Contrasting reflex influences of cardiac afferent nerves during coronary occlusion

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Abstract
Afferent neurons contained within cardiac sympathetic nerves may have important influences on the circulation when activated during myocardial ischemia. Although such activation reflexly excites upper thoracic sympathetic efferent neurons, effects on other components of sympathetic outflow are unknown. Cardiac sympathetic afferent nerves were stimulated by occlusion of coronary arteries to investigate their reflex influences on renal sympathetic nerve activity and systemic arterial blood pressure. Responses were observed in anesthetized cats in which sympathetic and/or vagal cardiac afferent nerves remained intact and arterial baroreceptors remained intact or were denervated. Stimulating sympathetic afferent neurons caused excitation of renal nerve activity, which was accompanied by variable changes in arterial pressure. Stimulation of vagal afferents by coronary occlusion consistently produced inhibition of renal nerve activity and marked depressor responses. When both components of cardiac innervation remained intact, increases or decreases in renal nerve activity and blood pressure were elicited by coronary artery occlusion in the presence or absence of arterial baroreceptors. Cardiac sympathetic afferent nerves evidently can contribute significantly to cardiovascular control during myocardial ischemia.