Cellular sodium transport in essential hypertension

The 370 Da inhibitor of the sodium pump in the plasma of haemodialysis patients

BACKGROUND

Previous studies have shown that a molecule of mass 370 Da that inhibits the sodium pump can be extracted from human placentas and from the concentrated plasma or ultrafiltrate of volume-expanded patients.

AIM

To study the abundance of the 370 Da molecule and its changes across dialysis in a population of patients with renal failure treated by haemodialysis.

METHODS

4 mL pre- and post-dialysis blood samples (2 mL plasma) were taken from patients receiving intermittent haemodialysis and analysed by high performance liquid chromatography (HPLC) coupled to high sensitivity mass spectrometry.

RESULTS

In over half the study population, the 370 Da molecule was present in an abundance that exceeded the limit of quantitation. Most patients experienced a marked fall in the abundance of the molecule over a haemodiafiltration (HDF) session, though exceptions were seen in two individuals both of whom showed clear evidence for the presence of two structural isomers of the 370 Da molecule.

CONCLUSIONS

Advanced renal failure is frequently accompanied by an increased abundance of a 370 Da inhibitor of the sodium pump and that abundance is strongly impacted by haemodialysis. The technique described here could readily be applied to other clinical situations where sodium pump inhibition might be anticipated, such as hypertension, pregnancy and fetal medicine and thereby lead to a better understanding of the physiology and patho-physiology of these conditions.

Peritubular membrane potential in kidney proximal tubular cells of spontaneously hypertensive rats

Peritubular membrane potential in kidney proximal tubular cells of spontaneously hypertensive rats (SHR-Okamoto strain adult rats) was measured with conventional 3 mol KCl microelectrodes, in vivo. Peritubular cell membrane potential was not different in SHR (-66.5 ± 0.7 mV) as compared with normotensive control Wistar rats (-67.5 ± 1.2 mV). To test the effects of possible altered sodium membrane transport in SHR on proximal tubule peritubular membrane potential, we allowed SHR and control rats to drink 1% NaCl for two weeks. Again, proximal tubule peritubular membrane potential was not different in SHR on 1% NaCl (-67.0 ± 1.0 mV) as compared with control rats on 1% NaCl (-64.7 ± 1.3 mV). From these results we concluded that peritubular membrane potential in kidney proximal tubular cells of SHR was not different from normotensive Wistar control rats, and if some alteration of sodium transport in kidney proximal tubular cells of SHR could exist, that was not possible to evaluate from the measurements of peritubular membrane potential in kidney proximal tubular cells.

Selective inhibition of the cellular sodium pump by emicymarin and 14ß anhydroxy bufadienolides

Partial inhibition of the sodium pump (Na/K-ATP-ase) by a circulating inhibitor is known to occur in humans. The objectives of this study were to determine the effects of novel bufadienolides lacking an oxygen at C14 on sodium pumps in human erythrocytes and leucocytes, dog kidney and pig brain and to document the importance of the stereochemistry at C17 on the ability to inhibit these sodium pumps. 14α bufadienolides were weak inhibitors of all preparations studied. 3ß-OH,5ß,14ß bufadienolide produced near-total inhibition of dog kidney and pig brain Na/K-ATP-ase. Over the same concentration range, it maximally inhibited the sodium pump of erythrocytes by 70% and leucocytes by 47%. The inhibition profile induced in the leucocyte sodium pump deviated significantly from the simple sigmoidal relationship present in the other preparations over the 3×10(-5) to 1×10(-7) mol/l concentration range. Allo-emicymarin (17α) was confirmed to be a weak inhibitor of the sodium pump/ATP-ase compared with emicymarin (17ß) but both were weaker inhibitors of the leucocyte sodium pump than that of the other preparations. Molecules with the C14 in the ß configuration are more efficacious than in the α configuration. In the case of emicymarin, the attachment of the furone at C17 in the α configuration results in substantially weaker inhibitory activity than in the beta configuration, seen in most cardenolides and bufadienolides. Unlike ouabain and bufalin that show no specificity of action in these preparations, 3ß- OH,5ß,14ß bufadienolide selectively inhibits the activity of at least one low-prevalence subset of the leucocyte Na/K-ATP-ase.

Hypertension and the genetics of red cell membrane abnormalities

Hypertension represents the upper 15-25% of the blood pressure distribution in industrialized countries. The trait is practically absent in primitive societies and is made manifest by diet and lifestyles in industrialized countries. High blood pressure is an important risk factor for strokes, heart disease and renal disease. The frequency of hypertension is higher among blacks than among whites in the USA. Various twin, family and adoption studies indicate a strong genetic effect on blood pressure. The genetic mechanisms are unknown. Membrane transport variability has been studied in red cells as a surrogate for analogous alterations in smooth muscle or renal cells. Among the various transport systems, erythrocyte sodium-lithium countertransport (CT) has been consistently elevated in variable proportions of Caucasian hypertensives. Genetic studies of countertransport levels have shown familial aggregation and higher concordance for monozygotic than dizygotic twins. Complex segregation analysis suggests the action of a major gene superimposed on a polygenic background. The postulated gene (B) raises CT activity and has a population frequency of 0.25. CT levels of the common AA homozygotes and AB heterozygotes cannot be distinguished from each other, whereas CT activity of BB homozygotes (6% of the population) is significantly elevated. Although the CT gene contributes only 2.7% to 3.5% of the variability of blood pressure over its entire range, 14% to 20% of persons with systolic hypertension (greater than 140 mmHg) are BB homozygotes rather than the expected 6% to 7%. A much lower frequency of elevated countertransport activity among black hypertensives suggests genetic heterogeneity in the pathogenesis of high blood pressure. Further investigations on the mechanism and genetic linkage relationships of the putative CT gene may aid in elucidating an important mechanism of blood pressure elevation and will allow molecular approaches in the future.

Regulation of sodium-glucose cotransporter SGLT1 in the intestine of hypertensive rats

Experimental models of hypertension, such as spontaneously hypertensive rats (SHR), show alterations in cellular sodium transport that affects Na+-coupled cotransport processes and has been involved in the pathogenesis of this disease. The objective of the present study was to analyze the kinetic properties of the sodium-dependent glucose transport in the jejunum and ileum of SHR and its genetic control, Wistar-Kyoto (WKY) rats, as well as the regulation of the transporter, SGLT1. In hypertensive rats, the increased systolic blood pressure was accompanied by an enhancement of serum aldosterone levels compared with WKY rats, but no alterations were found in their body weight or serum glucose/insulin levels. The values for d-glucose maximal rate of transport (Vmax) were 42 and 60% lower, respectively, in the jejunum and ileum of SHR than those from WKY rats. On the other hand, the values for the Michaelis constant (Km) were similar in both animal groups, as was the diffusive component of transport (Kd). Immunoblotting and Northern blot analysis revealed the existence of a lower abundance of SGLT1 protein and mRNA in SHR. Moreover, hypertensive rats showed a decrease in the molecular mass of SGLT1 that could not be explained in terms of different glycosylation and/or phosphorylation levels or an alternative splicing in the expression of the protein. These findings demonstrate that SGLT1 is regulated at a transcriptional level in the intestine of hypertensive rats, and suggest that this transporter might participate in the dysregulation of sodium transport observed in hypertension.

