Coronary kinin generation mediates nitric oxide release after angiotensin receptor stimulation

Sex Difference in MasR Expression and Functions in the Renal System

Renin-angiotensin system (RAS), as a critical system for controlling body fluid and hemostasis, contains peptides and receptors, including angiotensin 1-7 (Ang 1-7) and Mas receptor (MasR). Ang 1-7 implements its function via MasR. Ang II is another peptide in RAS that performs its actions via two Ang II type 1 and 2 receptors (AT1R and AT2R). The functions of AT2R and MasR are very similar, and both have a vasodilation effect, while AT1R has a vasoconstriction role. MasR affects many mechanisms in the brain, heart, blood vessels, kidney, lung, endocrine, reproductive, skeletal muscle, and liver and probably acts like a paracrine hormone in these organs. The effect of Ang 1-7 in the kidney is complex according to the hydroelectrolyte status, the renal sympathetic nervous system, and the activity level of the RAS. The MasR expression and function seem more complex than Ang II receptors and have interacted with Ang II receptors and many other factors, including sex hormones. Also, pathological conditions including hypertension, diabetes, and ischemia-reperfusion could change MasR expression and function. In this review, we consider the role of sex differences in MasR expression and functions in the renal system under physiological and pathological conditions.

Synergism between Angiotensin receptors ligands: Role of Angiotensin-(1-7) in modulating AT2 R agonist response on nitric oxide in kidney cells

Angiotensin-(1-7), an endogenous agonist for the MasR, has been shown to interact with ang-II AT1 R and AT2 R. Earlier we showed a physical and functional interaction between MasR and AT2 R in response to their respective agonists ang-(1-7) and C21. Moreover, ang-(1-7) is cardio-protective via AT1 R and alters ang-II function. Such complex nature of ang-(1-7) function is not clearly understood, particularly in relation to its functional interaction with these receptors. We tested how ang-(1-7) affects AT2 R function by utilizing HK-2 cells. The HK-2 cells were treated with a wide range of concentrations of angiotensin receptor agonists. The generation of NO• in response to agonists was determined as a readout and subjected to Bliss definition (δ score) to assess the nature of functional interaction between these receptors. Preincubation with ang-(1-7) followed by incubation with endogenous AT1 R/AT2 R agonist ang-II (δ = 162) or selective AT2 R agonist C21 (δ = 304) synergized NO• formation. The synergism was also observed when the order of incubation with ang-(1-7)/C21 was reversed (δ = 484), but not when the cells were simultaneously incubated with a mixture of ang-(1-7) and C21 (δ = 76). The synergism with nonpeptidic MasR agonist AVE0991 followed by C21 (δ = 45) was minimal. Ligand binding experiment suggested the binding of ang-(1-7) with these three receptors. However, the synergism observed with ang-(1-7) and ang-II/C21 was sensitive to the antagonists of AT2 R (PD123319) and AT1 R (candesartan), but not MasR (A779). Ang-(1-7) at lower concentrations synergies the AT2 R function in an AT1 R-dependent but MasR-independent manner. This phenomenon may have a physiological significance.

Role of Kinins in Hypertension and Heart Failure

The kallikrein-kinin system (KKS) is proposed to act as a counter regulatory system against the vasopressor hormonal systems such as the renin-angiotensin system (RAS), aldosterone, and catecholamines. Evidence exists that supports the idea that the KKS is not only critical to blood pressure but may also oppose target organ damage. Kinins are generated from kininogens by tissue and plasma kallikreins. The putative role of kinins in the pathogenesis of hypertension is discussed based on human mutation cases on the KKS or rats with spontaneous mutation in the kininogen gene sequence and mouse models in which the gene expressing only one of the components of the KKS has been deleted or over-expressed. Some of the effects of kinins are mediated via activation of the B2 and/or B1 receptor and downstream signaling such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and/or tissue plasminogen activator (T-PA). The role of kinins in blood pressure regulation at normal or under hypertension conditions remains debatable due to contradictory reports from various laboratories. Nevertheless, published reports are consistent on the protective and mediating roles of kinins against ischemia and cardiac preconditioning; reports also demonstrate the roles of kinins in the cardiovascular protective effects of the angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARBs).

Drug Treatment of Hypertension: Focus on Vascular Health

Hypertension, the most common preventable risk factor for cardiovascular disease and death, is a growing health burden. Serious cardiovascular complications result from target organ damage including cerebrovascular disease, heart failure, ischaemic heart disease and renal failure. While many systems contribute to blood pressure (BP) elevation, the vascular system is particularly important because vascular dysfunction is a cause and consequence of hypertension. Hypertension is characterised by a vascular phenotype of endothelial dysfunction, arterial remodelling, vascular inflammation and increased stiffness. Antihypertensive drugs that influence vascular changes associated with high BP have greater efficacy for reducing cardiovascular risk than drugs that reduce BP, but have little or no effect on the adverse vascular phenotype. Angiotensin converting enzyme ACE inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs) improve endothelial function and prevent vascular remodelling. Calcium channel blockers also improve endothelial function, although to a lesser extent than ACEIs and ARBs. Mineralocorticoid receptor blockers improve endothelial function and reduce arterial stiffness, and have recently become more established as antihypertensive drugs. Lifestyle factors are essential in preventing the adverse vascular changes associated with high BP and reducing associated cardiovascular risk. Clinicians and scientists should incorporate these factors into treatment decisions for patients with high BP, as well as in the development of new antihypertensive drugs that promote vascular health.

Cardioprotective effects of angiotensin II type 1 receptor blockade with candesartan after reperfused myocardial infarction: role of angiotensin II type 2 receptor

To determine whether angiotensin II (Ang II) type 2 (AT2)-receptor activation associated with cardioprotection induced by Ang II type 1 (AT1)-receptor blockade during ischaemia-reperfusion (IR) might be reflected in increased AT 2-receptor, IP3-(1,4,5- inositol trisphosphate type 2) receptor and PKC-ε (protein kinase C-ε) proteins and tissue cGMP (cyclic guanosine monophosphate), we measured in vivo left ventricular (LV) systolic and diastolic function and remodelling (echocardiogram/Doppler) and haemodynamics, and ex vivo infarct size, AT1-/AT 2receptor, IP3-receptor and PKC-ε proteins (immunoblots) and cGMP (enzyme immunoassay) in dogs with reperfused anterior acute myocardial infarction (MI) (90-minute ischaemia, 120-minute reperfusion). Compared with controls (C, n=6) in vivo, candesartan (1 mg/kg i.v. over 30-minute pre-ischaemia, n=6) effectively inhibited the Ang II pressor response (Δ%, -14±22% vs. -80±11, p<0.003) and decreased preload (122±35 vs. -2±16%, p<0.01), improved LV systolic ejection fraction (-29±4 vs. -11±5, p<0.03) and diastolic function (E/A ratio, -25±7 vs. 33±13, p<0.004), decreased the extent of LV asynergy (26±20 vs. -31±10% LV, p<0.05) and limited acute LV remodelling (expansion index 19±6 vs. -3±5, p<0.05; thinning ratio -22±2 vs. -4±2, p<0.0003). Ex vivo, candesartan decreased infarct size (55±2 vs. 27±2% risk, p<0.001) and increased infarct zone (IZ) AT2 -receptor protein by 8-fold (but not AT1-receptor protein), IP3-receptor protein by 12-fold, PKC-ε protein by 5-fold and cGMP by 40%. Cardioprotective effects of AT1-receptor blockade on acute IR injury, LV function, and remodelling may also involve AT 2-receptor activation and downstream signalling via IP3-receptor, PKC-ε and cGMP.

