Effects of high potassium or low sodium diet on vascular Na+,K+-ATPase activity and blood pressure in young spontaneously hypertensive rats

These studies were designed to investigate whether the antihypertensive effects of high potassium or low sodium diets are related to changes in vascular Na+,K+-adenosine triphosphatase (ATPase) activity. Vascular Na+,K+-ATPase was measured as ouabain-sensitive rubidium uptake in aorta incubated in buffer or plasma from spontaneously hypertensive rats (SHR) fed either a high potassium, a low sodium, or a normal diet for 2 weeks. The high potassium diet significantly increased Na+,K+-ATPase activity, whereas the low sodium diet significantly decreased activity. There was no evidence of a ouabainlike factor in plasma. The increased pump activity on the high potassium diet appeared to be due to an increase in maximum activity (Vmax) of the enzyme, rather than to an increased affinity for potassium. Potentially, an increase in Na+,K+-ATPase activity could contribute to the antihypertensive effect of potassium by hyperpolarizing the cell membrane. The decrease in vascular Na+,K+-ATPase activity on a low sodium diet probably is unrelated to its depressor effect, but it may be a homeostatic mechanism for maintaining sodium balance in the animal.     

Alterations in renal Na+K+ATPase activity and [3H]ouabain binding in Goldblatt hypertensive rabbits

To evaluate the role of renal Na+K+ATPase in the presence of Goldblatt hypertension, the enzyme activity and [3H]ouabain binding were examined in cortical and medullary homogenates from two-kidney, one clip (2K1C), one-kidney, one clip (1K1C), unilaterally nephrectomized and normal rabbits. Four weeks after the surgery, systolic blood pressures (SBPs) of 2K1C and 1K1C rabbits were increased significantly to 128 +/- 3 and 129 +/- 2 mmHg, respectively. In contrast, SBPs in the normal controls and unilateral nephrectomized (1K) animals were 83 +/- 2 and 86 +/- 3 mmHg, respectively. In the 2K1C rabbits, atrophy (91%) occurred in the kidney on the ischaemic side and hypertrophy (110%) occurred in the contralateral kidney. Na+K+ATPase activity and number of [3H]ouabain binding sites were reduced in the homogenates of the ischaemic kidney of 2K1C rabbits. In the 1K1C rabbits, marked hypertrophy of the kidney (155%) occurred, and the activity of Na+K+ATPase and the number of [3H]ouabain binding sites increased slightly in the cortex and medulla, compared with the normal controls. 5'-Nucleotidase, a plasma membrane marker enzyme, remained unchanged in both groups of hypertensive rabbits. Dissociation constant (KD) values for [3H]ouabain binding did not differ significantly in the renal homogenates of of 2K1C and 1K1C, compared with findings in the normal controls. The inhibitory activity of plasma was measured by studying [3H]ouabain binding to Na+K+ATPase of renal tubular basolateral membrane vesicles purified by Percoll gradient. The inhibition was more pronounced with plasma from 2K1C, 1K1C and 1K rabbits than from the control animals. Our findings suggest that in the Goldblatt hypertensive model, changes in Na+K+ATPase activity were due to alterations in glomerular filtration rate (GFR).     

Alterations in erythrocyte Na+,K+-cotransport in normal and hypertensive human pregnancy

Many physiological variables known or thought to affect erythrocyte Na+,K+-cotransport are altered in pregnancy. The interrelationships of Na+,K+-cotransport and pregnancy were therefore examined. Values were elevated by more than 30% in both second and third trimesters with a return towards non-pregnant levels in the postpartum period. Although pregnancy was also associated with elevated plasma cholesterol, renin activity and aldosterone, there was no significant relationship within the pregnant group between Na+,K+-cotransport and any of these factors. No change could be demonstrated in Na+,K+-cotransport values after 7 days of either high (greater than 250 mmol/day) or low (less than 50 mmol/day) sodium intake and values for those who developed pregnancy-associated hypertension (PAH, pre-eclampsia) were not significantly different from those in continuously normotensive women in either the second or the third trimesters of pregnancy.     

