Renin-angiotensin system-mediated nitric oxide signaling in podocytes.

Nitric oxide (NO) is widely recognized for its role in regulating renal function and blood pressure. However, the precise mechanisms by which NO affects renal epithelial cells remain understudied. Our previous research has shown that NO signaling in glomerular podocytes can be initiated by Angiotensin II (ANG II) but not by ATP. This study aims to elucidate the crucial interplay between the renin-angiotensin system (RAS) and NO production in podocytes. To conduct our research, we used cultured human podocytes and freshly isolated rat glomeruli. A variety of RAS peptides were used, alongside confocal microscopy, to detect NO production and NO/Ca2+ cross talk. Dynamic changes in the podocyte cytoskeleton, mediated by RAS-NO intracellular signaling, were observed using fluorescent labeling for F-actin and scanning probe microscopy. The experiments demonstrated that ANG II and ANG III generated high levels of NO by activating the angiotensin II type 2 receptor (AT2R). We did not detect functional MAS receptor presence in podocytes, and the moderate NO response to ANG 1-7 was also mediated through AT2R. Furthermore, NO production impacted intracellular Ca2+ signaling and correlated with an increase in podocyte volume and growth. Scanning probe experiments revealed that AT2R activation and the corresponding NO generation are responsible for the protrusion of podocyte lamellipodia. Taken together, our data indicate that AT2R activation enhances NO production in podocytes and subsequently mediates changes in Ca2+ signaling and podocyte volume dynamics. These mechanisms may play a significant role in both physiological and pathophysiological interactions between the RAS and podocytes.NEW & NOTEWORTHY The renin-angiotensin system plays a crucial role in the production of intracellular nitric oxide within podocytes. This mechanism operates through the activation of the angiotensin II type 2 receptor, leading to dynamic modifications in intracellular calcium levels and the actin filament network. This intricate process is vital for linking the activity of angiotensin receptors to podocyte function.

Local aldosterone release and CYP11B2 expression in response to angiotensin peptides, glucose, and potassium - an ex vivo study on murine colon.

We have previously described local aldosterone synthesis in mouse colon. In the renin-angiotensin-aldosterone system (RAAS), angiotensin II (Ang II) peptide is the physiological factor which stimulates aldosterone synthesis in the adrenal glands. We have recently demonstrated that Ang II stimulates aldosterone synthesis also in mouse colon. Here, we conducted a 75-min ex vivo incubation of murine colonic tissue and evaluated the effects of three other Ang peptides, Ang I (1 µM), Ang III (0.1 µM) and Ang (1-7) (0.1 µM) on aldosterone synthesis. As a possible mechanism, their effects on tissue levels of the rate-limiting enzyme, aldosterone synthase (CYP11B2) were measured by ELISA and Western blot. Ang III significantly elevated the amount of tissue CYP11B2 protein in colon. The values of released aldosterone in colon tissue incubation were increased over the control in the presence of Ang I, II or III, however, being statistically non-significant. In Western blot analysis, the values of tissue CYP11B2 protein content were elevated by Ang I and II. Ang (1-7) alone in colon did not influence CYP11B2 protein levels in the incubation experiment but showed higher aldosterone release without statistical significance. Ang (1-7) showed an antagonistic effect towards Ang II in release of aldosterone in adrenal gland. An overall estimation of a single peptide (three measured variables), the results were always in an increasing direction. The responses of aldosterone synthesis to high levels of glucose (44 mM) and potassium (18.8 mM) as physiological stimulators in vivo were investigated in the colon incubation. Glucose, equal to four times the concentration of the control buffer in the incubation, showed higher values of aldosterone release in colon than control without statistical significance similarly to the effect seen in adrenal glands. Increasing the concentration of potassium in the incubation buffer exerted no effect on colonic aldosterone production. Intriguingly, no correlation was found between aldosterone release and the tissue CYP11B2 protein content in colon. In summary, the response of colonic aldosterone synthesis to different Ang peptides resembles, but is not identical to, the situation in the adrenal glands.

Roles of Angiotensin III in the brain and periphery.

