Alpha adrenergic receptor activity of epicardial coronary artery in the anesthetized dog

The epicardial coronary artery plays an important role not only as a conduit artery but also as a locus of coronary spasm. Accordingly, diameter change of the large epicardial coronary artery of the in situ canine heart was continuously measured by ultrasonic dimension gauge technique and the effects of alpha adrenergic stimulation on the caliber were studied. After the intravenous administration of phenylephrine the aortic pressure increased by 28 mmHg, however, the left circumflex coronary artery diameter decreased by 3.4% (p less than 0.01). Norepinephrine and sciatic nerve stimulation after propranolol (1 mg/kg) induced coronary vasoconstriction by 1.3 (p less than 0.025) and 2.5% (p less than 0.05) against the obvious increases of aortic pressure by 16 and 19 mmHg, respectively. Thus alpha adrenergic stimulation, in situ in dogs, was shown to directly constrict the large epicardial coronary artery.