Inhibitory effect of insulin on vasopressin-induced intracellular calcium response is blunted in hyperinsulinemic hypertensive patients: role of membrane fatty acid composition

Impaired insulin-mediated vasodilation has been implicated in hypertension that is associated with the metabolic syndrome. The aim of this study was to determine whether an abnormality in membrane fatty acid composition was related to a weakening of insulin's inhibitory effect on agonist-stimulated intracellular free calcium elevation. Mild to moderate hypertensive patients (n = 27) and normotensive controls (n = 11) were studied. Hypertensive patients were divided into normoinsulinemic patients (n = 14) and hyperinsulinemic patients (n = 13) according to the area under the curve of plasma insulin concentrations during a 75-g oral glucose tolerance test. Nonstimulated and arginine-vasopressin (AVP) (1 micromol/l)-stimulated intraplatelet free calcium concentrations (p[Ca(2+)](i)) were measured with or without insulin (100 microU/ml) preincubation. Platelet membrane fatty acid composition, intraerythrocyte sodium content, and the ouabain-sensitive sodium efflux rate constant (K (os)) of erythrocytes were also determined. Insulin preincubation reduced AVP-stimulated p[Ca(2+)](i) elevation in both normotensive controls and hypertensive patients. The inhibitory effect of insulin on AVP-stimulated elevation of p[Ca(2+)](i) (%Inhibition) was significantly (P < 0.05) blunted in hyperinsulinemic hypertensive patients (9.7% +/- 2.4%) as compared to normoinsulinemic hypertensive patients (17.4% +/- 2.7%) and normotensive controls (16.9% +/- 1.7%). In hypertensive patients, the %Inhibition was correlated negatively with saturated fatty acids (SFA) (r = -0.51, P < 0.05) and systolic blood pressure (r = -0.44, P < 0.05), and correlated positively with membrane polyunsaturated fatty acids (PUFA) (r = 0.53, P < 0.01) and K (os) (r = 0.53, P < 0.005). Multiple regression analysis showed that SFA, PUFA, and K (os) were the significant variables for %Inhibition. These findings indicate that an increase in SFA and a decrease in PUFA may cause insulin insensitivity in cellular calcium and sodium handling in hypertension with hyperinsulinemia.

Adverse interactions of rofecoxib with lisinopril in spontaneously hypertensive rats

BACKGROUND

Hypertension and arthritis are frequent comorbidities. Nonsteroidal anti-inflammatory drugs (NSAIDs) are well known to produce hypertension or attenuate the effects of antihypertensive agents in a few patients. The influence of selective NSAIDs on blood pressure and the cardiovascular and renal effects of coxibs have still to be investigated. The purpose of this study was to test the hypothesis that rofecoxib interferes with antihypertensive activity and cardiorenal protective effects of lisinopril in spontaneously hypertensive rats (SHRs).

METHODS

Twenty-one unanaesthetised, male spontaneously hypertensive rats (SHRs), 16 weeks old, were randomized to receive lisinopril (LS) 15 mg/kg/d or rofecoxib (RF) 20 mg/kg/d or combination of lisinopril (LS) and rofecoxib (RF) for 2 weeks. The arterial blood pressure changes were recorded each week. The Sodium Hydrogen Exchange (NHE) activity of erythrocytes was determined 2 weeks after the study. The surviving animals were sacrificed 24 h after the last dose, and the sections of their hearts and kidneys were assessed histologically for injury by a pathologist masked to the treatment.

RESULTS

RF completely prevented the hypotensive effects of LS during the first week of treatment but the antihypertensive efficacy of LS was restored during the second week of treatment. The NHE in erythrocytes of 18-week-old SHRs was found to be significantly lower than the age-matched Wistar rats (P < 0.05), and LS treatment reversed these values to Wistar control in SHRs. RF was devoid of any effect on NHE of erythrocytes. The histological examination revealed that the myocardial and renal protection induced by LS was attenuated by concomitant RF therapy.

CONCLUSIONS

These results indicate that COX-2 inhibitors should be used judiciously in patients with history of hypertension, ischemic heart disease, or chronic renal failure.

Determinants of Salt Sensitivity in Black and White Normotensive and Hypertensive Women

Salt sensitivity (SS) has been linked to human hypertension. We examined ethnic differences in the relation between SS; erythrocyte sodium (Na + i ), calcium (Ca 2+ i ), potassium (K + i ), and magnesium (Mg 2+ i ); and sodium pump activity in African-American (AA) and white women. In a crossover protocol, similar numbers of normotensive, hypertensive, AA, and white women were randomized to 7 days of a 20 meq/d and a >200 meq/d salt diet (n=199). After an overnight inpatient stay, group differences in supine blood pressure (BP), heart rate, erythrocyte cations, and sodium pump activity were measured. The prevalence of SS (53.5% vs 51%) and salt resistance (26.3% vs 30.0%) was similar in both races. Greater mean BP increase with salt loading was seen in AA vs white hypertensives but not between the normotensive women. In hypertensives, increase in mean arterial pressure was 12.6 vs 8.2 mm Hg in AAs vs whites, respectively ( P <0.01), and for systolic BP, it was 23 vs 14.8 mm Hg ( P <0.01). Higher Na + i and Ca 2+ i were noted in SS and salt-intermediate AA than in the corresponding white subjects. Na + i , Ca 2+ i , and the ratios of Na + i to K + i and of Ca 2+ i to Mg 2+ i were positively correlated with salt responsiveness in AA but not in white women. Sodium pump activity was similar between groups, although the change in maximal activity trended to vary inversely with SS in AA. In closely matched AA and white women, the prevalence of SS is similarly high in both races, although the magnitude of BP increase is greater in AA hypertensives. In AA but not in whites, SS is positively associated with Na + i , Ca 2+ i , and the ratios of Na + i to K + i and of Ca 2+ i to Mg 2+ i .

Angiotensin II-dependent increased expression of Na+-glucose cotransporter in hypertension

Glucose uptake is increased in hypertension. Thus we investigated Na+-glucose cotransporter (SGLT2) activity and expression in proximal tubules from renovascular hypertensive rats. Sham-operated rats, aortic coarctation rats, and aortic coarctation rats treated with either ramipril (2.5 mg.kg-1.day-1 for 21 days) or losartan (10 mg.kg-1.day-1 for 21 days) were used. Na+-dependent glucose uptake was measured in brush-border membrane vesicles (BBMV). Vmax in BBMV from hypertensive rats was greater compared with those from normotensive rats (3 +/- 0.2 vs. 1.5 +/- 0.1 nmol.mg protein-1.min-1) without a change in Km. Renal immunostaining was greater, and Western blot analysis and RT-PCR showed a higher expression of SGLT2 in hypertensive rats than in normotensive rats (1,029 +/- 71 vs. 5,003 +/- 292, 199 +/- 15 vs. 95 +/- 10, and 1.4 +/- 0.2 vs. 0.3 +/- 0.1 arbitrary units, respectively). In rats treated with either ramipril or losartan, Vmax decreased to 2.1 +/- 0.3 and 1.8 +/- 0.4 nmol.mg protein-1.min-1, respectively, as well as did the intensity of immunostaining and levels of protein and mRNA. We suggest that in renovascular hypertension, angiotensin II induced SGLT2 via the AT1 receptor, which was evidenced at both the functional and expression levels, probably contributing to increased absorption of Na+ and thereby to the development or maintenance of 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.

General overview of mineralocorticoid hormone action

The adrenal cortex elaborates two major groups of steroids that have been arbitrarily classified as glucocorticoids and mineralocorticoids, despite the fact that carbohydrate metabolism is intimately linked to mineral balance in mammals. In fact, glucocorticoids assured both of these functions in all living cells, animal and photosynthetic, prior to the appearance of aldosterone in teleosts at the dawn of terrestrial colonization. The evolutionary drive for a hormone specifically designed for hydromineral regulation led to zonation for the conversion of 18-hydroxycorticosterone into aldosterone through the catalytic action of a synthase in the secluded compartment of the adrenal zona glomerulosa. Corticoid hormones exert their physiological action by binding to receptors that belong to a transcription factor superfamily, which also includes some of the proteins regulating steroid synthesis. Steroids stimulate sodium absorption by the activation and/or de novo synthesis of the ion-gated, amiloride-sensitive sodium channel in the apical membrane and that of the Na+/K+-ATPase in the basolateral membrane. Receptors, channels, and pumps apparently are linked to the cytoskeleton and are further regulated variously by methylation, phosphorylation, ubiquination, and glycosylation, suggesting a complex system of control at multiple checkpoints. Mutations in genes for many of these different proteins have been described and are known to cause clinical disease.

Abnormal platelet Ca2+ handling accompanied by increased cytosolic free Mg2+ in essential hypertension

To test the hypothesis that abnormal platelet Ca2+ handling in essential hypertension results from cellular Mg2+ deficiency, cytosolic free Mg2+ concentration ([Mg2+]i) and Ca2+ metabolism were studied in mag-fura 2 and fura 2-loaded platelets from 30 essential hypertensive patients and 30 sex- and age-matched normotensive controls. Basal cytosolic free Ca2+ concentration ([Ca2+]i) and intracellular Ca2+ discharge capacity were higher in hypertensives than in normotensives (22 +/- 5 vs. 18 +/- 5 nM, P < 0.05; 743 +/- 250 vs. 624 +/- 144 nM, P < 0.05, respectively). The thrombin (0. 03-1.0 U/ml)-evoked [Ca2+]i response was also enhanced in platelets from hypertensives in both the absence and presence of extracellular Ca2+. However, basal [Mg2+]i was higher in hypertensives than in normotensives (437 +/- 110 vs. 353 +/- 85 microM, P < 0.05), whereas serum Mg2+ was similar in the two groups. These results oppose the Mg2+ deficiency hypothesis in platelets in essential hypertension.

