In situ demonstration of angiotensin-dependent and independent pathways for hyperaldosteronism during chronic extracellular fluid volume depletion

In wild-type mice, 2-wk administration of losartan, an angiotensin (Ang) II type 1 (AT1) receptor antagonist, along with dietary sodium restriction, resulted in an elevation of plasma aldosterone greater than that seen with sodium restriction alone (2.75 +/- 0.35 vs. 1.38 +/- 0.16 ng/ml, P < 0.01). Plasma potassium increased in sodium-restricted, losartan-treated mice (6.0 +/- 0.2 mEq/liter), while potassium remained unchanged in mice with sodium restriction alone. To study the effect of Ang II on glomerulosa cells that may operate independently of plasma potassium in situ, we used chimeric mice made of cells with or without the intact AT1A gene (Agtr1a). When animals were fed a normal diet or chronically infused with Ang II, the aldosterone synthase mRNA was detectable only in Agtr1a+/+ but not Agtr1a-/- zona glomerulosa cells. After 2 wk of sodium restriction, plasma aldosterone increased (1.51 +/- 0.27 ng/ml) and potassium remained on average at 4.5 +/- 0.2 mEq/liter, with aldosterone synthase mRNA expressed intensively in Agtr1a+/+, but not detectable in Agtr1a-/- cells. Simultaneous sodium restriction and losartan treatment caused increases in plasma potassium (5.5 +/- 0.1 mEq/liter) and aldosterone (1.84 +/- 0.38 ng/ml), with both Agtr1a-/- and Agtr1a+/+ cells intensively expressing aldosterone synthase mRNA. Thus, aldosterone production is regulated by Ang II in the adrenal gland during chronic alterations in extracellular fluid volume when plasma potassium is maintained within the normal range. In the light of a previous observation that dietary potassium restriction superimposed on sodium restriction abolished secondary hyperaldosteronism in angiotensinogen null-mutant mice, the present findings demonstrate that when the renin-Ang system is compromised, plasma potassium acts as an effective alternative mechanism for the volume homeostasis through its capacity to induce hyperaldosteronism.

Urinary vasodilator and vasoconstrictor angiotensins during menstrual cycle, pregnancy, and lactation

Since normal human pregnancy is characterized by normotension in the face of an increased renin-angiotensin-aldosterone system (RAAS), we evaluated the temporal pattern of urinary excretion of a novel vasodilator within this system, angiotensin-(1-7) (Ang-[1-7]), during the menstrual cycle, pregnancy, and lactation. The urinary profiles of Ang I, Ang II, human chorionic gonadotropin, 17beta-estradiol, and progesterone were also determined. During the menstrual cycle, urinary Ang-(1-7) and Ang II remained stable (mean cycle value: 94.6 +/- 11.3 and 11.4 +/- 1.1 pmol/g of creatinine, respectively) in nine females. In 10 normal pregnant women, urinary Ang-(1-7) and Ang II increased throughout gestation, averaging 1499.8 +/- 310 and 224.4 +/- 58 pmol/g of creatinine, respectively (p < 0.05) at wk 35 and falling during lactation to 394.0 +/- 95 and 65.7 +/- 20 pmol/ g of creatinine (p < 0.05), respectively. The Ang-(1-7)/Ang II ratio was unchanged in the different reproductive periods. During the menstrual cycle, Ang II and Ang-(1-7) correlated with 17beta-estradiol and progesterone using multivariate analysis (r = 0.31, p < 0.001) and r = 0.28, p < 0.02, respectively). During gestation, 17beta-estradiol and progesterone correlated with urinary Ang-(1-7) (r = 0.48, p < 0.001 and r = 0.47, p < 0.001, respectively) and Ang II (r = 0.24, p < 0.03 and r = 0.25, p < 0.03, respectively); by multiple regression, only Ang-(1-7) correlated with both steroids (r = 0.49,p < 0.001). The progressive rise of Ang-(1-7) throughout gestation, probably modulated by estrogen and progesterone, suggests a physiologic counterregulation within the RAAS.

