The SARS-CoV-2 receptor, ACE-2, is expressed on many different cell types: implications for ACE-inhibitor- and angiotensin II receptor blocker-based cardiovascular therapies

SARS-CoV-2 is characterized by a spike protein allowing viral binding to the angiotensin-converting enzyme (ACE)-2, which acts as a viral receptor and is expressed on the surface of several pulmonary and extra-pulmonary cell types, including cardiac, renal, intestinal and endothelial cells. There is evidence that also endothelial cells are infected by SARS-COV-2, with subsequent occurrence of systemic vasculitis, thromboembolism and disseminated intravascular coagulation. Those effects, together with the "cytokine storm" are involved in a worse prognosis. In clinical practice, angiotensin-converting enzyme inhibitors (ACE-Is) and angiotensin II receptor blockers (ARBs) are extensively used for the treatment of hypertension and other cardiovascular diseases. In in vivo studies, ACE-Is and ARBs seem to paradoxically increase ACE-2 expression, which could favour SARS-CoV-2 infection of host's cells and tissues. By contrast, in patients treated with ACE-Is and ARBs, ACE-2 shows a downregulation at the mRNA and protein levels in kidney and cardiac tissues. Yet, it has been claimed that both ARBs and ACE-Is could result potentially useful in the clinical course of SARS-CoV-2-infected patients. As detected in China and as the Italian epidemiological situation confirms, the most prevalent comorbidities in deceased patients with COVID-19 are hypertension, diabetes and cardiovascular diseases. Older COVID-19-affected patients with cardiovascular comorbidities exhibit a more severe clinical course and a worse prognosis, with many of them being also treated with ARBs or ACE-Is. Another confounding factor is cigarette smoking, which has been reported to increase ACE-2 expression in both experimental models and humans. Sex also plays a role, with chromosome X harbouring the gene coding for ACE-2, which is one of the possible explanations of why mortality in female patients is lower. Viral entry also depends on TMPRSS2 protease activity, an androgen dependent enzyme. Despite the relevance of experimental animal studies, to comprehensively address the question of the potential hazards or benefits of ACE-Is and ARBs on the clinical course of COVID-19-affected patients treated by these anti-hypertensive drugs, we will need randomized human studies. We claim the need of adequately powered, prospective studies aimed at answering the following questions of paramount importance for cardiovascular, internal and emergency medicine: Do ACE-Is and ARBs exert similar or different effects on infection or disease course? Are such effects dangerous, neutral or even useful in older, COVID-19-affected patients? Do they act on multiple cell types? Since ACE-Is and ARBs have different molecular targets, the clinical course of SARS-CoV-2 infection could be also different in patients treated by one or the other of these two drug classes. At present, insufficient detailed data from trials have been made available.

Brain Vasculature and Cognition

There is a complex interaction between the brain and the cerebral vasculature to meet the metabolic demands of the brain for proper function. Preservation of cerebrovascular function and integrity has a central role in this sophisticated communication within the brain, and any derangements can have deleterious acute and chronic consequences. In almost all forms of cognitive impairment, from mild to Alzheimer disease, there are changes in cerebrovascular function and structure leading to decreased cerebral blood flow, which may initiate or worsen cognitive impairment. In this focused review, we discuss the contribution of 2 major vasoactive pathways to cerebrovascular dysfunction and cognitive impairment in an effort to identify early intervention strategies.

Physiological and Molecular Responses to Altered Sodium Intake in Rat Pregnancy

Background In pregnancy, a high plasma volume maintains uteroplacental perfusion and prevents placental ischemia, a condition linked to elevated maternal blood pressure ( BP ). Reducing BP by increasing Na+ intake via plasma volume expansion appears contra-intuitive. We hypothesize that an appropriate Na+ intake in pregnancy reduces maternal BP and adapts the renin-angiotensin system in a pregnancy-specific manner. Methods and Results BP was measured by implanted telemetry in Sprague-Dawley rats before and throughout pregnancy. Pregnant and nonpregnant animals received either a normal-salt (0.4%; NS ), high-salt (8%; HS ), or low-salt (0.01%; LS ) diet, or HS (days 1-14) followed by LS (days 14-20) diet ( HS / LS ). Before delivery (day 20), animals were euthanized and organs collected. Food, water, and Na+ intake were monitored in metabolic cages, and urinary creatinine and Na+ were analyzed. Na+ intake and retention increased in pregnancy ( NS , LS ), leading to a positive Na+ balance ( NS , LS ). BP was stable during LS , but reduced in HS conditions in pregnancy. The renin-angiotensin system was adapted as expected. Activating cleavage of α- and γ-subunits of the renal epithelial Na+ channel and expression of-full length medullary β-subunits, accentuated further in all LS conditions, were upregulated in pregnancy. Conclusions Pregnancy led to Na+ retention adapted to dietary changes. HS exposure paradoxically reduced BP . Na+ uptake while only modestly linked to the renin-angiotensin system is enhanced in the presence of posttranslational renal epithelial Na+ channel modifications. This suggests (1) storage of Na+ in pregnancy upon HS exposure, bridging periods of LS availability; and (2) that potentially non-renin-angiotensin-related mechanisms participate in EN aC activation and consecutive Na+ retention.

Mercury-induced vascular dysfunction is mediated by angiotensin II AT-1 receptor upregulation

Low doses of mercury (Hg) promote deleterious effects on cardiovascular system, but the mechanisms implicated remain unclear. This study analyzed whether angiotensin II AT-1 receptors are involved in the vascular dysfunction caused by chronic exposure to low HgCl₂ doses. For this, rats were divided into four groups and untreated (saline by im injections and tap water by gavage) or treated for 30 days as follows: Mercury (HgCl₂im, first dose of 4.6 µg kg^-1 and subsequent doses of 0.07 µg kg^-1 day^-1, and tap water by gavage); Losartan (saline im and losartan, 15 mg kg^-1 day^-1, by gavage); Losartan-Mercury (HgCl₂im and Losartan by gavage). Systolic blood pressure was measured by tail plethysmography, vascular reactivity in aorta by isolated organ bath, oxidative stress by measuring the levels of reactive oxygen species (ROS), malondialdehyde (MDA) and antioxidant capacity (FRAP) and protein expression of AT-1 receptors by Western Blot. As results, co-treatment with losartan prevented the increased aortic vasoconstrictor responses to phenylephrine (Phe), the involvement of ROS and prostanoids on the response to Phe and the reduced negative endothelial modulation by nitric oxide on these responses. Moreover, this co-treatment avoided the increase in plasmatic and vascular oxidative stress and AT-1 protein expression in aorta. In conclusion, these results suggest that AT-1 receptors upregulation might play a key role in the vascular damage induced by Hg exposure by increasing oxidative stress and probably by reducing NO bioavailability.

Modulation of Calcium Signaling of Angiotensin AT1, Endothelin ETA, and ETB Receptors by Silibinin, Quercetin, Crocin, Diallyl Sulfides, and Ginsenoside Rb1

Angiotensin II and endothelin-1 are potent vasoconstrictive peptides that play a central role in blood pressure regulation. Both peptides exert their pleiotropic effects via binding to their respective G-protein-coupled receptors, i.e., angiotensin AT1 and endothelin type A and type B receptors. In the present study, we have selected six structurally different plant-derived compounds with known cardioprotective properties to evaluate their ability to modulate calcium signaling of the above-mentioned receptors. For this purpose, we used and validated a cellular luminescence-based read-out system in which we measured intracellular calcium signaling in Chinese hamster ovary cells that express the calcium sensitive apo-aequorin protein. Firstly, silibinin, a flavanolignan that occurs in milk thistle (Silybum marianum), was investigated and found to be an antagonist for the human angiotensin AT1 receptor with an affinity constant of about 9 µM, while it had no effect on endothelin type A or type B receptor activation. Quercetin and crocin partially impeded intracellular calcium signaling resulting in a non-receptor-related reduction of the responses recorded for the three investigated G-protein-coupled receptors. Two organosulfur compounds, diallyl disulfide and diallyl trisulfide, as well as the triterpene saponin ginsenoside Rb1 did not affect the activation of the angiotensin AT1 and endothelin type A and type B receptors. In conclusion, we were able, by using a nonradioactive cellular read-out system, to identify a novel pharmacological property of the flavanolignan silibinin.

