Proceedings of the Symposium ‘Angiotensin AT1 Receptors: From Molecular Physiology to Therapeutics’: ENDOGENOUS ANGIOTENSIN II LEVELS AND THE MECHANISM OF ACTION OF ANGIOTENSIN-CONVERTING ENZYME INHIBITORS AND ANGIOTENSIN RECEPTOR TYPE 1 ANTAGONISTS

Treatment with apoptosis inhibitor restores cognitive impairment in rats with myocardial infarction

We previously reported that apoptosis is responsible for cognitive impairment in rats with myocardial infarction (MI). Acute administration of an apoptosis inhibitor (Z-vad) effectively reduced brain inflammation in rats with cardiac ischemia/reperfusion injury. However, the beneficial effects of Z-vad on cognitive function, brain inflammation, mitochondrial function, cell death pathways, and neurogenesis in MI rats have not been investigated. Male rats were divided into sham or MI groups (left anterior descending coronary ligation). A successful MI was determined by a reduction of ejection fraction <50 %. Then, MI rats were allocated to receive vehicle, enalapril (10 mg/kg, a positive control), and Z-vad (1 mg/kg) for 4 weeks. Cardiac function, cognitive function, and molecular analysis were investigated. MI rats exhibited cardiac dysfunction, cognitive impairment, blood brain barrier (BBB) breakdown, dendritic spine loss, which were accompanied by an upregulation of oxidative stress, mitochondrial dysfunction, and apoptosis. Chronic treatment with Z-vad attenuated cardiac dysfunction following MI to the same extent as enalapril. Z-vad successfully improved cognitive function and restored dendritic spine density in MI rats through a reduction of systemic oxidative stress and brain mitochondrial dysfunction similar to enalapril. Moreover, Z-vad provided greater efficacy than enalapril in enhancing mitophagy, neurogenesis, synaptic proteins and reducing apoptosis in hippocampus of MI rats. Nevertheless, neither Z-vad nor enalapril increased BBB tight junction protein. In conclusion, treatment with an apoptosis inhibitor reduced cognitive impairment in MI rats via reducing oxidative stress, mitochondrial dysfunction, apoptosis, and restoring dendritic spine density, together with enhancing mitophagy and neurogenesis.

Kidney Angiotensin in Cardiovascular Disease: Formation and Drug Targeting

The concept of local formation of angiotensin II in the kidney has changed over the last 10-15 years. Local synthesis of angiotensinogen in the proximal tubule has been proposed, combined with prorenin synthesis in the collecting duct. Binding of prorenin via the so-called (pro)renin receptor has been introduced, as well as megalin-mediated uptake of filtered plasma-derived renin-angiotensin system (RAS) components. Moreover, angiotensin metabolites other than angiotensin II [notably angiotensin-(1-7)] exist, and angiotensins exert their effects via three different receptors, of which angiotensin II type 2 and Mas receptors are considered renoprotective, possibly in a sex-specific manner, whereas angiotensin II type 1 (AT1) receptors are believed to be deleterious. Additionally, internalized angiotensin II may stimulate intracellular receptors. Angiotensin-converting enzyme 2 (ACE2) not only generates angiotensin-(1-7) but also acts as coronavirus receptor. Multiple, if not all, cardiovascular diseases involve the kidney RAS, with renal AT1 receptors often being claimed to exert a crucial role. Urinary RAS component levels, depending on filtration, reabsorption, and local release, are believed to reflect renal RAS activity. Finally, both existing drugs (RAS inhibitors, cyclooxygenase inhibitors) and novel drugs (angiotensin receptor/neprilysin inhibitors, sodium-glucose cotransporter-2 inhibitors, soluble ACE2) affect renal angiotensin formation, thereby displaying cardiovascular efficacy. Particular in the case of the latter three, an important question is to what degree they induce renoprotection (e.g., in a renal RAS-dependent manner). This review provides a unifying view, explaining not only how kidney angiotensin formation occurs and how it is affected by drugs but also why drugs are renoprotective when altering the renal RAS. SIGNIFICANCE STATEMENT: Angiotensin formation in the kidney is widely accepted but little understood, and multiple, often contrasting concepts have been put forward over the last two decades. This paper offers a unifying view, simultaneously explaining how existing and novel drugs exert renoprotection by interfering with kidney angiotensin formation.

On the footsteps of Hippocrates, Sanctorius and Harvey to better understand the influence of cold on the occurrence of COVID-19 in European countries in 2020

COVID-19 pandemic has been characterized by a pattern of consecutive declines and regrowth in European countries in 2020. After being partially regressed during the summer, the reappearance of the infection during fall 2020 in many temperate countries strongly suggests that temperature and cold may play a role in influencing the infectivity and virulence of SARS-CoV-2. While promoting medicine as an art, Hippocrates interpreted with logical reasoning the occurrence of diseases such as epidemics, as a consequence of environmental factors, in particular climatic variations. During the Renaissance, Sanctorius was one of the first to perform quantitative measurements, and Harvey discovered the circulation of blood by performing experimental procedures in animals. We think that a reasoning mixing various observations, measurements and experiments is fundamental to understand how cold increases infectivity and virulence of SARS-CoV-2. By this review, we provide evidence linking cold, angiotensin-II, vasoconstriction, hypoxia and aerobic glycolysis (the Warburg effect) to explain how cold affects the epidemiology of COVID-19. Also, a low humidity increases virus transmissibility, while a warm atmosphere, a moderate airway humidity, and the production of vasodilator angiotensin 1-7 by ACE2 are less favorable to the virus entry and/or its development. The meteorological and environmental parameters impacting COVID-19 pandemic should be reintegrated into a whole perspective by taking into account the different factors influencing transmissibility, infectivity and virulence of SARS-CoV-2. To understand the modern enigma represented by COVID-19, an interdisciplinary approach is surely essential.