Central angiotensin and baroreceptor control of circulation

Angiotensin (Ang) receptors are located in many important central nuclei involved in the regulation of the cardiovascular system. While most interest has focused on forebrain circumventricular actions, areas of the brainstem such as the nucleus of the solitary tract and the ventrolateral medulla contain high concentrations of AT1 receptors. The present review encompasses the physiological role of Ang II in the hindbrain, particularly in relation to its influence on baroreflex control mechanisms. In rabbits there are sympatho-excitatory AT1 receptors in the rostral ventrolateral medulla (RVLM), accessible to Ang II from the cerebrospinal fluid. Activation of these receptors acutely increases renal sympathetic nerve activity (RSNA) and RSNA baroreflex responses. However, blockade of endogenous Ang receptors in the brainstem also shows sympathoexcitation, suggesting there is greater endogenous activity of a sympathoinhibitory Ang II action. Microinjections of angiotensin antagonists into the RVLM showed relatively little tonic activity of endogenous Ang II influencing sympathetic activity in conscious rabbits. However, Ang II receptors in the RVLM mediate sympathetic responses to airjet stress in conscious rabbits. Similarly with respect to heart rate baroreflexes, there appears to be little tonic effect of angiotensin in the brainstem in normal conscious animals. Chronic infusion of Ang II for two weeks into the fourth ventricle of conscious rabbits inhibits the cardiac baroreflex while infusion of losartan increases the gain of the reflex. These actions suggest that Ang II in the brainstem modulates sympathetic responses depending on specific afferent and synaptic inputs in both the short term but importantly also in the long term, thus forming an important mechanism for increasing the range of adaptive response patterns.

Development and application of a biological peptide pump for the study of the in vivo actions of angiotensin peptides

In the past few years, a great deal of interest has been focused on the possibility that angiotensin peptides could have direct effects on target tissues independent of their hemodynamic effects. In addition, there has been much speculation on the potential biological roles of angiotensin peptides other than angiotensin II. Unfortunately, a direct test of these possibilities in whole animals has been difficult due to limitations in existing biological systems. In this review, we describe the characteristics of an engineered protein capable of directing the production of a wide variety of peptides to specific tissues and cell types in transgenic animals and discuss its potential applications.

[Neuro-hormonal mechanisms in heart failure -- from physiopathology to treatment]

This review updates some recent advances of a new and exciting developments in basic and clinical cardiology: a) the role, in the congestive heart failure (CHF), of the neurohumoral systems (NHS) which act to maintain circulatory homeostatic equilibrium, and b) the therapeutic implications of such a role. Six NHS, acting in CHF, have presently been identified: three of them induce vasoconstriction and sodium retention (sympathetic nervous systems, renin-angiotensin-aldosterone system and arginine-vasopressine system); the remaining three offset or balance the former ones, acting, therefore as "counterregulators" (prostaglandins--PGE2 and PGI2--, dopaminergic system and atrial natriuretic factor). Each one of these NHS influences the "compensatory" mechanisms of heart failure, acting on the target-organs both by direct effects and by interaction with other NHS; consequently, in heart failure, all the NHS are stimulated with the respective increase in the plasma levels of their active agents. In asymptomatic stages of ventricular dysfunction the stimulation of the vasodilator-and-natriuretic systems appears to be predominant and able to maintain circulatory equilibrium. However, as the heart dysfunction increases and becomes symptomatic, the vasoconstrictor and sodium-retaining forces appear to predominate; this phenomenon becomes increasingly apparent as the functional class becomes more advanced. The hyperstimulation of these last systems has an extremely important role in the pathophysiology and clinical manifestations of congestive heart failure, as well as in its prognosis. Therefore, the attempts to correct these neurohormonal imbalance in patients with heart failure has a sound rational basis, not only to improve the symptoms and the exercise capacity but also to increase the survival of these patients. At the present time, amongst the potential pharmacological interventions acting on NHS in CHF, the blockade of the RAA system with ACE-inhibitors is generally accepted as the most feasible, the safest and the most effective therapeutic tool. In fact, its application has broadened from an earlier use in severe CHF to other symptomatic stages of cardiac failure, including the milder forms. In addition, preliminary data strongly suggest its unique usefulness in asymptomatic phase of ventricular dysfunction. Looking back at the medical therapy of heart failure, in can be concluded that we are starting a new era. Throughout 200 years (since the introduction of digitalis) the therapeutic goal in CHF has been the improvement of symptoms. With the developments of the present decade, a new and exciting goal is being offered to these patients, called by Packer "the second frontier", that is, the prolongation of their lives.

