Interrelationship of renal sodium and phosphate handling in cirrhosis

Although the sodium retention of cirrhosis is attributable primarily to enhanced tubular reabsorption of sodium, the precise nephron sites responsible remain the subject of continuing controversy. Since changes in phosphate clearance may be used as an index of proximal sodium reabsorption, we undertook to characterize the effects of immersion-induced volume expansion on renal sodium and phosphate handling in order to clarify further the nephron sites of enhanced Na reabsorption. 18 cirrhotic patients were studied twice while in balance on a 10-mEq sodium. 100-mEq potassium diet during a control period and during water immersion. Cirrhotic patients manifested a wide continuum of responses characterized by either a sluggish or barely discernible natriuretic response (group I, n = 5) or an appropriate natriuretic response (group II, n = 13). Despite widely varying natriuretic responses, group I patients manifested a phosphaturic response to water immersion which was virtually identical to that of group II patients. The current findings indicate that distal sodium reabsorption contributes importantly to the sodium content of the final urine in cirrhotic patients with sodium retention.