Renin-Angiotensin-Aldosterone System (RAAS) Inhibitors and Coronavirus Disease 2019 (COVID-19)

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the virus responsible for the coronavirus disease 2019 (COVID-19) pandemic. The angiotensin-converting enzyme 2 (ACE2) has been proven to be used by SARS-CoV-2 for host cell entry. Considering that angiotensin receptor blockers and ACE inhibitors (ACEIs) upregulate the expression of ACE2 in animal studies, there may be a concern about whether these drugs may increase COVID-19 susceptibility and severity. Recently, there has been a debate among clinicians about whether to continue or to stop ACEIs and angiotensin receptor blockers in the context of COVID-19. Also, some media outlets and health systems have called for the discontinuation of these drugs in the context of suspected COVID-19. This has necessitated an urgent release of guidance on the use of such medications in COVID-19 patients. To date, multiple theories relating to the pure effects of renin-angiotensin-aldosterone system (RAAS) inhibitors on COVID-19 infections have been postulated. Favorable effects include blocking the ACE2 receptors, preventing viral entry into the heart and lungs, and protecting against lung injury in COVID-19. Adverse effects include a possible retrograde feedback mechanism that upregulates ACE2 receptors. This review provides greater insight into the role of the RAAS axis in acute lung injury and the effects of RAAS inhibitors on SARS-CoVs. The hypothesis that RAAS inhibitors facilitate viral insertion and the alternative hypothesis of the beneficial role of these drugs are discussed. Up-to-date published data concerning the RAAS inhibitors and COVID-19 are summarized.

The role of the brain renin-angiotensin system (RAS) in mild traumatic brain injury (TBI)

There is considerable interest in traumatic brain injury (TBI) induced by repeated concussions suffered by athletes in sports, military personnel from combat-and non-combat related activities, and civilian populations who suffer head injuries from accidents and domestic violence. Although the renin-angiotensin system (RAS) is primarily a systemic cardiovascular regulatory system that, when dysregulated, causes hypertension and cardiovascular pathology, the brain contains a local RAS that plays a critical role in the pathophysiology of several neurodegenerative diseases. This local RAS includes receptors for angiotensin (Ang) II within the brain parenchyma, as well as on circumventricular organs outside the blood-brain-barrier. The brain RAS acts primarily via the type 1 Ang II receptor (AT₁R), exacerbating insults and pathology. With TBI, the brain RAS may contribute to permanent brain damage, especially when a second TBI occurs before the brain recovers from an initial injury. Agents are needed that minimize the extent of injury from an acute TBI, reducing TBI-mediated permanent brain damage. This review discusses how activation of the brain RAS following TBI contributes to this damage, and how drugs that counteract activation of the AT₁R including AT₁R blockers (ARBs), renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, and agonists at type 2 Ang II receptors (AT₂) and at Ang (1-7) receptors (Mas) can potentially ameliorate TBI-induced brain damage.

Unexpected BP Sensitivity to Angiotensin II in a Patient With Coronavirus Disease 2019, ARDS, and Septic Shock

We report the case of an 88-year-old man with coronavirus disease 2019 (COVID-19) who presented with ARDS and septic shock. The patient had exquisite BP sensitivity to low-dose angiotensin II (Ang-2), allowing for rapid liberation from high-dose vasopressors. We hypothesize that sensitivity to Ang-2 might be related to biological effect of severe acute respiratory syndrome coronavirus 2 infection. The case is suggestive of a potential role for synthetic Ang-2 for patients with COVID-19 and septic shock. Further studies are needed to confirm our observed clinical efficacy.

Understanding the renin-angiotensin-aldosterone-SARS-CoV axis: a comprehensive review

Importance

Coronavirus disease 2019 (COVID-19), the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been declared a global pandemic with significant morbidity and mortality since first appearing in Wuhan, China, in late 2019. As many countries are grappling with the onset of their epidemics, pharmacotherapeutics remain lacking. The window of opportunity to mitigate downstream morbidity and mortality is narrow but remains open. The renin–angiotensin–aldosterone system (RAAS) is crucial to the homeostasis of both the cardiovascular and respiratory systems. Importantly, SARS-CoV-2 utilises and interrupts this pathway directly, which could be described as the renin–angiotensin–aldosterone–SARS-CoV (RAAS–SCoV) axis. There exists significant controversy and confusion surrounding how anti-hypertensive agents might function along this pathway. This review explores the current state of knowledge regarding the RAAS–SCoV axis (informed by prior studies of SARS-CoV), how this relates to our currently evolving pandemic, and how these insights might guide our next steps in an evidence-based manner.