Opportunities for targeting the angiotensin-converting enzyme 2/angiotensin-(1-7)/mas receptor pathway in hypertension

It is well known that the renin-angiotensin system (RAS) plays a pivotal role in the pathophysiology of cardiovascular diseases. This is well illustrated by the great success of ACE inhibitors and angiotensin (Ang) II AT(1) blockers in the treatment of hypertension and its complications. In the past decade, the classical concept of RAS orchestrated by a series of enzymatic reactions culminating in the linear generation and action of Ang II has expanded and become more complex. From the discoveries of new components such as the angiotensin converting enzyme 2 and the receptor Mas emerged a novel concept of dual opposite branches of the RAS: one vasoconstrictor and pro-hypertensive composed of ACE/Ang II/AT1; and other vasodilator and anti-hypertensive composed of ACE2/Ang-(1-7)/Mas. In this review we will discuss recent findings concerning the biological role of the ACE2/Ang-(1-7)/Mas arm in the cardiovascular system and highlight the initiatives to develop potential therapeutic strategies based on this axis for treating hypertension.

Pertussis toxin up-regulates angiotensin type 1 receptors through Toll-like receptor 4-mediated Rac activation

Pertussis toxin (PTX) is recognized as a specific tool that uncouples receptors from G(i) and G(o) through ADP-ribosylation. During the study analyzing the effects of PTX on Ang II type 1 receptor (AT1R) function in cardiac fibroblasts, we found that PTX increases the number of AT1Rs and enhances AT1R-mediated response. Microarray analysis revealed that PTX increases the induction of interleukin (IL)-1beta among cytokines. Inhibition of IL-1beta suppressed the enhancement of AT1R-mediated response by PTX. PTX increased the expression of IL-1beta and AT1R through NF-kappaB, and a small GTP-binding protein, Rac, mediated PTX-induced NF-kappaB activation through NADPH oxidase-dependent production of reactive oxygen species. PTX induced biphasic increases in Rac activity, and the Rac activation in a late but not an early phase was suppressed by IL-1beta siRNA, suggesting that IL-1beta-induced Rac activation contributes to the amplification of Rac-dependent signaling induced by PTX. Furthermore, inhibition of TLR4 (Toll-like receptor 4) abolished PTX-induced Rac activation and enhancement of AT1R function. However, ADP-ribosylation of G(i)/G(o) by PTX was not affected by inhibition of TLR4. Thus, PTX binds to two receptors; one is TLR4, which activates Rac, and another is the binding site that is required for ADP-ribosylation of G(i)/G(o).

Diabetes and drug-associated hyperkalemia: effect of potassium monitoring

BACKGROUND

Renin-angiotensin-aldosterone system (RAAS) inhibitors are associated with hyperkalemia, but there is little evidence demonstrating patients who receive potassium monitoring have a lower rate of hyperkalemia.

OBJECTIVE

To evaluate the association between potassium monitoring and serious hyperkalemia-associated adverse outcomes among patients with diabetes newly initiating RAAS inhibitor therapy.

DESIGN

Retrospective observational study.

PARTICIPANTS

Patients with diabetes without end-stage renal disease initiating RAAS inhibitor therapy between 2001 and 2006 at three integrated health care systems.

MEASUREMENTS

Potassium monitoring and first hyperkalemia-associated adverse event during the initial year of therapy. Hyperkalemia-associated adverse events included hospitalizations, emergency department visits or deaths within 24 h of hyperkalemia diagnosis and/or diagnostic potassium >or=6 mmol/l. Incidence rates were calculated in person-years (p-y). We used inverse probability propensity score weighting to adjust for differences between patients with and without monitoring; Poisson regression was used to obtain adjusted relative risks.

RESULTS

A total of 19,391 of 27,355 patients (71%) received potassium monitoring. Serious hyperkalemia-associated events occurred at an incidence rate of 10.2 per 1,000 p-y. Compared to patients without monitoring, adjusted relative risk of hyperkalemia-associated adverse events among all patients with monitoring was 0.50 (0.37, 0.66); in the subset of patients who also had chronic kidney disease (n = 2,176), adjusted relative risk was 0.29 (0.18, 0.46).

CONCLUSIONS

Patients prescribed RAAS inhibitors who have both diabetes and chronic kidney disease and receive potassium monitoring are less likely to experience a serious hyperkalemia-associated adverse event compared to similar patients who did not receive potassium monitoring. This evidence supports existing consensus-based guidelines.

Role of the renin-angiotensin system in prostate cancer

Prostate cancer is highly prevalent in Western society, and its early stages can be controlled by androgen ablation therapy. However, the cancer eventually regresses to an androgen-independent state for which there is no effective treatment. The renin-angiotensin system (RAS), in particular the octapeptide angiotensin II, is now recognised to have important effects on growth factor signalling and cell growth in addition to its well known actions on blood pressure, fluid homeostasis and electrolyte balance. All components of the RAS have been recently identified in the prostate, consistent with the expression of a local RAS system in this tissue. This review focuses on the role of the RAS in the prostate, and the possibility that this pathway may be a potential therapeutic target for the treatment of prostate cancer and other prostatic diseases.

Partial correction of hypertension by angiotensin II blockade in a patient with phaeochromocytoma

This case report describes a patient with malignant hypertension and phaeochromocytoma in whom blockade of angiotensin II receptors by the competitive antagonist 1-sar-8-ala-angiotensin II (Saralasin) resulted in a partial correction of the elevated BP. Plasma renin activity was high and rose further during the blockade. Competitive inhibition of angiotensin II by Saralasin does not abolish the pressor effect of catecholamines. It was therefore interesting to observe that in this patient with phaeochromocytoma, independently, both alpha-adrenergic receptor blockade and angiotensin II receptor blockade were effective in lowering BP.

Hypothalamic angiotensinergic–noradrenergic systems interaction in fructose induced hypertension

OBJECTIVE

Several studies suggest the importance of the interaction between the renin angiotensin and sympathetic nervous systems in blood pressure control, especially in clinical situations such as the metabolic syndrome. Previously, we have demonstrated changes in noradrenergic hypothalamic control of blood pressure in an animal model of insulin resistance and hypertension. The aim of the present study was to evaluate the effects of the interaction between the noradrenergic and angiotensinergic systems on hypothalamic blood pressure regulation in fructose hypertensive rats.

METHODS

In control (C) and fructose-fed hypertensive (F) rats, we studied: 1) the effects of hypothalamic perfusion of irbesartan (AT(1) angiotensin receptor antagonist, 50 and 500 microg ml(-1)) and metoprolol (beta(1) adrenergic receptor antagonist, 10 and 100 microg ml(-1)) on blood pressure, heart rate and noradrenaline intrahypothalamic levels, by means of the microdialysis technique; and 2) the effects of intrahypothalamic microinjection of angiotensin II alone or after metoprolol pre-administration, on blood pressure and heart rate.

RESULTS

Meanwhile irbesartan perfusion did not modify neither mean arterial pressure (MAP) nor heart rate or noradrenaline hypothalamic levels in the C group, its highest dose diminished MAP (DeltaMAP: F: - 16.3+/-1 mm Hg, p<0.05) and noradrenaline levels (% of basal levels: 58+/-7%, p<0.05) in the F group, without affecting heart rate. Intrahypothalamic perfusion of metoprolol diminished MAP only in the F group (DeltaMAP: F: -12.1+/-1.1 mm Hg, p<0.05), but did not modify heart rate in both groups. On the other hand, it diminished noradrenaline hypothalamic levels in C (% of basal levels: 53+/-6%, p<0.05) but not in the F group. The pressor response to angiotensin II microinjection was increased in F rats (DeltaMAP: F: 13.3+/-1.5 mm Hg vs. C: 6.9+/-1.8 mm Hg; p<0.05). Previous administration of metoprolol markedly abolished this increment.

CONCLUSIONS

Our results suggest the existence of an increase in AT(1) and beta(1) adrenergic receptors tone in the hypothalamus of F rats, which could be related to the increase in blood pressure present in this experimental model. On the other hand, considering that the enhanced pressor response to angiotensin II intrahypothalamic injection in F rats was abolished by previous administration of a beta(1) adrenergic receptor antagonist, these results would indicate that beta(1) adrenergic receptors activation participates in the pressor response to angiotensin II in this experimental model of insulin resistance and hypertension.