Decreased myocardial Na+K+ATPase activity in rats with reduced renal mass-saline hypertension

Inhibition of cardiovascular Na,K-pump activity has been shown to promote an increase in the contractile activity of myocardial and vascular smooth muscle and a consequent rise in blood pressure (BP). It has also been shown that vascular Na,K-pump activity and myocardial Na+K+ATPase activity [the energy source for active sodium (Na) and potassium (K) transport] are decreased in rats with various forms of low renin hypertension including rats with reduced renal mass-saline (RRM-saline) hypertension. In the present study, left ventricular Na+K+ATPase activity from rats with RRM-saline hypertension was found to be decreased in membranes prepared by two independent methods: deoxycholate, sodium iodide (Nal)-treated microsomal fractions (method 1) and membranes prepared by the hypotonic, lithium bromide (LiBr) method (method 2). Relative to RRM normotensive control rats which drank distilled water, myocardial Na+K+ATPase activity from RRM-saline drinking rats was decreased by 18.2% in membranes prepared by method 1 and 33.6% in membranes prepared by method 2. The apparent affinities of Na+K+ATPase for K and for ouabain were unaltered relative to controls in membranes prepared from these hypertensive rats by method 1, and the sialic acid content and 5'-nucleotidase activity (two putative sarcolemmal markers) were unaltered in membranes from the hypertensive rats, prepared by methods 1 and 2 respectively. The Mg2+ATPase activity of membranes prepared by method 1 was increased in the RRM-saline hypertensive rats but because it was not increased in membranes prepared by method 2 the former observation does not appear to be of any pathophysiological importance. In other experiments, hypertension was reversed in RRM-saline hypertensive rats by restricting their salt intake (substitution of distilled water for drinking).(ABSTRACT TRUNCATED AT 250 WORDS)     

Blood pressure and erythrocyte Na+ transport systems in a French urban male population

This paper reports an investigation of blood pressure (taken as a continuous variable) as a function of: erythrocyte Na+ content; Na+,K+ pump; Na+,K+ cotransport and Na+,Li+ countertransport fluxes, and passive cation permeabilities in fresh erythrocytes from 129 French males who were living in an urban area and were not under treatment for any medical condition (after allowing for the effects of age, body mass index, alcohol and tobacco consumption). In contrast with previous findings in a North American population, we were unable to confirm that blood pressure was correlated with erythrocyte Na+ content and Na+,K+-AT-Pase activity. Conversely, the only transport parameter correlated (negatively) with blood pressure was outward Na+,K+ cotransport [r = -0.20, P less than 0.05 and r = -0.19, P less than 0.05, for systolic (SAP) and diastolic arterial pressure (DAP), respectively; n = 114]. When allowing for age, body mass index and alcohol consumption, the correlation coefficient between the Na+,K+ cotransport system and blood pressure increased from -0.20 to -0.28 (P less than 0.01) for SAP and from -0.19 to -0.28 (P less than 0.01) for DAP (n = 105). We conclude that the correlations between blood pressure and erythrocyte Na+ transport function could differ between North American and French (or Mediterranean) populations. In any case, a decreased pump or outward Na+,K+ cotransport activity may lead hypertensive subjects to a similar increase in cell Na+ (and Ca2+) content in the vascular wall.     

Altered erythrocyte Na+ + K+ pump in adolescent obesity

The number of $\text{Na}\text{K}$ pump units and the cation transport activity of the pump were measured in erythrocytes from two etiologically different groups of obese adolescents and a group of normal controls. There was a significant reduction in the number of pump units, as measured by saturation ouabain binding, in erythrocytes from adolescents with idiopathic, early onset obesity. Individuals whose obesity developed subsequent to the appearance of a variety of hypothalamic lesions showed no reduction in the red cell complement of $\text{Na}\text{K}$ pump when compared to controls and the cation transport activity of their cells was higher than both the controls and the subjects with idiopathic obesity. These results support data obtained in adults that reduced red cell $\text{Na}\text{K}$ pump levels are seen in a group of individuals with idiopathic obesity. They further suggest that such reductions are not likely to be secondary to the obese state per se.     

