Induction of cardiac angiotensin I-converting enzyme with dietary NaCl-loading in genetically hypertensive and normotensive rats

Biomarkers of high salt intake

High salt intake is associated with hypertension, which is a leading modifiable risk factor for cardiovascular disease (CVD) and chronic kidney disease (CKD). International Guidelines recommend a large reduction in the consumption of sodium to reduce blood pressure, organ damage, and mortality. In its early stages, the symptoms of CKD are generally not apparent. CKD proceeds in a "silent" manner, necessitating the need for urinary biomarkers to detect kidney damage at an early stage. Since traditional renal biomarkers, such as serum creatinine, are not sufficiently sensitive, difficulties are associated with detecting kidney damage induced by a high salt intake, particularly in normotensive individuals. Several new biomarkers for renal tubular damage, such as neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), vanin-1, liver-type fatty acid-binding protein (L-FABP), and monocyte chemotactic protein-1 (MCP-1), have recently been identified. However, few studies have investigated early biomarkers for CKD progression associated with a high salt diet. This chapter provides insights into novel biomarkers for CKD in normo- and hypertensive individuals with a high salt intake. Recent studies using spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) fed a high salt diet identified urinary vanin-1 and NGAL as early biomarkers for renal tubular damage in SHR and WKY, whereas urinary KIM-1 was a useful biomarker for salt-induced renal injury in SHR only. Clinical studies are needed to confirm these findings.

Inappropriate activity of local renin-angiotensin-aldosterone system during high salt intake: impact on the cardio-renal axis

Although there is a general agreement on the recommendation for reduced salt intake as a public health issue, the mechanism by which high salt intake triggers pathological effects on the cardio-renal axis is not completely understood. Emerging evidence indicates that the renin-angiotensin-aldosterone system (RAAS) is the main target of high Na⁺ intake. An inappropriate activation of tissue RAAS may lead to hypertension and organ damage. We reviewed the impact of high salt intake on the RAAS on the cardio-renal axis highlighting the molecular pathways that leads to injury effects. We also provide an assessment of recent observational studies related to the consequences of non-osmotically active Na⁺ accumulation, breaking the paradigm that high salt intake necessarily increases plasma Na⁺ concentration promoting water retention

Dietary sodium restriction specifically potentiates left ventricular ACE inhibition by zofenopril, and is associated with attenuated hypertrophic response in rats with myocardial infarction

Introduction In patients with myocardial infarction (MI)-induced heart failure, angiotensin-converting enzyme (ACE) inhibitors are proven effective therapy in inhibiting the progression towards overt heart failure. However, the prognosis in these patients is still very poor, and optimisation of therapy is warranted. The antihypertensive and renoprotective effects of ACE inhibitors (ACE-Is) can be substantially enhanced by dietary sodium restriction. In line with the latter, the aim of the present study was to explore whether dietary sodium restriction enhances the efficacy of ACE-I after MI.

Methods Rats with MI-induced left ventricular (LV) dysfunction received ACE-I therapy with zofenopril (5.5 mg/kg/day orally), with or without dietary sodium restriction. ACE activity was measured in non-infarcted LV tissue, kidneys and plasma. Effects on cardiac hypertrophy were examined by means of organ weight/body weight ratios. After blood pressure (BP) measurements, functional consequences of therapy were evaluated as LV pressure development in isolated perfused hearts.

Results Dietary sodium restriction alone had no effect on any of the measured parameters, whereas zofenopril alone significantly reduced plasma and kidney ACE activity, but not LV ACE activity, nor LV weight/body weight ratio. However, only when ACE-I therapy was combined with dietary sodium restriction was LV ACE activity significantly reduced. This effect was paralleled by inhibition of LV hypertrophy. BP was reduced after infarction, and further reduced by zofenopril, but not affected by dietary sodium. Neither treatment was associated with effects on the MI-induced reduction of LV function in vitro.

Conclusions Effects of ACE inhibition with zofenopril can be potentiated by additional dietary sodium restriction. However, these effects were tissue-specific, since LV, but not kidney or plasma, ACE activity was affected by the additional dietary sodium restriction. Effects on LV ACE activity were paralleled by reduced LV hypertrophy. Since the measured parameters did not indicate any adverse side-effects, dietary sodium restriction may provide a safe strategy to improve ACE-I efficacy in patients with infarction-induced LV dysfunction.