Plasticity and impact of the central renin–angiotensin system during development of ethanol dependence

Pharmacological and genetic interference with the renin-angiotensin system (RAS) seems to alter voluntary ethanol consumption. However, understanding the influence of the RAS on ethanol dependence and its treatment requires modeling the neuroadaptations that occur with prolonged exposure to ethanol. Increased ethanol consumption was induced in rats through repeated cycles of intoxication and withdrawal. Expression of angiotensinogen, angiotensin-converting enzyme, and the angiotensin II receptor, AT1a, was examined by quantitative reverse transcription polymerase chain reaction. Increased ethanol consumption after a history of dependence was associated with increased angiotensinogen expression in medial prefrontal cortex but not in nucleus accumbens or amygdala. Increased angiotensinogen expression also demonstrates that the astroglia is an integral part of the plasticity underlying the development of dependence. The effects of low central RAS activity on increased ethanol consumption were investigated using either spirapril, a blood-brain barrier-penetrating inhibitor of angiotensin-converting enzyme, or transgenic rats (TGR(ASrAOGEN)680) with reduced central angiotensinogen expression. Spirapril reduced ethanol intake in dependent rats compared to controls. After induction of dependence, TGR(ASrAOGEN)680 rats had increased ethanol consumption but to a lesser degree than Wistar rats with the same history of dependence. These data suggest that the central RAS is sensitized in its modulatory control of ethanol consumption in the dependent state, but pharmacological or genetic blockade of the system appears to be insufficient to halt the progression of dependence.

Direct Inhibition of Renin as a Cardiovascular Pharmacotherapy

The important role of renin-angiotensin-aldosterone system blockade in the treatment of systemic hypertension, heart failure, diabetic kidney disease, and atherogenesis has been clearly established. The theoretical therapeutic advantages for inhibiting the detrimental effects of the renin-angiotensin system at its most upstream point have served as the impetus for the development of renin inhibitors. The advent of aliskiren, the first in a novel class of orally active, nonpeptide, highly specific, human renin inhibitors, provides a new modality in the armamentarium of renin-angiotensin system antagonists. Studies in marmosets and rats demonstrated that aliskiren reduced blood pressure in a dose-dependent manner and is highly efficacious in blocking plasma renin activity with parallel reductions in the levels of the other downstream constituents of the renin-angiotensin system. Clinical trials in hypertensive patients have confirmed these benefits with aliskiren whose blood pressure-lowering efficacy is similar to or better than those of standard therapeutic doses of enalapril, losartan, irbesartan, and hydrochlorothiazide. Aliskiren is well tolerated, with few reported adverse effects even at the highest doses tested. Given the established beneficial effects of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in the treatment of cardiovascular and renovascular diseases, future studies may further elucidate a similar protective role for aliskiren both as a monotherapy and as part of a combination therapy.

Pharmacotherapy for chronic heart failure

BACKGROUND

Heart failure is a chronic and progressive disorder which results due to inability of the heart to pump adequate blood to meet up the metabolic demands of the body. Detecting patients with heart failure could be simple but rather complex of clinical decisions as presentation could be classical or non-specific with minimal symptoms and orsigns. Management is aimed at relieving symptoms, improving quality of life, preventing hospitalisation and arresting disease progression thus prolonging survival. In addition to pharmacologic measures, non-pharmacologic ones are also employed.

METHOD

Relevant literature was reviewed using medical journals and also via internet. The key words employed were: Heart failure, Chronic heart failure, Diuretics, Vasodilators, Angiotensin receptor blockers (ARBS) and Angiotensin converting enzyme inhibitors (ACEI). The National Heart, Lung and Blood Institute, Canadian Cardiovascular Society, American College of Cardiology websites were also used in the course of this review.

RESULTS

This review was able to support the use of betablockers, ACEI, ARBS, digitalis, diuretics, vasodilators and aldosterone antagonists in the management of chronic heart failure.

CONCLUSION

The objectives of drug therapy in heart failure includes the short-term goals of stabilising the patient, improving haemodynamic function and conferring symptomatic improvement, as well as the long-term goal of limiting disease progression, decreasing hospital re-admission rates and improving survival. The cause needs to be established and aggravating factors identified (and where possible treated). Most of the drugs, if not all, are used in combination with one another to achieve maximal therapeutic goal. Use of some drugs could be entertained as an add-on therapy depending on any co-existing medical condition.

Angiotensin II increases evoked release at the frog neuromuscular junction through a receptor sensitive to A779

Receptor mediated presynaptic modulation is a ubiquitous mechanism involved in synaptic plasticity. Here we show that angiotensin II increased quantal content at the frog neuromuscular junction. This presynaptic effect of angiotensin II was insensitive to losartan and PD123319, but was antagonized by a more potent partial agonist of the amphibian angiotensin receptor, L162313. In addition, A779, a blocker of the angiotensin-[1-7] receptor, also abolished the effect of angiotensin II. These results indicate that the effect of angiotensin II on evoked release is mediated through an angiotensin receptor. L162313 alone increased quantal content, and A779 also antagonized this effect of L162313. We conclude that the neuromuscular junction possesses angiotensin receptors involved in presynaptic modulation.

[Role of the renin-angiotensin system on the sympathetic response induced by the cold pressor test in humans]

Abstract. The aim of this study was to evaluate the role of AT1 angiotensin II receptor on the sympathetic response to the cold pressor test (CPT) in normotensive healthy volunteers. Eighty-two healthy volunteers were included in this double-blind, placebo-controlled study. Blood pressure and heart rate were determined before and one hundred and seventy five minutes after oral administration of placebo, losartan (50 mg), valsartan (80 mg) or eprosartan (600 mg). Immediately, the subjects underwent CPT and then the same hemodynamic parameters were measured. CPT increased arterial blood pressure (systolic, diastolic and mean) and HR in placebo-treated group. Pretreatment with a single dose of losartan, valsartan or eprosartan blunted CPT-induced pressor response, but not the rise in heart rate. Our results demonstrate that endogenous angiotensin II, through stimulation of AT1 receptor, supports sympathetic mediated stress-response in humans.

Evidence for a new angiotensin-(1-7) receptor subtype in the aorta of Sprague-Dawley rats

We have recently described, in the mouse aorta, the vasodilator effect of angiotensin-(1-7) (Ang-(1-7)) was mediated by activation of the Mas Ang-(1-7) receptor and that A-779 and D-Pro7-Ang-(1-7) act as Mas receptor antagonists. In this work we show pharmacological evidence for the existence of a different Ang-(1-7) receptor subtype mediating the vasodilator effect of Ang-(1-7) in the aorta from Sprague-Dawley (SD) rats. Ang-(1-7) induced an endothelium-dependent vasodilator effect in aortic rings from SD rats which was inhibited by removal of the endothelium and by L-NAME (100 microM) but not by indomethacin (10 microM). The Ang-(1-7) receptor antagonist D-Pro7-Ang-(1-7) (0.1 microM) abolished the vasodilator effect of the peptide. However, the other specific Ang-(1-7) receptor antagonist, A-779 in concentrations up to 10 microM, did not affect vasodilation induced by Ang-(1-7). The Ang II AT1 and AT2 receptors antagonists CV11974 (0.01 microM) and PD123319 (1 microM), respectively, the bradykinin B2 receptor antagonist HOE 140 (1 microM) and the inhibitor of ACE captopril (10 microM) did not change the effect of Ang-(1-7). Our results show that in the aorta of SD rats, the vasodilator effect of Ang-(1-7) is dependent on endothelium-derived nitric oxide. This effect is mediated by the activation of Ang-(1-7) receptors sensitive to D-Pro7-Ang-(1-7), but not to A-779, which suggests the existence of a different Ang-(1-7) receptor subtype.

