Responses to activation of cardiac sympathetic afferents with epicardial bradykinin.

Abstract

The cardiovascular reflex responses mediated by cardiac sympathetic afferent fibers (CSA) appear to differ depending on the nature of the activating stimulus. Although electrical stimulation of CSA may result in either excitatory of inhibitory reflex responses in both cats and dogs, topical application of bradykinin to these sensory endings elicits only excitatory reflex responses in cats. The present experiments were performed to determine whether CSA activated by epicardial bradykinin also mediate solely excitatory reflex responses in the dog. The changes in efferent cardiac or renal sympathetic nerve activity, mean arterial pressure, and heart rate resulting from application of bradykinin to the left ventricular epicardial surface were determined in 15 chloralose-anesthetized, sinoaortic-denervated vagotomized dogs. Activation of CSA with bradykinin (0.1--120 g/ml) elicited inhibitory responses in eight dogs, excitatory responses in four dogs, and biphasic responses in three dogs. Both excitatory and inhibitory reflexes were eliminated by cardiac sympathetic afferent denervation. The results show that, in the dog, cardiac receptors with sympathetic afferent fibers activated by epicardial bradykinin mediate nonuniform reflex responses that tend to be predominantly inhibitory.