Diuresis from atrial receptors after hypophysectomy and local ablation with no changes in plasma vasopressin

Stimulation of the left atrial receptors in dogs anaesthetized with chloralose results in a reflex diuresis and natriuresis. The efferent limb of this reflex is though to have at least three components: nervous, haemodynamic and humoral. The present study was designed to investigate the humoral component in dogs anaesthetized with chloralose; to determine whether a humoral agent, other than vasopressin, might be causative in this reflex diuresis. The nervous and haemodynamic components were prevented by pharmacological denervation. Any possible contribution to the diuresis by a decrease in the plasma concentration of vasopressin was prevented by the removal of the pituitary gland. In animals in which a spontaneous diuresis followed hypophysectomy, an infusion of arginine vasopressin sufficient to maintain urine flow in the normal range for these dogs anaesthetized with chloralose was given. Distension of small balloons at the pulmonary vein-atrial junctions and in the left atrial appendage discretely to stimulate the atrial receptors in eleven dogs anaesthetized with chloralose resulted in a significant diuresis. It was concluded that a blood-borne agent other than vasopressin was responsible for the observed diuresis. At the moment it is not known whether vasopressin or the diuretic agent, or both, are involved in the diuresis accompanying the stimulation of atrial receptors.