The effect of angiotensin II microinjection into the bed nucleus of the stria terminalis on serum lipid peroxidation and nitric oxide metabolite levels

BACKGROUND

Overactivity of renin-angiotensin system is involved in the pathophysiology of renal and cardiovascular diseases. It is suggested that endothelial cells can release nitric oxide (NO) and reactive oxygen species in response to angiotensin II (Ang II). Angiotensin type 1 (AT1) receptor of Ang II has been found in the bed nucleus of the stria terminalis (BST). BST is involved in autonomic function. This study was performed to find the role of central Ang II in serum lipid peroxidation product and in releasing NO into circulation.

MATERIALS AND METHODS

Twenty-one catheterized rats were placed in stereotaxic instrument. A hole was drilled above BST. In the control group, saline 0.9% (100 nl) was microinjected into the BST. In the second group, Ang II (100 μM, 100-150 nl) was microinjected into the BST. In the third group losartan (an AT1 antagonist) was microinjected (100 μM, 200 nl) before Ang II into the BST. Systolic blood pressure was recorded. The NO metabolite (nitrite) and malondialdehyde (MDA) were measured in the rat's serum.

RESULTS

The data indicated that microinjection of Ang II into the BST produced a pressor response (P < 0.0001). It also increased MDA and nitrite levels of the serum significantly (P < 0.001, P < 0.0001). Pretreatment with losartan before Ang II microinjection attenuated serum's levels of MDA and nitrite (P < 0.001, P < 0.0001).

CONCLUSION

Our findings suggest that central effect of Ang II on blood pressure is accompanied with increased levels of MDA and nitrite in the circulation.

Are there any new pharmacologic therapies on the horizon to better treat hypertension? A state-of-the-art paper

Hypertension is the most important cardiovascular risk factor. We have witnessed a significant improvement in hypertension treatment and control and an impressive growth in the pharmacologic options available to clinicians and hypertension specialists. With up to a third of patients with hypertension not at the recommended goal blood pressures, it is critically important to develop novel therapeutic approaches to better treat hypertension. This review will explore the ever-expanding horizon of antihypertensive treatment and will focus on 2 major areas of drug development. First, we will review novel targets for pharmacologic treatment and novel molecules and classes of drugs in various phases of development and recognize the limitations we face in their transition from research and development to clinical practice. Then, we will discuss an expanding array of combination strategies to better treat hypertension with the goal of minimizing the burden of cardiovascular and renal complications of hypertension.

The kallikrein-kinin system as a regulator of cardiovascular and renal function

Autocrine, paracrine, endocrine, and neuroendocrine hormonal systems help regulate cardio-vascular and renal function. Any change in the balance among these systems may result in hypertension and target organ damage, whether the cause is genetic, environmental or a combination of the two. Endocrine and neuroendocrine vasopressor hormones such as the renin-angiotensin system (RAS), aldosterone, and catecholamines are important for regulation of blood pressure and pathogenesis of hypertension and target organ damage. While the role of vasodepressor autacoids such as kinins is not as well defined, there is increasing evidence that they are not only critical to blood pressure and renal function but may also oppose remodeling of the cardiovascular system. Here we will primarily be concerned with kinins, which are oligopeptides containing the aminoacid sequence of bradykinin. They are generated from precursors known as kininogens by enzymes such as tissue (glandular) and plasma kallikrein. Some of the effects of kinins are mediated via autacoids such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and/or tissue plasminogen activator (tPA). Kinins help protect against cardiac ischemia and play an important part in preconditioning as well as the cardiovascular and renal protective effects of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARB). But the role of kinins in the pathogenesis of hypertension remains controversial. A study of Utah families revealed that a dominant kallikrein gene expressed as high urinary kallikrein excretion was associated with a decreased risk of essential hypertension. Moreover, researchers have identified a restriction fragment length polymorphism (RFLP) that distinguishes the kallikrein gene family found in one strain of spontaneously hypertensive rats (SHR) from a homologous gene in normotensive Brown Norway rats, and in recombinant inbred substrains derived from these SHR and Brown Norway rats this RFLP cosegregated with an increase in blood pressure. However, humans, rats and mice with a deficiency in one or more components of the kallikrein-kinin-system (KKS) or chronic KKS blockade do not have hypertension. In the kidney, kinins are essential for proper regulation of papillary blood flow and water and sodium excretion. B2-KO mice appear to be more sensitive to the hypertensinogenic effect of salt. Kinins are involved in the acute antihypertensive effects of ACE inhibitors but not their chronic effects (save for mineralocorticoid-salt-induced hypertension). Kinins appear to play a role in the pathogenesis of inflammatory diseases such as arthritis and skin inflammation; they act on innate immunity as mediators of inflammation by promoting maturation of dendritic cells, which activate the body's adaptive immune system and thereby stimulate mechanisms that promote inflammation. On the other hand, kinins acting via NO contribute to the vascular protective effect of ACE inhibitors during neointima formation. In myocardial infarction produced by ischemia/reperfusion, kinins help reduce infarct size following preconditioning or treatment with ACE inhibitors. In heart failure secondary to infarction, the therapeutic effects of ACE inhibitors are partially mediated by kinins via release of NO, while drugs that activate the angiotensin type 2 receptor act in part via kinins and NO. Thus kinins play an important role in regulation of cardiovascular and renal function as well as many of the beneficial effects of ACE inhibitors and ARBs on target organ damage in hypertension.

Metabolic actions of angiotensin II and insulin: a microvascular endothelial balancing act

Metabolic actions of insulin to promote glucose disposal are augmented by nitric oxide (NO)-dependent increases in microvascular blood flow to skeletal muscle. The balance between NO-dependent vasodilator actions and endothelin-1-dependent vasoconstrictor actions of insulin is regulated by phosphatidylinositol 3-kinase-dependent (PI3K)--and mitogen-activated protein kinase (MAPK)-dependent signaling in vascular endothelium, respectively. Angiotensin II acting on AT₂ receptor increases capillary blood flow to increase insulin-mediated glucose disposal. In contrast, AT₁ receptor activation leads to reduced NO bioavailability, impaired insulin signaling, vasoconstriction, and insulin resistance. Insulin-resistant states are characterized by dysregulated local renin-angiotensin-aldosterone system (RAAS). Under insulin-resistant conditions, pathway-specific impairment in PI3K-dependent signaling may cause imbalance between production of NO and secretion of endothelin-1, leading to decreased blood flow, which worsens insulin resistance. Similarly, excess AT₁ receptor activity in the microvasculature may selectively impair vasodilation while simultaneously potentiating the vasoconstrictor actions of insulin. Therapeutic interventions that target pathway-selective impairment in insulin signaling and the imbalance in AT₁ and AT₂ receptor signaling in microvascular endothelium may simultaneously ameliorate endothelial dysfunction and insulin resistance. In the present review, we discuss molecular mechanisms in the endothelium underlying microvascular and metabolic actions of insulin and Angiotensin II, the mechanistic basis for microvascular endothelial dysfunction and insulin resistance in RAAS dysregulated clinical states, and the rationale for therapeutic strategies that restore the balance in vasodilator and constrictor actions of insulin and Angiotensin II in the microvasculature.

Effect of naproxen and acetaminophen on blood pressure lowering by ramipril, valsartan and aliskiren in hypertensive patients

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) are frequently used for reducing pain and other symptoms in osteoarthritis (OA). NSAIDs have been associated with an increase in blood pressure (BP) in both normotensive and hypertensive individuals and a blunting effect on various anti-hypertensive medications. Acetaminophen effects on anti-hypertensive treatment, instead, are still a matter of debate.

OBJECTIVES

To assess the effect of naproxen versus acetaminophen on ramipril, valsartan and aliskiren therapy in hypertensive patients with OA in a double-blind, cross-over study, by measuring clinic, ambulatory BP and heart rate (HR).

