Coronary Vasomotor Tone in Large Epicardial Coronary Arteries with Special Emphasis on β-Adrenergic Vasomotion, Effects of β-Blockade

Changes in coronary vasomotor tone of large epicardial coronary arteries today can be assessed quite accurately by exact measurements of coronary diameters applying computer assisted systems. The effect of various vasodilators (nitrates, calcium antagonists, EDRF-dependent compounds) was tested in this way. It appears that normal coronary artery segments reach a maximum of dilator reserve with an increase of luminal diameter of approximately 30–40%; different patterns of kinetics were, however, encountered. β-Blocking agents, both non-selective (Propranolol) and selective (atenolol), were found to lead to a gradual vasoconstriction, i.e., a decrease in diameter by approximately 20–25% over 20 min, an effect which is overcome by nitrates. New β-blocking compounds with vasodilator properties, such as Celiprolol, show no constriction. The vasoconstrictor effect of Propranolol and atenolol may not only be due to the decrease of flow following the drop in myocardial oxygen consumption, but could also reflect an unopposed α-adrenergic tone. The clinical aspects of this observation are discussed.