Altered sodium permeability, calcium binding and Na-K-ATPase activity in the red blood cell membrane in essential hypertension

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.

Aluminum Trichloride Induces Hypertension and Disturbs the Function of Erythrocyte Membrane in Male Rats

Aluminum (Al) is the most abundant metal in the earth's crust. Al accumulates in erythrocyte and causes toxicity on erythrocyte membrane. The dysfunction of erythrocyte membrane is a potential risk to hypertension. The high Al content in plasma was associated with hypertension. To investigate the effect of AlCl3 on blood pressure and the function of erythrocyte membrane, the rats were intragastrically exposed to 0, 64(1/20 LD50), 128(1/10 LD50), and 256(1/5 LD50) mg/kg body weight AlCl3 in double distilled water for 120 days, respectively. Then, we determined the systolic and mean arterial blood pressures of rats, the osmotic fragility, the percentage of membrane proteins, the activities of Na(+)/K(+)-ATPase, Mg(2+)-ATPase, Ca(2+)-ATPase, catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-pX), and malondialdehyde (MDA) content of the erythrocyte membrane in this experiment. The results showed that AlCl3 elevated the systolic and mean arterial blood pressure of rats, increased the osmotic fragility, decreased the percentage of membrane protein, inhibited the activities of Na(+)/K(+)-ATPase, Mg(2+)-ATPase, Ca(2+)-ATPase, CAT, SOD and GSH-pX, and increased the MDA content of erythrocyte membrane. These results indicate that AlCl3 may induce hypertension by disturbing the function of erythrocyte membrane.

NKCC1 and NKCC2: The pathogenetic role of cation-chloride cotransporters in hypertension

This review summarizes the data on the functional significance of ubiquitous (NKCC1) and renal-specific (NKCC2) isoforms of electroneutral sodium, potassium and chloride cotransporters. These carriers contribute to the pathogenesis of hypertension via regulation of intracellular chloride concentration in vascular smooth muscle and neuronal cells and via sensing chloride concentration in the renal tubular fluid, respectively. Both NKCC1 and NKCC2 are inhibited by furosemide and other high-ceiling diuretics widely used for attenuation of extracellular fluid volume. However, the chronic usage of these compounds for the treatment of hypertension and other volume-expanded disorders may have diverse side-effects due to suppression of myogenic response in microcirculatory beds.

Long-term normalization of blood pressure in SHR and 1-kidney 1-clip rats by synthetic precursor of stable PAF analogue without systemic effects in normotensive rats

This study characterized the actions of the newly synthesized PAF precursor 1-hexadecyl-2-alkylcarbamoyl-glycerol (HAG) on blood pressure (BP) in male spontaneously hypertensive rats (SHR), SHR-stroke prone (SHRSP) and Wistar rats with 1-kidney 1-clip (1K1C) renovascular hypertension used as experimental models of human primary and secondary hypertension. Systolic blood pressure (SBP) in the tail artery and mean arterial pressure (MAP) in the abdominal aorta were measured by tail plethysmography and invasive pressure transducer, respectively. Intravenous treatment with 1mg/kg HAG in SHR resulted in a rapid decline of MAP from 151±4 to 127±4mmHg in 50min (p<0.001) that was maintained for 24h after injection (128±5mmHg, p<0.01). We also observed a profound hypotensive effect of HAG in SHRSP but not in normotensive Wistar rats. In 1K1C rats, the magnitude of the BP decline evoked by HAG was correlated with MAP measured before drug administration (R=0.74, p<0.005). In 1K1C rats with SBP>140mmHg, 5mg/kg/48h HAG, given orally for 14 days, decreased SBP by 20-30mmHg without an increase in the death rate and other adverse effects. Thus, our results show that intravenous and oral administration of HAG led to a long-lasting reduction of BP in experimental models of primary and secondary hypertension. In contrast to PAF and its derivatives, the hypotensive action of HAG was preserved for 24h after a single administration, was absent in normotensive animals, and was not accompanied by visible side-effects, at least during 2 weeks of treatment.

Molecular origin of Na(+)/Li(+) exchanger: Evidence against the involvement of major cloned erythrocyte transporters

Numerous studies have demonstrated heightened Na(+)/Li(+) countertransport (NLCT) activity in erythrocytes of patients with essential hypertension or diabetic nephropathy. The same carrier also contributes to the therapeutic action of lithium salt, widely used in the treatment of psychiatric disorders. However, the molecular origin of NLCT remains unknown. This study examined the role of major ion transporters in NLCT by comparative analysis of its activity and that of ion transporters providing inwardly directed (86)Rb, (22)Na and (32)P fluxes. NLCT was below the detection limit in rat erythrocytes and ∼50-fold higher in rabbits compared to humans. Unlike NLCT, the activities of Na(+),K(+)-ATPase, Na(+),K(+),2Cl(-) cotransporter and anion exchanger were somewhat similar in the erythrocytes of these species, whereas Na(+),P(i) cotransport was in 1:2:6 proportion in rats, humans and rabbits, respectively. Loading of erythrocytes with Li(+) for NLCT measurement did not affect the activity of Na(+),P(i) cotransporter. Keeping in mind that NLCT is much higher in rabbits vs humans and rats, we compared the set of membrane proteins in these species using 2-dimensional gel electrophoresis. This approach revealed 174 common spots, whereas 132 proteins were detected only in human and rabbit erythrocyte membranes. Among these proteins, we found 17 spots whose expression was higher by more than 5-fold in rabbit compared to human erythrocytes. Thus, our results argue against the involvement of major ion transporters in NLCT. They also show that comparative proteomics is a potent tool to identify the molecular origin of this carrier.

Changes in intraerythrocyte content and transmembrane fluxes of sodium during salt loading in subjects with and without family history of hypertension

We studied 17 young normotensive men with family history of hypertension (H) in two generations (father and grandfather) and 17 age matched control subjects (C) with respect to intraerythrocyte sodium (IeNa), sodium influx, and rate of sodium efflux. The investigation was done during ordinary salt intake and after four week's salt load. H had a significantly higher IeNa (9.5 +/- 0.4 mmol/l) compared to C (8.2 +/- 0.3 mmol/l), p less than 0.01. After salt loading H decreased significantly to 8.1 +/- 0.3 mmol/l while C did not change significantly (7.6 +/- 0.3 mmol/l). There was no significant difference between H and C in Na influx either on normal or on high salt intake. The rate constant for Na efflux was significantly lower on normal salt intake in H (0.0038 +/- 0.0003 vs 0.0050 +/- 0.0004 min-1, p less than 0.05). High salt intake increased the efflux rate constant significantly in H (0.0048 +/- 0.0003 min-1, p less than 0.05), while control subjects showed no difference (0.0053 +/- 0.0004 min-1) compared to pre-salt conditions. Our results suggest that young men with heredity for hypertension have a higher intraerythrocyte Na-content secondary to a lower rate of Na efflux. The Na influx did not differ between the two groups probably indicating an unchanged permeability for sodium in subjects with a family history of hypertension.

