Effects of microcrystalline plant sterol suspension and a powdered plant sterol supplement on hypercholesterolemia in genetically obese Zucker rats

Because dietary fat appears to be an effective vehicle for dispensing plant sterols into the diet, a special plant-sterol-containing ingredient has recently been developed. This ingredient is a plant sterol suspension in oil in which the sterols are in microcrystalline form. The objective of the present study was to analyse the cholesterol-lowering effects and safety of two different plant sterol preparations, an orally administered microcrystalline plant sterol suspension (MPS) in rapeseed oil and a powdered plant sterol supplement, in obese Zucker rats. Dietary plant sterol supplements (0.5%, w/w) were given concurrently with a high cholesterol diet (HCD, 1% cholesterol and 18% fat, w/w). No significant changes in serum triglyceride, blood glucose, serum glutamate oxaloacetic transaminase and glutamic pyruvic transaminase values or body and liver weights were observed. The powdered plant sterol supplement lowered the serum cholesterol by 25% (P< 0.05) and the MPS diet by 35% (P< 0.001) compared with HCD by the end of the 12-week experiment. Interestingly, the plant sterol supplements also produced a marked reduction in serum ubiquinone levels, suggesting a possible effect on isoprene synthesis. Unlike the powdered plant sterol, both MPS and plain rape-seed oil decreased the serum baseline diene conjugation values, suggesting that they protect against oxidative stress-induced lipid peroxidation in rats. This lipid peroxidation diminishing effect is probably due to some antioxidative components in rapeseed oil. These findings indicate that an unesterified plant sterol, such as the microcrystalline suspension in oil, effectively prevents cholesterol absorption in obese Zucker rats.

Site and mode of action of clonidine in the central nervous system

In urethane-anaesthetized rats clonidine was administered intravenously (i.v.), intracerebroventricularly (i.c.v.) or onto the surface of the area postrema which protrudes into the fourth cerebral ventricle. In each instance clonidine induced a dose-dependent lowering of the blood pressure. The region of the area postrema appears to be the most sensitive site for the action of clonidine so far studied. In order to obtain similar blood pressure effects, approximately 8 times higher amounts were needed i.c.v., and about 80 times higher amounts i.v., than onto the surface of the area postrema. A pretreatment of the rats with the specific histamine H2-receptor blocking drug, metiamide (4.5 micronmoles/rat i.c.v.) shifted the dose-response curve of clonidine (i.c.v.) to the right. The results suggest that clonidine exerts its hypotensive effect in the rat via a stimulation of histamine H2-receptors in, or in the vicinity of, the area postrema.

Central hypotensive effects of angiotensin II in the rat

The floor of the fourth cerebral ventricle of urethane-anesthetized rats was exposed through the occipital foramen. Angiotensin II (10-1000 ng), applied onto the surface of the area postrema, induced a rapid lowering of the blood pressure. Pretreatment of the rats with reserpine abolished the hypotensive response to angiotensin II. It is concluded that the local application of angiotensin II induced in the vicinity of the area postrema a release of some biogenic amine, which has an inhibitory effect on the cardiovascular centres.

Control of circulation by cerebral catecholaminergic and histaminergic mechanisms

Catecholamines are formed, released and metabolized in the cerebral regions known to regulate the cardiovascular system. The release of catecholamines in these brain areas is associated with changes in cardiovascular function. Injections of exogenous catecholamines into certain brain regions induce cardiovascular changes and mimic the effects of the release of endogenous catecholamines in the same regions. In addition, drugs with selective effects on cerebral catecholamine functions also induce cardiovascular changes. Changes in cerebral catecholamines have also been found in arterial hypertension. Taken together, these observations provide strong evidence that cerebral catecholaminergic mechanisms have a crucial role in both the normal and pathological control of circulation. Cerebral catecholaminergic mechanisms also mediate, at least in part, the therapeutic effects of clonidine, alpha-methyldopa and some other antihypertensive drugs. Recent findings suggest that histaminergic mechanisms in the brain may also be important in the control of circulation and in the mediation of drug effects. Since the cerebral mono-aminergic systems are necessary for the physiological control of circulation, it is likely that the cerebral catecholaminergic and possibly histaminergic pathways are also involved in the mediation of the effects of psychological stress factors on the cardiovascular system.

Effects of calcium and plant sterols on serum lipids in obese Zucker rats on a low-fat diet

Ca may interfere with fat and cholesterol metabolism through formation of insoluble soaps with fatty and bile acids in the intestine. In the present study, we examined the effects of different dietary Ca levels on the serum lipid profile and cholesterol metabolism in obese Zucker rats fed a low-fat diet. We also tested whether dietary Ca interfered with the lipid-lowering effects of a pine oil-derived plant sterol mixture. Increase in dietary Ca intake from 0·2 to 0·8 %, and further to 2·1 % (w/w) dose-dependently decreased serum total cholesterol (r -0·565,P=0·002,n27), LDL-cholesterol (r -0·538,P=0·006,n25), and triacylglycerol (r -0·484,P=0·014,n25) concentrations, and increased HDL-cholesterol (r 0·478,P=0·016,n25) and HDL : LDL cholesterol (r 0·672,P<0·001,n25) in rats fed a 1 % cholesterol diet. Analysis of serum campesterol : cholesterol and sitosterol : cholesterol suggested that Ca dose-dependently increased intestinal cholesterol absorption (r 0·913,P<0·001,n18), whereas serum desmosterol : cholesterol and lathosterol : cholesterol indicated that Ca dose-dependently increased endogenous cholesterol synthesis (r 0·691,P=0·003,n18). Therefore, the decrease of serum LDL-cholesterol appeared to be due to Ca-induced increase in the conversion of cholesterol to bile acids. The increase in Ca intake did not interfere with the beneficial effects of plant sterols on serum total cholesterol, LDL-cholesterol and HDL-cholesterol concentrations. The high-Ca diet with plant sterol supplementation further increased the HDL-cholesterol concentration and HDL : LDL cholesterol. The present findings indicate that the beneficial effects of dietary Ca on the serum lipid profile during a low-fat diet are dose-dependent, and resemble those of bile acid sequestrants. Increased dietary Ca did not impede the lipid-lowering effects of natural plant sterols.

Sodium intake and hypertension

In current diets, the level of sodium is very high, whereas that of potassium, calcium, and magnesium is low compared with the level in diets composed of unprocessed, natural foods. We present the biologic rationale and scientific evidence that show that the current salt intake levels largely explain the high prevalence of hypertension. Comprehensive reduction of salt intake, both alone and particularly in combination with increases in intakes of potassium, calcium, and magnesium, is able to lower average blood pressure levels substantially. During the past 30 years, the one-third decrease in the average salt intake has been accompanied by a more than 10-mm Hg fall in the population average of both systolic and diastolic blood pressure, and a 75% to 80% decrease in both stroke and coronary heart disease mortality in Finland. There is no evidence of any harmful effects of salt reduction. Salt-reduction recommendations alone have a very small, if any, population impact. In the United States, for example, the per capita use of salt increased by approximately 55% from the mid-1980s to the late 1990s. We deal with factors that contribute toward increasing salt intakes and present examples of the methods that have contributed to the successful salt reduction in Finland.

Why and how to implement sodium, potassium, calcium, and magnesium changes in food items and diets?

The present average sodium intakes, approximately 3000-4500 mg/day in various industrialised populations, are very high, that is, 2-3-fold in comparison with the current Dietary Reference Intake (DRI) of 1500 mg. The sodium intakes markedly exceed even the level of 2500 mg, which has been recently given as the maximum level of daily intake that is likely to pose no risk of adverse effects on blood pressure or otherwise. By contrast, the present average potassium, calcium, and magnesium intakes are remarkably lower than the recommended intake levels (DRI). In USA, for example, the average intake of these mineral nutrients is only 35-50% of the recommended intakes. There is convincing evidence, which indicates that this imbalance, that is, the high intake of sodium on one hand and the low intakes of potassium, calcium, and magnesium on the other hand, produce and maintain elevated blood pressure in a big proportion of the population. Decreased intakes of sodium alone, and increased intakes of potassium, calcium, and magnesium each alone decrease elevated blood pressure. A combination of all these factors, that is, decrease of sodium, and increase of potassium, calcium, and magnesium intakes, which are characteristic of the so-called Dietary Approaches to Stop Hypertension diets, has an excellent blood pressure lowering effect. For the prevention and basic treatment of elevated blood pressure, various methods to decrease the intake of sodium and to increase the intakes of potassium, calcium, and magnesium should be comprehensively applied in the communities. The so-called 'functional food/nutraceutical/food-ceutical' approach, which corrects the mineral nutrient composition of extensively used processed foods, is likely to be particularly effective in producing immediate beneficial effects. The European Union and various governments should promote the availability and use of such healthier food compositions by tax reductions and other policies, which make the healthier choices cheaper than the conventional ones. They should also introduce and promote the use of tempting nutrition and health claims on the packages of healthier food choices, which have an increased content of potassium, calcium, and/or magnesium and a lowered content of sodium. Such pricing and claim methods would help the consumers to choose healthier food alternatives, and make composition improvements tempting also for the food industry.

