Modulation of coronary vasomotor tone in humans: Progressive endothelial dysfunction with different early stages of coronary atherosclerosis

Abstract

The endothelium plays a critical role in the control of vasomotor tone by the release of vasoactive substances. Because endothelial injury or dysfunction is considered important very early in atherogenesis, we hypothesized that abnormal endothelial function precedes the angiographic detection of coronary atherosclerosis in the human coronary circulation. The coronary vasomotor responses to three different endothelium-mediated stimuli (intracoronary infusion of acetylcholine 10-8 to 10-6 M, increase in blood flow to induce flow-dependent dilation, and sympathetic stimulation by cold pressor testing) were assessed by quantitative angiography and subselective intracoronary Doppler flow velocity measurements within the left anterior descending coronary artery in 38 patients. All three stimuli elicited epicardial artery dilation in all 11 patients with smooth coronary arteries and absence of risk factors for coronary artery disease (group 1). All nine patients with smooth coronary arteries but with hypercholesterolemia (group 2) demonstrated a selective impairment in endothelial function with vasoconstriction (35±12.7% decrease in mean luminal area) in response to acerylcholine but showed a preserved flow-dependent dilation (15.5±4.4% increase in mean luminal area) and vasodilation in response to cold pressor testing (14.2±4.6% increase in mean luminal area). In all nine patients with an angiographically defined smooth coronary artery segment but with evidence of atherosclerosis elsewhere in the coronary system (group 3), both acetylcholine and cold pressor testing induced vasoconstriction (26.2±8.7% and 18.7±7.9% decrease in mean luminal area, respectively), whereas flow-dependent dilation was preserved (20.4±8.7% increase in mean luminal area). In the nine patients with angiographic evidence of wall irregularities (group 4), flow-dependent dilation was also abolished and vasoconstriction occurred in response to acetylcholine and cold pressor testing (34.5±10.7% and 19.9±6.3% decrease in mean luminal area, respectively). All coronary artery segments dilated in response to nitroglycerin, suggesting preserved function of vascular smooth muscle. Despite similar reductions in coronary vascular resistance in response to the smooth muscle relaxant papaverin, patients with hypercholesterolemia demonstrated a selective impairment of vasodilation of the resistance vasculature in response to acetylcholine (p<0.05 versus groups 1, 3, and 4). Thus, there is a progressive impairment of endothelial vasoactive functioning in coronary arteries of patients with different early stages of atherosclerosis, beginning with a selective endothelial dysfunction in angiographically defined normal arteries in patients with hypercholesterolemia and progressively worsening to a complete loss of endothelium-mediated vasodilation in angiographically defined atherosclerotic coronary arteries. The assessment of endothelial modulation of vasomotor tone in the intact human coronary circulation may add a new dimension to the angiographic evaluation of coronary artery disease by detecting early changes in endothelial vasoactive function important in the development of atherosclerosis rather than detecting atherosclerosis per se.