Erythrocyte and total body potassium in untreated primary hypertension

In a study of total body and erythrocyte potassium in mild hypertension we found decreased intracellular potassium concentrations in 41 hypertensives compared to controls but no correlation between intracellular potassium, measured by whole body counting, and erythrocyte potassium. A total body potassium corresponding to an intracellular potassium of 85% or less of the expected value was found in females. In the hypertensives, a negative correlation existed between serum and erythrocyte potassium. No correlation was found between potassium decrease and urinary aldosterone or plasma renin level. An inhibition of the active sodium-potassium exchange at the cellular level is proposed as an explanation of these findings.

Rubidium uptake of mononuclear leukocytes from normotensive and borderline hypertensive first degree relatives to patients with essential hypertension

Uptake of 86Rubidium of mononuclear leukocytes (MNL) was used as a measure of cellular sodium-potassium pump activity. 86Rb-uptake was determined with the pump stimulated mainly from inside the cells by sodium as well as with a combined stimulation from inside by sodium and from outside by Rb. In the first case there was an increased pump activity in MNL from borderline hypertensive offspring of hypertensive patients (BHO), and this may be related to an increased number of pump sites observed previously (10). Estimation of maximal pump activity (Vmax) of MNL suggested that Vmax of each pump site in MNL from BHO may be decreased compared to control value of MNL from healthy normotensive subjects.

Genetic and biochemical determinants of abnormal monovalent ion transport in primary hypertension

Data obtained during the last two decades show that spontaneously hypertensive rats, an acceptable experimental model of primary human hypertension, possess increased activity of both ubiquitous and renal cell-specific isoforms of the Na+/H+ exchanger (NHE) and Na+-K+-2Cl- cotransporter. Abnormalities of these ion transporters have been found in patients suffering from essential hypertension. Recent genetic studies demonstrate that genes encoding the beta- and gamma-subunits of ENaC, a renal cell-specific isoform of the Na+-K+-2Cl- cotransporter, and alpha3-, alpha1-, and beta2-subunits of the Na+-K+ pump are localized within quantitative trait loci (QTL) for elevated blood pressure as well as for enhanced heart-to-body weight ratio, proteinuria, phosphate excretion, and stroke latency. On the basis of the homology of genome maps, several other genes encoding these transporters, as well as the Na+/H+ exchanger and Na+-K+-2Cl- cotransporter, can be predicted in QTL related to the pathogenesis of hypertension. However, despite their location within QTL, analysis of cDNA structure did not reveal any mutation in the coding region of the above-listed transporters in primary hypertension, with the exception of G276L substitution in the alpha1-Na+-K+ pump from Dahl salt-sensitive rats and a higher occurrence of T594M mutation of beta-ENaC in the black population with essential hypertension. These results suggest that, in contrast to Mendelian forms of hypertension, the altered activity of monovalent ion transporters in primary hypertension is caused by abnormalities of systems involved in the regulation of their expression and/or function. Further analysis of QTL in F2 hybrids of normotensive and hypertensive rats and in affected sibling pairs will allow mapping of genes causing abnormalities of these regulatory pathways.

Can we use erythrocytes for the study of the activity of the ubiquitous Na+/H+ exchanger (NHE-1) in essential hypertension?

Both Na+/Li+ countertransport and electrochemical proton gradient (delta mu(H+))-induced Na+ and H+ fluxes are increased in erythrocytes from patients with essential hypertension. It was assumed that these abnormalities are related to ubiquitous (housekeeping) forms of the Na+/H+ exchanger (NHE-1). To examine this hypothesis, we compared kinetic and regulatory properties of erythrocyte Na+/Li+ countertransport and delta mu(H+)-induced Na+ and H+ fluxes with data obtained for cloned isoforms of the Na+/H+ exchanger. In human erythrocytes, Na+/Li+ countertransport exhibited a hyperbolic dependence on [Na+]0 with a K0.5 of approximately 30 to 40 mmol/L. The activity of this carrier was increased by two-fold in the fraction of erythrocytes enriched with the old cells, was inhibited by 0.1 mmol/L phloretin, and was insensitive to both 1 mmol/L amiloride and ATP depletion. In contrast, delta mu(H+)-induced 22Na influx was exponentially increased at [Na+]0 > 60 mmol/L, was insensitive to phloretin, was partly decreased by both 1 mmol/L amiloride and ATP depletion, and was the same in total erythrocytes and in the old cells. The values of Na+/Li+ countertransport and delta mu(H+)-induced Na+ influx in erythrocytes from different species were not correlating and their ratio in human, rat, and rabbit erythrocytes was 10:1:170 and 1:5:1 for Na+/ Li+ countertransport and delta mu(H+)-induced Na+ influx, respectively. In contrast to the majority of nonepithelial cells and cells transfected with an ubiquitous isoform of Na+/H+ exchanger, both delta mu(H+)-induced Na+ influx and Na+/Li+ countertransport in human erythrocytes were completely insensitive to ethylisopropyl amiloride (20 micromol/L) and cell shrinkage. Thus, our data strongly suggest that human erythrocyte Na+/Li+ countertransport and delta mu(H+)-induced Na+/H+ exchange are mediated by the distinct transporters. Moreover, because the properties of these erythrocyte transporters and NHE-1 are different, it complicates the use of erythrocytes for the identification of the mechanism for activating the ubiquitous form of Na+/H+ exchanger in primary hypertension.

Alterations in sodium metabolism as an etiological model for hypertension

An adequate matching for race, sex, stage of the menstrual cycle, family history of hypertension, and the amount of sodium and other electrolytes in the diet should be a prerequisite for valid conclusions when interpreting the erythrocyte concentration and fluxes of sodium in essential hypertensive patients in comparison with normal subjects. Alterations in intracellular sodium concentration and transmembrane sodium transport systems as causes of essential hypertension are postulated. This review article describes how this abnormal sodium and calcium metabolism translates into increased systemic vascular resistance through altered vasoactive responses and/or vasculature structural changes.