Cation fluxes and (Na+ + K+)-activated ATPase activity in erythrocytes of patients with essential hypertension

Various claims, partially conflicting, have been made in recent years for abnormalities in cation pumps and fluxes in erythrocytes of patients with essential hypertension. In view of the obvious significance of such abnormalities for diagnostic purposes, and possibly for our understanding of the pathophysiology of essential hypertension, we have investigated these claims. We have determined the following parameters of erythrocytes from essential hypertensives and normotensives: 1. (Na+ + K+)-ATPase activity and the Km values for Na+, K+ and ATP; 2. ouabain-sensitive fluxes of Na+ and K+ in Na+-enriched cells after cold treatment and after treatment with p-chloromercuribenzenesulphonate; 3. furosemide-sensitive, ouabain-insensitive cotransport efflux of Na+ + K+. No significant differences were observed, except for a slight decrease in the ouabain-sensitive K+ influx after cold treatment in hypertensives. Hence, we conclude that determination of these parameters in erythrocytes does not seem to be useful for the diagnosis of essential hypertension.     

Higher plasma Na+,K+-ATPase inhibitory activity in essential hypertensive patients

The ability of plasma to inhibit 86 rubidium uptake in rat aorta and to displace [3H]-ouabain from hog brain Na+,K+-ATPase was used as a measure of plasma Na+,K+-ATPase inhibitory activity in seven normotensive and eight hypertensive subjects. Rat aortae rings were incubated in oxygenated plasma containing 86 rubidium (2 microCi/mL) for 30 mins at 37 degrees C and uptake measured and expressed as mumol/kg wet weight/min. Plasma was extracted with a mixture of chloroform and methanol (2:1) and the extract separated by silicic acid column followed by thin layer chromatography and fractions assayed for ouabain displacement using digoxin as a standard. Total ouabain displacement was calculated as the sum of all fractions. There was a strong correlation between the two methods for total plasma Na+,K+-ATPase inhibitory activity (r = 0.761, P less than 0.01). There was a significant positive correlation between plasma Na+,K+-ATPase inhibitory activity and blood pressure in all subjects. Na+,K+-ATPase inhibitory activity was significantly higher in plasma of hypertensives by both methods (P less than 0.001). The increased Na+,K+-ATPase inhibitory activity in plasma from hypertensives was due to the nonesterified fatty acid, long chain acylcarnitine and diphosphatidylglycerol fractions.     

Erythrocyte Na+,K+ cotransport and Na+,K+ pump in black and caucasian hypertensive patients

Alterations in red blood cell (RBC) Na+,K+ pump and in Na+,K+ cotransport (CoT) have been described in essential hypertension (EH). We examined pump and CoT in 50 normotensive (NT) subjects and 58 EH subjects subdivided by race and family history of hypertension (+ FH). RBCs were preloaded with Na+ to obtain intracellular levels of 25 mM/liter cells by using the p-chloromercuribenzene sulfonic acid (pCMBS) method. Na+ and K+ efflux rates into a magnesium-sucrose medium were quantitated in the presence of ouabain and ouabain plus furosemide to define pump and CoT activity respectively. Mean intracellular Na+ content was higher (p less than 0.05) in black NT and HT subjects compared to Caucasians. Mean RBC CoT was lower in black EH compared to NT and compared to Caucasian NT and HT subjects. Conversely, Caucasian HT patients had higher mean CoT than NT subjects. Subdivision into + FH revealed very little effect of + FH on CoT in black NT and HT subjects. In Caucasian NT and HT subjects with + FH, mean CoT was significantly reduced (less than 0.3 mM/liter cells/hr) compared to those without + FH. A subgroup of Caucasian EH subjects displayed high CoT (greater than 0.6 mM/liter cells/hr); a + FH had little impact on the high CoT group. There was no correlation between RBC CoT activity and age, sex, severity of hypertension, urinary sodium excretion, and plasma aldosterone. There was a positive correlation (r = + 0.47; p less than 0.01) between CoT and upright plasma renin activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased plasma and urinary Na+-K+ ATPase inhibitory activity and elevated blood pressure in metoclopramide-treated rats

