Sodium transport parameters in erythrocytes of patients with primary aldosteronism

Erythrocyte Na(+)-H+ exchanger and Na(+)-Li+ countertransport activity in primary aldosteronism

Several authors have described increased Na-H exchanger activity in essential hypertension but no data are available in secondary forms of hypertension such as primary aldosteronism. We measured Na-H exchanger kinetics together with Na-Li countertransport Vmax in the erythrocytes of eight patients with primary aldosteronism and in 15 normotensive control subjects. Plasma aldosterone, plasma renin and plasma potassium were also evaluated. Na-H exchanger Vmax appear to be increased in patients with primary aldosteronism and Hill's n, an index of co-operativity amongst intracellular proton binding sites, was significantly lower in patients than in controls. No statistically significant differences were found between affinity for intracellular protons (K50%) and for Na-Li countertransport Vmax between the two groups studied. We were unable to find any correlations between Na-H exchanger Vmax and Na-Li countertransport Vmax in the two groups considered as a whole. From the present data Na-H exchanger overactivity would not appear to be a specific feature of essential hypertension but seems to be characteristic in patients with primary aldosteronism.

Effect of spironolactone on cytosolic free sodium concentration in platelets from hypertensive patients with primary aldosteronism

Cytosolic free sodium concentration ([Na+]i) was investigated in intact platelets from 5 hypertensive patients with primary aldosteronism (unilateral adenoma in 3 patients, and adrenal hyperplasia in 2 patients) and 21 normotensive control subjects. [Na+]i was measured using a novel sodium-sensitive fluorescent dye technique. [Na+]i was significantly decreased in platelets from patients with primary aldosteronism compared to control subjects (21.9 +/- 4.1 mM vs 35.8 +/- 2.2 mM, mean +/- SEM, P < 0.05). After administration of the mineralocorticoid antagonist spironolactone in 4 patients [Na+]i tended to be higher in platelets although the differences did not reach statistical significance (26.3 +/- 7.2 mM vs 18.2 +/- 2.4 mM, P = 0.125). From the present results it may be concluded that intracellular sodium is decreased by aldosterone-induced activation of Na-K-ATPase. That activation may be partly blocked by spironolactone.

Modulation of Na+/K+ pump in intact erythrocytes by cardioglycosides, steroid hormones and ouabain-like compounds

1. Pure erythrocytes preparations, free from platelets and white cells, were incubated for a long time without hemolysis. 2. Dose-response experiments performed with (a) cardioglycosides (ouabain and K-strophantoside), (b) steroid hormones and their glucuronides (tetrahydrocortisol, oestradiol and the respective 3-glucuronic derivatives) and (c) ouabain-like compounds purified in our laboratory (0.7 kDa and 2-4 kDa respectively) emphasise a modulatory effect [activation of Na+ efflux rate and K+ uptake at very low ligand concentrations, inhibition at higher levels; maximum enhancement of cation transport: (a) and (b) 10-0.1 nM (+40-50%), (c) 1-0.01 nM (2.5-fold)]. 3. Binding experiments show upward-curved Scatchard graphs, with the Kd values of 50 nM and 18 microM and the Bmax values of 10.2 and 984.5 fmol/100 microliters RBC (red blood cells) respectively.

Rapid effects of mineralocorticoids on sodium-proton exchanger: genomic or nongenomic pathway?

High-affinity aldosterone binding sites have been described in human mononuclear leukocytes (HML), and in vitro effects of aldosterone on intracellular sodium, potassium, and calcium concentrations and cell volume have been shown in HML. In the present paper, the response of the sodium-proton exchanger of the cell membrane to agonists and antagonists was studied by determining the kinetics of HML swelling in isotonic sodium propionate. Within 1-2 min of incubation, aldosterone significantly stimulated propionate-induced swelling by an additional 30-50% at concentrations as low as 0.07 nM. This effect was not blocked by the classical aldosterone antagonists potassium canrenoate or canrenone at concentrations of 140 or 700 nM. Hydrocortisone and dexamethasone were effective agonists only at much higher concentrations (4,000 nM). These data are not well explained by a mechanism of steroid action involving the interaction of a steroid receptor complex with nuclear DNA, since the effect on the sodium-proton exchanger is too fast. The findings could indicate distinct membrane receptors with a high affinity for aldosterone, but not hydrocortisone, and rapid direct membrane effects of aldosterone. These putative novel receptors may in turn bind novel aldosterone antagonists with possible diuretic and vasodilator effects distinct from those of spironolactones.

