Tissue distribution of rat angiotensinogen mRNA and structural analysis of its heterogeneity

Delayed Graft Function and the Renin-angiotensin System

Delayed graft function (DGF) is a form of acute kidney injury (AKI) and a common complication following kidney transplantation. It adversely influences patient outcomes increases the financial burden of transplantation, and currently, no specific treatments are available. In developing this form of AKI, activation of the renin-angiotensin system (RAS) has been proposed to play an important role. In this review, we discuss the role of RAS activation and its contribution to the pathophysiology of DGF following the different stages of the transplantation process, from procurement and ischemia to transplantation into the recipient and including data from experimental animal models. Deceased kidney donors, whether during cardiac or brain death, may experience activation of the RAS. That may be continued or further potentiated during procurement and organ preservation. Additional evidence suggests that during implantation of the kidney graft and reperfusion in the recipient, the RAS is activated and may likely remain activated, extrapolating from other forms of AKI where RAS overactivity is well documented. Of particular interest in this setting is the status of angiotensin-converting enzyme 2, a key RAS enzyme essential for the metabolism of angiotensin II and abundantly present in the apical border of the proximal tubules, which is the site of predominant injury in AKI and DGF. Interventions aimed at safely downregulating the RAS using suitable shorter forms of angiotensin-converting enzyme 2 could be a way to offer protection against DGF.

(Pro)renin Receptor and Blood Pressure Regulation: A Focus on the Central Nervous System

The renin-angiotensin system (RAS) is classically described as a hormonal system in which angiotensin II (Ang II) is one of the main active peptides. The action of circulating Ang II on its cognate Ang II type-1 receptor (AT1R) in circumventricular organs has important roles in regulating the autonomic nervous system, blood pressure (BP) and body fluid homeostasis, and has more recently been implicated in cardiovascular metabolism. The presence of a local or tissue RAS in various tissues, including the central nervous system (CNS), is well established. However, because the level of renin, the rate-limiting enzyme in the systemic RAS, is very low in the brain, how endogenous angiotensin peptides are generated in the CNS-the focus of this review-has been the subject of considerable debate. Notable in this context is the identification of the (pro)renin receptor (PRR) as a key component of the brain RAS in the production of Ang II in the CNS. In this review, we highlight cellular and anatomical locations of the PRR in the CNS. We also summarize studies using gain- and loss-of function approaches to elucidate the functional importance of brain PRR-mediated Ang II formation and brain RAS activation, as well as PRR-mediated Ang II-independent signaling pathways, in regulating BP. We further discuss recent developments in PRR involvement in cardiovascular and metabolic diseases and present perspectives for future directions.

ACE2 as a Therapeutic Target for COVID-19; its Role in Infectious Processes and Regulation by Modulators of the RAAS System

Angiotensin converting enzyme 2 (ACE2) is the recognized host cell receptor responsiblefor mediating infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). ACE2bound to tissue facilitates infectivity of SARS-CoV-2; thus, one could argue that decreasing ACE2tissue expression would be beneficial. However, ACE2 catalytic activity towards angiotensin I (AngI) and II (Ang II) mitigates deleterious effects associated with activation of the renin-angiotensinaldosteronesystem (RAAS) on several organs, including a pro-inflammatory status. At the tissuelevel, SARS-CoV-2 (a) binds to ACE2, leading to its internalization, and (b) favors ACE2 cleavage toform soluble ACE2: these actions result in decreased ACE2 tissue levels. Preserving tissue ACE2activity while preventing ACE2 shredding is expected to circumvent unrestrained inflammatoryresponse. Concerns have been raised around RAAS modulators and their effects on ACE2expression or catalytic activity. Various cellular and animal models report conflicting results invarious tissues. However, recent data from observational and meta-analysis studies in SARS-CoV-2-infected patients have concluded that RAAS modulators do not increase plasma ACE2 levels orsusceptibility to infection and are not associated with more severe diseases. This review presentsour current but evolving knowledge of the complex interplay between SARS-CoV-2 infection, ACE2levels, modulators of RAAS activity and the effects of RAAS modulators on ACE2 expression.

Adipocytes do not significantly contribute to plasma angiotensinogen

Recently, it has been reported that 25% of plasma angiotensinogen (Agt) is derived from fat. Meanwhile, liver-specific Agt knockout (KO) mice have markedly low plasma Agt, which may be due to reduced fat mass. To study the contribution of the fat to plasma Agt, we tested whether increasing fat mass can elevate plasma Agt and blood pressure in liver-Agt KO mice. Epididymal fat mass in liver-Agt KO mice fed a high-fat diet (HFD) was 4.1-fold larger than that in liver-Agt KO mice on a normal-fat diet (NFD). The liver-Agt KO mice on NFD were hypotensive with low levels of plasma Agt (on average, 0.11 vs 2.38 μg/ml). HFD slightly increased plasma Agt (0.17 μg/ml) without increase in blood pressure. To further increase fat mass, liver-Agt KO mice were fed HFD and simultaneously supplemented with low-dose angiotensin II and compared with control mice. Fat mass was comparable between the two groups. However, liver-Agt KO mice had uniformly low plasma Agt (0.09 vs 2.07 μg/ml) and systolic blood pressure (78±12 vs 111±6 mm Hg). In conclusion, adipocyte-derived Agt has essentially no contribution to the plasma concentration and no impact on blood pressure compared to liver-derived Agt.

Role of angiotensin in ovarian follicular development and ovulation in mammals: a review of recent advances

Angiotensin (Ang) II is widely known for its role in the control of systemic blood vessels. Moreover, Ang II acts on the vascular control of ovarian function, corpus luteum formation, and luteolysis. Over the past 10 years, our research group has been studying the new concept of the renin–angiotensin system (RAS) as an autocrine/paracrine factor regulating steroidogenesis and promoting different cellular responses in the ovary, beyond vascular function. We have developed and used differentin vivoandin vitroexperimental models to study the role of RAS in the ovary and a brief overview of our findings is presented here. It is widely accepted that there are marked species differences in RAS function in follicle development. Examples of species-specific functions of the RAS in the ovary include the involvement of Ang II in the regulation of follicle atresia in rats vs the requirement of this peptide for the dominant follicle development and ovulation in rabbits and cattle. More recently, Ang-(1–7), its receptor, and enzymes for its synthesis (ACE2, NEP, and PEP) were identified in bovine follicles, implying that Ang-(1–7) has an ovarian function. Other novel RAS components (e.g. (pro)renin receptor and renin-binding protein) recently identified in the bovine ovary show that ovarian RAS is poorly understood and more complex than previously thought. In the present review, we have highlighted the progress toward understanding the paracrine and autocrine control of ovarian antral follicle development and ovulation by ovarian tissue RAS, focusing onin vivostudies using cattle as a model.

Renin-angiotensin system in human coronavirus pathogenesis

Although initially considered relatively harmless pathogens, human coronaviruses (HCoVs) are nowadays known to be associated with more severe clinical complications. Still, their precise pathogenic potential is largely unknown, particularly regarding the most recently identified species HCoV-NL63 and HCoV-HKU1. HCoVs need host cell proteins to successively establish infections. Proteases of the renin–angiotensin system serve as receptors needed for entry into target cells; this article describes the current knowledge on the involvement of this system in HCoV pathogenesis.

