SUMMARY1. Activation of left atrial receptors by distension of balloons at the pulmonary vein-atrial junctions caused an increase in the cardiac sympathetic nerve activity, a decrease in the renal sympathetic nerve activity, and no change in the lumbar and splenic sympathetic nerve activity.2. The cardiac and renal nerve responses to balloon distension were abolished by vagal blockade in the neck.3. The results provide additional evidence that the reflex increase in the heart rate following stimulation of the left atrial receptors is mediated by selective activation of cardiac sympathetic nerve fibres.4. The inhibitory effect of atrial receptor activation on the renal sympathetic nerve activity suggests that a neural factor, possibly involving renal haemodynamics, may be a component of the diuretic response to the activation of the left atrial receptors.5. The results provide further evidence for the selective nature of the pattern of reflex responses to left atrial receptor activation and show for the first time a directionally fractionated response from sympathetic efferent neurones.

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