[Recent trends in studies of the etiology of hypertension: Renal mechanism of blood pressure regulation]

The kidney plays an important role in the control of systemic blood pressure by regulating the composition of body fluid and electrolyte and by producing and releasing various vasoactive substances such as renin-angiotensin and prostaglandins(PGs). The kidney possesses an intrinsic mechanism called 'pressure-natriuresis' in which an increase in perfusion pressure promotes natriuresis. According to this mechanism, hypertension can be classified as salt-sensitive or non-salt-sensitive based on the response to dietary sodium loading. Thus, a shift of the curve to the right and a decrease in the slope are the two basic abnormalities seen in the pressure-natriuresis relationship in hypertension, with each representing a different pathophysiology. In non-salt-sensitive essential hypertension, glomerular capillary pressure is within the normal range due to elevated preglomerular resistance, while it is elevated in salt-sensitive hypertension. Such differences may be reflected in the rate of progression of renal dysfunction as well as renal pathology. Finally, the mechanism responsible for the altered renal microcirculation involves dysregulation of intrinsic mechanisms(myogenic responses and tubuloglomerular feedback) as well as various local factors, in particular, angiotensin II, nitric oxide, and oxidative stress.

Angiotensin, fibrinolysis, and vascular homeostasis

There is strong evidence that imbalance of the fibrinolytic system is involved in the pathogenesis of ischemic cardiovascular events. A reduction in fibrinolytic function may also mediate part of the adverse response of the vasculature to conditions of low nitric oxide production. Because reduced nitric oxide activity predisposes to the development of atherosclerosis, imbalance of the fibrinolytic system is heavily implicated in the development of cardiovascular pathology. The renin-angiotensin system exerts substantial control over the fibrinolytic system, and pharmacologic interventions that reduce the activity of angiotensin II also have favorable effects on fibrinolytic balance and on the incidence of adverse cardiovascular events. This review summarizes the evidence for a link between activation of the renin-angiotensin system, fibrinolytic imbalance, and cardiovascular pathology.

Endothelin-converting enzyme inhibitors: current status and perspectives

Recent research has led to the discovery of potent selective or mixed endothelin-converting enzyme (ECE), ECE/neutral endopeptidase24.11 (NEP) and ECE/NEP24.11/angiotensin-converting enzyme (ACE) inhibitors. There is also increasing evidence, that the functions of the endothelin (ET), renin-angiotensin and NEP systems for the regulation of the cardiovascular homeostasis are connected by a complex regulation network. It will be the challenging task of future research with the newly available selective and mixed ECE-1 inhibitors to show whether the combined inhibition of more than one cardiovascular system is superior to selective inhibition.

Role of angiotensin and its inhibition in hypertension, ischemic heart disease, and heart failure

This is a personal historical account relating the events that led to the first application of angiotensin inhibition (either by ACE inhibitors or by angiotensin receptor blockade) to the investigation of the pathogenesis and treatment of hypertension, ischemic heart disease, and heart failure. Included are animal experiments, clinical observations, and the earliest clinical experimental studies that helped define some of the detrimental effects of angiotensin II and the beneficial hemodynamic results of its inhibition, which have been subsequently corroborated and amplified by large randomized outcome trials.

