Angiotensin-converting enzyme 2: a key enzyme in key organs

2020 marked the 20th anniversary of the discovery of the angiotensin-converting enzyme 2 (ACE2). This major event that changed the way we see the renin-angiotensin system today could have passed quietly. Instead, the discovery that ACE2 is a major player in the severe acute respiratory syndrome coronavirus 2 pandemic has blown up the literature regarding this enzyme. ACE2 connects the classical arm renin-angiotensin system, consisting mainly of angiotensin II peptide and its AT1 receptor, with a protective arm, consisting mainly of the angiotensin 1-7 peptide and its Mas receptor. In this brief article, we have reviewed the literature to describe how ACE2 is a key protective arm enzyme in the function of many organs, particularly in the context of brain and cardiovascular function, as well as in renal, pulmonary and digestive homeostasis. We also very briefly review and refer to recent literature to present an insight into the role of ACE2 in determining the course of coronavirus diseases 2019.

Nonclassical renin-angiotensin system and renal function

The renin-angiotensin system (RAS) constitutes one of the most important hormonal systems in the physiological regulation of blood pressure through renal and nonrenal mechanisms. Indeed, dysregulation of the RAS is considered a major factor in the development of cardiovascular pathologies, including kidney injury, and blockade of this system by the inhibition of angiotensin converting enzyme (ACE) or blockade of the angiotensin type 1 receptor (AT1R) by selective antagonists constitutes an effective therapeutic regimen. It is now apparent with the identification of multiple components of the RAS within the kidney and other tissues that the system is actually composed of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS can be defined as the ACE-Ang II-AT1R axis that promotes vasoconstriction, water intake, sodium retention, and other mechanisms to maintain blood pressure, as well as increase oxidative stress, fibrosis, cellular growth, and inflammation in pathological conditions. In contrast, the nonclassical RAS composed primarily of the AngII/Ang III-AT2R pathway and the ACE2-Ang-(1-7)-AT7R axis generally opposes the actions of a stimulated Ang II-AT1R axis through an increase in nitric oxide and prostaglandins and mediates vasodilation, natriuresis, diuresis, and reduced oxidative stress. Moreover, increasing evidence suggests that these non-classical RAS components contribute to the therapeutic blockade of the classical system to reduce blood pressure and attenuate various indices of renal injury, as well as contribute to normal renal function.

Angiotensins inhibit cell growth in GH3 lactosomatotroph pituitary tumor cell culture: a possible involvement of the p44/42 and p38 MAPK pathways

The local renin-angiotensin system is present in the pituitary. We investigated the effects of angiotensins on GH3 lactosomatotroph cells proliferation in vitro and the involvement of p44/42 and p38 MAPK inhibitors in the growth-regulatory effects of angiotensins. Materials and Methods. Cell viability using the Mosmann method and proliferation by the measurement of BrdU incorporation during DNA synthesis were estimated. Results. Ang II and ang IV decreased the viability and proliferation of GH3 cells. Inhibitor of p44/42 MAPK attenuated the effects of ang II on cell viability and proliferation but did not affect the ang 5-8-dependent actions. Inhibitor of p38 MAPK prevented the decrease in the number of GH3 cells in ang-II- and ang-IV-treated groups. Conclusions. The growth-inhibitory effect of ang II is possibly mediated by the p44/42 MAPK. The p38 MAPK appears to mediate the inhibitory effects of both ang II and ang 5-8 upon cell survival.

Cross-talk between aldosterone and angiotensin signaling in vascular smooth muscle cells

In hypertension or other forms of cardiovascular disease, the chronic activation of the renin-angiotensin-aldosterone system (RAAS) leads to dysfunction of the vasculature, including, increased vascular tone, inflammation, fibrosis and thrombosis. Cross-talk between the main mediators of the RAAS, aldosterone and angiotensin (Ang) II, participates in the development of this vascular dysfunction. Recent studies have highlighted the molecular mechanisms supporting this cross-talk in vascular smooth muscle cells (VSMCs). Some of the signaling pathways activated by the Ang II type 1 receptor (AT(1)R) are dependent on the mineralocorticoid receptor (MR) and vice versa. VSMC signaling pathways involved in migration and growth are under the control of cross-talk between aldosterone and Ang II. A synergistic mechanism leads to potentiation of signaling pathways activated by each agent. The genomic and non-genomic mechanisms activated by aldosterone cooperate with Ang II to regulate vascular tone and gene expression of pro-inflammatory and pro-fibrotic molecules. This cross-talk is dependent on the non-receptor tyrosine kinase c-Src, and on receptor tyrosine kinases, EGFR and PDGFR, and leads to activation of MAP kinases and growth, migration and inflammatory effects. These new findings will contribute to development of better treatments for conditions in which the RAAS is excessively activated.

Aberrant G-protein coupled receptor expression in relation to adrenocortical overfunction

The aberrant adrenal expression and function of one or several G-protein coupled receptors can lead to cell proliferation and abnormal regulation of steroidogenesis in unilateral adenomas, carcinomas or in ACTH-independent macronodular adrenal hyperplasia (AIMAH). Excess cortisol secretion leading to either sub-clinical or overt Cushing's syndrome is the most prevalent phenotype reported to date. In a few patients, aberrant regulation of androgen excess has been reported. More recently, initial studies suggest that similar mechanisms are involved in the renin-independent regulation of aldosterone secretion in primary aldosteronism. In recent years, cases of familial AIMAH have been identified, and specific aberrant hormone receptors are functional in the adrenal of affected members. The identification of aberrant receptors can offer specific pharmacological approach to prevent disease progression and control abnormal steroidogenesis; alternatively, unilateral or bilateral adrenalectomy remains the treatment of choice.