Sodium load increases renal angiotensin type 1 receptors and decreases bradykinin type 2 receptors

The regulation of both angiotensin receptors and bradykinin receptors during sodium intake is poorly understood. We hypothesized that an altered balance between renal angiotensin type 1 (AT1) receptors and bradykinin type 2 (B2) receptors might contribute to an increase in blood pressure during periods of high-sodium intake. We studied the effects of high-sodium intake on renal AT1 receptors and B2 receptors in 5-6-week-old spontaneously hypertensive rats (SHR) receiving high-sodium chloride (6% NaCl) or mineral salts (10.5%, composition: 57% NaCl, 28% KCl, 12% MgSO4) compared to those receiving a low-sodium (NaCl 0.125%) diet for 10 weeks. Mineral salt intake was included due to its beneficial effects on blood pressure and cardiac hypertrophy. Receptor densities were measured by quantitative autoradiography. AT1 receptors were quantified using incubation with 125I-Sar1-Ile8-angiotensin II and displacement was measured with PD123319 (10 micromol/l), whereas B2 receptors were quantified using 125I-HPP-icatibant and displacement was measured with icatibant (3 micromol/l). Compared to the SHR controls, a further increase in blood pressure occurred after 2 weeks in the 6% NaCl group and after 6 weeks in the mineral salt group. AT1 receptor density increased in the renal cortex by 41% (p<0.01) in the 6% NaCl group and by 26% (p<0.05) in the mineral salt group. B2 receptor density decreased in the renal medulla by 26% (p<0.01) in the 6% NaCl group, and decreased even more i.e., by 45% (p<0.001), in the mineral salt group. It was shown that a 6% NaCl or a 10.5% mineral salt loading was capable of increasing renal AT1 receptor density and decreasing renal B2 receptor density. An altered balance between these receptors might be associated with hypertension under conditions of sodium loading.

Effects of calcium and plant sterols on serum lipids in obese Zucker rats on a low-fat diet

Ca may interfere with fat and cholesterol metabolism through formation of insoluble soaps with fatty and bile acids in the intestine. In the present study, we examined the effects of different dietary Ca levels on the serum lipid profile and cholesterol metabolism in obese Zucker rats fed a low-fat diet. We also tested whether dietary Ca interfered with the lipid-lowering effects of a pine oil-derived plant sterol mixture. Increase in dietary Ca intake from 0.2 to 0.8%, and further to 2.1% (w/w) dose-dependently decreased serum total cholesterol (r -0.565, P=0.002, n 27), LDL-cholesterol (r -0.538, P=0.006, n 25), and triacylglycerol (r -0.484, P=0.014, n 25) concentrations, and increased HDL-cholesterol (r -0.478, P=0.016, n 25) and HDL: LDL cholesterol (r 0.672, P<0.001, n 25) in rats fed a 1% cholesterol diet. Analysis of serum campesterol: cholesterol and sitosterol: cholesterol suggested that Ca dose-dependently increased intestinal cholesterol absorption (r 0.913, P<0.001, n 18), whereas serum desmosterol: cholesterol and lathosterol: cholesterol indicated that Ca dose-dependently increased endogenous cholesterol synthesis (r 0.691, P=0.003, n 18). Therefore, the decrease of serum LDL-cholesterol appeared to be due to Ca-induced increase in the conversion of cholesterol to bile acids. The increase in Ca intake did not interfere with the beneficial effects of plant sterols on serum total cholesterol, LDL-cholesterol and HDL-cholesterol concentrations. The high-Ca diet with plant sterol supplementation further increased the HDL-cholesterol concentration and HDL: LDL cholesterol. The present findings indicate that the beneficial effects of dietary Ca on the serum lipid profile during a low-fat diet are dose-dependent, and resemble those of bile acid sequestrants. Increased dietary Ca did not impede the lipid-lowering effects of natural plant sterols.

Supplementation of plant sterols and minerals benefits obese Zucker rats fed an atherogenic diet

In most hypertensive rat models, serum total cholesterol is typically low and the cholesterol is primarily in the HDL rather than the LDL fraction. This difference from humans usually makes these animals unsuitable for experimental atherosclerosis studies. In the present study, we induced severe hypercholesterolemia including a 10-fold increase in serum LDL cholesterol, endothelial dysfunction and hypertension as well as vascular and renal damage in obese Zucker rats by feeding a human-type high fat, high cholesterol and high salt diet (butter 18, cholesterol 1 and NaCl 6 g/100 g dry weight). Supplementation of this atherogenic diet with plant sterols (1 g/100 g) and replacing the NaCl partially by calcium, magnesium and potassium effectively prevented the diet-induced increases in total and LDL cholesterols and 24-h systolic and mean blood pressures, and markedly improved endothelial function. Plant sterols and the minerals also protected against vascular and renal damage and extended the life span of the obese Zucker rats by 60% compared with the rats fed the atherogenic diet. Our findings suggest that human-type cardiovascular disorders can be induced in obese Zucker rats by feeding a human-type atherogenic diet. This seems to be a suitable animal model for experimental studies on atherosclerosis and hypertension as well as for evaluating new dietary approaches to reducing cardiovascular risk.

Effect of a diet based on low-fat foods enriched with nonesterified plant sterols and mineral nutrients on serum cholesterol

Plant sterols have been incorporated into nutritional fats to achieve cholesterol lowering, but studies using enrichment of low-fat foods with plant sterols have not been reported. Our study was aimed at determining the effect of dietary intake of low-fat foods containing natural nonesterified plant sterols together with recommended doses of calcium, magnesium, and potassium on serum cholesterol and low-density lipoprotein (LDL) cholesterol-lowering in persons with mild to moderate hypercholesterolemia. This was a randomized, double-blind, placebo-controlled feeding trial lasting 15 weeks and performed in 2 university hospital centers. Seventy-eight subjects aged 25 to 75 years with serum cholesterol concentrations varying between 6 mmol/L (232 mg/dl) and 8 mmol/L (310 mg/dl) were randomly allocated to active treatment consisting of intake of bread, meat products, and jam enriched with 1.25 to 5.0 g/day of plant sterols and the slightly elevated concentrations of mineral nutrients, or the corresponding placebo food items. Serum lipid, high-density lipoprotein cholesterol and calculated LDL cholesterol concentrations were determined. Seventy-one persons completed the trial. Reduction in serum total cholesterol was 8% in the active treatment group and 3% in the placebo group (p = 0.0071) and that of LDL cholesterol was 13% in the active treatment group and 5% in the placebo group (p = 0.0070). In conclusion, natural nonesterified plant sterols contained in low-fat food items and ingested in moderate doses reduced serum total and LDL cholesterol concentrations to the same extent as reported previously for esterified plant sterol derivatives added to nutritional fats. The presence of mineral nutrients in doses recommended for blood pressure-lowering did not interfere with the cholesterol-lowering efficacy of the sterols, providing a promising approach to dietary prevention of cardiovascular diseases.

Diet enrichment with calcium and magnesium enhances the cholesterol-lowering effect of plant sterols in obese Zucker rats

BACKGROUND AND AIM

Recent clinical studies have demonstrated that plant sterols moderately lower serum cholesterol levels in patients with mild hypercholesterolemia. Furthermore, there is evidence suggesting that mineral nutrients, such as calcium and magnesium, may also decrease serum cholesterol concentrations. In this study, we tested the hypothesis that supplementation with mineral nutrients may enhance the cholesterol-lowering effect of plant sterols in obese Zucker rats. Furthermore, we compared the lipid-lowering effects of monovalent sodium and potassium cations with those of divalent calcium and magnesium cations.

