Intracardiac detection of angiotensinogen and renin: a localized renin-angiotensin system in neonatal rat heart

Maintenance of Cardiac Microenvironmental Homeostasis: A Joint Battle of Multiple Cells

Various cells such as cardiomyocytes, fibroblasts and endothelial cells constitute integral components of cardiac tissue. The health and stability of cardiac ecosystem are ensured by the action of a certain type of cell and the intricate interactions between multiple cell types. The dysfunctional cells exert a profound impact on the development of cardiovascular diseases by involving in the pathological process. In this paper, we introduce the dynamic activity, cell surface markers as well as biological function of the various cells in the heart. Besides, we discuss the multiple signaling pathways involved in the cardiac injury including Hippo/YAP, TGF-β/Smads, PI3K/Akt, and MAPK signaling. The complexity of different cell types poses a great challenge to the disease treatment. By characterizing the roles of various cell types in cardiovascular diseases, we sought to discuss the potential strategies for preventing and treating cardiovascular diseases.

Epigenetic Regulation of Fibroblasts and Crosstalk between Cardiomyocytes and Non-Myocyte Cells in Cardiac Fibrosis

Epigenetic mechanisms and cell crosstalk have been shown to play important roles in the initiation and progression of cardiac fibrosis. This review article aims to provide a thorough overview of the epigenetic mechanisms involved in fibroblast regulation. During fibrosis, fibroblast epigenetic regulation encompasses a multitude of mechanisms, including DNA methylation, histone acetylation and methylation, and chromatin remodeling. These mechanisms regulate the phenotype of fibroblasts and the extracellular matrix composition by modulating gene expression, thereby orchestrating the progression of cardiac fibrosis. Moreover, cardiac fibrosis disrupts normal cardiac function by imposing myocardial mechanical stress and compromising cardiac electrical conduction. This review article also delves into the intricate crosstalk between cardiomyocytes and non-cardiomyocytes in the heart. A comprehensive understanding of the mechanisms governing epigenetic regulation and cell crosstalk in cardiac fibrosis is critical for the development of effective therapeutic strategies. Further research is warranted to unravel the precise molecular mechanisms underpinning these processes and to identify potential therapeutic targets.

The impact of medical therapy on left ventricular strain: Current state and future perspectives

The speckle tracking strain is becoming a frequently used marker of subclinical left ventricular systolic dysfunction. Despite the wide range of data concerning left ventricular strain variability in the general population and its changes in various pathologic conditions, the information about the impact of medical therapy on left ventricle strain is limited. This article provides an analysis of published studies of left ventricle strain changes in response to different agents and combinations of medical therapies used for hypertension and congestive heart failure.

Cardiovascular aspects of the (pro)renin receptor: Function and significance

Cardiovascular diseases (CVDs), including all types of disorders related to the heart or blood vessels, are the major public health problems and the leading causes of mortality globally. (Pro)renin receptor (PRR), a single transmembrane protein, is present in cardiomyocytes, vascular smooth muscle cells, and endothelial cells. PRR plays an essential role in cardiovascular homeostasis by regulating the renin-angiotensin system and several intracellular signals such as mitogen-activated protein kinase signaling and wnt/β-catenin signaling in various cardiovascular cells. This review discusses the current evidence for the pathophysiological roles of the cardiac and vascular PRR. Activation of PRR in cardiomyocytes may contribute to myocardial ischemia/reperfusion injury, cardiac hypertrophy, diabetic or alcoholic cardiomyopathy, salt-induced heart damage, and heart failure. Activation of PRR promotes vascular smooth muscle cell proliferation, endothelial cell dysfunction, neovascularization, and the progress of vascular diseases. In addition, phenotypes of animals transgenic for PRR and the hypertensive actions of PRR in the brain and kidney and the soluble PRR are also discussed. Targeting PRR in local tissues may offer benefits for patients with CVDs, including heart injury, atherosclerosis, and hypertension.

Fibroblast-mediated intercellular crosstalk in the healthy and diseased heart

Cardiac fibroblasts constitute a major cell population in the heart. They secrete extracellular matrix components and various other factors shaping the microenvironment of the heart. In silico analysis of intercellular communication based on single-cell RNA sequencing revealed that fibroblasts are the source of the majority of outgoing signals to other cell types. This observation suggests that fibroblasts play key roles in orchestrating cellular interactions that maintain organ homeostasis but that can also contribute to disease states. Here, we will review the current knowledge of fibroblast interactions in the healthy, diseased, and aging heart. We focus on the interactions that fibroblasts establish with other cells of the heart, specifically cardiomyocytes, endothelial cells and immune cells, and particularly those relying on paracrine, electrical, and exosomal communication modes.

The Tissue Renin-Angiotensin System and Its Role in the Pathogenesis of Major Human Diseases: Quo Vadis?

Evidence has arisen in recent years suggesting that a tissue renin-angiotensin system (tRAS) is involved in the progression of various human diseases. This system contains two regulatory pathways: a pathological pro-inflammatory pathway containing the Angiotensin Converting Enzyme (ACE)/Angiotensin II (AngII)/Angiotensin II receptor type 1 (AGTR1) axis and a protective anti-inflammatory pathway involving the Angiotensin II receptor type 2 (AGTR2)/ACE2/Ang1–7/MasReceptor axis. Numerous studies reported the positive effects of pathologic tRAS pathway inhibition and protective tRAS pathway stimulation on the treatment of cardiovascular, inflammatory, and autoimmune disease and the progression of neuropathic pain. Cell senescence and aging are known to be related to RAS pathways. Further, this system directly interacts with SARS-CoV 2 and seems to be an important target of interest in the COVID-19 pandemic. This review focuses on the involvement of tRAS in the progression of the mentioned diseases from an interdisciplinary clinical perspective and highlights therapeutic strategies that might be of major clinical importance in the future.

The emerging role of angiotensinogen in cardiovascular diseases

Angiotensinogen (AGT) is the unique precursor of all angiotensin peptides. Many of the basic understandings of AGT in cardiovascular diseases have come from research efforts to define its effects on blood pressure regulation. The development of novel techniques targeting AGT manipulation such as genetic animal models, adeno-associated viral approaches, and antisense oligonucleotides made it possible to deeply investigate the relationship between AGT and cardiovascular diseases. In this brief review, we provide contemporary insights into the emerging role of AGT in cardiovascular diseases. In light of the recent progress, we emphasize some newly recognized features and mechanisms of AGT in heart failure, hypertension, atherosclerosis, and cardiovascular risk factors.

Maternal and fetal thyroid dysfunction following porcine reproductive and respiratory syndrome virus2 infection

To better understand the host response to porcine reproductive and respiratory virus-2 (PRRSV2) we evaluated circulating thyroid hormone and associated gene expression in a late gestation challenge model. Pregnant gilts were inoculated at gestation day 85 and fetal samples collected at either 12 or 21 days post-infection (dpi). A subset of fetuses was selected for analysis based on viability and viral load categorized as either uninfected-viable (UNIF), high viral load viable (HV-VIA) or high viral load meconium stained (HV-MEC) and were compared with gestational age matched controls (CON). In dams, circulating levels of total T3 and T4 decreased in the acute period following infection and rebounded by 21 dpi. A similar effect was observed in fetuses, but was largely restricted to HV-VIA and HV-MEC, with minimal decrease noted in UNIF relative to CON at 21 dpi. Gene expression in fetal heart at 12 dpi showed significant decompensatory transcription of thyroid hormone transporters (SLC16A2) and deiodinases (DIO2, DIO3), which was not observed in brain. Correspondingly, genes associated with cell cycle progression (CDK1,2,4) were downregulated in only the heart of highly infected fetuses, while expression of their inhibitor (CDKN1A) was upregulated in both tissues. Finally, expression of genes associated with cardiac stress including CAMKD and AGT were upregulated in the hearts of highly infected fetuses, and a shift in expression of MYH6 to MYH7 was observed in HV-MEC fetuses specifically. Collectively, the results suggest PRRSV2 infection causes a hypothyroid state that disproportionally impacts the fetal heart over the brain.