Prevention of pulmonary hypertension by Angiotensin-converting enzyme 2 gene transfer

In spite of recent advancements in the treatment of pulmonary hypertension, successful control has yet to be accomplished. The abundant presence of angiotensin-converting enzyme 2 (ACE2) in the lungs and its impressive effect in the prevention of acute lung injury led us to test the hypothesis that pulmonary overexpression of this enzyme could produce beneficial outcomes against pulmonary hypertension. Monocrotaline (MCT) treatment of mice for 8 weeks resulted in significant increases in right ventricular systolic pressure, right ventricle:left ventricle plus septal weight ratio, and muscularization of pulmonary vessels. Administration of a lentiviral vector containing ACE2, 7 days before MCT treatment prevented the increases in right ventricular systolic pressure (control: 25+/-1 mm Hg; MCT: 44+/-5 mm Hg; MCT+ACE2: 26+/-1 mm Hg; n=6; P<0.05) and right ventricle:left ventricle plus septal weight ratio (control: 0.25+/-0.01; MCT: 0.31+/-0.01; MCT+ACE2: 0.26+/-0.01; n=8; P<0.05). A significant attenuation in muscularization of pulmonary vessels induced by MCT was also observed in animals overexpressing ACE2. These beneficial effects were associated with an increase in the angiotensin II type 2 receptor:angiotensin II type 1 receptor mRNA ratio. Also, pulmonary hypertension-induced increases in proinflammatory cytokines were significantly attenuated by lentiviral vector-containing ACE2 treatment. Furthermore, ACE2 gene transfer in mice after 6 weeks of MCT treatment resulted in a significant reversal of right ventricular systolic pressure. These observations demonstrate that ACE2 overexpression prevents and reverses right ventricular systolic pressure and associated pathophysiology in MCT-induced pulmonary hypertension by a mechanism involving a shift from the vasoconstrictive, proliferative, and fibrotic axes to the vasoprotective axis of the renin-angiotensin system and inhibition of proinflammatory cytokines.

Development of fetal brain renin-angiotensin system and hypertension programmed in fetal origins

Since the concept of fetal origins of adult diseases was introduced in 1980s, the development of the renin-angiotensin system (RAS) in normal and abnormal patterns has attracted attention. Recent studies have shown the importance of the fetal RAS in both prenatal and postnatal development. This review focuses on the functional development of the fetal brain RAS, and ontogeny of local brain RAS components in utero. The central RAS plays an important role in the control of fetal cardiovascular responses, body fluid balance, and neuroendocrine regulation. Recent progress has been made in demonstrating that altered fetal RAS development as a consequence of environmental insults may impact on "programming" of hypertension later in life. Given that the central RAS is of equal importance to the peripheral RAS in cardiovascular regulation, studies on the fetal brain RAS development in normal and abnormal patterns could shed light on "programming" mechanisms of adult cardiovascular diseases in fetal origins.

Extravascular sources of lung angiotensin peptide synthesis in idiopathic pulmonary fibrosis

Previous work from this laboratory demonstrated de novo synthesis of angiotensin (ANG) peptides by apoptotic pulmonary alveolar epithelial cells (AEC) and by lung myofibroblasts in vitro and in bleomycin-treated rats. To determine whether these same cell types also synthesize ANG peptides de novo within the fibrotic human lung in situ, we subjected paraffin sections of normal and fibrotic (idiopathic pulmonary fibrosis, IPF) human lung to immunohistochemistry (IHC) and in situ hybridization to detect ANG peptides and angiotensinogen (AGT) mRNA. These were analyzed both alone and in combination with cell-specific markers of AEC [monoclonal antibody (MAb) MNF-116] and myofibroblasts [α-smooth muscle actin (α-SMA) MAb] and an in situ DNA end labeling (ISEL) method to detect apoptosis. In normal human lung, IHC detected AGT protein in smooth muscle underlying normal bronchi and vessels, but not elsewhere. Real-time RT-PCR and Western blotting revealed that AGT mRNA and protein were 21-fold and 3.6-fold more abundant, respectively, in IPF lung biopsies relative to biopsies of normal human lung (both P < 0.05). In IPF lung, both AGT protein and mRNA were detected in AEC that double-labeled with MAb MNF-116 and with ISEL, suggesting AGT expression by apoptotic epithelia in situ. AGT protein and mRNA also colocalized to myofibroblast foci detected by α-SMA MAb, but AGT mRNA was not detected in smooth muscle. These data are consistent with earlier data from isolated human lung cells in vitro and bleomycin-induced rat lung fibrosis models, and they suggest that apoptotic AEC and myofibroblasts constitute key sources of locally derived ANG peptides in the IPF lung.

Tissue angiotensin-converting enzyme inhibitors: are they more effective than serum angiotensin-converting enzyme inhibitors?

Since their discovery in the 1980s, angiotensin-converting enzyme (ACE) inhibitors have been shown to decrease angiotensin formation, prevent breakdown of bradykinin, and may also act on peptides of the renin-angiotensin system. They are effective in reducing the risk of heart failure, myocardial infarction, and death from cardiovascular causes in patients with left ventricular systolic dysfunction or heart failure, and have been shown to reduce atherosclerotic complications in patients who have vascular disease without heart failure. They may preserve endothelial function and counteract initiation and progression of atherosclerosis. Broadly, ACE inhibitors can be divided into tissue specific or serum ACE inhibitors. Tissue-specific ACE inhibitors as a group are not superior to serum ACE inhibitors in the treatment of coronary artery disease. Pending direct comparator clinical trials between a tissue ACE inhibitor and a plasma ACE inhibitor, both ramipril and perindopril can be recommended for secondary risk prevention, based on the evidence.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Angiotensin II reverses the inhibitory action produced by theca cells on bovine oocyte nuclear maturation

The presence of prorenin, renin, angiotensinogen, angiotensin-converting enzyme, angiotensin II (Ang II) and Ang II receptors in the ovary is suggestive of a functional ovarian renin-angiotensin system (RAS). In cattle, the expression of Ang II is greatest in large follicles, suggesting that it is important during follicular growth and maturation. The present study was designed to investigate the role of Ang II in bovine oocyte nuclear maturation. Bovine cumulus-oocyte complexes (COCs) were cultured with or without follicular cells and Ang II or saralasin (Ang II antagonist). In the absence of follicular cells, Ang II at 0, 10(-11), 10(-9) and 10(-7) M did not affect the percentage of oocytes reaching the germinal vesicle breakdown (GVBD), metaphase I (MI) and metaphase II (MII) stage after 7-h (41.3 +/- 4.3, 35.3 +/- 4.0, 31.3 +/- 9.7, 38.7 +/- 8.6), 12-h (31.6 +/- 7.0, 34.7 +/- 6.1, 31.7 +/- 5.3, 28.9 +/- 9.1; mean +/- S.E.M.) and 18-h (44.9 +/- 7.3, 58.4 +/- 8.4, 53.1 +/- 7.4, 44.9 +/- 7.3) of culture, respectively. Similarly, saralasin at 0, 10(-11), 10(-9) and 10(-7) M did not affect the percentage of oocytes reaching MII stage after 18-h of culture (37.6 +/- 7.4, 34.4 +/- 7.7, 30.0 +/- 10.8 and 31.2 +/- 5.1, respectively). The theca cells (MII = 22.9%) or medium conditioned with follicular cells (GV = 65.5%, MI = 23.6%) inhibited oocyte maturation; however, theca cells (MII = 35.5 +/- 4.9; P < 0.05) or medium conditioned with follicular cells (GV = 34.6%, MI = 52.7%; P < 0.01) were not able to inhibit nuclear maturation when Ang II (10(-11) M) was present in the culture system. Theca cells remained viable during the culture period when Ang II was present. Therefore, results supported the idea of a role of Ang II in blocking the inhibitory effect of theca cells on nuclear maturation of bovine oocytes.