METHODS AND RESULTS

A Western-type high-fat/high-cholesterol diet increased serum cholesterol by 175% and liver cholesterol by 65% in comparison with a low-fat/low-cholesterol control diet. On the contrary, the high-fat/high-cholesterol diet decreased intestinal cholesterol absorption, as assessed by means of serum campesterol-, sitosterol-, and sitostanol-to-cholesterol ratios, thus indicating that it was under negative feedback regulation. Supplementation of the high-fat/high-cholesterol diet with plant sterols or mineral nutrients partially prevented the diet-induced increased in serum cholesterol and, when given concurrently, their cholesterol-lowering effect was enhanced. Their combination also effectively prevented the diet-induced increase in liver cholesterol concentration, and had beneficial effects on liver and myocardial hypertrophy, and the development of obesity. These beneficial effects were at least partially mediated by an enhanced blockade of intestinal cholesterol absorption. Interestingly, only divalent cations enhanced the cholesterol-lowering effect of plant sterols, thus supporting the idea that the lipid-lowering effect of divalent cations is related to the formation of insoluble and inabsorbable calcium and magnesium chelates with fatty acids.

CONCLUSIONS

Our findings indicate that the cholesterol-lowering effect of plant sterols is enhanced by the co-administration of divalent calcium and magnesium cations but not by monovalent sodium and potassium cations.

Dietary potassium and magnesium supplementation in cyclosporine-induced hypertension and nephrotoxicity

BACKGROUND

Cyclosporine A (CsA)-induced hypertension and nephrotoxicity are aggravated by high sodium intake. Accumulating evidence suggests that potassium and magnesium supplementation could protect against the detrimental effects of dietary salt. In the present study, we tested the hypothesis of whether concurrent supplementation with potassium and magnesium could protect against the development of CsA-induced hypertension and nephrotoxicity more effectively than supplementation with one mineral alone.

METHODS

Eight-week-old spontaneously hypertensive rats (SHRs) were divided into four groups (N = 10 in each group): (1) CsA group (5 mg/kg subcutaneously) receiving high-sodium diet (Na 2.6%, K 0.8%, Mg 0.2% wt/wt); (2) CsA group receiving a high-sodium, high-potassium diet (Na 2.6%, K 2.4%, Mg 0.2%); (3) CsA group receiving high-sodium, high-magnesium diet (Na 2.6%, K 0.8%, Mg 0.6%); and (4) CsA group receiving high-sodium, high-potassium, high-magnesium diet (Na 2.6%, K 2.4%, Mg 0.6%).

RESULTS

CsA induced severe hypertension and deteriorated renal functions in SHRs on high-sodium diet. Histologically, the kidneys showed severe thickening of the media of the afferent artery with fibrinoid necrosis. Potassium supplementation lowered blood pressure (198 +/- 5 vs. 212 +/- 2 mm Hg, P < 0.05) and partially prevented the development of proteinuria (-25%, P < 0.05). Magnesium supplementation decreased blood pressure to the same extent but improved renal functions more effectively than potassium. The greatest protection against CsA toxicity was achieved when dietary potassium and magnesium supplementations were combined. Urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion, a marker for renal proximal tubular damage, increased progressively in CsA-treated SHRs on the high-sodium diet. Neither potassium nor magnesium influenced urinary NAG excretion. We also estimated the activity of the renal dopaminergic system by measuring 24-hour urinary dopamine excretion rates. CsA suppressed the renal dopaminergic system during high-sodium diet. Magnesium supplementation, alone and in combination with potassium, protected against the development of renal dopaminergic deficiency in CsA-treated SHRs on high-sodium diet. Magnesium supplementation increased plasma-free ionized magnesium (iMg) and bone magnesium by 50 and 16%, respectively.

CONCLUSIONS

Our findings indicate that both potassium and magnesium supplementations showed beneficial effects against CsA-induced hypertension and nephrotoxicity. The protective effect of magnesium clearly exceeded that of potassium. The greatest protection against CsA toxicity was achieved when potassium and magnesium were combined. We also provide evidence that the development of CsA-induced glomerular, tubular, and vascular lesions are associated with renal dopaminergic deficiency.

Endothelial Dysfunction and Salt-Sensitive Hypertension in Spontaneously Diabetic Goto-Kakizaki Rats

P182

Dysfunction of vascular endothelium has been associated with several cardiovascular risk factors including hypertension, hypercholesterolemia, and congestive heart failure. We tested the hypothesis whether or not endothelial dysfunction also participates in the pathogenesis of spontaneously diabetic Goto-Kakizaki (GK) rats, an animal model for type 2 diabetes. Furthermore we evaluated the influence of high sodium diet (6 % NaCl w/w) and chronic AT1 receptor blockade (valsartan 10 mg/kg p.o. for 8 weeks starting at age 8 weeks). Compared to age-matched non-diabetic Wistar controls, GK rats had higher b-glucose levels (9.3±0.5 vs 6.9±0.2 mmol/l), 2.7-fold higher s-insulin levels, impaired glucose tolerance in oral glucose tolerance test, and moderately increased s-cholesterol and s-triglyserides levels (all variables p<0.05). Mean arterial blood pressure, measured by radiotelemetry, was 15 mm Hg higher in GK rats (p<0.01), whereas no difference in heart rate was observed. Heart weight- and kidney weight -to-body weight ratios were higher in GK rats (p<0.05), and 24-hour albuminuria was 1.5-fold. Endothelium-mediated vascular relaxation of noradrenaline-precontracted mesenteric arterial rings to acetylcholine was markedly impaired in GK rats compared to Wistar rats (p<0.05), whereas the endothelium-independent relaxations to sodium nitroprusside were similar in both strains. Semiquantitative scoring of ED-1 positive cells showed perivascular monocyte/macrophage infiltration in kidneys of GK rats. High sodium diet increased blood pressure in GK rats by 24 mm Hg, 24-hour albuminuria by 350 %, induced cardiac hypertrophy, and further impaired endothelium-dependent vascular relaxation (all variables p<0.05). Inflammatory cell response was also aggravated by high sodium diet. Chronic AT1 receptor blockade did not decrease blood pressure, but partially protected against albuminuria, inflammatory cell response, and endothelial dysfunction in salt-loaded GK rats. Our findings indicate that hypertension in diabetic GK rats is salt-sensitive and associated with endothelial dysfunction and perivascular inflammation.

Development of chronic allograft rejection and arterial hypertension in Brown Norway rats after renal transplantation

The cardiovascular and renal pathophysiology associated with chronic renal allograft rejection under triple drug immunosuppressive treatment was studied using a recently developed model (Brown Norway (BN) rats) in a 6-week experiment. Renal transplantation was performed to 10-week-old rats in a rat strain combination of Dark Agouti (DA) --> BN. The right kidney was removed from another group of BN rats (uninephrectomized). A triple drug treatment comprising cyclosporine (10 mg/kg subcutaneously, s.c.), azathioprine (2 mg/kg s.c.) and methylprednisolone (1.6 mg/kg s.c.) was given to each rat daily for 6 weeks. A control group underwent no operations nor drug treatment. After the transplantation, the systolic blood pressure in this group was increased from 116 +/- 2 to 166 +/- 2 mmHg, while in the uninephrectomized group the rise was from 115 +/- 4 to 146 +/- 4 mmHg, and no change was observed in the blood pressures of the control group. The vascular relaxation responses of mesenteric arterial rings in vitro to acetylcholine were inhibited in both the transplantation group and the uninephrectomized group as compared with the control group, but few significant differences were found in the contraction responses to noradrenaline and potassium chloride. Graft histology was examined after 6 weeks, quantified by using the chronic allograft damage index (CADI). Changes specific to a chronic rejection reaction were observed in the allografts (CADI mean 6.0) but no injuries were seen in the rats' own kidneys (CADI mean 1.2). Our findings show that allograft rejection in BN rats after renal transplantation is associated with the development of arterial hypertension. The combination of cyclosporine, methylprednisolone and azathioprine also rises blood pressure in uninephrectomized BN rats. The hypertensive effects of the drug treatment and graft rejection are associated with endothelial dysfunction.

Beneficial effects of dietary magnesium and potassium on cardiac and renal morphologic features in cyclosporin A-induced damage in spontaneously hypertensive rats

BACKGROUND

Cyclosporin A-induced hypertension is dependent on the level of dietary salt. We investigated whether dietary magnesium or potassium could protect against cyclosporin A-induced cardiac and renal damage in spontaneously hypertensive rats (SHRs) on high-sodium diet.