Angiotensin (Ang) III, a biologically active peptide of the renin angiotensin system (RAS) is predominantly known for its central effects on blood pressure. Our understanding of the RAS has evolved from the simplified, classical RAS, a hormonal system regulating blood pressure to a complex system affecting numerous biological processes. Ang II, the main RAS peptide has been widely studied, and its deleterious effects when overexpressed is well-documented. However, other components of the RAS such as Ang III are not well studied. This review examines the molecular and biological actions of Ang III and provides insight into Ang III's potential role in metabolic diseases.

The Level and Significance of Circulating Angiotensin-III in Patients with Coronary Atherosclerosis.

OBJECTIVE: Angiotensin-III (Ang-III) is the downstream product of angiotensin-II (Ang-II) metabolized by aminopeptidase A (APA). At present, the research of Ang-III mainly concentrates on hypertension and the central renin-angiotensin system (RAS). However, few studies have focused on the relationship between Ang-III and coronary atherosclerosis (CAS). METHODS AND RESULTS: Plasma Ang-III and APA levels were measured by the enzyme-linked immunosorbent assay (ELISA) in 44 normal subjects and 84 patients confirmed as having CAS by coronary angiography. Circulating Ang-III levels were significantly lower in patients with CAS than in normal controls (P = 0.013). APA levels were slightly lower in the CAS group (P = 0.324). According to the severity of atherosclerosis, CAS patients were divided into two groups. Compared with the controls, the APA and Ang-III levels were lower in the high scoring group and APA decreased significantly. CONCLUSIONS: Circulating Ang-III levels were reduced in patients with CAS, and the possible reason may be related to the decrease in the APA level.

The C-terminal cleavage of angiotensin II and III is mediated by prolyl carboxypeptidase in human umbilical vein and aortic endothelial cells.

The renin-angiotensin system, with the octapeptide angiotensin II as key player, is important in the renal, cardiac and vascular physiology. Prolyl carboxypeptidase (PRCP), prolyl endopeptidase (PREP) and angiotensin converting enzyme 2 (ACE2) are reported to be involved in the conversion of angiotensin II to angiotensin (1-7). Previous investigations showed that the processing of angiotensin II is cell- and species-specific and little is known about its conversion in human endothelial cells. Therefore, we aimed to investigate the C-terminal processing of angiotensin II and III in comparison to the processing of des-Arg9-bradykinin in human endothelial cells. To this end, human umbilical vein and aortic endothelial cells (HUVEC and HAoEC) were incubated with the peptides for different time periods. Mass spectrometry analysis was performed on the supernatants to check for cleavage products. Contribution of PRCP, ACE2 and PREP to the peptide cleavage was evaluated by use of the selective inhibitors compound 8o, DX600 and KYP-2047. The use of these selective inhibitors revealed that the C-terminal cleavage of angiotensin II and III was PRCP-dependent in HUVEC and HAoEC. In contrast, the C-terminal cleavage of des-Arg9-bradykinin was PRCP-dependent in HUVEC and PRCP- and ACE2-dependent in HAoEC. With this study, we contribute to a better understanding of the processing of peptides involved in the alternative renin-angiotensin system. We conclude that PRCP is the main enzyme for the C-terminal processing of angiotensin peptides in human umbilical vein and aortic endothelial cells. For the first time the contribution of PRCP was investigated by use of a selective PRCP-inhibitor.

The Ang III/AT2R Pathway Enhances Glucose Uptake by Improving GLUT1 Expression in 3T3-L1 Adipocytes.

Angiotensin III (Ang III) is a heptapeptide derived from Ang II that has been confirmed as the preferred agonist of angiotensin II type 2 receptor (AT2R). Recent studies have revealed AT2R mainly exerts anti-inflammation effects. However, the effects of the Ang III/AT2R pathway on adipocytes remain unknown. Here, the effects of Ang III on glucose uptake were examined. The results showed that AT2R expression was upregulated during adipogenesis in 3T3-L1 preadipocytes, whereas AT1R expression was diminished. Also, Ang III (10 nM) significantly increased glucose uptake by 3T3-L1 adipocytes, which was blocked by PD123319, an AT2R blocker, but not by irbesartan, an AT1R blocker. Ang III also induced the expression of glucose transporter type 1 (GLUT1). These stimulatory effects were inhibited by pretreatment with PD123319, but not with irbesartan. Together, these results indicate that Ang III enhances glucose uptake by upregulating GLUT1 expression via AT2R.