RESULTS

One hundred seventy four patients were randomly treated with ramipril, valsartan or aliskiren for 8 weeks and 135 patients with normalized BP were randomized to receive naproxen or acetaminophen for 2 weeks. Naproxen significantly increased clinic and ambulatory systolic/diastolic BP (SBP/DBP) values in patients treated with ramipril (p < 0.01) or valsartan (p < 0.05), but did not affect aliskiren effects. Also acetaminophen slightly but significantly affected clinic and ambulatory SBP/DBP in all three groups and, surprisingly, it also produced a slight increase in HR (+3.1, +3.3 and +3.4 b/min day-time HR values, for ramipril, valsartan and aliskiren, respectively; p < 0.05).

CONCLUSIONS

Both naproxen and acetaminophen can affect anti-hypertensive therapy with ramipril, valsartan or aliskiren with a different extent. When acetaminophen is chosen for OA management in subjects with hypertension, patients should be evaluated as carefully as when traditional NSAIDs are given.

Angiotensin 1-7 and Mas decrease thrombosis in Bdkrb2-/- mice by increasing NO and prostacyclin to reduce platelet spreading and glycoprotein VI activation

Bradykinin B2 receptor-deleted mice (Bdkrb2(-/-)) have delayed carotid artery thrombosis times and prolonged tail bleeding time resulting from elevated angiotensin II (AngII) and angiotensin receptor 2 (AT2R) producing increased plasma nitric oxide (NO) and prostacyclin. Bdkrb2(-/-) also have elevated plasma angiotensin-(1-7) and messenger RNA and protein for its receptor Mas. Blockade of Mas with its antagonist A-779 in Bdkrb2(-/-) shortens thrombosis times (58 ± 4 minutes to 38 ± 4 minutes) and bleeding times (170 ± 13 seconds to 88 ± 8 seconds) and lowers plasma nitrate (22 ± 4 μM to 15 ± 5 μM), and 6-keto-PGF1α (259 ± 103 pg/mL to 132 ± 58 pg/mL). Bdkrb2(-/-) platelets express increased NO, guanosine 3',5'-cyclic monophosphate, and cyclic adenosine monophosphate with reduced spreading on collagen, collagen peptide GFOGER, or fibrinogen. In vivo A-779 or combined L-NAME and nimesulide treatment corrects it. Bdkrb2(-/-) platelets have reduced collagen-related peptide-induced integrin α2bβ3 activation and P-selectin expression that are partially corrected by in vivo A-779, nimesulide, or L-NAME. Bone marrow transplantations show that the platelet phenotype and thrombosis time depends on the host rather than donor bone marrow progenitors. Transplantation of wild-type bone marrow into Bdkrb2(-/-) hosts produces platelets with a spreading defect and delayed thrombosis times. In Bdkrb2(-/-), combined AT2R and Mas overexpression produce elevated plasma prostacyclin and NO leading to acquired platelet function defects and thrombosis delay.

Aldosterone and angiotensin: Role in diabetes and cardiovascular diseases

The present review shall familiarize the readers with the role of renin-angiotensin aldosterone system (RAAS), which regulates blood pressure, electrolyte and fluid homeostasis. The local RAAS operates in an autocrine, paracrine and/or intracrine manner and exhibits multiple physiological effects at the cellular level. In addition to local RAAS, there exists a complete pancreatic RAAS which has multi-facet role in diabetes and cardiovascular diseases. Aldosterone is known to mediate hyperinsulinemia, hypertension, cardiac failure and myocardial fibrosis while angiotensin II mediates diabetes, endothelial dysfunction, vascular inflammation, hypertrophy and remodeling. As the understanding of this biology of RAAS increases, it serves to exploit this for the pharmacotherapy of diabetes and cardiovascular diseases.

Oxidative stress-mediated effects of angiotensin II in the cardiovascular system

Angiotensin II (Ang II), an endogenous peptide hormone, plays critical roles in the pathophysiological modulation of cardiovascular functions. Ang II is the principle effector of the renin-angiotensin system for maintaining homeostasis in the cardiovascular system, as well as a potent stimulator of NAD(P)H oxidase, which is the major source and primary trigger for reactive oxygen species (ROS) generation in various tissues. Recent accumulating evidence has demonstrated the importance of oxidative stress in Ang II-induced heart diseases. Here, we review the recent progress in the study on oxidative stress-mediated effects of Ang II in the cardiovascular system. In particular, the involvement of Ang II-induced ROS generation in arrhythmias, cell death/heart failure, ischemia/reperfusion injury, cardiac hypertrophy and hypertension are discussed. Ca²⁺/calmodulin-dependent protein kinase II is an important molecule linking Ang II, ROS and cardiovascular pathological conditions.

How does angiotensin AT(2) receptor activation help neuronal differentiation and improve neuronal pathological situations?

The angiotensin type 2 (AT(2)) receptor of angiotensin II has long been thought to be limited to few tissues, with the primary effect of counteracting the angiotensin type 1 (AT(1)) receptor. Functional studies in neuronal cells have demonstrated AT(2) receptor capability to modulate neuronal excitability, neurite elongation, and neuronal migration, suggesting that it may be an important regulator of brain functions. The observation that the AT(2) receptor was expressed in brain areas implicated in learning and memory led to the hypothesis that it may also be implicated in cognitive functions. However, linking signaling pathways to physiological effects has always proven challenging since information relative to its physiological functions has mainly emerged from indirect observations, either from the blockade of the AT(1) receptor or through the use of transgenic animals. From a mechanistic standpoint, the main intracellular pathways linked to AT(2) receptor stimulation include modulation of phosphorylation by activation of kinases and phosphatases or the production of nitric oxide and cGMP, some of which are associated with the Gi-coupling protein. The receptor can also interact with other receptors, either G protein-coupled such as bradykinin, or growth factor receptors such as nerve growth factor or platelet-derived growth factor receptors. More recently, new advances have also led to identification of various partner proteins, thus providing new insights into this receptor's mechanism of action. This review summarizes the recent advances regarding the signaling pathways induced by the AT(2) receptor in neuronal cells, and discussed the potential therapeutic relevance of central actions of this enigmatic receptor. In particular, we highlight the possibility that selective AT(2) receptor activation by non-peptide and selective agonists could represent new pharmacological tools that may help to improve impaired cognitive performance in Alzheimer's disease and other neurological cognitive disorders.

Vascular mechanisms involved in angiotensin II-induced venoconstriction in hypertensive rats

To investigate the venoconstrictor effect of angiotensin II (Ang II) in spontaneously hypertensive rats (SHR), we used preparations of mesenteric venular beds and the circular muscle of the portal veins. Vessels were tested with Ang II in the presence or absence of losartan, PD 123319, HOE 140, L-NAME, indomethacin, or celecoxib. In the mesenteric venular bed of SHR, the effect of Ang II (0.1 nmol) was nearly abolished by losartan and enhanced by HOE 140, indomethacin, and celecoxib, while PD123319 and L-NAME had no effect. In portal vein preparations, cumulative-concentration response curves (CCRC) to Ang II (0.1-100 nmol/L) exhibited a lower maximal response (E(max)) in SHR compared to Wistar rats. AT(1) receptor expression was similar in the two strains, while AT(2) receptor levels were lower in SHR portal veins when compared to Wistar. In SHR portal veins, losartan shifted the CCRC to Ang II to the right, while indomethacin and HOE 140 increased the E(max) to Ang II. PD 123319, celecoxib, and L-NAME had no effect. Taken together, our results suggest that Ang II-induced venoconstriction in SHR is mediated by activation of AT(1) receptors and this effect may be counterbalanced by kinin B(2) receptor and COX metabolites. Furthermore, our data indicate that there are different cellular and molecular mechanisms involved in the regulation of venous tonus of normotensive and hypertensive rats. These differences probably reflect distinct factors that influence arterial and venous bed in hypertension.