FGF23-Mediated Activation of Local RAAS Promotes Cardiac Hypertrophy and Fibrosis

Patients with chronic kidney disease (CKD) are prone to developing cardiac hypertrophy and fibrosis, which is associated with increased fibroblast growth factor 23 (FGF23) serum levels. Elevated circulating FGF23 was shown to induce left ventricular hypertrophy (LVH) via the calcineurin/NFAT pathway and contributed to cardiac fibrosis by stimulation of profibrotic factors. We hypothesized that FGF23 may also stimulate the local renin–angiotensin–aldosterone system (RAAS) in the heart, thereby further promoting the progression of FGF23-mediated cardiac pathologies. We evaluated LVH and fibrosis in association with cardiac FGF23 and activation of RAAS in heart tissue of 5/6 nephrectomized (5/6Nx) rats compared to sham-operated animals followed by in vitro studies with isolated neonatal rat ventricular myocytes and fibroblast (NRVM, NRCF), respectively. Uremic rats showed enhanced cardiomyocyte size and cardiac fibrosis compared with sham. The cardiac expression of Fgf23 and RAAS genes were increased in 5/6Nx rats and correlated with the degree of cardiac fibrosis. In NRVM and NRCF, FGF23 stimulated the expression of RAAS genes and induced Ngal indicating mineralocorticoid receptor activation. The FGF23-mediated hypertrophic growth of NRVM and induction of NFAT target genes were attenuated by cyclosporine A, losartan and spironolactone. In NRCF, FGF23 induced Tgfb and Ctgf, which were suppressed by losartan and spironolactone, only. Our data suggest that FGF23-mediated activation of local RAAS in the heart promotes cardiac hypertrophy and fibrosis.

The possible role of gastrointestinal endocrine cells in the pathophysiology of irritable bowel syndrome

The etiology of irritable bowel syndrome (IBS) is unknown, but several factors appear to play a role in its pathophysiology, including abnormalities of the gastrointestinal endocrine cells. The present review illuminates the possible role of gastrointestinal hormones in the pathophysiology of IBS and the possibility of utilizing the current knowledge in treating the disease. Areas covered: Research into the intestinal endocrine cells and their possible role in the pathophysiology of IBS is discussed. Furthermore, the mechanisms underlying the abnormalities in the gastrointestinal endocrine cells in IBS patients are revealed. Expert commentary: The abnormalities observed in the gastrointestinal endocrine cells in IBS patients explains their visceral hypersensitivity, gastrointestinal dysmotility, and abnormal intestinal secretion, as well as the interchangeability of symptoms over time. Clarifying the role of the intestinal stem cells in the pathophysiology of IBS may lead to new treatment methods for IBS.

Angiotensin receptors in Dupuytren's tissue: Implications for the pharnnacological treatment of Dupuytren's disease

The role of Angiotensin II as a pro-fibrotic mediator has been established in models of cardiac, hepatic and renal fibrosis. The administration of Angiotensin-Converting Enzyme (ACE) – inhibitors to these models results in a reduction in the myofibroblast population and collagen synthesis. In rodent excisionat wound-healing experiments, an ACE inhibitor reduced the rate of wound contraction, collagen deposition and angiogenesis. Using immunohistochemistry, the presence of Angiotensin I receptors was identified within tissue samples from patients with Dupuytren's disease. These were found to be co-localised with areas of myofibrobtast expression. This co-localisation has implications for the potential of pharmacological regulation of Dupuytren's disease. Further research is necessary to confirm whether the use of ACE-inhibitors can modulate this disease process, which until now has not been responsive to safe, effective pharmacological treatment.

Dual Alpha2C/5HT1A Receptor Agonist Allyphenyline Induces Gastroprotection and Inhibits Fundic and Colonic Contractility

BACKGROUND

Allyphenyline, a novel α2-adrenoceptor (AR) ligand, has been shown to selectively activate α2C-adrenoceptors (AR) and 5HT1A receptors, but also to behave as a neutral antagonist of α2A-ARs. We exploited this unique pharmacological profile to analyze the role of α2C-ARs and 5HT1A receptors in the regulation of gastric mucosal integrity and gastrointestinal motility.

METHODS

Gastric injury was induced by acidified ethanol in Wistar rats. Mucosal catalase and superoxide dismutase levels were measured by assay kits. The effect of allyphenyline on electrical field stimulation (EFS)-induced fundic and colonic contractions was determined in C57BL/6 mice.

RESULTS

Intracerebroventricularly injected allyphenyline (3 and 15 nmol/rat) dose dependently inhibited the development of mucosal damage, which was antagonized by ARC 239 (α2B/C-AR and 5HT1A receptor antagonist), (S)-WAY 100135 (selective 5HT1A receptor antagonist), and JP-1302 (selective α2C-AR antagonist). This protection was accompanied by significant elevation of mucosal catalase and superoxide dismutase levels. Allyphenyline (10(-9)-10(-5) M) also inhibited EFS-induced fundic contractions, which was antagonized by ARC 239 and (S)-WAY 100135, but not by JP-1302. Similar inhibition was observed in the colon; however, in this case only ARC 239 reduced this effect, while neither selective inhibition of α2C-ARs and 5HT1A receptors nor genetic deletion of α2A- and α2B-ARs influenced it.

CONCLUSIONS

Activation of both central α2C-ARs and 5HT1A receptors contributes to the gastroprotective action of allyphenyline in rats. Its inhibitory effect on fundic contractions is mediated by 5HT1A receptors, but neither α2-ARs nor 5HT1A receptors take part in its inhibitory effect on colonic contractility in mice.

Dietary guidance normalizes large intestinal endocrine cell densities in patients with irritable bowel syndrome

Background/Objectives:

To determine the large intestinal endocrine cell types affected following dietary guidance in patients with irritable bowel syndrome (IBS).

Subjects/Methods:

The study included 13 IBS patients and 13 control subjects. The patients received three sessions of individualized dietary guidance. Both the control subjects and the patients were scheduled for colonoscopies at baseline and again for the patients at 3–9 months after dietary guidance. Biopsy samples were taken from the colon and rectum and were immunostained for all types of large intestinal endocrine cells. The endocrine cells were quantified using computerized image analysis.

Results:

The daily total consumption (mean±s.e.m. values) of fruits and vegetables rich in FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) decreased significantly from 16.2±5.3 g before receiving dietary guidance to 9.2±3.2 g after receiving dietary guidance (P=0.02). In the total colon, the densities of serotonin cells were 46.8±8.9, 10.5±2.1 and 22.6±3.2 cells/mm² in control subjects and in IBS patients before and after receiving dietary guidance, respectively (P=0.007); the corresponding densities of peptide YY cells were 11.6±1.8, 10.8±1.7 and 16.8±2.1 cells/mm², respectively (P=0.06). The cell densities for both serotonin and peptide YY did not change significantly in the rectum. The densities of somatostatin cells in the rectum were 13.5±3.0, 13.2±3.0, and 22.3±3.2 cells/mm² for control subjects and for IBS patients before and after receiving dietary guidance, respectively (P=0.01).

Conclusions:

The densities of the large intestinal endocrine cells tend to normalize following dietary guidance that may have contributed to the improvement of the patients with IBS symptoms.

Effect of dietary management on the gastric endocrine cells in patients with irritable bowel syndrome

Background/objectives:

The gastric endocrine cells in patients with irritable bowel syndrome (IBS) tend to normalize following dietary guidance. The aim of the present study was to identify the gastric endocrine cell types that are changed following such dietary guidance.

