The Bezold-Jarisch reflex in the conscious dog

Abstract

The Bezold-Jarisch reflex was studied in 22 conscious, instrumented dogs. Specific left ventricular receptor stimulation was elicited by the circumflex coronary artery injection of veratridine in doses ranging from 0.01 to 0.40 μg/kg. None of these doses resulted in any hemodynamic effects when given intravenously. Heart rate, arterial blood pressure, left ventricular pressure, left ventricular dp/dt, and cardiac output were monitored and total peripheral resistance calculated. Dose-related decreases in arterial blood pressure and heart rate were observed following intracoronary injection of veratridine. Decreases were also noted in dp/dt max, left ventricular pressure, and cardiac output. With the heart paced to prevent bradycardia, the decrease in all the above parameters was significantly attenuated; however, a significant decrease in total peripheral resistance was still observed (-30.2 ± 3.7%). Cardiac pacing plus the administration of the α-adrenergic blocking agent, phentolamine, blocked the decrease in total peripheral resistance when compared to pacing alone. The administration of atropine significantly attenuated the bradycardia, hypotension, decrease in dp/dt max, and decrease in total peripheral resistance in response to intracoronary veratridine. Atropine plus phentolamine abolished the decrease in total peripheral resistance that was evoked by intracoronary veratridine. The decrease in dp/dt max which resulted from veratridine administration was induced largely by the associated bradycardia, since both cardiac pacing and atropine significantly attenuated it. These experiments indicate that the chemical stimulation of left ventricular receptors in the conscious dog mediates a bradycardia, hypotension and decrease in total peripheral resistance which is produced by sympathetic withdrawal as well as cholinergic vasodilation. There is no significant inotropic effect elicited by the stimulation of these receptors.