Our recent studies demonstrated that dopaminergic receptor may play an important role in controlling blood pressure and renal sodium handling. This study was designed to investigate whether endogenous Na+-K+ ATPase inhibitors are related to changes in blood pressure and sodium balance, caused by the administration of metoclopramide (MC), a dopamine (D2) receptor antagonist, and sodium loading. Young male Wistar rats (250 approximately 300 g) were raised under three different conditions, control (control group), 1% NaCl loading (NaCl group) and 1% NaCl plus 1.5 mg/kg/day of metoclopramide (MC group) for 7 days. Systolic blood pressure (SBP), urinary and plasma Na+-K+ ATPase inhibitory activity (ATPI), urinary sodium, potassium and catecholamine excretions were measured. SBP in the MC group elevated from 116 +/- 2 mmHg to 134 +/- 4 mmHg, but there were no changes in SBP in the control and NaCl groups. Urine volume and urinary sodium excretion significantly increased in not only the NaCl group but also in the MC group. Plasma ATPI in both the NaCl and MC groups was higher than in the control group (p less than 0.001), and the level of ATPI in the MC group was significantly higher than in the NaCl group (p less than 0.05). Urinary ATPI in the control group was not detected after 7 days, but that in the NaCl and MC groups was clearly increased. The excretions of urinary catecholamines remained unchanged in all groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Na+K+ATPase activity and ouabain binding sites in erythrocytes in hyperthyroidism before and after treatment.

Erythrocyte sodium pump is decreased in hyperthyroid patients. We described the effect of untreated hyperthyroidism on Na+K+ATPase activity, ouabain binding sites and intracellular sodium concentration. We found a reduction in Na+K+ATPase activity and in number of ouabain binding sites with a concomitant increase in intracellular sodium. B-blockade therapy failed to restore normal pump activity and sodium concentration, where only thionamide treatment was successful when it was able to decrease free T3.     

Angiotensin II modulates the activity of the Na+/K+ATPase in eel kidney

We have previously shown that angiotensin II (Ang II) has a role at the level of the eel gill chloride cell regulating sodium balance, and therefore osmoregulation; the purpose of the present study was to extend these findings to another important osmoregulatory organ, the kidney. By catalytic histochemistry Na(+)/K(+)ATPase activity was found in both sea water (SW)- and freshwater (FW)-adapted eel kidney, particularly at the level of both proximal and distal tubules. Quantitation of tubular cell Na(+)/K(+)ATPase activity, by imaging, gave values in SW-adapted eels which were double those found in FW-adapted eels (Student's t-test: P<0.0001). This was due to a reduced number of positive tubules present in FW-adapted eels compared with SW-adapted eels. By conventional enzymatic assay, the Na(+)/K(+)ATPase activity in isolated tubular cells from SW-adapted eels showed values 1.85-fold higher those found in FW-adapted eels (Student's ttest: P<0.0001). Perfusion of kidney for 20 min with 100 nM Ang II provoked a significant increase (1.8-fold) in Na(+)/K(+)ATPase activity in FW, due to up-regulation of Na(+)/K(+)ATPase activity in a significantly larger number of tubules (Student's t-test: P<0.0001). The effect of 100 nM Ang II in SW-adapted kidneys was not significant. Stimulation with increasing Ang II concentrations was performed on isolated kidney tubule cells: Ang II provoked a dose-dependent stimulation of the Na(+)/K(+)ATPase activity in FW-adapted eels, reaching a maximum at 100 nM (1.82-fold stimulation), but no significant effect was found in SW-adapted eels (ANOVA: P<0.001 and P>0.05 respectively). Isolated tubule cells stimulated with 100 nM Ang II showed a significant generation of inositol trisphosphate (InsP(3)) and an increment in calcium release from intracellular stores. In conclusion, our results suggest that tubular Na(+)/K(+)ATPase is modulated by environmental salinity, and that Ang II has a role in regulating its activity in FW-adapted eels, probably through an InsP(3)-dependent mechanism.     