Involvement of insulin-regulated aminopeptidase and/or aminopeptidase N in the angiotensin IV-induced effect on dopamine release in the striatum of the rat

Locally administered angiotensin IV causes a dose-dependent increase of the dopamine levels in the striatum of the rat. The aminopeptidases insulin-regulated aminopeptidase (IRAP) and/or aminopeptidase N (AP-N) are proposed to be involved in this effect since both enzymes are inhibited by angiotensin IV. In agreement with this hypothesis we demonstrate that by using the AP-N selective inhibitor 7B, about 60% of the aminopeptidase activity in striatal membranes could be attributed to AP-N (pK(i)=9.20). Higher concentrations of 7B are capable of inhibiting IRAP as well (pK(i)=7.26). Interestingly, in vivo, inhibition of IRAP or AP-N activity does not appear to be involved in the angiotensin IV-mediated effect in the striatum since 7B itself is not capable to induce dopamine release such as observed with angiotensin IV. However, 7B at a concentration selective for inhibition of AP-N (100 nM) potentiates the angiotensin IV-mediated increase of dopamine, suggesting that inhibition of AP-N lengthens the half-life of angiotensin IV. On the other hand, inhibition of both AP-N and IRAP by perfusion of 500 nM 7B completely abolishes the effect of angiotensin IV. We therefore hypothesize that the effect of angiotensin IV on dopamine release in the striatum is mediated via activation of IRAP and/or AP-N, possibly acting as receptors for angiotensin IV.

Effects of angiotensin 1-7 on the actions of angiotensin II in the renal and mesenteric vasculature of hypertensive and streptozotocin-induced diabetic rats

Angiotensin 1-7, a heptapeptide derived from metabolism of either angiotensin I or angiotensin II, is a biologically active peptide of the renin-angiotensin system. The present study investigated the effect of angiotensin 1-7 on the vasopressor action of angiotensin II in the renal and mesenteric vasculature of Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHR) and streptozotocin-induced diabetic rats. Angiotensin II-induced dose-dependent vasoconstrictions in the renal vasculature. The pressor response was enhanced in the SHR and reduced in the streptozotocin-diabetic rat compared to WKY rats. Angiotensin 1-7 attenuated the angiotensin II pressor responses in the renal vasculature of WKY and SHR rats. However, the ability to reduce angiotensin II response was diminished in diabetic-induced rat kidneys. The effect of angiotensin 1-7 was not inhibited by 1-[(4-(Dimethylamino)-3-methylphenyl] methyl]-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid ditrifluoroacetate (PD123319), an angiotensin AT(2) receptor antagonist. (D-ALA(7))-Angiotensin I/II (1-7) (D-ALA) (an angiotensin 1-7 receptor antagonist), indomethacin (a cyclo-oxygenase inhibitor), and N(omega)-Nitro-L-Arginine Methyl Ester (L-NAME)(a nitric oxide synthetase inhibitor) abolished the attenuation by angiotensin 1-7 in both WKY rats and SHR, indicating that its action is mediated by angiotensin 1-7 receptor that is either coupled to the release of prostaglandins and/or nitric oxide. The vasopressor responses to angiotensin II in mesenteric vasculature bed was also dose-dependent but smaller in magnitude compared to the renal vasculature. The responses to angiotensin II were relatively smaller in SHR but no significant difference was observed between WKY and streptozotocin-induced diabetic rats. Angiotensin 1-7 attenuated the angiotensin II pressor responses in WKY, SHR and diabetic-induced mesenteric bed. The attenuation was observed at the lower concentrations of angiotensin II in WKY and diabetic-induced rats but at higher concentrations in SHR. Similar observation as in the renal vasculature was seen with PD123319, D-ALA, and L-NAME. Indomethacin reversed the attenuation by angiotensin 1-7 only in the SHR mesenteric vascular bed. The present findings support the regulatory role of angiotensin 1-7 in the renal and mesenteric vasculature, which is differentially altered in hypertension and diabetes.

Valsartan improves the lower limit of cerebral autoregulation in rats

The effects of angiotensin II type 1 receptor blockers (ARBs) on cerebral blood flow (CBF) autoregulation have not been fully clarified. Thus, we examined the acute effect of valsartan, the most selective ARB, on CBF autoregulation in spontaneously hypertensive rats. Intravenous administration of valsartan (0.3 mg/kg) reduced the mean arterial pressure (MAP) from 184+/-5 (mean+/-SEM) to 174+/-5 mmHg (p<0.001) without affecting CBF as measured by laser-Doppler flowmetry. The lower limit of CBF autoregulation (the MAP at which the CBF was 80% of the baseline value) in the valsartan-treated group (122+/-3 mmHg) was significantly lower than that in the control group (135+/-4 mmHg, p<0.05). Reverse transcribed-polymerase chain reaction and immunohistochemical staining demonstrated that both angiotensin II type 2 receptors and angiotensin II type 1 receptors (AT1Rs) were expressed in endothelial and smooth muscle cells of the rat cerebral arteries. These results suggest that specific inhibition of AT1Rs in the cerebral circulation causes the leftward shift of the lower limit of autoregulation.

Intrarenal aminopeptidase N inhibition augments natriuretic responses to angiotensin III in angiotensin type 1 receptor-blocked rats

The renal angiotensin angiotensin type 2 receptor has been shown to mediate natriuresis, and angiotensin III, not angiotensin II, may be the preferential angiotensin type 2 receptor activator of this response. Angiotensin III is metabolized to angiotensin IV by aminopeptidase N. The present study hypothesizes that inhibition of aminopeptidase N will augment natriuretic responses to intrarenal angiotensin III in angiotension type 1 receptor-blocked rats. Rats received systemic candesartan for 24 hours before the experiment. After a 1-hour control, cumulative renal interstitial infusion of angiotensin III at 3.5, 7, 14, and 28 nmol/kg per minute (each dose for 30 minutes) or angiotensin III combined with aminopeptidase N inhibitor PC-18 was administered into 1 kidney. The contralateral control kidney received renal interstitial infusion of vehicle. In kidneys infused with angiotensin III alone, renal sodium excretion rate increased from 0.05+/-0.01 micromol/min in stepwise fashion to 0.11+/-0.01 micromol/min at 28 nmol/kg per minute of angiotensin III (overall ANOVA F=3.68; P<0.01). In angiotensin III combined with PC-18, the renal sodium excretion rate increased from 0.05+/-0.01 to 0.32+/-0.08 mumol/min at 28 nmol/kg per minute of angiotensin III (overall ANOVA F=6.2; P<0.001). The addition of intrarenal PD-123319, an angiotensin type 2 receptor antagonist, to renal interstitial angiotensin III plus PC-18 inhibited the natriuretic response. Mean arterial blood pressure and renal sodium excretion rate from control kidneys were unchanged by angiotensin III +/- PC-18 + PD-123319. Angiotensin III plus PC-18 induced a greater natriuretic response than Ang III alone (overall ANOVA F=16.9; P=0.0001). Aminopeptidase N inhibition augmented the natriuretic response to angiotensin III, suggesting that angiotensin III is a major agonist of angiotensin type 2 receptor-induced natriuresis.

The bradykinin B2 receptor antagonist icatibant (Hoe 140) blocks aminopeptidase N at micromolar concentrations: Off-target alterations of signaling mediated by the bradykinin B1 and angiotensin receptors

The N-terminal sequence of icatibant, a widely used peptide antagonist of the bradykinin B(2) receptors, is analogous to that of other known aminopeptidase N inhibitors. Icatibant competitively inhibited the hydrolysis of L-Ala-p-nitroanilide by recombinant aminopeptidase N (K(i) 9.1 microM). In the rabbit aorta, icatibant (10-30 microM) potentiated angiotensin III, but not angiotensin II (contraction mediated by angiotensin AT(1) receptors), and Lys-des-Arg(9)-bradykinin, but not des-Arg(9)-bradykinin (effects mediated by the bradykinin B(1) receptors), consistent with the known susceptibility of these agonists to aminopeptidase N. At concentrations possibly reached in vivo (e.g., in kidneys), icatibant alters physiological systems different from bradykinin B(2) receptors.

Interférence des médicaments cardiovasculaires avec l'anesthésie et la chirurgie

Decisions about chronic treatments during the perioperative period must be made at the presurgical anesthesia consultation. It is increasingly rare to stop treatment during this period, because: This new rule is applied particularly to patients with cardiovascular disorders. Beta blockers have a special role in preventing the onset of postoperative cardiovascular events. The role of statins requires further precision but they appear to fit into the same preventive approach. Interruption of antiplatelet agents appears to be associated with a risk of arterial thrombosis in patients with coronary conditions, notably those with conventional stents and most especially those with drug-eluting stents.

