The natriuretic hormone and essential hypertension

Role of endogenous digitalis-like factors in the clinical manifestations of severe preeclampsia: a sytematic review

Endogenous digitalis-like factor(s), originally proposed as a vasoconstrictor natriuretic hormone, was discovered in fetal and neonatal blood accidentally because it cross-reacts with antidigoxin antibodies (ADAs). Early studies using immunoassays with ADA identified the digoxin-like immuno-reactive factor(s) (EDLF) in maternal blood as well, and suggested it originated in the feto-placental unit. Mammalian digoxin-like factors have recently been identified as at least two classes of steroid compounds, plant derived ouabain (O), and several toad derived bufodienolides, most prominent being marinobufagenin (MBG). A synthetic pathway for MBG has been identified in mammalian placental tissue. Elevated maternal and fetal EDLF, O and MBG have been demonstrated in preeclampsia (PE), and inhibition of red cell membrane sodium, potassium ATPase (Na, K ATPase (NKA)) by EDLF is reversed by ADA fragments (ADA-FAB). Accordingly, maternal administration of a commercial ADA-antibody fragment (FAB) was tested in several anecdotal cases of PE, and two, small randomized, prospective, double-blind clinical trials. In the first randomized trial, ADA-FAB was administered post-partum, in the second antepartum. In the post-partum trial, ADA-FAB reduced use of antihypertensive drugs. In the second trial, there was no effect of ADA-FAB on blood pressure, but the fall in maternal creatinine clearance (CrCl) was prevented. In a secondary analysis using the pre-treatment maternal level of circulating Na, K ATPase (NKA) inhibitory activity (NKAI), ADA-FAB reduced the incidence of pulmonary edema and, unexpectedly, that of severe neonatal intraventricular hemorrhage (IVH). The fall in CrCl in patients given placebo was proportional to the circulating level of NKAI. The implications of these findings on the pathophysiology of the clinical manifestations PE are discussed, and a new model of the respective roles of placenta derived anti-angiogenic (AAG) factors (AAGFs) and EDLF is proposed.

Salt, aldosterone, and insulin resistance: impact on the cardiovascular system

Hypertension and type 2 diabetes mellitus (T2DM) are powerful risk factors for cardiovascular disease (CVD) and chronic kidney disease (CKD), both of which are leading causes of morbidity and mortality worldwide. Research into the pathophysiology of CVD and CKD risk factors has identified salt sensitivity and insulin resistance as key elements underlying the relationship between hypertension and T2DM. Excess dietary salt and caloric intake, as commonly found in westernized diets, is linked not only to increased blood pressure, but also to defective insulin sensitivity and impaired glucose homeostasis. In this setting, activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system (RAAS), as well as increased signaling through the mineralocorticoid receptor (MR), result in increased production of reactive oxygen species and oxidative stress, which in turn contribute to insulin resistance and impaired vascular function. In addition, insulin resistance is not limited to classic insulin-sensitive tissues such as skeletal muscle, but it also affects the cardiovascular system, where it participates in the development of CVD and CKD. Current clinical knowledge points towards an impact of salt restriction, RAAS blockade, and MR antagonism on cardiovascular and renal protection, but also on improved insulin sensitivity and glucose homeostasis.

The Renin-Angiotensin System in the Development of Salt-Sensitive Hypertension in Animal Models and Humans

Hypertension is still one of the major causes of death from cardiovascular failure. Increased salt intake may aggravate the rise in blood pressure and the development of consequential damage of the heart, the vessels and other organs. The general necessity of restricted salt intake regardless of blood pressure or salt sensitivity has been a matter of debate over the past decades. This review summarizes the main pathogenic mechanisms of hypertension and salt sensitivity in rat models, particularly in the spontaneously hypertensive rat (SHR), and in patients with essential hypertension (EH). Although SHRs are commonly considered to be salt-resistant, there is much evidence that salt loading may deteriorate blood pressure and cardiovascular function even in these animals. Similarly, EH is not a homogenous disorder - some patients, but not all, exhibit pronounced salt sensitivity. The renin-angiotensin system (RAS) plays a key role in the regulation of blood pressure and salt and fluid homeostasis and thus is one of the main targets of antihypertensive therapy. This review focuses on the contribution of the RAS to the pathogenesis of salt-sensitive hypertension in SHRs and patients with EH.

The Camerano study on hypertension: the problem of arterial hypertension in the elderly

The Camerano study on arterial hypertension (AH) was a cross-sectional study, carried out on a large population sample in a small town in central Italy. The main goal was to reveal both the prevalence and certain characteristics of AH in the population examined. The main results, can be summarized as follows: (i) The occurrence of AH in the old (65-74 years) and very old (> or = 75 years) groups was 43.3 and 57.4%, respectively. (ii) isolated systolic hypertension (ISH) was found in 1.7, 23.6 and 3.9% in the adult, old and very old subjects, respectively. (iii) The association of AH with some of the more common cardiovascular risk factors (dyslipidemia, hyperglycemia, obesity, etc.) was significant for all the risk factors in the adult group, while in the old group there was a significant association only with the body mass index. (iv) Blood pressure (BP) values during the medical visits were evaluated, and adult versus old subjects were compared, but no significant differences were found.