The role of pump number and intracellular sodium and potassium in determining Na,K pump activity in human erythrocytes

The factors that determine the activity of the Na,K pump in vivo were investigated by measuring Na,K pump activity under in vivo conditions in human red cells and relating it to the intracellular content of sodium ([Na]i) and potassium ([K]i) and the number of pump units per cell (pump number). Na,K pump activity was measured as ouabain-sensitive K+ influx, pump number was determined from the maximal binding of 3H-ouabain to intact cells, and [Na]i and [K]i were measured by atomic absorption spectrophotometry in washed, packed cells. In the 81 samples studied, pump activity per cell was significantly correlated with pump number (r = .64, P less than 0.001), but was negatively correlated with [Na]i (r = -.28, P less than 0.02) and was not correlated with [K]i. An inverse relationship was found between pump number and [Na]i. When pump activity was expressed as activity per pump unit, rather than per cell, a significant relationship was seen between pump activity and [Na]i (r = .50, P less than 0.001), and a negative correlation existed between the activity per pump unit and [K]i (r = -.29, P less than 0.01). The effect of intracellular Na+ at physiologic levels on pump activity was not strong, with the activity per pump unit increasing only 25% with a doubling of [Na]i. These results indicate that pump number is the major determinant of pump activity in human red cells in vivo, while [Na]i and [K]i are of secondary importance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of arginine vasopressin-stimulated Na+ K+ ATPase activity by difluoromethyl ornithine in the rat renal medulla

Arginine vasopressin (AVP) stimulates Na+ K+ ATPase and ornithine decarboxylase (ODC) activity in the rat medullary thick ascending limb. The effect of difluoromethyl ornithine (DFMO), a specific inhibitor of ODC activity, on AVP-stimulated Na+ K+ ATPase activity was evaluated using a cytochemical bioassay. Peaks in Na+ K+ ATPase activity in cultured rat renal segments which occurred after tissue had been exposed to 1 fmol AVP/l were completely inhibited by the addition of 20 mmol DFMO/l to the culture medium containing AVP. The addition of 20 mmol DFMO/l to the culture medium containing AVP in the concentration range 0.001-10 fmol/l inhibited completely the stimulation of Na+ K+ ATPase activity by AVP. The response of Na+ K+ ATPase to increasing doses of ATP (10-40 g polypeptide/l) was not influenced by the addition of 20 mmol DFMO/l to the culture medium containing AVP, suggesting that the prevention of AVP-stimulated Na+ K+ ATPase activity by DFMO was not due to a direct effect on the enzyme.     

(Na+ + K+) ATPase inhibitors and intracellular electrolytes in essential hypertension

White blood cell (WBC) Na+ and K+ concentrations, plasma (Na+ + K+)ATPase inhibition and blood pressure were determined in normotensive control subjects and patients with essential hypertension. While the untreated hypertensive group had significantly lower WBC K+ concentrations than the normotensive group (mean +/- SEM, 121.6 +/- 4.4 vs. 134.7 +/- 2.8 mEq/kg, p less than 0.05), no significant difference was observed in WBC Na+ concentrations between the 2 groups. The mean of plasma (Na+ + K+)-ATPase inhibition in untreated hypertensive patients was higher than that in normotensive controls (14.8 +/- 1.7 vs. 7.2 +/- 1.8%, p less than 0.05). The correlations between (Na+ + K+)ATPase inhibition and mean blood pressure and between WBC Na+/K+ ratio and mean blood pressure were significant (r = 0.278, p less than 0.05 and 0.270, p less than 0.05, respectively), but both were weak. However, untreated hypertensive patients with higher (Na+ + K+)ATPase inhibition had significantly higher WBC Na+/K+ ratios than untreated patients with less (Na+ + K+)ATPase inhibition. These results suggest a contribution of plasma (Na+ + K+)ATPase inhibition in the production of high blood pressure in a subset of patients with essential hypertension, which results in altered intracellular K+ concentrations.     

