A sulphonylthiourea (BM 20) related to torasemide: a new loop diuretic with relative potassium-sparing properties

A series of sulphonylthioureas related to torasemide, a high ceiling loop diuretic, were synthesized and found to inhibit the Na+ 2Cl- K+ co-transporter of the thick ascending limb of the loop of Henlé. Their diuretic properties were studied (30 mg kg-1) after oral administration to rats. Lipophilic derivatives, very active in-vitro, were found inactive orally and intraperitoneally in rats. The four most active compounds were examined for their dose-dependent diuresis. Three of them showed a potency, water and electrolyte excretion similar to torasemide. The fourth molecule, a sulphonylthiourea (BM 20), exhibited relative potassium-sparing properties and a minimal diuretic dose of 0.001 mg kg-1, 200 times lower than torasemide.

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.

Red blood cell Na-Li countertransport, hypertensive heredity, and cardiovascular risk in young adults

The erythrocyte Na-Li countertransport (CT) has been considered as a marker of genetic propension to essential hypertension, but also to be linked to atherosclerosis risk factors. We have evaluated these relationships by measuring the Na-Li CT, blood pressure levels, the family predisposition to hypertension, body mass index, subscapular skin-fold thickness, waist/hip ratio, and plasma lipids in 43 young adults (22 to 23 years; 13 with a positive family history of hypertension), followed since adolescence (+/- 10 years) to analyze the natural history of blood pressure in this period of life. The Na-Li CT was negatively correlated with the HDL cholesterol (r = -0.37) and the HDL cholesterol/total cholesterol ratio (r = -0.44). This transport system was positively correlated to family history of hypertension (r = 0.38), waist/hip ratio, and the diastolic blood pressure. When the family history of hypertension was present, Na-Li CT and diastolic blood pressure were higher (P < .05), but the HDL cholesterol was lower (P < .01). After separating people according to the blood pressure level during adolescence in two groups, one lower than the 75th percentile (P75), and one higher, we notice that the latter remains characterized by a higher systolic blood pressure. But neither the Na-Li CT nor family history of hypertension and plasma lipids could explain the difference in the blood pressure behavior during this period. Thus, an increase of RBC Na-Li CT activity in young adults would suggest a higher cardiovascular risk rather than to be a simple marker of a hypertensive risk.

Plasma Na-K ATPase inhibitor activity and intracellular ions during hemodialysis

We have investigated the relationship between plasma Na-K ATPase inhibitor activity (EDLS) and intracellular ions in 37 uremic hemodialysed hypertensive patients, and in 20 normotensive non uremic controls (NC). As compared with the NC population, significantly enhanced values for erythrocyte (RBC) Na, Ca, platelet cytosolic Ca and EDLS were observed in all the uremic patients tested just before a dialysis session, as well as a decrease in RBC Ca ATPase and in the platelet pH. In uremia, significant correlations have been noted between RBC Na and platelet Ca (r = 0.6) or systolic BP (r = 0.45); between platelet Ca and systolic blood pressure (r = 0.8) or diastolic BP (r = 0.5) and between EDLS and RBC Na, Ca or platelet Ca (r = 0.5). Anti-hypertensive treatment has no influence on these parameters. During dialysis, a significant decrease has been noted in RBC Na, Ca, platelet Ca, SBP (only in untreated patients) and EDLS and an increase in RBC Ca ATPase and platelet pH. These modifications are significantly correlated with the weight change.

Importance of weight loss and sodium restriction in the treatment of mild and moderate essential hypertension

The effectiveness of non pharmacological treatment of chronic arterial hypertension has been evaluated in 116 treated or not primary hypertensive out-patients. Those receiving diuretics were however excluded. This population was requested to follow for 3 months a modification of their usual diet characterized by salt restriction combined with energy intake restriction when the patients were above their ideal body weight. Only 62 patients (53%) completed the study. However, this approach was effective by decreasing blood pressure and total cholesterol. The weight loss appears the most effective way to decrease blood pressure in untreated patients, but needs 3 months to be significant. In drug-treated patients, the sodium restriction significantly influences the blood pressure level, already after 1 month. However, salt sensitivity has been noted, especially in the most severe forms of the hypertensive disease. The combination of both modifications (weight loss and sodium restriction) does not appear to be more effective than each separate dietary measure.