[The regulators of vascular tonus]

The regulation of vessel function seems to play an important role in maintaining the homeostasis of systemic or organ circulation. Most of all, since it has been clarified that vascular endothelial cells play an important role in adjusting vascular tones recently, endothelial cells have come to be recognized as an essential tissue that produces a variety of vasoactive agents. In this paper, we explained and discussed representative vasoactive agents such as nitric oxide, adenosine, and prostanoid.

Advances in the renin angiotensin system focus on angiotensin-converting enzyme 2 and angiotensin-(1-7)

The contribution of the renin angiotensin system to physiology and pathology is undergoing a rapid reconsideration of its mechanisms from emerging new concepts implicating angiotensin-converting enzyme 2 and angiotensin-(1-7) as new elements negatively influencing the vasoconstrictor, trophic, and pro-inflammatory actions of angiotensin II. This component of the system acts to oppose the vasoconstrictor and proliferative effects on angiotensin II through signaling mechanisms mediated by the mas receptor. In addition, a reduced expression of the vasodepressor axis composed by angiotensin-converting enzyme 2 and angiotensin-(1-7) may contribute to the expression of essential hypertension, the remodeling of heart and renal function associated with this disease, and even the physiology of pregnancy and the development of eclampsia.

Angiotensin modulation of rostral ventrolateral medulla (RVLM) in cardiovascular regulation

The rostral ventrolateral medulla (RVLM) and the presympathetic bulbospinal neurons in this region play a critical role in cardiovascular regulation. However, there is ambiguity regarding the precise anatomical coordinates of the RVLM and much still needs to be learned regarding the regulation and neurochemistry of this region. This brief review discusses some of these issues and focuses on the role of angiotensin-mediated signaling in the RVLM in blood pressure regulation.

Central neural regulation of cardiovascular function by angiotensin: a focus on the rostral ventrolateral medulla

Angiotensin II acts through specific receptors to alter several brain functions including fluid and electrolyte control, neuroendocrine function and autonomic efferent activity. This review discusses one brain site, the rostral ventrolateral medulla, where the actions of angiotensin II have been intensively studied. The rostral ventrolateral medulla plays a critical role in the generation and regulation of sympathetic activity to the cardiovascular system and hence is important for blood pressure control. Current evidence indicates that angiotensin II activates neurons in the rostral ventrolateral medulla via the AT(1A) receptor. In some models of cardiovascular disease, blockade of AT(1) receptors in the rostral ventrolateral medulla reduces sympathetic nerve activity and blood pressure suggesting that overactivity of the angiotensin system in this nucleus may play a role in the maintenance of high blood pressure.

PAI-1 and kidney fibrosis

Substantial evidence demonstrates a link of increased plasminogen activator inhibitor-1 (PAI-1) and glomerulosclerosis and kidney fibrosis, providing a novel therapeutic option for prevention and treatment of chronic kidney diseases. Several mechanisms contributing to increased PAI-1 will be addressed, including classic key profibrotic factors such as the renin-angiotensin-system (RAS) and transforming growth factor-beta (TGF-b???and novel molecules identified by proteomic analysis, such as thymosin- b4. The fibrotic sequelae caused by increased PAI-1 in kidney depend not only on its classic inhibition of tissue-type and urokinase-type plasminogen activators (tPA and uPA), but also its influence on cell migration.

Angiotensinergic regulation of autonomic and neuroendocrine outputs: critical roles for the subfornical organ and paraventricular nucleus

Considerable recent work has focused on identifying the mechanisms through which circulating angiotensin II acts in the central nervous system (CNS) to control a variety of different autonomic and neuroendocrine effectors. The following review will focus on work identifying the subfornical organ (SFO), and its efferent projections to the paraventricular nucleus of the hypothalamus (PVN), as a critical component of the CNS circuitry activated by circulating angiotensin II. It will also summarize the current knowledge describing cellular mechanisms through which this peptide controls the excitability of both SFO and PVN neurons.

Jacques Benoit lecture: the neuroendocrine view of the angiotensin and apelin systems

The hyperactivity of the brain renin-angiotensin system (RAS) has been implicated in the development and maintenance of hypertension in several types of experimental and genetic hypertension animal models. Among the main bioactive peptides of the brain RAS, angiotensin (Ang) II and Ang III display the same affinity for type 1 and type 2 Ang II receptors. Both peptides, injected intracerebroventricularly, similarly increase arginine vasopressin (AVP) release and blood pressure (BP); however, because Ang II is converted in vivo to Ang III, the identity of the true effector is unknown. We review new insights into the predominant role of brain Ang III in the control of BP, underlining the fact that brain aminopeptidase A (APA), the enzyme generating brain Ang III, may therefore be an interesting candidate target for the treatment of hypertension. This justifies the development of potent systemically active APA inhibitors, such as RB150, as prototypes of a new class of antihypertensive agents for the treatment of certain forms of hypertension. We also searched for a putative angiotensin receptor subtype specific for Ang III and isolated a seven transmembrane-domain G protein-coupled receptor corresponding to the receptor for apelin, a newly-discovered peptide isolated from bovine stomach. Apelin and its receptor are expressed in magnocellular vasopressinergic neurones in the hypothalamus. The central injection of apelin in lactating rats decreases the phasic electrical activity of vasopressinergic neurones and the systemic secretion of AVP, inducing water diuresis. Apelin is therefore a natural inhibitor of the antidiuretic effect of AVP. In addition, systemic administration of apelin decreases BP, improves cardiac contractility and reduces cardiac loading. The development of nonpeptide agonists of the apelin receptor may provide new therapeutic tools for treating water retention, hyponatraemia and cardiovascular diseases. Angiotensins and apelin thus exert opposing but complementary effects, and are thereby determinant for the maintenance of body fluid homeostasis and cardiovascular functions.