Signal transduction from bradykinin, angiotensin, adrenergic and muscarinic receptors to effector enzymes, including ADP-ribosyl cyclase

Muscarinic acetylcholine receptors in NG108-15 neuroblastoma x glioma cells, and beta-adrenergic or angiotensin II receptors in cortical astrocytes and/or ventricular myocytes, utilize the direct signaling pathway to ADP-ribosyl cyclase within cell membranes to produce cyclic ADP-ribose (cADPR) from beta-NAD+. This signal cascade is analogous to the previously established transduction pathways from bradykinin receptors to phospholipase Cbeta and beta-adrenoceptors to adenylyl cyclase via G proteins. Upon receptor stimulation, the newly-formed cADPR may coordinately function to upregulate the release of Ca2+ from the type II ryanodine receptors as well as to facilitate Ca2+ influx through voltage-dependent Ca2+ channels. cADPR interacts with FK506, an immunosuppressant, at FKBP12.6, FK506-binding-protein, and calcineurin, or ryanodine receptors. cADPR also functions through activating calcineurin released from A-kinase anchoring protein (AKAP79). Thus, some G(q/11)-coupled receptors can control cADPR-dependent modulation in Ca2+ signaling.

Role of the angiotensin receptor in the development of the mammalian kidney and urinary tract

Recent gene targeting and pharmacological studies have shown that the renin-angiotensin system is essential for the development of the mammalian kidney and urinary tract system. We have generated mutant mice carrying a targeted null mutation of the angiotensin type 1 receptor (AT1) or type 2 receptor (AT2) gene. Analyses of these two mutant mice revealed that both mutants have a distinct phenotype in the kidney and urinary tract system. Thus, some AT2 null mutants (Agtr2 -/Y) show anomalies that mimic human congenital anomalies of the kidney and urinary tract as a result of a defect in the in utero organogenesis of the excretory system, while AT1 null mutants (Agtr1 -/-) exhibit hydronephrosis due to a defective development of the urinary peristaltic machinery during the perinatal period. In this review, we discuss chronologically from embryos to adults how the angiotensin receptors regulate the morphogenesis of the excretory system.

Angiotensin and angiotensin receptors in cartilaginous fishes

In mammals, a principal bioactive component of the renin-angiotensin system (RAS), angiotensin II (ANG II), is known to be vasopressor, dipsogenic, a stimulant of adrenocortical secretion and to control glomerular and renal tubular function. Historically, a RAS analogous to that found in mammals was thought to have first evolved in the bony fishes. Recent research has identified the unusually structured elasmobranch [Asp(1)-Pro(3)-Ile(5)] ANG II. Physiological studies have demonstrated that ANG II in elasmobranchs is vasopressor, and stimulates interrenal gland production of the elasmobranch corticosteroid 1alpha-hydroxycorticosterone. The specific binding of ANG II in elasmobranchs has been reported in gills, heart, interrenal gland, gut and rectal gland. The precise osmoregulatory role ANG II plays in cartilaginous fishes is not yet known; however, putative evidence is emerging for a role in the control of drinking rate, rectal gland secretion, and kidney function.

Angiotensin signaling and receptor types in teleost fish

Despite advances characterizing mammalian angiotensin receptors, the phylogeny of fish angiotensin receptors remains unclear. Three aspects of receptor function: (1) the nature of the ligand; (2) the second messenger system activated by it; and (3) the pharmacological profile of specific antagonists, are examined to provide insight into the fish receptor. (1) The octapeptide sequences of fish and mammalian angiotensin II (ANG II) are nearly homologous, differing only at the first and fifth residues. Both peptides are almost equally efficacious and equipotent in heterologous systems and both contain key agonist switches Tyr(4) and Phe(8) necessary to activate mammalian AT(1)-type receptors. (2) ANG II increases inositol trisphosphate production, and elevates intracellular calcium in fish tissues consistent with activation of the AT(1) receptor. (3) However, the specific mammalian sartan-type AT(1) antagonists, e.g. losartan, produce inconsistent results in fish often acting as partial agonists, or inhibiting only at elevated concentrations. Because sartans and ANG II act at distinct sites on the AT(1) receptor, we propose that the teleost receptor is an AT(1)-type receptor that is fairly well conserved with respect to both the ANG binding site and coupling to the second messenger system, whereas the sartan binding site has been poorly conserved. The evidence for non-AT(1) type ANG II receptors in teleosts is limited. Mammalian AT(2) receptor antagonists are generally ineffective but may block at elevated, non-specific doses. Truncated ANG II fragments, ANG III and ANG IV, are often less potent than ANG II, however, their receptors have not been examined. Preliminary studies in trout indicate that angiotensin 1-7 may have a mild vasodilatory effect; additional work is needed to determine if non-AT(1)-type receptors are involved.