METHODS

Eight-week-old SHRs were divided into 4 groups: (1) receiving a high-sodium diet, (2) receiving a high-sodium, high-potassium diet, (3) receiving a high-sodium, high-magnesium diet, and (4) receiving a high-sodium, high-potassium, high-magnesium diet. The effects of cyclosporin A in SHRs on a relatively low-sodium diet and in normotensive Wistar-Kyoto rats were also examined. Cardiac and renal morphologic condition was assessed, and tissue damage was scored by light microscopy after 6 weeks of cyclosporin A treatment.

RESULTS

In SHRs on a high-sodium diet, cyclosporin A caused luminal narrowing of the coronary arteries, left ventricular scarring, and damage in the renal arterioli and glomeruli. Dietary magnesium supplementation alone and in combination with potassium protected against these changes, whereas potassium alone was less effective. Cyclosporin A treatment caused only minor histopathologic changes in SHRs receiving a low-sodium diet. Interestingly, the detrimental interaction between cyclosporin A and a high-sodium diet was also observed in normotensive Wistar-Kyoto rats.

CONCLUSIONS

Dietary magnesium, especially in combination with potassium, protects against cyclosporin A-induced cardiac and renal damage.

Magnesium. An update on physiological, clinical and analytical aspects

There is an increased interest in the role of magnesium ions in clinical medicine, nutrition and physiology. The characteristics of the binding of magnesium and calcium ions to various components, macromolecules and biological membranes are described. Magnesium affects many cellular functions, including transport of potassium and calcium ions, and modulates signal transduction, energy metabolism and cell proliferation. The mechanism of cellular uptake and efflux of magnesium, its intracellular transport, intestinal absorption, renal excretion and the effect of hormones on these are reviewed. Magnesium deficiency is not uncommon among the general population: its intake has decreased over the years especially in the western world. The magnesium supplementation or intravenous infusion may be beneficial in various diseased states. Of special interest is the magnesium status in alcoholism, eclampsia, hypertension, atherosclerosis, cardiac diseases, diabetes, and asthma. The development of instrumentation for the assay of ionized magnesium is reviewed, as are the analytical procedures for total magnesium in blood and free magnesium in the cytosol. The improved procedures for the assay of different magnesium states are useful in understanding the role of magnesium in health and disease.

Down-regulation of renal glutathione synthesis by systemic nitric oxide synthesis inhibition in spontaneously hypertensive rats

Nitric oxide stimulates in vitro the synthesis of glutathione, an abundant thiol with a number of functions such as detoxification of xenobiotics and reactive oxygen species. In order to study this relationship in an animal model of hypertension, we treated spontaneously hypertensive rats (SHR) either with a nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) or with a nitric oxide donor isosorbide-5-mononitrate (IS-5-MN). Inhibition of nitric oxide synthesis led to malignant hypertension and to a marked decrease in glutathione synthesis through down-regulation of the rate-limiting enzyme gamma-glutamylcysteine synthetase (GCS). The reduction in GCS activity was further augmented in SHR on a high sodium diet. Renal GCS activity in untreated SHR was 234 +/- 14 and 240 +/- 18 nmol/min/mg protein (mean +/- SD) on a low and high sodium diet, respectively. When L-NAME was included in the diet, the activities dropped to 173 +/- 28 and 123 +/- 28 for the low and high sodium diets, respectively. IS-5-MN attenuated the rise in blood pressure induced by sodium chloride, but did not affect the GCS activity. The mechanism of GCS stimulation by nitric oxide is not known, but our results combined with the literature suggest that a relatively high concentration of nitric oxide is needed.

Effects of ACE inhibition on cyclosporine A-induced hypertension and nephrotoxicity in spontaneously hypertensive rats on a high-sodium diet

Cyclosporine A (CsA)-induced hypertension has been shown to be dependent on the level of dietary salt. The present study assessed the role of the renin-angiotensin system in the development of CsA-induced hypertension and nephrotoxicity in spontaneously hypertensive rats (SHR) on a high-sodium diet. In addition, we examined whether ACE inhibition prevents the detrimental effects of CsA on blood pressure, kidney function and vascular morphology in SHR on high sodium intake. Eight-week-old SHR were divided into three different groups (n = 8 in each group): (i) SHR control group receiving a high-sodium diet (Na 2.6% of the dry weight of the chow), (ii) CsA group (5 mg/kg s.c.) on a high-sodium diet and (iii) CsA + enalapril group (30 mg/kg p.o.) on a high-sodium diet. At the end of the six-week experimental period, systolic blood pressure in the CsA group was significantly higher compared to the control group (245+/-6 vs 208+/-9 mmHg, respectively, p < 0.05). Plasma renin activity was increased 20-fold by CsA treatment (p < 0.05 compared to controls). CsA increased serum creatinine by 22%, the 24-h urinary protein excretion by 190% and the 24-h urinary excretions of calcium, phosphorus and magnesium by 150%, 25% and 140%, respectively (p < 0.05 compared to controls). Histologically, the kidneys of CsA-treated SHR showed severe thickening of the media of the afferent arteriole and fibrinoid necrosis of the arteriolar wall. Interestingly, CsA induced vascular injury also in the small myocardial arteries. Enalapril treatment prevented CsA-induced hypertension and deterioration of kidney function as well as CsA-induced vascular injuries in the kidneys and myocardium. Enalapril also decreased left ventricular weight-to body weight ratio and prevented CsA-induced increases in urinary calcium and phosphorus excretions. Our findings indicate that CsA has a detrimental effect on blood pressure, kidney function and vascular morphology in SHR on high sodium intake. ACE inhibition prevents the CsA-induced hypertension, nephrotoxicity and vascular injuries. Our findings thus suggest that increased activity of the renin-angiotensin system is involved in the pathogenesis of CsA-induced hypertension and nephrotoxicity in SHR on a high-sodium diet.

Interrelationships between low density lipoprotein receptor defect, serum fatty acid composition, and serum cholesterol concentration

It is known that, in the general human population, serum fatty acid composition is correlated with serum triacylglycerol and cholesterol concentrations. The goal of the present study was to analyze whether the same is true of individuals who have a low density lipoprotein receptor (LDL-R) defect. Concentrations of 16 different fatty acids, cholesterol, triacylglycerol, and major lipoproteins in serum were determined in eight individuals who had (FH-North Karelia), the most common LDL-R defect in Finland, which causes familial hypercholesterolemia, and in their 30 relatives belonging to a single large pedigree as controls. The average number of double bonds (i.e., degree of desaturation) in serum fatty acids correlated negatively with the concentrations of serum total cholesterol (r = 0.27, P < 0.05) and total triacylglycerol (r = -0.71, P < 0.001) and positively with the number of fish meals per week (r = 0.50, P < 0.01), which was analyzed in all pedigree members jointly. These effects were similar in individuals having LDL-R defect, in which group the correlation coefficients were -0.31 (P = NS), -0.99 (P < 0.001), and 0.79 (P = NS) for serum total cholesterol, triacylglycerol, and weekly fish meals, respectively. Thus, LDL-R defect does not impair the correlation between serum fatty acid composition and serum triacylglycerol concentration. This result is in agreement with dietary studies that have shown that familial hypercholesterolemia patients respond very favorably to dietary therapy.

Increased kidney xanthine oxidoreductase activity in salt-induced experimental hypertension

Clinical and experimental studies have established an association between high sodium intake and arterial hypertension. The renal mechanisms resulting in impaired sodium excretion in hypertension-prone subjects are not clear. In hypertension-prone rats, high blood pressure results in increased renal mass and hemodynamic changes, both of which may alter renal oxygen distribution. Xanthine oxidoreductase (XOR) oxidizes ATP metabolites hypoxanthine and xanthine to urate. Because XOR is induced by hypoxia, we assessed kidney XOR activity in 2 models of salt-sensitive hypertension, spontaneously hypertensive rats (SHR) and Dahl salt-sensitive (Dahl S) rats. Increasing sodium intake from basal (0.08%) to high (2.56% wt/dry wt in the diet) increased renal XOR activity dose-dependently from 68+/-8 to 143+/-21 microU/mg protein in the Dahl S (P<0.05) but not in Dahl salt-resistant (Dahl R) rats. On basal and high sodium diets, SHR had higher renal XOR activity (101+/-10 and 134+/-26 microU/mg protein, respectively) than normotensive Wistar-Kyoto rats (55+/-2 and 58+/-6 microU/mg protein, P<0.05). Sodium restriction (0.02% wt/wt) downregulated kidney XOR activity in both Dahl S and R rats by nearly 40%. In SHR, allopurinol treatment totally inhibited renal XOR activity, but neither systolic blood pressure nor renal mass changed. The results suggest that renal XOR induction is a consequence of increased salt intake or the resulting hypertension. However, further studies on renal XOR activity during the development of hypertension are needed to assess the importance of XOR in the pathophysiology of arterial hypertension.