Erythrocyte Na/K ATPase activity and diabetes: relationship with C-peptide level

Summary Erythrocyte Na/K ATPase activity is decreased in Type I diabetic patients; for Type II diabetic patients, literature data are controversial. Therefore, we have compared this enzymatic activity in 81 patients with Type I diabetes mellitus, 87 with Type II diabetes mellitus and 75 control subjects. Mean erythrocyte Na/K ATPase activity was lower in the Type I diabetic patients (285 ± 8 nmol Pi · mg protein^–1· h^–1) than in the control subjects (395 ± 9 nmol Pi · mg protein^–1· h^–1) whereas that of the Type II diabetic patients did not differ from that of control subjects. Sex, age, body mass index, and HbA_{1 c} levels did not influence erythrocyte Na/K ATPase activity. The 25 Type II diabetic patients treated with insulin, however, had lower Na/K ATPase activity than the 62 on oral treatment (264 ± 18 vs 364 ± 16 nmol Pi · mg protein^–1· h^–1, p < 0.001) but similar to that of Type I diabetic patients. Among the Type II diabetic patients, stepwise regression analysis showed that fasting C-peptide level was the only factor independently correlated with Na/K ATPase activity; it explained 23 % of its variance. In fact, in the insulin-treated patients, those with almost total endogenous insulin deficiency (C-peptide < 0.2 nmol · l^–1) had the lower Na/K ATPase activity (181 ± 21 vs 334 ± 17 nmol Pi · mg protein^–1· h^–1, p < 0.0001). The biological effects of treatment with C-peptide have recently led to the suggestion that this peptide could have a physiological role through the same signalling pathway as insulin, involving G-protein and calcium phosphatase and thus restoring Na/K ATPase activity. The relationship we describe between endogenous C-peptide and this activity is a strong argument for this physiological role. [Diabetologia (1998) 41: 1080–1084] Received: 6 November 1997 and in final revised form: 10 April 1998     

Dietary sodium restriction, blood pressure and sympathetic activity in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were started at birth on sodium diets ranging from severely deficient (9 mumol) to a regular intake (101 mumol Na+/g food). Blood pressure and sympathetic activity were assessed at 6 and 16 weeks of age. At either age, SHR on 9 mumol Na+ failed to develop hypertension. Spontaneously hypertensive rats on 17 mumol Na+ exhibited significant blunting of the hypertension; SHR on 26 mumol showed a small amelioration. At 6 weeks, basal plasma noradrenaline was similar in SHR and WKY on 9 and 101 mumol Na+, whereas plasma adrenaline was increased in SHR at the lowest sodium level. At 16 weeks, both catecholamines were significantly increased in SHR on the 9 and 17 mumol sodium diet versus SHR on the control diet. Blood pressure responsiveness to noradrenaline was significantly decreased on 9 mumol Na+, but to a similar extent in both strains. In contrast, the blood pressure lowering effect of ganglionic blockade was markedly blunted in SHR on 9 mumol Na+ and to a lesser extent on 17 mumol Na+ (both for percentage and absolute decrease) and 26 mumol Na+ (only for absolute fall); however, this did not occur in WKY over the diet-range used. We conclude that a sodium-deficient diet from birth prevents/blunts the development of hypertension in SHR, at least partly by decreasing the pressor effect of the sympathetic nervous system.