Red cell cotransport activity and sodium content in black men. Relationship to essential hypertension.

Furosemide-sensitive sodium and potassium cotransport and intracellular sodium content ([Na]i) were measured in erythrocytes (red blood cells, RBCs) from a population of 90 adult black men with and without essential hypertension (EH). The mean values for sodium cotransport activity, expressed as furosemide-sensitive Na efflux (mmol/liter RBC/hr), were not significantly different among the EH patients and two control groups, normotensive subjects with a positive history (N+) and those with a negative family history (N-) for hypertensive disease (EH: 154 +/- 123, n = 53; N+: 167 +/- 93, n = 12; and N-: 207 +/- 142, n = 20; all values are means +/- SD). The mean [Na]i 9.66 +/- 3.02 mmol/liter RBC (n = 56) for the EH group was greater than the mean value for the N- control group (7.96 +/- 1.97, n = 20; p less than 0.05). The N+ group also displayed a higher mean [Na]i (10.38 +/- 3.18, n = 12; N+ vs N- p less than 0.01). Although there was substantial overlapping of [Na]i values between the groups and no clear dividing line, the distribution curve of the [Na]i values in EH was skewed toward higher concentrations than in N-. Nevertheless, we must conclude that erythrocyte cotransport and [Na]i are not clinically useful in the identification of EH in black men.