Heterogenous nuclear ribonucleoprotein F modulates angiotensinogen gene expression in rat kidney proximal tubular cells

An insulin-responsive element (IRE) in the rat angiotensinogen (ANG) gene promoter that binds to two nuclear proteins with apparent molecular weights of 48 and 70 kD was identified previously from rat immortalized renal proximal tubular cells (IRPTC). The present studies aimed to identify and clone the 48-kD nuclear protein and to define its action on ANG gene expression. Nuclear proteins were isolated from IRPTC and subjected to two-dimensional electrophoresis. The 48-kD nuclear protein was detected by Southwestern blotting and subsequently identified by mass spectrometry, revealing that it was identical to 46-kD heterogeneous nuclear ribonucleoprotein F (hnRNP F), a nuclear protein that binds to TATA-binding protein and associates with RNA polymerase II and also interacts with nuclear cap-binding complex. The hnRNP F cDNA was cloned from IRPTC by reverse transcriptase-PCR. Bacterially expressed recombinant hnRNP F bound to the rat ANG-IRE, as revealed by gel mobility shift assay. The addition of polyclonal antibodies against hnRNP F yielded a supershift in gel mobility. Transient transfer of sense and antisense hnRNP F cDNA in IRPTC inhibited and enhanced ANG gene expression, respectively. High glucose stimulated and insulin inhibited hnRNP F expression in IRPTC. Expression studies indicated that hnRNP F is present in the kidney, testis, liver, lung, and brain but not in the spleen. In conclusion, these studies demonstrate that hnRNP F binds to rANG-IRE and modulates renal ANG gene expression, implicating that dysregulation of hnRNP F might affect renin-angiotensin system activation and, subsequently, kidney injury in diabetes.

Genetic targeting of the brain renin-angiotensin system in transgenic rats: Impact on stress-induced renin release

The advance of genetic technologies to permit tissue-specific targeted gene manipulation allowed the development of transgenic models with alterations of the renin-angiotensin (RAS) solely in the brain. We have used such methodology to develop a transgenic rat with a brain specific alteration of the RAS [TGR(ASrAOGEN)], in order to elucidate a causative role for the brain RAS and its relevance in different pathophysiological processes. The TGR(ASrAOGEN) rats have decreased levels of angiotensinogen (AOGEN) throughout the brain because of an antisense inhibition of the astroglial AOGEN synthesis. In this review we aimed at summarizing the experience obtained from utilizing the TGR(ASrAOGEN) rat model to study the brain RAS and present novel results providing evidence for the involvement of this system in stress-induced renin release.

TTF-1, a homeodomain-containing transcription factor, participates in the control of body fluid homeostasis by regulating angiotensinogen gene transcription in the rat subfornical organ

In recent years, it has become increasingly evident that angiotensins synthesized in the brain contribute to regulating body fluid homeostasis. Although angiotensinogen, the unique angiotensin precursor, is produced in the brain, the factors that regulate its gene expression remain unknown. We recently found that TTF-1, a homeodomain-containing transcription factor essential for the development of the fetal diencephalon, is postnatally expressed in discrete areas of the hypothalamus. We now report that the subfornical organ, an important site of angiotensinogen synthesis, is an extra-hypothalamic site of TTF-1 expression. Double in situ hybridization histochemistry demonstrated the presence of TTF-1 mRNA in angiotensinogen-producing cells of the rat subfornical organ. RNase protection assays showed that TTF-1 and angiotensinogen mRNA levels are simultaneously increased in the subfornical organ by water deprivation. The angiotensinogen promoter contains seven presumptive TTF-1 binding motifs, four of which are recognized by the TTF-1 homeodomain. In the C6 glioma cell line, TTF-1 transactivates the angiotensinogen promoter in a dose-dependent manner. This transactivation is abolished by deletion of the TTF-1 binding motif at -125. Intracranial administration of an antisense TTF-1 oligodeoxynucleotide decreased angiotensinogen mRNA in the subfornical organ and dramatically reduced the animal's water intake while increasing urine excretion. Moreover, plasma arginine vasopressin content was decreased by the same treatment. These results demonstrate a novel role for TTF-1 in the regulation of body fluid homeostasis, exerted via the transactivational control of angiotensinogen synthesis in the subfornical organ.

Molecular phenotyping for analyzing subtle genetic effects in mice: application to an angiotensinogen gene titration

The angiotensinogen M235T polymorphism in humans is linked to differential expression of the human angiotensinogen gene (AGT) gene and hypertension, but the homeostatic responses resulting from this polymorphism are not known. We therefore investigated how mice respond to five genetically determined levels of mouse angiotensinogen gene (Agt) expression covering the range associated with the M235T variants. By using high-throughput molecular phenotyping, tissue RNAs were assayed for expression of 10 genes important in hypertension. Significant positive and negative responses occurred in both sexes as Agt expression increased twofold, including a three-fold increase in aldosterone synthase expression in adrenal gland, and a two-fold decrease in renin expression in kidney. In males, cardiac expression of the precursor of atrial natriuretic peptide B and of adrenomedullin also increased approximately twofold. The relative expression of all genes studied except Agt differed significantly in the two sexes, and several unexpected relationships were encountered. A highly significant correlation between renal expression of the angiotensin type 1a receptor and kallikrein, independent of Agt genotype, is present in females (P < 0.0001) but not males (P = 0.4). The correlation between blood pressure (BP) and liver Agt expression within the five Agt genotypes is significant in females (P = 0.0005) but not in males (P = 0.2), whereas correlation of BP with differences between the genotypes is less in females (P = 0.06) than in males (P = 0.001). The marked gender differences in gene expression in wild-type mice and the changes induced by moderate alterations in Agt expression and BP emphasize the need to look for similar differences in humans.

Definitive molecular evidence of renin-angiotensin system in human uterine decidual cells

The tissue renin-angiotensin system (RAS) has been suggested to be present in human gestational tissues, but uncertainty exists about the authenticity of this RAS, and the cellular origin of this RAS has not been defined. In the present study, we confirmed the presence of authentic renin and angiotensinogen in the prolactin-producing decidual tissue by sequencing the cDNAs generated through reverse transcription-polymerase chain reaction, confirming cDNA product sizes, and by performing Northern blot analysis of the RNA. Our comparative data demonstrate that prolactin has the highest expression in the decidual tissue, followed by renin, and that angiotensinogen has the least expression. We demonstrated with fluorescent in situ hybridization that prolactin-expressing endocrine decidual cells are the same cells that express both renin and angiotensinogen. These results have implications in regard to how the decidual RAS may be regulated and what potential role this local RAS may have in the pathogenesis of preeclampsia.

Renal vascular and biochemical responses to systemic renin inhibition in dogs at low renal perfusion pressure

Renin is produced by the kidney and secreted into the systemic circulation. However, its biochemical and physiological role of regulating renal blood flow with changing renal perfusion pressure (RPP) is not fully understood. In this study, the function of the intrarenal renin for production of angiotensin (Ang) I and maintenance of vascular tone was evaluated in dogs under normal conditions and when the kidney was perfused at low RPP. The dog left kidney was perfused first at normal (100 mm Hg) and then at low (30 mm Hg) RPP in the presence or absence of the renin inhibitor ciprokiren (3 mg/kg, i.v.). Both hemodynamic and biochemical parameters were measured. Lowering RPP markedly reduced left renal blood flow and elevated left renal vascular resistance. These effects were prevented by ciprokiren, which blocked the intrarenal production of Ang I. Lowering RPP increased the renal venous/ arterial ratio from 1.4+/-0.1 to 3.6+/-0.3 for plasma renin activity and from 2.4+/-0.2 to 9.8+/-1.1 for Ang I, but did not change the venous/arterial ratio for Ang II. The net renal venous conversion rate of Ang I to Ang II decreased from 0.22 to 0.09 after RPP was lowered, whereas the conversion rate in arterial blood was 1.35 and did not decrease significantly. Our results demonstrated the importance of intrarenal renin-angiotensin system for Ang I production and for the maintenance of the vascular tone, especially at low RPP. Our study also shows the limited capacity for Ang I conversion in the renal vasculature in vivo.

