinergic relaxation, but in the majority of experiments induced a further increase in tone. Maximal contraction with noradrenaline was significantly higher in normal compared to de-endothelialized vessels. Therefore, endothelium-derived relaxation as in arteries did not occur in human saphenous veins and the existence of an endothelial-derived contracting factor in response to acetylcholine and noradrenaline is a possibility.