Development of progressive albuminuria in male Munich Wistar Frömter rats is androgen dependent

Munich Wistar Frömter (MWF) rats develop spontaneous albuminuria that is linked to autosomal genetic loci and inherit a nephron deficit in both female and male animals, respectively. However, albuminuria and kidney damage are clearly more pronounced in males. Here we tested whether androgens and the androgen receptor influence albuminuria in male MWF. We first demonstrated in a pilot study that orchiectomy (Ox) of male MWF led to a significant suppression of urinary albumin excretion (UAE), while continuous testosterone supplementation in MWF Ox led to UAE levels similar to sham-operated (Sham) MWF rats. Subsequently, we performed a comparative main study between male MWF and normal Wistar rats to evaluate the effect of the androgen receptor on UAE development in adult animals up to the age of 18 wk. MWF Sham developed a marked increase in UAE compared with Wistar Sham (48.30 ± 6.16 vs. 0.42 ± 0.08 mg/24 h, P < 0.0001). UAE was significantly lower in MWF Ox compared with MWF Sham (-55%, P < 0.0001). In MWF Ox animals supplemented with testosterone and treated with the androgen receptor antagonist flutamide (OxTF) UAE at 18 wk was even lower compared with MWF Ox (-71%, P < 0.01) and similar to age-matched female MWF. The mRNA expression of renal tubular injury markers Kim1 and NGAL was increased in MWF Sham compared with Wistar Sham (P < 0.0008, respectively) and expression decreased significantly in MWF OxTF (P < 0.0004, respectively). Thus, the sexual dimorphism in albuminuria development in MWF can be attributed to testosterone and the androgen receptor in male rats.

[Salt consumption and cardiovascular risk : a plea for salt reduction]

High salt intake over long term is associated with increased incidence of arterial, predominantly systolic, hypertension and increased risk of cardiovascular diseases, e.g., stroke, heart failure, and renal insufficiency. High salt consumption is a vascular risk factor generating aortic stiffness and decreased vascular compliance leading to central blood pressure augmentation, higher cardiac load, and diminished diastolic perfusion. The development of heart failure can be a consequence of this sequelae. Randomized trials show a reduction in blood pressure with lower sodium intake. In long-term clinical trials, a reduction in cardiovascular morbidity and mortality has been demonstrated. Recommendations should emphasize the simultaneous reduction in sodium intake and increase in potassium intake.

Vascular structure and oxidative stress in salt-loaded spontaneously hypertensive rats: effects of losartan and atenolol

BACKGROUND

Renin-angiotensin system (RAS) modulation by high dietary sodium may contribute to salt-induced hypertension, oxidative stress, and target organ damage. We investigated whether angiotensin II (Ang-II) type 1 (AT1)-receptor blockade (losartan) could protect the aorta and renal arteries from combined hypertension- and high dietary salt-related oxidative stress.

METHODS

Spontaneously hypertensive rats (3-month-old, n = 10/group) received tap water (SHR), water containing 1.5% NaCl (SHR+S), 1.5% NaCl and 30 mg losartan/kg/day (SHR+S+L), or 50 mg atenolol/kg/day (SHR+S+A). Atenolol was used for comparison. Ten Wistar-Kyoto rats (WKY) were controls. Systolic blood pressure (SBP) was determined by tail plethysmography. After 5 months of treatment, vascular remodeling and oxidative stress (superoxide production and NAD(P)H-oxidase activity (chemiluminescence), malondialdehyde (MDA) content (high-performance liquid chromatography), endothelial nitric oxide synthase (eNOS) activity [(14)C-arginine to (14)C citrulline], CuZn-SOD activity (spectrophotometry)) were studied.

RESULTS

In SHR, salt-loading significantly aggravated hypertension, urinary protein excretion, intraparenchymal renal artery (IPRArt) perivascular fibrosis, aortic and renal artery oxidative stress, and induced endothelial cell loss in IPRArts. In salt-loaded SHR, 5-month losartan and atenolol treatments similarly reduced SBP, but only losartan significantly prevented (i) urinary protein excretion increase, (ii) or attenuated hypertension-related vascular remodeling, (iii) aortic MDA accumulation, (iv) renal artery eNOS activity lowering, and (v) aortic and renal artery superoxide dismutase (SOD) activity reduction. In SHR+S, the contributions to aortic superoxide production were as follows: uncoupled eNOS > xanthine oxidase (XO) > NAD(P)H oxidase.

