Humoral nature of the urine response to simulation of atrial receptors.

The diuretic response to stimulation of left atrial receptors by distending small balloons located at the pulmonary vein--left atrial junctions and in the left atrial appendage was studied in anaesthetized dogs in which bretylium tosylate, atenolol and atropine had been administered to effect blockade of renal nerves and to prevent increases in heart rate resulting from stimulation of atrial receptors. In these dogs, distension of the balloons was not associated with significant changes in heart rate, left atrial pressure or arterial blood pressure, and resulted in increases in urine flow, decreases in urinary sodium concentration and no significant changes in urinary sodium excretion. It is concluded that the humoral mechanism is responsible for the diuresis in response to stimulation of atrial receptors and has no significant effect on the response of natriuresis known to involve a decrease in the activity in the renal nerves and haemodynamic changes associated with stimulation of atrial receptors.