Effects of deafferentation or sequential occlusions on cardiac sympathetic activity during ischemia

In 39 anesthetized dogs, we compared the effects of selective afferent sympathectomy, vagotomy, epicardial phenol painting, or a previous coronary occlusion on cardiac sympathetic activities recorded during 30 min of acute myocardial ischemia. Efferent innervation patterns were verified by electrical stimulation, and cardiac efferent activities were simultaneously recorded from two thoracic sympathetic nerves. One nerve was selected for recording because it was shown to innervate the proposed ischemic region, whereas the other nerve was selected because it was shown to innervate nonischemic regions. Left ventricular ischemia was produced by occlusion of a small branch of either the left anterior descending (LAD) or left circumflex (LCX) coronary arteries. Heart rate was paced. Reflex changes in sympathetic activities to ischemic regions were prevented by elimination of afferent fibers with either phenol or bilateral vagotomy. Ablation of sympathetic afferents prevented ischemia-induced reflex changes to nonischemic regions but did not prevent reflex changes to ischemic regions. Reflex changes in cardiac sympathetic activities during a second coronary occlusion of 30 min were vastly different from the initial occlusion but were similar to those observed after local deafferentation. Our findings indicate that 1) differential reflex changes in cardiac sympathetic activities during 30 min of left ventricular ischemia are due to afferent signals originating from the ischemic region, 2) both sympathetic and vagal afferent fibers participate in the ischemia-induced cardio-cardiac reflex, and 3) the nature of the sympathetic reflex response to acute ischemia is influenced by a previous ischemic insult.