Subjects/methods:

Fourteen IBS patients and 14 healthy subjects were included in the study. Patients received three sessions of individual dietary management guidance. Gastroscopy was performed on both the controls and the patients at baseline and then again for the patients at 3–9 months after dietary guidance. Biopsy samples from the corpus and antrum were immunostained for all gastric endocrine cell types. Endocrine cells were quantified by computerized image analysis.

Results:

The densities of the ghrelin cells for the controls and IBS patients before and after dietary guidance were 149.6±36.2 (mean±s.e.m.; 95% confidence interval (CI) 71.3–227.8), 114.5±32.7 and 161.8±37.8 cells/mm², respectively. The densities of the gastrin cells in these groups were 155.8±21.0 (95% CI 110.3–201.2), 159.4±24.3 and 211.6±28.0 cells/mm², respectively; the corresponding densities of serotonin cells in the corpus were 18.2±3.9 (95% CI 9.8–26.6), 10.6±3.4 and 14±2.0 cells/mm² and in the antrum were 44.6±12.2 (95% CI 18.1–71.1), 1.7±0.5 and 14.7±6.3 cells/mm². The densities of the somatostatin cells in the corpus were 40.0±7.7 (95% CI 23.5–56.5), 23.0±3.0 and 37.3±4.2 cells/mm², respectively, and in the antrum were 138.9±22.0 (95% CI 91.4–186.3), 95.6±15.9 and 86.0±16.9 cells/mm², respectively.

Conclusions:

The densities of all of the gastric endocrine cell types changed towards the healthy control values in the IBS patients following a change in food intake.

Changes in the symptom pattern and the densities of large-intestinal endocrine cells following Campylobacter infection in irritable bowel syndrome: a case report

Background

Irritable bowel syndrome (IBS) is a common chronic functional gastrointestinal disorder. Post-infectious IBS (PI-IBS) is a subset of IBS that accounts for a large proportion of IBS patients. The PI-IBS symptoms meet the Rome criteria for IBS with diarrhoea (IBS-D) or IBS with mixed bowel habits (IBS-M). A low-grade inflammation has been reported to occur in PI-IBS. Abnormalities in intestinal endocrine cells have been reported in both sporadic IBS and PI-IBS.

Case presentation

A 20-year-old female with a diagnosis of IBS with constipation (IBS-C), according to Rome III criteria, contracted Campylobacter-induced gastroenteritis, after which her symptom pattern changed to IBS-M. She showed an intestinal low-grade inflammation that was manifested by an increase in the number of intraepithelial and lamina propria leucocytes and lymphocytes and an increase in the density of mast cells in lamina propria. There was also an increase in the density of intestinal serotonin and peptide YY (PYY) cells and a decrease in the density of rectal somatostatin cells. Follow-up of the patient at 4-months post-infection revealed reduction of IBS symptoms and an improvement in her quality of life. However, 6 months following the Campylobacter infection, the patient switched back from IBS-M to IBS-C, probably due to recovery from PI-IBS. The patient was treated with prucalopride, which is serotonin 5HT₄ receptor agonist. Six months later following this treatment, the symptoms were reduced and the quality of life improved in the reported patient.

Conclusions

Gastroenteritis in patients with IBS-C causes a post-infectious, low-grade inflammation. Interaction between immune-cells and intestinal endocrine cells increases the density of certain endocrine cells, which in turn might be responsible for the change in the symptom pattern, the milder symptoms and the improvement in the quality of life seen in the reported patient. The findings in this case raise the question as to whether intestinal infections are responsible for the previously reported switching of IBS from one subtype to another over time.

Serotonin signalling in the gut--functions, dysfunctions and therapeutic targets

Serotonin (5-HT) has been recognized for decades as an important signalling molecule in the gut, but it is still revealing its secrets. Novel gastrointestinal functions of 5-HT continue to be discovered, as well as distant actions of gut-derived 5-HT, and we are learning how 5-HT signalling is altered in gastrointestinal disorders. Conventional functions of 5-HT involving intrinsic reflexes include stimulation of propulsive and segmentation motility patterns, epithelial secretion and vasodilation. Activation of extrinsic vagal and spinal afferent fibres results in slowed gastric emptying, pancreatic secretion, satiation, pain and discomfort, as well as nausea and vomiting. Within the gut, 5-HT also exerts nonconventional actions such as promoting inflammation and serving as a trophic factor to promote the development and maintenance of neurons and interstitial cells of Cajal. Platelet 5-HT, originating in the gut, promotes haemostasis, influences bone development and serves many other functions. 5-HT3 receptor antagonists and 5-HT4 receptor agonists have been used to treat functional disorders with diarrhoea or constipation, respectively, and the synthetic enzyme tryptophan hydroxylase has also been targeted. Emerging evidence suggests that exploiting epithelial targets with nonabsorbable serotonergic agents could provide safe and effective therapies. We provide an overview of these serotonergic actions and treatment strategies.

Evidence for a role of an intracardiac renin-angiotensin system in normal and failing hearts

Although substantial evidence of a cardiac RAS has been obtained in the past decade, a number of important questions remain unanswered. These include identification and localization of the cell types responsible for production of the system's components as well as the regulation of synthesis, storage, and secretion pathways for each component. Future studies, which will utilize tools of molecular biology that have become recently available (for example, transgenic animal models), renin inhibitors, angiotensin receptor antagonists, and bradykinin antagonists, will help to elucidate specific roles of the cardiac RAS in normal and failing hearts.

Roles of Non-cholinergic Intrapancreatic Nerves, Serotonergic Nerves, on Pancreatic Exocrine Secretion in the Isolated Perfused Rat Pancreas

It has been rereported that axons which display 5-hydroxytryptamine (5-HT) immunoreactivity are abundant in the pancreas and the majority of serotonergic axons terminate within intrapancreatic ganglia, islet and acini. This histological result strongly suggests that intrapancreatic serotonergic nerves could affect to the pancreatic endocrine and exocrine secretion. Thus, this study was aimed to investigate whether intrapancreatic serotonergic nerves could affect pancreatic exocrine secretion and an action mechanism of the intrapancreatic serotonergic nerves. The rats were anesthetized with a single injection of urethane. The median line and the abdominal aorta was carefully dissected and cannulated with PE-50 tubing just above the celiac artery, and then tightly ligated just below the superior mesenteric artery. The pancreatic duct was also cannulated with Tygon microbore tubing. With the addition of serotonin, pancreatic volume flow and amylase output were significantly inhibited electrical field stimulation (EFS). On the other hand, pancreatic volume flow and amylase output were significantly elevated in EFS with the addition of spiperone. EFS application, however, pancreatic volume flow and amylase output had no significant change in cholecystokinin (CCK) alone when serotonin was applied under a 5.6 mM glucose background. Pancreatic volume flow and amylase output under 18 mM glucose background were significantly elevated in CCK plus serotonin than in CCK alone. These data suggest that intrapancreatic serotonergic nerves play an inhibitory role in pancreatic exocrine secretion and an important role in the insulin action or release.