Low sodium diet in essential hypertension. Effect on blood cell ions and hemodynamic parameters

The influence of salt restriction for 3 months on blood pressure, peripheral vascular resistance (observed by occlusive plethysmography), erythrocyte sodium, platelet calcium, and pH, was studied in eight untreated essential hypertensive patients. A low salt diet decreases blood pressure, vascular resistances, erythrocyte sodium, and platelet calcium, but not platelet pH. A strong positive correlation was noted between baseline platelet calcium and vascular resistances (r = 0.95, P less than .01). But during the salt restriction period, a negative correlation has been observed between the changes in these parameters, which casts doubt on the use of the platelet as a model of the smooth muscle cell.

[Effect of dietary sodium in hypertension not treated with drugs]

The usefulness of salt restriction in essential hypertension is still now disputed. This study was designed to test the influence of a diet with and without salt restriction in 19 untreated essential hypertensives (12 with and 7 without family history of hypertension) and free of cardiovascular and renal complications. Each patient was examined after a placebo period, after 1 month of salt restriction, and after 1 month of salt supplementation. Weight, blood pressure, 24 hours urinary sodium excretion and red blood cell ionic fluxes were measured. In patients with hypertensive heredity, the blood pressure did not change. The intracellular sodium concentration, the cotransport and the countertransport remained stable. The ouabain sensitive sodium pump slightly increased during salt restriction and remained stable after salt supplementation. In patients without such hypertensive heredity (who were older and heavier), sodium restriction period was characterized by significant decrease in blood pressure, weight, intracellular sodium concentration and increase in sodium pump activity. When salt was increased, all the parameters remained stable. A more balanced diet with sodium restriction decreases the blood pressure in relation to age, weight and the blood pressure level. Hypertensive heredity does not seem to be a parameter of salt sensitivity. The blood pressure decrease is also related to the quantitative importance of sodium restriction. The ouabain sensitive pump activity changes during diet especially in relation to weight loss and decreasing salt intake.

[Arguments for the existence of an endogenous inhibitor of renal Na-K ATPase with steroid structure and natriuretic action]

In order to explain the opposite effect of 6,7-dihydroxylated isomers of 6, 7 - dihydrocanrenone on the urinary sodium and potassium excretion, we have tested the effect of these substances isolated from human urine on the Na(+)-K+ pump from different tissue preparation: rabbit kidney slices as well as NA-K ATPase purified from the kidney. Our results show an inhibition of pump as well as enzyme activity by the 6 beta 7 alpha isomer while the 2 other isomers are either uneffective or slightly stimulating. The 6 beta 7 alpha dihydroxy-6, 7-dihydrocanrenone could be one of the plasma ouabain-like substance incriminated in the pathogenesis of volume-expanded hypertension.

[Does dopamine play a role in renal anomaly in sodium excretion, a marker for hereditary predisposition to arterial hypertension?]

Since Dahl's observation, a renal defect os sodium excretion is proposed as one of pathogenetic mechanism of hypertension (HTA). Our study has tried to verify this concept in 20 young normotensives with (n = 12) and without (n = 8) familial predisposition to HTA, allowing to test the genetic transmission of such potential renal abnormality of sodium balance. Each people was submitted to 3 different Na diet (20, 170 and 340 mM NaCl) each for 1 week. At each visit, blood pressure, vascular resistances, biological values were determined at rest (plasma renin activity, creatinine clearance, 24 hours before the test, catecholamines, aldosterone and ion urinary excretion). Then 1 liter of isotonic saline was perfused in 30 minutes with measures of blood pressure and 3 hours urinary dopamine and Na excretion. During the low and medium Na diets, but not during the high Na diet, the natriuresis and dopamine excretion were lower in the 3 hour urine collection in patients with a family history of HTA (p less than 0.02 and p less than 0.005, respectively). No other clinical or biological difference was noted between the 2 groups. Thus, genetic hypertensive predisposition seems to be characterized by a lower Na excretion during acute Na loading in normal or depleted Na diet, linked to an impaired urinary dopamine excretion. These findings suggest that the defect responsible for the susceptibility to sodium intake is at the kidney level. Some dopamine agonists would be of great therapeutical value in treating such patients when blood pressure begins to rise.

