An Intrinsic Adrenergic Vasodilator Mechanism in the Coronary Vascular Bed of the Dog.

• Considerable evidence indicates that an adrenergic vasoconstrictor mechanism exists in the coronary vascular bed. In the classification advanced by Ahlquist,' the sites mediating this response are termed alpha receptors. Whether or not an adrenergic dilator mechanism exists also in the coronary vessels remains controversial, since it is unclear whether the decrease of coronary resistance that occurs during adrenergic stimulation of the myocardium represents a direct effect of cathecholamines on the vessels'" or is a consequence of the increased myocardial activity. The present study was undertaken to examine the reaction of the coronary vessels to isoproterenol, an agent known to effect vasodilatation in other vascular beds by stimulation of so-called beta receptors. The effects of isoproterenol were studied first in the beating canine heart; then, in order to eliminate its stimulating action on the myocardium, its effects were also studied in the isolated perfused canine heart arrested with potassium. The findings indicate that the coronary vessels of the dog do contain an intrinsic adrenergic dilator mechanism.