Molecular crosstalk in host-parasite relationships: schistosome- and leech-host interactions

The host-parasite relationship is based on subtle interplay between parasite survival strategies and host defense mechanisms. In this context, parasites often use the same or similar immune signaling molecules and/or molecular mimicry to escape host immunosurveillance. Both processes represent an adaptive strategy to ensure host immunocompatibility. This bidirectional communication between parasites and their hosts includes the renin-angiotensin, opioid and opiate systems. Here, Michel Salzet, André Capron and George Stefano review recent work on the interaction of common signaling mechanisms in schistosomes, leeches and their host.

Effects of a reversible 'nephrectomy' on renal sympathetic activity and blood pressure in the rat: evidence for an acute angiotensin-mediated hypertension

OBJECTIVE

To verify whether the normal kidney exerts a supportive, facilitatory action on renal sympathetic nerve activity (RSNA), the effects of unilateral and bilateral nephrectomy on RSNA have been studied.

METHODS

The RSNA, rectal temperature (T), rate of breathing (RB), arterial blood pressure (BP) and heart rate (HR) were continuously recorded in three groups of pentobarbital anaesthetized, spontaneously breathing Sprague-Dawley rats: group 1 (n = 5): both kidneys intact; group 2 (n = 5): left surgical nephrectomy; group 3 (n = 5): left surgical nephrectomy and functional exclusion of the right kidney (functional right nephrectomy, FRN), produced by a tight ligature of the renal hilum which was maintained for 3 h. In a fourth group (n = 7), in which nerve activity was not recorded, reopening of the right renal hilum was preceded or followed by intravenous administration of captopril (3 mg/kg).

RESULTS

In groups 1 and 2 RSNA increased from 22.3 +/- 2.1 to 122.9 +/- 13.6 and from 26.7 +/- 1.2 to 93.2 +/- 14.0 impulses/s (mean +/- SEM), respectively, without concomitant changes in cardiovascular parameters. In group 3 RSNA decreased from 39.1 +/- 3.1 to 13.7 +/- 2.6 impulses/s during the 3 h of FRN. In group 3 the reopening of the right renal hilum was followed by a marked increase in BP and HR that was prevented or reversed by intravenous captopril in rats of group 4.

CONCLUSIONS

The decrease in RSNA observed in rats during bilateral nephrectomy, in contrast to the increase observed in rats with one or both kidneys intact, suggests that the kidney as a whole exerts a supportive role on sympathetic nerve activity. The hypertension and tachycardia that follows the reopening of the right kidney hilum appears to be caused by the generation of endogenous angiotensin II; this is the first evidence of an acute angiotensin-mediated renal hypertension.

Angiotensin in the nucleus tractus solitarii contributes to neurogenic hypertension caused by chronic nitric oxide synthase inhibition

Activation of the sympathetic nervous system and renin-angiotensin system has been suggested to contribute to the hypertension caused by chronic nitric oxide synthase inhibition. The aim of the present study was to determine whether angiotensin within the nucleus tractus solitarii (NTS) plays a role in activation of the sympathetic nervous system in this model. Rats were treated with N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 mg. kg(-1). d(-1) in drinking water) for 2 weeks. Experiments were performed on anesthetized rats with denervated arterial and cardiopulmonary baroreceptors. Arterial pressure, heart rate, and renal sympathetic nerve activity (RSNA) were measured. Microinjection of an angiotensin II type 1 (AT(1)) receptor antagonist (CV11974) or an angiotensin II type 2 (AT(2)) receptor antagonist (PD123319) into the depressor region within the NTS (identified by prior injection of L-glutamate) was performed. Microinjection of CV11974, but not of PD123319, produced greater decreases in arterial pressure, heart rate, and RSNA in L-NAME-treated rats than in control rats. The administration of hexamethonium resulted in a larger fall in arterial pressure in L-NAME-treated rats than in control rats. The ACE mRNA level in the brain stem was greater in L-NAME-treated rats than in control rats. These results suggest that increased sympathetic nerve activity plays a role in hypertension caused by chronic nitric oxide synthase inhibition and that activation of the renin-angiotensin system in the NTS is involved at least in part in this increased sympathetic nerve activity via AT(1) receptors.

