Reflex parasympathetic coronary vasodilation elicited from cardiac receptors in the dog

Veratrum alkaloids injected into the coronary circulation stimulate myocardial receptors to produce reflex bradycardia and arterial hypotension (the Bezold-Jarisch reflex). This study investigated the hypothesis that parasympathetic coronary vasodilation occurs as part of the Bezold-Jarisch reflex. Blood flow in the circumflex coronary artery was measured in chloralose-anesthetized, closed-chest dogs with a newly developed cannula-tip flow transducer. Alpha-receptor blockade with Dibozane (2 mg/kg) was used to prevent peripheral vasodilation, and beta-receptor blockade with propranolol (1 mg/kg) was used to prevent adrenergic cardiac effects. Electrical pacing was used to maintain a constant heart rate. Under these conditions, veratridine injected into the anterior descending coronary artery but not into the circumflex coronary artery produced a 63% increase in circumflex coronary blood flow and an 88% increase in diastolic coronary conductance. The effect was abolished when the reflex arc was interrupted by either vagotomy or atropine administration. It is concluded that a cardiocoronary reflex parasympathetic coronary vasodilation can be elicited by stimulating cardiac receptors with veratridine.