Effect of renal perfusion pressure on renal function, renin release and renin and angiotensinogen gene expression in rats

1. A study was undertaken to examine the influence of acute renal perfusion pressure (RPP) reduction on renin release, renal renin and angiotensinogen gene expression and the role played by angiotensin II in these responses. 2. In chloralose-urethane anaesthetised rats, reduction of RPP to 60 mmHg for 3 h in vehicle or losartan-treated (5 days at 10 mg kg-1 bis in die (b.i.d.)) rats decreased renal blood flow by 46 and 29 % (both P < 0.001), respectively, glomerular filtration rate by 45 and 57 % (both P < 0.001), respectively, and sodium excretion by 96 and 98 % (both P < 0.01). 3. Chloralose-urethane anaesthesia and surgery caused a rise in plasma renin activity but was associated with a suppression of renal renin (50 %, P < 0.01) and angiotensinogen (40 %, P < 0.05) gene expression. Following reduction of RPP to 60 mmHg for 3 h, plasma renin activity was increased more than 7-fold (P < 0.001) and renal renin gene expression about 2-fold (P < 0.05). 4. Chronic (5 days) blockade of angiotensin II receptors with losartan elevated plasma renin activity some 29-fold (P < 0.001) and caused a marked increase (30-fold, P < 0.05) in renal renin gene expression, compatible with angiotensin II exerting a negative feedback control on renin release and gene expression. Reduction of RPP to 60 mmHg for 3 h in these animals had little effect on renal renin gene expression. 5. From these findings it can be concluded that (a) chloralose-urethane anaesthesia and surgery had a stimulatory effect on renin release but suppressed basal levels of renal renin and angiotensinogen gene expression; (b) acute reduction of RPP for 3 h could stimulate renin gene expression in the renin producing cells; and (c) the negative feedback control of angiotensin II on renin release and synthesis which was evident following chronic losartan treatment was not apparent during short-term reduction of RPP.

Transcriptional regulation of angiotensinogen gene expression

The renin--angiotensin system (RAS) is an extracellular hormonal system implicated in acute, homeostatic control of peripheral vascular resistance and electrolyte homeostasis. In this tightly regulated system, physiological regulators of blood pressure and fluid balance induce the production of the potent vasoactive angiotensin peptides by sequential proteolysis of the angiotensinogen (AGT) prohormone. AGT is the only known precursor of the angiotensin peptides, whose circulating concentrations influence the tonic activity of the RAS. AGT abundance is regulated at the transcriptional level through hormonal and cell-type specific regulators. In this review, we will discuss the identified mechanisms controlling AGT expression separately for the rodent and human genes. The most intensively investigated gene (rodent AGT) is regulated constitutively by multiple positive- and negative-acting cis factors that function in a cell-type dependent fashion. Inducible rodent AGT expression is mediated through a multihormone-inducible enhancer that integrates signals from steroid and cytokine hormones into AGT transcription. We review recent advances in understanding the mechanism of the nuclear factor-kappa B (NF-kappa B) family in mediating cytokine-induced AGT expression and our recent discoveries on the existence of differentially inducible pools of cytoplasmic NF-kappa B. Constitutive control of the human AGT gene will be discussed; there is surprisingly little information on the cis- and trans-acting regulators controlling inducible expression of human AGT. Finally, we will explore some of the recent developments in gene linkage studies where human AGT alleles have been associated with hypertensive phenotypes through a mechanism that may involve enhanced transcription. These studies have provided a molecular explanation for a subset of heritable hypertensive disorders in humans.

Angiotensin II: a reproductive hormone too?

It has long been known that angiotensin II (Ang II) can affect reproductive tissues such as the uterus. However, the existence of a local renin-angiotensin system (RAS) in female as well as male reproductive tissues is a relatively recent observation. Of great interest is the discovery that all components of the RAS are present in the ovary, that the ovary secretes components of the RAS into the bloodstream, and that the ovary itself is responsive to Ang II. Recent studies suggest that the primary role of Ang II in the ovary is to cause atresia in non-ovulatory follicles; however, there is also compelling data to suggest that Ang II facilitates ovulation. Male reproductive structures also contain all of the components of the RAS, gonadotropins regulate the activity of these components, and these tissues have Ang II receptors. Of great interest is the expression of testis-specific angiotensin-converting enzyme (ACE), which is located on germ cells. Recent studies using gene knock-out techniques indicate that testis ACE plays an important role in male fertility. However, the overall significance of the RAS for normal reproductive function remains questionable. There is now a body of evidence implicating the RAS in pathophysiologies associated with reproductive function, which gives rise to the possibility that drugs acting on the RAS might ameliorate some of these disorders. Considerable work remains to determine the role of Ang II in reproductive functions.

Pituitary-dependent expression of the testicular angiotensin II receptor and its subtypes in rats

Angiotensin II (AT2) has been implicated in the growth and/or differentiation of its target tissues. In the present study, testicular AT2 receptor and its subtypes in hypophysectomized rats were examined using quantitative in vitro autoradiography and Northern blot analysis in an attempt to determine possible involvement of pituitary hormones in their expression. Prepubescent (3 weeks of age) male Sprague-Dawley rats underwent hypophysectomy or sham operation. From 10 days thereafter, they were treated with vehicle, growth hormone, human chorionic gonadotrophin or human menopausal gonadotrophin for 10 days. Testicular AT2 receptors were labelled with 125I-[Sar1,Ile8] AT2 and differentiated into its subtypes (AT1 and FAT2) according to their susceptibility to AT1 (losartan, 5 microM) and AT2 (CGP42112B, 1 microM) antagonists. Hypophysectomy led to a marked increase in AT2 receptor concentration (sham-operated rats: 0.7 +/- 0.2 fmol/mg protein, hypophysectomized rats: 2.5 +/- 0.6 fmol/mg protein, mean +/- SEM, n = 11-12, p < 0.01) with predominant occurrence of AT1 receptors. Both human chorionic gonadotrophin and human menopausal gonadotrophin decreased testicular AT2 receptor concentration, whereas growth hormone did not affect AT2 receptor expression. Northern blot analysis revealed both testicular AT1 and AT2 receptor mRNA expression to be significantly increased after hypophysectomy and reduced by gonadotrophin treatment. These results suggest that the expression of testicular AT2 receptors is regulated by pituitary gonadotrophins and that AT2 may play a role in testicular growth and/or differentiation.

Human vascular renin-angiotensin system and its functional changes in relation to different sodium intakes

A growing body of evidence supports the existence of a tissue-based renin-angiotensin system (RAS) in the vasculature, but the functional capacity of vascular RAS was not investigated in humans. In 28 normotensive healthy control subjects, the metabolism of angiotensins through vascular tissue was investigated in normal, low, and high sodium diets by the measurement of arterial-venous gradient of endogenous angiotensin (Ang) I and Ang II in two different vascular beds (forearm and leg), combined with the study of 125I-Ang I and 125I-Ang II kinetics. In normal sodium diet subjects, forearm vascular tissue extracted 36+/-6% of 125I-Ang I and 30+/-5% of 125I-Ang II and added 14.9+/-5.1 fmol x 100 mL(-1) x min(-1) of de novo formed Ang I and 6.2+/-2.8 fmol x 100 mL(-1) x min(-1) of Ang II to antecubital venous blood. Fractional conversion of 125I-Ang I through forearm vascular tissue was about 12%. Low sodium diet increased (P<.01) plasma renin activity, whereas de novo Ang I and Ang II formation by forearm vascular tissue became undetectable. Angiotensin degradation (33+/-7% for Ang I and 30+/-7% for Ang II) was unchanged, and vascular fractional conversion of 125I-Ang I decreased from 12% to 6% (P<.01). In high sodium diet subjects, plasma renin activity decreased, and de novo Ang I and Ang II formation by forearm vascular tissue increased to 22 and 14 fmol x 100 mL(-1) x min(-1), respectively (P<.01). Angiotensin degradation did not significantly change, whereas fractional conversion of 125I-Ang I increased from 12% to 20% (P<.01). Leg vascular tissue functional activities of RAS paralleled those of forearm vascular tissue both at baseline and during different sodium intake. These results provide consistent evidence for the existence of a functional tissue-based RAS in vascular tissue of humans. The opposite changes of plasma renin activity and vascular angiotensin formation indicate that vascular RAS is independent from but related to circulating RAS.

