The atrial receptors responsible for the decrease in plasma vasopressin caused by distension of the left atrium in the dog.

In dogs anaesthetized with chloralose, the effects of cooling the cervical vagi on the reflex decrease in plasma concentration of vasopressin, caused by distension of a large balloon in the lumen of the left atrium, were examined. Distension of the balloon in ten dogs with the vagi at 37 degrees C resulted in a decrease in plasma concentration of vasopressin and, as before, an increase in urine flow. The responses were not significantly affected by cooling to 16-18 degrees C but were abolished at 9 degrees C. At 16-18 degrees C the increase in activity in myelinated vagal afferent fibres is largely unchanged and at 9 degrees C is abolished (Kappagoda, Linden & Sivananthan, 1979; Sivananthan, Kappagoda & Linden, 1981). It is concluded that the decrease in plasma concentration of vasopressin during distension of the left atrium is mediated by the Paintal-type atrial receptors with myelinated vagal afferent fibres.