Increased dietary NaCl intake influences lens transport properties in Sprague-Dawley rats

Several years ago, we reported a high frequency of cataracts in Dahl salt-sensitive rats (DS) which led us to carry out a series of studies, such as longitudinal ouabain-sensitive lens 86Rb uptake measurements. Yet, throughout all of our work, we used the Dahl salt-resistant rat (DR) as our control group, despite the fact that DR is a strain resistant to even experimental hypertension such as that resulting from renal cellophane wrapping. Thus, in the present study we assessed lens short-circuit current (Isc) in adult Sprague-Dawley rats (SD) from which DS and DR were derived. Sprague-Dawley rats were studied during chronic normal vs high NaCl intake. These studies showed that basal Isc and calculated translenticular potential difference (PDt) were nearly doubled by this dietary regimen. Sequential addition of BaCl2 and ouabain to the isolated lens anterior surface bath also revealed increased BaCl2-sensitive as well as BaCl2- and ouabain-insensitive lens Isc in SD kept on a high NaCl diet. There was a statistically insignificant tendency for lens ouabain-sensitive Isc to increase in SD given a high NaCl diet. These findings were unrelated to levels of arterial blood pressure which were not altered by chronic high NaCl intake in adult SD. Our data suggest the possibility of increased lens barium and ouabain insensitive ionic permeabilities combined with possibly increased lens fiber potassium concentration, as a response to chronic high dietary NaCl in the normal rat. The nature of the barium and ouabain insensitive component of the lens Isc that rises during chronic high NaCl intake requires elucidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective effect of nicardipine treatment on renal microanatomical changes in spontaneously hypertensive rats

The effects of nicardipine administration on kidney morphology were studied in spontaneously hypertensive rats (SHR). Male 12-week-old SHR received an oral dose of 1 mg/Kg/day of nicardipine or vehicle for 8 weeks Age-matched Wistar-Kyoto rats were used as normotensive reference animals. At 20 weeks, the non treated SHR exhibited hypertension, albuminuria, decreased urinary sodium excretion and renal microanatomical changes. These changes were characterized by vascular alterations consisting in hypertrophy of the tunica media accompanied by a decrease of luminal surface. Glomerular changes consisting primarily in signs of glomerulosclerosis of varying degrees were noticeable in the kidneys of SHR. Treatment with nicardipine significantly reduced blood pressure and albuminuria and increased urinary sodium excretion. Moreover, hypertrophy of the tunica media and the luminal surface were decreased and increased respectively in nicardipine-treated SHR. The above results suggest that treatment with nicardipine reduces blood pressure in SHR and counteracts hypertension-dependent changes in the morphology of the kidney. The protective effect of the drug on hypertensive changes of renal microanatomy probably have functional relevance given of the influence of nicardipine treatment on albuminuria and urinary sodium excretion in SHR.

Erythrocyte sodium ion transport system in DOC-salt, Goldblatt, and spontaneously hypertensive rats

Altered erythrocyte Na+ transport has been observed in relation to the pathogenesis of essential hypertension. In the present study, intracellular Na+ and K+ levels, Na(+)-K+ pump activity, Na(+)-K+ cotransport, and Na+ passive permeability were measured in erythrocytes of DOC-salt hypertensive (DSH) rats, two-kidney, one clip Goldblatt hypertensive (2KH) rats, and spontaneously hypertensive rats (SHR). The results were as follows: 1. In comparison with the control groups, no change in the erythrocyte Na+ level was noted in the DSH and 2KH groups, whereas a significant increase was seen in the SHR group. 2. Although no change was noted in the erythrocyte K+ level in the 2KH and SHR groups when compared with the control groups, a significant decrease was seen in the DSH group. 3. Na(+)-K+ pump activity of erythrocytes was not changed in the DSH and 2KH groups when compared with the control group, but a significant increase was noted in the SHR group. 4. Na(+)-K+ cotransport of erythrocytes was not changed in any hypertensive rats when compared with the controls. 5. Na+ passive permeability in the erythrocyte membrane was not changed in the DSH and 2KH groups when compared with the control groups, but a significant increase was noted in the SHR group. These findings suggest that increased erythrocyte Na+ levels in SHR are due to increased Na+ passive permeability of the erythrocyte membrane, and increased Na(+)-K+ pump activity may be compensating for the increased intracellular Na+ concentration in erythrocytes. Furthermore, the increase in Na+ passive permeability observed in SHR might not result from hypertension itself but from abnormalities in the erythrocyte cell membrane, because no increase in Na+ passive permeability was noted in either DSH or 2KH rats.

Acute effects of angiotensin-converting enzyme inhibitor on erythrocyte sodium ion transport in essential hypertension

The acute effects of angiotensin-converting enzyme inhibitor, captopril, on sodium ion transport systems were investigated in essential hypertensive and normotensive subjects. The passive sodium efflux through the erythrocyte membrane was significantly higher and erythrocyte sodium-potassium cotransport was lower in patients with essential hypertension when compared with normal subjects. However, sodium-potassium pump activity and sodium-lithium countertransport did not differ significantly between the hypertensive patients and the normal subjects. Immediately after captopril administration, erythrocyte passive sodium efflux and sodium-potassium cotransport returned to normal levels in the hypertensive subjects. Although the plasma renin activity and plasma aldosterone concentration were altered by captopril, they did not correlate with changes in any sodium transport system. These results suggest that the changes in sodium transport systems which occur immediately after captopril administration may contribute, at least in part, to its antihypertensive action.