Therapeutic perspectives in hypertension: novel means for renin-angiotensin-aldosterone system modulation and emerging device-based approaches

The conventional antihypertensive therapies including renin–angiotensin–aldosterone system antagonists (converting enzyme inhibitors, receptor blockers, renin inhibitors, and mineralocorticoid receptor blockers), diuretics, β-blockers, and calcium channel blockers are variably successful in achieving the challenging target blood pressure values in hypertensive patients. Difficult to treat hypertension is still a commonly observed problem world-wide. A number of drugs are considered to be used as novel therapies for hypertension. Renalase supplementation, vasopeptidase inhibitors, endothelin antagonists, and especially aldosterone antagonists (aldosterone synthase inhibitors and novel selective mineralocorticoid receptor blockers) are considered an option in resistant hypertension. In addition, the aldosterone antagonists as well as (pro)renin receptor blockers or AT₂ receptor agonists might attenuate end-organ damage. This array of medications has now been complemented by a number of new approaches of non-pharmacological strategies including vaccination, genomic interference, controlled breathing, baroreflex activation, and probably most successfully renal denervation techniques. However, the progress on innovative therapies seems to be slow and the problem of resistant hypertension and proper blood pressure control appears to be still persisting. Therefore the regimens of currently available drugs are being fine-tuned, resulting in the establishment of several novel fixed-dose combinations including triple combinations with the aim to facilitate proper blood pressure control. It remains an exciting question which approach will confer the best blood pressure control and risk reduction in this tricky disease.

Angiotensin II upregulation of cardiomyocyte adiponectin production is nitric oxide/cyclic GMP dependent

INTRODUCTION

Adiponectin is a circulating cytokine that is now known to be synthesized by cardiomyocytes. Accumulating evidence has shown that adiponectin production is upregulated in patients with heart failure, with activation of the renin-angiotensin system and increased formation of angiotensin (Ang) II playing a critical role in left ventricular remodeling and heart failure. To determine whether Ang II upregulates adiponectin in hypertrophic cardiomyocytes, the authors need to explore the underlying mechanisms that could be involved.

METHODS

To test this hypothesis, neonatal rat ventricular myocytes (NRVMs) were treated with various concentrations of Ang II, and adiponectin expression was measured by quantitative real-time reverse transcription-polymerase chain reaction and Western immunoblotting.

RESULTS

Adiponectin mRNA expression was significantly increased by Ang II at concentrations from 10(-6) to 10(-8) M and was increased in a time-dependent manner at concentrations of 10(-7) M. Angiotensin type-2 receptor activation is required for Ang II-stimulated effects on adiponectin. A nitric oxide synthase inhibitor (Nx-nitro-l-arginine methyl ester hydrochloride) and an analog of cGMP antagonist (Rp-8-Br-CGMP-S) blocked Ang II-mediated upregulation of adiponectin.

CONCLUSIONS

These data suggest a mechanism whereby Ang II upregulates adiponectin in NRVMs via the angiotensin type-2 receptor/nitric oxide/cGMP/ protein kinase G signaling pathway.

Angiotensin-(1-7) upregulates cardiac nitric oxide synthase in spontaneously hypertensive rats

It has been shown that angiotensin (ANG)-(1-7) activates nitric oxide synthase (NOS) in isolated ventricular myocytes from normotensive rats. Since many ANG-(1-7) actions are enhanced in situations of increased ANG II activity, as in hypertension, in this study we investigated the in vivo effect of ANG-(1-7) on NOS activity and expression of endothelial (eNOS), neuronal (nNOS), and inducible NOS (iNOS) in ventricles from spontaneously hypertensive rats (SHR). Rats were subjected to a 60-min ANG-(1-7) infusion (0.35 nmol/min); controls received saline. NOS activity was measured using the NADPH diaphorase histochemical method and by the conversion of L-[(14)C]arginine to citrulline, and NOS phosphorylation and expression were determined using Western blotting. In SHR, ANG-(1-7) infusion diminished mean arterial pressure from 180 ± 9 to 146 ± 9 mmHg (P < 0.05), and this effect was prevented by nitro-l-arginine methyl ester (l-NAME), a NOS inhibitor. In addition, NOS activity and eNOS phosphorylation were increased by ANG-(1-7) infusion. Ventricular eNOS and nNOS expression were increased 67.4 ± 6.4 and 51 ± 10%, respectively, by ANG-(1-7), whereas iNOS was not changed. In another set of experiments, we evaluated the mechanism by which ANG-(1-7) modifies NOS activity. Isolated ventricle slices preincubated with ANG-(1-7) showed an increase in NOS activity and eNOS phosphorylation, which was blocked by an AT(2) and a bradykinin B(2) receptor antagonist, but not by the Mas receptor antagonist. Our results show that in rats in a hypertensive state, ANG-(1-7) infusion upregulates cardiac NOS expression and activity through an AT(2)- and bradykinin-dependent mechanism. In this way ANG-(1-7) may elicit its cardioprotective action and contribute to some of the counterregulatory AT(2) receptor effects that oppose the AT(1) receptor-mediated effects.

Novel therapeutic targets for hypertension

Despite the existence of established, effective therapies for hypertension, new methods of blood pressure and cardiovascular risk reduction are still needed. Novel approaches are targeted towards treating resistant hypertension, improving blood-pressure control, and achieving further risk reduction beyond blood-pressure lowering. Modulation of the renin-angiotensin-aldosterone system (RAAS) provides the rationale for current antihypertensive therapies, including the relatively new agents eplerenone and aliskiren. Novel targets for antihypertensive therapy are also likely to be RAAS-related. The stimulation of angiotensin II type 2 receptors, or supplementation with renalase, could counteract the effects of angiotensin II type 1 receptor stimulation or catecholamine release. Combined angiotensin-converting-enzyme and neutral endopeptidase blockade decreases blood pressure, but is associated with a high incidence of angioedema. Aldosterone synthase inhibitors might improve tolerability in aldosterone antagonism. A (pro)renin-receptor blocker could prevent the deleterious angiotensin-independent actions of renin that are not inhibited by aliskiren. Finally, new minimally invasive surgical procedures have revived the concept of renal denervation, and could be a therapeutic option for patients with resistant hypertension. All of these strategies are exciting prospects, but which of them will prove valuable in clinical setting remains to be discovered.

Angiotensin receptors in the eyes of arterial hypertensive rats

PURPOSE

The aim of the present study was to determine whether the eye tissues of arterial hypertensive rats evince expression of angiotensin receptors (AT(1) and AT(2)) as well as the novel Mas receptor, whose endogenous ligand is vasorelaxing Angiotensin (1-7) [Ang (1-7)].

METHODS

Enucleated eyes from spontaneously hypertensive rats (SHR) and double transgenic rats harbouring human renin and angiotensinogen genes (dTGR) and their normotensive controls were used. Half of the rats were pretreated orally with an Angiotensin II (Ang II) type 1 receptor blocker (ARB). The eyes were snap-frozen in isopentane at -40 degrees and stored at -70 degrees for subsequent reverse transcriptase polymerase chain reaction (RT-PCR) analysis or in vitro autoradiography.

RESULTS

The mRNA expression of AT(1a) and AT(2) as well as the novel Mas receptor was detected in all rat groups, being markedly higher in the retina than in the ciliary body. dTGR had significantly more receptors than SHR, but no direct relation to blood pressure level was seen. According to the autoradiography, treatment with ARB blocked a part of AT(1) receptors but had no clear effect on AT(2) receptors.

CONCLUSION

The novel Mas receptor was found by RT-PCR in eye tissue for the first time. Its specific ligand, Ang (1-7), may be involved in the regulation of intraocular pressure--as recently demonstrated by us--and in the pathogenesis of retinal diseases as a counter-regulatory component for the vascular and proliferative actions of Ang II. The results suggest that the density of AT(1) receptors in the eye is independent of the blood pressure level of the animal.

