Enhanced red cell sodium permeability in patients with borderline hypertension

Red cell membrane sodium permeability was studied in 41 untreated patients with essential hypertension (20 borderline hypertensives and 21 established hypertensives) and 21 age matched normotensive subjects by means of the measurement of unidirectional passive influx of 22Na+ into ouabain-treated erythrocytes. The mean value (+/- SD) of 22Na+ influx was greater in the hypertensives than in the normotensives (0.183 +/- 0.047 vs 0.152 +/- 0.047 mmol/l . cells/hr, respectively, p less than 0.02). Among the patients with essential hypertension, the borderline hypertensives demonstrated a higher 22Na+ influx than the established hypertensives (0.207 +/- 0.043 vs 0.160 +/- 0.038 mmol/l . cells/hr, respectively, p less than 0.001), and 22Na+ influx positively correlated with plasma renin activity (r = 0.44, p less than 0.005). In 16 of 20 borderline hypertensives, 5 year blood pressure changes were examined retrospectively, and a positive correlation was observed between mean blood pressure increase and 22Na+ influx value in these subjects (r = 0.64, p less than 0.01). These results suggest that passive sodium influx may be altered in the course of the development of hypertension in relation to the changes in blood pressure level and that enhanced sodium permeability may be a characteristic of the early stage of essential hypertension.