ASSOCIATION OF INCREASED ERYTHROCYTE NA+ H+ EXCHANGER WITH RENAL NA+ RETENTION IN PATIENTS WITH ESSENTIAL-HYPERTENSION/

The goal of this study was to investigate the activity of the Na+/H+ e xchanger in erythrocytes of patients with essential hypertension and i ts relation with urinary Na+ excretion. The study was performed in cel ls from 27 untreated hypertensive patients and 30 normotensive control s with similar age and sex distribution. All subjects were studied aft er 4 days on a controlled Na+ diet (145 mmol/ day). The activity of th e Na+/H+ exchanger was determined by acidifying cell pH and measuring the initial rate of the net Naf-dependent Hf efflux. The activity of t he Na+/H+ exchanger was higher in hypertensive patients than in contro ls (301 +/- 45 v 162 +/- 23 mmol/L cells/h, mean +/- SEM; P < .01). Wi th the upper limit of the normotensive population as a cut-off point ( 385 mmol/L cells/h), a subgroup of 12 hypertensive patients had an abn ormally high activity of Na+/H+ exchanger. Compared with controls and with patients with normal exchanger activity, patients with increased exchanger activity were characterized by lower net (P < .01) and fract ional (P < .05) Na+ excretion. The accumulative Na+ balance was higher (P < .01) in hypertensive patients with increased activity of the exc hanger (39.90 +/- 3.47 mmol) than in the remaining hypertensive patien ts (0.59 +/- 6.96 mmol) or in the normotensive population (-5.71 +/- 6 .12 mmol). After analyzing the relationship of renin activity with Na excretion it was observed that renin activity was inappropriately low in 9 (75%) patients with increased exchanger, in 6 (40%) patients wit h normal exchanger, and in 6 (20%) normotensives, these differences be ing significant (P < .01). A reciprocal correlation was found between the activity of the exchanger and plasma renin activity in the group o f hypertensive patients (r = 0.60, P < .001). These results indicate t hat increased activity of the erythrocyte Na+/H+ exchanger is associat ed with increased tubular Na+ reabsorption, Na+ retention, and low ren in secretion in a subgroup of essential hypertensive patients. These f indings suggest that erythrocyte Na+/H+ exchanger overactivity may be a marker of deranged Na+ handling in essential hypertension.