Erythrocyte passive potassium flux is increased in patients with ischemic coronary disease (ICD) and in subjects with family history of ICD

BACKGROUND

It has been proposed that ischemic coronary disease (ICD) associated potassium loss could be due to modifications of potassium permeability. We investigated whether a positive family history of ICD can influence this parameter. We have compared potassium permeability in erythrocytes from ICD patients and from positive family history subjects (FICD) with control subjects.

METHODS

All patients and subjects were carefully selected for the absence of hypertension and dysmetabolic pathologies. ICD group: 24 patients (19 males, 5 females; ages 43 to 69) all affected by ischemic coronary disease, under no drug treatment; FICD group: 18 subjects (all males, ages 27 to 42) with a verified positive ICD family history, without hypertensive family history and cardiovascular pathology; control group: 16 subjects (11 males, 5 females; ages 28 to 48) without positive family history of ICD. Passive potassium efflux (PPE) was spectrophotometrically measured in K-free medium containing ouabain and bumetanide. The kinetic constant was calculated by dividing PPE by the erythrocyte potassium concentration.

RESULTS

No statistically significant differences were noted between the intracellular potassium content of the three groups. However, (1) the passive potassium permeability of the ICD group was significantly higher (kK=0.055 +/- 0.021 h(-1), n=24) than that of the control group (kK=0.023 +/- 0.008 h(-1), n= 16; p<0.00001), (2) the FICD group was higher (kK=0.036 +/- 0.012 h(-1), n=18) than the control group (p<0.001), and (3) the ICD group was higher than the FICD group (p<0.001).

CONCLUSIONS

Our results suggest an inheritability of ICD, paralleling the familial aggregation of the pathology. Erythrocyte potassium permeability could represent an early marker of ischemic coronary disease and be used as a prophylactic tool.

A possible mechanism for alteration of human erectile function by digoxin: inhibition of corpus cavernosum sodium/potassium adenosine triphosphatase activity

PURPOSE

Digoxin use has long been recognized to affect adversely male sexual function but the underlying mechanism is poorly understood. Digoxin is a known inhibitor of sodium/potassium adenosine triphosphatase (sodium pump), a plasma membrane enzyme that has a role in the regulation of smooth muscle tone. We investigated the effects of digoxin on human corpus cavernosum smooth muscle contractility and overall erectile function.

MATERIALS AND METHODS

In human corporeal smooth muscle strips the in vitro effects of digoxin were assessed on sodium pump activity as measured by digoxin inhibitable uptake of 86rubidium, basal tone and endothelium dependent, neurogenic and nitric oxide donor induced relaxation. An in vivo prospective double-blind, placebo controlled, crossover, 4-period investigation was performed in 6 healthy male volunteers. The effects of digoxin on serum hormones, erectile function questionnaire, visual sexual stimulation and nocturnal penile tumescence were recorded.

RESULTS

In vitro digoxin caused concentration dependent inhibition of 86rubidium uptake (half maximum effect at 0.01 microM.) and contraction of corporeal smooth muscle (half maximum effect at 0.8 microM.). Therapeutic concentrations of digoxin (2 nM.) also inhibited relaxation induced by acetylcholine and electrical field stimulation, which release nitric oxide from corpus cavernosum endothelial cells and nonadrenergic noncholinergic nerves, respectively. In vivo digoxin diminished penile rigidity during visual sexual stimulation and nocturnal penile tumescence testing compared to placebo without influencing libido or serum testosterone, estrogen or luteinizing hormone levels.

CONCLUSIONS

Digoxin associated alteration of human erectile function may be explained, in part, by inhibition of corporeal smooth muscle sodium pump activity, which promotes contraction and impedes nitric oxide induced relaxation. Such findings suggest therapeutic use of digoxin for treatment of recurrent priapism states.

Role of ion channels and exchangers in mechanical stretch-induced cardiomyocyte hypertrophy

We have previously reported that stretching of cardiomyocytes activates the phosphorylation cascade of protein kinases, including Raf-1 kinase and mitogen-activated protein (MAP) kinases, followed by an increase in protein synthesis partly through enhanced secretion of angiotensin II and endothelin-1. Membrane proteins, such as ion channels and exchangers, have been postulated to first receive extracellular stimuli and evoke intracellular signals. The present study was performed to determine whether mechanosensitive ion channels and exchangers are involved in stretch-induced hypertrophic responses. Neonatal rat cardiomyocytes cultured on expandable silicone dishes were stretched after pretreatment with a specific inhibitor of stretch-sensitive cation channels (gadolinium and streptomycin), of ATP-sensitive K+ channels (glibenclamide), of hyperpolarization-activated inward channels (CsCl), or of the Na+-H+ exchanger (HOE 694). Pretreatment with gadolinium, streptomycin, glibenclamide, and CsCl did not show any inhibitory effects on MAP kinase activation by mechanical stretch. HOE 694, however, markedly attenuated stretch-induced activation of Raf-1 kinase and MAP kinases by approximately 50% and 60%, respectively, and attenuated stretch-induced increase in phenylalanine incorporation into proteins. In contrast, HOE 694 did not inhibit angiotensin II-and endothelin-1-induced Raf-1 kinase and MAP kinase activation. These results suggest that among many mechanosensitive ion channels and exchangers, the Na+-H+ exchanger plays a critical role in mechanical stress-induced cardiomyocyte hypertrophy.

Sodium chloride and hypertension

The hypothesis that sodium chloride deficiency, and not its overuse, is prime cause of hypertension and arteriosclerosis is presented. In the author's home town--a farflung part of northern China--hypertension is a rare disease and arteriosclerosis is a virtually unknown condition. The average intake of sodium chloride for these people is > 30 g/day compared with the typical sodium chloride intake of 10-12 g per day in the USA. When the 10-12 g salt ingested is mixed with the average daily water intake (2100 ml), 0.47% to 0.57% saline mixture is produced, which is hypotonic to extracellular fluid in salt content. Thus sodium conservation becomes necessary. All the hormones and ions involved in sodium conservation are inducers of hypertension; these include aldosterone, angiotensin 11, glucocorticoids, catecholamine, and vasopression. Plus, potassium waste, induced under the influence of aldosterone excess, participates in the development of hypertension.

Baseline sodium-lithium countertransport and 6-year incidence of hypertension. The Gubbio Population Study

BACKGROUND

Sodium-lithium countertransport (Na-Li CT) activity is high in persons with hypertension. This study investigated whether high Na-Li CT relates to development of hypertension.

METHODS AND RESULTS

At the baseline visit of the Gubbio Population Study, 4210 people of the 5376 surveyed were 18 to 74 years old; of these, 1599 were hypertensive (systolic pressure > or = 140 mm Hg, or diastolic pressure > or = 90 mm Hg, or on antihypertensive drug therapy). Of the 2611 nonhypertensives, 302 did not have Na-Li CT measured and 580 did not participate in 6-year follow-up. This analysis, therefore, deals with data collected on 1729 men 18 to 74 years old and women 18 to 74 years old who at baseline were nonhypertensive and had Na-Li CT measurement. Compared with individuals who were nonhypertensive at baseline and follow-up, individuals with incident hypertension at follow-up (systolic pressure > or = 140 mm Hg, or diastolic pressure > or = 90 mm Hg, or on antihypertensive drug therapy) had higher baseline values of Na-Li CT, blood pressure, age, body mass index, plasma cholesterol, and alcohol intake (P < .05). Baseline Na-Li CT was positively associated (P < .05) with development of hypertension in quartile analysis, with highest incidence of hypertension among men and women with Na-Li CT in the highest quartile (for men, > or = 376 and for women, > or = 311 mumol Li-L red blood cells-1.h-1). In univariate logistic regression, incidence of hypertension was related to baseline value of Na-Li CT, blood pressure, age, body mass index, plasma cholesterol, and alcohol intake (P < .05). In multiple logistic regression analysis, individuals with baseline Na-Li CT higher by 127 mumol (pooled SD for men and women) had 1.23 times greater risk of incident hypertension with control for sex and baseline age, body mass index, systolic pressure, and other confounders (P < .001).

