Effect of acute changes in left atrial pressure on urine flow in unanesthetized dogs

Abstract

The effect of an acute rise in left atrial pressure on urine flow, urine specific gravity, and sodium excretion was studied in chronic preparations with and without anesthesia and at different hydration levels. Left atrial pressure was changed by an exteriorized purse string about the mitral annulus. In 56 of 58 experiments (including each of the above conditions) a transient increase of urine flow was found during atrial distention, accompanied by an increase in sodium excretion and a fall in urine specific gravity. Absolute volume and percentage increase of the diuresis varied directly with the degree of prehydration. Vasopressin infusions modified the response only in prehydrated animals. Arterial pressure and renal blood flow (electromagnetic flowmeter) were increased during atrial distention. At least two mechanisms interplay in the diuretic response: 1) hemodynamic and 2) humoral (ADH or Jahn's "diuretic factor"). The degree of prehydration seems to determine the threshold of the ADH mechanism. Our data speak against homeostatic fluid volume control by stretch receptors in the left atrium or its inflow tract.