CYP3A5 and ABCB1 genes and hypertension

Hypertension is the first single modifiable cause of disease burden worldwide. Genes encoding proteins that are involved in the metabolism (CYP3A5) and transport (ABCB1) of drugs and hormones might contribute to blood pressure control in humans. Indeed, recent data have suggested that CYP3A5 and ABCB1 gene polymorphisms are associated with blood pressure in the rat as well as in humans. Interestingly, the effects of these genes on blood pressure appear to be modified by dietary salt intake. This review summarizes what is known regarding the relationships of the ABCB1 and CYP3A5 genes with blood pressure, and discusses the potential underlying mechanisms of the association. If the role of these genes in blood pressure control is confirmed in other populations and other ethnic groups, these findings would point toward a new pathway for blood pressure control in humans.

Combination of renin-angiotensin system polymorphisms is associated with altered renal sodium handling and hypertension

Genes of the renin-angiotensin-aldosterone system (RAAS) are natural candidates for sodium homeostasis and blood pressure regulation. To investigate the effect of a combination of polymorphisms of RAAS genes on renal sodium handling and blood pressure, 918 participants to the Olivetti Heart Study were genotyped for the following polymorphisms: I/D of angiotensin converting enzyme (ACE), M235T of angiotensinogen (AGT), A1166C of angiotensin II type-1 receptor (AT1R), and C-344T of aldosterone synthase (CYP11B2). The segmental renal sodium handling was evaluated by the fractional excretions of exogenous lithium (FE-Li), uric acid (FE-UA), and sodium (FE-Na). Twenty-eight carriers of triple homozygosity for M (AGT), A (AT1R), and C (CYP11B2) in the presence of the D allele of ACE (DD/ID) showed lower FE-Li (20.0%+/-5.9% versus 25.0%+/-7.5%; P=0.004; mean+/-sD), FE-UA (6.3%+/-2.0% versus 8.2%+/-2.7%; P=0.001), and FE-Na (0.96%+/-0.41% versus 1.22%+/-0.61%; P=0.004) as compared with all other allelic combinations (n=890), independently from age and body mass, suggesting an enhanced rate of proximal tubular sodium reabsorption. The carriers of the MM, AA, CC, DD/ID combination showed a substantially higher probability of being hypertensive (OR: 3.4 [(99% CI: 1.1 to 10.1]), independently of age and body mass. This relatively rare combination of allelic variants of candidate genes of the RAAS is associated with a significant alteration in proximal renal sodium handling and with higher risk of hypertension, suggesting that a combination of polymorphic variants at different candidate loci may affect phenotypic expression even in the absence of detectable effects of each variant at any single locus.

Altered renal handling of sodium in human hypertension: short review of the evidence

A pathogenic role of the kidney in hypertension has been strongly supported by experimental studies by Guyton and Dahl since the 1960s. In the early 1980s, de Wardener and MacGregor proposed that in hypertensive patients the ability of the kidneys to excrete a sodium load could be genetically impaired. Since then, "sodium-sensitive" hypertension has been the object of numerous studies, mostly on animal models because of the difficulty to investigate the renal handling of sodium in humans. More recently, considerable progress in this field has been made thanks to the in vivo study of segmental renal tubular function by the clearance of lithium and to the growing knowledge of the genetics of renal tubular sodium transport systems. The scope of this review is to briefly review the most relevant information gathered by the investigation of segmental renal tubular sodium handling in humans as related to blood pressure regulation and hypertension. In aggregate, the results of these studies strongly support the association between altered renal sodium handling and high blood pressure and suggest a causal role of genetic, nutritional, metabolic, and neurohormonal factors. All of these factors, alone or in combination, may be able to impair the normal renal tubular sodium handling and influence blood pressure homeostasis. The paradigm of the pathogenic role of the kidney in hypertension is thus relentlessly shifting toward the definition of inherited as well as acquired renal tubular defects and molecular alterations, providing a plausible explanation for the alteration in blood pressure levels.

Epithelial sodium channel activity is not increased in hypertension in whites

Abnormal renal sodium transport causing excess reabsorption of sodium may be one mechanism that causes high blood pressure. For example, increased activity of epithelial sodium channels in the distal tubule is the cause of high blood pressure in Liddle's syndrome, a rare familial form of hypertension. We have shown that the increase in sodium channel activity can be detected in the nose using transepithelial potential difference measurements in 1 family with Liddle's syndrome. We therefore used nasal potential difference measurements to look for increased sodium channel activity in white patients with essential hypertension. Transnasal potential difference was measured in 42 white hypertensive (HT) subjects and 38 white normotensive (NT) subjects before and after topical application of 10(-4) mol/L of amiloride. There was no difference in maximum potential between HT and NT subjects (HT, -18.8+/-0.9 mV; NT, -18.2+/-1.0 mV) (values mean+/-SEM; lumen-negative with respect to the submucosa). However, the postamiloride potential was significantly higher (HT, -12.6+/-0.7 mV; NT, -10.5+/-0.7 mV; P=0. 015) and the change in potential in response to amiloride significantly lower (HT, 6.2+/-0.5 mV, 33.1+/-2.0%; NT, 7.7+/-0.6 mV, 41.9+/-2.0%; P=0.046 and 0.003, respectively) in HT than in NT subjects. These results suggest that sodium channel activity is not increased in whites with essential hypertension and indicate that sodium channel overactivity similar to that seen in Liddle's syndrome is unlikely to be the cause of high blood pressure in this group. Increased postamiloride potential may reflect increased activity of chloride channels or amiloride-insensitive sodium channels.

Association of hypertension with T594M mutation in beta subunit of epithelial sodium channels in black people resident in London

BACKGROUND

Liddle's syndrome is a rare inherited form of hypertension in which mutations of the epithelial sodium channel result in increased renal sodium reabsorption. Essential hypertension in black patients also shows clinical features of sodium retention so we screened black people for the T594M mutation, the most commonly identified sodium-channel mutation.

