Erythrocyte sodium content and transport in borderline and mild hypertension

Sodium content and transport of red blood cells were examined in 98 male blood donors. Regarding their blood pressure they were classified into the following groups: (a) 57 normotensives, (RR less than 140/90 mm Hg); (b) 24 borderline hypertensives (140/90 less than or equal to RR less than 160/95 mm Hg); and (c) 17 hypertensives (RR greater than 160/100 mm Hg). Compared with the normotensives the borderline hypertensives have significantly reduced red cell sodium content. The ouabain-resistant net Na+ uptake and the relative Na+ uptake, as a measure of the Na+/K+ pump, were significantly increased. With rising blood pressures the measured values turn to normal, so that no difference exists between the normotensive and hypertensive groups. It is supposed that in the initial or even prehypertensive state a considerable enhancement of the pump activity occurs, simultaneously accompanied by less marked increases in sodium influx, leading to a reduced intracellular sodium content. In the course of hypertension, possibly caused by the formation of a pump inhibitor, the sodium content of red cells turns to normal or supernormal values.