Selective activation of human atrial Galpha12 and Galpha13 by Galphaq-coupled angiotensin and endothelin receptors

Galphaq-coupled receptors such as alpha1-adrenergic, angiotensin, and endothelin receptors, play key roles in cardiac physiology. These receptors have also been shown to couple to G proteins of the G12 family, including Galpha12 and Galpha13. In this report, we determined whether these G proteins interact with endothelin, angiotensin, and alpha1-adrenergic receptors in the human heart. We find that these receptors activate cardiac Galpha12 and Galpha13 differentially; endothelin receptors activate only Galpha12 (to 218 +/- 22% of unstimulated levels), angiotensin receptors activate only Galpha13 (to 236 +/- 49% of unstimulated levels), and alpha1-adrenergic receptors activate neither Galpha12 (123 +/- 18% of unstimulated levels) nor Galpha13 (113 +/- 12% of unstimulated levels). Consistent with these data, translocation of guanine nucleotide exchange factor p115RhoGEF, which responds to Galpha13, occurs only after stimulation of angiotensin receptors (shifting from 73 +/- 12% to 41 +/- 10% cytosolic). These differences in the activation of Galpha12 and Galpha13 by Galphaq-coupled receptors may underlie reported differences in the functions of these receptors.

Angiotensin blockade as sole treatment for proteinuric kidney disease in children

BACKGROUND

The traditional management of children with proteinuric kidney disease is treatment with high dose steroids regardless of comorbid conditions such as obesity. This study evaluated the effect of angiotensin blockade (AB) alone as the sole management of children with non-diabetic proteinuric kidney disease.

METHODS

Retrospective chart analysis was performed in 146 children. Seventeen were identified to have received angiotensin-converting enzyme inhibitor and/or angiotensin receptor blocker exclusively for management of proteinuria. Total proteinuria (Upr/cr), albuminuria (Ualb/cr), estimated glomerular filtration rate (eGFR), serum potassium and blood pressure were assessed at baseline and at 3-month intervals for over 24 months.

RESULTS

Mean age was 11.2+/-4.8 years with 12 females. Eleven of 17 patients (65%) were overweight or obese. There was a significant decline in total proteinuria and albuminuria after 3-6 months of AB therapy and a further decline with longer duration of treatment (P<0.001). Although single vs dual AB were similarly effective in lowering total proteinuria, dual therapy was more effective in lowering albuminuria (single 57+/-23% vs dual 71+/-15%; P<0.02). The eGFR decreased from 'hyperfiltration' levels prior to initiation of AB to normal at the end of the treatment period (145+/-41-111+/-17 ml/min/1.73 m2; P=0.01). Systemic blood pressures remained normal throughout the study period.

CONCLUSIONS

Angiotensin blockade alone appears to effectively control proteinuria and stabilize kidney function in children. This may provide an alternative to more toxic therapies, especially corticosteroids, in children with glomerular disorders such as those associated with obesity.

Pathophysiology of volume overload in acute heart failure syndromes

The inability to effectively regulate volume status is a major consequence of acute heart failure syndromes (AHFS). A variety of pathophysiologic processes contribute to this impairment, most notably neurohormonal activation of the renin-angiotensin-aldosterone system, arginine vasopressin, and the sympathetic nervous system. As a result, addressing volume overload is one of the most challenging aspects of AHFS management. Neurohormonal activation leads to substantial changes in hemodynamics and myocardial remodeling, which further contribute to the severity of heart failure (HF) disease and thereby cyclically increase the risk of further neurohormonal activation. Pulmonary capillary wedge pressure is a dependable reflection of volume status and has been used as a surrogate marker in recent studies to assess disease progression in response to innovative HF treatment strategies. Future approaches to HF treatment should focus on the more accurate assessment and management of volume status in an effort to improve patient care.

Mass-spectrometric identification of a novel angiotensin peptide in human plasma

OBJECTIVE

Angiotensin peptides play a central role in cardiovascular physiology and pathology. Among these peptides, angiotensin II (Ang II) has been investigated most intensively. However, further angiotensin peptides such as Ang 1-7, Ang III, and Ang IV also contribute to vascular regulation, and may elicit additional, different, or even opposite effects to Ang II. Here, we describe a novel Ang II-related, strong vasoconstrictive substance in plasma from healthy humans and end-stage renal failure patients.

METHODS AND RESULTS

Chromatographic purification and structural analysis by matrix-assisted laser desorption/ionisation time-of-flight/time-of-flight (MALDI-TOF/TOF) revealed an angiotensin octapeptide with the sequence Ala-Arg-Val-Tyr-Ile-His-Pro-Phe, which differs from Ang II in Ala1 instead of Asp1. Des[Asp1]-[Ala1]-Ang II, in the following named Angiotensin A (Ang A), is most likely generated enzymatically. In the presence of mononuclear leukocytes, Ang II is converted to Ang A by decarboxylation of Asp1. Ang A has the same affinity to the AT1 receptor as Ang II, but a higher affinity to the AT2 receptor. In the isolated perfused rat kidney, Ang A revealed a smaller vasoconstrictive effect than Ang II, which was not modified in the presence of the AT2 receptor antagonist PD 123319, suggesting a lower intrinsic activity at the AT1 receptor. Ang II and Ang A concentrations in plasma of healthy subjects and end-stage renal failure patients were determined by matrix-assisted laser desorption/ionisation mass-analysis, because conventional enzyme immunoassay for Ang II quantification did not distinguish between Ang II and Ang A. In healthy subjects, Ang A concentrations were less than 20% of the Ang II concentrations, but the ratio Ang A/Ang II was higher in end-stage renal failure patients.

