Intrarenal Determinants of Sodium Retention in Mild Heart Failure

Abstract

Abstract The onset and the mechanisms leading to Na + retention in incipient congestive heart failure (CHF) have not been systematically investigated. To investigate renal Na + handling in the early or mild stages of CHF, Na + balance and renal clearances were assessed in 10 asymptomatic patients with idiopathic or ischemic dilated cardiomyopathy and mild heart failure (HF) off treatment (left ventricular ejection fraction, 29.7±2%) and in 10 matched normal subjects during a diet containing 100 mmol/d of NaCl and after 8 days of high salt intake (250 mmol/d). Six patients were studied again after 6 weeks of treatment with enalapril (5 mg/d PO). At the end of the high salt diet, in patients with mild HF the cumulative Na + balance exceeded by 110 mmol that of normal subjects (F=3.86, P <.001). During high salt intake, renal plasma flow and glomerular filtration rate were similarly increased in both normal subjects and mild HF patients. In spite of comparable increases of filtered Na + in the two groups, fractional excretion of Na + , fractional clearance of free water, and fractional excretion of K + (indexes of distal delivery of Na + ) increased in normal subjects and were reduced in patients with mild HF. During enalapril treatment, in the mild HF patients the cumulative Na + balance was restored to normal; furthermore, enalapril significantly attenuated the abnormalities in the distal delivery of Na + . Our results indicate that a defective adaptation of Na + reabsorption in the proximal nephron is associated with Na + retention in response to increased salt intake in the early or mild stages of HF. These abnormalities of renal Na + handling are largely reversed by enalapril.