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.

Effect of oral contraception on water-suppressed proton NMR spectra of plasma

Lipid linewidths were measured in the plasma proton spectra of young women. The individuals taking a contraceptive pill associating ethinyloestradiol and levonorgestrel or norethisterone were found with an average linewidth 2.5 Hz narrower than controls. As this drug regimen systematically induces an increase in plasma VLDL and a decrease in HDL/LDL ratio, our observation supports the theory that the Fossel test reflects plasma lipids abnormalities in cancer patients.

Cardiovascular structural changes induced by isolation-stress hypertension in the rat

The cardiovascular structural remodelling associated with psychogenic hypertension was investigated in genetically normotensive rats subjected to isolation stress. Male Wistar rats were stressed by intermittent social isolation and compared to control rats living in groups. The stressed rats had higher systolic blood pressures than the control rats throughout the study. After 1 week of isolation, ornithine decarboxylase activity, a marker for hypertrophy, was increased in the right ventricle of the stressed rats. After 6 weeks of intermittent isolation, the myocardium of the stressed rats was hypertrophied, involving both right and left ventricles. The aorta was also hypertrophied, whereas the tail artery remained unaffected. Later, after 12 weeks of isolation, the left ventricular hypertrophy persisted whereas the right ventricle and aorta returned to normal. It seems, therefore, that social stress hypertension is accompanied by very early structural changes, which affect at least the heart and the aorta, and cannot be directly linked to the severity or duration of hypertension.

[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.

[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)

Alterations of intestinal membrane-bound enzymes in three types of hypertensive rats

Alkaline phosphatase, sucrase, Na+,K+-ATPase and Mg2+-ATPase specific activities of crude membrane fractions, prepared from duodenal, jejunal, ileal and colonic mucosa, have been estimated in three types of hypertensive rats: the spontaneously hypertensive rat (SHR), the DOCA-saline treated rat and the renovascular rat (Goldblatt one-kidney, one-clip rat; 1K-1C). Alkaline phosphatase and sucrase specific activities have been measured in purified jejunal brush-border membranes. When compared with its normotensive age-matched control (WKY rat), the SHR has a lower activity of alkaline phosphatase in duodenal and jejunal crude membrane fractions, whereas a higher activity in colonic Na+,K+-ATPase is recorded. In purified jejunal brush-border membranes, lower alkaline phosphatase activity and higher sucrase activity were found. These differences occur in the young prehypertensive SHR as well as in the adult animal. In the DOCA-treated rat, the only significant alteration in crude membrane fractions is a decreased Mg2+-ATPase activity at all regions of intestinal mucosa. In purified jejunal brush-border membranes both alkaline phosphatase and sucrase activities are increased at 4 or 7 weeks but especially at 13 weeks of hypertension. In the 1K-1C rat, no significant modification appears in crude membrane fractions or in purified jejunal brush-border membranes, but a decrease in alkaline phosphatase and in sucrase activities is probable after 13 weeks of hypertension. Since alterations of the intestinal enzymes are different in the three types of hypertensive rats it is concluded that the changes are not secondary to the hypertension condition. In the SHR, these alterations are present in the young prehypertensive animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial metabolism as studied in vitro by NMR: preliminary results in normotensive and hypertensive aortas

Arterial tissue has been analysed by 31P-, 13C-, 23Na- and 1H-NMR spectroscopy. Rabbit thoracic aortas were mounted on a system with perfusate circulation and studied in basal conditions. Phosphorus spectra remained stable for hours and showed low levels of phosphocreatine (PCr) compared to skeletal, cardiac or even to nonvascular smooth muscle. Significant levels of sugar-phosphates (SP), phosphodiesters (PDE) were detected, as well as occasionnally a peak in the diphosphodiester region. Experiments with phosphate-free perfusate demonstrated a very low level of intracellular inorganic phosphate. As expected from previous data, free ADP levels in tonic arterial tissue were found much higher than in any other muscle. Addition of norepinephrine into the perfusate induced transient decrease in ATP and PCr levels, associated with an increased production of phosphorylated intermediates. At the early stage of renovascular hypertension, aortic energetic pattern was characterized by an increased ADP/ATP ratio. Natural abundant 13C spectra were recorded from dog aortic fragments and showed mainly resonances attributed to fatty components. After addition of a shift-reagent, dysprosium tripolyphosphate, 23Na-NMR allowed separation of intra- and extracellular Na of perfused rabbits aortas. Proton NMR of lyophilized aortic fragments revealed several peaks originating from biologically relevant molecules, lactate, creatine, taurine... These preliminary data demonstrate the feasability of multinuclear NMR spectroscopy of vascular tissue and are suggestive of the potential of the method when it will be combined with monitoring of functional parameters.