CONCLUSIONS

Ang A is a novel human strong vasoconstrictive angiotensin-derived peptide, most likely generated by enzymatic transformation through mononuclear leukocyte-derived aspartate decarboxylase. Plasma Ang A concentration is increased in end-stage renal failure. Because of its stronger agonism at the AT2 receptor, Ang A may modulate the harmful effects of Ang II.

[Angiotensin and EGF receptor cross-talk in chronic kidney diseases: towards a new therapeutic approach]

Angiotensin plays a major role in renal deterioration, and inhibition of the renin-angiotensin system slows the progression of renal lesions after nephron reduction both in animal models and in humans with chronic kidney diseases. The EGF receptor (EGFR) has recently been recognized as a key molecule in the progression of chronic renal failure, but the interaction between angiotensin and EGF is poorly understood. We show that transgenic mice harboring a dominant negative form of EGFR are resistant to the progression of renal lesions induced by nephron reduction or angiotensin infusion. TGF-alpha, an EGFR ligand, and its sheddase TACE, are overexpressed after angiotensin infusion, and angiotensin-induced renal lesions are blunted in TGF-alpha knockout mice and by pharmacological TACE blockade. After nephron reduction, angiotensin-converting-enzyme inhibitors and angiotensin receptor antagonists prevent TGF-alpha and TACE accumulation. These results indicate that EGFR transactivation by angiotensin plays a crucial role in renal deterioration and that pharmacological inhibitors of TACE might be useful for preventing the progression of chronic kidney diseases.

The hematopoietic system: a new niche for the renin–angiotensin system

The role of the renin-angiotensin system was previously thought to be restricted to the cardiovascular system. It now appears that this system also has important functions in other tissues. Hematopoiesis can be affected by inhibitors of the renin system in patients and in various experimental models. The renin system, particularly angiotensin II, has a role in different stages of hematopoiesis, notably during the first wave in the chick embryo (primitive hematopoiesis) and in the human adult (definitive hematopoiesis). In addition, the renin-angiotensin system in mice is involved in reconstitutive hematopoiesis following experimental irradiation; inhibition of this system improved the hematopoietic recovery in this situation. The clinical relevance and therapeutic applications of these findings offer a new area of clinical research. In this article, we review the evidence for a role for the renin system in the control of hematopoiesis at its different stages.

Advanced Glycation End Products: A Possible Link to Angiotensin in an Animal Model

Advanced glycation end products (AGEs) have been associated with progressive vascular and renal damage in a variety of pathological conditions such as renal failure and diabetes mellitus. The formation of AGEs is generally attributed to increased oxidative and carbonyl stress or hyperglycemia. Activation of the cellular receptor of AGE (RAGE) leads to subsequent cellular activation and proinflammatory responses. Angiotensin (Ang) produces cellular oxidative stress and similarly promotes end organ damage via its type 1 receptor. We investigated the interrelation between these two systems in a new transgenic rat (TGR) model with Ang II-dependent hypertension and renal damage and in nontransgenic controls. TGR showed increased systolic blood pressure (approximately 210 mmHg), proteinuria, and increased renal collagen I mRNA expression compared with normotensive nontransgenic controls. Immunohistochemical staining of kidney sections showed colocalization for Nepsilon-carboxy(methyl)lysine, RAGE, and NF-kappaB in TGR glomeruli. These features were absent in nontransgenic controls. Our observations suggest a possible link between Ang II-dependent end-organ damage and the AGE/RAGE axis in vivo. TGRs provide an excellent model to study the interrelation between the renin-angiotensin system and the AGE/RAGE axis in promoting cardiovascular end-organ damage, which would otherwise not be possible in humans.

[The renin-angiotensin system]

The history of the renin-angiotensin system goes back to the 19th century. ANG II is still considered to be the most effective component of the RAS. This octapeptide plays an important role in the control of body fluid volume, in blood pressure regulation and in cardiovascular remodeling through the mediation of the direct effects on protein synthesis, on the cell growth and the cell differentiation, on the induction of growth-promoting genes and on the suppression of synthesis of oxygen species, prostanoids and cytokines.

Biosynthesis and physio-pharmacological actions of angiotensin peptides: 1. Synthetic enzymes

The present work introduces a brief review of the actual knowledge concerning the enzymes involved in the biosynthesis of the active angiotensins, followed by a presentation of their main physio-pharmacological actions. The enzymatic pathways that generate active ang. II (1-8) are complemented with data concerning its transformation into angiotensin III (2-8), ang. IV (3-8), ang. V (1-5) and ang. 1-7. Besides the classic renin of renal origin, the tissue isorenins, represented by tonin and cathepsins D and G, inactive angiotensin-I-forming are also reviewed. Furthermore, chymase and the new angiotensin-converting enzyme 2 (ACE2), which generates angiotensin 1-7, having opposite properties from the mother-substance (Ang. II) are discussed at length. The presentation of properties of angiotensin-generating enzymes is followed by the presentation of the action of angiotensinases (aminopetidases, carboxypeptidase and endopeptidases), which are involved both in the generation of biologically active angiotensin peptides and in their inactivation.