Extra-adrenal glucocorticoids and mineralocorticoids: evidence for local synthesis, regulation, and function

Glucocorticoids and mineralocorticoids are steroid hormones classically thought to be secreted exclusively by the adrenal glands. However, recent evidence has shown that corticosteroids can also be locally synthesized in various other tissues, including primary lymphoid organs, intestine, skin, brain, and possibly heart. Evidence for local synthesis includes detection of steroidogenic enzymes and high local corticosteroid levels, even after adrenalectomy. Local synthesis creates high corticosteroid concentrations in extra-adrenal organs, sometimes much higher than circulating concentrations. Interestingly, local corticosteroid synthesis can be regulated via locally expressed mediators of the hypothalamic-pituitary-adrenal (HPA) axis or renin-angiotensin system (RAS). In some tissues (e.g., skin), these local control pathways might form miniature analogs of the pathways that regulate adrenal corticosteroid production. Locally synthesized glucocorticoids regulate activation of immune cells, while locally synthesized mineralocorticoids regulate blood volume and pressure. The physiological importance of extra-adrenal glucocorticoids and mineralocorticoids has been shown, because inhibition of local synthesis has major effects even in adrenal-intact subjects. In sum, while adrenal secretion of glucocorticoids and mineralocorticoids into the blood coordinates multiple organ systems, local synthesis of corticosteroids results in high spatial specificity of steroid action. Taken together, studies of these five major organ systems challenge the conventional understanding of corticosteroid biosynthesis and function.

Angiotensin-(1-9) regulates cardiac hypertrophy in vivo and in vitro

BACKGROUND

Angiotensin-(1-9) is present in human and rat plasma and its circulating levels increased early after myocardial infarction or in animals treated with angiotensin-converting enzyme inhibitor. However, the cardiovascular effects of this peptide are unknown.

OBJECTIVE

To determine whether angiotensin-(1-9) is a novel anti-cardiac hypertrophy factor in vitro and in vivo and whether this peptide is involved in the pharmacological effects of cardiovascular drugs acting on the renin-angiotensin system.

METHODS AND RESULTS

The administration of angiotensin-(1-9) to myocardial infarcted rats by osmotic minipumps (450 ng/kg per min, n = 6) vs. vehicle (n = 8) for 2 weeks decreased plasma angiotensin II levels, inhibited angiotensin-converting enzyme activity and also prevented cardiac myocyte hypertrophy. However, cardiac myocyte hypertrophy attenuation triggered by angiotensin-(1-9) was not modified with the simultaneous administration of the angiotensin-(1-7) receptor antagonist A779 (100 ng/kg per min, n = 6). In experiments in vitro with cultured cardiac myocytes incubated with norepinephrine (10 micromol/l) or with insulin-like growth factor-1 (10 nmol/l), angiotensin-(1-9) also prevented hypertrophy. In other experimental setting, myocardial infarcted rats (n = 37) were randomized to receive either vehicle (n = 12), enalapril (10 mg/kg per day, n = 12) or angiotensin II receptor blocker candesartan (10 mg/kg per day, n = 13) for 8 weeks. Both drugs prevented left ventricle hypertrophy and increased plasma angiotensin-(1-9) levels by several folds. Angiotensin-(1-9) levels correlated negatively with different left ventricular hypertrophy markers even after adjustment for blood pressure reduction.

CONCLUSION

Angiotensin-(1-9) is an effective and a novel anti-cardiac hypertrophy agent not acting via the Mas receptor.

Diabetic cardiomyopathy

Diabetic cardiomyopathy is a distinct primary disease process, independent of coronary artery disease, which leads to heart failure in diabetic patients. Epidemiological and clinical trial data have confirmed the greater incidence and prevalence of heart failure in diabetes. Novel echocardiographic and MR (magnetic resonance) techniques have enabled a more accurate means of phenotyping diabetic cardiomyopathy. Experimental models of diabetes have provided a range of novel molecular targets for this condition, but none have been substantiated in humans. Similarly, although ultrastructural pathology of the microvessels and cardiomyocytes is well described in animal models, studies in humans are small and limited to light microscopy. With regard to treatment, recent data with thiazoledinediones has generated much controversy in terms of the cardiac safety of both these and other drugs currently in use and under development. Clinical trials are urgently required to establish the efficacy of currently available agents for heart failure, as well as novel therapies in patients specifically with diabetic cardiomyopathy.

Diabetic cardiomyopathy--a distinct disease?

Diabetic individuals have a significantly increased likelihood of developing cardiovascular disease. Whilst part of this association is explained by the presence of concomitant risk factors, large epidemiological studies have consistently reported diabetes as a strong risk factor for the development of heart failure after adjusting for such covariates. This has resulted in the notion that there is a distinct cardiomyopathy specific to diabetes, termed 'diabetic cardiomyopathy'. The natural history is characterized by a latent subclinical period, during which there is evidence of diastolic dysfunction and left ventricular hypertrophy, before overt clinical deterioration and systolic failure ensue. These clinical findings have been supported by a growing body of experimental data which support the notion that diabetes inflicts a direct insult to the myocardium, with cellular, structural and functional changes manifest as the diabetic myocardial phenotype. Several of these mechanisms appear to work in unison, forming complicated reciprocal pathways of disease. Reactive oxygen species and alterations in intracellular calcium homeostasis appear to play significant roles in many of these mechanisms. Determining the hierarchy of this cascade of disease will allow identification of the pathological trigger most responsible for disease. Translational research in this field is currently hindered by a lack of clinical studies and intervention trials specifically in patients with diabetic cardiomyopathy. Future clinical and experimental studies of accurate models of diabetic cardiomyopathy should help to define the true aetiology and lead to the development of specific pharmacotherapies for this condition, ultimately reducing the increased cardiovascular morbidity and mortality in diabetic patients.

Stretch-induced regulation of angiotensinogen gene expression in cardiac myocytes and fibroblasts: opposing roles of JNK1/2 and p38alpha MAP kinases

The cardiac renin-angiotensin system (RAS) has been implicated in mediating myocyte hypertrophy, remodeling, and fibroblast proliferation in the hemodynamically overloaded heart. However, the intracellular signaling mechanisms responsible for regulation of angiotensinogen (Ao), a substrate of the RAS system, are largely unknown. Here we report the identification of JNK1/2 as a negative, and p38alpha as a major positive regulator of Ao gene expression. Isolated neonatal rat ventricular myocytes (NRVM) and fibroblasts (NRFB) plated on deformable membranes coated with collagen IV, were exposed to 20% equiaxial static-stretch (0-24 h). Mechanical stretch initially depressed Ao gene expression (4 h), whereas after 8 h, Ao gene expression increased in a time-dependent manner. Blockade of JNK1/2 with SP600125 increased basal Ao gene expression in NRVM (10.52+/-1.98 fold, P<0.001) and NRFB (13.32+/-2.07 fold, P<0.001). Adenovirus-mediated expression of wild-type JNK1 significantly inhibited, whereas expression of dominant-negative JNK1 and JNK2 increased basal and stretch-mediated (24 h) Ao gene expression, showing both JNK1 and JNK2 to be negative regulators of Ao gene expression in NRVM and NRFB. Blockade of p38alpha/beta by SB202190 or p38alpha by SB203580 significantly inhibited stretch-induced (24 h) Ao gene expression, whereas expression of wild-type p38alpha increased stretch-induced Ao gene expression in both NRVM (8.41+/-1.50 fold, P<0.001) and NRFB (3.39+/-0.74 fold, P<0.001). Conversely, expression of dominant-negative p38alpha significantly inhibited stretch response. Moreover, expression of constitutively active MKK6b (E) significantly stimulated Ao gene expression in the absence of stretch, indicating that p38 activation alone is sufficient to induce Ao gene expression. Taken together p38alpha was demonstrated to be a positive regulator, whereas JNK1/2 was found to be a negative regulator of Ao gene expression. Prolonged stretch diminished JNK1/2 activation, which was accompanied by a reciprocal increase in p38 activation and Ao gene expression. This suggests that a balance in JNK1/2 and p38alpha activation determines the level of Ao gene expression in myocardial cells.