Cardiovascular effects of dietary salts and isosorbide-5-mononitrate in spontaneously hypertensive rats

The influence of isosorbide-5-mononitrate (IS-5-MN) on the cardiovascular effects of high dietary salt intake (NaCl, 6.6% of dry weight of food) and that of a potassium, magnesium and l-lysine-enriched salt alternative (Pansalt 10.5%, producing a 6.6% content of NaCl) was studied in spontaneously hypertensive rats in an 8-week experiment. Common salt produced a marked rise in blood pressure and induced cardiac and renal hypertrophy, while the salt alternative, although containing the same amount of NaCl, neither increased blood pressure nor caused any significant cardiac hypertrophy. IS-5-MN treatment at a daily dose of approximately 60-70 mg/kg (mixed with food) attenuated the rise in blood pressure induced by common salt, but did not prevent the cardiac or renal hypertrophy. IS-5-MN did not offer any additional benefit to the use of the salt alternative diet alone in treatment of high blood pressure. Mesenteric arterial responses in vitro were examined at the end of the study. IS-5-MN treatment during the moderately low-salt (NaCl 0.7%) control diet tended to decrease the contractile response to noradrenaline and increase the relaxation to acetylcholine. Common salt, but not the salt alternative, induced a 50% increase in the 24-h urinary excretion of cyclic GMP. Both salt supplements induced an 8-9-fold increase in the excretion of calcium, and about a 2-fold increase in the excretion of phosphorus. Common salt also increased the excretion of magnesium by 50%. IS-5-MN treatment had no significant effect on the excretion of the mineral elements. Our findings show that increased intake of potassium and magnesium reduces the harmful effects of common salt. Pressure-independent mechanisms are involved in salt-induced left ventricular and renal hypertrophy, since they remained unaffected despite the prevention of the salt-induced rise in blood pressure by IS-5-MN treatment.

Detrimental effect of dietary sodium and beneficial effect of dietary magnesium on glomerular changes in cyclosporin-A-treated spontaneously hypertensive rats

BACKGROUND

Cyclosporin A (CsA) causes renal magnesium wasting, hypertension, and occasionally irreversible renal damage. We examined the effect of dietary sodium and magnesium on renal histology in spontaneously hypertensive rats (SHR) receiving CsA.

METHODS

Forty-six 8-week-old SHR were divided into six groups and given different dietary levels of sodium (low 0.3%, high 2.6%) and magnesium (low 0.2%, high 0.6%). Low-dose CsA (5 mg/kg/d) was given subcutaneously for 6 weeks in four groups. Systolic blood pressure, serum creatinine, degree of proteinuria, and renal tissue CsA and calcium concentrations were determined. Kidney wet weight to total body-weight ratio was calculated as an index of renal hypertrophy. Renal histological alterations were scored according to glomerular changes: 100 glomeruli were assigned for severity of change a score from 0 to 3. The number of affected glomeruli was multiplied by the damage score to obtain a damage index.

RESULTS

In the CsA-treated high-sodium diet group systolic blood pressure and glomerular damage index were increased, and renal hypertrophy was the most common. These changes were prevented by oral magnesium supplementation. The glomerular damage index correlated positively with increases in systolic blood pressure, serum creatinine, proteinuria, and renal calcium concentration.

CONCLUSIONS

Dietary sodium enhanced CsA-induced functional and morphological renal changes in SHR and aggravated hypertensive renal arteriolar and glomerular lesions. Dietary magnesium supplementation protected against the deleterious effects of sodium and CsA.

Influence of dietary salts on the cardiovascular effects of low-dose combination of ramipril and felodipine in spontaneously hypertensive rats

1 In spontaneously hypertensive rat (SHR) we examined over a 4-week period the influence of control low sodium diet, common salt-enriched diet (sodium chloride 6% of the dry weight of the chow) and a novel mineral salt-enriched diet (potassium-, magnesium-, and l-lysine-enriched mineral salt added at a 75% higher level of 10.5% to produce the same sodium chloride concentration of 6%) on the cardiovascular effects produced by a low-dose combination of an angiotensin converting enzyme inhibitor ramipril (0.25 mg kg(-1) day(-1) in the food) and a calcium channel blocker felodipine (0.4 mg kg(-1) day(-1) subcutaneously via an osmotic minipump). 2 Common salt, but not the mineral salt, accelerated the development of hypertension and induced left ventricular and renal hypertrophy in SHR. Neither common salt nor mineral salt significantly affected heart rate. 3 The combination of ramipril and felodipine decreased systolic blood pressure and prevented the development of left ventricular hypertrophy effectively during the common salt diet without any significant effect on the heart rate. The cardiovascular effects of the drug combination were improved by the low sodium diet or by replacement of high common salt in the diet by mineral salt. 4 Responses of endothelium-intact mesenteric arterial rings in vitro were examined at the end of the four-week study. The combination of ramipril and felodipine markedly improved the endothelium-dependent vascular relaxation responses to acetylcholine and enhanced the endothelium-independent vascular relaxation responses to sodium nitroprusside in SHR on control and common salt diets. Replacement of common salt in the diet by mineral salt improved the endothelium-dependent vascular relaxation responses to acetylcholine. The drug combination attenuated the alpha-adrenoceptor-mediated vascular contractile responses to noradrenaline during the common salt diet. 5 Ramipril and felodipine in combination increased plasma renin activity by 1.9-3.2 fold without affecting serum aldosterone levels. 6 Our findings suggest that the cardiovascular effect of the low-dose combination of ramipril and felodipine was maintained during high salt intake. However, salt restriction or replacement of common salt in the diet by the potassium- and magnesium-enriched mineral salt improved the cardiovascular effects of the drug combination. In the face of a high intake of sodium, a part of the beneficial cardiovascular effects of the drug combination is apparently mediated by improved endothelium-dependent and endothelium-independent vascular relaxation responses and attenuated alpha-adrenoceptor-mediated vascular contractile responses.

Cardiovascular effects of chronic inhibition of nitric oxide synthesis and dietary salt in spontaneously hypertensive rats

The cardiovascular effects of chronic inhibition of nitric oxide synthesis and dietary salt were studied in 9-wk-old spontaneously hypertensive rats (SHR). N omega-nitro-L-arginine methyl ester (L-NAME, 0.025% in food, about 20 mg/kg/d) was given to rats receiving diets containing low, moderate, and high salt levels (NaCl 0.2%, 1.1%, and 6.0% of the dry weight of the chow) for 3 wk, L-NAME increased systolic blood pressure by 50 to 60 mmHg in all treated groups, as compared with an average rise of 10 to 20 mmHg in the control SHR. The high-salt diet did not further increase blood pressure. L-NAME also induced cardiac and renal hypertrophy, and these changes were aggravated by the high-salt diet. In addition, 19 of the 30 rats treated with L-NAME suffered strokes and all of them had several myocardial infarctions and renal damage, while the rats not treated with L-NAME had no evidence of stroke or myocardial or renal injury. Responses of mesenteric arterial rings in vitro were studied at the end of the experiment. The vascular contractile responses to noradrenaline were increased, and the relaxation responses to acetylcholine were inhibited in the L-NAME treated groups. In addition, the high-salt diet alone tended to inhibit the response to acetylcholine. Plasma renin activity was markedly increased by L-NAME treatment and decreased by the high-salt diet. The 24-h urine protein excretion was increased both by the L-NAME treatment and by the high-salt diet. The combination of L-NAME and the high-salt diet markedly raised the serum creatinine concentration. Our findings show that the coronary and renal functions are particularly vulnerable in SHR during impaired nitric oxide synthesis, and that the end-organ damage is worsened by an increased intake of dietary salt. We suggest that dysfunction of the endothelium is the primary cause of the effects observed in this study.