Decreased cell membrane magnesium in some essential hypertension patients

The concentrations of total ([T-Mg]), ultrafilterable ([UF-Mg]), and protein-bound or nonfilterable ([NF-Mg]) magnesium were measured in the plasma and in the intracellular compartment of blood from 8 essential hypertensive patients and 9 normotensive subjects. In the former, [T-Mg] was unchanged in the plasma but decreased in whole blood due to decreases of both [UF-Mg] and [NF-MG]; [UF-Mg] was increased in plasma but decreased intracellularly while [NF-Mg] was decreased in plasma and unchanged intracellularly. These concentrations correlated significantly with the average blood pressures. Decreased Mg binding to the erythrocyte membrane was also observed in 13 additional essential hypertensive patients. This decreased binding may well be responsible for the decreased intracellular [UF-Mg] in the blood of such patients. The cause of the decreased Mg binding to the erythrocyte membrane is unknown, but the binding is returned to normal by incubating erythrocytes from essential hypertensive patients with blood plasma from normotensive subjects. Decreased Mg binding to cell membranes must also occur in frankly Mg-deficient patients, some of whom, as a consequence of the primary deficiency of this mineral, are hypertensive. Normal Mg binding to erythrocyte membranes was observed in two patients with hypertension indicating that hypertension per se does not cause decreased Mg binding to cell membranes. These observations suggest that decreased Mg binding to cell membranes may be an important contributing factor in some cases of essential hypertension.

The ATPase activity of saponin-treated rat erythrocytes: regulation by monovalent cations, calcium, ouabain, and furosemide

The ATPase activities were studied in rat erythrocytes permeabilized with saponin. The concentrations of calcium and magnesium ions were varied within the range of 0.1-60 microM and 50-370 microM, respectively, by using EGTA-citrate buffer. The maximal activity of Ca2(+)-ATPase of permeabilized erythrocytes was by one order of magnitude higher, whereas the Ca2(+)-binding affinity was 1.5-2 times higher than that in erythrocyte ghosts washed an isotonic solution containing EGTA. Addition of the hemolysate restored the kinetic parameters of ghost Ca2(+)-ATPase practically completely, whereas in the presence of exogenous calmodulin only part of Ca2(+)-ATPase activity was recovered. Neither calmodulin nor R24571, a highly potent specific inhibitor of calmodulin-dependent reactions, influenced the Ca2(+)-ATPase activity of permeabilized erythrocytes. At Ca2+ concentrations below 0.7 microM, ouabain (0.5-1 mM) activated whereas at higher Ca2+ concentrations it inhibited the Ca2(+)-ATPase activity. Taking this observation into account the Na+/K(+)-ATPase was determined as the difference of between the ATPase activities in the presence of Na+ and K+ and in the presence of K+ alone. At physiological concentration of Mg2+ (370 microM), the addition of 0.3-1 microM Ca2+ increased Na+/K(+)-ATPase activity by 1.5-3-fold. Higher concentrations of this cation inhibited the enzyme. At low Mg2+ concentration (e.g., 50 microM) only Na+/K(+)-ATPase inhibition by Ca2+ was seen. It was found that at [NaCl] less than 20 mM furosemide was increased ouabain-inhibited component of ATPase in Ca2(+)-free media. This activating effect of furosemide was enhanced with a diminution of [Na+] upto 2 mM and did not reach the saturation level unless the 2 mM of drug was used. The activating effect of furosemide on Na+/K(+)-ATPase activity confirmed by experiments in which the ouabain-inhibited component was measured by the 86Rb+ influx into intact erythrocytes.

Attenuated vasodilator responses to Mg2+ in young patients with borderline hypertension

Limb vascular responses to magnesium (Mg2+) and potassium (K+) ions were studied in 19 young patients with borderline hypertension (BHT) and compared with those of 22 age-matched normotensive subjects (NT) by measuring the forearm blood flow response to intra-arterial infusion of magnesium sulfate and potassium chloride using venous occlusion plethysmography. Percent decrements of forearm vascular resistance with Mg2+ infusions were significantly less in BHT subjects than in NT (-37.2 +/- 4.2% versus -53.0 +/- 2.0%, p less than 0.05, during the infusion of 0.1 meq Mg2+/min, and -52.2 +/- 4.3% versus -65.6 +/- 1.5%, p less than 0.05, during the infusion of 0.2 meq Mg2+/min). Moreover, the relation of the magnitude of Mg2+ response to initial vascular resistance in six of 10 BHT subjects lies above the 95% confidence interval for predicted values calculated for response points in 11 NT subjects, suggesting attenuated vasodilator responses of Mg2+ in a significant proportion of BHT subjects. In contrast, the response points to K+ in eight of nine BHT subjects fall within the 95% confidence interval, suggesting normal vasodilator responses to K+ in the majority of BHT subjects. Furthermore, the effect of small increments in local serum calcium concentrations on Mg2(+)- and K(+)-induced vasodilation was studied in normal volunteers. Isosmolar CaCl2 solution infused into the same brachial artery at a rate of 0.09 meq/min severely blunted the vasodilating actions of Mg2+ (-30.1 +/- 6.5% versus -65.8 +/- 3.2%, p less than 0.01, during the infusion of 0.2 meq Mg2+/min) but did not affect those of K+ (-63.1 +/- 3.1% versus -55.9 +/- 3.8%, NS, during the infusion of 0.154 meq K+/min). It appears that Mg2(+)-induced vasodilation should be due to the antagonistic action of Mg2+ to calcium, but K(+)-induced vasodilation might not be directly related to calcium movement. Thus, these attenuated responses to Mg2+ but normal responses to K+ in BHT subjects may indicate an underlying defect in vascular Mg2+ metabolism, which ultimately may be related to the alterations in calcium handling by plasma membranes rather than to the abnormalities of membrane Na(+)-K+ pump activity.

Diuretic effect of bumetanide in isolated perfused kidneys of Milan hypertensive rats

The Milan hypertensive strain of rats (MHS) is characterized in the prehypertensive phase (4 weeks of age) by a significantly faster bumetanide-sensitive cell membrane Na+,K+,Cl(-)-cotransport as compared to matched normotensive controls (MNS). The isolated kidney preparation, which allows the study of renal function under controlled in vitro conditions, was chosen to compare the natriuretic effect of the loop diuretic, bumetanide, to that of two other diuretics (amiloride and hydrocholorothiazide) acting on different parts of the nephron. Concentrations ranging from 10(-7) to 10(-4) M were tested in 4-week-old MHS and MNS. Our results showed that the natriuretic response to all diuretics was greater in MHS as compared to MNS when evaluated as absolute Na+ excretion (UNA+); this is likely because of the faster basal glomerular filtration rate (GFR) in the hypertensive strain (874 +/- 126 in MHS vs. 556 +/- 33 microliters.min-1.g-1 k wt in MNS, P less than 0.05). However, when calculated either as a difference from basal values (delta UNa+), or per ml of glomerular filtration rate, the response of MHS kidneys to amiloride and hydrochlorothiazide was similar in the two strains: delta UNa+ after amiloride at (10(-4) M was + 2.1 +/- 0.7 in MHS versus + 1.2 +/- 0.2 mumol.g-1.g-1 k wt in MNS; after hydrochlorothiazide 10(-4) M it was + 1.7 +/- 0.9 in MHS versus + 1.1 +/- 0.4 mumol.min-1.g-1 k wt in MNS, values not statistically different.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte concentrations and transmembrane fluxes of sodium and potassium in essential hypertension: role of intrinsic and environmental factors