Observations

This review discusses the role of the RAAS–SCoV axis in acute lung injury and the effects, risks and benefits of pharmacological modification of this axis. There may be an opportunity to leverage the different aspects of RAAS inhibitors to mitigate indirect viral-induced lung injury. Concerns have been raised that such modulation might exacerbate the disease. While relevant preclinical, experimental models to date favour a protective effect of RAAS–SCoV axis inhibition on both lung injury and survival, clinical data related to the role of RAAS modulation in the setting of SARS-CoV-2 remain limited.

Conclusion

Proposed interventions for SARS-CoV-2 predominantly focus on viral microbiology and aim to inhibit viral cellular injury. While these therapies are promising, immediate use may not be feasible, and the time window of their efficacy remains a major unanswered question. An alternative approach is the modulation of the specific downstream pathophysiological effects caused by the virus that lead to morbidity and mortality. We propose a preponderance of evidence that supports clinical equipoise regarding the efficacy of RAAS-based interventions, and the imminent need for a multisite randomised controlled clinical trial to evaluate the inhibition of the RAAS–SCoV axis on acute lung injury in COVID-19.

The interplay of SARS-CoV-2 with the renin–angiotensin–aldosterone system probably accounts for much of its unique pathology. Appreciating the degree and mechanism of this interaction highlights potential therapeutic options, including blockade (ARBs).https://bit.ly/3aue4tS

Targeting toll-like receptor 4 signalling pathways: can therapeutics pay the toll for hypertension?

The immune system plays a prominent role in the initiation and maintenance of hypertension. The innate immune system, via toll-like receptors (TLRs), identifies distinct signatures of invading microbes and damage-associated molecular patterns and triggers a chain of downstream signalling cascades, leading to secretion of pro-inflammatory cytokines and shaping the adaptive immune response. Over the past decade, a dysfunctional TLR-mediated response, particularly via TLR4, has been suggested to support a chronic inflammatory state in hypertension, inducing deleterious local and systemic effects in host cells and tissues and contributing to disease progression. While the underlying mechanisms triggering TLR4 need further research, evidence suggests that sustained elevations in BP disrupt homeostasis, releasing endogenous TLR4 ligands in hypertension. In this review, we discuss the emerging role of TLR4 in the pathogenesis of hypertension and whether targeting this receptor and its signalling pathways could offer a therapeutic strategy for management of this multifaceted disease. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Investigation into the Mechanism of Homo- and Heterodimerization of Angiotensin-Converting Enzyme

Angiotensin-converting enzyme (ACE) plays a central role in the renin-angiotensin system (RAS), which is primarily responsible for blood pressure homeostasis. Studies have shown that ACE inhibitors yield cardiovascular benefits that cannot be entirely attributed to the inhibition of ACE catalytic activity. It is possible that these benefits are due to interactions between ACE and RAS receptors that mediate the protective arm of the RAS, such as angiotensin II receptor type 2 (AT2R) and the receptor MAS. Therefore, in this study, we investigated the molecular interactions of ACE, including ACE homodimerization and heterodimerization with AT2R and MAS, respectively. Molecular interactions were assessed by fluorescence resonance energy transfer and bimolecular fluorescence complementation in human embryonic kidney 293 cells and Chinese hamster ovary-K1 cells transfected with vectors encoding fluorophore-tagged proteins. The specificity of dimerization was verified by competition experiments using untagged proteins. These techniques were used to study several potential requirements for the germinal isoform of angiotensin-converting enzyme expressed in the testes (tACE) dimerization as well as the effect of ACE inhibitors on both somatic isoforms of angiotensin-converting enzyme expressed in the testes (sACE) and tACE dimerization. We demonstrated constitutive homodimerization of sACE and of both of its domains separately, as well as heterodimerization of both sACE and tACE with AT2R, but not MAS. In addition, we investigated both soluble sACE and the sACE N domain using size-exclusion chromatography-coupled small-angle X-ray scattering and we observed dimers in solution for both forms of the enzyme. Our results suggest that ACE homo- and heterodimerization does occur under physiologic conditions.

Critical developmental periods in the pathogenesis of hypertension

Hypertension is one of the major risk factor of cardiovascular diseases, but after a century of clinical and basic research, the discrete etiology of this disease is still not fully understood. One reason is that blood pressure is a quantitative trait with multifactorial determination. Numerous genes, environmental factors as well as epigenetic factors should be considered. There is no doubt that although the full manifestation of hypertension and other cardiovascular diseases usually occurs predominantly in adulthood and/or senescence, the roots can be traced back to early ontogeny. The detailed knowledge of the ontogenetic changes occurring in the cardiovascular system of experimental animals during particular critical periods (developmental windows) could help to solve this problem in humans and might facilitate the age-specific prevention of human hypertension. We thus believe that this approach might contribute to the reduction of cardiovascular morbidity among susceptible individuals in the future.

