Erythrocyte 22Na efflux and urinary sodium excretion in essential hypertension.

1. The rate constant for total 22Na efflux from erythrocytes was examined in patients with mild to moderate hypertension and in normotensive controls. No difference in 22Na efflux rate constant was found when the cells from both groups were incubated in artificial medium. When the cells from both groups were incubated in their own plasma, the rate constant for Na efflux was significantly elevated for hypertensive patients compared with controls (0.40 +/- 0.02, 0.36 +/- 0.01 respectively; P < 0.05). 2. In hypertensive patients sodium efflux rate constant varied inversely with 24 h urinary sodium excretion when erythrocytes were incubated in artificial medium (r = -0.34, P < 0.05) or in plasma (r = -0.42, P < 0.05). No association between sodium efflux rate constant and urinary sodium excretion occurred in normotensive subjects. 3. These findings provide further evidence that sodium is an important aetiological factor in hypertension. In 'salt-sensitive' individuals dietary sodium may interact with the regulation of cellular sodium transport via both humoral and cellular mechanisms to elevate blood pressure.