CONCLUSIONS

Na-Li CT is a predictor of hypertension risk in adults.

Altered intracellular calcium and phorbol 12,13-dibutyrate binding to intact platelets in young obese subjects

The study was designed to examine cytosolic free calcium ((Ca2+)i) and phorbol dibutyryl ester binding in intact platelets of young obese subjects as compared with the platelets of age-matched subjects with non-insulin-dependent diabetes mellitus (NIDDM) and those of healthy control subjects. The assay was studied in basal and thrombin-stimulated conditions. The binding parameter of phorbol ester is a criterion for active protein kinase C (PKC) units in the platelet plasma membrane. The resting (Ca2+)i correlated with body mass index (BMI)(r = 0.385, p = 0.0034) and plasma insulin level (r = 0.316, p = 0.0269), and the resting (Ca2+)i level was higher in the obesity group (160.6 +/- 15.8 nmol/L; n = 25) than controls (78.9 +/- 7.6 nmol/L; n = 24, p < 0.0001). Among the obesity and control groups, there was a correlation between BMI and fasting plasma insulin level (r = 0.399, p = 0.0237). Systolic blood pressure correlated with BMI(r = 0.504, p = 0.0005). The mean systolic blood pressure of the obesity group was higher than those of the other two groups. The mean Hill coefficient for thrombin-treated platelets of phorbol dibutyrate binding was higher in the obesity group when compared with healthy controls and the subjects with NIDDM (1.47 +/- 0.21 vs 1.06 +/- 0.16 and 0.99 +/- 0.09, respectively; p < 0.05). In conclusion, young subjects with simple obesity have already developed altered platelet Ca2+ regulation that is usually observed in adult patients with a number of metabolic diseases. These data are interpreted to indicate that a relationship exists between dysregulation of PKC and impaired glucose tolerance that precedes other complications of obesity.

Altered contractility of urinary bladder in diabetic rabbits: relationship to reduced Na+ pump activity

We studied the effect of alloxan-induced diabetes on Na+ pump activity in isolated rabbit bladder strips. In addition, the effects of diabetes and the Na+ pump inhibitor ouabain on contractions induced by carbachol (CCh) and KCl were studied. In bladder strips from diabetic rabbits, ouabain-sensitive 86Rb+ uptake (a measure of Na+ pump activity) was approximately 50% less compared with strips from normal bladder. Diabetes also reduced the maximum contractions induced by CCh and KCl. Treatment of bladder strips with ouabain alone caused an acute concentration-dependent increase in tone. In contrast, longer incubation with ouabain inhibited CCh- and KCl-induced contractions in normal and diabetic bladders. Furthermore, differences in agonist-mediated contractions observed between normal and diabetic bladders were abolished in the presence of the maximally effective concentration of ouabain (10 microM). The ability of CCh to cause contraction in normal and diabetic rabbit bladders was also significantly inhibited by the Na+ ionophore monensin but not by the Ca2+ ionophore A-23187 or by depolarization with KCl. Monensin also inhibited KCl-induced contractions in normal bladder strips. These results indicate that 1) Na+ pump activity is an important modulator of bladder smooth muscle tone, 2) diabetes diminishes Na+ pump activity and inhibits agonist-induced contractions in bladder, and 3) an increase in intracellular Na+ concentration, secondary to inhibition of bladder smooth muscle Na+ pump activity, is associated with reduced responsiveness to contractile agonists. Diminished Na+ pump activity in diabetes may, in part, contribute to the development of bladder cystopathy.

Sodium-lithium countertransport and blood pressure change over time: the Gubbio study

Sodium-lithium countertransport activity in red blood cells relates to blood pressure (BP) and the prevalence of hypertension. This study investigated in adults the relation of sodium-lithium (Na-Li) countertransport to BP change from baseline to 6-year follow-up. In the Gubbio Population Study, 4210 men and women were 18 to 74 years old at baseline (1983-1986), and 3766 had a valid baseline Na-Li countertransport measurement; of these, 2729 were reexamined at 6 years of follow-up (1989-1992) and made up the study cohort. At baseline, data collection included age, height, weight, BP, pulse rate, drug treatment, alcohol intake, ratio of sodium to potassium in spot urine, plasma cholesterol, and Na-Li countertransport in red blood cells. At 6-year follow-up, data for age, BP, and drug treatment were collected as at baseline. From baseline, average BP declined for people on antihypertensive medication at follow-up and for those with baseline BP greater than or equal to 140/90 mm Hg (systolic/diastolic) and did not change or increased for the remaining participants. In quartile and correlation analyses controlled for sex, baseline BP, and antihypertensive treatment, BP change related significantly and directly to baseline Na-Li countertransport. In multiple linear regression analyses done for the entire cohort with control for other confounders, the regression coefficient of baseline Na-Li countertransport to BP change over time was positive and borderline significant. The Na-Li countertransport coefficient was positive and significant when analyses were done with the use of a categorical value of baseline Na-Li countertransport (quartile 4 and quartiles 1 through 3 combined). In both models, the Na-Li countertransport coefficient was the strongest for people with baseline BP greater than or equal to 120/80 mm Hg or for people with baseline age of 45 years or older. In conclusion, Na-Li countertransport significantly relates to BP change over time in adults.

Erythrocyte Na+, K+ and Ca2+, Mg(2+)-ATPase activities in hypertensives on angiotensin-converting enzyme inhibitors

OBJECTIVE

To investigate erythrocyte membrane Na+, K(+)- and Ca2+, Mg(2+)-ATPase activities in newly diagnosed hypertensive patients before and after 2, 4, and 6 months of treatment with enalapril or captopril as monotherapy.

METHODS AND RESULTS

Na+, K(+)-ATPase activity (nmol ATP hydrolysed/min per mg protein) rose by 6 months of treatment in both groups when values were compared in each treated group over time (4.5 +/- 0.8 to 9.9 +/- 1.2; 4.9 +/- 0.8 to 10.5 +/- 1.7, respectively, p < 0.001 for both). When the treated groups were compared with controls at each period of time, Na+, K(+)-ATPase activity was higher at months 4 and 6 (p < 0.001) for both groups, respectively). Ca2+, Mg(2+)-ATPase activity (nmol ATP hydrolyzed/min per milligram protein) in the absence and in the presence of calmodulin increased in the enalapril (6.4 +/- 0.7 to 8.9 +/- 0.95, p < 0.05; 13.4 +/- 1.2 to 17.2 +/- 1.2, p < 0.05, respectively) and captopril (7.0 +/- 0.6 to 8.5 +/- 0.7; 14.4 +/- 1.1 to 16.0 +/- 1.0, p < 0.05, respectively) groups after 6 months of treatment compared within each treated group over time. When patient groups were compared with controls at time 0, 2, 4, and 6 months, the pump activity was higher in the treated groups at 6 months.

CONCLUSION

The long-term enhancement of cell membrane Na+, K(+)-and Ca2+, Mg(2+)-ATPase activity associated with enalapril and captopril therapy may represent a specific effect of these agents or alternatively, a nonspecific outcome of blood pressure reduction.

Increased sodium-dependent D-glucose transport in the jejunal brush-border membrane of spontaneously hypertensive rat

The current studies explore the effect of hypertension on D-glucose transport into jejunal brush-border membrane vesicles (BBMV). Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, as a control group, were used. The purity of the BBMV from both groups of animals was validated by the finding that the specific activity of brush-border enzyme marker, sucrase, was severalfold greater in membrane vesicles compared with corresponding values in mucosal homogenate. D-glucose uptake was Na+ dependent in both groups of animals, with a transient increase in the intravesicular concentration of D-glucose. However, the initial rate and the magnitude of the accumulation of Na+-dependent D-glucose was significantly higher in SHR compared with WKY rats. In order to investigate the mechanism(s) for the increase in Na+-dependent D-glucose transport in SHR, several experiments were performed: (1) an experiment that indicated 22Na uptake, as an indicator for Na+ permeability, was similar between SHR and WKY rats, (2) kinetic studies that indicated that Vmax values of SHR were significantly greater that those of WKY rats. In contrast, similar Km values for glucose were found between SHR and WKY rats, (3) Na+-dependent phlorizin binding measurements that were not altered by hypertension and (4) a study of the brush-border membrane lipid composition that showed a significant increase in the free cholesterol/phospholipid ratio in SHR. We conclude that altered membrane cholesterol content and consequently altered lipid fluidity could be, at least in part, responsible for the observed increase in Na+-dependent D-glucose transport in SHR.