Brain ACE2 activation following brain aminopeptidase A blockade by firibastat in salt-dependent hypertension.

In the brain, aminopeptidase A (APA), a membrane-bound zinc metalloprotease, generates angiotensin III from angiotensin II. Brain angiotensin III exerts a tonic stimulatory effect on the control of blood pressure (BP) in hypertensive rats and increases vasopressin release. Blocking brain angiotensin III formation by the APA inhibitor prodrug RB150/firibastat normalizes arterial BP in hypertensive deoxycorticosterone acetate (DOCA)-salt rats without inducing angiotensin II accumulation. We therefore hypothesized that another metabolic pathway of brain angiotensin II, such as the conversion of angiotensin II into angiotensin 1-7 (Ang 1-7) by angiotensin-converting enzyme 2 (ACE2) might be activated following brain APA inhibition. We found that the intracerebroventricular (icv) administration of RB150/firibastat in conscious DOCA-salt rats both inhibited brain APA activity and induced an increase in brain ACE2 activity. Then, we showed that the decreases in BP and vasopressin release resulting from brain APA inhibition with RB150/firibastat were reduced if ACE2 was concomitantly inhibited by MLN4760, a potent ACE2 inhibitor, or if the Mas receptor (MasR) was blocked by A779, a MasR antagonist. Our findings suggest that in the brain, the increase in ACE2 activity resulting from APA inhibition by RB150/firibastat treatment, subsequently increasing Ang 1-7 and activating the MasR while blocking angiotensin III formation, contributes to the antihypertensive effect and the decrease in vasopressin release induced by RB150/firibastat. RB150/firibastat treatment constitutes an interesting therapeutic approach to improve BP control in hypertensive patients by inducing in the brain renin-angiotensin system, hyperactivity of the beneficial ACE2/Ang 1-7/MasR axis while decreasing that of the deleterious APA/Ang II/Ang III/ATI receptor axis.

Hypothalamic Renin-Angiotensin System and Lipid Metabolism: Effects of Virgin Olive Oil versus Butter in the Diet.

The brain renin-angiotensin system (RAS) has been recently involved in the homeostatic regulation of energy. Our goal was to analyse the influence of a diet rich in saturated fatty acids (butter) against one enriched in monounsaturated fatty acids (olive oil) on hypothalamic RAS, and their relationship with the metabolism of fatty acids. Increases in body weight and visceral fat, together with an increase in aminopeptidase A expression and reductions in AngII and AngIV were observed in the hypothalamus of animals fed with the butter diet. In this group, a marked reduction in the expression of genes related to lipid metabolism (LPL, CD36, and CPT-1) was observed in liver and muscle. No changes were found in terms of body weight, total visceral fat and the expression of hepatic genes related to fatty acid metabolism in the olive oil diet. The expressions of LPL and CD36 were reduced in the muscles, although the decrease was lower than in the butter diet. At the same time, the fasting levels of leptin were reduced, no changes were observed in the hypothalamic expression of aminopeptidase A and decreases were noted in the levels of AngII, AngIV and AngIII. These results support that the type of dietary fat is able to modify the hypothalamic profile of RAS and the body energy balance, related to changes in lipid metabolism.

Targeting Brain Aminopeptidase A: A New Strategy for the Treatment of Hypertension and Heart Failure.

