Renal response to graded intravenous hypertonic NaCl infusion in healthy and hypertensive subjects:dose-related impairment in distal NaCl reabsorption

Abstract

The effects of graded acute intravenous hypertonic NaCl loads on the baseline relationship between osmolal clearance and free water reabsorption established during high NaCl dietary intake and on the fractional excretion of various ions were investigated in 15 healthy subjects and in 12 “normal renin” essential hypertensive patients. No significant influence on the baseline relationship could be demonstrated after a moderate NaCl load in the healthy subjects, while free water reabsorption was depressed by the same intervention in the hypertensive patients. High NaCl loads induced depression of free water reabsorption in a dose-related fashion in both groups. No difference was found in phosphaturia between the groups after the same NaCl load as well as in the healthy persons after different NaCl loads, supporting the contention that the observed differences in free water reabsorption were not due to changes in the proximal nephron. It was concluded that: (1) impaired NaCl reabsorption in Henle's loop (depression of free water reabsorption) may also occur in response to acute NaCl loadings in healthy subjects, and (2) “exaggerated natriuresis” is the consequence of a normal renal response (imparied NaCl transport in Henle's loop) to a certain degree of volume expansion reset abnormally to a lower level in hypertensive patients.