Alpha-adrenoceptor blockade prevents exercise-induced vasoconstriction of stenotic coronary arteries

OBJECTIVES The study aimed to evaluate the role of alpha-adrenergic mechanisms during dynamic exercise in both normal and stenotic coronary arteries. BACKGROUND Paradoxical vasoconstriction of stenotic coronary arteries has been reporte d during dynamic exercise and may be due to several factors such as alpha-a drenergic drive, a decreased release of nitric oxide, platelet aggregation with release of serotonin, or a passive collapse of the vessel wall. METHODS Twenty-six patients were studied at rest, during two levels of supine bicyc le exercise and after 1.6 mg sublingual nitroglycerin The alpha-blocker phe ntolamine was given to 16 patients before exercise, five of whom had also t aken a beta-adrenergic-blocker the same morning. Ten patients served as con trols. The cross-sectional areas of a normal and a stenotic coronary vessel were determined by biplane quantitative coronary arteriography. RESULTS In the normal vessel segments, coronary cross-sectional area did not change after phentolamine injection, but increased in all patient groups similarl y during exercise. Although coronary vasoconstriction existed in stenotic v essel segments in control patients, phentolamine-treated patients showed ex ercise-induced vasodilation without difference in Twenty-six patients were patients with and without chronic beta-blockade. CONCLUSIONS Exercise-induced vasoconstriction of stenotic coronary arteries is prevente d by intracoronary administration of phentolamine There was no difference i n coronary vasomotion between patients receiving phentolamine alone;md pati ents receiving phentolamine in addition to a beta-blocker. This finding sug gests that exercise-induced vasoconstriction is mediated not only by endoth elial dysfunction but also by alpha-adrenergic mechanisms. (C) 1999 by the American College of Cardiology.