[Effector peptides of the brain renin-angiotensin system in central mechanisms of learned and natural forms of drinking behavior in rats]

Central mechanisms of angiotensin involvement in initiation and realization of operant forms of drinking behavior were investigated. It was suggested that intracerebroventricular microinjection of angiotensin-II and angiotensin-IIl specifically affected the learned forms of drinking behavior. The experiments demonstrated that [des-Asp1]-angiotensin-I produced only the natural forms of drinking behavior. Angiotensins modulated specific forms of thirst-associated behavior such as exploring, grooming, and ingestive behavior. Injections of AT1 receptor antagonist losartan were associated with acute water intake decrease and sharp operant behavior inactivation.

Body mass index and angiotensin-dependent control of the renal circulation in healthy humans

Obesity is increasingly recognized as a risk factor for renal disease, but the mechanism is unclear. Renal plasma flow response to captopril, as an index of renin-angiotensin system activity, was measured by para-aminohippurate clearance technique in 100 healthy, normotensive subjects in balance on a high-salt diet. Of the 100 subjects, body mass index exceeded 25 in 56 and exceeded 30 in 22. The average vasodilator response to captopril was 27+/-7 mL/min per 1.73 m2 (P<0.0001). After adjustment for other predictors of the renal plasma flow response to captopril using a multivariate linear regression model, there was a highly significant relationship between age- and plasma renin activity-adjusted body mass index and the renal plasma flow response to captopril; however, a quadratic model provided a substantially better fit (r=0.55; P<0.0001; P=0.03 versus linear correlation). The strong association between increasing body mass index and angiotensin-dependent control of the renal circulation suggests that this may be a mechanism by which obesity contributes to renal disease. Weight loss should be considered in the overweight or obese patient for renal protection.

[Effects of penile vasoactive mediators on the development of erectile dysfunction]

Penile corpus cavernosum can be seen as a special kind of vascular structure. The cause of erectile dysfunction (ED) is often related to the changes of penile vasoactive mediators which modulate the functional conditions of penile erectile tissues. The penile vasoactive mediators including angiotensin and kinins, prostaglandins, endothelins, endothelium-derived hyperpolarizing factors (EDHF), NOS and NO, RhoA/Rho-kinases, etc., may play an important role in the development of ED. Further researches on these mediators can furnish some theoretical evidence for the clinical treatment of ED.

Which is responsible for the haemodynamic response due to laryngoscopy and endotracheal intubation? Catecholamines, vasopressin or angiotensin?

BACKGROUND AND OBJECTIVE

We have investigated the concentrations of epinephrine, norepinephrine, vasopressin and angiotensin converting enzyme activity to explore the role of these mediators in the neuroendocrine response to laryngoscopy and tracheal intubation.

METHODS

One hundred (50 male, 50 female) ASA I patients aged 20-50 yr (mean+/-SEM; 35.59+/-0.99) were included in the study. They were undergoing elective surgery under standard anaesthesia induction and maintenance using tracheal intubation. Plasma concentrations of epinephrine, norepinephrine and vasopressin as well as plasma angiotensin converting enzyme activity were determined at four time points, before (T1) and after (T2) induction, and 2 (T3) and 5 min (T4) after intubation. Blood pressure and heart rate were recorded at corresponding times to reveal if any correlation existed between haemodynamic parameters and neuroendocrine response.

RESULTS

Heart rate increased after induction and intubation (P<0.05) and decreased significantly at T4 (P<0.05). Systolic blood pressure decreased significantly (P<0.05) after induction and increased slightly after intubation decreasing to below baseline value (P<0.05) at T4. Diastolic blood pressure increased slightly after intubation and decreased significantly (P<0.05) at T4. Plasma epinephrine and norepinephrine concentrations decreased after induction and increased at T3 and T4 without reaching significance. Vasopressin concentrations increased slightly at T2 and T3 and decreased significantly at T4 (P<0.05). Angiotensin converting enzyme activity was unaffected when compared with baseline values.

CONCLUSIONS

Blood pressure, heart rate, plasma epinephrine, norepinephrine and vasopressin concentrations increased slightly in response to laryngoscopy and intubation, all returning to or below baseline 5 min later with no change in angiotensin converting enzyme activity in normotensive patients.

Influence of brain angiotensin on thermoregulation and hydromineral balance during pregnancy in rats

During mammalian pregnancy, body temperature decreases and there are changes in fluid and electrolyte balance. Angiotensin signaling mechanisms in the brain have been shown to influence thermoregulation and body fluid balance in the nonpregnant state. We hypothesized that brain angiotensin is also implicated in adjusting these physiological systems in the pregnant rat. We compared core temperature and fluid regulation in three groups of pregnant rats: untreated rats, rats receiving continuous infusion of an AT1 antagonist candesartan (5 μg·kg−1·day−1) into a lateral cerebral ventricle to block brain AT1 receptors, and rats receiving vehicle [artificial cerebrospinal fluid (aCSF)] vehicle. Untreated and aCSF-treated rats showed a decrease in colonic temperature (−0.5 and −0.8°C respectively) by day 20 of gestation. However, rats treated with candesartan had increased colonic temperature compared with baseline (+0.9°C), and their temperature was significantly higher on days 7 ( P < 0.05), 17 ( P < 0.05), and 20 ( P < 0.001) compared with the other groups (aCSF and untreated). Daily food and water intakes and body weight were not different between the three groups. Similarly, litter sizes and pup weights were equal in all groups. Finally, the expected decreases in plasma Na+ and osmolality during pregnancy were equivalent in all groups. This study suggests that brain angiotensin mediates the progressive decrease in body temperature that occurs during pregnancy. However, the changes in fluid balance associated with pregnancy are not dependent on brain angiotensin.