The intraerythrocyte sodium concentration is increased in the erythrocytes of Zaïrean Bantu with untreated hypertension, while the red blood cell potassium is not different from that of normotensive subjects. Compared with whites, normotensive healthy blacks have a higher intracellular concentration of sodium due to a depressed activity of the sodium-potassium pump. Normotensive healthy males with a positive familial background of hypertension display higher erythrocyte sodium and lower cotransport activity. None of the two measurements offer a clear-cut genetic marker of essential hypertension. In healthy women, the erythrocyte sodium concentration is lowered during the luteal as compared with the follicular phase of the menstrual cycle. This variability explains the difference observed between men and women. A low-sodium diet stimulates the activity of the sodium-potassium ATPase pump, which leads to a decrease in the erythrocyte sodium concentration. Both alterations reverse only slowly during sodium repletion. It is therefore suggested that an adequate matching for race, sex, stage of the menstrual cycle (in women), family history of hypertension, and the amount of sodium in the diet should be a prerequisite for valid conclusions when interpreting the erythrocyte concentration and fluxes of sodium.

Dietary linoleic acid prevents the development of deoxycorticosterone acetate-salt hypertension

The aim of this study was to elucidate the effect of dietary variations of linoleic acid on the development of deoxycorticosterone acetate (DOCA)-salt hypertension in rats. All rats were divided into three groups and fed one of the following isocaloric diets with 8% NaCl: a high linoleic acid (HLA) (20% sunflower oil), a moderate linoleic acid (5% lard oil + 15% sunflower oil), or a low linoleic acid (DLA) (20% lard oil). After 4 weeks of feeding, we determined intraerythrocyte sodium, potassium, and magnesium concentrations, intra-aortic and lymphocyte magnesium content, and erythrocyte ouabain-sensitive 22Na efflux rate constant. Cytoplasmic free calcium concentration of lymphocytes from thymus was also determined with quin-2 as a fluorescent indicator. In the HLA group, the elevation of systolic blood pressure was significantly attenuated, and intraerythrocyte sodium concentration was significantly lower than in the DLA group. There were greater intraerythrocyte potassium and magnesium concentrations, intra-aortic and lymphocyte magnesium contents, and erythrocyte ouabain-sensitive 22Na efflux rate constant in the HLA group as compared with other groups. Cytoplasmic free calcium concentration in the HLA group was significantly lower than in other groups. Systolic blood pressure significantly correlated negatively with intraerythrocyte and intra-aortic magnesium concentrations and intraerythrocyte potassium concentration, and correlated positively with cytoplasmic free calcium concentration. Erythrocyte ouabain-sensitive 22Na efflux rate constant significantly correlated positively with intraerythrocyte magnesium concentration. These findings suggest that dietary linoleic acid can attenuate the development of DOCA-salt hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte rheology

Two main subjects of erythrocyte rheology, deformation and aggregation, are discussed in detail, on the basis of biochemical structure. The close relationship between the life span (or cell aging) and the rheology of individual erythrocytes is also briefly described. A currently important problem is emphasized, that is, the molecular aspect of the dynamic cytoskeletal structure and the mechanism of its regulation. This concerns not only the rheological function and the survival of circulating erythrocytes, but also the pathophysiology of abnormal erythrocytes.

Brain synaptosomal Ca2+ uptake: comparison of Sprague-Dawley, Wistar-Kyoto and spontaneously hypertensive rats

1. K(+)-stimulated 45Ca2+ uptake by synaptosomes was measured with respect to the strain differences between Sprague-Dawley (SD), Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). 2. 45Ca2+ uptake by synaptosomes isolated from cerebral cortex of SD, WKY and SHR was measured at 15, 30, 60, 120 and 240 sec time periods. 3. The sequence of both the magnitude and rate of resting and depolarization-dependent 45Ca2+ uptake was SHR greater than WKY greater than SD. 4. The fastest rates of resting and depolarization-dependent 45Ca2+ uptake occurred in each rat during the first 15 sec and uptake rates dropped off quickly in both resting and depolarization states. 5. At 15 sec, there were significant differences between SHR and WKY, while there were no significant differences between WKY and SD. 6. The results suggest that an important alteration in Ca2+ channel characteristics may occur in SHR brain synaptosomes.

Increased 22Na+-influx in lymphocytes from offspring of essential hypertensive patients

Lymphocytes were used as a cellular model for the in vitro measurements of 22Na+-influx during sodium pump inhibition by ouabain. The measurements were made using lymphocytes from young men at increased risk of developing essential hypertension in order to assess any changes and to analyse whether any such changes were associated to borderline hypertension and/or heredity. Four groups were evaluated: 28 normotensive and 20 borderline hypertensive offspring of hypertensives, 12 borderline hypertensives and 28 normotensives with normotensive parents. 22Na+-influx was significantly increased in offspring of hypertensive parents especially in the normotensive offspring of hypertensive parents. The association between heredity and increased 22Na+-influx found by us in vitro may be caused by either an increased passive sodium-influx and/or an increased sodium-sodium exchange mechanism.

Increased number of ouabain binding sites in lymphocytes from borderline hypertensives

Lymphocytes were used as a cellular model for the in vitro measurements of maximal ouabain binding sites in order to assess any changes in young men at increased risk of developing essential hypertension, and to analyse whether any such changes were associated to borderline hypertension and/or heredity. Four groups were evaluated; 28 normotensive (NTO) and 20 borderline hypertensive (BHO) offspring of hypertensives. Twelve borderline hypertensives (BH) and 28 normotensive subjects (NT) with normotensive parents. The number of ouabain binding sites were significantly increased in the borderline hypertensives irrespective of heredity. The borderline hypertensives were heavier than the normotensives. A stepwise multiple regression model was therefore used in order to control confoundings by body mass index (BMI) and other factors such as age, gamma glutamyl transferase, 24 h sodium excretion, serum triglyceride, and serum cholesterol, which may influence the number of ouabain binding sites. Only BMI entered the stepwise model. These results indicate the presence of an increased number of sodium-potassium pumps in lymphocytes from borderline hypertensives. This difference may be attributed to the blood pressure disease or increased body mass.