Renin angiotensin aldosterone system blockade and renal disease in patients with type 2 diabetes: a subanalysis of Japanese patients from the RENAAL study

BACKGROUND

The Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan (RENAAL) study has previously shown losartan to confer significant benefits to patients with type 2 diabetes and nephropathy. The original study of 1513 patients included 96 Japanese patients; the present study is a post-hoc analysis of the effects of losartan in this Japanese subpopulation.

METHODS

This double-blind, randomized study compared losartan (50 to 100 mg once daily) with placebo. The study medication was taken in addition to conventional antihypertensive treatment, and the mean follow-up period for the Japanese patients was 2.8 years. The primary endpoint was the composite of doubling of serum creatinine, endstage renal disease, or death. Secondary endpoints included changes in proteinuria levels. Safety was also evaluated.

RESULTS

The primary composite endpoint was reached in fewer Japanese patients receiving losartan than placebo (50.0% versus 65.4%, respectively). The treatment effects of losartan were more robust when data were corrected for differences in proteinuria at baseline--a significant relative risk reduction of 45% with losartan (P=0.0397) was apparent. Treatment benefit exceeded that attributable to blood pressure changes alone. Levels of proteinuria were reduced with losartan compared with placebo, with an overall losartan treatment effect of 37.8% (P<0.001). Overall, losartan was similarly well tolerated in both the Japanese patients and the total population.

CONCLUSIONS

In Japanese patients with type 2 diabetes and nephropathy, losartan offers renal protection and is generally well tolerated.

Cerebroprotective effect of angiotensin IV in experimental ischemic stroke in the rat mediated by AT(4) receptors

Recent studies have reported potential roles of angiotensins in an adaptative physiological mechanism of protection against cerebral ischemia-induced neurological damages. In the present study, we examined the protective role of angiotensin IV (AngIV) in a rat model of embolic stroke induced by intracarotid injection of calibrated microspheres (50 microm). Internal carotid infusions of increasing doses of AngIV (0.01, 0.1 and 1 nmol/0.1 mL saline) dose dependently decreased mortality, neurological deficit and cerebral infarct size at 24 hours. With the highest dose of AngIV, mortality was reduced from 55 % in saline infused controls to 10 % (p=0.003), neurological deficit was reduced from 3.8 +/- 0.3 to 1.4 +/- 0.3 , (p<0.0001) and cerebral infarct size at 24 hours was decreased from 432 +/- 26 mm(3) to 185 +/- 19, (p=0.0001). The AT(4) antagonist divalinal-AngIV (10(-9) mol/0.1 mL), or pretreatment with L-NAME (10(-7) mol/0.1 mL), both completely abolished the protective effect of AngIV (1 nmol). The AT(2) antagonist PD123319 (10(-7) mol/0.1 mL) partially prevented the protective effect of AngIV on the neurological score. Sequential cerebral arteriographies revealed that AngIV induced a redistribution of blood flow to the ischemic areas within minutes. These results suggest that pharmacological doses of AngIV are protective against acute cerebral ischemia by triggering an AT(4)-mediated, NO-dependent intracerebral hemodynamic mechanism.

[Endothelin-1, angiotensin II and cancer]

Endothelin-1 (ET-1) and angiotensin II (AngII), two potent vasoactive peptides involved in the regulation of cardiovascular homeostasis, also induce mitogenic and pro-angiogenic responses in vitro and in vivo. Both peptides are produced by cleavage of inactive precursors by metalloproteases (endothelin-converting enzyme and angiotensin-converting enzyme, respectively) and activate two subtypes of membrane receptors (ETA-R and ETB-R for ET-1, AT1R and AT2R for AngII) that all belong to the superfamily of G-protein coupled receptors. There is increasing evidence that ETA-R, ETB-R and AT1R are expressed in a variety of cancer cells and tissues, and may play a role on tumor growth, angiogenesis and invasion in vivo. This review summarizes the similarities and differences between the ET-1 and AngII systems with regard to their reported effects on various aspects of cancer. In addition to being expressed on vascular endothelium, ET-1 and AngII receptors participate in tumor angiogenesis through the production of the angiogenic factor VEGF. Furthermore, recent clinical studies indicate that a selective ETA-R antagonist has beneficial effects in prostate cancer, suggesting that a similar approach using ETB-R and AT1R blockers might be envisioned. Experimental data presented here suggest that a combined therapy targeting both ET-1 and AngII systems may prove valuable for future treatments of highly angiogenic tumors.

ANG II type 2 receptors and neural control of intrarenal blood flow

We tested the hypothesis that activation of angiotensin type 2 (AT(2)) receptors, by both exogenous and endogenous ANG II, modulates neurally mediated vasoconstriction in the renal cortical and medullary circulations. Under control conditions in pentobarbital-anesthetized rabbits, electrical stimulation of the renal nerves (RNS; 0.5-8 Hz) reduced renal blood flow (RBF; -88 +/- 3% at 8 Hz) and cortical perfusion (CBF; -92 +/- 2% at 8 Hz) more than medullary perfusion (MBF; -67 +/- 6% at 8 Hz). Renal arterial infusion of ANG II, at a dose titrated to reduce RBF by approximately 40-50% (5-50 ng.kg(-1).min(-1)) blunted responses of MBF to RNS, without significantly affecting responses of RBF or CBF. Subsequent administration of PD123319 (1 mg/kg plus 1 mg.kg(-1).h(-1)) during continued renal arterial infusion of ANG II did not significantly affect responses of RBF or CBF to RNS but enhanced responses of MBF, so that they were similar to those observed under control conditions. In contrast, administration of PD123319 alone blunted responses of CBF and MBF to RNS. Subsequent renal arterial infusion of ANG II in PD123319-pretreated rabbits restored CBF responses to RNS back to control levels. In contrast, ANG II infusion in PD123319-pretreated rabbits did not alter MBF responses to RNS. These data indicate that exogenous ANG II can blunt neurally mediated vasoconstriction in the medullary circulation through activation of AT(2) receptors. However, AT(2)-receptor activation by endogenous ANG II appears to enhance neurally mediated vasoconstriction in both the cortical and medullary circulations.

[Chronic renal failure]

The elevated cardiovascular mortality seen in patients with renal insufficiency makes it imperative that this condition be detected and treated in good time. The results of recent studies have led to fundamental changes in the therapeutic approach to the patient with kidney disease. A range of new medications is now available for the treatment of complications of renal failure.

Acute and long-term effects of clinical doses of antenatal glucocorticoids in the developing fetal sheep kidney

OBJECTIVES

The controversy regarding potential long-term side effects of antenatal steroid administration for accelerating fetal lung maturation is still unresolved despite more than 30 years of experience. Studies in animals have demonstrated that administration of glucocorticoids during pregnancy alters renal expression of several key regulatory molecules at different developmental stages followed in most cases with the development of hypertension in the adult. We studied the effects of betamethasone on the expression of (1) NA,K-ATPAse pump; (2) the Na/H exchanger 3 (NAHE3); (3) angiotensin receptor (AT1 and AT2); and (4) the type 1 dopamine receptor (D1R).

METHODS

Pregnant sheep were treated with either 0.17 mg/kg betamethasone or vehicle 24 hours apart at 80 and 81 days' gestation. Fetal kidneys were harvested at 81 and 135 days' gestation. Protein and mRNA levels were measured in kidney cortex.

RESULTS

Betamethasone had acute and long-term effects on fetal kidney cortex gene expression. Acutely, mRNA abundance for AT2 was significantly lower and that of NHE3 significantly higher than in controls (0.4 +/- 0.02 vs 0.7 +/- 0.05; 1.2 +/- 0.16 vs 0.4 +/- 0.04; P < .05). At 135 days' gestation, AT2 receptor abundance remained lower than control (0.2 +/- 0.02 vs 0.4 +/- 0.02; P < .05), whereas D1R expression was higher (0.8 +/- 0.17 vs 0.5 +/- 0.06; P < .05). No changes in Na,K-ATPase of AT1 receptor at either of the two time points studied were observed. Antenatal steroid administration was not associated with premature labor or a reduction in either body weight or kidney weight.

CONCLUSION

Our findings strongly suggest that antenatal glucocorticoid administration according to National Institutes of Health (NIH) consensus guidelines may alter human fetal renal development. Further studies are needed to establish a direct relationship between alterations in fetal renal gene expression and the development of hypertension in adulthood.

