Vagal and sympathetic reflexes of left ventricular origin on the efferent activity of cardiac and renal nerves on anaesthetized cats

Abstract

The influence of reflexes of left ventricular origin on the postganglionic sympathetic activity and heart rate was investigated in anaesthetized cats. The experiments were to clarify 1. whether there are regionally different reflex adjustments due to an activation of ventricular receptors, 2. whether an increase of left ventricular diastolic pressure, which is known to activate afferent vagal fibres, causes an inhibition of sympathetic activity, 3. whether a coronary artery occlusion can activate a pressor reflex and a depressor reflex. Left ventricular receptors were stimulated by obstruction of the aortic root, coronary artery occlusion and mechanical stretch of the ventricular wall. In animals with intact CNS, all stimuli led to an inhibition of the activity of the inferior cardiac and renal sympathetic nerves and bradycardia. These reflex effects are initiated by mechanoreceptors and abolished by vagotomy. The inhibition of sympathetic activity was equally pronounced in the cardiac and renal nerves. After coronary artery occlusion and aortic obstruction, inhibition occurred as soon as the ventricular diastolic pressure had risen about 2 mmHg. In spinal animals both stimuli caused a sympathetic activation which was mainly restricted to the cardiac nerve. This activation is not due to mechanical changes, but rather a direct result of myocardial ischaemia. Coronary artery occlusion is able to produce both inhibition and activation of sympathetic fibres, but the activation is normally suppressed and thus seems not to be particularly important for circulatory control.

Renal nerve and blood pressure responses to stimulation of cardiac receptors in dogs and cats by bradykinin

“…The intact groups in their study showed only hypotensive response. Equally impressive data by Vogt and Thamer (22) in the SAD cat demonstrated that significant reductions in RNA and inferior cardiac nerve activity were evoked with LAD occlusion associated with a prominent hypotension. In this latter study, the systemic responses, except for the reduction in ABP, were abolished with vagotomy.…”

“…However, in some patients during myocardial infarction and in dogs during coronary occlusion, a depressor response and bradycardia have been observed (8,19,25). Since the inhibitory and excitatory responses have been observed in vagotomized dogs and cats in which mechanical changes were minimal (22), these contrasting affects were most likely due to reflexes mediated by sympathetic afferent nerves.…”