Synergistic effect of dexamethasone and isoproterenol on the expression of angiotensinogen in immortalized rat proximal tubular cells

To investigate whether the expression of angiotensinogen (ANG) in rat kidney proximal tubules is stimulated by dexamethasone and isoproterenol, immortalized rat proximal tubular cells (IRPTC) were cultured in a monolayer. Immunoreactive rat ANG (IR-rANG) in the culture medium was measured by a specific radioimmunoassay (RIA) for rANG. This RIA was developed by employing rabbit antiserum against the purified recombinant rat ANG (rANG). The purified rANG from plasma and the iodinated rANG were used as the hormone standard and tracer, respectively. The RIA is specific for rat ANG and it has no cross-reactivity with other pituitary hormone preparations or other rat plasma proteins. The sensitivity of detection of the RIA is approximately 2 ng of rANG. The levels of IR-rANG in the culture media of IRPTC ranged from 2 to 5 ng/ml/24 hr/10(6) cells. The addition of dexamethasone (10(-13) to 10(-5) M) stimulated the expression and secretion of rANG from IRPTC in a dose-dependent manner, whereas the addition of isoproterenol alone had no effect. However, a combination of both dexamethasone and isoproterenol synergistically stimulated the expression and secretion of rANG by IRPTC. The synergistic effect of dexamethasone and isoproterenol was blocked by the presence of RU 486 (a glucocorticoid receptor antagonist) or propranolol (beta-adrenoceptor blocker). These studies suggest that the addition of dexamethasone and isoproterenol acts synergistically to stimulate the expression and secretion of ANG protein in rat proximal tubules in vivo.

Adrenal, kidney, and heart angiotensins in female murine Ren-2 transfected hypertensive rats

We analyzed by high-performance liquid chromatography and radioimmunoassay angiotensin I (Ang I), Ang II, Ang-(1-7), and metabolites in the adrenal, kidney and heart of normotensive female Sprague-Dawley (SD) and transgenic hypertensive [TGR(mRen-2)27] rats carrying the murine Ren-2d renin gene. The monogenetic model of hypertensive rats had significant increases in adrenal Ang II; whereas in the kidney Ang II was unchanged, but Ang I and Ang-(1-7) were significantly lower. Cardiac Ang I, Ang II, and Ang-(2-10) were significantly reduced in transgenic rats, while Ang-(2-7) was increased. In SD and transgenic rats kidney and adrenal angiotensins increased primarily during estrus or proestrus. In female transgenic rats the increased adrenal Ang II and the sustained renal Ang II may contribute to the established phase of hypertension.

Effect of angiotensin-converting enzyme inhibition on myocardial fibrosis and function in hypertrophied and failing myocardium from the spontaneously hypertensive rat

BACKGROUND

After a period of stable hypertrophy, male spontaneously hypertensive rats (SHR) develop heart failure between 18 to 24 months of age, with depression of active myocardial function and increased passive stiffness. We tested the hypothesis that chronic ACE inhibition by captopril would prevent and possibly reverse impairment of myocardial function.

METHODS AND RESULTS

Male SHR and normotensive Wistar-Kyoto rats (WKY) were assigned to no treatment or captopril treatment (2 g/L in drinking water) begun at ages 12, 18, and 21 months; animals were studied at 24 months of age, or earlier when evidence of heart failure was found in SHR (mean age, 19+/-2 months). In an additional group, captopril treatment was begun when SHR developed heart failure; surviving animals were studied at 24 months of age. In untreated SHR, relative to WKY, isometric stress development at Lmax, maximum rate of stress development, and shortening velocity were depressed, whereas passive stiffness was increased, in association with the development of myocardial fibrosis. In the SHR treated before cardiac dysfunction, captopril administration attenuated hypertrophy and prevented contractile dysfunction, fibrosis, and increased passive stiffness. Captopril treatment begun after cardiac function was impaired reduced left ventricular hypertrophy but did not restore intrinsic contractile function or reduce fibrosis or passive stiffness.

CONCLUSIONS

In the male SHR, early treatment with captopril was associated with the most marked attenuation of dysfunction relative to the untreated SHR. Treatment initiated after the onset of heart failure improved clinical signs of heart failure and decreased left ventricular hypertrophy in surviving animals but did not reverse the fibrosis and contractile dysfunction associated with heart failure.

Captopril modifies gene expression in hypertrophied and failing hearts of aged spontaneously hypertensive rats

The spontaneously hypertensive rat (SHR) exhibits a transition from stable compensated left ventricular (LV) hypertrophy to heart failure (HF) at a mean age of 21 months that is characterized by a decrease in alpha-myosin heavy chain (alpha-MHC) gene expression and increases in the expression of the atrial natriuretic factor (ANF), pro-alpha1(III) collagen, and transforming growth factor beta1 (TGF-beta1) genes. We tested the hypotheses that angiotensin-converting enzyme inhibition (ACEI) in SHR would prevent and reverse HF-associated changes in gene expression when administered prior to and after the onset of HF, respectively. We also investigated the effect of ACEI on circulating and cardiac components of the renin-angiotensin system. ACEI (captopril 2 g/L in the drinking water) was initiated at 12, 18, and 21 months of age in SHR without HF and in SHR with HF. Results were compared with those of age-matched normotensive Wistar-Kyoto (WKY) rats, and to untreated SHR with and without evidence of HF. ACEI initiated prior to failure prevented the changes in alpha-MHC, ANF, pro-alpha1(III) collagen, and TGF-beta1 gene expression that are associated with the transition to HF. ACEI initiated after the onset of HF lowered levels of TGF-beta1 mRNA by 50% (P<.05) and elevated levels of alpha-MHC mRNA two- to threefold (P<.05). Circulating levels of renin and angiotensin I were elevated four- to sixfold by ACEI, but surprisingly, plasma levels of angiotensin II were not reduced. ACEI increased LV renin mRNA levels in WKY and SHR by two- to threefold but did not influence LV levels of angiotensinogen mRNA. The results suggest that the anti-HF benefits of ACEI in SHR may be mediated, at least in part, by effects on the expression of specific genes, including those encoding alpha-MHC, ANF, TGF-beta1, pro-alpha1(III) collagen, and renin-angiotensin system components.

Beneficial effects of bradykinin on myocardial energy metabolism and infarct size

There is growing evidence for a local kallikrein-kinin system in the heart. In the ischemic heart the enhanced generation and release of kinins seem to have cardioprotective actions. In isolated rat hearts with ischemia-reperfusion injuries, perfusion with bradykinin reduces the duration and incidence of ventricular fibrillations, improves cardiodynamics, reduces release of cytosolic enzymes, and preserves energy-rich phosphates and glycogen stores. In anesthetized animals, intracoronary infusion of bradykinin is followed by comparable beneficial changes and limits infarct size. Inhibition of breakdown of bradykinin and related peptides induces similar beneficial cardiac effects. Treatment with angiotensin-converting enzyme (ACE) inhibitors such as ramipril increases cardiac kinins and reduces postischemic reperfusion injuries in isolated rat hearts as well as infarct size and remodeling in postinfarcted animals, respectively. Blockade of B2 kinin receptors increases ischemia-induced effects. In isolated hearts, ischemia-reperfusion injuries intensify with the B2 kinin receptor antagonist icatibant, which also abolishes the cardioprotective effects of ACE inhibitors and of exogenous bradykinin. Infarct size reduction by ACE inhibitors and bradykinin in anesthetized animals is reversed by icatibant. Kinins contribute to the cardioprotective effects associated with ischemic preconditioning. Preconditioning or bradykinin-induced antiarrhythmic and infarct size-limiting effects are attenuated by icatibant.