Erythrocyte sodium-potassium activities, plasma natriuretic activity, and peripheral vascular resistances during hemodialysis or hemofiltration

The effect of hemodialysis (acetate buffer) or hemofiltration on blood pressure, heart rate, peripheral vascular resistances, red blood cells ionic fluxes, and plasma natriuretic activity has been studied in six male patients treated for end-stage renal disease. The hemodynamic response to these two modes of treatment markedly differs. Whereas, peripheral resistances increase and heart rate is not affected during hemofiltration, a decrease in blood pressure, tachycardia, and vasodilation is observed during hemodialysis. However, in both therapeutic approaches, red blood cell ouabain-sensitive sodium-potassium pump activity increases in a similar way, and the plasmatic natriuretic activity decreases, whereas the vascular response to norepinephrine is reduced. All of these changes were strongly correlated to the amount of fluid removed. The natriuretic activity may thus play a role in the regulation of blood pressure and hemodynamic adjustments to fluid removal in chronic renal failure between two dialyses, but its action is not predominant during the dialysis session itself.

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.

The erythrocyte sodium-potassium cotransport in hypertensive patients: advantages and limitations

The Na-K cotransport activity was measured in erythrocytes of 123 normotensive and 92 hypertensive patients, using the methodology described by Dagher and Garay. Large overlap of the values obtained in the two populations is observed, in such a way this laboratory test cannot be applied for the discrimination between primary and secondary hypertension. Moreover, the abnormalities described for the Na-K cotransport do not appear specific for primary hypertension. In this study, the influence of hypertensive heredity, but also obesity on this cotransport system could not be demonstrated. However, this transport activity is significantly decreased in patients with chronic renal failure, during treatment with oestro-progestatives or during the oestrogenic phase of the menstrual cycle. These data strongly suggest that the cotransport activity could be modified not only by the hypertensive familial predisposition but also by environmental and hormonal influences.

Evolution of aortic hyperplasia after reversal of renovascular hypertension in the rat

Unclipping of Goldblatt one-kidney, one clip hypertensive rats leads to a rapid correction of the high blood pressure. Simultaneously, the aortic smooth muscle cell proliferation wave is stopped. Any further proliferation is prevented but the proliferation changes previously established cannot be reversed. Thus, provided clip removal is performed at the earliest phase of hypertension, it can modify the time-course of the aortic proliferation changes. On the contrary, the heart hypertrophy is significantly improved regardless of the unclipping time. Accordingly, the response of the hypertensive cardiovascular modifications to an antihypertensive therapy cannot be regarded as a whole since it is dependent on the cardiovascular target as well as on the onset time of treatment.

Hyperplasia of rat arteries smooth muscle cells associated with development and reversal of renal hypertension

1. Renal hypertension produces a marked and rapidly detectable hypertrophy of the rat aorta, due to smooth muscle cell hyperplasia and connective tissue deposition. 2. As we described previously for collagen synthesis, cell hyperplasia is a very early event which reaches a maximum at a time when the blood pressure is far from its highest level, and thereafter progressively decreases. 3. Reserpine prevents the vascular wall changes on the arterial as well as the venous side of the circulation. On the other hand, captopril although effective in preventing the blood pressure rise does not suppress the hyperplastic response. 4. The arterial hypertensive disease appears to be reversible, when renal ischaemia is corrected. The smooth muscle cell hyperplasia is, however, only partly and slowly reversible. 5. These data suggest that blood pressure is not the only determinant of the vascular wall response, and that the effect of a drug on the blood pressure does nt necessarily predict the vascular wall response.

The relationship between blood pressure and aortic collagen metabolism in renal hypertensive rats

1. Biosynthesis and deposition of collagen, as well as DNA and total proteins, are increased in aortae of rats after 1, 3 and 6 weeks of hypertension. 2. The maximal increase in the rate of synthesis of collagen is observed within one week of hypertension when the stress to the arterial wall is maximal. 3. Reserpine administration prevents hypertension and inhibits the increase of collagen metabolism. 4. At any time of evolution of the hypertension, a linear positive correlation is found between the collagen content in the aorta and the level of blood pressure. 5. These data suggest that synthesis of matrix components by the arterial smooth-muscle cells is controlled by variation in the blood pressure level and is not a direct consequence of circulating humoral factors liberated by the ischaemic kidney.

Ionic composition of arterial wall in experimental hypertension

1. To obtain additional information on the role of the ionic composition of the vascular wall in the pathogenesis of arterial hypertension, we studied the distribution of ions in aorta and tail arteries of rats with experimental renal hypertension.

2. The water content of rat aorta is markedly increased in hypertensive animals [1992 ml/kg-dry weight (DW) compared with 1688 ml/kg DW].

3. Na, K, Ca, Mg and to a less extent Cl content is increased in both aorta and tail arteries.

4. These modifications are not affected by incubation in vitro.

5. Compartmental analysis as well as pharmacological studies suggest that part of the water increase and most of the potassium excess are related to a hypertrophy of smooth-muscle cells in hypertensive arteries.

6. The sodium excess in the vessels of hypertensive rats is bound in the extracellular space on anionic sites.

7. From these observations, it seems unlikely that the ionic modification described could affect the membrane potential of smooth-muscle cells, since the ratio between extra- and intra-cellular concentration is not markedly affected.

8. The bound sodium could affect the viscoelastic properties of the arteries of hypertensive animals. Cell hypertrophy by itself could explain at least partly the modification of the ionic composition and the increased reactivity of hypertensive vessels.