CONCLUSIONS

In this salt-sensitive genetic hypertension model, losartan protects from hypertension- and high dietary salt-related vascular oxidative stress, exceeding the benefits of BP reduction. Also, during salt overload, BP-independent factors contribute to vascular remodeling, at least part of which derive from AT1-receptor activation.

Salt-induced renal injury in spontaneously hypertensive rats: effects of nebivolol

BACKGROUND

we investigated renal effects of nebivolol, a selective β(1)-receptor blocker with additional antioxidative ability, in spontaneously hypertensive rats (SHR) where increased salt intake induces oxidative stress and worsens renal function as a result of further activation of the renin-angiotensin and sympathetic nervous systems.

METHODS

male SHR were given an 8% salt diet (HS; n = 22) for 5 weeks; their age-matched controls (n = 9) received standard chow. Nebivolol was given at a dose of 10 mg/kg/day for 5 weeks in 11 HS rats.

RESULTS

HS increased blood pressure, plasma renin concentration, urinary protein excretion, and renal nitroxidative stress while decreasing renal blood flow and angiotensin 1-7 receptor (mas) protein expression. There was no change in angiotensin II type 1 receptor expression among the experimental groups. Nebivolol did not alter the salt-induced increase in blood pressure but reduced urinary protein excretion, plasma renin concentration, and nitroxidative stress. Nebivolol also increased neuronal NOS expression while preventing the salt-induced decrease in renal blood flow and mas protein expression.

CONCLUSION

nebivolol prevented salt-induced kidney injury and associated proteinuria in SHR through a blood pressure-independent mechanism. Its protective effects may be related to reduction in oxidative stress, increases in neuronal NOS and restoration of angiotensin II type 1/mas receptor balance.

Genetic locus on MWF rat chromosome 6 affects kidney damage in response to L-NAME treatment in spontaneously hypertensive rats

A major quantitative trait locus (QTL) on rat chromosome (RNO)6 was linked to albuminuria in Munich Wistar Frömter rats (MWF). We tested whether transfer of MWF RNO6 into the background of albuminuria-resistant spontaneously hypertensive rats (SHR) induces albuminuria in consomic SHR-6(MWF) animals. Male MWF, SHR, and SHR-6(MWF) were sham operated and treated between 6 and 24 wk of age with normal water (Sham) or with water containing 20 mg/l N(G)-nitro-L-arginine methyl ester (L-NAME) or unilaterally nephrectomized (Nx). Compared with SHR albuminuria was not increased in SHR-6(MWF) in both Sham and Nx groups. All animals survived the observation period in Sham and Nx groups, while premature mortality occurred from 12-14 wk on in L-NAME-treated SHR and SHR-6(MWF) compared with MWF L-NAME animals, in which survival was not affected (P < 0.005, respectively). Subsequent further analysis of L-NAME-treated animals at 12 wk of age showed significantly increased arterial blood pressures in both SHR and SHR-6(MWF) compared with control (P < 0.05), with higher levels in SHR compared with consomics (P < 0.05). However, L-NAME-treated consomic animals demonstrated increased albuminuria compared with SHR (12.7 +/- 3.5 vs. 0.8 +/- 0.2 mg/24 h; P < 0.05) and an induction of tubulointerstitial structural injury and expression of neutrophil gelatinase-associated lipocalin mRNA (P < 0.05 vs. other strains). Our study demonstrates that isolation of the RNO6 albuminuria QTL from the MWF background and transfer into SHR fails to induce an albuminuria phenotype during normal conditions or after nephron reduction. Moreover, our data indicate that genes on RNO6 contribute to the development of L-NAME-induced renal damage in the SHR strain.

Decreased cardiac Ang-(1-7) is associated with salt-induced cardiac remodeling and dysfunction

OBJECTIVE

Angiotensin II has a critical role in the regulation of blood pressure and cell growth and excess activity of the peptide is implicated in the pathogenesis of salt-induced cardiovascular injury. On the other hand, the role of counteracting angiotensin-(1-7) in cardiac structural and functional responses to high salt diet has not been elucidated. Therefore, the present study examined the changes in cardiac angiotensin-(1-7), its forming enzyme angiotensin converting enzyme 2 (ACE2) and receptor mas in response to a high salt diet in spontaneously hypertensive rats (SHR).