The cardiac renin-angiotensin system: novel signaling mechanisms related to cardiac growth and function

Angiotensin II, the effector peptide of the renin-angiotensin system, has been demonstrated to be involved in the regulation of cellular growth of several tissues in response to developmental, physiological, and pathological processes. The recent identification of renin-angiotensin system components and localization of angiotensin II receptors in cardiac tissue suggests that locally synthesized Ang II can modulate functional and growth responses in cardiac tissue. In this review, regulation of the cardiac RAS is discussed, with an emphasis on growth-related Ang II signal transduction systems.

Regulation of aminopeptidase A in human brain tumor vasculature: evidence for a role of transforming growth factor-beta

Angiotensin peptides are potent vasoconstrictors, cell growth factors, and neuromodulators in normal and pathological situations. To assess the potential role of the angiotensins in brain tumor-associated vessels, the expression of the enzymes of the angiotensin cascade were evaluated in these tumors. The production of these bioactive peptides is dependent on the activities of exopeptidases, including several aminopeptidases and carboxypeptidases, producing angiotensin (Ang) I, II, III, IV and Ang 1-7. Human cerebral parenchymal and glioblastoma cells expressed renin, and tumor vasculature, but not glioblastoma cells, expressed angiotensin-converting enzyme. High aminopeptidase A (APA) activity, but no aminopeptidase N/B activity, was observed in human brain tumor vasculature, suggesting a predominant production of Ang III. Grafting of rat glioma cells in rat brains yielded tumors with high APA and low aminopeptidase N/B activities in tumor vessels, confirming human results. Tumor growth and APA activity in tumor vessels were not affected by chronic angiotensin-converting enzyme inhibition. The brain-derived EC219 endothelial cells expressed high APA activity, which was not involved in endothelial cell proliferation, but was down-regulated by exposure of cells to transforming growth factor-beta (TGF beta) or to TGF beta-secreting tumor cells, suggesting a role for this peptide in the control of APA activity in cerebral vasculature. Thus, APA is a potential marker of chronic dysfunction, involving loss of TGF beta function, of the metabolic blood-brain barrier, but not of neovascularization.

Blockade of angiotensin signaling improves myocardial function in hypercholesterolemia independent of changes in eicosanoid release