Effect of protein kinase C activation on cytoskeleton and cation transport in human erythrocytes. Reproduction of some membrane abnormalities revealed in essential hypertension

Certain manifestations of alterations of membrane cytoskeleton, protein kinase C activity, and ion transport were revealed in erythrocytes of patients with essential hypertension: 1) the average volume of erythrocytes is reduced by 4%; 2) about 7% of the total number of erythrocytes is represented by cup-shaped forms compared with 1.5 to 3.0% in the control group; 3) basal phosphorylation of Band 4.9 protein is increased 1.6-fold to 1.8-fold; 4) activity of protein kinase C is increased by 60 to 70%; 5) the rate of proton electrochemical gradient (delta mu H+)-induced Na+-H+ exchange is increased twofold. Treatment of erythrocytes of healthy donors with protein kinase C activator (12-O-tetradecanoylphorbol-13-acetate) leads to similar but more marked changes in cell shape (17% of cup-shaped forms), volume reduction (by 7%), an increase of Band 4.9 protein phosphorylation (threefold), and an increase in the rate of Na+-H+ exchange (fourfold). Protein kinase activation does not modify Na+-Li+ exchange and slightly increases (by 20-50%) Na+-K+ pump activity, Na+-K+ cotransport, and the rate of 45Ca influx. It may be assumed that the increase of protein kinase C activity is one of the most probable molecular mechanisms conditioning abnormalities of the membrane skeleton and Na+-H+ exchange in primary hypertension.

Abnormal Na+-K+ ATPase kinetics in a subset of essential hypertensive patients

We have performed a kinetic analysis of the interaction of Na+-K+ ATPase with internal Na+ in erythrocytes of 30 normotensive controls and 72 essential hypertensive patients. Neither the maximal rate of ouabain-sensitive sodium efflux (Vmax) nor the internal Na+ content required for half-maximal stimulation (K50%) were significantly different between normotensive and hypertensive patients. Nevertheless, using the 95% confidence limits of the K50% in the normotensive group as a cut-off point, 13 (18.06%) essential hypertensive patients exhibited increased values of this parameter (29.16 +/- 4.31 mmol l-1 cells) revealing decreased affinity of Na+-K+ ATPase for internal Na+ (Pump-hypertensives). The Vmax was also higher in the Pump '-' subset (14.08 +/- 4.85 mmol (1 cells h)-1 vs. 6.92 +/- 1.80; P = 0.0002) and 10 of these 13 hypertensives exhibited a Vmax above the upper end limit of 10.5 mmol (1 cells h)-1, suggesting a compensatory effect. No differences were observed between the Pump '-' subset and the remaining 59 hypertensives without Na+-K+ pump abnormality when basal erythrocyte Na+ content and clinical parameters of hypertension were examined. Decreased apparent affinity of Na+-K+ pump for internal Na+ present in 9-27% of essential hypertensives may be implicated in pathogenetic mechanisms of hypertension.

Erythrocyte water, Na+-K+ cotransport, and forearm vascular function in humans

We examined the relationships between erythrocyte (RBC) composition (Na+, K+, and water content) and ouabain-insensitive transports (Na+-K+ cotransport, Li+-Na+ countertransport) and forearm vascular hemodynamics under standardized basal conditions and during vasoconstriction (intra-arterial infusion of graded doses of norepinephrine and angiotensin II) and vasodilation (intra-arterial phentolamine and postischemic exercise). RBC water content correlated positively and significantly (r = 0.53, p = 0.001) with minimum forearm vascular resistance, a measure of vascular structural change, and negatively with maximal forearm blood flow (r = -0.55, p less than 0.001). Similar correlations with forearm vascular resistance and blood flow were observed under all experimental conditions. RBC Na+-K+ cotransport correlated positively and significantly (r = 0.43, p = 0.01) with the change in forearm blood flow produced by phentolamine, a functional measure of alpha-adrenergic tone, and was as strong an independent predictor of phentolamine-induced blood flow change as was arterial norepinephrine concentration. RBC Na+-K+ cotransport was also significantly positively correlated with residual forearm blood flow and resistance after phentolamine administration, where nonadrenergic influences predominate. RBC water correlated negatively with Li+-Na+ countertransport (r = -0.33, p less than 0.05) and Na+-K+ cotransport (r = -0.44, p less than 0.01). We propose that RBC water is a marker for a vascular structural property that contributes to vascular reactivity. RBC Na+-K+ cotransport seems to relate most strongly to the sympathetically mediated control of forearm blood flow and may also be linked to the intrinsic myogenic tone of the forearm vasculature.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced Na-K-Cl cotransport in vascular smooth muscle cells from spontaneously hypertensive rats

We have previously demonstrated the presence of a prominent, cyclic nucleotide-sensitive Na-K-Cl cotransport in vascular smooth muscle cells (VSMC). Others have observed that Na-K-Cl cotransport levels are reduced in erythrocytes of patients with essential hypertension and have proposed that a defect in this Na transport system may play a role in the pathogenesis of the disease. However, such a defect has not been demonstrated in the putative target tissue for essential hypertension, i.e., the VSMC. In the present study, we compared Na-K-Cl cotransport of VSMC from spontaneously hypertensive rats (SHR) with Na-K-Cl cotransport of VSMC from normotensive Wistar-Kyoto rats (WKY). We found that Na-K-Cl cotransport of SHR VSMC is significantly reduced relative to that of WKY VSMC (3.09 vs. 4.39 mumol K.g protein-1.min-1). The apparent ion affinities for Na-K-Cl cotransport of SHR VSMC did not differ from those determined for WKY VSMC. Furthermore, cyclic nucleotide regulation of cotransport also appeared to be the same for the two types of VSMC. In contrast, maximal saturable binding of [3H]bumetanide observed in SHR VSMC was markedly reduced compared with that of WKY VSMC, but the Kd values were similar. Our data suggest that the reduction in cotransport observed in SHR VSMC is the result of a decrease in the number of available cotransport sites.