METHODS

In a case-control study, 206 hypertensive (mean age 48.0 [SD 11.8] years, men:women 80:126) and 142 normotensive (48.7 [7.4] years; 61:81) black people who lived in London, UK, were screened for T594M. Part of the last exon of the epithelial sodium-channel beta subunit from genomic DNA was amplified by PCR. The T594M variant was detected by single-strand conformational polymorphism analysis of PCR products and confirmed by DNA sequencing.

FINDINGS

17 (8.3%) of 206 hypertensive participants compared with three (2.1%) of 142 normotensive participants possessed the T594M variant (odds ratio [OR]=4.17 [95% CI 1.12-18.25], p=0.029). A high proportion of participants with the T594M variant were women (15 of 17 hypertensive participants and all three normotensive participants), whereas women comprised a lower proportion of the individuals screened (61.2% hypertensive, 57.7% normotensive). However, the association between the T594M variant and hypertension persisted after adjustment for sex and body-mass index (Mantel-Haenszel OR=5.52 [1.40-30.61], p=0.012). Plasma renin activity was significantly lower in 13 hypertensive participants with the T594M variant (median=0.19 ng mL(-1) h(-1)) than in 39 untreated hypertensive individuals without the variant (median=0.45 ng mL(-1) h(-1), p=0.009).

INTERPRETATION

Among black London people the T594M sodium-channel beta subunit mutation occurs more frequently in people with hypertension than those without. The T594M variant may increase sodium-channel activity and could raise blood pressure in affected people by increasing renal tubular sodium reabsorption. These findings suggest that the T594M mutation could be the most common secondary cause of essential hypertension in black people identified to date.

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.

Hypertension and the kidney--an overview

The kidney plays a major role in the genesis of any type of hypertension, as demonstrated by experiments which show that hypertension can be "transplanted" when the kidney itself is transplanted. Hypertension is common in patients with renal disease, and may occur even at normal glomerular filtration rates. The mechanisms that promote hypertension and are involved in renal disease comprise both activation of pressor mechanisms and failure of depressor mechanisms, the latter having been considerably less well studied. The major pressor mechanisms are an abnormal pressure-natriuresis relationship and inappropriate activity of the renin-angiotensin system.

Membrane ATPase, erythrocyte sodium and potassium in haemodialysis patients

This study was undertaken to evaluate the effect of chronic renal failure as well as dialysate sodium concentration during haemodialysis on membrane ATPase activity and erythrocyte sodium and potassium concentration. Intracellular Na and K were not changed in patients when compared to normal subjects. There was, however, a significant decrease of Na-K-ATPase activity in patients versus controls. Erythrocyte sodium increased during haemodialysis with low and normal sodium dialysate. The present results suggest that sodium dialysate concentration has an influence on the intracellular cationic homeostasis.

Increased proximal tubular reabsorption of sodium in childhood diabetes mellitus

Type 1 diabetes mellitus is associated with an increase in total exchangeable body sodium. To delineate a site of possible altered sodium handling, proximal tubular sodium reabsorption (PTRNa) was measured in 30 diabetic children, age 12.0 (range 7-16) yr, duration of diabetes 4.5 (range 0.2-12) yr, and compared with 10 non-diabetic children, age 10.0 (range 8.6-12.5) yr. PTRNa was calculated from the fractional clearance of lithium, which was determined from a single blood sample and a random untimed urine sample, taken between 0700 and 0830 h at home, fasting, before insulin therapy. PTRNa was significantly increased in the diabetic children compared with the non-diabetic children (81.6(SE 1.0) vs 74.2(2.6)%, p = 0.014). There was no relationship of PTRNa with age, duration of diabetes, metabolic control (glycosylated haemoglobin, plasma and urinary glucose, plasma lactate), or urinary protein excretion (albumin, N-acetyl-beta-D-glucosaminidase). Elevated sodium reabsorption in the proximal renal tubule may account for the high total exchangeable body sodium found in Type 1 diabetic patients.

Endogenous digoxin-like substance as an important factor in the development of hypertension in children

In this study, endogenous digoxin-like substance within the plasma was measured by radio-immunoassay in 122 children with the systolic blood pressure equal to or greater than the 75th percentile (age = 12.3 +/- 2.5 years) and 136 children with the systolic blood pressure at or less than the 50th percentiles (age = 11.9 +/- 2.8 years) after a follow-up of one year. The levels of digoxin-like substance in the plasma of children with the higher blood pressure were much higher than those in the controls (32.7 +/- 17.3 versus 22.7 +/- 12.7 pg/ml, P less than 0.001) and were positively correlated to the blood pressure (r = 0.21, P less than 0.05 for systolic blood pressure; and r = 0.41, P less than 0.01 for diastolic), and to the sodium content of the red cells (r = 0.36, P less than 0.001), plasma (r = 0.25, P less than 0.01) and 8-hour overnight urinary output (r = 0.32, P less than 0.05). The children in the group with higher blood pressure exhibited an exaggerated natriuresis after an oral saline-water load. We believe that a circulating inhibitor of sodium transport may play an important role in the early stage of the evolution of hypertension.