The pathophysiology of heart failure (HF) and hypertension are thought to involve brain renin-angiotensin system (RAS) hyperactivity. Angiotensin III, a key effector peptide in the brain RAS, provides tonic stimulatory control over blood pressure (BP) in hypertensive rats. Aminopeptidase A (APA), the enzyme responsible for generating brain angiotensin III, constitutes a potential therapeutic target for hypertension treatment. We focus here on studies of RB150/firibastat, the first prodrug of the specific and selective APA inhibitor EC33 able to cross the blood-brain barrier. We consider its development from therapeutic target discovery to clinical trials of the prodrug. After oral administration, firibastat crosses the gastrointestinal and blood-brain barriers. On arrival in the brain, it is cleaved to generate EC33, which inhibits brain APA activity, lowering BP in various experimental models of hypertension. Firibastat was clinically and biologically well tolerated, even at high doses, in phase I trials conducted in healthy human subjects. It was then shown to decrease BP effectively in patients of various ethnic origins with hypertension in phase II trials. Brain RAS hyperactivity leads to excessive sympathetic activity, which can contribute to HF after myocardial infarction (MI). Chronic treatment with oral firibastat (4 or 8 weeks after MI) has been shown to normalize brain APA activity in mice. This effect is accompanied by a normalization of brain RAS and sympathetic activities, reducing cardiac fibrosis and hypertrophy and preventing cardiac dysfunction. Firibastat may therefore represent a novel therapeutic advance in the clinical management of patients with hypertension and potentially with HF after MI.

Importance of Tyr409 and Tyr414 in constructing the substrate pocket of human aminopeptidase B.

Aminopeptidase B (APB, EC 3.4.11.6) preferentially hydrolyzes basic amino acids of synthetic substrates and requires a physiological concentration of chloride anions for optimal activity. Several amino acid residues of APB responsible for its enzymatic activity have been elucidated. In this study, we further searched for residues critical to its enzymatic activity, especially toward peptide substrates. APB residues Tyr409 (Y409) and Tyr414 (Y414), both of which were critical to its hydrolytic activity toward synthetic substrates, were predicted by molecular modeling to be involved in cleaving peptide substrates via its interaction with amino acids in the P1' cleavage site. Using site-directed mutagenesis, several mutant APBs were prepared. In contrast to synthetic substrates, wild-type and Y409F/Y414F double mutant enzymes showed P1'-dependent cleavage of peptide substrates, indicating that both tyrosine residues were not indispensable for hydrolytic activity toward peptide substrates. Moreover, the Y409F/Y414F double mutant enzyme cleaved peptides with a Pro residue at the P1' site, which is uncommon among the M1 family of aminopeptidases. These results suggested that Tyr409 and Tyr414 of APB play important roles in enzymatic function and characteristic properties of APB via proper formation of the S1' site.

Renal functional effects of the highly selective AT2R agonist, ß-Pro7 Ang III, in normotensive rats.

Recently, we designed a group of peptides by sequential substitution of the naturally occurring α-amino acid throughout the Ang III peptide sequence with the corresponding ß-amino acid. ß-Amino acid substitution at the proline residue of Ang III (ß-Pro7-Ang III) resulted in a highly selective AT2R ligand, demonstrating remarkable selectivity for the AT2R in both binding and functional studies. To provide additional functional evidence for the suitability of ß-Pro7 Ang III as a novel AT2R agonist, we tested effects of acute systemic administration of ß-Pro7-Ang III on renal hemodynamic and excretory function in anesthetized normotensive male and female rats. We also compared the natriuretic effects of acute intrarenal administration of native Ang III and ß-Pro7-Ang III in the presence of systemic AT1R blockade in anesthetized female rats to allow for the differentiation of systemic versus direct intrarenal natriuretic actions of ß-Pro7-Ang III. In both male and female rats, acute systemic administration of ß-Pro7-Ang III elicited renal vasodilatation and natriuresis. Notably, greater renal vasodilatory effects were observed in female versus male rats at the highest dose of ß-Pro7-Ang III administered. Moreover, intra-renal administration of ß-Pro7-Ang III produced significant natriuretic effects in female rats and, like Ang III, evoked AT2R translocation to the apical plasma membrane in renal proximal tubular cells. Taken together, our findings support the use of ß-Pro7-Ang III as a novel AT2R agonist and experimental tool for exploring AT2R function and its potential as a therapeutic target. Furthermore, our findings provide further evidence of a sex-specific influence of AT2R stimulation on renal function.