In hypercholesterolemia in the presence or absence of atherosclerosis, cardiovascular dysfunction and altered signaling of angiotensin, nitric oxide, or prostanoids are closely related to enhanced oxidant stress. We analyzed the potentially beneficial effects of the specific angiotensin-converting enzyme inhibitor enalapril and the specific angiotensin receptor blocker losartan on cardiac performance, eicosanoid metabolism, and parameters of oxidant stress in hypercholesterolemic animals. Guinea pigs were fed a 1% cholesterol diet for 8 weeks (Chol) with or without equieffective doses of either enalapril (1.5 mg/kg/d; Ena) or losartan (3 mg/kg/d; Los). Hemodynamics were analyzed in Langendorff hearts. Detection of eicosanoids was by enzyme immunoassay. Estimation of plasma xanthine oxidase (XO) activity was determined by spectrophotometry. In hypercholesterolemic guinea pigs, enhanced oxidant stress (e.g., increased plasma XO activities) was associated with profound myocardial and coronary (e.g., endothelial) dysfunction. Both enalapril and losartan lowered plasma cholesterol levels slightly, but only the angiotensin receptor antagonist effectively suppressed the increased plasma XO activities (from 11.4 +/- 0.7 to 7.6 +/- 2.2 U/L), and at the same time decreased the augmented coronary flow (from 26.0 +/- 1.0 to 23.0 +/- 1.0 mL/min/g tissue) observed in hypercholesterolemic animals. Assessment of left ventricular pressure and contractility (e.g., dp/dtmax) as well as the diastolic relaxation parameter (tau) revealed substantial myocardial dysfunction (systolic and diastolic) in Chol that was more substantially (and comparably) improved during administration of losartan (Los) than during enalapril (Ena). Surprisingly, angiotensin signaling blockade by either antagonist further suppressed the diminished coronary dilator responses to bradykinin (BK; not significant for enalapril) or adenosine (Ado) was demonstrated in Chol Langendorff hearts [delta CPPBK/Ado: from 5.0 +/- 0.5/0.9 +/- 0.1 to 4.4 +/- 1.5/0.4 +/- 0.1 (Ena) or to 1.9 +/- 0.5/0.4 +/- 0.1 (Los) cm2 (area under the curve), respectively]. Finally, as expected from control studies using heart preparations from normocholesterolemic guinea pigs, enhanced cardiac release of eicosanoids, prostacyclin, and thromboxane in Chol (0.48 +/- 0.03 and 0.6 +/- 0.1 ng/min/g) was augmented even further by treatment with enalapril (Ena: 1.6 +/- 0.4 and 1.0 +/- 0.1 ng/min/g), but was significantly reduced to or below control levels in losartan-treated animals (Los: 0.4 +/- 0.1 and 0.2 +/- 0.1 ng/min/g). Blockade of angiotensin signaling via angiotensin-converting enzyme inhibition or receptor antagonism--although differentially acting on enhanced cardiac prostanoid metabolism and oxidant stress--efficiently restored proper systolic and diastolic myocardial performance (losartan was more beneficial than enalapril), probably by counterbalancing altered angiotensin II-->angiotensin receptor signaling in the cardiovascular system of hypercholesterolemic animals. Impaired coronary vasodilator capacity seems to be irreversible after 8 weeks of a high-cholesterol diet, as shown by the unexpected lack of a dilator effect with both enalapril and losartan.

Advances in the molecular mechanisms of heart failure

Congestive heart failure is a common clinical problem resulting in significant morbidity and mortality. Although considerable progress has been made in elucidating the pathophysiologic mechanisms that lead to the development of this process, much remains unknown. The techniques of modern molecular biology now allow a detailed and systematic analysis of this disease. Recent data linking cardiac hypertrophy, aberrant signaling, or cytoskeletal abnormalities to the development of heart failure have provided new insights into this process. These studies have confirmed the importance of many classical pathways but also revealed novel pathways. This review will focus on the recent advances that have been made and will highlight the importance they have had in our understanding and treatment of heart failure.

The role of vasoactive compounds, growth factors and cytokines in the progression of renal disease

A number of kidney diseases, and their progression to end-stage renal disease, are driven, in part, by the effects of angiotensin II. Increasing levels of angiotensin II may in turn up-regulate the expression of growth factors and cytokines, such as transforming growth factor-beta1 (TGF-beta1), tumor necrosis factor-alpha (TNF-alpha), osteopontin, vascular cell adhesion molecule-1 (VCAM-1), nuclear factor-kappaB (NF-kappaB), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF) and insulin-like growth factor. Most of these compounds promote cell growth and fibrosis. Angiotensin II also stimulates oxidative stress. This stress in turn may potentiate the vasoconstrictor effect of the peptide due, in part, to increased catabolism of nitric oxide (NO). Oxidative stress, fueled in part by angiotensin II, up-regulates the expression of adhesion molecules, chemoattractant compounds and cytokines. The angiotensinogen gene, which provides the precursor for angiotensin production, is stimulated by NF-kappaB activation. NF-kappaB is activated by angiotensin in the liver and in the kidney. This provides an autocrine reinforcing loop that up-regulates angiotensin production. Angiotensin II activates NF-kappaB through both AT1 and AT2 receptors. In addition, angiotensin-converting enzyme (ACE) inhibition markedly decreases NF-kappaB activation in the setting of renal disease.