Increase in plasma digitalis-like activity during percutaneous transluminal coronary angioplasty in patients with coronary stenosis

Despite the fact that numerous studies have been published regarding the possible presence in plasma of an endogenous Na-K pump inhibitor with a digitalis-like structure in essential hypertension, very little is known about this factor in heart disease in general, and in situations characterized by low cardiac output. We measured the ability of plasma obtained from the femoral vein to inhibit a human renal Na(+)-K+ ATPase before and immediately after percutaneous transluminal coronary angioplasty (PTCA) in 6 patients suffering from angina pectoris and severe coronary stenosis. Intraerythrocyte sodium and potassium concentrations were also measured simultaneously. Na(+)-K+ ATPase inhibition proved significantly greater after angioplasty as compared to basal activity (percentage inhibition: 31.5 +/- 7.8 vs 16.1 +/- 12.2). No significant changes in intraerythrocyte sodium and potassium were detected. Though we are not in a position to define the mechanism underlying the increase in the digitalis-like factor, a plausible hypothesis may be that the reduction in cardiac output during PTCA by raising cardiac pressures may stimulate the production of a factor of compensatory inotropic significance.

Relationship between urinary excretion of sodium and dopamine in type 1 diabetic patients with an without microalbuminuria

The relationship between urinary sodium and dopamine excretion was investigated in 40 normal males and in 48 normotensive, Type 1 diabetic males, 11 with microalbuminuria and 37 with normal albumin excretion. In all three groups a significant correlation was demonstrated and the regression lines were similar. Thus, no evidence was found that a defect in dopamine mobilization contributes to the early renal pathophysiological changes of Type 1 diabetes.

Increased proximal tubular sodium reabsorption in hypertensive patients with type 2 diabetes

Hyperinsulinaemia and sodium retention have been studied in 22 Type 2 diabetic patients (10 normotensive, 12 hypertensive) and 10 normal control subjects matched for age, sex, and body mass index. Exchangeable sodium was similar in the three groups. Plasma renin activity and plasma angiotensin II were lower in both groups of diabetic patients than in the normal control subjects (p less than 0.01). Plasma atrial natriuretic peptide was increased in the hypertensive patients (7.3 +/- 1.1 vs normotensive 4.7 +/- 1.1 pmol l-1 and control 4.0 +/- 0.2 pmol l-1, p less than 0.01). Fractional lithium clearance, a measure of sodium clearance from the proximal tubule, was decreased (18.5 +/- 1.4, p less than 0.01) and fractional excretion of sodium in the distal tubule was increased (6.66 +/- 0.66, p less than 0.01) in untreated hypertensive diabetic patients compared with both normotensive diabetic patients (25.3 +/- 1.6 and 3.96 +/- 0.52 respectively) and normal control subjects (25.2 +/- 2.9 and 3.31 +/- 0.38, respectively). Fasting serum insulin was higher in hypertensive than in normotensive diabetic patients (18.5 +/- 3.0 vs 10.7 +/- 1.1 mU l-1, p less than 0.01) and higher in both groups than in normal control subjects (5.6 +/- 0.1 mU l-1, both p less than 0.01). Creatinine clearance was higher in both groups of diabetic patients than in normal control subjects (p less than 0.05). Thus there appears to be increased proximal renal tubular sodium reabsorption in these hypertensive Type 2 diabetic patients, matched by a reduction in distal sodium reabsorption so that net sodium excretion was maintained. This was associated with fasting hyperinsulinaemia.

Digoxin-like immunoreactive substances in chronic liver disease

Digoxin-like immunoreactive substances, which cross-react with digoxin antibody, have been found to have natriuretic effect and Na+,K+-ATPase inhibitory effect. The role of digoxin-like immunoreactive substances in chronic liver disease was studied by radioimmunoassay in 63 serum and 60 urine samples from 58 patients with chronic liver disease and compared with 16 controls. Although the mean serum digoxin-like immunoreactive substances level of compensated chronic liver disease patients (0.06 +/- 0.05 ng per ml, p less than 0.01) was higher than that of controls (0.02 +/- 0.03 ng per ml), only four patients had serum digoxin-like immunoreactive substances higher than 0.10 ng per ml. Mean serum digoxin-like immunoreactive substances level was much higher in patients with decompensated chronic liver disease who had ascites (0.32 +/- 0.17 ng per ml, p less than 0.001), hepatorenal syndrome (0.57 +/- 0.20 ng per ml, p less than 0.001) and hepatic encephalopathy (0.43 +/- 0.20 ng per ml, p less than 0.001). Five patients with recent variceal hemorrhage requiring transfusions and saline infusion had significantly increased serum digoxin-like immunoreactive substances (mean: 0.16 +/- 0.06 ng per ml, p less than 0.001) before the development of clinically detectable ascites.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte Na+, K+ pump inhibition after saline infusion in essentially hypertensive subjects: effects of canrenone administration

The effects of a 2-litre isotonic saline infusion, with and without prior oral canrenone (150 mg) administration, on erythrocyte Na+, K+ pump, urinary sodium excretion and arterial pressure were evaluated in nine patients with essential hypertension. Ouabain-sensitive Na+ efflux in fresh erythrocytes was used as an index of Na+, K+ pump activity, and the inhibitory effect on this ion efflux of preincubation of erythrocytes in plasma was used to test the presence of a circulating ouabain-like substance. Erythrocyte Na+, K+ pump activity decreased significantly (P less than 0.01) after saline infusion; canrenone administration was able to prevent this inhibition. Plasma from hypertensive patients obtained before saline infusion significantly (P less than 0.01) inhibited the Na+, K+ pump of erythrocytes from normal subjects, while plasma taken after the saline infusion plus canrenone was unable to produce any significant inhibition. Both systolic and diastolic arterial pressure fell significantly (P less than 0.05) only at the end of saline infusion with prior canrenone administration. This study supports the hypothesis that protection of Na+, K+ pump against endogenous inhibitors, other than exogenous, seems to be a pharmacological effect of canrenone, and may partly explain its antihypertensive activity.