Influence of age on cardiovascular effects of increased dietary sodium and angiotensin-converting enzyme inhibition in normotensive Wistar rats

Recent studies have shown that increased intake of dietary sodium chloride produces blood pressure-independent increase in cardiac and renal mass even in young normotensive rats. With advancing age the harmful cardiovascular effects of increased dietary sodium are not so well known. In the present study the influence of advancing age on the cardiovascular effects of increased intake of sodium (control diet, 0.3% and high-sodium diet, 2.6% sodium in the chow) were examined in young and aged (3 and 18 months old, respectively, at the beginning of the experiment) male normotensive Wistar rats in a six-week study. Moreover, the potential role of renin-angiotensin system in ageing during normal and a high-sodium intake was studied using a pharmacological tool, angiotensin converting enzyme (ACE) inhibitor ramipril. Ageing did not significantly modify basal systolic blood pressure measured by the tail cuff method. A high intake of sodium chloride increased blood pressure significantly only in aged rats, while in young rats it increased renal weight. Left ventricular weight was not affected by high-sodium diet in either age group. The ACE inhibition during control diet lowered blood pressure and decreased left ventricular weight in young rats only and these effects were completely blocked by a high-sodium diet. The maximal vascular contraction force of mesenteric arterial rings to noradrenaline was decreased with ageing while endothelium-dependent and -independent relaxation responses were unaltered with ageing. The sensitivity to sodium nitroprusside was impaired by the high-sodium diet in young rats. In both age groups the urinary excretion of calcium was increased during the high-sodium diet. In conclusion, the increased intake of sodium produced different changes in cardiovascular function in normotensive rats depending on age. With advancing age, the sensitivity to sodium-induced increase in blood pressure was increased. In aged rats a high intake of dietary sodium elevated blood pressure, while in young rats it increased renal mass without increase in blood pressure. In both age groups sodium did not affect left ventricular hypertrophy. Both high-sodium intake and ageing attenuated or even abolished the cardiovascular effects of ACF inhibition.

Influence of different dietary salts on the cardiovascular and renal effects of moxonidine in spontaneously hypertensive rats

The influence of common salt (NaCl) and a novel potassium-, magnesium-, and L-lysine-enriched mineral salt on the cardiovascular and renal effects of the selective imidazoline I1-receptor agonist moxonidine was examined in spontaneously hypertensive rats (SHR). Common salt was added at the level of 6% of the dry weight of the chow, and mineral salt at a 75% higher level of 10.5% thereof to produce the same NaCl concentration of 6% as in the common salt group. During the control diet an 8-week oral treatment with moxonidine (117 mg/1000 g of the dry weight of the chow producing an approximate daily dose of 10 mg/kg), lowered blood pressure by 13 mmHg. The common salt diet alone raised blood pressure by 27 mmHg. Moxonidine lowered blood pressure by 21 mmHg during the common salt diet, but the blood pressure remained 19 mmHg higher than in the moxonidine-treated SHR receiving the control diet (P<0.05). Unlike common salt, mineral salt alone did not raise blood pressure nor did it interfere with the antihypertensive effect of moxonidine. Moxonidine showed a kidney-protective effect during the control diet measured as decreased urinary protein excretion, but it did not affect the development of left ventricular hypertrophy. Moxonidine increased plasma renin activity during the control diet and it raised the serum aldosterone level both during the control and mineral salt diets. The vascular relaxation responses of the mesenteric arterial rings to both acetylcholine (an indicator of endothelium-dependent vascular relaxation) and nitroprusside and nitroprusside (an indicator of endothelium-independent vascular relaxation) were attenuated by the common salt diet alone but maintained during the moxonidine treatment. Our findings are consistent with the concept that moxonidine is able to improve the excretion of sodium. This effect might explain the maintenance of normal vascular relaxation during a high intake of common salt. These effects may partly account for the antihypertensive effect of moxonidine.

Influence of age and dietary sodium on the cardiovascular and renal effects of ramipril in spontaneously hypertensive rats

The aim of the present study was to investigate the influence of age and an increased intake of dietary sodium on the cardiovascular and renal effects of the angiotensin converting enzyme inhibitor, ramipril. Male spontaneously hypertensive rats (SHR) aged 10 and 60 weeks received either control or a high level of sodium (0.3% vs. 2.6% Na) and ramipril (2 mg/kg/day) mixed in the chow for 6 weeks. Blood pressure was measured weekly by tail-cuff method. Arterial functions were determined by measuring vascular contractile and relaxation responses of mesenteric arterial rings in vitro at the end of the study. An age-related increase in systolic blood pressure, left ventricular (LVH) and renal hypertrophy (RH) as well as proteinuria were found in SHR. The vascular relaxation to nitroprusside was impaired in aged SHR. The high sodium intake accelerated the development of hypertension only in young SHR but increased LVH and RH in both age groups. Ramipril effectively lowered blood pressure in both age groups, but decreased the LVH significantly only in young rats. Ramipril markedly improved the vascular relaxation to acetylcholine and nitroprusside only in young rats. The vascular contractile responses to noradrenaline and potassium chloride were not affected by age, sodium intake or ramipril treatment. The high sodium intake markedly attenuated the cardiovascular effects of ramipril. The high-sodium diet enhanced the urinary excretion of cyclic GMP in both age groups, while it increased urinary excretion of protein in young SHR only. In conclusion, the cardiovascular effects of ramipril were impaired with advanced age even in the presence of a control intake of sodium. A high sodium intake attenuated or even abolished the cardiovascular effects of ramipril in both young and aged SHR.

Cardiovascular and renal effects of the combination of felodipine and metoprolol during a high-salt and a moderate-salt diet in spontaneously hypertensive rats

In the present study the influence of dietary salt on the cardiovascular and renal effects of the calcium channel blocker felodipine (1.2 mg/kg sc) and the beta 1-adrenoceptor blocking drug metoprolol (250 mg/kg po), alone and in combination, was examined in the spontaneously hypertensive rats (SHRs) in a 4-week study. In addition, the influence of different diet and drug regimens on vascular functions was assessed by measuring the vascular relaxation and contractile responses of mesenteric arterial rings in vitro at the end of the experimental period. In SHRs, a high-salt diet caused a marked rise in blood pressure, impaired the endothelium-dependent vascular relaxation responses to acetylcholine and induced left ventricular hypertrophy (LVH) and renal hypertrophy. Metoprolol had little if any effect on salt-induced changes in blood pressure, endothelium-dependent vascular relaxation or renal hypertrophy, but it partially prevented the development of salt-induced LVH. Felodipine during the high-salt diet lowered blood pressure to normotensive level and completely prevented salt-induced left ventricular and renal hypertrophy as well as endothelial dysfunction. Felodipine produced tachycardia, especially at the beginning of drug treatment. The combination of felodipine and metoprolol abolished the effects of the individual drugs on heart rate. The drug combination also completely prevented the detrimental cardiovascular and renal effects induced by a high salt intake. Although salt restriction did not further enhance the profound antihypertensive effect of the combination of metoprolol and felodipine, it enhanced the effects of the drug combination on LVH and renal hypertrophy. Our findings indicate that felodipine treatment, alone and in combination with metoprolol, normalizes blood pressure and prevents the development of salt-induced LVH and renal hypertrophy. During the high-salt diet the beneficial vascular effects of felodipine as well as those of the combination of felodipine and metoprolol are mediated, at least in part, by prevention of salt-induced endothelial dysfunction. The only apparent benefit from the use of metoprolol in combination with a relatively high dose of felodipine was the prevention of tachycardia.

