Studies on the Reflex Mechanism in Relation to Coronary Circulation (II) : PRESSOREFLEX ARISING FROM THE LEFT CORONARY ARTERY

The concept of a cardiovascular reflex originated with the discovery of the depressor nerve by Cyon & Ludwig in 1866. At about the same time von Bezold and Hirt described the powerful depressor effect caused by the injection of veratrine, which was elicited from the heart through a reflex via afferent fibres in the vagus. Seventy years later Jarisch and his colleagues investigated this problem in detail, confirming that the mechanism of the depressor effect was a reflex in nature. Dawes showed that the intracoronary injection of veratrine evoked the Bezold reflex with very small doses. The exact location of the receptors of the veratrine is still uncertain, but they should be accessible only through the coronary artery.The Bezold reflex had been considered a coronary chemoreflex and its significance was debated. On the other hand pressoreflex from the coronary artery has never been reported. The author has experimentally investigated the problem and has found a pressoreflex arising from the left coronary artery.Dogs weighing 10-15 kg with open-chest and artificial respiration were used under sodium thiopental or morphine-urethane anesthesia. Heparinized (10 mg/kg) blood was circulated from the right femoral artery into the left coronary orifice. A syringe was attached to this perfusing system and was fiilled with heparinized blood taken from the circuit. The stimulation, which raised the pressure in the coronary artery, was given by injecting 10-15 cc of blood from the syringe into the circuit during 3-6 seconds. The changes in the systemic pressure by the procedure were observed on soot paper as determined in the left femoral artery.(1) A rise of coronary perfusing pressure caused a fall of systemic pressure. The depressor effect was found in 62 of 106 cases. It was reflex in origin, because it was completely abolished after cutting cervical vagi without any exception. No marked changes in the heart rate were found.(2) These depressor effects were still obtained after cutting the sinus nerves or the aortic nerves.(3) In order to establish the afferent pathway, the ventricular branches of cardiac nerves which innervate the left ventricle were blocked on the surface of the ventricle or auricle. The author refered the ventricular nerves as the anterior and posterior ventricular branches. After blocking the anterior branch the depressor effects could be abolished in 12 of 16 cases, while it was abolished in only one of 7 cases after cutting the posterior branch.From these results it was concluded that the pressoreflex arised from the left coronary artery, and that the anterior ventricular branch participiated more in the reflex than the posterior one as the afferent pathway.