METHODS

Eight-week-old male spontaneously hypertensive rats (SHR) were given an 8% salt diet for 5 weeks (n = 8). Age- and gender-matched controls received standard chow (n = 6).

RESULTS

Salt excess increased arterial pressure (p < 0.05) and plasma renin and angiotensin II concentrations (p < 0.05). Salt-induced left ventricular remodeling and diastolic dysfunction were associated with diminished levels of angiotensin-(1-7) in the heart (p < 0.05) and no changes in cardiac angiotensin II levels. Exposure to high salt intake decreased cardiac ACE2 mRNA and protein level (p < 0.05). There was no difference in the protein levels of angiotensin II type 1 and mas receptors between the two experimental groups.

CONCLUSION

The adverse cardiac effects of excessive salt intake may result not only from the undesirable action of angiotensin II but may also be a consequence of diminished protective effects of the angiotensin-(1-7).

Gender-specific regulation of pancreatic islet blood flow, insulin levels and glycaemia in spontaneously diabetic Goto-Kakizaki rats

Patients with diabetes are often treated with a statin for hyperlipidaemia and an ACE (angiotensin-converting enzyme) inhibitor or angiotensin receptor antagonist for hypertension or albuminuria. These drugs may also exert beneficial metabolic effects, causing improved glucose tolerance in patients. Gender-related differences have also been observed in the clinical responsiveness to these drugs, but the mechanism behind this is unclear. In the present study, we have investigated whether these drugs and the fatty acid palmitate influence the pancreatic microcirculation, thereby having an impact on insulin secretion and glycaemia in vivo, in spontaneously diabetic male and female Goto-Kakizaki rats. In male rats, pancreatic IBF (islet blood flow) and total PBF (pancreatic blood flow) were increased significantly by pravastatin, captopril and irbesartan. Serum insulin levels were increased by pravastatin and captopril. Palmitate suppressed pancreatic IBF and increased blood glucose. In female animals, pancreatic IBF was stimulated by captopril, candesartan and irbesartan. Total PBF was increased by captopril, candesartan and irbesartan, and by pravastatin. Palmitate suppressed pancreatic IBF and serum insulin secretion. In conclusion, the present study lends support to the view that a local pancreatic RAS (renin-angiotensin system) and pravastatin may be selectively influencing the pancreatic microcirculation and therefore affecting insulin secretion and glycaemia. NEFAs (non-esterified fatty acids) impaired pancreatic IBF, suppressed insulin secretion and increased blood glucose. Substantial gender-related differences in the vascular and metabolic responses to these drugs prevail in this animal model of diabetes.

Aging and the brain renin-angiotensin system: relevance to age-related decline in cardiac function

This article discusses evidence that impairments in control of autonomic outflow mediated by the brain renin-angiotensin system (RAS) contribute to the decline in baroreceptor reflex function and the development of insulin resistance that accompany hypertension and excess salt intake, especially during aging. Imbalances in the regulation of the sympathetic and parasympathetic limbs of the autonomic nervous system observed in older subjects underlie changes in heart-rate variability and play a role in the regulation of overall cardiac function. Age-related alterations in autonomic nervous system function may also explain the age-associated alterations in metabolism. Reduced heart-rate variability is linked to increased mortality in patients with cardiovascular disorders and, coupled with information that is known about local changes in the cardiac and brain RAS during aging, the evidence reveals potential mechanisms for the protective effects of systemic blockade of the RAS against age-related changes that impact the heart.

AT1 receptor antagonism attenuates target organ effects of salt excess in SHRs without affecting pressure