Novel roles of nuclear angiotensin receptors and signaling mechanisms

The renin-angiotensin system (RAS) constitutes an important hormonal system in the physiological regulation of blood pressure. The dysregulation of the RAS is considered a major influence in the development and progression of cardiovascular disease and other pathologies. Indeed, experimental and clinical evidence indicates that blockade of this system with angiotensin-converting enzyme (ACE) inhibitors or angiotensin type 1 receptor (AT1R) antagonists is an effective therapy to attenuate hypertension and diabetic renal injury, and to improve heart failure. Originally defined as a circulating system, multiple tissues express a complete RAS, and compelling evidence now favors an intracellular system involved in cell signaling and function. Within the kidney, intracellular expression of the three predominant ANG receptor subtypes is evident in the nuclear compartment. The ANG type 1 receptor (AT1R) is coupled to the generation of reactive oxygen species (ROS) through the activation of phosphoinositol-3 kinase (PI3K) and PKC. In contrast, both ANG type 2 (AT2R) and ANG-(1-7) (AT7R) receptors stimulate nitric oxide (NO) formation, which may involve nuclear endothelial NO synthase (eNOS). Moreover, blockade of either ACE2-the enzyme that converts ANG II to ANG-(1-7)-or the AT7 receptor exacerbates the ANG II-ROS response on renal nuclei. Finally, in a model of fetal programmed hypertension, the nuclear ROS response to ANG II is enhanced, while both AT2 and AT7 stimulation of NO is attenuated, suggesting that an imbalance in the intracellular RAS may contribute to the development of programming events. We conclude that a functional intracellular or nuclear RAS may have important implications in the therapeutic approaches to cardiovascular disease.

Valsartan use in pediatric hypertension

Hypertension affects up to 5% of school-aged children and is defined by an average systolic or diastolic blood pressure greater than the 95th percentile for age, sex and height. In prepubertal children a secondary cause for hypertension including renal disease, coarctation of the aorta or endocrine disease should be excluded by appropriate evaluation. The incidence and prevalence of essential hypertension in adolescents has increased together with the increase in obesity and now accounts for at least 50% of hypertension in this age group. Many children with primary hypertension and most children with secondary causes for hypertension require drug therapy. There are numerous drug classes that are presently used to treat hypertensive pediatric patients, which include β-blockers, peripheral α-blockers, direct vasodilators, ACE inhibitors, calcium channel blockers, diuretics and ARBs. This article will review the pharmacology of the ARB valsartan with respect to its efficacy, tolerability and safe use in hypertensive pediatric patients.

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.

Liver disease and the renin-angiotensin system: recent discoveries and clinical implications

The renin-angiotensin system (RAS) is a key regulator of vascular resistance, sodium and water homeostasis and the response to tissue injury. Historically, angiotensin II (Ang II) was thought to be the primary effector peptide of this system. Ang II is produced predominantly by the effect of angiotensin converting enzyme (ACE) on angiotensin I (Ang I). Ang II acts mainly through the angiotensin II type-1 receptor (AT(1)) and, together with ACE, these components represent the 'classical' axis of the RAS. Drug therapies targeting the RAS by inhibiting Ang II formation (ACE inhibitors) or binding to its receptor (angiotensin receptor blockers) are now in widespread clinical use and have been shown to reduce tissue injury and fibrosis in cardiac and renal disease independently of their effects on blood pressure. In 2000, two groups using different methodologies identified a homolog of ACE, called ACE2, which cleaves Ang II to form the biologically active heptapeptide, Ang-(1-7). Conceptually, ACE2, Ang-(1-7), and its putative receptor, the mas receptor represent an 'alternative' axis of the RAS capable of opposing the often deleterious actions of Ang II. Interestingly, ACE inhibitors and angiotensin receptor blockers increase Ang-(1-7) production and it has been proposed that some of the beneficial effects of these drugs are mediated through upregulation of Ang-(1-7) rather than inhibition of Ang II production or receptor binding. The present review focuses on the novel components and pathways of the RAS with particular reference to their potential contribution towards the pathophysiology of liver disease.

Angiogenic protection from focal ischemia with angiotensin II type 1 receptor blockade in the rat

Angiogenesis within an ischemic region of the brain may increase tissue viability and act to limit the extent of an infarct. The ANG II pathway can both stimulate and inhibit angiogenesis depending on the tissue and the activated receptors. Previous work showed that 2-wk losartan administration (ANG II type 1 receptor blockade) initiates a significant cerebral angiogenic response. We hypothesized that administration of losartan in the drinking water of rats for 2 wk before initiation of focal ischemia would decrease the extent of the resulting infarct. Adult male Sprague-Dawley rats were given losartan (50 mg/day) in drinking water for 2 wk before initiation of cerebral focal ischemia produced by cauterization of cortical surface vessels. Controls received normal drinking water. In control animals, three main vessels feeding the whisker barrel cortex were cauterized, resulting in cessation of blood flow. The same protocol was followed for losartan-treated animals but did not result in cessation of blood flow in the whisker barrel cortex. Another group of losartan-treated animals received between 8 and 14 cauterizations of surface vessels feeding the whisker barrel cortex, and cessation of blood flow was verified. Rats were killed 72 h after surgery. Morphological examination revealed angiogenesis, maintained vascular delivery, and significantly decreased infarct size in losartan-treated animals compared with controls. These results demonstrate that pretreatment with losartan reduces infarct size after cerebral focal ischemia and support the hypothesis that cerebral angiogenesis may be one of the mechanisms responsible.

