The effects of stimulation of left atrial receptors on efferent vagal nerves to the dog heart.

There is a controversy as to whether the increase in heart rate in response to stimulation of atrial receptors is mediated solely by the sympathetic or by both the sympathetic and vagal nerves to the heart. In dogs anaesthetized with chloralose the activity in vagal efferent nerve fibres from the cardiac branches of the right vagus nerve was recorded. The effects of distension of small balloons at the right pulmonary vein-atrial junctions on this activity was investigated. Distension of the small balloons caused an increase in heart rate in all dogs. Distension of the small balloons had no effect on vagal efferent fibres whether these were affected by carotid occlusion or not (seven dogs), or whether they were affected by changes in the pressure or nature of the blood perfusing the vascularly isolated carotid sinuses or not (nine dogs). It is concluded that the increase in heart rate seen in response to stimulation of left atrial receptors by distension of small balloons at the pulmonary vein-atrial junctions does not involve vagal efferent nerves.