Our recent studies have demonstrated that salt excess in the spontaneously hypertensive rat (SHR) produces a modestly increased arterial pressure while promoting marked myocardial fibrosis and structural damage associated with altered coronary hemodynamics and ventricular function. The present study was designed to determine the efficacy of an angiotensin II type 1 (AT(1)) receptor blocker (ARB) in the prevention of pressure increase and development of target organ damage from high dietary salt intake. Eight-week-old SHRs were given an 8% salt diet for 8 wk; their age- and gender-matched controls received standard chow. Some of the salt-loaded rats were treated concomitantly with ARB (candesartan; 10 mg kg(-1) day(-1)). The ARB failed to reduce the salt-induced rise in pressure, whereas it significantly attenuated left ventricular (LV) remodeling (mass and wall thicknesses), myocardial fibrosis (hydroxyproline concentration and collagen volume fraction), and the development of LV diastolic dysfunction, as shown by longer isovolumic relaxation time, decreased ratio of peak velocity of early to late diastolic waves, and slower LV relaxation (minimum first derivative of pressure over time/maximal LV pressure). Without affecting the increased pulse pressure by high salt intake, the ARB prevented the salt-induced deterioration of coronary and renal hemodynamics but not the arterial stiffening or hypertrophy (pulse wave velocity and aortic mass index). Additionally, candesartan prevented the salt-induced increase in kidney mass index and proteinuria. In conclusion, the ARB given concomitantly with dietary salt excess ameliorated salt-related structural and functional cardiac and renal abnormalities in SHRs without reducing arterial pressure. These data clearly demonstrated that angiotensin II (via AT(1) receptors), at least in part, participated importantly in the pressure-independent effects of salt excess on target organ damage of hypertension.

Non-pressure-related effects of dietary sodium

After the demonstration of a positive correlation between sodium intake and arterial pressure in large population studies, the effect of short-term reduction in sodium intake demonstrated the efficacy of this nonpharmacological therapy. In addition, a positive relation between urinary sodium (the most reliable estimate of salt intake) and left ventricular hypertrophy was found; and in recent years it was shown that cardiovascular morbidity clearly progressed with increasing sodium intake, despite one contradictory study. The role of non-pressure-related effects of dietary sodium is discussed in order to bring more arguments for a large-scale attempt to reduce sodium intake by 30% to 50%.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Myocardial fibrosis, impaired coronary hemodynamics, and biventricular dysfunction in salt-loaded SHR

Arterial pressure in most experimental and clinical hypertensions is exacerbated by salt. The effects of salt excess on right and left ventricular (RV and LV, respectively) functions and their respective coronary vasodilatory responses have been less explored. We therefore examined the effects of 8 wk of NaCl excess (8% in food) on arterial pressure, RV and LV functions (maximal rate of increase and decrease of ventricular pressure; dP/dt(max) and dP/dt(min)), coronary hemodynamics (microspheres), and collagen content (hydroxyproline assay and collagen volume fraction) in young adult normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR), aged 16 wk by the end of the study. Prolonged salt excess in WKY and SHR elevated pressure only modestly, but it markedly increased LV mass, especially in SHR. Moreover, salt excess significantly impaired RV and LV diastolic function in SHR but only LV diastolic function in WKY rats. However, salt loading affected neither RV nor LV contractile function in both strains. Interstitial and perivascular collagen deposition was increased, whereas coronary vasodilatory responses to dipyridamole diminished in both ventricles in the salt-loaded SHR but not in WKY rats. Therefore, accumulation of ventricular collagen as well as altered myocardial perfusion importantly contributed to the development of salt-related RV and LV dysfunctions in this model of naturally occurring hypertension. The unique effects of salt loading on both ventricles in SHR, but not WKY rats, strongly suggest that nonhemodynamic mechanisms in hypertensive disease participate pathophysiologically with salt-loading hypertension. These findings point to the conclusion that the concept of "salt sensitivity" in hypertension is far more complex than simply its effects on arterial pressure or the LV.

Cardiorenal abnormalities associated with high sodium intake: correction by spironolactone in rats

Reversal by the mineralocorticoid receptor antagonist spironolactone on cardiac and renal abnormalities, associated with long-term (since weaning) administration of a high (2 and 8% NaCl chow, HS2 and HS8) sodium diet, was assessed in Sprague-Dawley rats. At the age of 5 mo, spironolactone (20 or 100 mg/kg, gavage) or placebo were given for 14 days to HS2 and HS8 rats. A group fed a regular diet (0.8% NaCl, NS) remained untreated. High sodium intake had no detectable effect on blood pressure; however, cardiac mass index and cross-sectional area of the carotid artery, as well as albuminuria, were increased only in the HS8 group compared with the control group on NS diet. In addition, a marked reduction in glomerular filtration rate (by 40%), associated with a nonproportional fall in renal plasma flow (thus resulting in a decrease in filtration fraction), was observed only in the HS8 group. No change in cardiac and renal fibrosis was detected. Production of the reactive oxygen species (ROS) by aortic tissue was increased in HS8 rats, whereas ROS production by the heart was unaffected. Only the high dose of spironolactone was effective, as it markedly reversed the cardiac hypertrophy and renal hypofiltration associated with the HS8 feeding. The changes were observed in the absence of any effect on systemic blood pressure and production of ROS. These observations favor aldosterone’s role in the deleterious effects of marked and prolonged increases in sodium intake.