Intracellular cations and hypertension in blacks

Considerable attention has been focused in recent years on the role of intracellular ions in the pathophysiology of hypertension in African Americans. Following the identification of marked differences in red cell sodium content and sodium-lithium counter-transport between blacks and whites, the hypothesis emerged that cation metabolism at the cellular level might account for part of the ethnic difference in susceptibility to hypertension. Unfortunately, findings in the red cell have not significantly increased our understanding of the physiologic pathways and may prove to be anomalous. Interest has recently shifted to calcium metabolism, because of its greater physiologic relevance, and a new series of questions are being defined. With the development of fluoroprobes to measure sodium and calcium simultaneously, wider application of pharmacologic agonists and the use of single cell techniques have provided a new direction for this field. Whether the ethnic contrasts observed for sodium in the red cell can be reproduced in platelets remains to be seen. It may be that the earlier red cell differences were epiphenomena, unrelated to the control of blood pressure, and that the more closely one approaches basic physiologic mechanisms, the greater the cross-ethnic group similarity. Rather than drawing attention to unusual phenotypic characteristics, the study of hypertension in blacks may be more instructive for the insight it provides into the basic physiology of this disorder, common to all ethnic groups.

Influence of physiological factors on the age-related increase in blood pressure in healthy men

The independent and collective influences of several physiological factors on the age-related increase in blood pressure in healthy men were examined. Twenty-seven younger and 25 older, mostly normotensive, healthy men were studied. Blood pressure, body fat, body fat distribution, maximal oxygen consumption (VO2max), plasma norepinephrine, dietary Na, and erythrocyte Na-K pump activity were measured. Older men showed 57% higher percent body fat, 40% higher plasma norepinephrine concentration, 14% greater mean arterial blood pressure (MAP), and 5% higher plasma K concentration than younger men (all p < 0.01). Older men showed a 38% (p < 0.01) lower VO2max, 19% (p < 0.05) lower energy intake, 18% (p < 0.05) lower Na-K pump rate constant, and a 17% (p < 0.05) lower Na-K pump rate. Group means for MAP were adjusted for combinations of plasma norepinephrine, waist:thigh ratio, VO2max, and the Na-K pump rate constant, to determine if any one variable or combination could account for the age related increase in MAP. Statistical adjustment for plasma norepinephrine, waist:thigh ratio, and Na-K pump rate constant eliminated the significant difference between MAPs for the two groups. Thus, alterations in sympathetic nervous system activity, body fat distribution, and the membrane Na-K pump activity independently contribute to the age-related increase in MAP in healthy men.

Up-regulation of intracellular signalling pathways may play a central pathogenic role in hypertension, atherogenesis, insulin resistance, and cancer promotion--the 'PKC syndrome'

The modern diet is greatly different from that of our paleolithic forebears' in a number of respects. There is reason to believe that many of these dietary shifts can up-regulate intracellular signalling pathways mediated by free intracellular calcium and protein kinase C, particularly in vascular smooth muscle cells; this disorder of intracellular regulation is given the name 'PKC syndrome'. PKC syndrome may entail either a constitutive activation of these pathways, or a sensitization to activation by various agonists. The modern dietary perturbations which tend to induce PKC syndrome may include increased dietary fat and sodium, and decreased intakes of omega-3 fats, potassium, calcium, magnesium and chromium. Insulin resistance may be both a cause and effect of PKC syndrome, and weight reduction and aerobic training should act to combat this disorder. PKC syndrome sensitizes vascular smooth muscle cells to both vasoconstrictors and growth factors, and thus promotes both hypertension and atherogenesis. In platelets, it induces hyperaggregability, while in the microvasculature it may be a mediator of diabetic microangiopathy. In vascular endothelium, intimal macrophages, and hepatocytes, increased protein kinase C activity can be expected to increase cardiovascular risk. Up-regulation of protein kinase C in stem cells may also play a role in the promotion of 'Western' fat-related cancers. Practical guidelines for combatting PKC syndrome are suggested.

Estimated urinary albumin index: a predictor of microalbuminuria in type 2 diabetes

This study examined factors contributing to the development of microalbuminuria in diabetic patients. A total of 236 patients with Type 2 diabetes were studied: 143 were normoalbuminuric and 86 were also normotensive. Multiple regression analysis was used to identify factors influencing the urinary albumin index (UAI), an index of proteinuria based on urinary albumin adjusted for urinary creatinine. Significant factors (retinopathy, systolic blood pressure, and glycosylated haemoglobin) were used to generate a formula for estimating the log(e) UAI. Target values for systolic blood pressure and glycosylated haemoglobin to maintain the urinary albumin index at or below 22 were determined for different degrees of retinopathy. Normoalbuminuric patients were followed for 3 years to evaluate their progression to microalbuminuria. Each month, blood pressure, urinary albumin and creatinine, and glycosylated haemoglobin were measured. In normotensive, normoalbuminuric patients, initial urinary albumin index and log(e) UAI were significantly higher in patients who subsequently developed microalbuminuria. Patients with initial log(e) UAI > 3.09 or initial glycosylated haemoglobin > 6.0% also showed greater progression to microalbuminuria. Hyperglycaemia was an independent factor for the development of microalbuminuria in Type 2 diabetes. The urinary albumin index was most significantly affected by retinopathy, systolic blood pressure, and glycosylated haemoglobin. The estimated loge UAI calculated from these factors is a useful predictor of progression to microalbuminuria.

Serum insulin levels, 24-hour blood pressure profile, and left ventricular mass in nonobese hypertensive patients

In essential hypertensive patients, considered to be insulin-resistant, a blunted decline in nocturnal blood pressure is associated with increased adrenergic tone and left ventricular mass. Since insulin stimulates the sympathetic system, we tested whether insulin resistance and insulinemia influence left ventricular mass and the 24-hour blood pressure profile. We studied 29 nonobese hypertensive patients with office diastolic pressure between 95 and 110 mm Hg and normal oral glucose tolerance test after a 4-month washout period. They were then assigned to M-mode echocardiographic evaluation and 24-hour ambulatory blood pressure monitoring. The glucose and insulin responses to a 75-g oral glucose load were compared with those obtained in 16 weight-matched normotensive control subjects. During the oral glucose tolerance test the hypertensive patients compared with control subjects presented higher levels of glucose at 60 minutes (138.7 +/- 30.3 versus 108.7 +/- 35.7 mg/dL; P < .05) and 90 minutes (114.0 +/- 23.8 versus 94.8 +/- 31.1 mg/dL; P < .05) and insulin at 60 minutes (287.1 +/- 259.4 versus 142.1 +/- 83.9 pmol/L; P < .05). However, peak insulin levels after glucose load did not correlate with ambulatory blood pressure values or left ventricular mass index. Left ventricular mass index showed significant correlation with mean sleeping systolic pressure (rs = 56, P < .05) and diurnal systolic pressure (rs = .37, P < .05) but not with mean diurnal or sleeping diastolic pressures. In conclusion, our results indicate that in nonobese hypertensive patients, insulin resistance does not have any influence on the 24-hour blood pressure profile or on left ventricular mass index.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible role of Na(+)-K(+)-ATPase in the regulation of human corpus cavernosum smooth muscle contractility by nitric oxide