The angiotensin II type 2 receptor in cardiovascular disease

Angiotensin II (Ang II) is considered the major final mediator of the renin-angiotensin system. The actions of Ang II have been implicated in many cardiovascular conditions, such as hypertension, atherosclerosis, coronary heart disease, restenosis, and heart failure. Ang II can act through two different receptors: Ang II type 1 (AT(1)) receptor and Ang II type 2 (AT(2)) receptor. The AT(1) receptor is ubiquitously expressed in the cardiovascular system and mediates most of the physiological and pathophysiological actions of Ang II. The AT(2) receptor is highly expressed in the developing foetus, but its expression is very low in the cardiovascular system of the normal adult. Expression of the AT(2) receptor can be modulated by pathological states associated with tissue remodelling or inflammation such as hypertension, atherosclerosis, and myocardial infarction. The precise role of the AT(2) receptor remains under debate. However, it appears that the AT(2) receptor plays a vasodilatory role, and may be enhanced as a countervailing mechanism in cardiac hypertrophy, and in presence of vascular injury in hypertension and atherosclerosis. Signalling pathways induced by the stimulation of the AT(2) receptor are poorly understood, but three main mechanisms have been described: (a) activation of protein phosphatases causing protein dephosphorylation; (b) activation of bradykinin/nitric oxide/cyclic guanosine 3',5'-monophosphate pathway; and (c) stimulation of phospholipase A(2) and release of arachidonic acid. Vasodilatory effects of the AT(2) receptor, probably the only well-established role of the AT(2) receptor, have been attributed to the second of these mechanisms. The participation of the AT(2) receptor in cardiovascular remodelling and inflammation is more controversial. In vitro, AT(2) receptor stimulation clearly inhibits cardiac and vascular smooth muscle growth and proliferation, and stimulates apoptosis. In vivo, the situation is less clear, and depending on the studies, the AT(2) receptor appears to be required for cardiac hypertrophic growth or contrariwise, the AT(2) receptor has demonstrated no effects on cardiac hypertrophy. Similar controversial findings have been reported in atherosclerosis. Here we discuss the role of the AT(2) receptor on cardiovascular structure and disease, and the signalling pathways induced by its activation.

AT2 receptors: functional relevance in cardiovascular disease

The renin angiotensin system (RAS) is intricately involved in normal cardiovascular homeostasis. Excessive stimulation by the octapeptide angiotensin II contributes to a range of cardiovascular pathologies and diseases via angiotensin type 1 receptor (AT1R) activation. On the other hand, tElsevier Inc.he angiotensin type 2 receptor (AT2R) is thought to counter-regulate AT1R function. In this review, we describe the enhanced expression and function of AT2R in various cardiovascular disease settings. In addition, we illustrate that the RAS consists of a family of angiotensin peptides that exert cardiovascular effects that are often distinct from those of Ang II. During cardiovascular disease, there is likely to be an increased functional importance of AT2R, stimulated by Ang II, or even shorter angiotensin peptide fragments, to limit AT1R-mediated overactivity and cardiovascular pathologies.

Sex and the renin-angiotensin system: inequality between the sexes in response to RAS stimulation and inhibition

The purpose of this review is to examine sex differences in response to stimulation and inhibition of the renin-angiotensin system (RAS). The RAS plays a prominent role in the development of chronic renal disease, and there are known sex differences not only in the expression level of components of the RAS but also in how males and females respond to perturbations of the RAS. In men, renal injury increases in parallel with increased activation of the RAS, while in women, increases in ANG II do not necessarily translate into increases in renal injury. Moreover, both epidemiological and experimental studies have noted sex differences in the therapeutic benefits following angiotensin-converting enzyme inhibitor and angiotensin receptor blocker treatment. Despite these differences, RAS inhibitors are the most commonly prescribed drugs for the treatment of chronic renal disease, irrespective of sex. This review will examine how males and females respond to stimulation and inhibition of the RAS, with a focus on renal disease.

Pleiotropic effects of cardiac drugs on healing post-MI. The good, bad, and ugly

Healing after myocardial infarction (MI) is a well-orchestrated time-dependent process that involves inflammation, tissue repair with extracellular collagen matrix (ECCM) deposition and scar formation, and remodeling of myocardial structure, matrix, vasculature, and function. Rapid early ECCM degradation followed by slow ECCM replacement and maturation during post-MI healing results in a prolonged window of enhanced vulnerability to adverse remodeling. Decreased ECCM results in adverse ventricular remodeling, dysfunction, and rupture. Inflammation, a critical factor in normal healing, if impaired results in adverse remodeling and rupture. Several therapeutic drugs prescribed after MI exert pleiotropic effects that suppress ECCM and inflammation during healing and may have good, bad, or ugly consequences. This article reviews the potential impact of pleiotropic effects of some prototypic cardiac drugs such as renin-angiotensin-aldosterone system (RAAS) inhibitors, statins, and thrombolytics during healing post-ST-segment-elevation MI (STEMI), with special focus on inflammation, ECCM and remodeling, and implications in the elderly.

Does the renin-angiotensin system also regulate intra-ocular pressure?

The renin-angiotensin-aldosterone system is known to play an essential role in controlling sodium balance and body fluid volumes, and thus blood pressure. In addition to the circulating system which regulates urgent cardiovascular responses, a tissue-localized renin-angiotensin system (RAS) regulates long-term changes in various organs. Many recognized RAS components have also been identified in the human eye. The highly vasoconstrictive angiotensin II (Ang II) is considered the key peptide in the circulatory RAS. However, the ultimate effect of RAS activation at tissue level is more complex, being based not only on the biological activity of Ang II but also on the activities of other products of angiotensinogen metabolism, often exerting opposite effects to Ang II action. In recent studies, orally administered angiotensin II type 1 receptor blockers and angiotensin-converting enzyme inhibitors lower intra-ocular pressure (IOP), likewise topical application of these compounds, the effect being more prominent in ocular hypertensive eyes. Based on previous findings and our own experimental data, it can strongly be suggested that the RAS not only regulates blood pressure but is also involved in the regulation of IOP.

Reduced circulating levels of angiotensin-(1--7) in systemic sclerosis: a new pathway in the dysregulation of endothelial-dependent vascular tone control

OBJECTIVE

Systemic sclerosis (SSc) impairs endothelium-dependent vasodilatation. Among angiotensin I (Ang I)-derived compounds, vasoconstrictor angiotensin II (Ang II) and vasodilator angiotensin-(1-7) (Ang-(1-7)), cleaved from ACE and neutral endopeptidase (NEP) 24.11, respectively, play an important role in vascular tone regulation. Ang-(1-7) may act independently or by activating other vasodilating molecules, such as nitric oxide (NO) or prostaglandin I2 (PGI2). Our aim was to assess, in patients with SSc, circulating levels of Ang I, Ang II and Ang-(1-7), with their metabolising enzymes ACE and NEP, and levels of NO and PGI2, and to correlate them to the main characteristics of SSc.

METHODS

Levels of Ang I, Ang II, Ang-(1-7), NEP, ACE, NO and PGI2 were measured in 32 patients with SSc, who were also assessed for humoral and clinical characteristics, and 55 controls.

RESULTS

Plasma Ang I, Ang II and Ang-(1-7) levels were lower in patients with SSc than in controls (p<0.001in all cases). When Ang II and Ang-(1-7) levels were expressed as a function of the available Ang I, lower Ang-(1-7) levels in patients with SSc than in controls were confirmed (p<0.001), while no difference was found for Ang II levels. In patients with SSc, the Ang II/Ang-(1-7) ratio indicated a prevalence of Ang II over Ang-(1-7), while in controls Ang-(1-7) was prevalent (p<0.001). Levels of ACE, NEP, NO and PGI2 were lower in patients with SSc than in controls (p<0.05 in all cases).