Angiotensin II: a hormone involved in and contributing to pro-hypertrophic cardiac networks and target of anti-hypertrophic cross-talks

Angiotensin II (Ang II) plays a major role in the progression of myocardial hypertrophy to heart failure. Inhibiting the angiotensin converting enzyme (ACE) or blockade of the corresponding Ang II receptors is used extensively in clinical practice, but there is scope for refinement of this mode of therapy. This review summarizes the current understanding of the direct effects of Ang II on cardiomyocytes and then focus particularly on interaction of components of the renin-angiotensin system with other hormones and cytokines. New findings described in approximately 400 papers identified in the PubMed database and published during the 2.5 years are discussed in the context of previous relevant literature. The cardiac action of Ang II is influenced by the activity of different isoforms of ACE leading to different amounts of Ang II by comparison with other angiotensinogen-derived peptides. The effect of Ang II is mediated by at least two different AT receptors that are differentially expressed in cardiomyocytes from neonatal, adult and failing hearts. The intracellular effects of Ang II are influenced by nitric oxide (NO)/cGMP-dependent cross talk and are mediated by the release of autocrine factors, such as transforming growth factor (TGF)-beta1 and interleukin (IL)-6. Besides interactions with cytokines, Ang II is involved in systemic networks including aldosterone, parathyroid hormone and adrenomedullin, which have their own effects on cardiomyocytes that modify, amplify or antagonize the primary effect of Ang II. Finally, hyperinsulemia and hyperglycaemia influence Ang II-dependent processes in diabetes and its cardiac sequelae.

Serotonin pharmacology in the gastrointestinal tract: a review

Serotonin (5-hydroxytryptamine or 5-HT) plays a critical physiological role in the regulation of gastrointestinal (GI) function. 5-HT dysfunction may also be involved in the pathophysiology of a number of functional GI disorders, such as chronic constipation, irritable bowel syndrome and functional dyspepsia. This article describes the role of 5-HT in the enteric nervous system (ENS) of the mammalian GI tract and the receptors with which it interacts. Existing serotonergic therapies that have proven effective in the treatment of GI functional disorders and the potential of drugs currently in development are also highlighted. Advances in our understanding of the physiological and pathophysiological roles of 5-HT in the ENS and the identification of selective receptor ligands bodes well for the future development of more efficacious therapies for patients with functional GI disorders.

High-glucose-induced regulation of intracellular ANG II synthesis and nuclear redistribution in cardiac myocytes

The prevailing paradigm is that cardiac ANG II is synthesized in the extracellular space from components of the circulating and/or local renin-angiotensin system. The recent discovery of intracrine effects of ANG II led us to determine whether ANG II is synthesized intracellularly in neonatal rat ventricular myocytes (NRVM). NRVM, incubated in serum-free medium, were exposed to isoproterenol or high glucose in the absence or presence of candesartan, which was used to prevent angiotensin type 1 (AT1) receptor-mediated internalization of ANG II. ANG II was measured in cell lysates and the culture medium, which represented intra- and extracellularly synthesized ANG II, respectively. Isoproterenol increased ANG II concentration in cell lysates and medium of NRVM in the absence or presence of candesartan. High glucose markedly increased ANG II synthesis only in cell lysates in the absence and presence of candesartan. Western analysis showed increased intracellular levels of angiotensinogen, renin, and chymase in high-glucose-exposed cells. Confocal immunofluorocytometry confirmed the presence of ANG II in the cytoplasm and nucleus of high-glucose-exposed NRVM and along the actin filaments in isoproterenol-exposed cells. ANG II synthesis was dependent on renin and chymase in high-glucose-exposed cells and on renin and angiotensin-converting enzyme in isoproterenol-exposed cells. In summary, the site of ANG II synthesis, intracellular localization, and the synthetic pathway in NRVM are stimulus dependent. Significantly, NRVM synthesized and retained ANG II intracellularly, which redistributed to the nucleus under high-glucose conditions, suggesting a role for an intracrine mechanism in diabetic conditions.

Role of cardiac overexpression of ANG II in the regulation of cardiac function and remodeling postmyocardial infarction

ANG II has a clear role in development of cardiac hypertrophy, fibrosis, and dysfunction. It has been difficult, however, to determine whether these actions are direct or consequences of its systemic hemodynamic effects in vivo. To overcome this limitation, we used transgenic mice with cardiac-specific expression of a transgene fusion protein that releases ANG II from cardiomyocytes (Tg-ANG II-cardiac) without involvement of the systemic renin-angiotensin system and tested whether increased cardiac ANG II accelerates remodeling and dysfunction postmyocardial infarction (MI), whereas those mice show no evidence of cardiac hypertrophy under the basal condition. Male 12- to 14-wk-old Tg-ANG II-cardiac mice and their wild-type littermates (WT) were subjected to sham-MI or MI by ligating the left anterior descending coronary artery for 8 wk. Cardiac ANG II levels were approximately 10-fold higher in Tg-ANG II-cardiac mice than their WT, whereas ANG II levels in plasma and other tissues did not differ between strains. Systolic blood pressure and heart rate were similar between groups with or without MI. In sham-MI, Tg-ANG II-cardiac mice had increased collagen deposition and decreased capillary density. The differences between strains became more pronounced after MI. Although cardiac function was well preserved in the Tg-ANG II-cardiac mice with sham-MI, cardiac remodeling and dysfunction post-MI were more severe than WT. Our results demonstrate that, independent of systemic hemodynamic effects, cardiac ANG II may act locally in the heart, causing interstitial fibrosis in sham-MI and accelerating deterioration of cardiac dysfunction and remodeling post-MI.

EFFECT OF HIGH SALT INTAKE ON LOCAL RENIN-ANGIOTENSIN SYSTEM AND VENTRICULAR DYSFUNCTION FOLLOWING MYOCARDIAL INFARCTION IN RATS

1. This study was performed to evaluate the effect of chronic high salt intake on local cardiac and renal components of the renin-angiotensin system (RAS) and its impact on cardiac remodelling and function after myocardial infarction (MI). 2. Rats submitted to coronary artery ligation to produce MI or sham operation (SO) were randomized to receive 1% NaCl solution or tap water as drinking water for 4 weeks. Plasma renin activity (PRA) and angiotensin-converting enzyme (ACE) activity were quantified. Tissue angiotensin (Ang) II and ACE activity were determined by ELISA and a fluorimetric assay, respectively. Renal and cardiac AT(1) and AT(2) receptor protein levels were quantified by western blot. 3. Independent of the lower PRA levels, MI promoted a significant increase in the left ventricular/bodyweight ratio and impaired cardiac function. The cardiac RAS was activated after MI with a significant increase in ACE activity, AngII and AT(1) receptor levels. The RAS was slightly attenuated under high-salt conditions. 4. Interestingly, high salt intake increased the expression of the AT(2) receptor by approximately twofold in the kidney of MI rats compared with the SO control group. Because of its natriuretic effect, the AT(2) receptor may counterbalance the salt overload and prevent the additional impairment of cardiac function. 5. The present study indicates that 4 weeks after MI, high salt intake did not further increase cardiac hypertrophy or further impair cardiac function in MI rats. A chronic increase in salt intake significantly suppressed PRA, but did not prevent activation of the local RAS or the progression of cardiac remodelling and left ventricular dysfunction caused by MI. 6. The present results show that inhibition of systemic renin production with salt overload does not affect ventricular remodelling after MI in rats. This suggests that local activation of the RAS in the heart, which was not suppressed by salt overload, exerts a predominant role for local adaptations of the heart after MI.