Erythrocyte Na,K pump activity and arterial hypertension in uremic dialyzed patients

We have evaluated in 26 uremic patients [21 on hemodialysis, 5 on continuous ambulatory peritoneal dialysis (CAPD)], 11 normotensive, and 15 hypertensive (MAP greater than 110 mm Hg) patients the following properties: a) erythrocyte (RBC) Na concentration [Nai] and ouabain-sensitive and -resistant Na effluxes; b) the effect of uremic sera on ouabain-sensitive Na efflux in normal RBC; c) serum digoxin-like immunoreactivity; d) cardiac index and total peripheral resistance. In 19 healthy subjects a) and c) were also evaluated. RBC Na,K pump activity was lower in uremic patients than in normal subjects (P less than 0.0005), and lower in hypertensive (P less than 0.02) than in normotensive patients. Serum from uremic patients inhibited ouabain-sensitive Na efflux in normal RBC, the inhibition being correlated with both the rate constant for ouabain-sensitive Na efflux (r = -0.67; P less than 0.005) and [Nai] (r = 0.43; P less than 0.05) of RBC of patients from whom the serum was obtained. Inhibition of ouabain-sensitive Na efflux was significantly higher with serum from hypertensive than from normotensive patients (P less than 0.05). Serum digoxin-like immunoreactivity was present in all uremic patients (0.402 +/- 0.054 ng/ml in normotensive and 0.428 +/- 0.040 ng/ml in hypertensive, P = ns), while it was not detectable in normal subjects. Hypertensive patients had peripheral resistance significantly higher than normotensive (P less than 0.05), while cardiac index was similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Digoxin-like immunoreactive substances in severe acute liver disease due to viral hepatitis and paracetamol overdose

The levels of endogenous serum digoxin-like immunoreactive substances were investigated during development of encephalopathy in patients with fulminant hepatic failure. The 67 patients studied had varying degrees of hepatic failure as a result of viral hepatitis or paracetamol overdose. Serum levels of digoxin-like immunoreactive substances were significantly increased in both viral hepatitis and paracetamol overdose, with mean values of 0.42 +/- S.D. 0.25 ng per ml (n = 36) and 0.53 +/- 0.19 ng per ml (n = 31), respectively, as compared to normal control subjects with mean values of 0.01 +/- 0.02 ng per ml (n = 21, p less than 0.001). A statistically significant correlation was found between serum digoxin-like immunoreactive substances and the degree of encephalopathy in the viral hepatitis patients and with the serum creatinine in the paracetamol overdose patients where renal failure was more severe. No correlation was found with liver damage as assessed by the prolongation of the prothrombin time, serum AST or bilirubin values. Experiments with ultrafiltration and heating showed that both free nonprotein-bound digoxin-like immunoreactive substances and the total digoxin-like immunoreactive substances measured were increased. Column chromatography of ultrafiltrates of fulminant hepatic failure serum on Sephadex G-25 demonstrated at least two peaks with digoxin-like immunoreactive activity. Reduced renal function is an important factor in the increased serum level of digoxin-like digoxin-like immunoreactive substances, but their presence due to liver failure, where there is increased permeability of the blood-brain barrier, could be relevant to the development of hepatic encephalopathy.

'Sodium sensitivity' in man

Increased cell membrane permeability to sodium is proposed as the initial event leading to high blood pressure in susceptible subjects when sodium intake is increased. All cells, including circulating cells, would be affected, but a key role for endothelial cells in the pathophysiology of the diastolic blood pressure elevation is proposed. Involvement of capillary endothelium could increase capillary permeability to proteins, and thereby would contribute to the altered fluid distribution on the high sodium diet which has been observed. If movement of fluid into the interstitium raised interstitial fluid pressure, venous capacitance would fall and right atrial pressure would rise. Several mechanisms would cause vascular smooth muscle tone to increase. Altered fluid distribution correlates with the rise in diastolic blood pressure from reduced sodium to high sodium diet, but arteriolar constriction would reduce capillary flow so altered fluid distribution occurs first. Arteriolar constriction could serve as a negative feedback to the raised atrial filling pressure by reducing raised capillary flow, which would decrease both altered fluid distribution and interstitial fluid pressure rise. Consequently, diastolic blood pressure would be chronically raised in 'sodium sensitive' subjects taking increased amounts of sodium in the diet. The relationship of the findings to "essential" hypertension and to premorbid cardiovascular sequelae, and the key role of capillary endothelium in the development of "essential" hypertension is discussed.

Digoxin-like immunoreactive substance in patients with aneurysmal subarachnoid haemorrhage

Digoxin was measured by radioimmunoassay in the plasma of 25 patients with aneurysmal subarachnoid haemorrhage who had not received digoxin treatment. After heating the plasma an endogenous substance cross reacting with antibodies to digoxin was identified in 18 cases. The presence of this substance was significantly related to the total amount of blood and to the presence of blood in the frontal interhemispheric fissure and could not be explained by hypertension or intake of water and sodium. A negative sodium balance and volume depletion occurred more often in patients who were positive for digoxin, but this relation did not reach statistical significance. It is concluded that a digoxin-like natriuretic factor is released in response to a subarachnoid haemorrhage, probably as a result of hypothalamic damage.

The uridine nucleotides constitute a natriuretic pressor system

1. Uridine monophosphate was tested in the conscious rat for natriuretic properties and an immunoperoxidase technique was used to localize uridine-containing compounds in the rat kidney. 2. Uridine monophosphate, infused in a moderate pressor dose, caused a significant natriuresis compared to the effect of control infusions of solvent vehicle. 3. Uridine-containing compounds were found in most tubular elements with particularly dense staining in the distal and collecting tubules. 4. While the increased sodium excretion may have been due to increased renal perfusion pressure, the high density of uridine staining in distal nephrons suggests that the uridine nucleotides have a specific nephron function, possibly relating to sodium transport.