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.

Le système rénine-angiotensine : données actuelles

The renin-angiotensin system (RAS) is a major physiological regulator of vascular tone and is implicated in cardiovascular pathophysiology. More recently, basic research has however continuously extended our understanding of the complexicity of the systemic and tissular RASs. The peptid hormone, angiotensin II, acts primarily via type I (AT1) and type II (AT2) angiotensin receptors. Most, if not all, of the peripheral and central actions of angiotensin II, including vasoconstriction, renal salt and water retention, facilitation of sympathetic transmission, modification of vascular and cardiac structure, oxydative stress stimulation and proinflammatory action were all thought to be mediated by the angiotensin type 1 receptor, AT1. Angiotensin II/III exerts actions through the AT2 receptor, which are directly opposed to those mediated by the AT1 receptor. Most notably, proteolytic fragments of angiotensin II also have biological activity via ther own receptors: angiotensin-(1-7)/AT1-7 and angiotensin IV/AT4. They are vasodilators in many arterial beds. The identification of these angiotensins opens the way to develop new therapeutics.

Hypoxia-driven proliferation of human pulmonary artery fibroblasts: cross-talk between HIF-1alpha and an autocrine angiotensin system

Pulmonary artery adventitial fibroblasts (FBPA) may play a central role in lung vascular remodeling under conditions of hypoxia and inflammation, the result being pulmonary hypertension and cor pulmonale. In cultured human FBPA, both angiotensin II (Ang II) and hypoxia promoted cell cycle progression and cell proliferation and suppressed apoptosis. These effects were further enhanced when both stimuli were applied simultaneously. Hypoxia elevated the expression of hypoxia-inducible factor 1alpha (HIF-1alpha) and increased the expression of genes regulated by the hypoxia-responsive element (HRE). Up-regulation of both angiotensin-converting enzyme (ACE) and Ang II receptor type 1 (AT1) was also observed. Exogenous Ang II further increased HIF/HRE-dependent signaling in FBPA, whereas suppression of the autocrine ACE-Ang II-AT1 loop with inhibitors of ACE, AT1, and phosphatidylinositol 3-kinase (PI3K) reduced the proliferative response to both hypoxia and exogenous Ang II. Overexpression of HIF-1alpha by transient transfection caused the same proliferative effect and up-regulation of AT1 expression that were observed under hypoxic conditions. In contrast, small interfering RNA targeting HIF-1alpha inhibited hypoxia-induced ACE and AT1 expression. Our studies indicate that the ACE-Ang II-AT1 system serves as a positive feedback loop and fosters FBPA proliferation under hypoxic conditions, with the PI3K-HIF-HRE axis as the central effector pathway. This pathway may thus facilitate vascular remodeling under hypoxic conditions.

Angiotensin peptides modulatory system: how is it implicated in the control of seizure susceptibility?

Accumulated studies support the concept that angiotensin peptides, ANG II, ANG III, and ANG IV act as neurotransmitters or neuromodulators in specific neuronal pathways in the brain stem, the hypothalamus, and the forebrain. They have been implicated in the regulation of several physiological processes, particularly in excitable brain structures that express high concentration of their receptors. With the help of pharmacological approaches it was shown that angiotensin peptides appear to be anticonvulsant in a variety of experimental seizure models. Thus, ANG II increases the threshold for pentylenetetrazol (PTZ)-, bicuculline-and picrotoxin-induced seizures in mice. It also attenuates the intensity of clonic seizures evoked by PTZ and 3-mercaptopropionic acid and is effective in the maximal electroshock test. Furthermore, ANG II, ANG III, and ANG IV protect against the clonic convulsions in the PTZ kindling model of epilepsy in mice. From the accumulated results it could be assumed that the angiotensin peptides appear to realize their effects acting directly on their receptors (AT(1), AT(2) and AT(4)) and through close interaction with different neurotransmitter/neuromodulator systems as dopamine (DA)-, gamma-aminobutyric acid (GABA)-and adenosine. This may contribute to a new potential use of angiotensin drugs either alone or in combination with other neuroprotective agents acting through the above mentioned systems, thus providing a more rational strategy for the treatment of neurodegenerative disorders such as epilepsy.

Regulatory and functional interaction of vasoactive factors in the kidney and extracellular pH

A growing body of evidence suggests that vasoactive factors produced in the kidney such as nitric oxide, endothelins, angiotensin, and prostaglandins participate actively in the regulation of acid-base homeostasis under physiologic conditions. In addition, recent reports indicate that alterations in the systemic acid-base status may also influence the generation of vasoactive cytokines in the kidney, which in turn may mediate the renal effector processes that tend to restore normality under such conditions. Metabolic acidosis, which so frequently accompanies many forms of chronic renal failure (CRF), may contribute to down-regulation of intrarenal nitric oxide production that characterizes CRF. Reduced extracellular pH inhibits inducible nitric oxide production in mesangial cells by altering the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) oxidation, an important posttranslational mechanism in the inducible nitric oxide synthase (iNOS) activation. The underlying defects resulting in the uncoupling of NADPH oxidation in acidemic microenvironment are discussed. Acidosis stimulates renal production of endothelins, which mediate proximal tubular acidification by enhancing sodium-hydrogen exchanger-3 (NHE-3) activity. Renal endothelins mediate enhanced urinary acid excretion following dietary acid ingestion, an effect that is effectively blocked by endothelin receptor blockers. Reduced extracellular pH stimulates endothelin secretion from renal microvascular endothelial cells, which may promote enhanced acid excretion from the distal tubule under conditions of acidosis. These phenomena as well as the role of angiotensin and renal prostaglandins in mediating renal acidification in normal and acidotic conditions are discussed in this review, which describe the regulatory interaction between extracellular pH and renal vasoactive factors.