The contribution of brain angiotensin II to the baroreflex regulation of renal sympathetic nerve activity in conscious normotensive and hypertensive rats

Angiotensin II receptor density in the brain is elevated when dietary salt intake is raised or in the state of hypertension. The aim of this study was to evaluate whether the angiotensin II modulation of the baroreceptor control of renal sympathetic nerve activity was altered under these conditions. Wistar rats, fed either a regular (0.25% w/w sodium) or high-salt diet (3.1% w/w sodium), or stroke-prone spontaneously hypertensive rats (SHRSPs) were implanted with cannulae in the carotid artery, jugular vein and the cerebroventricle and with recording electrodes on the renal sympathetic nerves. Three days later, baroreceptor gain curves were generated for renal sympathetic nerve activity and heart rate before and following intracerebroventricular (i.c.v.) administration of losartan (15 mug) to block angiotensin AT1 receptors. The rats fed a regular diet had a mean blood pressure of 116 +/- 3 mmHg and heart rate of 467 +/- 25 beats min(-1), which remained unchanged after the i.c.v. administration of losartan. The sensitivity or curvature coefficient of the baroreceptor curve for renal sympathetic nerve activity was increased by 36% (P < 0.05) following losartan. In the rats fed a high-salt diet, all cardiovascular variables and the losartan-induced increase in the baroreceptor curvature coefficient for renal sympathetic nerve activity (29%) were similar to values in rats on the regular sodium diet. The heart rate baroreceptor curvature coefficient was not altered in either the rats fed a regular or a high-salt diet. The slope of the renal sympathetic nerve activity baroreflex gain curve in the SHRSPs was less and the increase following administration of losartan (54%) was greater than in the Wistar rats. These data indicate that in the conscious state, the tonic inhibitory action of brain angiotensin II on the baroreflex regulation of renal sympathetic nerve activity was unaffected by raised dietary sodium, but its role was enhanced in the SHRSPs.

Signaling pathways involved with the stimulatory effect of angiotensin II on vacuolar H+-ATPase in proximal tubule cells

It has been documented that angiotensin II (ANG II) (10(-9) M) stimulates proton extrusion via H(+)-adenosine triphosphatase (ATPase) in proximal tubule cells. In the present study, we investigated the signaling pathways involved in the effects of ANG II on H(+)-ATPase activity and on the cytosolic free calcium concentration in immortalized rat proximal tubule cells, a permanent cell line derived from rat proximal tubules. The effects of ANG on pH(i) and [Ca(+2)](i) were assessed by the fluorescent probes, 2',7-bis (2-carboxyethyl)-5(6)-carboxyfluorescein-acetoxy-methyl ester and fluo-4-acetoxy-methyl ester, in the absence of Na(+) to block the Na(+)/H(+) exchanger. In the control situation, the pH recovery rate following intracellular acidification with NH(4)Cl was 0.073+/-0.011 pH units/min (n=12). This recovery was significantly increased with ANG II (10(-9 )M), to 0.12+/-0.015 pH units/min, n=10. This last effect was also followed by a significant increase of Ca(+2) (i), from 99.72+/-1.704 nM (n=21) to 401.23+/-33.91 nM (n=39). The stimulatory effect of ANG II was blocked in the presence of losartan, an angiotensin II subtype 1 (AT(1)) receptor antagonist. H89 [protein kinase A (PKA) inhibitor] plus ANG II had no effect on the pH recovery. Staurosporine [protein kinase C (PKC) inhibitor] impaired the effect of ANG II. Phorbol myristate acetate (PKC activator) mimicked in part the stimulatory effect of ANG II, but reduced Ca(+2) (i). 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (intracellular calcium chelator) alone reduced the pH(i) recovery rate below control levels and impaired the effect of ANG II, in a way similar to that of trimethoxy benzoate (a blocker of Ca(+2) (i) mobilization). We conclude that ANG II regulates rat proximal tubule vacuolar H(+)-ATPase by a PKA-independent mechanism and that PKC and intracellular calcium play a critical role in this regulation.

Do Angiotensin-Converting Enzyme Inhibitors or Angiotensin II Receptor Blockers Decrease the Risk of Hospitalization Secondary to Community-Acquired Pneumonia? A Nested Case-Control Study

STUDY OBJECTIVE

As studies have shown that angiotensin-converting enzyme (ACE) inhibitors may lower the risk of developing pneumonia by increasing the cough reflex, we sought to explore the potential association between use of ACE inhibitors and the risk of hospitalization secondary to community-acquired pneumonia (CAP). To test this hypothesis further, we also looked at the risk for CAP in those taking angiotensin II receptor blockers (ARBs), as these drugs have a similar mechanism of action to that of ACE inhibitors but have minimal or no effect on the cough reflex. In addition, the putative protection against pneumonia may instead be related to general inhibition of the renin-angiotensin system.

DESIGN

Nested case-control study.

DATA SOURCE

Universal Quebec, Canada, administrative health databases.

PATIENTS

From a cohort of 47,148 patients with coronary artery disease who had a revascularization procedure between 1996 and 2000, 1666 patients with CAP and 33,315 time-matched control subjects (20 controls for each case) were identified.

MEASUREMENTS AND MAIN RESULTS

Conditional logistic regression analysis was used to estimate rate ratios, while controlling for potential confounders. No association was observed between patients receiving ACE inhibitors and hospitalization for CAP (rate ratio [RR] 0.98, 95% confidence interval [CI] 0.69-1.40). A similar lack of association was noted for those receiving ARBs (RR 1.02, 95% CI 0.70-1.49).

CONCLUSION

In this case-control study, no association was found between use of ACE inhibitors or ARBs and risk of hospitalization secondary to CAP. Future studies are necessary to explore this association further.

Estradiol and progesterone modulation of angiotensin II receptors in the arcuate nucleus of ovariectomized and lactating rats

The expression of angiotensin II (Ang II) receptors in the brain is modulated by estradiol and progesterone. Considering that Ang II plays a critical role in controlling prolactin secretion and that neurons in the arcuate nucleus (ARC) are the main regulator of this function, the present study aimed to evaluate ARC Ang II receptor binding in 2 experimental models with different estradiol and progesterone plasma levels. Animals were divided into 4 groups: ovariectomy (OVX) plus oil vehicle, OVX plus estradiol and progesterone replacement, lactating rats on day 7 postpartum, and lactating rats on day 20. Animals were killed by decapitation, and the brains were removed. Ang II receptors were quantified by autoradiography in ARC. Trunk blood samples were collected, and plasma estradiol and progesterone were measured by radioimmunoassay. Treatment of OVX rats with estradiol and progesterone increased Ang II receptor binding when compared to OVX vehicle-treated animals. Plasma estradiol (r = +0.77) and progesterone (r = +0.87) were highly correlated with Ang II receptors in ovariectomized animals. Lactating rats (day 20) showed a significant decrease in Ang II receptor binding and plasma progesterone when compared to lactating rats (day 7), however, no difference was seen in plasma estradiol. Plasma levels of progesterone (r = +0.81), but not estradiol (r = +0.32), were highly correlated with Ang II receptors in lactating rats. In conclusion, present results show that ARC Ang II receptors decreases on day 20 of lactation compared to day 7 and are highly correlated with plasma progesterone, indicating a pivotal role for progesterone in this regulation.

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.

Signaling crosstalk angiotensin II receptor subtypes and insulin

Insulin-resistant states are often associated with hypertension, and the accumulated data indicate that ARB decrease new-onset of diabetes with vasoprotective effects. Recent evidence suggests that activation of Ang II receptor subtypes could regulate insulin sensitivity at multiple sites of insulin signaling in various diabetic animal models and regulate vascular remodeling in concert with insulin in potentially distinct fashions. Moreover, the roles of Ang II receptor subtypes have been highlighted in insulin resistance in obesity, which is one of the major risk factors for the development of hypertension. More detailed analysis of the crosstalk of Ang II and insulin-mediated signaling in various tissues would provide further information to understand the clinical relevance of the effect of ARB on insulin resistance, thereby preventing cardiovascular events associated with insulin resistance.