Sumatriptan is an agonist at 5-HT receptors on myenteric neurones in the guinea-pig gastric antrum

Sumatriptan, a 5-hydroxytryptamine(1D) (5-HT(1D))-receptor agonist used in the treatment in migraine, inhibits gastric motility via the enteric nervous system. As no studies have reported enteric neuronal 5-HT(1D) receptors, we used conventional intracellular recordings to characterize the actions of sumatriptan on 145 guinea-pig antral myenteric neurones. In 24 of 29 neurones with a 5-HT(1P) receptor-mediated depolarizing response to 5-HT, application of sumatriptan caused a dose-dependent depolarization, accompanied by increased membrane resistance and enhanced excitability. Depolarizing responses to sumatriptan occurred both in cholinergic and in nitrergic neurones. Sumatriptan did not mimic the 5-HT(3) receptor-mediated fast-depolarizing responses or 5-HT(1A) receptor-mediated inhibitory responses to 5-HT. Sumatriptan had no effect on neurones not responding to 5-HT. The depolarizing response to sumatriptan was inhibited by renzapride, but not by 5-HT(1-7) receptor antagonists. We conclude that sumatriptan behaves as an agonist at the 5-HT(1P) receptor on myenteric neurones in the guinea-pig gastric antrum. The actions of sumatriptan on gastric motility seem to be attributable to a direct action on enteric neurones.

TRPC3 and TRPC6 are essential for angiotensin II-induced cardiac hypertrophy

Angiotensin (Ang) II participates in the pathogenesis of heart failure through induction of cardiac hypertrophy. Ang II-induced hypertrophic growth of cardiomyocytes is mediated by nuclear factor of activated T cells (NFAT), a Ca(2+)-responsive transcriptional factor. It is believed that phospholipase C (PLC)-mediated production of inositol-1,4,5-trisphosphate (IP(3)) is responsible for Ca(2+) increase that is necessary for NFAT activation. However, we demonstrate that PLC-mediated production of diacylglycerol (DAG) but not IP(3) is essential for Ang II-induced NFAT activation in rat cardiac myocytes. NFAT activation and hypertrophic responses by Ang II stimulation required the enhanced frequency of Ca(2+) oscillation triggered by membrane depolarization through activation of DAG-sensitive TRPC channels, which leads to activation of L-type Ca(2+) channel. Patch clamp recordings from single myocytes revealed that Ang II activated DAG-sensitive TRPC-like currents. Among DAG-activating TRPC channels (TRPC3, TRPC6, and TRPC7), the activities of TRPC3 and TRPC6 channels correlated with Ang II-induced NFAT activation and hypertrophic responses. These data suggest that DAG-induced Ca(2+) signaling pathway through TRPC3 and TRPC6 is essential for Ang II-induced NFAT activation and cardiac hypertrophy.

Restoration of diabetes-induced abnormal local Ca2+ release in cardiomyocytes by angiotensin II receptor blockade

Stimulation of local renin-angiotensin system and increased levels of oxidants characterize the diabetic heart. Downregulation of ANG II type 1 receptors (AT(1)) and enhancement in PKC activity in the heart point out the role of AT(1) blockers in diabetes. The purpose of this study was to evaluate a potential role of an AT(1) blocker, candesartan, on abnormal Ca(2+) release mechanisms and its relationship with PKC in the cardiomyocytes from streptozotocin-induced diabetic rats. Cardiomyocytes were isolated enzymatically and then incubated with either candesartan or a nonspecific PKC inhibitor bisindolylmaleimide I (BIM) for 6-8 h at 37 degrees C. Both candesartan and BIM applied on diabetic cardiomyocytes significantly restored the altered kinetic parameters of Ca(2+) transients, as well as depressed Ca(2+) loading of sarcoplasmic reticulum, basal Ca(2+) level, and spatiotemporal properties of the Ca(2+) sparks. In addition, candesartan and BIM significantly antagonized the hyperphosphorylation of cardiac ryanodine receptor (RyR2) and restored the depleted protein levels of both RyR2 and FK506 binding protein 12.6 (FKBP12.6). Furthermore, candesartan and BIM also reduced the increased PKC levels and oxidized protein thiol level in membrane fraction of diabetic rat cardiomyocytes. Taken together, these data demonstrate that AT(1) receptor blockade protects cardiomyocytes from development of cellular alterations typically associated with Ca(2+) release mechanisms in diabetes mellitus. Prevention of these alterations by candesartan may present a useful pharmacological strategy for the treatment of diabetic cardiomyopathy.

Renin increments the inward calcium current in the failing heart

BACKGROUND

Evidence is available that activation of the renin-angiotensin system is involved in cardiac remodeling. It is unknown whether renin can change the inward calcium current (ICa) in the failing heart. This problem was investigated in the present study.

METHODS

Cardiomyocytes were isolated from the ventricle of 4-month-old cardiomyopathic hamsters and measurements of the L-type ICa were performed using the patch-clamp technique in a whole-cell configuration.

RESULTS

Extracellular renin (128 pmol Ang I/ml per min) plus angiotensinogen (110 pmol angiotensin I generated by renin to exhaustion) incremented the peak ICa density significantly, an effect suppressed by enalapril maleate (10 mol/l) or by losartan (10 mol/l) added to the bath, indicating that the effect of renin plus angiotensinogen was related to the formation of angiotensin I and its conversion to angiotensin II at the surface cell membrane. Renin internalization seems to increment the ICa because intracellular dialysis of renin (128 pmol Ang I/ml per min) plus angiotensinogen (110 pmol angiotensin I generated by renin to exhaustion) also increased the peak ICa density significantly, an effect suppressed by intracellular losartan (10 mol/l) but not by extracellular losartan (10 mol/l).

CONCLUSIONS

Extracellular renin plus angiotensinogen increases the ICa in isolated myocytes from the failing heart of cardiomyopathic hamsters through the formation of angiotensin II and the activation of angiotensin type 1 receptors at the surface cell membrane. A similar increment of ICa was found with intracellular administration of renin plus angiotensinogen. This finding might indicate that renin internalization is involved in control of inward calcium current in the failing heart.

Cardiac-specific overexpression of AT1 receptor mutant lacking G alpha q/G alpha i coupling causes hypertrophy and bradycardia in transgenic mice

Ang II type 1 (AT1) receptors activate both conventional heterotrimeric G protein-dependent and unconventional G protein-independent mechanisms. We investigated how these different mechanisms activated by AT1 receptors affect growth and death of cardiac myocytes in vivo. Transgenic mice with cardiac-specific overexpression of WT AT1 receptor (AT1-WT; Tg-WT mice) or an AT1 receptor second intracellular loop mutant (AT1-i2m; Tg-i2m mice) selectively activating G(alpha)q/G(alpha)i-independent mechanisms were studied. Tg-i2m mice developed more severe cardiac hypertrophy and bradycardia coupled with lower cardiac function than Tg-WT mice. In contrast, Tg-WT mice exhibited more severe fibrosis and apoptosis than Tg-i2m mice. Chronic Ang II infusion induced greater cardiac hypertrophy in Tg-i2m compared with Tg-WT mice whereas acute Ang II administration caused an increase in heart rate in Tg-WT but not in Tg-i2m mice. Membrane translocation of PKCepsilon, cytoplasmic translocation of G(alpha)q, and nuclear localization of phospho-ERKs were observed only in Tg-WT mice while activation of Src and cytoplasmic accumulation of phospho-ERKs were greater in Tg-i2m mice, consistent with the notion that G(alpha)q/G(alpha)i-independent mechanisms are activated in Tg-i2m mice. Cultured myocytes expressing AT1-i2m exhibited a left and upward shift of the Ang II dose-response curve of hypertrophy compared with those expressing AT1-WT. Thus, the AT1 receptor mediates downstream signaling mechanisms through G(alpha)q/G(alpha)i-dependent and -independent mechanisms, which induce hypertrophy with a distinct phenotype.