CONCLUSION

In patients with SSc, prevalence of the vasoconstricting Ang II over the vasodilator Ang-(1-7) suggests a dysfunction of the angiotensin-derived cascade that may contribute to dysregulation of vascular tone.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

Evidence for enhanced eNOS function in coronary microvessels during the second window of protection

Nitric oxide (NO) derived from endothelial NO synthase (NOS) (eNOS) has been identified as a trigger for the second window of protection (SWOP), but its role as a mediator during the SWOP is a matter of debate. Eighteen mongrel dogs were chronically instrumented to measure left ventricular function, coronary blood flow, and wall thickening. Myocardial preconditioning was induced by 10 min coronary artery occlusion. After 24 h of reperfusion (during the SWOP), the hearts were excised. Coronary microvessels were isolated and incubated in presence of 1) the endothelium-dependent agonists carbachol and bradykinin, 2) the calcium ionophore A23187, and 3) the angiotensin-converting enzyme (ACE) inhibitors enalaprilat and ramiprilat. Nitrite, a metabolite of NO, was measured. Under baseline conditions, nitrite production in microvessels from SWOP was 30% higher than that from normal (96 ± 4 vs. 74 ± 3 pmol/mg, P < 0.01, respectively). Nitrite production in response to carbachol, bradykinin, and A23187 was also enhanced in microvessels from SWOP ( P < 0.05). These enhanced responses were abolished by NG-nitro-l-arginine methyl ester (l-NAME) or the endothelial receptor-specific antagonists atropine and HOE-140. The level of eNOS protein in the SWOP myocardium was twofold higher than that in the non-SWOP myocardium. Nitrite production in response to the ACE inhibitors was greater in microvessels from SWOP. These effects were blocked by l-NAME, HOE-140, or dichloroisocoumarin (which inhibits kinin formation). We found that a brief ischemic episode induced delayed, enhanced NO production in coronary microvessels and an upregulation of eNOS protein. These findings suggest that eNOS is a mediator during the SWOP. The ability of ACE inhibitors to enhance NO release during the SWOP points to an additional clinical application for these drugs.

Valsartan in the treatment of heart attack survivors

Survivors of myocardial infarction (MI) are at high risk of disability and death. This is due to infarct-related complications such as heart failure, cardiac remodeling with progressive ventricular dilation, dysfunction, and hypertrophy, and arrhythmias including ventricular and atrial fibrillation. Angiotensin (Ang) II, the major effector molecule of the renin–angiotensin–aldosterone system (RAAS) is a major contributor to these complications. RAAS inhibition, with angiotensin-converting enzyme (ACE) inhibitors were first shown to reduce mortality and morbidity after MI. Subsequently, angiotensin receptor blockers (ARBs), that produce more complete blockade of the effects of Ang II at the Ang II type 1 (AT₁) receptor, were introduced and the ARB valsartan was shown to be as effective as an ACE inhibitor in reducing mortality and morbidity in high-risk post-MI suvivors with left ventricular (LV) systolic dysfunction and and/or heart failure and in heart failure patients, respectively, in two major trials (VALIANT and Val-HeFT). Both these trials used an ACE inhibitor as comparator on top of background therapy. Evidence favoring the use of valsartan for secondary prevention in post-MI survivors is reviewed.

Interaction of endothelial nitric oxide and angiotensin in the circulation

Discovery of the unexpected intercellular messenger and transmitter nitric oxide (NO) was the highlight of highly competitive investigations to identify the nature of endothelium-derived relaxing factor. This labile, gaseous molecule plays obligatory roles as one of the most promising physiological regulators in cardiovascular function. Its biological effects include vasodilatation, increased regional blood perfusion, lowering of systemic blood pressure, and antithrombosis and anti-atherosclerosis effects, which counteract the vascular actions of endogenous angiotensin (ANG) II. Interactions of these vasodilator and vasoconstrictor substances in the circulation have been a topic that has drawn the special interest of both cardiovascular researchers and clinicians. Therapeutic agents that inhibit the synthesis and action of ANG II are widely accepted to be essential in treating circulatory and metabolic dysfunctions, including hypertension and diabetes mellitus, and increased availability of NO is one of the most important pharmacological mechanisms underlying their beneficial actions. ANG II provokes vascular actions through various receptor subtypes (AT1, AT2, and AT4), which are differently involved in NO synthesis and actions. ANG II and its derivatives, ANG III, ANG IV, and ANG-(1-7), alter vascular contractility with different mechanisms of action in relation to NO. This review article summarizes information concerning advances in research on interactions between NO and ANG in reference to ANG receptor subtypes, radical oxygen species, particularly superoxide anions, ANG-converting enzyme inhibitors, and ANG receptor blockers in patients with cardiovascular disease, healthy individuals, and experimental animals. Interactions of ANG and endothelium-derived relaxing factor other than NO, such as prostaglandin I2 and endothelium-derived hyperpolarizing factor, are also described.

Effect of Losartan Therapy on Endothelial Function in Hypertensive Patients

The aim of the study was to evaluate the effect of losartan therapy on endothelial function by measuring serum nitric oxide (NO) levels and urinary excretion of NO in patients with essential hypertension. A group of 30 untreated stage 2 hypertensive patients (15 males and 15 females; age, 51.3 +/- 1.5 years) were included in the study. Office systolic and diastolic blood pressure (BP) was measured by using a mercury sphygmomanometer according to phase I and V of Korotkoff sounds. NO levels in serum and 24-hour urine were determined at baseline and after 6 weeks of daily dosing with losartan (50-100 mg). Losartan therapy resulted in a significant fall in systolic/diastolic BP (from 169.7 +/- 4.1/105 +/- 1.8 mm Hg at baseline to 146 +/- 2.7/91 +/- 1.9 mm Hg at the end of losartan treatment; P < 0.001). The therapy also caused significant increases in both serum NO level (32.74 +/- 3.01 microM/L at baseline versus 79.04 +/- 5.17 microM/L; P < 0.001 after therapy) and urinary NO excretion (58.21 +/- 3.72 microM/L at baseline versus 113.21 +/- 8.63 microM/L; P < 0.001 after therapy). Losartan therapy also reduced serum malondialdehyde (MDA), which is a measure of oxidative stress, by 0.201 nM (15.3%; P = 0.009). Losartan at a dose of 50 to 100 mg per day was effective in reducing elevated BP. The increase in serum NO levels and urinary NO excretion and a decrease in serum MDA levels by losartan treatment indicate a reduction in oxidative stress and enhances NO availability, both of which improve endothelial function. Thus, losartan therapy improves endothelial function in hypertensive patients with essential hypertension.

Tissue kallikrein and kinin receptor expression in an angiogenic co-culture neuroblastoma model

The sprouting of new blood vessels from pre-existing vasculature (angiogenesis) is essential for tumour survival, influenced by tumour cell-endothelial cell interactions and is tightly regulated by biochemical cues including the kallikrein-kinin system (KKS). We examined the structural interaction between neuroblastomas and endothelial cells (HUVECs) in 2-D and 3-D (matrigel) in vitro, co-culture models by light microscopy, and performed in situ mono- and co-labelling of various KKS proteins. Neuroblastomas formed footplate-like multiple contacts on angiogenic HUVECs without disrupting differentiation of HUVECs into cord-like structures. Tissue kallikrein and the kinin B1R and B2R receptors were demonstrated on interacting neuroblastomas and HUVECs to varying degrees, as well as at actual heterogeneous contact zones in both 2-D and 3-D models. This KKS immuno-reactivity was generally confined to peri-nuclear regions on HUVECs but concentrated on cell extensions on neuroblastomas. The KKS, known to enhance DNA synthesis and process pro-angiogenic precursors of both tumour cells and the extra-cellular matrix, may, by its multi-functional activities at sites of tumour-blood vessel interactions, regulate aspects of both angiogenesis and tumourigenesis.