Cardiovascular effects of a low-dose combination of ramipril and felodipine in spontaneously hypertensive rats

1. Cardiovascular effects of submaximal antihypertensive doses of the angiotensin converting enzyme inhibitor, ramipril (0.25 mg kg-1 day-1 in the food), and the calcium channel blocker, felodipine (0.4 mg kg-1 day-1 subcutaneously by osmotic minipump), both alone and in combination, were examined in spontaneously hypertensive rats (SHR) in a four-week study. 2. Both ramipril and felodipine as monotherapy decreased systolic blood pressure. The antihypertensive effect of the drug combination was more than that of ramipril treatment alone, but not significantly better than that of felodipine monotherapy. Ramipril or felodipine treatments did not significantly affect the heart rate, either alone or in combination. 3. The beneficial effect of ramipril monotherapy on left ventricular hypertrophy was more prominent than that of felodipine. The cardioprotective effect of felodipine was improved when combined to ramipril. The systolic blood pressure at the end of the experimental period correlated only weakly with left ventricular hypertrophy. 4. Responses of mesenteric arterial rings in vitro were examined at the end of the four-week study. Ramipril and felodipine monotherapies as well as their combination markedly improved the endothelium-dependent vascular relaxation responses to acetylcholine. The combination of ramipril and felodipine slightly enhanced the endothelium-independent vascular relaxation responses to sodium nitroprusside. Ramipril treatment alone slightly diminished the vascular contractile responses to noradrenaline. Neither ramipril nor felodipine alone or in combination affected the vascular contractile responses to potassium chloride. 5. Ramipril treatment, both alone and in combination with felodipine, caused a three fold increase in plasma renin activity. Serum aldosterone, fasting blood glucose level, serum insulin and the 24 hour urinary excretions of sodium, potassium, magnesium, calcium, phosphorus or protein were not significantly affected by the drug treatments. 6. Our findings suggest that a better overall control of hypertension and end-organ damages, without an increase in adverse effects, can be achieved by the combination of submaximal antihypertensive doses of felodipine and ramipril than by monotherapy with either drug alone.

Delayed increase in blood pressure induced by spontaneously hypertensive rat plasma after high sodium intake

Plasma from spontaneously hypertensive rats (SHR) and from patients with essential hypertension has been suggested to contain a substance with a delayed pressor effect, parathyroid hypertensive factor (PHF), associated with salt-sensitive forms of hypertension. In order to study whether high sodium intake would increase plasma levels of PHF-like activity, determined by bioassay, SHR received either a high-sodium (2.6% Na in the chow) or a normal-sodium (0.3% Na) diet for 6 weeks. Intravenous injection of plasma from SHR on a high-sodium diet (6 ml/kg) to urethane-anaesthetized Wistar rats induced a delayed increase in mean arterial blood pressure 70-80 min after bolus injection. No delayed pressor effects could be demonstrated by plasma from SHR or Wistar rats on a normal-sodium diet. It is concluded that a factor with a delayed blood pressure-increasing effect appears to be present in plasma from SHR on a high-sodium diet but not in plasma from normotensive Wistar rats or SHR on a normal-sodium diet. Further studies to characterize this factor and its possible relation to salt-induced hypertension are warranted.

Effects of dietary sodium and magnesium on cyclosporin A-induced hypertension and nephrotoxicity in spontaneously hypertensive rats

Arterial hypertension, nephrotoxicity, and magnesium loss are common side effects of the immunosuppressive agent cyclosporin A (CsA). In the present study, the effects of dietary sodium and magnesium on CsA toxicity were examined in spontaneously hypertensive rats. A 6-week treatment with CsA during a moderately low-sodium diet (Na 0.3%, Mg 0.2% of the dry weight of the chow) raised blood pressure only slightly, without evidence of nephrotoxicity. By contrast, CsA during a high-sodium diet (Na 2.6%) produced a pronounced rise in blood pressure as well as marked nephrotoxicity, comprising decreased creatinine clearance, increased levels of serum creatinine and urea, and increased urinary protein excretion. During the high-sodium diet, CsA decreased myocardial and bone magnesium concentration and increased myocardial and renal calcium concentration. Magnesium supplementation (Mg 0.6%) protected against the CsA-induced hypertension and nephrotoxicity during the high-sodium diet. Magnesium supplementation also completely prevented the CsA-induced myocardial magnesium depletion and calcium accumulation in the heart and kidney during the high-sodium diet. Our findings indicate a detrimental interaction between increased sodium intake and CsA treatment and a marked protection by concomitant oral magnesium supplementation.

Interrelationships between salt and fish oil in stroke-prone spontaneously hypertensive rat

The cardiovascular effects of a partially purified extract of fish oil, enriched in the n-3 series fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were studied in stroke-prone spontaneously hypertensive rats (SHR-SP) fed with high- and low-sodium diets during 5 weeks. Addition of salt to the low-salt control diet at a level commonly found in human food items (6% NaCl of the dry weight of the diet) produced a remarkable rise in blood pressure, an increase in left ventricular weight-to-body weight ratio (LVH-index) and an increase in kidney weight-to-body weight ratio (RH-index). Fish oil (20% of the dry weight of the diet) did not significantly influence the blood pressure or LVH-index or RH-index during the low-salt control diet. However, fish oil completely prevented the remarkable rise in blood pressure and clearly antagonized the rise of both LVH- and RH-indices, induced by the high-salt diet. The fish oil supplementation increased the levels of the polyunsaturated fatty acids of the n-3 series and decreased those of the n-6 series in plasma and kidney, irrespective of the salt content of the diet. Fish oil lowered serum thromboxane B2 concentration by approximately 75%. During the high-salt diet, fish oil markedly decreased water intake and urine volume, and increased urinary sodium concentration by about 60%. Our findings show that, in addition to an antihypertensive effect, fish oil also decreases LVH and RH. These effects appear to be due to an improved ability to excrete sodium and could be explained by the observed changes in the fatty acid composition and metabolism.

Adherence to and population impact of non-pharmacological and pharmacological antihypertensive therapy

Efforts in Finland to implement the recommended non-pharmacological and pharmacological principles for the control of hypertension, stroke and ischaemic heart disease have been accompanied by an approximately 10 mm Hg fall in the population average of diastolic blood pressure, and about 60% decrease in deaths from both stroke and ischaemic heart disease among 30-59-year-old men and women from 1972 to 1992. Adherence to antihypertensive drug therapy has been quite good. However, the drug treatment does not seem to account for more than 5-6% of the observed fall of blood pressure, and 10-15% of the decrease in deaths from strokes and ischaemic heart disease. There has been no overall adherence to several non-pharmacological recommendations, and marked increases in the intake of alcohol, obesity among men, and smoking among women have been observed. However, the population adherence to recommendations to decrease the intakes of sodium and saturated fats, and to reduce the sodium-to-potassium ratio and the saturated-to-unsaturated fat ratio, has been good. These dietary changes appear to account for a major part of the fall of blood pressure and the decrease in the cardiovascular diseases. Currently a rapid further population-wide decrease in the dietary sodium-to-potassium ratio is taking place, due to a decrease in the use of salt and replacement of common salt by a novel sodium-reduced, potassium-, magnesium-, and l-lysine HCI-enriched salt, both in home kitchens and in the food industry.

Effects of enalapril and hydrochlorothiazide on the salt-induced cardiac and renal hypertrophy in normotensive rats

Recent studies have shown that, not only in hypertensive animals but even in normotensive rats, dietary salt (sodium chloride) produces a dose-related increase in the left ventricular and renal mass. In the present study the effects of the angiotensin converting enzyme inhibitor (ACEI) enalapril and the thiazide-type diuretic, hydrochlorothiazide, on the development of the salt-induced left ventricular and kidney hypertrophy were examined in normotensive Wistar-Kyoto and Wistar rats. A high intake of sodium chloride (6% of the dry weight of the chow to mimic the level found in many human food items) during eight weeks produced a marked increase in the mass of the left ventricle and the kidneys in both rat strains with little or no effect on blood pressure. The cardiac hypertrophy correlated strongly with the renal hypertrophy. These salt-induced changes in the heart and in the kidneys were completely blocked by hydrochlorothiazide, while enalapril was devoid of any significant effects during the high-salt diet. However, during a low-salt diet enalapril, but not hydrochlorothiazide, effectively lowered the blood pressure and decreased the left ventricular mass of the normotensive rats. There was a 3- to 4-fold increase in the urinary excretion of calcium during the high intake of sodium chloride. Hydrochlorothiazide decreased the urinary excretion of calcium even during the low salt diet, and it completely blocked the salt-induced hypercalciuria. Enalapril had no significant effect on the urinary calcium excretion. During the low-salt diet hydrochlorothiazide increased the calcium and decreased the potassium concentration in the heart while enalapril increased the phosphorus concentration. In conclusion, a high intake of sodium chloride produced hypertrophy both in the heart and in the kidneys, even in the absence of a rise in blood pressure. Salt also remarkably increased the urinary calcium excretion. These harmful effects of salt were blocked by the thiazide diuretic hydrochlorothiazide but not by the ACEI enalapril. However, this study does not allow to make any direct comparison between the effects of enalapril and hydrochlorothiazide.