Functional gastrointestinal disorders and mast cells: implications for therapy

The pathophysiology of functional gastrointestinal disorders is poorly understood. Accepted common mechanisms include psychosocial factors, abnormal gastrointestinal motility and disturbed visceral sensory perception, but the underlying causes remain unclear. Mast cells (MCs) are immunocytes widely distributed throughout the gastrointestinal tract. Several stimuli (e.g. allergens, neuropeptides and stress) lead to MC activation with consequent mediator release (e.g. histamine, tryptase and prostanoids). The MC mediators interact with nerves supplying the gut leading to altered gut physiology and increased sensory perception. The intestinal mucosa of irritable bowel syndrome patients contains on average an increased number of MCs. These cells release an increased amount of mediators in close vicinity to mucosal innervation. The MC activation and their close proximity to nerve fibres is correlated with the severity of perceived abdominal painful sensations. These data provide a strong basis for considering MCs as important participants in visceral hypersensitivity and pain perception in irritable bowel syndrome. Inhibition of MC function may ameliorate irritable bowel symptoms. Novel drugs with an increased potential in the control of MC function (e.g., anti-IgE antibodies, the intracellular protein tyrosine kinase inhibitor Syk) and mediator release (e.g., second generation antihistamines, proteinase-activated receptor antagonists) may be useful pharmacological tools for these common disorders.

N-domain angiotensin-converting enzyme isoform expression in tissues of Wistar and spontaneously hypertensive rats

BACKGROUND

Angiotensin I-converting enzyme (ACE) is a protein containing two active sites, called N- and C-domains, according to their position in the protein.

AIM

The aim of the present study was to verify whether the expression of the N-domain ACEs detected in the urine of Wistar and spontaneously hypertensive (SHR) rats was restricted to the kidney.

METHODS

Adrenal, aorta, heart, liver, lung, kidney and testicle tissue from Wistar rats and spontaneously hypertensive rats were homogenized in assay buffer and analyzed by gel filtration, Western blotting and radio-immunoassay.

RESULTS

Two peaks (at 136 and 69 kDa) with ACE activity upon ZPhe-His-Leu were separated by gel filtration from homogenate tissues of Wistar rats, in contrast with the tissue from hypertensive rats, which showed ACE forms of 96 and 69 kDa. The bands detected by Western blotting for all studied tissue from Wistar and spontaneously hypertensive rats showed a correspondence with the two peaks containing ACE activity detected in the polyacrylamide gel slices. Angiotensin II levels were increased in hypertensive rat tissue when compared with Wistar rat tissues. In addition, captopril 3 micromol/l inhibited the enzymic activity, where the Km was in the order of mmol/l and micromol/l using hippuryl-His-Leu and Abz-Ser-Asp-Lys(Dnp)Pro-OH as substrates, respectively. All tissues from Wistar rats presented ACE with 136 kDa, similar to somatic ACE, and N-domain ACE with 69 kDa. In the same tissue of spontaneously hypertensive rats, 96 and 69 kDa N-domain ACEs were detected.

CONCLUSIONS

Our results demonstrated that N-domain ACEs were not exclusively produced in the kidney and excreted in the urine; they were expressed in all tissue studied, suggesting that these enzymes could influence local angiotensin II production, contributing to organ-specific regulation.

Cardiac intracrine renin angiotensin system. Part of genetic reprogramming?

The hypothesis that intracrine renin-angiotensin system activated during heart failure is part of the tendency of the heart to return to embryological conditions when organogenesis is possible is presented and discussed. The hypothesis proposes that the change in genetic makeup, which is known to occur during heart failure, includes a drastic change of intercellular chemical and electrical communication such as second messengers and other signal molecules which are involved in cell proliferation and growth. The role of angiotensin II, which is a growth factor, reduces cell coupling in the failing heart through the activation of AT1 receptors and intracellular pathways, such as PKC, MAPK family and increment of intracellular calcium, might play a key role in the genetic reprogramming of the failing heart.

Activation of protein kinase A by atrial natriuretic peptide in neonatal rat cardiac fibroblasts: role in regulation of the local renin-angiotensin system

There is an inverse relationship between renin and atrial natriuretic peptide (ANP) levels in the plasma. Since both the ANP and renin-angiotensin system (RAS) are upregulated in development and cardiac hypertrophy, we tested whether ANP differentially regulates RAS in cardiac cells. Cardiac fibroblasts isolated from neonatal rats were treated with ANP(1-28), a biologically active fragment of ANP. Renin and angiotensinogen (Ao) mRNA levels were measured by quantitative multiplex RT-PCR and protein levels determined by Western blot analysis. ANP(1-28) increased renin and Ao mRNA levels (737+/-131% and 178+/-51.3%) with EC50 values of 4.12+/-0.3 and 8.67+/-0.22 nmol/L, respectively. At the protein level, secretion of renin and Ao was significantly enhanced resulting in approximately 4-fold increase in ANG II level in the medium. The effect of ANP(1-28) on renin and Ao mRNA expression were reproduced by 8-bromo-cyclic GMP. Inhibition of protein kinase G (PKG) with KT5823 blunted ANP(1-28)-induced upregulation of renin, but not Ao mRNA, while inhibition of protein kinase A (PKA) with KT5720 attenuated the upregulation of both renin and Ao mRNA. These findings suggest that unlike in plasma, ANP positively regulates the RAS in cardiac fibroblasts, which may have a significant role in development of the fetal heart.

Pharmacology of gap junctions. New pharmacological targets for treatment of arrhythmia, seizure and cancer?

Intercellular communication in many organs is maintained via intercellular gap junction channels composed of connexins, a large protein family with a number of isoforms. This gap junction intercellular communication (GJIC) allows the propagation of action potentials (e.g., in brain, heart), and the transfer of small molecules which may regulate cell growth, differentiation and function. The latter has been shown to be involved in cancer growth: reduced GJIC often is associated with increased tumor growth or with de-differentiation processes. Disturbances of GJIC in the heart can cause arrhythmia, while in brain electrical activity during seizures seems to be propagated via gap junction channels. Many diseases or pathophysiological conditions seem to be associated with alterations of gap junction protein expression. Thus, depending on the target disease opening or closure of gap junctions may be of interest, or alteration of connexin expression. GJIC can be affected acutely by changing gap junction conductance or--more chronic--by altering connexin expression and membrane localisation. This review gives an overview on drugs affecting GJIC.

Role of angiotensin II AT1 receptor blockers in the treatment of arterial hypertension

Hypertension is a very common condition and the most important risk factor for the occurrence of cardiovascular events. The hyperactivity of the renin-angiotensin-aldosterone system is considered a cardiovascular risk factor in subjects with essential hypertension. The intrinsic vascular abnormality in which the renin-angiotensin-aldosterone system is clearly the milieu for the development of the pathologic changes in blood vessel walls is one of the causes of the establishment of hypertension. Many drugs with different mechanisms of action have been used for the treatment of hypertension and its vascular complications. Nevertheless, the utilities of many drugs are limited by their adverse effects. Continuous research in the search for new pharmacological agents for the treatment of hypertension has led to the development of angiotensin II receptor type AT1 blockers. The most important functions mediated by AT1 receptors include: vasoconstriction, induction of the production and release of aldosterone, renal reabsorption of sodium, cardiac cellular growth, proliferation of vascular smooth muscle, increase of peripheral noradrenergic action and the central activity of the sympathetic nervous system, stimulation of vasopressin release, and inhibition of renin release from the kidney. The angiotensin II receptor type AT1 blockers inhibit the interaction of angiotensin II with its AT1 receptor. These agents lower blood pressure without producing cough as a side effect since, unlike the angiotensin-converting enzyme inhibitors they do not influence the levels of bradykinin or substance P. Hence, these drugs are suitable for the treatment of hypertensive patients who require therapy with a drug blocking the effect of angiotensin-converting enzyme but cannot use angiotensin-converting enzyme inhibitors due to cough as a side effect.