Intracellular calcium and sodium in hypertensive patients

Untreated subjects with mild to moderate hypertension were compared with normotensive controls recruited from the same ambulatory screening clinic. All subjects were black. Resting levels of cytosolic free calcium were estimated in washed platelets with the fluorescent intracellular probe fura 2, and sodium and potassium were measured in red blood cells. Calcium levels were 21% higher in the hypertensive subjects (p = 0.02), and a 9% increase in sodium was observed in an expanded sample (p = 0.04). Neither intracellular calcium nor intracellular sodium had a significant linear correlation with blood pressure when hypertensive subjects and controls were examined separately or when the two groups were combined. Potassium was slightly but not significantly increased in hypertensive subjects. Among the participants for whom both calcium and sodium measurements were available, a weak, nonsignificant correlation between these ions was noted (r = 0.2; n = 48). This correlation was significant among participants in the control group examined separately (r = 0.3; n = 33; p = 0.05). Although the measurements were performed in different cell lines, these findings demonstrate increases in both intracellular calcium and sodium in hypertensive humans.

Effect of inhibition of Na+-K+ ATPase on the prostacyclin generation of cultured human vascular endothelial cells

Prostacyclin (PGI2) generation of cultured human vascular endothelial cells (VEC) was observed coincidentally with the increase of 45Ca net influx. Ca ionophore A23187 enhanced not only PGI2 generation and 45Ca net influx but also 45Ca efflux. PGI2 generation was completely abolished by the pretreatment with Ca++ immobilizer, TMB-8. A Na+-K+ ATPase inhibitor, ouabain increased 45Ca net influx, but decreased 45Ca efflux, and enhanced PGI2 generation. These observation indicate that PGI2 generation of VEC may be regulated by not only Ca++ but also Na+, and it was suggested that enhanced PGI2 generation by ouabain might be derived from the increased cytosolic Ca++concentration by the decreased Ca++ efflux, and it was considered to be originated from the suppression of Na+-Ca++ exchange systems by the increased intracellular Na+ concentration via inhibition of Na+-K+ ATPase activity by ouabain. Enhancement of PGI2 generation of VEC by the increased ouabain like substances (OLS) in hypertension is suspected to be beneficial on the maintenance of vascular homeostasis.

Stable gene amplification and overexpression of sodium- and potassium-activated ATPase in HeLa cells

Cell lines stably resistant to ouabain were isolated from an unstably resistant HeLa line after growth in nonselective medium. Stable resistant lines bound ouabain at levels 10-fold higher than did HeLa cells and at similar levels to those bound by the unstable C+ line previously described (J. F. Ash, R. M. Fineman, T. Kalka, M. Morgan, and B. Wire, J. Cell Biol. 99: 971-983). Expression and synthesis of the Na+, K+ -ATPase alpha chain showed a similar amplification over that for HeLa cells by Western blots and [35S]methionine pulse-labeling. In addition, a glycoprotein labeled with [3H]fucose and comigrating with the Na+, K+ -ATPase beta chain was eight- to ninefold amplified in stably resistant lines. Dot blots with a cDNA clone specific for Na+, K+ -ATPase alpha chain gene sequences confirmed the amplification of this gene. Karyotyping suggested that the amplification is associated with an expanded, abnormal banded region on the long (q) arm of one chromosome 17.

Ouabain-like and non-ouabain-like factors in plasma of patients with essential hypertension

Circulating inhibitor of Na+,K+-ATPase and ouabain-like immunoreactivity were studied in patients with essential hypertension. In the plasma of patients, two types of Na+,K+-ATPase inhibitors (ouabain-like and non-ouabain-like inhibitors) and ouabain-like immunoreactivity were detected. Ouabain-like inhibitor was clearly detected at a low KCl concentration (0.1 mM) in the assay buffer, and non-ouabain-like inhibitor was detected at a high KCl concentration (10 mM). The plasma level of ouabain-like inhibitor correlated significantly with that of ouabain-like immunoreactivity (p less than 0.001) and with a mean blood pressure (p less than 0.01). The plasma level of non-ouabain-like inhibitor was not correlated with the levels of either ouabain-like immunoreactivity or mean blood pressure. The level of plasma ouabain-like inhibitor did not correlate with that of plasma non-ouabain like inhibitor. Both ouabain-like inhibitor and ouabain-like immunoreactivity in the plasma of patients with essential hypertension were significantly higher than those in normotensive subjects, but the plasma level of non-ouabain-like inhibitor in patients with essential hypertension was not higher than that in normotensive subjects. These results suggest that the plasma from patients with essential hypertension contains ouabain-like factor(s) which is important to maintain the high blood pressure.

The effect of antihypertensive treatment on the circulating hypertensive factor in the spontaneously hypertensive rat

To elucidate the role of circulating hypertensive factors in the spontaneously hypertensive rat and the effects of antihypertensive treatment on the circulating hypertensive factor, cross circulation was performed in 54 couples of spontaneously hypertensive and normotensive rats. In normotensive rats cross-circulated with untreated spontaneously hypertensive rats mean arterial pressure increased by 20.9 +/- 12.2 mm Hg (p less than 0.01). Increases in mean arterial pressure were also obtained by cross-circulation with spontaneously hypertensive rats pretreated with propranolol, furosemide, and nifedipine. Mean arterial pressure was not changed by cross circulation after pretreatment of the spontaneously hypertensive rats with alpha methyldopa. It is concluded that in this strain of spontaneously hypertensive rats a circulating hypertensive factor exists, the secretion of which can be suppressed by the centrally acting drug, alpha methyldopa. Therefore either the central nervous system may take part in the regulation of the factor or the factor may be synthetized in the central nervous system.