Renal angiotensin II receptors, hyperinsulinemia, and obesity

Angiotensin II, via activation of AT1 receptors in the kidney regulates sodium/fluid homeostasis and blood pressure. An exaggerated action of angiotensin II mediated via activation of AT1 receptors has been implicated in the increased renal sodium retention and the resetting of the pressure natriuresis in obesity related hypertension. Treatment of obese Zucker rats with AT1 receptor blockers reduces blood pressure to a greater extent and produces greater natriuresis. Also, there is an increased membranal AT1 receptor numbers and angiotensin II produces greater activation of sodium transporters in the isolated tubules from obese Zucker rats. Interestingly, AT2 receptors, which are believed to be beneficial to the renal and cardiovascular function in terms of their action on kidney and blood vessels, are greatly increased in proximal tubular membranes of obese Zucker rats. Whole animal and in vitro studies indicate that higher plasma insulin level, generally associated with obesity, is responsible for the up-regulation of both AT1 and AT2 receptors in the kidney. Determining the consequence of selective blocking of AT1 receptors and/or activation of the AT2 receptors on renal and cardiovascular function, and the effect of lowering insulin on these receptors present an important area of further investigation in obesity.

Cardiovascular status following combined angiotensin-converting enzyme and AT1 receptor inhibition in conscious spontaneously hypertensive rats

1. Combined treatment of spontaneously hypertensive rats (SHR) with AT1 receptor antagonists and angiotensin-converting enzyme (ACE) inhibitors has been shown to reduce mean arterial pressure (MAP) more than monotherapy with either agent. The aims of the present study were to investigate the effects of chronic dual renin-angiotensin system (RAS) inhibition using non-hypotensive doses of the AT1 receptor antagonist candesartan cilexetil and the ACE inhibitor perindopril on cardiovascular function and structure. 2. Adult male SHR, aged 15 weeks, were divided into four groups: (i) candesartan cilexetil (0.5 mg/kg per day in drinking water); (ii) perindopril (0.3 mg/kg per day in drinking water); (iii) combined treatment (dual RAS inhibition); or (iv) the appropriate vehicle (0.1% ethanol/0.1% polyethylene glycol/1.5 mmol/l sodium bicarbonate dissolved in water for candesartan cilexetil; distilled water for perindopril). Systolic blood pressure was measured weekly using the tail-cuff method and urinary microalbuminuria was measured fortnightly. 3. After 4 weeks, rats were instrumented for intravenous drug administration and measurement of MAP. At this time, the cardiovascular effects of angiotensin (Ang) I and AngII (5-20 ng) and sodium nitroprusside (SNP) and acetylcholine (ACh; 1-5 micro g) were assessed. In addition, left ventricular : bodyweight and media : lumen ratios were determined as indices of cardiac and vascular hypertrophy, respectively. 4. Candesartan cilexetil and perindopril alone had minimal effect on MAP when measured both directly and indirectly, whereas direct MAP was significantly decreased in the combined treatment group (131 +/- 6 mmHg; P < 0.05) compared with the vehicle group (156 +/- 9 mmHg). Pressor responses to AngI were significantly decreased in all groups compared with the vehicle-treated group and pressor responses to AngII were significantly decreased in the candesartan cilexetil-treated (P < 0.01) and combined treatment groups (P < 0.01) compared with the vehicle-treated group. Depressor responses to ACh and SNP were not significantly affected by any of the antihypertensive therapies compared with vehicle-treated SHR. 5. Vascular hypertrophy was significantly decreased in the candesartan cilexetil and combined groups compared with the vehicle-treated group, whereas cardiac hypertrophy was reduced, with the rank order of effect being: dual RAS inhibition > perindopril > candesartan cilexetil. Urinary albumin tended to decrease with dual RAS inhibition, but was not significantly affected by this short-term treatment. 6. These results demonstrate the efficacy of low-dose dual RAS inhibition as an antihypertensive modality, at least in SHR, not only in reducing arterial pressure, but also in improving cardiovascular structure.

Angiotensin-converting enzyme inhibition in adult hypertensive rats: a stereological study of renal filtration surface area