1. This study was designed to determine the role of sodium-potassium adenosine triphosphatase (Na(+)-K(+)-ATPase) in the regulation of human corpus cavernosum smooth muscle contractility by nitric oxide (NO). In addition, we determined if the modulation of Na(+)-K(+)-ATPase activity by NO is dependent on the increase in intracellular cyclic GMP concentration. 2. The effect of NO donors, sodium-nitroprusside (SNP) and S-nitroso-glutathione (S-NO-Glu), and a permeable cyclic GMP analogue, 8-bromo-cyclic GMP, on Na(+)-K(+)-ATPase activity (measured as ouabain-sensitive 86Rb-uptake) was studied in human cultured corpus cavernosum smooth muscle cells (HCCSMC). In addition, the effect of the cyclic GMP lowering agent, methylene blue, on NO-induced increase in Na(+)-K(+)-ATPase activity was studied. 3. SNP (1 microM) caused time-dependent increases in ouabain-sensitive Rb-uptake (33-72%) over 2-20 min in HCCSMC. The stimulation of ouabain-sensitive Rb-uptake by SNP was concentration-dependent (30 and 102% with 0.1 and 1 microM SNP, respectively). Similarly, significant increases in ouabain-sensitive Rb-uptake were obtained with 1 and 10 microM S-NO-Glu. In contrast, incubation of HCCSMC with 8-bromo-cyclic GMP (100 microM) did not increase ouabain-sensitive Rb-uptake. 4. S-NO-Glu induced-increase in intracellular cyclic GMP synthesis, but not the increase in ouabain-sensitive Rb-uptake, was completely inhibited by methylene blue in HCCSMC. 5. The Na(+)-K(+)-ATPase inhibitor, ouabain, caused a concentration-dependent increase in tension (0.5 to 2 fold) in tissues contracted with 15 mM KCl. SNP and S-NO-Glu caused a concentration-dependent relaxation (concentration required to cause half maximal relaxation (ED50) = 0.04 and 0.2 microM, respectively) of HCC strips contracted with 15 mM K+. Ouabain (0.1 to 10 microM) inhibited the response to SNP and S-NO-Glu by shifting the concentration-response curves to the right and preventing full smooth muscle relaxation.6. These results indicate that the activity of Na+-K+-ATPase modulates the contractility of HCC smooth muscle, and that NO stimulates Na+-K+-ATPase activity in HCCSMC independently of its ability to increase the intracellular cyclic GMP concentration. They also suggest that stimulation of Na+-K+-ATPase activity plays an important role in NO-induced relaxation of HCC smooth muscle

Insulin resistance in systemic hypertension: pharmacotherapeutic implications

Systemic hypertension, a vascular disease with multiple origins, now is being linked to subtle abnormalities in glucose metabolism, which include insulin resistance and hyperinsulinemia. These conditions often occur together in patients with obesity, noninsulin-dependent diabetes, or both. Hyperinsulinemia and insulin resistance may cause systemic hypertension through multiple mechanisms. Insulin has a salt-retaining effect on the kidney. Also, insulin can augment catecholamine release, increase vascular sensitivity to vasoconstrictor substances, and decrease vascular sensitivity to vasodilator substances. In addition, insulin can increase production of tissue growth factors and help retain sodium and calcium in cells. Insulin resistance in patients can be treated with regular aerobic exercise, weight reduction, and a high-fiber diet. Pharmacologic approaches include hypoglycemic drugs, weight-reducing agents, and certain antihypertensive drugs that may have a favorable impact on both blood pressure and insulin resistance.

Erythrocyte Na+/K(+)-ATPase and membrane and serum lipid profiles: as related to alcohol, body mass index and blood pressure

Erythrocyte Na+/K(+)-pump activities have been measured in hypertensives, alcohol consumers and obese persons, but the results have been variously reported as decreased, increased or unchanged. We analyzed the relationships between erythrocyte Na+/K(+)-ATPase activities and the membrane and serum lipid profiles in 83 middle-aged men, to clarify the reasons for these inconsistencies. Increases in erythrocyte Na+/K(+)-ATPase activity related closely to decreases in cholesterol to phospholipid (C/P) ratio of the erythrocyte membrane. Decreases in the C/P ratio in turn related closely to elevations of serum triglycerides (TG) with increasing body mass index, and weakly to the volume of alcohol consumed. Thus, erythrocyte Na+/K(+)-ATPase activities depend largely on the membrane and serum lipid profiles as related to body weight and alcohol consumption, and which may be a cause of the previous conflicting findings. Erythrocyte Na+/K(+)-ATPase showed a positive association with blood pressure, independently of age, body mass index and serum gamma-glutamyl transpeptidase levels. Although the biological link of elevated erythrocyte Na+/K(+)-ATPase with the rise in blood pressure remains unclear, it may be a reflection of hyperinsulinemia in the subjects with a higher blood pressure due to overweight or excessive alcohol consumption.

Depressed cheek cell sodium transport in human hypertension

Na+ transport activity was measured in cheek cells from untreated hypertensive subjects and age-matched normotensive controls identified from a blood pressure screening program. Cheek cells were isolated by a simple mouth wash procedure and Na+ transport activity was measured as the proton-dependent uptake of 22Na+ using a rapid filtration assay. The rate of Na+ uptake was about 45% lower in hypertensive subjects and this difference persisted in a follow up study 2 years later involving those subjects who remained untreated for their hypertension. The proton independent Na+ uptake was also reduced by about 46% in the hypertensive group. The increase in the rate of cheek cell Na+ transport with increasing transcellular proton gradient values was also significantly lower in hypertensive subjects. The reduced cheek cell Na+ transport observed in hypertensive subjects may indicate decreased activity of the Na+/H+ antiporter and/or changes in the ion permeability properties of the cheek cell plasma membrane in the hypertensive state. This novel assay provides a biochemically based method for discriminating between normotensive and hypertensive subjects and makes use of tissue which can be obtained in a relatively non-invasive manner.

The lymphocyte Na+/H+ antiport: activation in primary hypertension and during chronic NaCl-loading

Increased activity of the Na+/H+ antiport may be a major abnormality in essential hypertension. The activity of this transport system was investigated in lymphocytes from 13 patients with untreated essential hypertension (Ht) and 13 normotensive control subjects (Nt) on an ad libitum (130-170 mmol d-1) NaCl intake. Furthermore, the effects of different states of NaCl balance on lymphocyte Na+/H+ antiport were evaluated in two groups of Nt volunteers receiving 20 vs. 300 mmol d-1 (n = 8) and 85 vs. 200 mmol d-1 (n = 14) of NaCl for 1 week each and in seven Ht patients (20 vs. 300 mmol NaCl d-1 for 1 week each). Additionally, during the 20 and 300 mmol/d NaCl intake red blood cell membrane transport was studied in eight subjects. For the determination of lymphocyte antiport activity, cells were loaded with the cytosolic pH (pHi) indicator bis-carboxyethyl carboxyfluorescein (BCECF-AM) and acidified by addition of different amounts of Na(+)-propionate (5-40 mM). Initial pHi-recovery was taken as the activity of the antiport system and plotted against pHi-values after acidification. Non-linear regression analysis yielded higher 'apparent' maximal transport rates in Ht than Nt (Nt: 2.00 +/- 0.22; Ht: (3.81 +/- 0.59) x 10(-3) s-1; P < 0.025). In contrast, baseline pHi-values and pHi-values at half-maximal activity (pK) were identical in Nt and Ht. In normotensive control subjects on an NaCl intake of 20, 85, 200 and 300 mmol d-1 for 7 d, 'apparent' maximal transport rates averaged 2.75 +/- 0.20, 2.89 +/- 0.17, 2.81 +/- 0.18 and (3.62 +/- 0.25) x 10(-3) s-1, respectively. Thus, antiport activity was significantly (P < 0.05) stimulated on the 300 mmol d-1 intake as compared to the three other NaCl intakes. The extreme intakes of NaCl (20 vs. 300 mmol d-1) in normotensive volunteers did not affect the erythrocyte Na+/K+ pump, Na+/K+ cotransport and Na+/Li+ countertransport. Our study supports the concept that a group of patients with primary hypertension exhibit an activated Na+/H+ antiport. Furthermore, our data demonstrate that a chronic high intake of NaCl is associated with an increase in lymphocyte antiport activity towards the high values observed in primary hypertension.

