Enhanced adrenergic constriction of iliac artery with removal of endothelium in conscious dogs

We studied, in conscious dogs, the effects of removal of endothelium on the responses of iliac artery diameter and iliac blood flow to intra-arterial infusions of adrenergic agonists. With endothelium intact, iliac diameter increased with intra-arterial infusion of nitroglycerin (4.7 ± 0.4%), acetylcholine (4.2 ± 0.6%), and epinephrine (4.5 ± 1.3%), and decreased with norepinephrine (-7.5 ± 1.7%), phenylephrine (-6.6 ± 1.0%), and B-HT 920 (-2.1 ± 0.6%). One to five days following removal of endothelium with a balloon-tipped catheter, base-line iliac diameter was unchanged, and still increased with nitroglycerin (4.6 ± 0.5%), but not with acetylcholine, and epinephrine actually decreased diameter (-3.5 ± 1.3%). Removal of the endothelium also enhanced the constriction observed with norepinephrine (-12.5 ± 2.0%) and phenylephrine (-11.4 ± 1.6%), but not with B-HT 920 (-1.8 ± 0.5). The changes in arterial pressure, iliac blood flow, iliac vascular resistance, and heart rate induced by any of the agonists did not differ before and after removal of the endothelium. These results indicate that the endothelium mediates the dilation in response to epinephrine and also serves an important role in protecting against α₁-adrenergic vasoconstriction of large iliac arteries.