Angiotensin receptor blockers: Cardiovascular protection in the metabolic syndrome

It is well recognised that the metabolic syndrome, a constellation of risk factors including obesity, hypertension, insulin resistance and dyslipidaemia, is associated with an increased risk of cardiovascular complications and the development of Type 2 diabetes. Consequently, timely identification and management of all components of the metabolic syndrome is warranted. In particular, guidelines have emphasised the importance of targeting elevated blood pressure (BP) and dyslipidaemia as a method of reducing global cardiovascular risk. Findings from the Valsartan Antihypertensive Long-term Use Evaluation (VALUE) trial show that the angiotensin receptor blocker, valsartan, reduces cardiovascular events and the development of Type 2 diabetes in high-risk individuals. This profile is being further explored in the ongoing Nateglinide And Valsartan in Impaired Glucose Tolerance Outcomes Research (NAVIGATOR) trial. Given the potential advantages to patients and physicians of tackling more than one of the components of the metabolic syndrome, antihypertensive agents such as valsartan would appear to be and important addition to the management of vulnerable patients at high risk of cardiovascular events.

PPAR-γ inhibits ANG II-induced cell growth via SHIP2 and 4E-BP1

The present study evaluated the effects of peroxisome proliferator-activated receptor (PPAR)-γ activators on ANG II-induced signaling pathways and cell growth. Vascular smooth muscle cells (VSMC) derived from rat mesenteric arteries were treated with ANG II, with/without the AT1 receptor blocker valsartan or the AT2 receptor blocker PD-123319, after pretreatment for 24 h with the PPAR-γ activators 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) or rosiglitazone. Both 15d-PGJ2 and rosiglitazone decreased ANG II-induced DNA synthesis. Rosiglitazone treatment increased nuclear PPAR-γ expression and activity in VSMC. However, rosiglitazone did not alter expression of PPAR-α/β, ERK 1/2, Akt, or ANG II receptors. 15d-PGJ2 and rosiglitazone decreased ERK 1/2 and Akt peak activity, both of which were induced by ANG II via the AT1 receptor. Rosiglitazone inhibited ANG II-enhanced phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), as well as Src homology (SH) 2-containing inositol phosphatase 2 (SHIP2). PPAR-γ activation reduced ANG II-induced growth associated with inhibition of ERK 1/2, Akt, 4E-BP1, and SHIP2. Modulation of these pathways by PPAR-γ activators may contribute to regression of vascular remodeling in hypertension.

Angiotensin II receptors are upregulated by estradiol and progesterone in the locus coeruleus, median preoptic nucleus and subfornical organ of ovariectomized rats

Angiotensin II (Ang II) receptors in specific brain areas and in the anterior pituitary are controlled by reproductive hormones. Since Ang II also plays a role in controlling reproductive functions, such as luteinizing hormone and prolactin secretion, the objective of the present study was to evaluate the regulation of Ang II receptors by estradiol (E(2)) and progesterone (P) in areas of the brain involved in homeostatic and reproductive functions, such as the locus coeruleus (LC), median preoptic nucleus (MnPO) and subfornical organ (SFO). Adult female rats were ovariectomized under anesthesia and divided into 2 groups after 2 weeks: OVX plus E(2)/P replacement (OVXE(2)P) and OVX plus oil vehicle (OVX). E(2) was injected for 3 consecutive days followed by an injection of P on the 4th day. Animals were killed by decapitation and the brains were removed and frozen. Consecutive coronal brain sections were cut in a cryostat and Ang II receptors were quantified by autoradiography in the MnPO, LC and SFO. Treatment of OVX rats with E(2) and P induced a significant increase in the Ang II receptor binding (fmol/mg protein) in the MnPO (OVX: 4.48 +/- 0.58 and OVXE(2)P: 9.89 +/- 1.65), LC (OVX: 2.72 +/- 0.37 and OVXE(2)P: 8.03 +/- 0.9) and SFO (OVX: 5.45 +/- 0.66 and OVXE(2)P: 10.73 +/- 1.79) compared to OVX animals treated with the vehicle, P < 0.05. In conclusion, these results show that Ang II receptors are upregulated by E(2) and P in the LC, MnPO and SFO of ovariectomized rats.

Constrictor and dilator effects of angiotensin II on cerebral arterioles

BACKGROUND AND PURPOSE

In light of the equivocal data on the cerebral vasoconstrictor and vasodilator actions of angiotensin II (Ang II) and the potential clinical importance of this, we investigated the effects of Ang II on rat pial arterioles.

METHODS

We determined the effect of Ang I (3.10(-6) mol/L) in the absence and presence of the converting enzyme inhibitor, captopril (10(-5) mol/L) in cerebral arterioles of male Wistar rats (open-skull preparation), and those of Ang II (3.10(-12) to 3.10(-6) mol/L) in the absence and presence of the Ang II receptor (AT1) antagonist, telmisartan (10(-5) mol/L) or the AT2 antagonist, PD123319 (10(-5) mol/L). We examined the effect of PD123319 (10(-5) mol/L) and the Ca2+-activated K+ (BKCa) channel blocker, tetraethylammonium (10(-4) mol/L) on the Ang II responses in the presence of telmisartan (10(-5) mol/L).

RESULTS

Ang II-induced dose-dependent constriction with a maximum decrease of -20.1+/-1.0% at 10(-6) mol/L. Captopril significantly decreased Ang I-induced vasoconstriction (-4.0+/-0.9 versus -21.3+/-2.5%; n=4). Telmisartan reversed Ang II-induced vasoconstriction (9.5+/-2.5 versus -20.1+/-1% at 10(-6) mol/L; n=5). PD123319 significantly increased Ang II-induced vasoconstriction (-12.9+/-0.8 versus -10.2+/-0.4% at 10(-6) mol/L; n=5). PD123319 abolished (-2.6+/-0.7 versus 9.3+/-1.1% at 10(-6) mol/L; n=5) whereas tetraethylammonium reversed (-12.1+/-1.6 versus 9.9+/-1.0% at 10(-6) mol/L; n=4) Ang II-induced vasodilatation in the presence of telmisartan.

CONCLUSIONS

Angiotensin is converted locally into Ang II; the overall effect of Ang II is vasoconstrictor following stimulation of the AT1 receptor, but a vasodilator response can be evoked following stimulation of the AT2 receptor and activation of BKCa.

[The renin-angiotensin-aldosterone system -- more complex as previously thought]

BACKGROUND

Angiotensin II (ANG II) is an important factor for the progression of renal diseases. ANG II has many pleiotropic effects on the kidney such as pro-inflammatory and profibrotic actions besides the well-known blood pressure-increasing effect.

NOVEL KNOWLEDGE

Organs have local ANG II-generating systems that work independently from their classic systemic counterpart. Renal proximal tubular cells could generate and secrete ANG II into the urine in concentrations that are 10,000 times higher than those found in serum. These local systems are only incompletely blocked by currently used doses of ACE inhibitors or AT(1) antagonists. There are other enzyme systems besides ACE that contribute to the formation of ANG II. Alternative pathways generate peptides such as angiotensin 1-7 that have antagonistic effect compared with ANG II. Degradation products of ANG II such as angiotensin IV bind at separate receptors and could mediate fibrosis. The discovery of AT(1) receptor dimers and agonistic antibodies against AT(1) receptors contributes to the complexity of the system.

CLINICAL RELEVANCE

The complexity of the renin-angiotensin-aldosterone system (RAAS) implies that dual blockade with ACE inhibitors and AT(1) receptor antagonists makes sense for pathophysiological reasons. First clinical studies have shown that such as dual therapy reduces progression of chronic renal disease more efficiently that the respective monotherapies in certain risk populations. This shows that novel pathophysiological data could lead to innovative clinical treatment strategies.

A new role for the renin-angiotensin system in the rat periaqueductal gray matter: angiotensin receptor-mediated modulation of nociception

Renin-angiotensin (Ang) system (RAS) peptides injected into the periaqueductal gray matter (PAG) elicit antinociception. Saralasin blocks Ang II-elicited antinociception. Thus, it is possible that endogenous RAS peptides could participate on the modulation of nociception in the PAG. This possibility was tested here injecting, in the PAG, the specific Ang type 1 and type 2 receptor (AT1 receptor and AT(2 receptor) antagonists losartan and CGP42,112A, respectively, either alone or before Ang II. The effects of Ang II, losartan and CGP42,112A on nociception were measured using the tail flick test and the model of incision allodynia. Ang II increased tail-flick latency, an effect inhibited by both losartan and CGP42,112A. Ang II reduced incisional allodynia. Either losartan or CGP42,112A alone increased incision allodynia, suggesting that endogenous Ang II and/or an Ang-peptide participates in the control of allodynia by the PAG. AT1 and AT2 receptors were immunolocalized in neuronal cell bodies and processes in the ventrolateral PAG. Taken together, the antinociceptive effect of Ang II injection into the ventrolateral PAG, the increase of allodynia elicited by injecting either losartan or CGP42,112A alone in the PAG, and the presence of AT1 and AT2 receptors in neurons and neuronal processes in the same region, represent the first evidence that part of the tonic nociceptive control mediated by the PAG is carried out locally by endogenous Ang II and/or an Ang-peptide acting on AT1 and AT2 receptors.

