Blood flow- and endothelium-mediated vasomotion of iliac arteries in conscious dogs.

The effects of removal of endothelium and changes in blood flow in conscious dogs on the responses of large iliac artery diameter to local infusion of nitroglycerin, acetylcholine, epinephrine, and norepinephrine into the iliac artery were studied. Infusion of agonists did not change mean arterial pressure or heart rate. In vessels with intact endothelium, iliac diameter increased with nitroglycerin (5.1 +/- 0.5%), acetylcholine (4.5 +/- 0.5%), and epinephrine (3.5 +/- 0.9%) and decreased with norepinephrine (-6.7 +/- 1.7%). Preventing increases in blood flow during infusions of agonists abolished the dilation with epinephrine but not with nitroglycerin or acetylcholine. When blood flow was completely stopped by occlusion of the iliac artery, local injection of nitroglycerin (5.7 +/- 0.7%) and acetylcholine (3.0 +/- 0.6%) dilated, but epinephrine constricted (-9.1 +/- 1.7%), the iliac artery. Removal of the iliac artery endothelium did not change the dilation with nitroglycerin (4.6 +/- 0.5%), abolished the dilation with acetylcholine (0.0 +/- 0.3%), reversed the dilation with epinephrine to constriction (-3.3 +/- 0.7%), and enhanced the constriction with norepinephrine (-13.6 +/- 1.6%). These results indicate that epinephrine and acetylcholine dilate the iliac artery via a mechanism mediated by the endothelium. The endothelium-dependent dilation observed with epinephrine is mediated by an increase in iliac blood flow, while that observed with acetylcholine is due partially to a direct effect on the endothelium as well as an effect of blood flow superimposed on the direct effect. The results further indicate that the endothelium attenuates vasoconstriction produced by the alpha-adrenergic agonists, norepinephrine and epinephrine.