Decreased water and potassium content in erythrocytes in essential hypertension

Red blood cell K+ could be a marker of K+ changes in other cells involved in blood pressure regulation

The aim of this study is to determine whether red blood cell K(+) content (RBC(Ki)) is associated with blood pressure levels and, if so, could RBC(Ki) be a marker of potassium changes in other cells involved in blood pressure regulation. The study was performed on 50 untreated hypertensives, 32 of their offspring and 50 age- and sex-matched controls. Systolic (SBP) and diastolic (DBP) blood pressures, height, weight, plasma, urine and red blood cell electrolytes were measured in all subjects. RBC(Ki) was significantly lower in hypertensives than in offspring of hypertensives and normotensive controls. Offspring of hypertensives had significantly lower RBC(Ki) than normotensive controls. Plasma K(+) was significantly lower both in hypertensives and offspring of hypertensives when compared to normotensive controls. A significant negative correlation was found in hypertensives between RBC(Ki) and DBP (r=-0.27, P=0.04) and in offspring of hypertensives between RBC(Ki) and DBP (r=-0.43, P=0.02). A significant correlation was found in hypertensives between RBC(Ki) and plasma K(+) (r=0.3, P=0.02). A positive correlation with borderline significance was found in hypertensives between RBC(Ki) and ionized Ca(2+) (r=0.2, P=0.1). In conclusion, our results support the hypothesis that RBC(Ki) is associated with blood pressure levels and that the measurement of RBC(Ki) levels may represent a biochemical marker for K(+) changes in other cells involved in blood pressure regulation. Further studies are necessary to explain the exact mechanisms of reduced RBC(Ki) levels in hypertensive patients and their offspring.

Red blood cell sodium and potassium concentration and blood pressure. The Gubbio Population Study

The relations of red blood cell sodium (RBC Na) and potassium (RBC K) concentrations to blood pressure and prevalence of hypertension were assessed for 1805 men and women, aged 25 to 74 years, who participated in the baseline examination of the Gubbio Population Study in north central Italy. In men, in univariate analyses, RBC Na concentration was not significantly related to systolic or diastolic blood pressure, while RBC K concentration was significantly and inversely related to blood pressure. In women RBC Na values correlated significantly and directly with systolic and diastolic pressure, but RBC K concentration was not significantly related to blood pressure. Results of the multivariate analyses indicated in men a significant independent and inverse relationship of RBC K concentration with hypertension and blood pressure, and in women a significant positive association of RBC Na concentration with hypertension. RBC Na did not relate independently to either systolic or diastolic blood pressure in men or women. Age-specific analyses suggested that the relationships between RBC K level and blood pressure in men and the relationship between RBC Na level and hypertension in women were stronger in older (age 55 to 74 years) compared to younger participants (25 to 54 years). These findings indicate that the associations of RBC Na and K concentrations and hypertension may be sex and age specific. The nature of these gender- and age-specific associations remains to be clarified. Prospective data are also needed for further clarification of the relation of intracellular Na metabolism to the etiology of hypertension.

Gravimetric determination of the water concentration in whole blood, plasma and erythrocytes and correlations with hematological and clinicochemical parameters

We have assessed gravimetric methods for determination of intravascular water, established whole blood-, plasma- and erythrocyte water reference values in a healthy volunteer group (n = 97, 48 females) and correlated these variables with 30 simultaneous hematological, clinicochemical and body parameters. The water standard was 55.56 mol/kg = 100 mass %. For erythrocyte water determination three methods were evaluated: 2 indirect methods were easy to perform, the third, using a hematocrit centrifuge, was the most reliable. Imprecision (within-batch coefficient of variation (CV), %) was excellent: whole blood 0.2, plasma 0.1, erythrocytes 0.7-2.2 and recoveries (means, %) 99.7-100.1. Serum water was found to be slightly higher than plasma water. Volunteer group, mean reference values, mass %: whole blood water 79.7, plasma water 91.2, erythrocyte water, three methods 66.2, 64.6 and 64.2, respectively. Females had mean 1.6 mass % higher whole blood water and 0.9-1.0 mass % higher erythrocyte water than males with no difference in plasma water. In the volunteer group whole blood water correlated strongly with hematocrit (r = -0.96), hemoglobin (r = -0.94) and erythrocytes (r = -0.85) and centrifuge hematocrit (r = -0.91). Plasma water correlated strongly with plasma total protein (r = -0.74, all correlations P < 0.001). Hemoglobin and hematocrit can serve as surrogate parameters for whole blood water when water determination is not available; total protein reflects plasma water.

Acute effects of angiotensin-converting enzyme inhibitor on erythrocyte sodium ion transport in essential hypertension

The acute effects of angiotensin-converting enzyme inhibitor, captopril, on sodium ion transport systems were investigated in essential hypertensive and normotensive subjects. The passive sodium efflux through the erythrocyte membrane was significantly higher and erythrocyte sodium-potassium cotransport was lower in patients with essential hypertension when compared with normal subjects. However, sodium-potassium pump activity and sodium-lithium countertransport did not differ significantly between the hypertensive patients and the normal subjects. Immediately after captopril administration, erythrocyte passive sodium efflux and sodium-potassium cotransport returned to normal levels in the hypertensive subjects. Although the plasma renin activity and plasma aldosterone concentration were altered by captopril, they did not correlate with changes in any sodium transport system. These results suggest that the changes in sodium transport systems which occur immediately after captopril administration may contribute, at least in part, to its antihypertensive action.

Erythrocyte water content in spontaneously hypertensive rats and DOCA-salt hypertensive rats

Intra-erythrocyte water, sodium and potassium contents were measured in spontaneously hypertensive rats (SHR) and deoxycorticosterone acetate (DOCA)-salt rats. In 12 week old SHR, the intra-erythrocyte water content was slightly but significantly lower than that in age-matched Wistar-Kyoto (WKY) rats. SHR also exhibited a significantly lower intra-erythrocyte potassium content, but sodium content tended to be elevated. Although sodium content was not correlated with the water content, potassium content was. In DOCA-salt hypertensive rats, the intra-erythrocyte sodium content was higher than that in age-matched normotensive Sprague-Dawley rats by about 33%, but the water and potassium contents were similar. There were no significant correlations between these parameters. These findings provide no evidence of water retention in erythrocytes from DOCA-salt rat or SHR even though intra-erythrocyte sodium content was increased.