Divergent regulation of circulating and intrarenal renin-angiotensin systems in response to long-term blockade

BACKGROUND/AIMS

Long-term treatment with angiotensin-converting enzyme (ACE) inhibitors or angiotensin (Ang) II type I (AT(1)) receptor blockers can improve kidney function and attenuate the progressive decline in kidney function associated with age. In this study in Wistar rats medicated for 22 months, we determined the effects of enalapril (10 mg/kg/day) and losartan (30 mg/kg/day) treatment, in comparison with vehicle (tap water), on renal AngII receptor density and circulating and urinary components of the renin-angiotensin system (RAS).

METHODS

Kidney sections were incubated with [(125)I-sarcosine(1)-threonine(8)]AngII (0.6 nM) for Ang receptor density, and Ang peptides were determined using radioimmunoassays.

RESULTS

Receptor density was approximately 50% higher in vasa recta, glomeruli, and tubulointerstitium in enalapril-treated rats and lower in vasa recta and glomeruli in losartan-treated relative to vehicle-treated rats. Losartan and enalapril treatment elevated plasma levels of AngI and Ang-(1-7) while AngII increased only in losartan-treated rats. In contrast, both treatments were associated with a reduction in urinary excretion of all three Ang peptides as compared with control rats.

CONCLUSION

The reduction in urinary Ang peptides with losartan and enalapril treatment suggests that blockade of intrarenal AngII may be an important mechanism underlying the renoprotection seen with such treatments.

Angiotensin receptor blockade and arterial compliance in chronic kidney disease: a pilot study

BACKGROUND

Almost 20 million people in the US have chronic kidney disease (CKD). Cardiovascular disease and arterial wall abnormalities are common in this population. Because angiotensin II may have adverse effects on the arterial wall, we hypothesized that an angiotensin receptor blocker (ARB) would improve arterial compliance as compared with placebo in subjects with CKD.

METHODS

We performed a double-blinded, placebo-controlled pilot study in which 25 subjects with stages 2 or 3 CKD and proteinuria <1 g were randomized to either the ARB, eprosartan, or placebo and titrated to achieve a goal blood pressure (BP) <130/85 mm Hg. Arterial compliance was measured at baseline and at 8 weeks.

RESULTS

Baseline characteristics were similar between the groups and included mean estimated glomerular filtration rate 63 +/- 14 ml/min/1.73 m(2), heart rate 76 +/- 10 beats/min, BP 142 +/- 12/81 +/- 8 mm Hg, 64% diabetic, 44% male, and 40% white, though subjects in the eprosartan group were younger (60 +/- 12 vs. 70 +/- 6 years, p = 0.01). There were no significant differences between the groups in large or small artery compliance measurements either at baseline or at 8 weeks, but there was a statistically significant improvement from baseline in small artery compliance in the eprosartan group (from median 2.5 ml/mm Hg x 100 [90% CI (1.1, 4.7)] to 4.0 ml/mm Hg x 100 [90% CI (1.9, 6.7)] (p = 0.01)) not seen in the placebo group.

CONCLUSION

Use of an ARB to achieve recommended BP is associated with improved small artery compliance in people with CKD, though larger studies are needed to confirm these findings.

Angiotensin as a target for the treatment of Alzheimer’s disease, anxiety and depression

The brain renin-angiotensin system (RAS), which is comprised of a variety of peptides including angiotensin II, angiotensin III and angiotensin IV acting on AT<inf>1</inf>, AT<inf>2</inf> and AT<inf>4</inf> receptors, is important in cognition and anxiety. Perturbation of the RAS improves basal cognition and reverses age-, scopolamine-, ethanol- and diabetes-induced deficits. In studies of dementias and Alzheimer's disease (AD), some studies have shown that antihypertensive drugs, including angiotensin-converting enzyme inhibitors, have some moderate effects on cognitive decline, but that the angiotensin receptor antagonist losartan has a significantly beneficial effect. These findings suggest that angiotensin receptor ligands may have potential in the prevention or even reversal of vascular dementias and AD. With respect to depression and anxiety, there is similar experimental evidence from animal models that drugs acting on the RAS may be antidepressant or anxiolytic, but insufficient clinical data exist. Such effects, if proven, could promote the use of such agents in the treatment of hypertension coexisting with depression or anxiety.

Rationale for the use of combination angiotensin-converting enzyme inhibitor and angiotensin II receptor blocker therapy in heart failure

BACKGROUND

The present multicenter study investigated whether the combination of angiotensin-converting enzyme inhibitor (ACEI) and angiotensin II receptor blocker (ARB) is more beneficial for preventing left ventricular remodeling and suppressing neurohumoral factors than either ACEI or ARB alone.

METHODS AND RESULTS

One hundred and six patients with mild-to-moderate congestive heart failure treated in 26 Japanese institutes were randomly assigned to the combination therapy or monotherapy. Changes in physical activity (New York Heart Association functional classes, Specific Activity Scale (SAS)), concentrations of neurohumoral factors (plasma renin activity, angiotensin II, aldosterone, and brain natriuretic peptide (BNP)), and cardiac function for 6 months were compared between the 2 groups. It was found that the combination therapy, which was administered at doses standard in Japan, increased the SAS score (4.5 +/- 1.5 to 4.9 +/- 1.5, p<0.05) and decreased the plasma BNP concentration (183 +/- 163 to 135 +/- 118 pg/ml, p<0.05). In contrast, there were no changes in SAS score (4.5 +/- 1.4 to 4.6 +/- 1.4, NS) or BNP concentration (156 +/- 157 to 151 +/- 185 pg/ml, NS) in the patients receiving monotherapy.

CONCLUSIONS

The results of the study demonstrate that the combination therapy, even at the standard doses for Japan, improves physical activity and plasma BNP concentration more than the monotherapy. A larger study is required to assess the effects of the combination therapy on major clinical outcomes.

Extracellular signal regulated kinase and SMAD signaling both mediate the angiotensin II driven progression towards overt heart failure in homozygous TGR(mRen2)27

Angiotensin (Ang) II is a key player in left ventricular (LV) remodeling and cardiac fibrosis. Its effects are thought to be transferred at least in part by mitogen-activated protein kinases (MAPK), transforming growth factor (TGF) beta1, and the Smad pathway. In this study we sought to elucidate whether Ang II related effects on LV dysfunction and fibrosis in vivo are mediated via MAPK or rather via Smad stimulation. We treated homozygous REN2 rats (7-11 weeks) with placebo, Ang II type 1 (AT1) receptor blocker or tyrphostin A46 (TYR), an inhibitor of epidermal growth factor receptor tyrosine kinase that blocks extracellular signal-regulated kinase (ERK) activity. REN2 rats had LV hypertrophy (LVH) and LV dysfunction that progressed to heart failure between 10 and 13 weeks. Blood pressure normalized over time. Renin, N-terminal atrial natriuretic peptide (N-ANP), and ERK were activated while p38 MAPK was not. Treatment with AT1 receptor blockade prevented LVH and right ventricular hypertrophy, normalized systolic and diastolic d P/d t, N-ANP levels, and reduced collagen apposition. Similarly, TYR reduced LVH, N-ANP levels, and collagen apposition. Myocardial ERK activation did not depend on AT1 receptor signaling as it was not affected by AT1 receptor blockade. TYR abolished myocardial ERK activity. Smad2 activation was inhibited by AT1 receptor blockade but was unaltered by TYR. Ang II induced LV remodeling and fibrosis are dependent on both ERK and Smad2 activation. This process is prevented by both AT1 receptor blockade and TYR, and therefore inhibition of either pathway is equally efficacious in restoring LV function and architecture.