The ovarian renin-angiotensin system in reproductive physiology

The identification of the presence of prorenin, renin, angiotensinogen, angiotensin-converting enzyme, angiotensin II (Ang II), and Ang II receptors in the ovary suggests that there is a functional ovarian renin-angiotensin system (RAS). It could play a significant role in such areas of ovarian physiology as follicular development, steroidogenesis, oocyte maturation, ovulation, and follicle atresia. Expression of the ovarian RAS is regulated by gonadotropins. Ang II, a bioactive octapeptide of RAS, has important effects as a paracrine/autocrine regulator at different stages of the reproductive cycle. Ang II modulates ovarian steroidogenesis and formation of the corpus luteum and also stimulates oocyte maturation and ovulation via Ang II receptors on granulosa cells. In addition, increasing evidence demonstrates that Ang II is a major factor in regulating the function of atretic follicles. In any physiologic system, aberrations result in the development of pathologic states. Disturbances in the ovarian RAS can be the cause or the result of such reproductive disorders as polycystic ovary syndrome, ovarian hyperstimulation syndrome, ovarian tumors, and ectopic pregnancy. Data support the concept of an active and regulated RAS in ovarian follicles. Species differences observed in the expression of ovarian RAS suggest varying functional roles among species with respect to ovarian physiology.

Hepatic and extrahepatic angiotensinogen gene expression in rats with acute nephrotic syndrome

Plasma concentration and urine excretion of the renin-angiotensin system proteins are altered in rats with nephrotic syndrome (NS). In this work the messenger ribonucleic acid (mRNA) levels of angiotensinogen (Ao) were analyzed with the slot-blot hybridization technique in liver and other extrahepatic tissues: kidney, heart, brain, and adrenal gland from control, nephrotic, and pair-fed (PF) rats. NS was induced by a single injection of puromycin amino-nucleoside (PAN). Although a great urinary excretion and half-normal plasma levels of Ao were observed on day 6 after PAN injection, when NS was clearly established, hepatic Ao mRNA levels did not change. Furthermore, the Ao mRNA levels did not change in any of the extrahepatic tissues studied on day 6, nor did its hepatic levels at days 1, 3, 5, or 7 after PAN injection. These data suggest that the hepatic and extrahepatic Ao mRNA levels are unaltered during the development of the acute NS induced by PAN.

Novel perspectives on pituitary and brain angiotensinogen

All the angiotensin peptides originate from angiotensinogen, a glycoprotein synthesized by several tissues, including the brain and the anterior pituitary. In the rat, immunohistochemistry has been used to localize angiotensinogen in gonadotropes and in uncharacterized cells surrounding sinusoids. Both cell types are capable of secreting angiotensinogen in cell culture; only the gonadotropes contain angiotensin II (AngII) and are capable of secreting it in culture. It has been asserted that the perisinusoidal cells are the only source of angiotensinogen for the generation of AngII by gonadotropes. Our current data favor the existence of a complete intracellular renin-angiotensin system (RAS) in gonadotropes and a separate extracellular system which utilizes the high concentration of angiotensinogen from perisinusoidal cells. Furthermore, we postulate that gonadotrope AngII serves mainly reproductive functions, while the proximity of angiotensinogen-secreting cells to folliculostellate cells, and their access to the intercellular sinusoidal and follicular spaces, places the extracellular RAS in a strategic position to affect pituitary growth and the mediation of acute-phase immune responses. In the rat brain, angiotensinogen is expressed by the 16-18th day of fetal life and by areas generally concerned with vasopressor, electrolyte, and fluid homeostasis. Antisense deoxyoligonucleotides to angiotensinogen mRNA lower blood pressure in hypertensive rats and inhibit in vitro growth of neuroblastoma cells, indicating a significant role for angiotensinogen in mitogenic and homeostatic functions. It is commonly agreed that astrocytes express angiotensinogen. Neuronal angiotensinogen has also been demonstrated by immunohistochemistry, as a secretion from neuronal cell cultures, and by reverse-transcriptase polymerase chain reaction. The fate of secreted astrocytic and neuronal angiotensinogen remains obscure. Angiotensinogen is regulated in a tissue-specific manner with smaller or absent responses observed for brain tissue. By using astrocyte and neuronal cultures the actions on angiotensinogen production of growth hormone, IGF-1, inflammatory lipopolysaccharide, and phorbol ester have been examined. Recent observations show that angiotensinogen is regulated positively or negatively by glucocorticoids and that a positive synergism between cAMP and glucocorticoids exists. On the basis of analogous systems for other proteins, a scheme involving glucocorticoid receptors, CREB, and AP-1 transcription factors is formulated to explain glucocorticoid-cAMP interactions. These transcriptional interactions may form a significant functional link between the RAS and adrenergic mechanisms.

Electrophysiologic and morphologic abnormalities in the failing heart: effect of enalapril on the electrical properties

BACKGROUND

Knowledge of the electrophysiologic abnormalities in the failing heart is meager. In this work morphologic and electrophysiologic changes were investigated in the cardiomyopathic hamster (BIO TO-2) at 11 months of age. The results were compared with control hamsters (F1B) of the same age.

METHODS AND RESULTS

Conventional KCl microelectrodes were used to measure membrane potential, conduction velocity, and refractoriness. Histologic studies consisted of Harris' hematoxylin and eosin, Masson trichrome, and von Kossa's calcium stain. The resting potential of myopathic fibers (-67.8 mV; SEM 1 0.83) in the cardiomyopathic hamsters was less negative than the control subjects' potential (-78.5 V; SEM + 1), and the action potential duration measured at 50% of repolarization was increased by 213%. The conduction velocity (36.9 cm/s) was 15.7% lower than that of the control subjects. Enalapril (50 micrograms/mL) caused a hyperpolarization of 6.8 mV, it increased the action potential duration at 90% of repolarization by 110%, and the conduction velocity of the myopathic fibers was appreciably increased compared to the control hamsters'. The refractoriness of myopathic and normal ventricular fibers was also increased by enalapril. Histologic studies performed on the right and left ventricular wall indicated interstitial fibrosis, necrotic foci, and extensive calcification.

CONCLUSIONS

The results indicate severe morphologic and electrophysiologic abnormalities in the failing ventricular muscle. The effect of enalapril on membrane potential and conduction velocity might indicate that the activation of the cardiac renin-angiotensin system during the process of heart failure is, in part, responsible for the abnormalities described here. The improvement of impulse propagation and the increase in refractoriness seem to represent important factors involved in the antiarrhythmic action of enalapril.

Ontogeny of hormonal and excretory function of the meso- and metanephros in the ovine fetus

Using reverse-transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry we investigated the ontogeny of renin, angiotensinogen and angiotensin converting enzyme (ACE) in the mesonephros at 27 and 41 days of gestation, and the metanephros at 41 and 64 days of gestation in ovine fetuses (term is 145 to 150 days). The volume and composition of fetal urine, stored as allantoic fluid were measured in 12 fetuses at 27 days, and 13 fetuses at 41 days. Renin, angiotensinogen and ACE were identified in both meso- and metanephroi at 41 days but not in the mesonephros at 27 to 30 days. Allantoic fluid volumes were 21 +/- 3 and 45 +/- 5 ml at 27 to 30 days and 41 days, respectively. This fluid was significantly different in composition to that of amniotic fluid or maternal plasma. The results suggest that the mesonephros can substantially modify its glomerular filtrate by 27 days of gestation, and can produce local angiotensin II by 41 days.