Angiotensin III induces p38 Mitogen-activated protein kinase leading to proliferation of vascular smooth muscle cells.

BACKGROUND: Mitogen-activated protein kinases (MAPKs) are essential molecular transducers of extracellular stimuli into intracellular responses. MAPKs are crucial in mediating actions of the renin-angiotensin-aldosterone system (RAAS), in particular, functions mediated by Angiotensin (Ang) II, the main biological peptide produced by this system. We have shown that another biologically active heptapeptide Ang III also induces MAPKs in the central nervous system. The ability of Ang III to induce MAPKs in the periphery is unknown and was the focus of this study. METHODS: We determined whether Ang III induced p38 MAPK in vascular smooth cells (VSMCs) isolated from Wistar and spontaneously hypertensive rats (SHRs) and compared these actions to those of Ang II. Further, the role of this MAPK in Ang III-mediated VSMC proliferation was also determined. RESULTS: Both Ang peptides similarly induced p38 MAPK phosphorylation in VSMCs of Wistar VSMCs in a concentration- and time-dependent manner. SHR VSMCs were less sensitive to Ang III, which caused less of an effect on p38 MAPK phosphorylation in these cells. The Ang III effect was specific and occurred by activation of the Ang type 1 (AT1) receptor. The p38 MAPK pathway was also involved in Ang III-induced VSMC growth, as measured by DNA synthesis. CONCLUSIONS: These findings suggest that the p38 MAPK signaling pathway is an important cascade in regulating the actions of Ang III in VSMCs. Most importantly, dysregulation of Ang III actions in these cells are apparent and may contribute to pathological conditions associated with dysfunctions in VSMCS.

Effects of angiotensin III on c-Jun N terminal kinase in Wistar and hypertensive rat vascular smooth muscle cells.

Proliferation of vascular smooth muscle cells (VSMCs) and inflammation are well known actions associated with hypertension. Angiotensin (Ang) II mediates these physiological actions through the c-Jun N terminal Kinase (JNK), mitogen-activated proteins kinase (MAPK) pathway. Ang III effects on this pathway in VSMCs are unknown. The aim of this study was to determine whether Ang III activates JNK MAPK in Wistar VSMCs and determined whether the response was different in spontaneously hypertensive rat (SHR) VSMCs. We also ascertained whether this effect leads to VSMC proliferation. Western blots were used to determine the time and concentration effects of Ang II on JNK MAPK phosphorylation in Wistar VSMCs. Similar studies were conducted for Ang III in Wistar and SHR VSMCs. Both peptides induced JNK phosphorylation in a concentration- and time-dependent manner in Wistar VSMCs. Ang III also increased JNK phosphorylation in a concentration- and time-dependent fashion in SHR VSMCs as well. However, the ability of Ang III to induce JNK MAPK was different in SHR VSMCs as the phosphorylation levels of JNK were significantly higher in Wistar VSMCs as compared to SHR VSMCs at several time points and concentrations. Further, Ang III-mediated DNA synthesis, a measure of VSMC proliferation, occurred through activation of JNK MAPK. This study is the first to show Ang III effects on the JNK MAPK pathway in VSMCs and the role of JNK in Ang III-mediated cellular proliferation. These findings impart key information for the understanding of Ang III functions, especially in VSMCs and possible cardiovascular diseases.

Angiotensin III Induces JAK2/STAT3 Leading to IL-6 Production in Rat Vascular Smooth Muscle Cells.