Sodium directly impairs target organ function in hypertension

PURPOSE OF REVIEW

A large body of epidemiologic evidence has been amassed attesting to the relation of increased salt ingestion to the prevalence of hypertension; however, only a minority of patients with essential hypertension are salt sensitive. This report discusses the hypothesis that salt sensitivity need not be demonstrated exclusively by a marked rise in arterial pressure with salt loading; it may also be manifested by evidence of impaired target organ structure and function.

RECENT DEVELOPMENTS

This discussion summarizes the authors' recent experience with the spontaneously hypertensive rat, the best experimental model for naturally occurring hypertension, which demonstrates that salt loading precipitates the common structural and functional cardiac and renal changes associated with long-standing hypertension.

SUMMARY

As a result of salt loading, left ventricular diastolic dysfunction and impaired renal excretory function with massive proteinuria occur. Both are associated with marked ischemia and fibrosis and only a small additional increase in arterial pressure.

Lifestyle modification and progressive renal failure

There is increasing evidence that lifestyle factors impact on the risk of developing chronic kidney disease (CKD) and the risk of progression of CKD. Equally important is the consideration that patients with CKD are more likely to die from cardiovascular disease than to reach the stage of end-stage renal failure. It is advantageous that manoeuvres that interfere with progression at the same time also reduce the risk of cardiovascular events. Lifestyle factors that aggravate progression include, among others, smoking, obesity and dietary salt intake. Alcohol consumption, according to some preliminary information, has a bimodal relationship to cardiovascular risk and progression, with moderate consumption being protective.

Cardiac structural and functional responses to salt loading in SHR

Increased dietary salt intake induces cardiac fibrosis in the spontaneously hypertensive rat (SHR), yet little information details its effects on left ventricular (LV) function. Additionally, young normotensive rats are more sensitive to the trophic effect of dietary sodium than older rats. Thus cardiac responses to salt loading were evaluated at two ages in the SHR; LV collagen content was also examined. SHR (8 or 20 wk of age) were given an 8% salt diet; their age-matched controls received standard chow. Echocardiographic indexes, arterial pressure, and LV hydroxyproline concentration were measured at 16 and 52 wk in the younger and older SHR groups, respectively. In most SHR, salt excess increased arterial pressure, LV mass, and hydroxyproline concentration and impaired LV relaxation manifested by prolonged isovolumic relaxation time, decreased early and atrial filling velocity ratio (V(E)/V(A)), and slower propagation velocity of E wave (V(P)). LV systolic function remained normal. However, one-quarter of the young salt-loaded SHR developed cardiac failure with systolic and diastolic dysfunction associated with greater LV mass and ventricular fibrosis. They also had lower arterial pressure, decreased fractional shortening, and a restrictive pattern of mitral flow. Moreover, the shorter deceleration time of the E wave and increased V(E)/V(P), an index of LV filling pressure, indicated increased LV stiffness in these rats. These findings demonstrated that sodium sensitivity in SHR is manifested not only by further pressure elevation but also by significant LV functional impairment that most likely is related to enhanced ventricular fibrosis. Moreover, the SHR are more susceptible to cardiac damage when high dietary salt is introduced earlier in life.

Local cardiac renin-angiotensin system: hypertension and cardiac failure

In addition to the effect on arterial pressure, angiotensin II, the effector peptide of the renin-angiotensin system (RAS), exerts mitogenic and growth promoting effects on cardiac myocytes and non-myocytic elements; and both of these effects significantly contribute to the development and progression of hypertensive heart disease (HHD). The traditional concept of the RAS as a systemic, endocrine system has been expanded and the identification of its components in many organs and tissue has been amassed. This paper reviews evidence that supports the concept that the cardiac RAS participate importantly in the development and risk of HHD.