Differential regulation of angiotensinogen transcripts after renin infusion

To investigate angiotensinogen regulation in high-renin hypertension, we infused porcine renin intravenously at either a low (4 mU/kg per hour, n = 6) or high (20 mU/kg per hour, n = 9) dose into male Sprague-Dawley rats (225 to 250 g) for 5 days using osmotic minipumps. Control rats received 0.9% NaCl. In renin-infused rats, mean arterial pressure and plasma renin activity were significantly elevated. Both low- and high-renin infusions lowered plasma angiotensinogen levels. Plasma angiotension II was elevated in rats given renin but reached statistical significance only at the higher dose. Angiotensinogen mRNA isolated from the liver, adrenal gland, kidney, and brain was measured by slot blot analysis. Both renin doses were associated with significant decreases in the levels of liver and hypothalamic angiotensinogen mRNA. In the medulla oblongata, angiotensinogen mRNA was reduced only by the higher renin dose. The lower dose increased angiotensinogen mRNA in the adrenal gland, and in kidney, angiotensinogen mRNA level was unchanged by renin infusion. Angiotensinogen mRNA visualized on Northern blots showed that the number of mRNA species in liver decreased from three in control rats to a single mRNA species after renin infusion. Tissue differences in the size of the major angiotensinogen mRNA species were also apparent. This, together with changes in the total hybridization signal of angiotensinogen mRNA in tissues, suggests that renin differentially affects the different angiotensinogen mRNA transcripts. Results of this study indicate that angiotensinogen gene expression is regulated not only by alterations in levels of circulating angiotensin II but also by other mechanisms, presently unidentified, that are activated by renin infusions.

Elevated des-AngI-angiotensinogen levels by nephrectomy and adrenalectomy

This study investigates the time course of plasma levels of angiotensinogen (Aogen) and of the Aogen metabolite des-AngI-angiotensiongen (des-AngI-Aogen) in nephrectomized rats with and without adrenals for 24 h. After nephrectomy the plasma Aogen levels increased 5-fold over the following 24 h. The increase is significantly lower after sham nephrectomy (3.7-fold, P < 0.05) and if the kidneys are withdrawn without decapsulization (2.4-fold, P < 0.05). A small and transient increase arise after nephrectomy plus adrenalectomy (1.6-fold after 8 h, P < 0.005). After adrenalectomy alone Aogen levels continuously shrink to 38% of control values after 24 h. Plasma des-AngI-Aogen levels increase 2.1- to 3.7-fold 24 h after the different nephrectomy procedures. In connection with recent findings these data support the notion that the increase in Aogen plasma levels after bilateral nephrectomy is triggered by renin, released during surgery. High plasma levels of des-AngI-Aogen after nephrectomy indicate that AngI is generated by tissue renin, e.g., in the adrenals. This suggests that after nephrectomy the plasma des-AngI-Aogen levels should be a valuable proof for the evaluation of the amount of generated angiotensin.

Renin-angiotensin system and cell communication in the failing heart

The influence of heart failure on the process of cell communication was investigated in cell pairs isolated from the ventricle of cardiomyopathic hamsters (11 months old) and the results compared with age-matched normal hamsters. The gap junctional conductance (gj) was measured with two voltage-clamp amplifiers. The results showed two major populations of cell pairs with respect to gj values: one with very low values (0.8 to 2.5 nS) and the other with higher values (7 to 35 nS). In normal hamsters, the most frequent gj values were in the range of 40 to 100 nS. Angiotensin II (Ang 11, 1 microg/mL) caused cell uncoupling in myopathic myocytes with low gj but reduced gj by 53 +/- 6.6 percent (+/- SE) in cell pairs with higher gj values (7 to 35 nS). The effect of Ang II on gj of myopathic cell pairs was suppressed by losartan (10(-7) mol/L). In cardiomyopathic cell pairs with low gj (0.8 to 2.5 nS), enalapril (1 microg/mL) caused an appreciable increase in gj (219 +/- 20.3 percent), whereas in cell pairs with higher gj (7 to 35 nS), the gj increment was smaller (80 +/- 10.8 percent) but still larger than that seen in controls (33 +/- 5.4 percent). Intracellular dialysis of Ang I (10(-8) mol/L) abolished cell communication in myopathic cell pairs with low gj (0.8 to 2.5 nS) and reduced gj by 66 +/- 1.7 percent in the other pairs (7 to 35 nS). The effect of Ang I on gj was greatly reduced by enalaprilat (10(-9) mol/L) added to the cytosol. Dialysis of Ang II (10(-8) mol/L) into the myopathic cell reduced gj by 48 +/- 4.2 percent, an effect abolished by losartan (10(-8) mol/L). The results indicate that the decline in gj seen in the ventricle of cardiomyopathic hamsters is in part due to activation of the cardiac renin-angiotensin system.

Mechanisms for inducible control of angiotensinogen gene transcription

The intravascular renin-angiotensin system is an endocrine system designed to maintain cardiovascular homeostasis in response to hypotension. Under normal conditions, angiotensinogen concentrations circulating in the plasma are rate limiting for the maximum velocity of angiotensin I formation. In the liver, the major site of circulating angiotensinogen synthesis, angiotensinogen expression is under exquisite hormonal control. We review the mechanisms by which hormones effect transcriptional control of angiotensinogen expression. Adrenal-derived glucocorticoids produce the translocation of the glucocorticoid receptor into the nucleus. It in turn binds to two glucocorticoid response elements and stimulates angiotensinogen gene transcription. Inflammation activates angiotensinogen transcription as a result of the macrophage-derived cytokines interleukin-1 and tumor necrosis factor-alpha. These cytokines change the abundance of two transcription factor families that bind a single regulatory site in the angiotensinogen promoter, the acute-phase response element. These proteins include the nuclear factor-kappaB complex and the CCAAT/enhancer binding protein family. Activation of the renin-angiotensin system, through production of angiotensin II, results in feedback stimulation of angiotensinogen synthesis (the "positive feedback loop"). We have discovered that the nuclear factor-kappaB transcription factor is regulated by angiotensin II, a finding that provides a mechanism for the transcriptional component of angiotensinogen gene synthesis in the positive feedback loop. These studies underscore the concept that induction of the angiotensinogen gene by diverse physiological stimuli is mediated through changes in the nuclear abundance of sequence-specific transcription factors. The intracellular convergence of cytokine- and angiotensin II-induced signaling pathways on the nuclear factor-kappaB transcription factor provides a point for "cross talk" between angiotensin- and cytokine-activated second messenger pathways.

Human renin-dependent hypertension in rats transgenic for human angiotensinogen

To examine the utility of rats transgenic for human angiotensinogen in the study of human renin-induced hypertension, we first developed assays to measure both the human and rat renin-angiotensin systems in these rats. We used human and mouse renin, transgenic human angiotensinogen, and the human renin inhibitor Ro 42-5892 to determine human- and rat-specific plasma angiotensinogen concentrations, renin activity, and renin concentration. The assays were validated with rat and human plasma mixed in known amounts and with plasma from rats transgenic for human renin. We then tested the human angiotensinogen-transgenic rats by infusing recombinant human renin over 10 days (50 ng/h, n=4) with osmotic minipumps. High human angiotensinogen transgene expression was found in the liver, brain, kidney, gastrointestinal tract, and aorta, whereas rat angiotensinogen gene expression was detected in the liver and brain. During human renin infusion, blood pressure increased to >200/150 mm Hg. Before infusion, human angiotensinogen was 100-fold greater than rat angiotensinogen (141 +/- 73 versus 1.2 +/- 0.16 microg angiotensin l/mL); the relation was not changed by renin infusion. Plasma renin activity increased 300-fold; human plasma renin concentration increased to very high levels (449 +/- 262 ng of angiotensin I per mL per hour), whereas rat plasma renin concentration decreased to undetectable levels. Thus, chronic human renin infusion resulted in severe hypertension with extreme plasma renin activity and plasma renin concentration. However, even at these levels, human angiotensinogen was not rate limiting and angiotensin II was not a significant stimulus for angiotensinogen production. We conclude that these transgenic rats represent a novel model of human renin-dependent hypertension.