Racial differences in aldosterone excretion and plasma aldosterone concentrations in children

Blacks are more likely to have hypertension, have lower levels of plasma renin activity, and typically consume less potassium than whites. Whether blacks and whites secrete different amounts of aldosterone is less clear. We estimated aldosterone secretion indirectly in 715 children, 249 of whom were black, by measuring their nocturnal rates of urinary excretion of aldosterone. Dietary sodium and potassium intakes were estimated from their excretion rates. The mean (+/- SE) aldosterone-excretion rate was lower in the black children than in the white children (0.045 +/- 0.003 vs. 0.078 +/- 0.004 nmol per micromole of creatinine per kilogram of body weight; P less than 0.001). The potassium-excretion rate was also lower in the black children than in the white children (0.13 +/- 0.01 vs. 0.18 +/- 0.01 mmol per micromole of creatinine per kilogram; P less than 0.001). Aldosterone excretion was highly correlated with potassium excretion (P less than 0.001), but the lower aldosterone-excretion rate in blacks was explained only in part by their lower dietary intake of potassium. Systolic blood pressure was higher in black children (P less than 0.001), as was diastolic pressure (P = 0.037). In a second study of 99 children, the plasma aldosterone level was found to be significantly lower in black children than in white children (230 +/- 30 vs. 400 +/- 30 pmol per liter; P less than 0.001). Plasma renin activity and plasma cortisol levels were the same in both groups. In summary, we found that black children secrete about 40 percent less aldosterone than white children. The role of the lower aldosterone-secretion rate in the genesis of the higher blood pressures observed in black children is not known.

Clinical application of sodium-23 nuclear magnetic resonance for measurement of red cell sodium concentrations

Red cell sodium (RBC-Na+) concentrations were measured using 23Na nuclear magnetic resonance (NMR), without the destruction of erythrocyte membranes. Subjects were categorized into four groups: 20 normotensive subjects (NT group), 20 age-matched essential hypertensive patients (EHT group), 10 patients with primary aldosteronism (PA group), and 18 patients treated with digoxin (DIG group). Although RBC-Na+ concentrations were similar between the NT group (6.14 +/- 0.80 (Mean +/- SD) mmol/l) and the EHT group (5.92 +/- 0.99), they were significantly higher in both the PA group (7.55 +/- 0.88, p less than 0.001) and the DIG group (8.43 +/- 3.81, p less than 0.02). In the PA group, RBC-Na+ concentrations decreased significantly after resection of the adenoma, and there was an inverse relationship between serum potassium and RBC-Na+ concentrations (r = -0.65, p less than 0.01). In the DIG group, RBC-Na+ concentrations tended to increase in proportion to serum digoxin levels (r = 0.53, p less than 0.05). These results support the view that RBC-Na+ concentrations are determined primarily by Na+/K+-pump activity of red cell membranes. This study showed also that Na+ NMR is an useful method determining intracellular Na+ concentrations.

Erythrocyte sodium transport and blood pressure in white subjects

The mechanisms that define the relation between blood pressure and sodium handling are not yet well understood. Although several abnormalities in sodium transport have been associated with hypertension, a link between the blood pressure of normotensive subjects and the erythrocyte sodium-potassium adenosine triphosphatase pump, the principal sodium transporter of sodium, has not been previously demonstrated. Data from independent measurements of erythrocyte intracellular sodium, ouabain-sensitive sodium efflux, and the number of sodium pump sites per red blood cell were used to calculate a second-order rate constant for ouabain-sensitive sodium efflux. Among 20 normotensive white subjects, this rate constant correlated significantly (p less than 0.005) with mean arterial blood pressure. A significant correlation was not observed between the rate constant and the blood pressure of 22 hypertensive subjects. A hypothesis is proposed, which suggests that the sodium efflux rate constant of erythrocytes is related to the control of sodium reabsorption via the sodium pump of the renal tubules and that an elevated erythrocyte rate constant may be associated with chronic increased sodium reabsorption, which leads to volume expansion and the development of hypertension.

Influence of race, sex, and blood pressure on erythrocyte sodium transport in humans

Sodium transport of erythrocytes from normotensive and essential hypertensive subjects was evaluated by determining ouabain-sensitive and ouabain-insensitive sodium efflux rates, Na+-Li+ countertransport rates, Li+-K+ cotransport rate constants (lithium replacing sodium), intracellular sodium concentrations, and the number of Na+,K+-adenosine triphosphatase (ATPase) sites per erythrocyte. Subjects included men and women, blacks and whites. Hypertensive subjects had significantly higher sodium transport than did normotensive subjects for ouabain-sensitive sodium efflux (p less than 0.025) and Na+-Li+ countertransport (p less than 0.001). Sexual differences were noted for ouabain-sensitive (p less than 0.001) and ouabain-insensitive (p less than 0.001) sodium efflux, for intracellular sodium concentration (p less than 0.025), and for the Li+-K+ cotransport rate constant (p less than 0.005), all with higher values for men than for women. Racial differences were noted for ouabain-insensitive sodium efflux (p less than 0.005), Na+-Li+ countertransport (p less than 0.001), and the Li+-K+ cotransport rate constant (p less than 0.001); values were higher in whites than blacks for all three measurements. The number of [3H]ouabain binding sites was lower for blacks (p less than 0.001) and the intracellular sodium concentration was higher for blacks (p less than 0.001). Among all subjects, significant (p less than 0.001) correlations were found between intracellular sodium concentration and the number of Na+,K+-ATPase sites per erythrocyte (r = -0.78) and between the ouabain-sensitive sodium efflux per site and intracellular sodium concentration (r = 0.85, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)