Intralymphocytic sodium and free calcium and plasma renin in essential hypertension

Intracellular sodium, potassium, and free calcium concentrations were investigated in lymphocytes of 30 patients with essential hypertension and 30 normotensive controls. All subjects were placed on a diet containing 8 to 10 g of sodium chloride per day. Lymphocyte sodium concentration was higher in hypertensive patients than in normotensive controls (19.8 +/- 1.8 vs 18.4 +/- 1.8 mmol/kg wet weight; p less than 0.01), whereas lymphocyte potassium concentration was similar in both groups. Lymphocyte free calcium concentration was also higher in hypertensive patients than in normotensive controls (134.6 +/- 13.2 vs 120.2 +/- 16.4 nmol/L; p less than 0.01). There was a positive correlation between lymphocyte sodium and free calcium concentrations in normotensive controls, in hypertensive patients, and in the subjects combined (r = 0.59, p less than 0.01; r = 0.71, p less than 0.001; and r = 0.70, p less than 0.001, respectively). Lymphocyte potassium concentration was not related to lymphocyte sodium or free calcium concentration in each group. In patients with essential hypertension, intracellular sodium and free calcium concentrations were negatively correlated with plasma renin activity (r = -0.66, p less than 0.001; r = -0.60, p less than 0.001, plasma norepinephrine concentration. These results suggest that a considerable relationship exists between intracellular sodium and free calcium in lymphocytes and that, in essential hypertension, the alteration in cellular metabolism of sodium and calcium may be linked to the renin system but not to blood pressure, age, or adrenergic activity.

Systemic hypertension in diabetes mellitus

Hypertension occurs more frequently in diabetics and markedly exacerbates the vascular morbidity and mortality resulting from this metabolic disorder. However, the etiology of hypertension in diabetics remains poorly understood. Like aging persons, diabetics have increased systemic resistance and a probable reduction in baroreceptor sensitivity. They also have an expanded total body sodium pool and a tendency to lower levels of plasma renin activity. Some of these factors suggest that a subtle calcium deficiency could also be of etiologic importance.

A role of calcium in altered sodium ion transport of hypertensives?

Research on the etiology of essential hypertension has led to many reports of altered ion transport in cells from hypertensive patients and animal models. Abnormalities in sodium and calcium ion gradients and transport in vascular smooth muscle, neuronal tissue, cardiac muscle as well as erythrocytes have been extensively investigated. It is not clear whether these abnormalities are of primary or secondary nature. The current knowledge of sodium and calcium ion transport in essential hypertension is briefly reviewed here. Furthermore, evidence is presented which suggests a role of calcium in the regulation of sodium transport activity.

The effects of calcium and vitamin D on blood pressure in conscious sheep

The metabolic and haemodynamic effects of elevating plasma calcium levels were examined in both normal and ACTH-hypertensive sheep. Six weeks of dietary Ca++ supplementation did not alter plasma calcium levels, blood pressure or heart rate. Five days of CaCl2 infusion (2 mmol/h) or intravenous vitamin D injections elevated plasma ionised and total Ca++ levels and heart rate but mean arterial pressure was unchanged. As in other species, elevation of plasma Ca++ levels over 4 hours by infusion of CaCl2 at 2, 5, and 10 mmol/h increased mean arterial pressure and decreased heart rate. The course of ACTH-induced hypertension was not altered in animals supplemented with CaCl2 in their drinking water for 6 weeks nor by intravenous injection of vitamin D for 5 days. This study does not support a major role for altered plasma ionised or total Ca++ levels in the genesis of ACTH-dependent hypertension in the sheep.

The influence of potassium and bicarbonate on red blood cell sodium in the DOCA-hypertensive pig

The effects of plasma potassium, and blood bicarbonate on red blood cell sodium were studied in vivo in seven pigs implanted subcutaneously with DOCA (100 mg/kg) impregnated in Silastic. Mean arterial pressure, red blood cell sodium, plasma sodium, plasma potassium, and blood bicarbonate were measured from 5 days pre-implant to 30 days post-implant. One day post-implant, the pigs had significant increases in mean arterial pressure and red cell sodium content, and a significant decrease in plasma potassium concentration. In KCl infusion studies when plasma potassium was raised an average of 2.13 +/- 0.17 mEq/L, red blood cell sodium fell 0.61 +/- 0.10 mEq/L cells. When blood bicarbonate was raised 6.9 mEq/L by infusing NaHCO3, red blood cell sodium increased 0.79 mEq/L cells. The changes in red blood cell sodium were rapid, occurring within one hour after either of these plasma electrolyte shifts. We conclude that either plasma potassium or blood bicarbonate, or both, can serve as regulators of red blood cell sodium content in vivo, and cause the elevated level of red blood cell sodium that we have found in the DOCA-hypertensive pig. If these plasma electrolyte changes cause a similar increase in intracellular sodium in vascular smooth muscle or in a blood pressure regulating center in the brain, they may play a role in producing the arterial pressure elevation of mineralocorticoid-induced hypertension.

Genetic variability in response to dietary calcium

Supplemental dietary calcium has been shown to reduce blood pressure in spontaneously hypertensive rats while restricted calcium diets cause an elevation in blood pressure. This latter nutrient effect has been enhanced by modest sodium restriction and is associated with a reduction in serum ionized calcium concentration. To determine whether alterations of dietary calcium and sodium have a similar influence on blood pressure in genetically normotensive rats, Fisher 344, Wistar Furth, and ACI rats were fed either a low (0.1%) calcium, low (0.25%) sodium diet or normal (1.0%) calcium, normal sodium (0.45%) diet from 4 weeks of age through 29 weeks of age. Indirect measurements of systolic blood pressure showed that only the Fisher 344 rats consistently responded to the low calcium/low sodium diets with an elevation of blood pressure. There was considerable variation in serum electrolytes across strains in the normal diets but all three strains experienced a reduction in ionized calcium and an elevation in phosphorus and magnesium on the restricted diets. In the Fisher 344 rats there were significant (p less than .05) inverse correlations among systolic blood pressure and serum ionized and total calcium concentrations and positive correlations among systolic blood pressure, phosphorus, and magnesium. There was no significant correlation between serum electrolytes and blood pressure in the other two strains. The data indicate that there is genetic variability in the blood pressure response to alterations in dietary calcium and sodium. The pattern of change in serum electrolytes across strains suggests that diet-induced alterations of serum electrolytes, specifically calcium, are not necessarily predictive of a pressor response. It would appear that some other calcium-sensitive physiological process involved in blood pressure regulation must respond differentially to calcium availability across strains.

