Observations on the Innervation of the Coronary Vessels of the Dog1

It has been generally held in the past that the innervation of the coronary vessels of the mammal is peculiar with respect to the systemic blood vessels in that the parasympathetics, the vagi, were considered to be coronary vasoconstrictors and the sympathetic nerves, primarily coronary vasodilators. The evidence for this comes largely from work reported by Wiggers (l), Anrep and Segall (Z), Hochrein (3, 4) and Rein (5). However, in the case of both the vagus and sympathetic nerves, contrary results have been reported. Coronary vasodilators in the vagus nerves have been reported to exist by Meyer (6), Martin (7), Drury and Smith (8), Greene (9), Danielopolu and Marcou (lo), Hinrichsen and Ivy (1 l), Kountz et al. (12) and Klisiecki and Flek (13). The subject has been recently reviewed by Wiggers (14) and further details need not be given here. Recently, Greene (9) has presented evidence tending to show that some sympathetic vasodilator fibers are contained in the lower cervical portion of the vagus trunks. More recently Heymans (15) and his collaborators, Jourdan and Nowak (16), have claimed that the sympathetic fibers which are bundled in the vagus join the vagus within the skull and originate in the medulla. However, Kabat (17) has cast grave doubt upon the interpretation of Heymans and his collaborators. It has been argued that the supposedly peculiar innervation of the coronary vessels serves to permit their needed dilatation when other systemic vessels are constricted as is the case in exercise. This argument is fallacious, since such adjustments of coronary flow actually occur through dynamic and humoral control and not because of the peculiarity of anatomical bundling of efferent vasomotor fibers. The discrepancy between coronary innervation and innervation of systemic vessels has induced us to reinvestigate the subject. In order to evaluate accurately vasomotor nerves, it the active changes in is necessary 1, to use a coronary vessel caliber due to measure of coronary flow which