The Janus kinase-2/ signal transducer and activators of transcription-3 (JAK2/STAT3) pathway and interleukin-6 (IL-6) are pleiotropic signal transduction systems that are responsible for induction of many cytokines and growth factors. It is unknown whether the renin angiotensin aldosterone system (RAAS) peptide, angiotensin (Ang) III induces JAK2/STAT3 and IL-6 in vascular smooth muscle cells (VSMCs). Thus, the purpose of this study was to investigate whether Ang III induces the JAK2/STAT3 pathway leading to IL-6 production in cultured VSMCs isolated from Wistar rats and determine whether differences exist in spontaneously hypertensive rat (SHR) VSMCs. We gauged Ang III's effects on this pathway by measuring its action on STAT3 as well as IL-6 production. Ang III behaved similarly as Ang II in stimulation of STAT3 phosphorylation in Wistar and SHR VSMCs. Moreover, there were no differences in this Ang III effect in SHR versus Wistar VSMCs. In Wistar VSMCs, Ang II and Ang III significantly induced IL-6 protein secretion and mRNA expression. However, IL-6 protein secretions mediated by these peptides were significantly greater in SHR VSMCs. Ang III induced the JAK2/STAT3 pathway, leading to IL-6 protein secretion and IL-6 mRNA expression via actions on AT1Rs. Moreover, the actions of Ang III to induce IL-6 production was dysregulated in SHR VSMCs. These findings suggest that Ang III acts on AT1Rs to induce JAK2/STAT3, leading to an increase in IL-6 in cultured VSMCs. These findings are important in establishing Ang III as an important physiologically relevant peptide in VSMCs.

Levels of angiotensin peptides in healthy and cardiovascular/renal-diseased paediatric population-an investigative review.

The renin-angiotensin-aldosterone system (RAAS) plays a major role in the regulation of blood pressure and homeostasis. Therefore, it is a commonly used target for pharmacotherapy of cardiovascular diseases in adults. However, the efficacy of this pharmacotherapy can only be limitedly derived into children. Comprehensive knowledge of the humoral parameters acting in the paediatric RAAS (e.g. angiotensin I, angiotensin II, angiotensin 1-7, angiotensin III, and angiotensin IV) might facilitate a more effective and rational pharmacotherapy in children. Therefore, this review aims to provide an overview of the maturing RAAS. Out of 925 identified records, 35 publications were classified as relevant. Physiological and pathophysiological concentrations of angiotensin peptides were compiled and categorised according to European Medicines Agency age groups. Age has a major impact on circulating angiotensin I, angiotensin II, and angiotensin 1-7, which is reflected in an age-dependent decrease during childhood. In contrast to data obtained in adults, no gender-related differences in angiotensin levels were identified. The observed increase in peptide concentrations regarding cardiac- and renal-diseased children is influenced by surgical repair, while evidence for a pharmacological impact is conflicting. A comprehensive set of angiotensin I, angiotensin II, and angiotensin 1-7 values from neonates up to adolescents was compiled. Indicating age as a strong effector. However, evidence about potential promising targets of the RAAS like angiotensin III and angiotensin IV is still lacking in children.

Angiotensin III/AT2 Receptor/NHE3 Signaling Pathway in the Proximal Tubules of the Kidney: A Novel Natriuretic and Antihypertensive Mechanism in Hypertension.

See Article Kemp et al.

Defective Renal Angiotensin III and AT2 Receptor Signaling in Prehypertensive Spontaneously Hypertensive Rats.

Background Previous studies demonstrated that angiotensin (Ang) III , not Ang II , is the predominant endogenous agonist for Ang type-2 receptor ( AT 2R)-induced natriuresis in normal rats, and that hypertensive 12-week-old spontaneously hypertensive rats ( SHR ) lack natriuretic responses to Ang III . This study tested whether prehypertensive SHR already have defective Ang III -induced natriuresis and determined possible mechanisms. Methods and Results Female and male normotensive 4-week-old SHR and Wistar Kyoto rats were studied after 24-hour systemic AT 1R blockade. Left kidneys received 30 minute renal interstitial infusions of vehicle followed by Ang III (3.5, 7.0, 14, and 28 nmol/kg per min; each dose for 30 minutes). Right kidneys received vehicle infusions. In 4-week-old Wistar Kyoto rats, renal interstitial Ang III increased urine sodium (Na+) excretion but failed to induce natriuresis in 4-week-old SHR . Renal Ang III levels were similar between Wistar Kyoto rats and SHR , making increased Ang III degradation as a possible cause for defective natriuresis in SHR unlikely. In Wistar Kyoto rats, renal interstitial Ang III induced translocation of AT 2Rs to apical plasma membranes of renal proximal tubule cells. Simultaneously, Ang III induced retraction of the major Na+ transporter Na+-H+ exchanger-3 ( NHE -3) from apical membranes and internalization of Na+/K+ ATP ase ( NKA ) from basolateral membranes of renal proximal tubule cells. Consistent with NHE -3 and NKA retraction, Ang III increased pS er552- NHE -3 and decreased pS er23- NKA . In contrast, in SHR , intrarenal Ang III failed to induce AT 2R translocation, NHE -3 or NKA retraction, pS er552- NHE -3 phosphorylation, or pS er23- NKA dephosphorylation. Conclusions These results indicate impaired Ang III / AT 2R signaling as a possible primary defect in prehypertensive SHR .