Improvement of cardiovascular effects of metoprolol by replacement of common salt with a potassium- and magnesium-enriched salt alternative

1. The influence of sodium chloride (NaCl)-enrichment of the diet (6% of the dry weight) and that of a novel sodium-reduced, potassium-, magnesium-, and L-lysine-enriched salt alternative on the cardiovascular effects of the beta 1-adrenoceptor blocking drug, metoprolol, was studied in stroke-prone spontaneously hypertensive rats. 2. Increased dietary sodium chloride intake produced a marked rise in blood pressure and induced left ventricular and renal hypertrophy. By contrast, the salt alternative did not increase blood pressure and caused remarkably less cardiac and renal hypertrophy than did sodium chloride. 3. Metoprolol treatment at a daily dose of 250 mg kg-1 lowered blood pressure and decreased left ventricular hypertrophy index during the control diet. Sodium chloride-enrichment blocked the antihypertensive effect of metoprolol, while a partial protective effect on left ventricular and renal hypertrophy persisted. In the presence of the salt alternative-enrichment both at the level of 6% and 10.5% (corresponding to a NaCl level of 6%), metoprolol was fully able to exert its beneficial cardiovascular and renal effects. 4. Both salt supplementations, irrespective of metoprolol treatment, induced a 3 to 4 fold increase in the urinary excretion of calcium. There was a linear correlation between the urinary excretions of sodium and calcium. The urinary excretion of magnesium rose by 90% and that of potassium by 110% in the salt alternative group. 6. Our findings suggest that replacement of common salt by a potassium-, and magnesium-enriched salt alternative in the diet produces beneficial cardiovascular effects and improves the antihypertensive efficacy of metoprolol in stroke-prone spontaneously hypertensive rats. Increased intake of potassium and/or magnesium and L-lysine from the salt alternative is involved in the beneficial effects of the salt alternative. The NaCl-induced myocardial and renal hypertrophies appear to be partially mediated by Beta-adrenoceptor activation.

Replacement of salt by a novel potassium- and magnesium-enriched salt alternative improves the cardiovascular effects of ramipril

1. The influence of salt (sodium chloride; NaCl) (an additional 6% in the diet) and that of a novel sodium-reduced, potassium-, magnesium-, and L-lysine-enriched salt alternative on the cardiovascular effects of ramipril was studied in stroke-prone spontaneously hypertensive rats in a 6-week study. The intake of sodium chloride was adjusted to the same level by adding the salt alternative at a 1.75 times higher amount than regular salt. 2. Salt produced a marked rise in blood pressure and induced cardiac hypertrophy and significant mortality, while the salt alternative neither increased blood pressure nor caused any mortality and produced less cardiac hypertrophy than salt. 3. Ramipril treatment at a daily dose of 3 mg kg-1 normalized blood pressure and prevented the development of cardiac hypertrophy of rats on control diet. These effects of ramipril were blocked by the addition of salt but were only slightly attenuated by the addition of the salt alternative. The mortality in the salt group was prevented by ramipril. 4. Responses of mesenteric arterial rings in vitro were examined at the end of the study. Salt, but not the salt alternative, increased vascular contractile responses to noradrenaline. Ramipril treatment improved the arterial relaxation responses to acetylcholine and to sodium nitroprusside. The vascular relaxation enhancing effect of ramipril was blocked by salt but only slightly attenuated by the salt alternative. 5. Ramipril treatment did not significantly increase plasma renin activity in the presence or in the absence of salt supplementation. The salt alternative did not cause hyperkalaemia, either alone or in combination with ramipril treatment. 6. Both salt supplementations, irrespective of ramipril treatment, induced a six to eight fold increase in the urinary excretion of calcium. There was an expected 90 to 140% rise in the urinary excretion of magnesium and 200% rise in the urinary excretion of potassium in the salt alternative group. Salt also produced an approximately 50% increase in magnesuria.7. Our findings suggest that replacement of salt by the potassium-, magnesium- and L-lysine-enriched salt alternative improves the cardiovascular effects of ramipril. In the present study the beneficial effect was related to the increased intakes of potassium and/or magnesium and L-lysine from the salt alternative because the amount of sodium chloride was the same.

Cardiovascular effects of felodipine are not antagonized by dietary salt

Increased dietary intake of regular salt (sodium chloride) interferes markedly with the therapeutic effects of angiotensin converting enzyme inhibitors. To study further the interactions between dietary salt intake and antihypertensive drug treatment, we examined the effects of felodipine, a dihydropyridine derivative Ca2+ channel antagonist with natriuretic properties, on blood pressure and the development of left ventricular hypertrophy in the stroke-prone spontaneously hypertensive rats during different levels of sodium chloride in the diet. We also compared the influence of regular salt on the cardiovascular effects of felodipine with that of a novel K(+)-, Mg(2+)- and l-lysine-enriched and Na(+)-reduced salt alternative, which in previous studies markedly improved the therapeutic effects of enalapril and ramipril. During the 28-day experiment regular salt produced a marked rise in blood pressure and induced left ventricular hypertrophy, while the salt alternative neither induced any rise of blood pressure nor caused cardiac hypertrophy. Felodipine had an enhanced antihypertensive effect during the increased intake of sodium chloride, and lowered the blood pressure to the same normotensive level as it did during the control and the salt alternative diets. Felodipine also completely blocked the development of the sodium chloride-induced cardiac hypertrophy. The heart rate of the felodipine-treated animals was significantly increased during the first two study weeks but thereafter it did not differ from that of the controls. Hence, unlike regular salt, the novel Na(+)-reduced, K(+)-, Mg(2+)-, and l-lysine-enriched salt alternative did not raise blood pressure and produced little if any left ventricular hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effects of a potassium- and magnesium-enriched salt alternative

The effects on blood pressure and the development of cardiac hypertrophy of sodium chloride (regular salt) and a novel potassium-, magnesium-, and l-lysine-enriched salt alternative, which in a previous study prolonged the life span of hypertensive rats nearly threefold as compared with the animals receiving regular salt, were compared both in spontaneously hypertensive rats and their hypertension-resistant genetic controls. In particular, the possible protective effect of increased intakes of potassium, magnesium, and l-lysine during a high intake of sodium chloride was examined. Therefore, the salt alternative was added at 1.75 times higher levels to produce the same dietary levels of sodium chloride in the regular salt and the salt alternative groups. Regular salt produced a remarkable left ventricular hypertrophy in both rat strains, but as compared with the respective control groups, it induced an increase of blood pressure only in the spontaneously hypertensive rats. The salt alternative did not induce a rise in blood pressure in either of the rat strains, nor did it produce left ventricular hypertrophy in the hypertension-resistant rats and, in the spontaneously hypertensive animals, significantly less hypertrophy than regular salt. The salt alternative appeared to prevent the sodium chloride-induced volume load since plasma levels of atrial natriuretic peptide were increased in the regular salt groups but remained normal in the salt alternative groups. Therefore, potassium, magnesium, and/or l-lysine of the salt alternative produced a powerful protection against the harmful effects of sodium chloride.

Minerals and blood pressure

The mineral elements sodium, potassium, calcium and magnesium play a central role in the normal regulation of blood pressure. In particular, these mineral elements have important interrelationships in the control of arterial resistance. These elements, especially sodium and potassium, also regulate the fluid balance of the body and, hence, influence the cardiac output. Evidence shows that the present levels of intake of mineral elements are not optimum for maintaining normal blood pressure but predispose to the development of arterial hypertension. Research results suggest that without sodium chloride (common salt) and other sodium compounds being added to the diet arterial hypertension would be virtually non existent. Moreover, blood pressure would not rise with age. In communities with a high consumption of added sodium, a high intake of potassium and, possibly, magnesium seem to protect against the development of arterial hypertension and the rise of blood pressure with age. A marked reduction of sodium intake is effective in treating even severe hypertension. A moderate restriction of sodium intake or an increase in potassium intake exert remarkable antihypertensive effects, at least in some hypertensive patients. Magnesium and possibly also calcium supplements may be effective in reducing blood pressure in some hypertensives. In hypertensive patients treated with drugs sodium restriction and potassium and magnesium supplementation enhance the therapeutic effect, reduce the number and dosage, and lessen the adverse effects of prescribed antihypertensive drugs. Hence, a fall in sodium consumption and increases in potassium and magnesium consumption are useful in preventing and treating arterial hypertension.