1. Angiotensin-converting enzyme (ACE) inhibitor treatment leads to beneficial effects on kidney function. The aim of the present study was to determine whether ACE inhibition at high or low doses affects glomerular capillary surface area and length, glomerular number or total renal filtration surface area in rats with established hypertension and, if so, to determine whether these effects are mediated through bradykinin potentiation. 2. Spontaneously hypertensive rats (SHR) were treated with the ACE inhibitor perindopril at either 3 or 0.1 mg/kg per day (high and low doses, respectively) from 16 to 24 weeks of age. Some rats were concomitantly treated with the bradykinin B2 receptor antagonist S16118 (10 nmol/kg per day). Blood pressure was measured twice weekly during the treatment period. At 24 weeks of age, rats were perfusion fixed at 140 mmHg, the kidneys removed, embedded in resin and examined stereologically to estimate glomerular number and volume, length and surface area of glomerular capillaries and total renal filtration surface area. 3. High- and low-perindopril treatment significantly reduced systolic blood pressure compared with control SHR. However, the rats treated with low-dose perindopril were still considered hypertensive. Neither low-dose nor high-dose perindopril treatment had any observable effect on glomerular number (23 876 +/- 1201 vs 26 240 +/- 1465 glomeruli/kidney, respectively) or volume (2.25 +/- 0.21 and 1.96 +/- 0.06 x 10-3 mm3, respectively) compared with controls (glomerular number 25866 +/- 1210 glomeruli/kidney; glomerular volume 2.24 +/- 0.21 x 10-3 mm3). As a result, there was no significant difference in total renal filtration surface area between any of the experimental groups (8161.6 +/- 550.9, 8699.7 +/- 427.6, 9081.9 +/- 453.6, 8830.2 +/- 521.2 and 8559.4 +/- 341.4 mm2 for SHR, SHR low-dose perindopril, SHR low-dose perindopril + B2 antagonist, SHR high-dose perindopril and SHR high-dose perindopril + B2 antagonist, respectively). Coadministration of the bradykinin antagonist had no observable effect on any of the parameters studied. 4. In conclusion, because neither high-dose nor low-dose perindopril had any effect on total renal filtration surface area, the observed beneficial effects of ACE inhibition on kidney function are not the result of enhancement in glomerular capillary surface area.

Renin-angiotensin system inhibition: how much is too much of a good thing?

Inhibitors of the renin-angiotensin system (RAS) are valuable therapeutic agents for a wide range of clinical conditions. Increasingly, consideration is being given to the combination of angiotensin-converting enzyme (ACE) inhibitors and angiotensin-II receptor (AR) antagonists to obtain more complete inhibition of the RAS than can be achieved by either agent alone. Beta-blockers also inhibit the RAS by inhibiting renin secretion. Whereas the combination of an ACE inhibitor and AR antagonist represents dual RAS inhibition, the combination of both of these agents with beta-blocker therapy represents triple RAS inhibition. Animal studies indicate that complete blockade of the RAS produces adverse effects. Moreover, post-hoc analysis of the recent Valsartan Heart Failure Trial study suggests that the combination of ACE inhibitor and AR antagonist therapies may have an adverse effect in heart failure when combined with beta-blocker therapy. There is therefore a need for caution in the combination of ACE inhibition and AR antagonism, particularly in patients receiving beta-blockers, until the impact of this strategy is evaluated.

Chronic renal ischemia: implications for cardiovascular disease risk

Chronic renal ischemia caused by atherosclerotic renal artery stenosis (RAS) is gaining recognition as a potentially important risk factor for cardiovascular (CV) morbidity and mortality. The etiology of increased risk of CV events is multifaceted and includes direct physiologic changes that increase risk as well as intermediate clinical effects that are associated with worse outcome. Physiologic changes associated with increased CV risk in patients with RAS include increased production of fibrogenic and vasoactive peptides such as renin, angiotensin, endothelin, and catecholamines, as well as endothelial cell dysfunction. Clinical intermediate conditions associated with higher incidences of CV events seen in patients with renal ischemia include hypertension, systemic atherosclerosis, chronic renal failure, and left ventricular hypertrophy and dysfunction. More thorough understanding of the myriad physiologic changes seen in patients with RAS will likely improve patient selection for renal artery revascularization. Clinical trials should examine a full range of CV and renal outcomes, not just blood pressure, to adequately assess the merits of revascularization.

Forebrain renin-angiotensin system has a tonic excitatory influence on renal sympathetic nerve activity

All elements of the renin-angiotensin system (RAS) are present in the forebrain, particularly in circumventricular organs surrounding the third cerebral ventricle. We tested the hypothesis that forebrain angiotensin-converting enzyme (ACE) has a tonic excitatory influence on sympathetic drive. Neurally intact and sinoaortic-denervated pentobarbital-anesthetized rats were treated with forebrain-directed intracarotid artery (ICA) versus intravenous injections of angiotensin I (ANG I) and of the ACE inhibitor captopril. In intact rats, ICA ANG I elicited a rise in arterial pressure and a concomitant reduction in renal sympathetic nerve activity (RSNA; ICA captopril elicited the opposite responses). In barodenervated rats, ICA ANG I increased and ICA captopril decreased arterial pressure and RSNA in parallel; intravenous ANG I had no effect on RSNA. The findings suggest that the intrinsic forebrain RAS has a tonic excitatory influence on sympathetic drive that is overshadowed in normal rats by baroreflex mechanisms, but may assume a more prominent role in pathophysiological states (e.g., heart failure) in which baroreflex mechanisms are impaired and RAS activity is augmented.

New drugs in the treatment of heart failure

New therapeutic strategies as well as the development of drugs with more specific targets have been fueled by disappointments in the treatment of adult heart failure. Calcium sensitizers, vesnarinone and angiotensin channel blockers will be addressed in this manuscript. The physiologic and pharmacologic principles that justify their use in the management of heart failure are reviewed. Calcium sensitizers increase myocardial contractility and in part they bypass the adenylyl cyclase cascade, which gives them a more favorable energy profile. Vesnarinone is a quinolinone derivative with ion channel modulation properties, which result in a positive inotropic effect and prolongation of the action potential. In addition vesnarinone has immunomodulatory properties. Angiotensin-converting enzyme inhibitors are the cornerstones for the treatment of heart failure. The discovery of some putative drawbacks to ACE inhibition has challenged this supremacy. Angiotensin receptor blockers have been developed hoping to overcome these deficiencies. Myocardial developmental differences highlight the shortcomings of attempting to extrapolate data on drugs and cellular physiology in adults to children. Studies are needed addressing standards of care, quality of life, morbidity and mortality, neurohumoral activation, its modulation and the consequences of these therapies in pediatric heart failure.