Direct demonstration of an inhibitor of sodium, potassium dependent adenosine triphosphatase (Na+, K+-ATPase) in plasma from normotensive and hypertensive subjects

An endogenous inhibitor of Na+, K+-ATPase was extracted from human plasma and sera and concentrated by a novel reverse-phase octadecylsilane chromatography method. The active extracts (eluates) were dried and reconstituted in the minimum volume of the non-adsorbed fraction of the plasma from which they had been derived. Reconstituted eluates, non-adsorbed plasma fractions and native plasma samples were then tested for their ability to inhibit phosphate production in standard Na+, K+-ATPase incubation mixtures. In a pilot study 31 samples of pooled normal human sera were assayed. The eluates gave a significantly lower production of phosphate than the non-adsorbed fractions or the native sera (n = 31, p less than 0.0025). Further concentration of the eluates by repeated chromatography increased the inhibitory power of the eluate proportional to the concentration achieved, as quantified by ouabain dose-equivalents. In clinical studies, samples from 12 normotensive subjects and from 12 untreated patients with essential hypertension were tested. Significant inhibition of the ATPase by the eluates, as compared to the corresponding non-adsorbed fractions was seen for samples from both normotensive (p less than 0.05) and hypertensive (p less than 0.05) subjects. There was no significant difference in incidence or degree of inhibition between the normotensive and hypertensive groups. This study provides direct evidence for the presence of an endogenous inhibitor of Na+, K+-ATPase in human plasma.

Reduction of erythrocyte (Na+-K+)ATPase activity in type 1 (insulin-dependent) diabetic subjects and its activation by homologous plasma

The (Na+-K+)ATPase and (Mg2+)ATPase activities of erythrocyte membranes of Type 1 (insulin-dependent) diabetic patients were found to be significantly reduced compared to matched controls (p less than 0.005). On the contrary, erythrocyte Na+ and K+ contents were similar in diabetic patients and in normal subjects. When erythrocyte membranes from diabetic patients were incubated with their own plasma, a significant increase was observed in sodium-potassium ATPase activity (p less than 0.005), whereas (Mg2+)ATPase activity was not affected. The plasma stimulatory effect showed saturation kinetics. Maximum average stimulation was 96% (+/- 21.3). A similar stimulation pattern, although more limited in extent (maximum 48.3% +/- 12.2), was found when erythrocyte membranes from normal subjects were incubated with diabetic plasma. Normal plasma exhibited a modest stimulatory effect on erythrocyte (Na+-K+)ATPase activity. Similar stimulatory effects by diabetic plasma were observed on a (Na+-K+) ATPase preparation from beef heart. It is proposed that diabetic plasma contains a specific (Na+-K+)ATPase activator in a higher concentration than normal plasma. This may explain why a normal cellular electrolyte content was found in diabetic erythrocytes in spite of a reduced Na+-K+ pump activity. Purification experiments indicate that the plasma activator is a protein with a molecular weight greater than 50,000. Both the (Na+-K+)ATPase activity and the stimulatory effect of diabetic plasma were not influenced by the metabolic control, since they did not correlate significantly with fasting blood glucose and daily insulin dosage. Moreover, no correlation was found with duration of diabetes or age at diagnosis of diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

What's new in cellular cation exchange and humoral factors in primary hypertension?

In essential hypertension abnormalities of cellular Na+ and Ca++ handling have been described. The latter disturbance probably offers an explanation for the increased vasoconstriction in essential hypertension. The etiology of those disturbances in cellular Na+ and Ca++ metabolism may be related to genetic disturbances of membrane transport, or to a humoral factor influencing cellular cation metabolism.

Stable gene amplification and overexpression of sodium- and potassium-activated ATPase in HeLa cells

Cell lines stably resistant to ouabain were isolated from an unstably resistant HeLa line after growth in nonselective medium. Stable resistant lines bound ouabain at levels 10-fold higher than did HeLa cells and at similar levels to those bound by the unstable C+ line previously described (J. F. Ash, R. M. Fineman, T. Kalka, M. Morgan, and B. Wire, J. Cell Biol. 99: 971-983). Expression and synthesis of the Na+, K+ -ATPase alpha chain showed a similar amplification over that for HeLa cells by Western blots and [35S]methionine pulse-labeling. In addition, a glycoprotein labeled with [3H]fucose and comigrating with the Na+, K+ -ATPase beta chain was eight- to ninefold amplified in stably resistant lines. Dot blots with a cDNA clone specific for Na+, K+ -ATPase alpha chain gene sequences confirmed the amplification of this gene. Karyotyping suggested that the amplification is associated with an expanded, abnormal banded region on the long (q) arm of one chromosome 17.

Cell membrane sodium transport: a correlation between human resistance vessels and leucocytes

Sodium efflux was studied in leucocytes and resistance vessels from omental fat from 18 subjects undergoing laparotomy. The efflux of sodium was considerably faster from resistance vessels than from leucocytes, but there was a significant correlation between total efflux rate constants in the two tissues. This was attributable to a highly significant correlation between active sodium pumping as assessed by the ouabain-sensitive sodium efflux rate constants observed in both tissues. These results indicate that intrinsic characteristics of cell membrane electrolyte transport are shared by the leucocyte and vascular smooth muscle in human beings. Therefore, leucocytes can be used to provide information about altered vascular ion handling.