Specific Inhibition of Brain Angiotensin III Formation as a New Strategy for Prevention of Heart Failure After Myocardial Infarction.

AIMS: Inhibition of brain angiotensin III by central infusion of aminopeptidase A (APA) inhibitor firibastat (RB150) inhibits sympathetic hyperactivity and heart failure in rats after myocardial infarction (MI). This study evaluated effectiveness of systemic treatment with firibastat compared with AT1R blocker, losartan. METHODS AND RESULTS: MI was induced by ligation of left coronary artery in male Wistar rats. Rats were treated from 1 to 5 weeks after MI in protocol 1 with vehicle, or firibastat at 50 mg/kg/d subcutaneously (s.c.) or 150 mg/kg/d oral, once daily, and in protocol 2, with vehicle, firibastat 150 mg/kg or losartan 50 mg/kg oral twice daily. At 5 weeks, left ventricle function was evaluated by echocardiography and Millar catheter. After MI, rats developed moderate severe heart failure. Both s.c. and oral firibastat inhibited brain APA and attenuated left ventricle dysfunction. Oral firibastat and losartan similarly improved left ventricular end diastolic pressure. However, whereas firibastat improved dP/dtmax, losartan lowered dP/dtmax and left ventricular peak systolic pressure, and increased plasma creatinine by ~50%. On the other hand, losartan more effectively inhibited cardiac fibrosis. CONCLUSION: Inhibition of the brain renin-angiotensin system by oral APA inhibitor is at least as effective as oral AT1R blocker to inhibit cardiac dysfunction after MI but without hypotension or renal dysfunction.

Angiotensinergic Innervation of the Human Right Atrium: Implications for Cardiac Reflexes.

BACKGROUND: The right atrium is densely innervated and provides sensory input to important cardiocirculatory reflexes controlling cardiac output and blood pressure. Its angiotensin (Ang) II-expressing innervation may release Ang II as a neuropeptide cotransmitter to modulate reflexes but has not yet been characterized. METHODS: Intraoperative surgical biopsies from human right atria (n = 7) were immunocytologically stained for Ang II, tyrosine hydroxylase (TH), and synaptophysin (SYN). Tissue angiotensins were extracted and quantified by radioimmunoassay. RESULTS: Angiotensinergic fibers were frequent in epicardial nerves and around vessels with variable TH co-localization (none to >50%/bundle). Fibers were also widely distributed between cardiomyocytes and in the endocardium where they were typically nonvaricose, TH/SYN-negative and usually accompanied by varicose catecholaminergic fibers. In the endocardium, some showed large varicosities and were partially TH or SYN-positive. A few endocardial regions showed scattered nonvaricose Ang fibers ending directly between endothelial cells. Occasional clusters of thin varicose terminals co-localizing SYN or TH were located underneath, or protruded into, the endothelium. Endocardial density of Ang and TH-positive fibers was 30-300 vs. 200-450/mm2. Atrial Ang II, III, and I concentrations were 67, 16, and 5 fmol/g (median) while Ang IV and V were mostly undetectable. CONCLUSIONS: The human right atrium harbors an abundant angiotensinergic innervation and a novel potential source of atrial Ang II. Most peripheral fibers were noncatecholaminergic afferents or preterminal vagal efferents and a minority was presumably sympathetic. Neuronal Ang II release from these fibers may modulate cardiac and circulatory reflexes independently from plasma and tissue Ang II sources.