Cardiac angiotensin-(1-7) in ischemic cardiomyopathy

BACKGROUND

Accumulating evidence suggests that angiotensin-(1-7) (Ang-[1-7]) may play an important role in counteracting the pressor, proliferative, and profibrotic actions of angiotensin II in the heart. Thus, we evaluated whether Ang-(1-7) is expressed in the myocardium of normal rats and those in which myocardial infarction was produced 4 weeks beforehand.

METHODS AND RESULTS

The left coronary artery in 10-week-old Lewis rats was either ligated (n=5) or exposed but not occluded in age-matched controls (sham; n=5). Left ventricular end-diastolic pressures were significantly elevated 4 weeks after myocardial infarction (25+/-1 versus 5+/-1 mm Hg for sham; P<0.001), whereas left ventricular systolic pressures were significantly reduced (ligated 86+/-4 versus sham 110+/-5 mm Hg; P<0.01). Hemodynamic effects of coronary artery ligation were accompanied by significant cardiac hypertrophy (heart weight to body weight: ligated 4.3+/-0.1 versus sham 2.9+/-0.1 mg/g; P<0.001). In both ligated and sham rats, Ang-(1-7) immunoreactivity was limited to cardiac myocytes and absent in interstitial cells and coronary vessels. Ang-(1-7) immunoreactivity was significantly augmented in ventricular tissue surrounding the infarct area in the heart of rats with myocardial infarction.

CONCLUSIONS

Development of heart failure subsequent to coronary artery ligation leads to increased expression of Ang-(1-7),which was restricted to myocytes.

Cysteinyl leukotriene-dependent [Ca2+]i responses to angiotensin II in cardiomyocytes

With the use of fura 2 measurements in multiple and single cells, we examined whether cysteinyl leukotrienes (CysLT) mediate angiotensin II (ANG II)-evoked increases in cytosolic free Ca(2+) concentration ([Ca(2+)](i)) in neonatal rat cardiomyocytes. ANG II-evoked CysLT release peaked at 1 min. The angiotensin type 1 (AT(1)) antagonist losartan, but not the AT(2) antagonist PD-123319, attenuated the elevations in [Ca(2+)](i) and CysLT levels evoked by ANG II. Vasopressin and endothelin-1 increased [Ca(2+)](i) but not CysLT levels. The 5-lipoxygenase (5-LO) inhibitor AA-861 and the CysLT(1)-selective antagonist MK-571 reduced the maximal [Ca(2+)](i) responses to ANG II but not to vasopressin and endothelin-1. While MK-571 reduced the responses to leukotriene D(4) (LTD(4)), the dual CysLT antagonist BAY-u9773 completely blocked the [Ca(2+)](i) elevation to both LTD(4) and LTC(4). These data confirm that ANG II-evoked increases, but not vasopressin- and endothelin-1-evoked increases, in [Ca(2+)](i) involve generation of the 5-lipoxygenase metabolite CysLT. The inositol (1,4,5)-trisphosphate [Ins(1,4,5)P(3)] antagonist 2-aminoethoxydiphenyl borate attenuated the [Ca(2+)](i) responses to ANG II and LTD(4). Thus AT(1) receptor activation by ANG II is linked to CysLT-mediated Ca(2+) release from Ins(1,4,5)P(3)-sensitive intracellular stores to augment direct ANG II-evoked Ca(2+) mobilization in rat cardiomyocytes.

Possible involvement of the adipose tissue renin-angiotensin system in the pathophysiology of obesity and obesity-related disorders

Angiotensin II (Ang II), acting on the AT1 and AT2 receptors in mammalian cells, is the vasoactive component of the renin-angiotensin system (RAS). Several components of the RAS have been demonstrated in different tissues, including adipose tissue. Although the effects of Ang II on metabolism have not been studied widely, it is intriguing to assume that components of the RAS produced by adipocytes may play an autocrine, a paracrine and/or an endocrine role in the pathophysiology of obesity and provide a potential pathway through which obesity leads to hypertension and type 2 diabetes mellitus. In the first part of this review, we will describe the production of Ang II, the different receptors through which Ang II exerts its effects and summarize the concomitant intracellular signalling cascades. Thereafter, potential Ang II-induced mechanisms, which may be associated with obesity and obesity-related disorders, will be considered. Finally, we will focus on the different pharmaceutical agents that interfere with the RAS and highlight the possible implications of these drugs in the treatment of obesity-related disorders.

Angiotensin II type 2 receptor blockade partially negates antihypertrophic effects of type 1 receptor blockade on pressure-overload rat cardiac hypertrophy

We investigated the effects of angiotensin II type 2 (AT2) receptor blockade on the antihypertrophic effects of type 1 receptor (AT1) blockade in pressure-overload cardiac hypertrophy in adult rats. Cardiac hypertrophy was induced by banding the abdominal aorta above the renal arteries. The rats were treated with either an AT1 receptor antagonist TCV-116 (TCV, 10 mg/kg/day), an AT2 receptor antagonist PD123319 (PD, 20 mg/kg/day), or both for 4 weeks after the aortic banding. We measured systolic and diastolic blood pressure (BP), body weight (BW), left ventricular weight (LVW), and serum and cardiac angiotensin converting enzyme (ACE) activities. Aortic banding increased BP and LVW/BW, and TCV reversed both these increases. PD affected neither BP nor LVW/BW. TCV+PD reversed the increase in BP but not LVW/BW. Thus, PD was considered to counteract the antihypertrophic effect of TCV without affecting BP. All three treatments reduced cardiac ACE activity without affecting serum ACE activity. Our data demonstrated that AT2 receptor blockade negates the antihypertrophic effects of AT1 receptor blockade in an adult rat model of pressure-overload cardiac hypertrophy. AT2 receptors may mediate the signaling pathways involved in growth inhibition, which could counteract mediation of the cellular growth signaling pathways by AT1 receptors.

A novel muscle-specific enhancer identified within the deletion overlap region of two XLDC patients lacking muscle exon 1 of the human dystrophin gene

Previous studies point to the involvement of several discrete transcriptional enhancers in the modulation of dystrophin gene expression in skeletal and cardiac muscle. Analysis of deletion breakpoints in two X-linked dilated cardiomyopathy patients with mutations that remove muscle exon 1 identified a 3.2-kb deletion overlap region (XLDC3.2) between -1199 and +2057 bp predicted to contain regulatory elements essential for dystrophin gene expression in cardiac muscle. A novel-sequence-based search strategy was used to identify a 543-bp region downstream of muscle exon 1 rich in cardiac-specific transcriptional elements. Designated dystrophin muscle enhancer 2 (DME2), this candidate enhancer was seen to function in a position- and orientation-independent manner in muscle cell lines but not in fibroblasts. As only modest activity was observed in primary neonatal rat cardiomyocytes, DME2 is thought to play a role in dystrophin gene regulation at later stages of cardiac muscle development.

Role of the local renin-angiotensin system in cardiac damage: a minireview focussing on transgenic animal models

The local generation of all components of the renin-angiotensin system (RAS) in the heart has been the basis for the postulation of a tissue RAS in this organ. Since angiotensin II is involved in the induction of cardiac hypertrophy and fibrosis the local generation of this peptide may be of highest clinical importance. Several transgenic animal models have been generated to evaluate the functional importance of the cardiac RAS. We have established a new hypertensive mouse model lacking local angiotensinogen expression in the heart. In these animals, cardiac weight and collagen synthesis are increased compared to normotensive control mice but to a lesser extent than in mice with equally enhanced blood pressure but intact cardiac angiotensinogen generation. Thus, we have shown that local synthesis of this protein is involved but not essential in the development of cardiac hypertrophy and fibrosis.