Effects of losartan + L-arginine on nitric oxide production, endothelial cell function, and hemodynamic variables in patients with heart failure secondary to coronary heart disease

The purpose of the present study was to evaluate the effects of losartan and the combination of losartan and L-arginine on endothelial function and hemodynamic variables in patients with heart failure (HF). Endothelium-dependent vasodilation is impaired in patients with HF. It was hypothesized that the administration of losartan and the combination of losartan and L-arginine might increase nitric oxide production and have a beneficial additive effect on endothelial function and hemodynamic variables in patients with HF. Nine patients with HF (ejection fraction<35%) were given losartan 50 mg orally on 2 consecutive days. On the second day, 1 hour after losartan 50 mg administration, L-arginine 20 g was given by intravenous infusion. Endothelial function in the form of endothelium-dependent brachial artery flow-mediated vasodilation (FMV) was measured by ultrasound. Hemodynamic variables were estimated using Doppler echocardiography at baseline and at 2 and 4 hours after losartan alone and after combination therapy. Urinary levels of nitrite (NO2) or nitrate (NO3) were measured. Four hours after losartan administration, significant reductions in systemic vascular resistance and estimated end-systolic elastase were observed. On the second day, 1 hour after L-arginine infusion, an additive hemodynamic effect was observed, with significant increases in the cardiac index and stroke volume and significant reductions in systemic vascular resistance and calculated left ventricular end-diastolic pressure. A trend toward improved FMV was observed with losartan alone, but without statistical significance. Combination therapy significantly improved postintervention FMV compared with baseline. The increase in urinary nitric oxide excretion after losartan treatment and combination therapy was significantly correlated with improved hemodynamic variables and improved FMV. In conclusion, losartan induces significant afterload reduction, reduced contractility, and increased nitric oxide urinary excretion. The combination of L-arginine and losartan seems to have superior effects on hemodynamic variables and endothelium-dependent vasodilation compared with losartan alone.

Cross-talk of the renin-angiotensin and kallikrein-kinin systems

The renin-angiotensin (RAS) and kallikrein-kinin (KKS) systems play a key role in multiple physiological and pathophysiological conditions, including growth and development, inflammation, blood pressure regulation and control of renal function. In many instances, kinins and angiotensin II work together, e.g., during development, whereas they oppose each other's actions in the regulation of vascular tone and renal function. The RAS and KKS systems also interact at multiple levels, so that changes in the activity of one system greatly impact the activity of the other. The purpose of this brief review is to highlight recent knowledge regarding interactions at the cellular and molecular levels between the two systems, with an emphasis on the coordinate developmental regulation of these phylogenetically conserved vasoactive systems.

Role of the kallikrein-kinin system in Ang-(1-7)-induced vasodilation in mesenteric arterioles of Wistar rats studied in vivo-in situ

Angiotensin-(1-7) [Ang-(1-7)], exerts a variety of actions in the cardiovascular system, with an important effect being vasodilation. In this work, we investigated the relationship between the vasodilatory activity of Ang-(1-7) and the kallikrein-kinin system. Intravital microscopy was used to study the vasodilation caused by Ang-(1-7) in the mesenteric vascular bed of anesthetized Wistar rats. The topical application of Ang-(1-7) caused vasodilation of mesenteric arterioles that was reduced by A-779, JE 049 and peptidase inhibitors (aprotinin, SBTI, PKSI 527, E-64, PMSF). These results indicated that the vasodilation induced by Ang-(1-7) in the mesenteric arterioles of Wistar rats was heavily dependent on the activation of kallikrein and subsequent kinin formation.

Biphasic actions of angiotensin IV on renal blood flow in the rat

Our aim was to investigate the changes in renal blood flow during brief exposure of the renal vasculature to angiotensin IV (Ang IV). Total renal blood flow was measured by electromagnetic flowmetry in pentobarbital-anesthetized male Sprague Dawley rats. Intrarenal injection of Ang I, Ang II and Ang III produced a dose-dependent vasoconstriction. In contrast, Ang IV and Ang-(3-10) produced a dose-dependent rapid vasoconstriction (lasting seconds) followed by a transient vasodilatation (lasting minutes). The biphasic response to Ang IV was unchanged in rats pre-treated with captopril, whereas the Ang-(3-10) response was abolished implying that its vasoactive activity was due to the generation of Ang IV. The vasodilatory component of Ang IV was unaffected by indomethacin. The biphasic vasoactive response of Ang IV was unaffected by divalinal-Ang IV (AT(4) receptor antagonist) or PD 123319 (AT(2) receptor antagonist), but greatly reduced by losartan or L-158,809 (AT(1) receptor antagonists). These results suggest that Ang IV is distinct from other angiotensins in that it possesses non-prostaglandin mediated renal vasodilatory activity that is apparently linked to the renal vascular AT(1) receptor.

Are multiple angiotensin receptor types involved in angiotensin (1-7) actions on isolated rat portal vein

Angiotensin (1-7) [Ang (1-7)] is a bioactive component of the renin angiotensin system. Ang (1-7) may interact with angiotensin type 1 (AT1) or type 2 (AT2) receptors and with Ang (1-7) - specific receptors. We examined the interactions between different doses of Ang (1-7) (1 nM-1 microM) and angiotensin II (Ang II) (10 and 100 nM) on isolated rat portal vein. In endothelium-denuded portal vein rings, Ang (1-7) inhibited contractile effects induced by Ang II. The effects of Ang (1-7) were modified by indomethacin, N(G)-nitro-L-arginine methyl ester (L-NAME), (D-Ala7)-Angiotensin (1-7) (H-2888) and losartan. Our results suggest that on rat isolated portal vein rings without endothelium, Ang (1-7) reduces Ang II-induced contractions by acting mostly on Ang (1-7) specific receptors, and this effect is mediated by vasodilatatory prostaglandins. At high concentrations, Ang (1-7) effects are mediated by AT1-receptors, though to a lesser extent than by Ang (1-7) specific receptors.

Role of angiotensin II receptor subtypes in porcine basilar artery: functional, radioligand binding, and cell culture studies

We aimed to clarify responsiveness to angiotensin (Ang) II in the porcine basilar artery and the role of Ang II receptor subtypes by functional, radioligand binding, and cell culture studies. Ang II induced more potent contractions in the proximal part than in the distal part of isolated porcine basilar arteries. The contraction induced by Ang II was inhibited by the Ang II type 1 (AT1) receptor antagonist losartan, but the Ang II type 2 (AT2) receptor antagonist PD123319 enhanced it. After removal of the endothelium, the effect of losartan remained but the effect of PD123319 was abolished. The specific binding site of [3H]Ang II on the smooth muscle membrane was inhibited by losartan, but not by PD123319. Stimulation of angiotensin II increased nitric oxide (NO) production in cultured basilar arterial endothelial cells. This production was inhibited by PD123319 and the NO synthase inhibitor L-NG-nitroarginine. These results suggest that the contraction induced by Ang II might be mediated via the activation of AT1 receptors on the basilar arterial smooth muscle cells and be modulated via the activation of AT2 receptors on the endothelial cells, followed by NO production.

The AT2 receptor--a matter of love and hate

In 1989, the development of specific angiotensin receptor antagonists which distinguish between two angiotensin receptor subtypes (AT1 and AT2) led to a breakthrough in angiotensin research. It turned out, that the AT1 receptor was almost entirely responsible for the "classical" actions of angiotensin II related to the regulation of blood pressure as well as volume and electrolyte balance. However, actions and signal transduction mechanisms coupled to the AT2 receptor remained enigmatic for a long time. The present review summarizes the current knowledge of AT2 receptor distribution, signaling and function with an emphasis on growth/anti-growth, differentiation and the regeneration of neuronal tissue.

