Red cell sodium and potassium in hypertension among blacks

Intracellular sodium and potassium were estimated in a series of normotensive (n = 120) and hypertensive (n = 97) blacks attending an outpatient screening clinic. All participants were free of other major medical illnesses and had not taken prescription medications, including antihypertensives, for at least two weeks. Mean intracellular sodium was 11% higher in the hypertensives than the normotensives (8.51 +/- 2.46 v 7.77 +/- 2.27 mmol, respectively, P = 0.02). A significant correlation was noted between diastolic blood pressure and cell sodium (r = 0.138, P = 0.04) when measurements from both groups were combined. Logistic regression analysis likewise demonstrated a borderline significant role of cell sodium in determining case-noncase status (P = 0.06); this finding was independent of other covariates, such as age and obesity. No relationship was noted between cell potassium and blood pressure. A significant correlation was noted between cell sodium and potassium (r = 0.272; P = 0.001); whereas no relationships were found among cell sodium and body mass index, age, sex, habitual alcohol intake, or educational achievement. These data, obtained from the largest series of US blacks reported to date, confirm and extend the finding that the intracellular concentration of sodium in the erythrocyte is increased in hypertensives. The data also lend support to the contention that abnormal sodium metabolism at the cellular level may play a role in the biochemical pathway leading to hypertension.