Effect of various 6-dehydro-corticosteroids, 9, 11-dehydro-DOCA and 9 alpha-fluoro-DOCA on the fluxes of sodium and potassium

The introduction of a double bond at carbons 6 and 7 (6-dehydro-derivatives) of deoxycorticosterone acetate (DOCA), cortisol-21-acetate, 9 alpha-fluorocortisol-21-acetate (9 alpha-F-C-ac) and aldosterone-21-acetate substantially reduces affinity for Type II receptors but not for Type I receptors. Such a modification changes the effect of these steroids on urinary excretion of Na+ and K+. 6-Dehydro-derivatives will thus bind preferentially to receptor Type I inducing the retention of sodium and compete with mineralocorticoids for such receptors. The increase in both natriuresis and kaliuresis when corticosteroids and their 6-dehydro-derivatives are administered together may be interpreted as evidence for a Type II receptor mediation of those ion fluxes. The ionic changes are not mediated by the (Na+ + K+)-ATPase system. The fluoration at 9 and the dehydrogenation at C9C11 of DOCA result in a strong increase of binding to Type I receptor and of sodium retention.

[Does ambulatory blood pressure measurement allow a better definition of arterial hypertension?]

The lack of effect of treatment of mild hypertension on the coronary heart disease has motivated researches for a better diagnosis of hypertension. One of the approaches presently under study uses the recording of ambulatory blood pressure using semi-automatic devices. The usefulness of these apparatus is however restricted by the lack of reference values recorded in normotensive control patients. We have recorded ambulatory blood pressure (PAA) in 24 normotensives, 22 untreated hypertensives and 45 treated hypertensive patients, and compared the data obtained to the blood pressure recorded during medical examination (PAC). If a good correlation is usually observed between PAA and PAC, very large and unpredictable discordances are frequently observed. No correlation is found between the difference PAA-PAC and the variability of PAA. This variability does not fully explain the difference observed between PAA and PAC. This variability expressed in mmHg increases with age and the level of BP. Ambulatory BP appears to be a very reproducible value which may allow to improve the definition of hypertension and there-fore the cardiovascular risk.

Interrelationship of hypertension, plasma lipids and atherosclerosis

The relationship between hypertension and atherosclerosis has been illustrated by epidemiological, clinical and experimental observations. Typical atherosclerotic lesions develop in arterial wall when hypercholesterolaemia is present. Hypertension aggravates these lesions by causing vascular structural changes. In clinical studies, however, the correction of high blood pressure does not decrease the incidence of coronary heart disease. Several hypotheses have been formulated to account for this observation: one is that reversibility of the structural vascular changes induced by hypertension is not complete when the blood pressure is lowered; another is that antihypertensive drugs have a deleterious effect on the vascular wall.

Influence of sodium balance on uremic red blood cell ion transport

This study was performed to test the effect of dialysis-induced acute modifications of plasma volume and sodium pool on red blood cell (RBC) ion transport in patients with end-stage renal disease. This approach confirmed the presence of an Na-K pump inhibitor in the plasma of uremic patients with extracellular fluid volume expansion. This factor cross-reacts with digoxin antibodies, and its concentration decreases during dialysis; this explains the increased activity of the RBC Na-K pump that is consistently observed during dialysis.

[Presence and regulation of plasma with natriuretic and Na-K ATPase inhibitory properties in normotensive subjects]

In hypertension, mainly low renin subjects, a plasma Na-K ATPase inhibitor has yet been demonstrated. Moreover, it has been established that the concentration of this activity may be modulated by variations of the sodium and water balance. In the present study, such an activity and its role has been searched in the plasma of young healthy normotensive population. Its potential natriuretic property has also been tested. Twenty male subjects, younger than 30, volunteered 3 very different sodium diets: normal (+/- 170 mM/d), very low (-20 mM/d) and very high sodium intake (+340 mM/d). At the end of each period, some clinical and biological parameters have been studied: blood pressure, weight, vascular resistances and reactivity to norepinephrine, 24 h natriuresis, and plasma renin activity. Furthermore, the plasma natriuretic activity has been tested after filtration of the plasma across different Amicon filters to measure the effect of plasma extracts from 500 to 10,000 daltons (LMW) on fractional sodium excretion (FENa) after injection of such extracts in vivo in rat renal artery. For detection of a plasma Na-K ATPase inhibitor activity, 1/5 th diluted fresh plasma and LMW extracts have been incubated with purified rabbit renal Na-K ATPase enzyme and compared with the activity of this enzyme without such an incubation of plasma. We have observed that when the amount of sodium in the diet is higher, weight, systolic blood pressure, and vascular reactivity to norepinephrine increase. In the same condition, there are greater natriuretic activity in the LMW extracts and Na-K ATPase inhibitor activity in fresh plasma and LMW extracts of the normotensive people.(ABSTRACT TRUNCATED AT 250 WORDS)