Angiotensin and Bradykinin: Targets for the Treatment of Vascular and Neuro-Glial Pathology in Diabetic Retinopathy

The renin-angiotensin system (RAS) and kallikrein-kinin system (KKS) are complex pathways linked by a number of molecules that participate in both systems. Apart from modulating a variety of normal physiological processes, both the RAS and KKS are up-regulated following tissue injury where they influence vascular function, inflammation, cell growth and differentiation and angiogenesis. The RAS exerts its effects by the generation of a family of bioactive angiotensin peptides in which angiotensin II (ANG II) and the angiotensin type 1 (AT1) and angiotensin type 2 (AT2) receptors are most well characterised. In the KKS, bradykinin (BK) and kallidin and their carboxypeptidase metabolites, des-Arg(9)-BK and des-Arg(10)-kallidin, are the effector peptides exerting their actions via BK type 1 (BK-B1) and BK type 2 (BK-B2) receptors. Emerging evidence suggests that an ocular RAS is activated in diabetic retinopathy and may contribute to progressive alterations to retinal cells such as pericytes, endothelial cells, neurons and glia. Less well studied is the retinal KKS, however recent studies indicate effects on retinal electrophysiology and angiogenesis. The pathogenetic actions of the RAS and KKS in many tissues and possibly the diabetic retina are mediated by specific growth factors such as vascular endothelial growth factor (VEGF) and connective tissue growth factor (CTGF). This review will examine the roles of the RAS and KKS in both retinal vascular and neuro-glial dysfunction in diabetic retinopathy, and the potential of blockade of these systems for the prevention and treatment of this serious diabetic complication.

Diabetes and retinal vascular disorders: role of the renin-angiotensin system

Angiotensin II, the effector peptide of the renin-angiotensin system (RAS), has potent growth factor properties in a variety of organs. In the retina, a complete RAS exists, with components residing in the vasculature, neurons and glia. There is increasing interest in a pathogenetic role for angiotensin II in ischaemic retinopathies such as diabetic retinopathy and retinopathy of prematurity. In these situations, the retinal RAS becomes activated and stimulates growth factors such as vascular endothelial growth factor, which contribute to vascular leakage, pericyte migration, angiogenesis and fibrosis. Blockade of the RAS, with either angiotensin-converting enzyme (ACE) inhibitors or antagonists selective for angiotensin type 1 (AT1) and angiotensin type 2 (AT2) receptors, attenuates many of the vascular abnormalities that develop in diabetic retinopathy and retinopathy of prematurity. Eagerly awaited are the findings of the Diabetic Retinopathy Candesartan Trial (DIRECT), evaluating the effects of AT1 receptor antagonism in patients with different stages of diabetic retinopathy. This review examines the role of the RAS in diabetic retinopathy and retinopathy of prematurity, and the potential of RAS blockade as a treatment strategy for these vision-threatening diseases.

Comparison of the role of endothelin, vasopressin and angiotensin in arterial pressure regulation during sevoflurane anaesthesia in dogs

BACKGROUND

In this study we aimed to clarify the role of endothelin in arterial pressure regulation during anaesthesia with increasing concentrations of sevoflurane (1-3 MAC) and compare it with those of vasopressin and angiotensin.

METHODS

After an awake control period, on different days, six dogs underwent each of the following four interventions: sevoflurane anaesthesia alone (1-3 MAC), sevoflurane after block of either endothelin receptors using tezosentan (3 mg kg(-1) followed by 3 mg kg(-1) h(-1)), vasopressin V(1a) receptors using [d(CH(2))(5)Tyr(Me(2))]AVP (40 micro g kg(--1)) or angiotensin receptors using losartan (6 mg kg(-1) h(-1)). Plasma concentrations of endothelin, big endothelin, vasopressin and renin were measured. Effects of sevoflurane in the presence and absence of the respective receptor block were analysed and compared using analysis of variance for repeated measures (ANOVA followed by Fisher's PLSD (protected least significant difference) (P<0.05)).

RESULTS

Mean arterial pressure decreased in a dose-dependent manner with sevoflurane during all interventions. At 1 MAC, this decrease was greatest during angiotensin receptor block (mean (SEM), -41 (3) mm Hg), intermediate during vasopressin and endothelin receptor block (-31 (4) and -30 (2) mm Hg respectively), and least during sevoflurane alone (-24 (3) mm Hg). The course of systemic vascular resistance mirrored the course of arterial pressure, while cardiac output did not differ between groups. Plasma concentrations of endothelin, big endothelin and renin did not change during any intervention, whereas vasopressin concentration increased from approximately 0.5 to 40 ng litre(-1) at 3 MAC as arterial pressure decreased in all groups.

CONCLUSIONS

At 1 MAC, angiotensin attenuated the decrease in arterial pressure during sevoflurane anaesthesia more than endothelin and vasopressin. However, at higher MAC only vasopressin was specifically activated to partly compensate for the arterial pressure decrease.