Cardiovascular effects of combination of perindopril, candesartan, and amlodipine in hypertensive rats

The combination therapy with ACE inhibitors, angiotensin II type 1 (AT(1)) receptor antagonists, or calcium channel antagonists may exert more beneficial effects on cardiovascular diseases than monotherapy. Perindopril, candesartan cilexetil, or amlodipine alone or the combination of low doses of each agent was administered orally to stroke-prone spontaneously hypertensive rats (SHRSP) for 4 weeks to compare the hypotensive or cardiovascular effects. Although perindopril (2 mg/kg), candesartan cilexetil (2 mg/kg), or amlodipine (3 mg/kg) alone caused comparable hypotensive effects in SHRSP, monotherapy with perindopril or candesartan decreased left ventricular (LV) weight; mRNA levels for atrial natriuretic factor, skeletal alpha-actin, and collagen types I and III; and aortic weight and platelet-derived growth factor-beta receptor tyrosine phosphorylation to a greater extent than monotherapy with amlodipine. Although monotherapy with a low dose (0.2 mg/kg) of perindopril or candesartan cilexetil did not significantly reduce the LV mRNA levels and aortic platelet-derived growth factor-beta receptor phosphorylation of the SHRSP, combination therapy at such a low dose normalized these parameters more potently than the use of amlodipine (3 mg/kg) alone. Although perindopril or candesartan cilexetil alone at 0.05 mg/kg did not decrease the blood pressure of the SHRSP, such a low dose of combination therapy decreased LV weight and atrial natriuretic factor mRNA levels of the SHRSP to a greater extent than amlodipine alone or amlodipine combined with perindopril or candesartan cilexetil. Our results provide evidence that suggests the combination of an ACE inhibitor and an AT(1) receptor antagonist may be more effective in the treatment of cardiac and vascular diseases than the combination of a calcium channel blocker with an ACE inhibitor or an AT(1) receptor antagonist or monotherapy with each agent.

Adult offspring long-term effects of high salt and water intake during pregnancy

Offspring from dams subjected to hypereninemia, hyperdipsia, and natriophilia by partial aortic ligation (PAL) showed a long-term modification of their ingestive behavior. These rats, upon reaching adulthood, showed an increased appetite for low-concentration saline solutions (0.1 M) when compared to control rats. They also presented a high intake of a medium concentration NaCl solution (0.45 M) after having been offered a very aversive highly concentrated NaCl solution (1.0 M) along with water for 2 days. An increase was also observed in their salt/water intake ratio following two different thirst challenges, 24-h fluid deprivation or sodium depletion by furosemide treatment. The demonstration of the long-term effect of pregnancy history on salt preference in adult offspring draws attention to the possible physiopathological aspects that may be of relevance, considering the well-established relationship between salt intake and hypertension, a disease most commonly occurring in the adult and aged population.

Functional analysis of cardiovascular renin-angiotensin system using a gain or loss of function approach

The study of the effect of autocrine-paracrine vasoactive modulators on cardiovascular biology is very difficult in vivo, because in vivo studies are limited. In particular, characterization of the role of components of the renin-angiotensin system (RAS) in vivo is limited by the difficulty in manipulating individual components of the RAS as well as by methodological limitations in studying the function of a local RAS in the absence of any contribution by the circulatory system. Recent progress in in vivo gene transfer technologies has provided us with the opportunity to study cellular responses to the manipulation of the individual components (i.e., by overexpression or inhibition). Many researchers have recently developed various in vivo gene transfer techniques for cardiovascular applications. Using in vivo gene transfer approaches, the roles of various tissues in the RAS, such as cardiac angiotensin, have been identified. Such an approach may increase our understanding of the biology and pathobiology of the autocrine-paracrine system. This review discusses the potential utility of in vivo gene transfer methods.