Harmful effects of dietary salt in addition to hypertension

In addition to raising the blood pressure dietary salt is responsible for several other harmful effects. The most important are a number which, though independent of the arterial pressure, also harm the cardiovascular system. A high salt intake increases the mass of the left ventricle, thickens and stiffens conduit arteries and thickens and narrows resistance arteries, including the coronary and renal arteries. It also increases the number of strokes, the severity of cardiac failure and the tendency for platelets to aggregate. In renal disease, a high salt intake accelerates the rate of renal functional deterioration. Apart from its effect on the cardiovascular system dietary salt has an effect on calcium and bone metabolism, which underlies the finding that in post-menopausal women salt intake controls bone density of the upper femur and pelvis. Dietary salt controls the incidence of carcinoma of the stomach and there is some evidence which suggests that salt is associated with the severity of asthma in male asthmatic subjects.

Cyclosporine induces myocardial connective tissue growth factor in spontaneously hypertensive rats on high-sodium diet

BACKGROUND

The introduction of cyclosporine (CsA) has led to an improvement in the prognosis of solid organ transplantation. However, drug-induced hypertension and nephrotoxicity, associated with the development of atherosclerosis and coronary heart disease, still worsen the long-term outcome of CsA-treated patients. Whether the CsA-induced myocardial changes are associated with the induction of connective tissue growth factor (CTGF), a recently found polypeptide implicated in extracellular matrix synthesis, is not known.

METHODS

Spontaneously hypertensive rats (8-9 weeks old) were treated with CsA (5 mg x kg(-1) x d(-1) subcutaneously) for 6 weeks. The influence of angiotensin-converting enzyme inhibition (enalapril 30 mg x kg(-1) x d(-1) orally) and angiotensin-1 receptor blockade (valsartan 3 and 30 mg x kg(-1) x d(-1) orally) on CsA toxicity was also investigated. Myocardial morphology was examined, and vascular lesions were scored. Localization and the quantitative expression of CTGF, as well as collagen I and collagen III, mRNA were evaluated by in situ hybridization and Northern blot.

RESULTS

CsA-induced hypertension and nephrotoxicity were associated with myocardial infarcts and vasculopathy of the coronary arteries. CsA increased myocardial CTGF, collagen I, and collagen III mRNA expressions by 91%, 198%, and 151%, respectively. CTGF mRNA expression colocalized with the myocardial lesions. Blockade of the renin-angiotensin system prevented vascular damage and the CsA-induced CTGF, collagen I, and collagen III mRNA overexpressions in the heart.

CONCLUSIONS

CsA increases CTGF, collagen I, and collagen III mRNA expressions in the heart. The induction of CTGF gene is mediated, at least in part, by angiotensin II.

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.

Roles of vascular angiotensin converting enzyme and chymase in two-kidney, one clip hypertensive hamsters

BACKGROUND

A chymase-dependent angiotensin II-forming pathway is present in human vascular tissues; however, the role, if it plays any, of chymase in the pathogenesis of hypertension is not known. When investigating the role of chymase, it is important to recognize marked differences in vascular angiotensin II-forming systems among species. We found recently that hamsters, like humans, possess the dual angiotensin II-forming system.

OBJECTIVE

To analyze the potential involvement of angiotensin converting enzyme and chymase in the pathogenesis of hypertension, and to further characterize the efficiency of angiotensin converting enzyme inhibitors and angiotensin II receptor antagonists for the treatment of hypertension.

METHODS AND RESULTS

The mean arterial pressure in the two-kidney, one clip hamster model had increased significantly 2 weeks after clipping (acute stage), reached a peak after 4 weeks, and was sustained at the high level until 32 weeks after clipping (chronic stage). Plasma renin activity increased markedly during the acute stage, but returned to the normal level during the chronic stage. Vascular angiotensin converting enzyme activity during 4-32 weeks after clipping was significantly higher than that in the control hamsters. By contrast, vascular chymase was not activated throughout the experimental period. Administrations of an angiotensin converting enzyme inhibitor, trandolapril, and an angiotensin II receptor antagonist, CV-11974, equally lowered the mean arterial pressure during the acute and chronic stages.

CONCLUSIONS

Vascular angiotensin converting enzyme plays a predominant role in the maintenance of two-kidney, one clip hypertension in hamsters, which, like humans, possess a dual system of formation of angiotensin II. Vascular chymase was not involved in the pathogenesis of two-kidney, one clip hypertension in the hamster.