What sets the long-term level of sympathetic nerve activity: is there a role for arterial baroreceptors?

Much of our knowledge of the influence of the sympathetic nervous system on the control of blood pressure is built on experimental approaches that focus very much on time scales <24 h. Although direct recordings of sympathetic nerve activity (SNA) over short time scales provide important information, it is difficult to place their relevance over the longer term where the development of chronic changes in blood pressure are likely to be a mixture of hormonal, renal, and neural influences. Recently new experimental approaches are now revealing a possible role for arterial baroreceptors in the chronic regulation of SNA. These studies reveal that chronic increases in blood pressure are associated with chronic changes in SNA that may be due to nonresetting of the blood pressure-SNA baroreflex relationship. This review discusses the implications of such information, highlighting new technologies for long-term recording of SNA that appear to hold much promise for revealing the role of SNA to the kidney for the long-term control of blood pressure.

[Renin-angiotensin system: molecular biology]

Renin-angiotensin system (RAS) have been extensively studied in last few decades. RAS regulates blood pressure, water and electrolytes balance. The disorders in function of RAS may play a potential role in development of some complex diseases like: hypertension, myocardial infarction, stroke, nephropathies and renal failure, chronic obstruction pulmonary disease and many more. RAS may take part in formation and progression of these diseases. In this work we focus on molecular biology of RAS and polymorphisms of RAS genes.

Tissue renin angiotensin systems

The RAAS is a powerful regulator of vascular tone and intravascular volume and of tissue architecture and a variety of other functions. The recent appreciation of the immunoregulatory role of angiotensin II and its possible involvement in the genesis of atherosclerosis and in plaque rupture all speak to the wide-ranging physiologic and pathophysiologic activities of the peptide. So do its actions in fat cell differentiation and in neuromodulation. The system exists in the circulation, and RAASs, whole or partial, exist in many tissues. These systems are regulated at many levels ranging from the synthesis of renin to the dimerization of angiotensin receptors. Regulation occurs in multiple tissues and, as a result, tissue concentrations of angiotensin II and the concentration of other RAS components and their active metabolites can vary independently of the circulating system in these tissues. An RAS seems also to function within certain cells. Therapeutic interventions involving ACEIs and ARBs seem likely to provide benefit at least in part through the interruption of local systems. It is to be expected that with enhanced understanding of the biology of the multiple RASs, new suggestions for therapeutic interventions will be forthcoming.

Effects of the Genetic Polymorphisms of the Renin-Angiotensin System on Focal Segmental Glomerulosclerosis

BACKGROUND/AIMS

We analyzed the influence of angiotensin-converting enzyme (ACE) I/D, angiotensinogen (AGT) M235T and angiotensin-II-type-1 receptor (AT1R) A1166C genetic polymorphisms on the clinical course of focal segmental glomerulosclerosis (FSGS).

METHODS

This study consisted of 71 patients with nephrotic syndrome due to biopsy proven FSGS and 100 healthy controls. According to the slope of the reciprocal serum creatinine (1/Cr, >or= or <-0.1 dl x mg(-1) x year(-1)) patients were classified into group A (slow progressors, n = 50) and group B (fast progressors, n = 21). Genotyping was performed using polymerase chain reaction (PCR).

RESULTS

There were no relevant differences in the allele frequencies of the investigated polymorphisms between patients with FSGS and controls. Patients carrying the T- allele of the AGT polymorphism required a larger number of antihypertensive agents (MM: 1.35 +/- 1.0 vs. MT/TT: 2.0 +/- 1.2, p < 0.05). The ACE-ID/DD genotypes were more frequently found in patients with fast progression (group A: II: 38.0%, ID/DD: 62.0% vs. group B: II: 14.3%, ID/DD: 85.7%, p < 0.05). The AT1R-A1166C polymorphism was not associated with any of the parameters studied.

CONCLUSION

The course of FSGS is in part genetically determined by polymorphisms of the renin-angiotensin-system. The ACE-I/D polymorphism was shown to be a risk factor of progression of renal disease and the AGT-M235T polymorphism was associated with the severity of arterial hypertension.

Adiposity is related to gender differences in impaired stress-induced pressure natriuresis

The purpose of this study was to determine if there are gender differences in stress-induced pressure natriuresis and to examine the effects of adiposity on these differences. The subjects were 151 boys and 141 girls 15 to 18 years of age who underwent a 5-hour stress protocol (2-hour prestress, 1-hour stress, 2-hour poststress) after being brought into similar levels of sodium balance. The gender-by-condition interaction was significant for systolic and diastolic blood pressure (P=0.001 for both), and the effect of condition was significant for sodium excretion (P=0.001). Systolic blood pressure was higher for boys throughout the protocol (P=0.001 for each) and correlated with body mass index at each condition (range in r=0.28 to 0.35; P<0.001 for each). Hemodynamically, in boys body mass index was correlated with cardiac output during stress (r=0.23; P=0.006), which was correlated with systolic blood pressure (r=0.21; P=0.01). With respect to natriuresis, body mass index was inversely correlated with sodium excretion during stress (r=-0.22; P=0.008) and positively correlated with angiotensin II in a subsample of boys (n=89: r=0.31; P=0.003). The inverse correlation between angiotensin II and sodium excretion during stress approached significance (r=-0.17; P<0.06). Similar results were not observed for girls. In conclusion, gender differences in stress-induced pressure natriuresis appear to be related to the influence of adiposity on both blood pressure and natriuresis.