The response in efferent cardiac sympathetic nerves to stimulation of atrial receptors, carotid sinus baroreceptors and carotid chemoreceptors.

The reflex increase in activity in efferent cardiac sympathetic nerve fibres in response to distension of small balloons in the pulmonary vein-atrial junctions was studied in dogs anaesthetized with chloralose; the carotid sinuses were isolated and perfused with blood. In the efferent cardiac nerves which responded to distension of the balloons there was no significant change in the control activity, or in the magnitude of the response during changes in carotid sinus pressure from 8 to 30 kPa, during changes in the blood perfusing the sinuses from arterial to venous or during stimulation of the cutaneous branch of the left radial nerve. In contrast, in efferent cardiac nerves which did not respond to the distension of the balloons, consistent and significant changes in activity resulted from stimulating arterial baroreceptors, chemoreceptors or a cutaneous branch of the radial nerve. It is concluded that efferent cardiac sympathetic nerve fibres which respond by an increase in activity to stimulation of the atrial receptors, constitute a group of nerve fibres which are separate from those responding to stimulation of receptors in the carotid region or to stimulation of peripheral somatic nerves.