Effect of ouabain on large coronary artery diameter

Cardiac glycosides have previously been shown to constrict small resistance vessels. This study evaluated the effect of a bolus intravenous dose of ouabain (20 μg/kg) on large left circumflex coronary arterial diameter measured by sonomicrometry in nine awake choronically instrumented dogs. Between 5 and 10 min after ouabain administration external circumflex coronary diameter decreased (3.87 ± 0.21 to 3.83 ± 0.21 mm, p < 0.05). Twenty minutes after ouabain administration, coronary diameter had returned to control. At the time of the peak decrease in coronary diameter, heart rate had decreased (104 ± 7 to 82 ± 7 beats/min, p < 0.05), circumflex coronary blood flow had decreased (45 ± 7 to 38 ± 6 ml/min, p < 0.05), total circumflex coronary resistance had increased (2.7 ± 0.4 to 3.5 ± 0.6 U, p < 0.05) and aortic pressure was unchanged (108 ± 4 to 113 ± 4 mm Hg). Alpha-adrenergic blockade with phentolamine did not prevent the decrease in circumflex coronary arterial diameter in each of five dogs (3.67 ± 0.28 to 3.60 ± 0.28 mm, p < 0.05). Therefore, intravenous ouabain caused vasoconstriction of large coronary arteries. These vasocontrictor effects were not mediated by alpha-adrenergic mechanism. This constriction could have important consequences in the presence of coronary stenoses.