Circulating factor with ouabain-like immunoreactivity in patients with primary aldosteronism

Circulating factor with ouabain-like immunoreactivity was studied in patients with primary aldosteronism. Anti-ouabain antibody was prepared from specific pathogen-free rabbits. In the plasma of patients with primary aldosteronism, the level of a factor with ouabain-like immunoreactivity was 2.59 +/- 1.39 pmol ouabain equivalent/ml plasma. This value was significantly (p less than 0.05) higher than that of age-matched normotensive subjects, 1.06 +/- 0.86 pmol ouabain equivalent/ml plasma. The plasma level of ouabain-like immunoreactivity correlated significantly (p less than 0.05) with blood pressure. These results indicate that the factor with ouabain-like immunoreactivity may play a pathophysiological role in the maintenance of the high blood pressure observed in patients with primary aldosteronism.

Endogenous "ouabain-like" activity in bovine plasma

An endogenous inhibitor of the sodium pump has been detected and concentrated 1000-fold from bovine plasma. The steps of purification included deproteinization and extraction with methanol, removal of lipids by coextractions with a lipophilic solvent, desalting and further concentration by adsorption on C18-SepPack cartridges and HPLC fractionation on a weak anionic exchange column. The material isolated displaces 3H-ouabain from brain synaptosomes, inhibits red cell membrane Na,K-ATPase without inhibiting Mg-ATPase or Ca,Mg-ATPase. Deproteinization of plasma by boiling may lead to appearance of non-specific inhibitors. The procedures developed should now permit isolation of sufficient amount of material for further purification and structural characterization.

Effects on blood pressure of cross circulation between spontaneously hypertensive and normotensive rats

In order to examine the role of humoral factors for the development of hypertension in the spontaneously hypertensive rat of the Münster strain (SHR) cross circulation experiments with normotensive Wistar Kyoto rats were performed. Cross circulation between SHR and normotensive rats for 30 min increased mean arterial pressure in the latter by 29.1 +/- 7.6 mm Hg (p less than 0.01). Transmission of hypertension by cross circulation was abolished by nephrectomy, adrenalectomy, volume depletion or chronic salt restriction in the SHR. It is concluded that hypertension in SHR is caused by a circulating hypertensive agent produced in kidneys and adrenals, the secretion of which can be suppressed by volume or salt depletion.

Monovalent and divalent cations in hypertension

The relationship of four cations (sodium, potassium, calcium, magnesium) to hypertension is reviewed. It seems reasonable to advise some reduction in sodium intake, and an initial goal of a mean intake of 120 mmole per day for men and 90-100 mmole per day for women is suggested. Some increase in potassium intake may well be justifiable but is better achieved through potassium-containing foods than by any artificial supplements. The data for calcium and magnesium are not sufficiently strong to warrant any recommendation for a change in intake at present.

The plasma membrane sodium-hydrogen exchanger and its role in physiological and pathophysiological processes

The plasma membranes of most if not all vertebrate cells contain a transport system that mediates the transmembrane exchange of sodium for hydrogen. The kinetic properties of this transport system include a 1:1 stoichiometry, affinity for lithium and ammonium ion in addition to sodium and hydrogen, the ability to function in multiple 1:1 exchange modes involving these four cations, sensitivity to inhibition by amiloride and its analogues, and allosteric regulation by intracellular protons. The plasma membrane sodium-hydrogen exchanger plays a physiological role in the regulation of intracellular pH, the control of cell growth and proliferation, stimulus-response coupling in white cells and platelets, the metabolic response to hormones such as insulin and glucocorticoids, the regulation of cell volume, and the transepithelial absorption and secretion of sodium, hydrogen, bicarbonate and chloride ions, and organic anions. Preliminary evidence raises the possibility that the sodium-hydrogen exchanger may play a pathophysiological role in such diverse conditions as renal acid-base disorders, essential hypertension, cancer, and tissue or organ hypertrophy. Thus, future research on cellular acid-base homeostasis in general, and on plasma membrane sodium-hydrogen exchange in particular, will enhance our understanding of a great variety of physiological and pathophysiological processes.

Right-side-out pumping Na,K-ATPase-liposomes: a new tool to study the enzyme's receptor function

The technology to prepare right-side-out pumping Na,K-ATPase-liposomes is described. The 50% right-side-out oriented pumps of ATP-containing liposomes are then activated by the addition of external Rb ions, leading to a ouabain-sensitive Rb-influx which is the mirror-image of the inside-out transport. The resulting internal Rb concentration is 4 to 10 fold larger than the external concentration. Finally, the accumulated Rb ions can be extruded by driving the 50% inside-out oriented pumps by external ATP.

Arguments for the presence of a Na-K ATPase pump inhibitor in the plasma of uremic and essential hypertensive patients

The effect of salt and/or volume depletion has been tested in 6 end-stage renal disease and 11 essential hypertensive patients (HTA) on red blood cell (RBC) ionic fluxes. Volume depletion promotes an increase in the RBC Na-K ATPase activity with, as a result, a significant decrease in intracellular sodium concentration [Na)ic). Moreover, a factor has been found in the plasma of uremic subjects which causes natriuresis when injected in rat renal arteries. The concentration of this factor decreases during dialysis in relation to the weight loss and the increase in the RBC Na-K pump activity. In essential hypertension, the effect of a low salt diet on the blood pressure is correlated with the improvement of RBC Na-K ATPase activity. These experiments illustrate the presence of a Na-K ATPase inhibitor in the plasma of these subjects, dependent on sodium and water balance.