The Mechanism of Salt Wastage in Chronic Renal Disease*

Abstract

The mechanism of salt wastage was studied in 17 patients with chronic renal disease. Persistent salt wastage could be demonstrated during rigid salt restriction in 10 of 14 patients during a 2-3 wk. metabolic balance. The minimal urinary Na concentration that could be elaborated during salt wastage was relatively high, ranging from 7 to 27 mEq per 1. Water diuresis increased urine flow without changing urinary Na concentration so that Na excretion rose in direct proportion to urine flow. The casue of the salt wastage was attributed to the failure of the patients with chronic renal disease to reduce the urinary Na concentration below a relatively high fixed value. Normal subjects during water diuresis and salt deprivation also exhibited complete flow dependence for Na excretion, but at very low concentrations of urinary Na. Mannitol diuresis in these subjects elevated the concentration of urinary Na at which flow dependence commenced. Flow dependence of urinary Na excretion, therefore, is a characteristic of the normal as well as the diseased kidney. Osmotic diuresis raises the minimal urinary Na concentration at which flow dependence commences. It is suggested that the higher concentration of urinary Na at which flow dependence commences in chronic renal disease is a consequence of osmotic diuresis through the distal nephron.