Identification of estrogen regulated genes in Fe33 rat hepatoma cells by differential display polymerase chain reaction and their hormonal regulation in rat liver and uterus

We applied the differential display RT-PCR (ddRT-PCR) technology to identify estrogen-regulated hepatic genes in the estrogen receptor expressing rat hepatoma cell line Fe33. Three genes of known sequences were detected by the ddRT-PCR approach: IGF binding protein-1 (IGFBP-1), vitamin D-dependent calcium-binding protein (CaBP9k) and major acute phase protein (MAP). Effects of ethinyl estradiol on the mRNA levels of these genes were confirmed by "Northern-blot" analysis. If given in combination with dexamethasone and glucagon, ethinyl estradiol caused 40-, 15- and 11-fold increases in the mRNA steady state level of IGFBP-1, CaBP9k and MAP, respectively, in Fe33 cells 24 h after addition of hormone. Besides ethinyl estradiol, the partial estrogen agonist OH-tamoxifen caused dose dependent effects on expression of MAP and IGFBP-1. Estrogen regulation of the respective genes and the modulatory effects of progesterone (10 mg/animal/day) were studied in ovariectomized rats treated subcutaneously for 14 days with 1 microgram/animal/day estradiol. "Northern-blot" analysis of liver RNA revealed a 6-fold stimulation of IGFBP-1 mRNA levels in estradiol-treated compared to vehicle-treated rats and a weak but detectable increase of MAP mRNA steady state level (1.6-fold) upon estradiol administration. No effect of estradiol treatment could be monitored for CaBP9k in rat liver. Modulatory effects of progesterone on estradiol-stimulated expression in the liver could be monitored for IGFBP-1 only. In an extension of our investigation on the expression of the three genes in rat liver, we determined their expression and hormonal regulation in the uterus of the same animals. In the uterus, estradiol caused an increase in CaBP9k mRNA. In contrast, IGFBP-1 mRNA levels increased dramatically upon progesterone administration, whereas no effect of estradiol treatment could be detected. MAP mRNA levels increased only after coadministration of estradiol and progesterone. In conclusion, the ddRT-PCR proved to be a powerful method to identify estrogen-regulated genes. The study on the hormonal regulation of three genes stimulated by estrogen in Fe33 cells revealed similarities and differences in their regulation in vivo and in vitro.

Renin gene expression in the aging kidney: effect of sodium restriction

The activity of the renin-angiotensin system as well as the ability of the kidney to retain sodium following salt restriction are reduced with age. The relationship between these age-related changes in renal function and the renin gene expression was presently investigated. The concentrations of renin and its mRNA were measured in kidney of 10- and 30-month-old control female WAG/Rij rats and of animals which were salt restricted for 4 days. In the senescent rats, the kidney renin concentration, like the plasma concentration of angiotensin II, was half that in adult rats. The intrarenal content of renin mRNA did not differ between 10- and 30-month-old animals, suggesting that the transcriptional rate of the renin gene is unchanged with age. During the early phase of adaptation to sodium depletion, the systemic angiotensin II concentration was not modified in either age groups. Four-days salt restriction did not significantly change the renal storage of renin. In contrast, this short term salt restriction induced a 2.3-fold increase in the renin mRNA in adult kidney, and a 1.9-fold increase in the senescent kidney. These data suggest that the age-related decrease in renal concentration of renin is linked to a modification in the rate of translation of renin mRNA, or to an alteration in the protein maturation. The difference in adaptation to the early phase of salt restriction with age should not be linked to changes in renin gene transcription, but more likely to a change in the tissue response to the local renin-angiotensin system.

Developmental consequences of the renin-angiotensin system

Molecular, cellular, and physiological studies indicate that the renin-angiotensin system (RAS) is highly expressed during early kidney development. We propose that a major function of the RAS during early embryonic development is the modulation of growth processes that lead the primitive kidney into a properly differentiated and architecturally organized organ suited for independent extrauterine life. As development progresses, the RAS acquires new and overlapping functions such as the endocrine and paracrine regulation of blood pressure and renal hemodynamics. Disease states in adult mammals often result in expression of RAS genes and phenotypic changes resembling the embryonic pattern, emphasizing the importance of undertaking developmental studies. Because of their importance in health and disease, the immediate challenge is to identify the mechanisms that regulate the unique development of the RAS and its role(s) in normal and abnormal growth processes.

Lack of association between the insertion/deletion polymorphism of the angiotensin-converting enzyme gene and idiopathic dilated cardiomyopathy

OBJECTIVES

We sought to investigate the role of polymorphisms of the gene for angiotensin-converting enzyme in the development and progression of idiopathic dilated cardiomyopathy.

BACKGROUND

Cardiovascular renin-angiotensin systems may be involved in cardiac remodeling and fibrosis. The absence (deletion [D]) of a 287-base pair marker in the angiotensin-converting enzyme gene (introm 16) is associated with increased serum angiotensin-converting enzyme levels. The DD genotype may be a risk factor for the development of end-stage heart failure due to cardiomyopathy. We therefore examined the relation of the angiotensin-converting enzyme genotype to idiopathic dilated cardiomyopathy and to markers of disease severity.

METHODS

We studied 364 control subjects and 99 consecutive patients with idiopathic dilated cardiomyopathy. When the incidence of the DD genotype in our control group was assumed to be similar to that previously reported (27%), this study had a power of 0.9 to detect a different incidence in the patient group, if the true incidence in patients was 42%. Deoxyribonucleic acid (DNA) was isolated from blood samples, and angiotensin-converting enzyme genotype was determined by specific polymerase chain reaction and separation of amplified fragments by agarose gel electrophoresis. We also compared genotype distribution with that in previously reported European control subjects. Functional status, clinical course over a mean +/- SD of 28 +/- 33 months and outcome were documented. Cardiac morphology and function and evidence of rhythm disturbance were noninvasively determined.

RESULTS

Angiotensin-converting enzyme genotype distribution and allele frequencies were similar in patients and control subjects to within 10% (with 95% confidence) and were also similar between patients and European control subjects. No markers of disease severity or progression other than duration of symptoms before diagnosis and the number of ventricular ectopic beats/h were significantly associated with the presence of the DD alleles.

CONCLUSIONS

We find no evidence to support an association between angiotensin-converting enzyme genotype and either the diagnosis of idiopathic dilated cardiomyopathy itself or progression of the disease.

Transient inhibition of angiotensinogen production in transgenic mice bearing an antisense angiotensinogen gene

Angiotensinogen is the precursor of the biologically active hormone angiotensin II. Enzyme kinetic parameters suggest that concentrations of plasma angiotensinogen are rate limiting in the renin reaction. It is therefore assumed that a decrease in angiotensinogen synthesis in vivo would result in a decrease in angiotensin II plasma levels and then of blood pressure. To test this hypothesis, we generated a transgenic mouse line that carries an inducible antisense angiotensinogen gene. Transient inhibition of angiotensinogen synthesis could be demonstrated in these transgenic animals. However, the amounts of liver angiotensinogen message and plasma angiotensinogen concentrations were rapidly back to levels observed in control animals.