© 1973 American Heart Association, Inc.
Impulses in Slowly Conducting Vagal Fibers from Afferent Endings in the Veins, Atria, and Arteries of Dogs and Cats
1 Cardiovascular Research Institute, University of California, San Francisco, California 94122, the Department Physiology, New York Medical College, New York 10029, the Department of Physiology, Royal Free Hospital School edicine, University of London, London W.C. 1, England, and the Department of Physiology, School of Medicine, University of Leeds, Leeds, England
Afferent impulses in 61 fine myelinated or unmyelinated vagal fibers arising from endings in large blood vessels ("vascular endings") were recorded in anesthetized dogs and cats. The endings had a sparse, irregular spontaneous discharge, or they were quiescent. They were stimulated by capsaicin, phenyl diguanide, or veratridine injected into the bloodstream but not by sodium cyanide or hypoxia. Unlike arterial baroreceptors and atrial receptors, which are concentrated in localized areas, vascular endings were widely distributed in the thoracic aorta, the pulmonary artery, the brachiocephalic artery, the splenic artery, the atriovenous junctions, the atrial appendages, the inferior vena cava, and the hepatic vein. Conduction velocity in 28 fibers ranged from 0.8 to 11.0 m/sec (mean 3.1 m/sec), and in 19 of these fibers the velocity was less than 2.5 m/sec (i.e., the fibers were C-fibers). Vascular endings were stimulated by distending the vessels with balloons. Endings in the pulmonary artery and the aorta did not respond to pressures within the physiological range, but they were stimulated by abnormally high pressures (pulmonary artery 60-110 mm Hg, aorta 200-215 mm Hg). The physiological role of the vascular endings is unknown.
Key Words: atriovenous receptors • arterial baroreceptors • vascular C-fibers • widespread vascular endings • chemoreflexes • cardiovascular reflexes • high-threshold baroreflexes • capsaicin • phenyl diguanide • veratridine
Submitted on December 4, 1972
Accepted on May 7, 1973
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