Differential effects of 17beta-estradiol and raloxifene on VSMC phenotype and expression of osteoblast-associated proteins

Several studies demonstrate an association between osteoporosis and arterial calcific disease, both of which being common in elderly women. Estradiol and raloxifene, a selective estrogen receptor modulator, prevent bone loss in postmenopausal women. Little is known regarding how these agents affect arterial calcification. The aim of this study was to determine whether or not 17beta-estradiol and raloxifene reduced vascular smooth muscle cell (VSMC) differentiation and expression of bone-associated proteins during phosphate-induced calcification in vitro. Aortic VSMC were cultured from adult, gonadally intact, and ovariectomized (OVX) female pigs. Calcifying medium was added, and cells were treated with solvent (control), 17beta-estradiol (E(2)), or raloxifene. Extent of calcification and phenotypic expression of bone-associated proteins [matrix gla protein (MGP), osteoprotegerin (OPG), and bone sialoprotein (BSP)] were examined at 3-day intervals over 2 wk. Calcium content increased in all groups but was greater in VSMC derived from intact compared with OVX animals. E(2) reduced calcification and preserved a contractile phenotype. Expression of OPG significantly decreased with time; this decrease was significantly greater in VSMC derived from OVX compared with gonadally intact pigs. E(2) and raloxifene preserved expression of OPG only in VSMC from intact pigs. Expression of MGP increased significantly with time and was not affected by E(2) or raloxifene treatments. E(2) treatment significantly inhibited synthesis of BSP in cells from both groups. In conclusion, E(2) slows differentiation of VSMC induced by excess phosphate. Effectiveness of raloxifene to preserve expression of bone cell-associated proteins depends on the hormonal status of the tissue donor.

The antiatherogenic potential of blocking the renin-angiotensin system

Angiotensin converting enzyme (ACE) inhibitors have proved effective in preventing or ameliorating clinical manifestations of atherosclerosis, such as myocardial infarction (MI) and heart failure. Experimental evidence demonstrates their anti-atherogenic potential; ACE inhibitors do not only suppress the formation of proatherogenic angiotensin II (AII), but also enhance the formation and release of anti-atherogenic nitric oxide (NO) at local tissue sites; both mechanisms are implicated in the suppression of neointima formation in the balloon-injured vessel wall. A similar anti-atherogenic potential is provided by the blockade of the renin-angiotensin system (RAS) at the level of the angiotensin type-1 (AT1) receptor. AT1 receptor antagonists do not only block the proatherogenic actions of AII, but also induce an enhanced formation and release of anti-atherogenic NO at local tissue sites. AT1 receptor antagonists may therefore prove as effective as ACE inhibitors in patients with manifest atherosclerosis.

High blood pressure reduction reverses angiotensin II type 2 receptor-mediated vasoconstriction into vasodilation in spontaneously hypertensive rats

BACKGROUND

We have previously shown that angiotensin II type 2 receptor (AT(2)R) stimulation causes endothelium-dependent vasodilation that does not desensitize after chronic angiotensin II type 1 receptor (AT1R) blockade, suggesting a role for AT2R in antihypertensive treatment.

METHODS AND RESULTS

We recorded mean arterial pressure (MAP) and investigated AT2R by Western blot analysis, immunohistochemistry, and function in isolated mesenteric resistance arteries (205 microm in diameter) from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) receiving the following for 4 weeks in drinking water: placebo, AT1R blockade (candesartan; 2 mg/kg per day), ACE inhibitor (perindopril; 3 mg/kg per day), nonselective vasodilator (hydralazine; 16 or 24 mg/kg per day), or candesartan plus hydralazine (16 mg/kg per day). In precontracted isolated arteries, AT2R stimulation (angiotensin II in the presence of candesartan) caused vasodilation in WKY rats (MAP=118 mm Hg) and vasoconstriction in SHR (MAP=183 mm Hg). In SHR treated with candesartan (MAP=146 mm Hg) or hydralazine (16 mg/kg per day; MAP=145 mm Hg), AT2R-induced contraction was reduced by 50%. In SHR treated with perindopril (MAP=125 mm Hg), AT2R stimulation induced vasodilation. In SHR treated with hydralazine (24 mg/kg per day; MAP=105 mm Hg) and in SHR treated with hydralazine (16 mg/kg per day) plus candesartan (MAP=102 mm Hg), an AT2R-mediated vasodilation was restored. Immunochemistry and Western blot analysis showed that AT2R expression, lower in SHR than in WKY rats, was restored to normal levels by treatments reducing arterial pressure in SHR.

CONCLUSIONS

Our results suggest that in resistance arteries of SHR, (1) AT2R is downregulated by hypertension, and (2) specific and nonspecific antihypertensive treatments restore AT(2)R expression and vasodilator functions.

Comparison of valsartan 160 mg with lisinopril 20 mg, given as monotherapy or in combination with a diuretic, for the treatment of hypertension: the Blood Pressure Reduction and Tolerability of Valsartan in Comparison with Lisinopril (PREVAIL) study

BACKGROUND

The goal of antihypertensive therapy is to provide good blood pressure (BP) control without eliciting adverse effects.

OBJECTIVE

This study compared the risk-benefit profile of the angiotensin II receptor blocker valsartan with that of the angiotensin-converting enzyme inhibitor lisinopril in patients with mild to severe hypertension. The primary objective was to show that the equipotent BP-lowering effect of the valsartan-based treatment is accompanied by a better tolerability profile.

METHODS

This 16-week, randomized, double-blind, parallel-group study was conducted at 88 outpatient centers across Italy. After a 2-week placebo run-in period, patients aged > or = 18 years with mild to severe hypertension (systolic BP [SBP], 160-220 mm Hg; diastolic BP [DBP], 95-110 mm Hg) were eligible. Patients were randomized to receive once-daily, oral, self-administered treatment with valsartan 160-mg capsules or lisinopril 20-mg capsules under double-blind conditions for 4 weeks. Responders continued monotherapy, whereas nonresponders had hydrochlorothiazide 12.5 mg added for the final 12 weeks of the study. The 2 primary variables used to assess the equivalence of therapeutic efficacy of the 2 regimens were sitting SBP and sitting DBP, which were measured at weeks 0 (baseline), 4, 8, and 16. The rate of drug-related adverse events (AEs) was used to assess whether 1 treatment had a better tolerability profile than the other. Tolerability was assessed by collecting information about AEs by means of questioning the patient or physical examination at each visit.

RESULTS

A total of 1213 patients were enrolled (635 men, 578 women; mean [SD] age, 54.5 [10.1] years [range, 28-78 years]). The study was completed by 1100 patients (553 receiving valsartan and 547 receiving lisinopril). Fifty-one patients (8.4%) treated with valsartan and 62 (10.2%) [corrected] treated with lisinopril withdrew, mainly because of AEs (9 [1.5%] and 23 patients [3.8%], respectively). The valsartan- and lisinopril-based treatments were similarly effective in reducing sitting BP, with mean SBP/DBP reductions of 31.2/15.9 mm Hg and 31.4/15.9 mm Hg, respectively. At the end of the study, BP was controlled in 82.6% [corrected] of the patients receiving valsartan and 81.6% of those receiving lisinopril. AEs were experienced by 5.1% of the patients treated with valsartan and 10.7% of those treated with lisinopril (P=.0001), with dry cough observed in 1.0% and 7.2% of patients, respectively (P<0.001).

CONCLUSIONS

Valsartan and lisinopril were both highly effective in controlling BP in these patients with mild to severe hypertension, but valsartan was associated with a significantly reduced risk for AEs, especially cough.