Long-term safety and antihypertensive efficacy of irbesartan: pooled results of five open-label studies

An analysis of 5 multicenter, open-label studies was conducted to evaluate the long-term safety and efficacy of irbesartan in 1,006 patients with seated diastolic blood pressure (SeDBP) 95-110 mm Hg. Irbesartan monotherapy was started at 75 mg and titrated to 300 mg at 2- to 4-week intervals to achieve normalized blood pressure (SeDBP <90 mm Hg). If normalized BP was not attained with irbesartan 300 mg alone, adjunctive medications could be added. At 12 months of therapy, the mean reduction in seated systolic blood pressure/SeDBP was 21.0/15.8 mm Hg, and 83% (684/821) of patients were normalized. Of those normalized, 64% were receiving irbesartan monotherapy and 86% were receiving irbesartan or irbesartan/hydrochlorothiazide only. No evidence of tachyphylaxis to the antihypertensive effect of irbesartan was noted. Thus, long-term irbesartan therapy, with or without other antihypertensives, achieved and maintained normalized BP in the majority of patients and was well tolerated.

AT(2) receptor stimulation enhances antihypertensive effect of AT(1) receptor antagonist in hypertensive rats

In the present study, we investigated the role of the angiotensin type 2 (AT(2)) receptor in the regulation of blood pressure in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). We tested the hypothesis that AT(2) receptor activation may contribute to the antihypertensive effects of angiotensin type 1 (AT(1)) receptor antagonists. Mean arterial pressure (MAP) and heart rate were measured over a 4-day protocol in various groups of rats that received the following drug combinations: the AT(1) receptor antagonist candesartan (0.01 or 0.1 mg/kg IV) alone, the AT(2) receptor agonist CGP42112 (1 microg/kg per minute) alone, and candesartan plus CGP42112. In both SHR and WKY, 4-hour infusions of saline and CGP42112 alone did not alter MAP. In WKY, both doses of candesartan alone caused small decreases in MAP, which were similar when combined with CGP42112. In SHR, candesartan (0.1 mg/kg) caused an immediate, marked decrease in MAP, which was unaffected when combined with CGP42112. By contrast, in separate SHR, a 10-fold lower dose of candesartan (0.01 mg/kg) caused a slower-onset depressor response, which was enhanced when combined with CGP42112. The involvement of AT(2) receptors was confirmed in another group of SHR, since this facilitation of the antihypertensive effect of candesartan by CGP42112 was abolished by the coinfusion of the AT(2) receptor antagonist PD123319 (50 microg/kg per minute) with the candesartan/CGP42112 combination. Collectively, these data suggest that in SHR, AT(2) receptor activation can facilitate the initial depressor response caused by an AT(1) receptor antagonist.

Interaction between lifetime captopril treatment and NaCI-sensitive hypertension in spontaneously hypertensive rats and Wistar-Kyoto rats

DESIGN

Previous studies that were based on daytime arterial pressure recordings indicate that lifetime treatment with captopril exacerbates the hypertensive response to a high NaCl diet in spontaneously hypertensive rats (SHR) but has no such effect in normotensive Wistar-Kyoto (WKY) rats. The present study used 24-h recording methods to examine the hypothesis that during the normal waking hours of rats (night-time) the hypertensive response to a high NaCl diet is exacerbated in SHR and induced in WKY rats treated with lifetime captopril.

METHODS

SHR and WKY rats were (1) untreated, (2), lifetime captopril treated or (3) lifetime captopril treated but removed from the treatment 2 weeks prior to exposure to a high (8%) NaCl diet

RESULTS

Compared to untreated SHR, in SHR that were continuously treated with captopril, the high NaCl diet caused a more rapid and greater rise in arterial pressure. Discontinuation of the captopril treatment did not significantly diminish this NaCl-sensitivity. In untreated WKY rats, the high NaCl diet did not alter mean arterial pressure, but in the lifetime captopril-treated WKY rats the high NaCl diet induced a rapid rise in arterial pressure. In WKY rats, discontinuation of the lifetime captopril treatment did not diminish this NaCl-induced rise in arterial pressure, even though baseline mean arterial pressure in this group is similar to that in untreated WKY rats.

CONCLUSIONS

Lifetime captopril treatment accelerates the hypertensive response to a high NaCl diet in SHR, and it induces a similar response in WKY rats. In both strains, the lifetime captopril treatment causes a change in the response that is not dependent on concurrent administration of the drug. This finding further suggests that lifetime captopril treatment causes a long-term resetting of cardiovascular response mechanisms.

