Attenuated natriuretic response to adrenomedullin in experimental heart failure

Background: The recently discovered vasodilating and positive inotropic peptide, adrenomedullin (ADM), has strong natriuretic actions. ADM-induced natriuresis is caused by an increase in glomerular filtration rate and a decrease in distal tubular sodium reabsorption. Although ADM is activated in human and experimental heart failure, the role of ADM in the kidney in heart failure remains undefined. Methods and Results: The present study was performed to determine the renal hemodynamic and urinary excretory actions of exogenously administered ADM in a canine model of acute heart failure produced by rapid ventricular pacing. Experimental acute heart failure was characterized by a decrease in cardiac output and an increase in pulmonary capillary wedge pressure with an increase in plasma ADM concentration. Intrarenal infusion of ADM (1 and 25 ng/kg/min) induced an increase in urinary sodium excretion in the normal control dogs (change in urinary sodium excretion [ΔUNaV], +94.5 μEq/min during 1 ng/kg/min ADM infusion and + 128.1 μEq/min during 25 ng/kg/min ADM infusion). In the acute heart failure dogs, intrarenal ADM infusion resulted in an attenuated increase in urinary sodium excretion (ΔUNaV, +44.8 μEq/min during 1 ng/kg/min ADM infusion and +51.8 μEq/min during 25 ng/kg/min ADM infusion). Both glomerular and tubular actions of ADM were attenuated in the acute heart failure group compared with responses in the normal control group. Conclusion: The present study shows that the renal natriuretic responses to ADM are markedly attenuated in experimental acute heart failure. This study provides insight into humoral mechanisms that may promote sodium retention in heart failure via a renal hyporesponsiveness to natriuretic actions of ADM.