Kinetic aspects of red blood cell sodium transport systems in essential hypertension

A kinetic study of the interaction of internal sodium with four different erythrocyte sodium transport pathways (ouabain-sensitive Na+-K+ pump, bumetanide-sensitive Na+-K+ cotransport system, Na+-Li+ countertransport, and Na+leak) has facilitated the distinction of the following subgroups of patients with essential hypertension: 1) Leak (+), exhibiting increased passive sodium permeability; 2) Co (-), showing low apparent affinity of the Na+-K+ cotransport system for internal sodium; 3) Counter (+), characterized by increased maximal rates of Na+-Li+ countertransport; and 4) Pump (-), characterized by an abnormally low apparent affinity of the Na+-K+ pump for internal sodium. We present here a new and simple sodium-loading method that allows a simultaneous kinetic study of the above abnormalities. The use of this kinetic assay may improve estimation of the frequencies, clinical features, and other properties of each subgroup of hypertensive patients in different populations.

The Milan hypertensive rat as a model for studying cation transport abnormality in genetic hypertension

Environmental factors, genetic polymorphisms, and different experimental designs have been the main impediments to evaluating a genetic association between cell membrane cation transport abnormalities and human essential or genetic hypertension. We review the results obtained in the Milan hypertensive strain of rats (MHS) and in its appropriate control normotensive strain (MNS) to illustrate our approach to defining the role of cation transport abnormality in a type of genetic hypertension. Before the development of a difference in blood pressure between the two strains, the comparison of kidney and erythrocyte functions showed that MHS had an increased glomerular filtration rate and urinary output, and lower plasma renin and urine osmolality. Kidney cross-transplantation between the strains showed that hypertension is transplanted with the kidney. Proximal tubular cell volume and sodium content were lower in MHS while sodium transport across the brush border membrane vesicles of MHS was faster. Erythrocytes in MHS were smaller and had lower sodium concentration, and Na+-K+ cotransport and passive permeability were faster. The differences in volume, sodium content, and Na+-K+ cotransport between erythrocytes of the two strains persisted after transplantation of bone marrow to irradiated F1 (MHS X MNS) hybrids. Moreover, in normal segregating F2 hybrid populations there was a positive correlation between blood pressure and Na+-K+ cotransport. These results suggest a genetic and functional link in MHS between cell membrane cation transport abnormalities and hypertension. Thus erythrocyte cell membrane may be used for approaching the problem of defining the genetically determined molecular mechanism underlying the development of a type of essential hypertension.

Natural variation in passive sodium permeability in human erythrocytes

The rate of influx of 22Na+ into human erythrocytes (RBC) varies greatly depending upon the donor. A high rate of influx may be related to a congenital predisposition to essential hypertension. In Northern Europeans, we find a threefold difference in the rate of 22Na+ influx between those with the least (LP) and most highly permeable (HP) RBC (from less than 0.15 to greater than 0.60 mmol Na+/liter RBC/hr). In order to further define determinants of these apparently hereditary differences in passive membrane Na+ transport, we identified two groups of normal laboratory and hospital personnel differing markedly (greater than twofold) in RBC 22Na+ influx rate. We find that the loop diuretics furosemide and bumetanide decrease by about 50% the influx of 22Na+ into HP RBC, but have a lesser influence on LP RBC. Impermeant polyanions such as citrate and pyrophosphate also specifically diminish 22Na+ influx into HP, but not LP, RBC. Therefore, the exaggerated 22Na+ influx into HP RBC probably occurs through a discrete pathway (perhaps via "Na/K/Cl cotransport"), which appears to be almost absent in LP RBC. The differences between HP and LP RBC most likely do not involve polymorphisms of RBC anion transport per se. The rate of RBC anion (35SO4(2-)) transport is the same in HP and LP RBC and is equally inhibited by furosemide and (to a lesser extent) bumetanide. Furthermore, the potent inhibitor of RBC anion transport, DIDS (diisothiocyanostilbene disulfonate) does not affect RBC Na+ permeability in either group. Nonetheless, the preferential reduction of Na+ permeation of HP RBC by loop diuretics may be of help in experimentally distinguishing HP from LP phenotypes. This information may be crucial in unraveling the structural basis of intrinsic differences in cell membrane Na+ permeability and their possible relationship to essential hypertension.

Phospholipase C activation and diacylglycerol kinase inactivation lead to an increase in diacylglycerol content in spontaneously hypertensive rat

Activities of three kinases, phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), and diacylglycerol (DG) kinases, and phospholipase C were measured in erythrocyte ghosts from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). PI kinase activity was significantly higher in SHR than WKY but there was no significant difference in PIP kinase activity between SHR and WKY. The activity of phospholipase C, which hydrolyzes PIP2, was also increased in SHR. However, DG kinase activity was, on the contrary, decreased in SHR. These results suggest that there is a tendency to accumulate DG in SHR. Indeed, DG content in erythrocytes of SHR increased 1.7-fold compared to that of WKY. Such DG accumulation may cause the sustained activation of protein kinase C in SHR, since DG is a physiological activator for protein kinase C.

'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.

Red blood cell Li+-Na+ countertransport, Na+-K+ cotransport, and the hemodynamics of hypertension

Red blood cell Li+-Na+ countertransport and Na+-K+ cotransport activities, home blood pressure, invasive systemic hemodynamics, and limb venous compliance were measured in 65 white men (23 normotensive, 22 borderline hypertensive, and 20 mild essential hypertensive subjects). Li+-Na+ countertransport activity was positively and significantly correlated with subject-determined home systolic blood pressure (r = 0.31, p less than 0.02) and with directly measured systolic (r = 0.29, p less than 0.02) and diastolic (r = 0.27, p less than 0.03) blood pressures in the hemodynamic laboratory, independent of potential confounding variables. Analysis of the hemodynamic determinants of blood pressure revealed a significant positive correlation of countertransport with vascular resistance (r = 0.30, p less than 0.02) but not with cardiac output or cardiac index. High red blood cell Na+-K+ cotransport activity was not independently associated with hypertension or with a characteristic hemodynamic pattern but was related to decreased venous compliance. Red blood cell Li+-Na+ countertransport deserves further study as a marker for the genetic substrate of human essential hypertension. Red cell Na+-K+ cotransport may be altered secondarily by factors related to high blood pressure and seems to be a valid marker for abnormalities of the venous system in hypertension.