Glucose-induced changes in Na+/H+ antiport activity and gene expression in cultured vascular smooth muscle cells. Role of protein kinase C

Increased Na+/H+ antiport activity has been implicated in the pathogenesis of hypertension and vascular disease in diabetes mellitus. The independent effect of elevated extracellular glucose concentrations on Na+/H+ antiport activity in cultured rat vascular smooth muscle cells (VSMC) was thus examined. Amiloride-sensitive 22Na+ uptake by VSMC significantly increased twofold after 3 and 24 h of exposure to high glucose medium (20 mM) vs. control medium (5 mM). Direct glucose-induced Na+/H+ antiport activation was confirmed by measuring Na(+)-dependent intracellular pH recovery from intracellular acidosis. High glucose significantly increased protein kinase C (PKC) activity in VSMC and inhibition of PKC activation with H-7, staurosporine, or prior PKC downregulation prevented glucose-induced increases in Na+/H+ antiport activity in VSMC. Northern analysis of VSMC poly A+ RNA revealed that high glucose induced a threefold increase in Na+/H+ antiport (NHE-1) mRNA at 24 h. Inhibiting this increase in NHE-1 mRNA with actinomycin D prevented the sustained glucose-induced increase in Na+/H+ antiport activity. In conclusion, elevated glucose concentrations significantly influence vascular Na+/H+ antiport activity via glucose-induced PKC dependent mechanisms, thereby providing a biochemical basis for increased Na+/H+ antiport activity in the vascular tissues of patients with hypertension and diabetes mellitus.

Insulin resistance--not hyperinsulinemia--is pathogenic in essential hypertension

A correlation between essential hypertension and insulin resistance/hyperinsulinemia is well documented, and there is adequate reason to believe that this association is causal. The common presumption that hyperinsulinemia mediates this connection is based on studies demonstrating various pressor effects of insulin, such as sodium retention, activation of the sympathetic nervous system, and stimulation of renin output. However, a consideration of physiological parameters in essential hypertensives indicates that these insulin-mediated pressor effects are unlikely to play a crucial pathogenic role in most cases of essential hypertension. Moreover, physiological elevation of insulin following a meal is typically associated with a reduction of blood pressure in hypertensives and the elderly. Euglycemic insulin clamps tend to reduce blood pressure in elderly subjects, and prolonged maintenance of hyperinsulinemia in animals does not raise blood pressure. In fact, insulin has long been known to have direct vasodilatory or antipressor effects on resistance vessels, and there is recent evidence that insulin reduces vascular resistance in skeletal muscles to facilitate glycogen storage after a meal. I propose that essential hypertensives experience a net deficit of insulin activity in vascular muscle, and that, in conjunction with other genetic or acquired defects of electrolyte transport, this leads to an increase in basal vascular tone and a hypersensitivity to pressor agents. Correction of insulin resistance usually aids blood pressure control, and in addition may mitigate the excess cardiovascular risk associated with hypertension.

Functional studies on alpha 1-adrenoceptor subtypes mediating inotropic effects in rat right ventricle

1. We have studied the alpha 1-adrenoceptor subtypes mediating inotropic effects of adrenaline in rat right ventricle and the Ca2+ sources used to elicit these effects. alpha 1A-Adrenoceptor-mediated contractile effects in rat vas deferens were studied for comparison in some cases. 2. Treatment with chloroethylclonidine did not affect the maximal beta-adrenoceptor-mediated inotropic effects in rat right ventricle or the maximal alpha 1A-adrenoceptor-mediated contractile effects in rat vas deferens; it did not alter the potency of isoprenaline in the ventricle and reduced the potency of the alpha-adrenoceptor antagonists in vas deferens only slightly. Treatment of right ventricular strips with CdCl2 markedly reduced resting tension and enhanced maximal inotropic effects of isoprenaline but did not affect its potency. 3. Inactivation of cardiac alpha 1B-adrenoceptors by treatment with chloroethylclonidine slightly enhanced the maximal inotropic effects of the full agonist, adrenaline and of several partial agonists. 4. Schild analysis of inhibition experiments with the alpha 1A-adrenoceptor-selective antagonists, 5-methyl-urapidil and (+/-)-tamsulosin, demonstrated that adrenaline causes its inotropic effects mainly via the alpha 1B-adrenoceptor subtype. Schild analysis of 5-methyl-urapidil inhibition experiments in chloroethylclonidine-treated ventricles indicated that only alpha 1A-adrenoceptors mediate the inotropic effects of adrenaline following inactivation of the alpha 1B-adrenoceptors. 5. In control ventricles the organic Ca2+ entry blocker, nitrendipine and treatment with the inorganic Ca2+ entry blocker, CdCl2 did not reduce inotropic effects of adrenaline whereas ryanodine treatment inhibited them. In contrast, nitrendipine and CdCl2 treatment had major inhibitory effects in chloroethylclonidine-treated but lacked inhibitory effects in phenoxybenzamine-treated ventricular strips. 6. We conclude that inotropic effects of adrenaline in rat heart are mediated mainly by alpha 1B-adrenoceptors via release of Ca2+ from an intracellular pool. Following inactivation of alpha 1B-adrenoceptors by chloroethylclonidine treatment, alpha lA-adrenoceptors can fully compensate and mediate inotropic effects by promoting influx of extracellular Ca2+ at least partly via voltage-operated channels.Therefore, we speculate that alpha 1B-adrenoceptors exert a tonic inhibitory effect on alpha 1A-adrenoceptors.

Erythrocyte Na+,K(+)-ATPase properties and adenylate energy charge in normotensives and in essential hypertensives

The activity and some kinetic properties of RBC Na+,K(+)-ATPase (EC 3.6.1.37) were investigated in essential hypertensives (EH; 40 subjects) and normotensives (NT; 20 subjects). A decrease in ouabain-sensitive 86Rb uptake as well as ouabain-sensitive ATPase activity was found in EH. [Na+]i and [K+]i of EH did not show any statistical difference from NT. Na+,K(+)-ATPase showed a reduced Mg2+ activation and the apparent Km value for Mg2+ was 2-fold increased in the EH group. The influence of temperature on the Na+,K(+)-ATPase showed a reduced modulation and a minor activity peak at 37 degrees C in the patients, consequently the calculated activation energy of the enzyme was increased at temperatures lower than 40 degrees C. Increased RBC adenylate energy charge (EC) was observed in EH when compared with NT. A negative correlation between EC and total Na+,K(+)-ATPase activity was found when all subjects were compared and also in both groups, showing a possible pump involvement in the regulation of the RBC metabolic flux in EH. These data provide evidence about some modifications in active Na+,K+ transport and in EC in RBC which allows a further characterization of membrane cation fluxes in EH.

Evidence for multiple genes determining sodium transport

Sodium transport comprises a set of interacting systems. Consequently, a defective sodium transport gene affects multiple sodium transport systems, and a sodium transport variable measured on a sample of individuals reflects genetic variation from a number of different genes, complicating the task of identifying the effect of a single gene. To test for genes which affect sodium transport, we first applied principal components analysis to 14 variables related to sodium transport, thereby defining uncorrelated sources of variation in the variables. The sample consisted of 1,218 members of 68 pedigrees ascertained through probands with early-onset stroke, hypertension, or coronary heart disease. Segregation analysis of the 14 principal components scores provided evidence for 8 genetic variants which alter sodium transport. One of the 8 variants is recessive, has homozygous genotype frequency estimated as 8.8% of the population, and increases sodium-lithium countertransport, the passive sodium leak, body mass index, and triglyceride; the genetic variant may coincide with an insulin resistance gene. A second of the 8 variants is also recessive, has homozygous genotype frequency estimated as 7.4% of the population, and increases intraerythrocytic sodium and the passive sodium leak while decreasing sodium pump number; the genetic variant may reduce pump number. Two of the 8 variants substantially increase sodium-lithium countertransport; frequency estimates for heterozygotes for the dominant variant and homozygotes for the recessive variant equal 1.8% and 3.1%, respectively. Another of the 8 variants is recessive, has homozygous genotype frequency estimated as 1.9%, and increases body mass index. Each of the 3 remaining variants is rare and expressed in less than 1% of the sample.

Altered erythrocyte transmembrane transport of sodium and potassium in patients with conventional or reservoir ileostomy

After proctocolectomy, the loss of the colonic absorptive capacity of sodium is compensated for by increased small intestine sodium absorption and renal conservation of Na by enhanced tubular reabsorption. These processes entail increased cellular sodium transport in the enterocytes and in the renal tubular cells. In order to evaluate if there is a general increase in cellular transport of Na after proctocolectomy for inflammatory bowel diseases erythrocyte Na and K contents and the transmembrane Na fluxes were determined in 35 patients with conventional ileostomy, 23 of which were reinvestigated after conversion to continent reservoir ileostomy. A selected group of another 12 patients having high output from their reservoir ileostomy and low urinary Na were studied concomitantly and 33 healthy subjects served as controls. The intracellular Na content did not differ between the groups while the intracellular K levels were higher in patients with conventional or continent ileostomy compared to controls. In addition, the Na influx and the efflux rate constant of Na were both increased after conversion to reservoir ileostomy. Na influx correlated positively with intake and urinary excretion of Na in conventional ileostomy patients. The results suggest that patients with ileostomy have an increased cellular K uptake and that construction of a reservoir ileostomy further alters cell cation transport by increasing the transmembrane Na turnover.