Blood pressure control, microalbuminuria and cardiovascular risk in Type 2 diabetes mellitus

Type 2 (noninsulin-dependent) diabetes mellitus (DM) affects about 3% of the UK population. Diabetes often coexists with a cluster of other potent cardiovascular risk factors, including hypertension, dyslipidaemia and increased tendency for thrombosis, and increases the risk of early death from cardiovascular causes by about threefold. Microalbuminuria or proteinuria also may be present, further increasing the risk of cardiovascular mortality. Cardiovascular risk factors must be treated aggressively in patients with Type 2 diabetes and control of blood pressure at 140/85 mm Hg or lower is a priority. The management of hypertension in patients from some ethnic groups demands special consideration because they have a high incidence of diabetes and hypertensive complications. Patients must be urged to adopt appropriate lifestyle changes in the first instance but additional drug treatment for hypertension is usually required. All the major classes of antihypertensive agents lower blood pressure in Type 2 diabetic patients but have different effects on metabolic risk factors in different ways. Low-dose thiazide diuretics, beta-blockers, calcium channel blockers and angiotensin converting enzyme (ACE) inhibitors have been shown to reduce cardiovascular risk. Individually, the effects of low-dose thiazide diuretics and beta-blockers on glucose and lipid metabolism is clinically insignificant, though in combination much larger metabolic effects are seen. ACE inhibitors and calcium channel blockers have no, or small, beneficial effects on glucose and lipid metabolism, while the greater beneficial effects of alpha1-blockers on lipid profiles may render them especially useful in the Type 2 diabetic patient. Long-acting calcium-channel blockers and ACE inhibitors protect renal function and are suitable as first line therapy in patients with microalbuminuria or proteinuria. Until results from the current batch of randomized, placebo-controlled trials comparing different classes of antihypertensive agents are available, the choice of antihypertensive agent is difficult. Addressing overall cardiovascular risk factors, rather than hypertension alone, is essential in the management of the hypertensive Type 2 diabetic patient.

[The renin-angiotensin system in cardiovascular diseases]

BACKGROUND

The renin-angiotensin system is mainly involved in several cardiovascular diseases and in the pathophysiology of heart failure. It exists as a circulating and a local system which can be differently regulated. Interventions in this system by angiotensin-converting enzyme (ACE) antagonists or angiotensin-receptor antagonists slow the progression of heart failure and result in prolongation of life expectancy and improvement of hemodynamics.

MECHANISMS OF ACTION

The main underlying mechanisms are: 1. Heart failure results in activation of the renin-angiotensin system as a compensatory mechanism with elevation of circulating angiotensin II, norepinephrine and vasopressin. Antagonists of this compensatory mechanisms acutely result in improvement of the hemodynamic situation. 2. Elevated circulating and local renin-angiotensin systems cause chronic structural myocardial and vascular effects. Angiotensin-converting enzyme antagonists and angiotensin-receptor blockers modulate and partly antagonize these structural changes such as myocardial hypertrophy, myocardial fibrosis and vascular proliferative responses. Gene and receptor regulation of the system are currently not fully understood and are subject of intensive research. 3. The renin-angiotensin system is closely related to the bradykinin system and thus indirectly to nitric oxide and endothelial function. Bradykinin has multiple other effects on the hemostatic system as a well as on the myocardium and vascular system.

CONCLUSION

These complex interactions require further evaluation. Research with specific bradykinin antagonists will give new insights into this system.

Regulation of renal renin release

Renal renin release is affected by several systemic and intrarenal factors. Systemic factors include sympathetic nerves, circulating angiotensin II, blood pressure and salt balance of the organism. Intrarenal factors involved are nitric oxide and the prostaglandins, which stimulate renin secretion.

Synergistic effects of combined converting enzyme inhibition and angiotensin II antagonism on blood pressure in conscious telemetered spontaneously hypertensive rats

OBJECTIVE

To investigate the chronic effects of combined administration of an angiotensin II receptor antagonist (valsartan) and an angiotensin converting enzyme inhibitor (benazeprilat) on blood pressure and heart rate in conscious telemetered spontaneously hypertensive rats.

METHODS

Blood pressure and heart rate were monitored (by radiotelemetry) during 2-week infusions of 0.5-10 mg/kg valsartan per day and 0.5-10 mg/kg benazeprilat per day, alone or in combination, into conscious spontaneously hypertensive rats. Also, responses of blood pressure in conscious spontaneously hypertensive rats to exogenous angiotensin I and II were determined.

RESULTS

Synergistic antihypertensive effects were observed when valsartan and benazeprilat were coadministered at submaximal monotherapy doses in the range 0.5-1.5 mg/kg per day. For all combination groups, the area over the curve (mmHg x days) for lowering of blood pressure was significantly greater (synergy) than that predicted from the sum of the monotherapy responses. Combination therapy abrogated pressor responses to angiotensin I more effectively than did comparable doses of the monotherapies.

CONCLUSIONS

These results demonstrate that combination therapy aimed at interrupting operation of the renin-angiotensin system simultaneously at multiple sites can prevent the partial escape which occurs during chronic angiotensin converting enzyme inhibitor monotherapy. Furthermore, multiple-site intervention results in a more efficacious antihypertensive response than that achieved with high doses of the individual monotherapies.