The nature of the atrial receptors responsible for a reflex decrease in activity in renal nerves in the dog.

1. In dogs anaesthetized with chloralose, distension of small balloons in the pulmonary vein-atrial junctions and left atrial appendage, to stimulate left atrial receptors, caused a reduction in activity in efferent renal nerves. This response was maintained during distension of the balloons for 30 min periods.2. In a second group of dogs, cooling the cervical vagi in steps reduced the magnitude of the response in renal nerves. In seven dogs, the response in fourteen preparations of renal nerves was slightly reduced with the vagi at 18 degrees C and markedly reduced or abolished at 12 degrees C. The effect of cooling the vagi was the same as the previously shown effect of cooling on the increase in activity in myelinated afferent vagal fibres during similar stimulation of atrial receptors.3. In a third group of dogs, the cervical vagi were cooled to 9 degrees C. In six dogs, fifty-four preparations of renal nerves showed no significant response to distension of the balloons.4. In a fourth group of dogs, both vagi were sectioned in the neck. In three dogs, twenty-four preparations of renal nerves then showed no response to distension of the balloons.5. It is concluded that the reduction in activity in efferent renal nerves during distension of small balloons in the pulmonary vein-atrial junctions and left atrial appendage involves only atrial receptors discharging into myelinated vagal fibres.