Intracellular cation concentrations in essential hypertension and chronic renal failure

The aim of this study was to test basal and after treatment erythrocyte sodium and calcium concentrations, and calcium-ATPase activity and platelet cytosolic free calcium and pH in 20 normotensive controls, 20 hemodialysis-dependent chronic renal failure patients and in 18 essential hypertensives. Prior to treatment, essential hypertensive and uremic patients presented similar higher platelet calcium concentrations and lower pH than the normotensive control group. The erythrocyte sodium, calcium, and magnesium concentrations were only significantly elevated in chronic renal failure, with a significant decrease in the calcium-ATPase activity in the latter population. Hemodialysis partially reversed these intracellular ionic abnormalities with normalization of platelet pH. Significant correlations have been noted between weight loss and decreases in platelet calcium concentration (r = 0.60, p < 0.01) or in erythrocyte sodium (r = 0.50, p < 0.05). The systolic blood pressure decrease was only correlated to the increase in calcium-ATPase activity (r = 0.57, p < 0.05). Antihypertensive treatment (captopril and nifedipine) only tended to normalize the intracellular calcium concentration with correlation between the decrease of the latter and blood pressure decrease (r = 0.64 for the systolic blood pressure and 0.68 for the diastolic blood pressure, p < 0.01). Thus, in essential hypertension and in uremia, some cellular ionic abnormalities exist in platelets in baseline condition. Moreover, in uremia, erythrocyte presents abnormal ionic pattern. Some, but not all of these abnormalities could be corrected by treatment affecting blood pressure (cellular calcium) in essential hypertension or by hemodialysis (cellular sodium, calcium, and pH). In the latter treatment, the changes are linked to extracellular fluid modification. In essential hypertension, the intracellular calcium reduction was linked to blood pressure decrease.

Membrane sodium-proton exchange and primary hypertension

Recent studies have revealed that an enhancement of sodium-proton exchange is a frequently observed ion transport abnormality in essential hypertension. An altered antiport activity not only is measurable in blood cells of hypertensive subjects ex vivo but also is detectable in skeletal muscle in vivo. Several lines of argument suggest that the altered antiport activity is not an epiphenomenon of hypertension: 1) the increased activity is found only in a subgroup of patients with high blood pressure, 2) it is not tightly correlated to the severity or duration of hypertension, and 3) high sodium-proton exchange activity persists over time and is not affected by antihypertensive treatment. Available evidence suggests that enhanced sodium-proton exchange is associated with or a cause for the structural alterations found in resistance vessels of hypertensive individuals (media hypertrophy) and left ventricular hypertrophy. This review summarizes some of the physiological properties and roles of the sodium-proton exchanger and discusses its kinetic properties in essential hypertension. Furthermore, the reasons for the enhanced antiport activity and its potential implications regarding the pathogenesis of hypertension are discussed.

A Na pump inhibitor from bovine posterior pituitary: purification, structure determination and its cardiovascular effect in rat

We examined the hypothesis that hypothalamo-hypophysial tissue contains an endogenous Na pump inhibitor. From bovine posterior pituitary, we purified a substance which inhibits Rb uptake by human erythrocytes. This inhibitory activity was found in the eluate of 10% acetonitrile from a C18 flash column and purified by subsequent three steps of reversed-phase high-performance liquid chromatography (HPLC). Sequence analysis revealed that this substance was identical to joining peptide, one of the major products of proopiomelanocortin (POMC). This peptide had hypertensive and tachycardiac effects in spontaneously hypertensive rats (SHR) after central administration, with weak Na,K-ATPase inhibitory activity (IC50 = 0.5 mM).

Insulin hypersecretion: a distinctive feature between essential and secondary hypertension

Several studies have demonstrated that patients with hypertension have greater plasma insulin levels than normotensive subjects. The aim of the present study was to clarify if hyperinsulinemia in hypertension is a consequence of either increased pancreatic secretion or decreased hepatic clearance, and to determine whether abnormalities of glucose metabolism are equally present in essential and secondary hypertension. In an observational cross-sectional study, fasting blood glucose, plasma insulin, and plasma C-peptide levels were measured in five patient groups: 34 lean normotensive, 19 overweight normotensive, 25 lean essential hypertensive, 27 overweight essential hypertensive, and 20 secondary hypertensive subjects. The blood glucose/plasma insulin and plasma insulin/plasma C-peptide ratios were calculated as indexes of insulin sensitivity and hepatic insulin clearance, respectively. Subjects with essential hypertension and, to a greater extent, those who were overweight, exhibited significantly higher fasting insulin and C-peptide levels and significantly lower glucose/insulin ratios as compared with lean normotensive subjects. In contrast, no differences were observed between secondary hypertensive and control subjects. Mean blood pressure was significantly and independently correlated to body mass index, plasma insulin and plasma C-peptide levels, and the glucose/insulin ratio. In lean essential hypertensive and secondary hypertensive subjects, the insulin/C-peptide ratios were comparable to controls, indicating normal hepatic insulin clearance. In both overweight groups, a trend to increased insulin/C-peptide ratios was observed. This study shows that in essential hypertensive subjects, hyperinsulinemia is caused by insulin hypersecretion, whereas in overweight subjects, both increased insulin secretion and decreased hepatic insulin clearance might be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypotensive drugs and the cellular energetic potential

Clinical and experimental investigations have revealed changes of the Na, K, Ca and Mg concentration in serum and cells in patients with essential arterial hypertension (EAH). Some hypotensive drugs correct, more or less, the electrolytic abnormalities at the same time as the decrease of arterial pressure. Epidemiological studies have shown a lower arterial blood pressure in populations with decreased intake of Na and an increased intake of K, Ca and Mg. However the most frequently encountered electrolyte anomaly in patients with EAH is hypophosphatemia, mainly induced by a shift of inorganic phosphate from serum into the cells. Probably the increased influx of inorganic phosphate from the serum, increases the arterial cellular energetic potential. As hypotensive drugs lead to a reduction of the inorganic phosphate shift from serum into the cells one may suggest that the obtained decrease of arterial blood pressure may be at least partially due to a diminished energetic potential of certain cells.

Endothelium-dependent inhibition of Na(+)-K+ ATPase activity in rabbit aorta by hyperglycemia. Possible role of endothelium-derived nitric oxide

Hyperglycemia has been shown to diminish Na(+)-K+ ATPase activity in rabbit aorta. To examine the basis for this effect, aortic rings were incubated for 3 h in Krebs-Henseleit solution containing 5.5 or 44 mM glucose, and Na(+)-K+ ATPase activity was then quantified on the basis of ouabain-sensitive (OS) 86Rb-uptake. Incubation with 44 mM glucose medium caused a 60% decrease in Na(+)-K+ ATPase activity in rings with intact endothelium (from 0.22 +/- 0.01 to 0.091 +/- 0.006 nmol/min per mg dry wt; P less than 0.01). Similar decreases (45%; P less than 0.01) in Na(+)-K+ ATPase activity were seen when rings incubated with 5.5 mM glucose were exposed to NG-monomethyl L-arginine (300 microM), an inhibitor of endothelium-derived nitric oxide (EDNO) synthesis or when the endothelium was removed (43% decrease). The decrease in Na(+)-K+ ATPase activity induced by hyperglycemia was totally reversed upon adding to the medium either L-arginine, a precursor of EDNO biosynthesis or sodium nitroprusside, which bypasses endothelium and directly activates the soluble guanylate cyclase in vascular smooth muscle. A decrease in Na(+)-K+ ATPase activity (42%; P less than 0.05), only seen in the presence of endothelium, was also observed in aortas taken directly from alloxan-induced diabetic rabbits. These studies suggest that the decrease in vascular Na(+)-K+ ATPase activity induced by hyperglycemia is related, at least in part, to a decrease in the basal release of EDNO. They also suggest that alterations in basal EDNO release and possibly Na(+)-K+ ATPase activity contribute to the impairment in vascular relaxation caused by hyperglycemia and diabetes.