The amino acid sequence of hypertensin. II

Angiotensin-Converting Enzyme Inhibitor-Induced Angioedema

Angioedema is a well-recognized and potentially lethal complication of angiotensin-converting enzyme inhibitor (ACEi) therapy. In ACEi-induced angioedema, bradykinin accumulates due to a decrease in its metabolism by ACE, the enzyme that is primarily responsible for this function. The action of bradykinin at bradykinin type 2 receptors leads to increased vascular permeability and the accumulation of fluid in the subcutaneous and submucosal space. Patients with ACEi-induced angioedema are at risk for airway compromise because of the tendency for the face, lips, tongue, and airway structures to be affected. The emergency physician should focus on airway evaluation and management when treating patients with ACEi-induced angioedema.

The non-cardiovascular actions of ACE

Angiotensin converting enzyme (ACE) is well known for its role producing the vasoconstrictor angiotensin II and ACE inhibitors are commonly used for treating hypertension and cardiovascular disease. However, ACE has many different substrates besides angiotensin I and plays a role in many different physiologic processes. Here, we discuss the role of ACE in the immune response. Several studies in mice indicate that increased expression of ACE by macrophages or neutrophils enhances the ability of these cells to respond to immune challenges such as infection, neoplasm, Alzheimer's disease, and atherosclerosis. Increased expression of ACE induces increased oxidative metabolism with an increase in cell content of ATP. In contrast, ACE inhibitors have the opposite effect, and in both humans and mice, administration of ACE inhibitors reduces the ability of neutrophils to kill bacteria. Understanding how ACE affects the immune response may provide a means to increase immunity in a variety of chronic conditions now not treated through immune manipulation.

Angiotensin-Converting Enzyme Inhibitor-Induced Angioedema

Angioedema is a well-recognized and potentially lethal complication of angiotensin-converting enzyme inhibitor (ACEi) therapy. In ACEi-induced angioedema, bradykinin accumulates due to a decrease in its metabolism by ACE, the enzyme that is primarily responsible for this function. The action of bradykinin at bradykinin type 2 receptors leads to increased vascular permeability and the accumulation of fluid in the subcutaneous and submucosal space. Patients with ACEi-induced angioedema are at risk for airway compromise because of the tendency for the face, lips, tongue, and airway structures to be affected. The emergency physician should focus on airway evaluation and management when treating patients with ACEi-induced angioedema.

What would Sérgio Ferreira say to your physician in this war against COVID-19: How about kallikrein/kinin system?

Coronavirus disease 2019 (COVID-19) is an infectious disease with fast spreading all over the world caused by the SARS-CoV-2 virus which can culminate in a severe acute respiratory syndrome by the injury caused in the lungs. However, other organs can be also damaged. SARS-CoV-2 enter into the host cells using the angiotensin-converting enzyme 2 (ACE2) as receptor, like its ancestor SARS-CoV. ACE2 is then downregulated in lung tissues with augmented serum levels of ACE2 in SARS-CoV-2 patients. Interestingly, ACE2⁺ organs reveal the symptomatic repercussions, which are signals of the infection such as dry cough, shortness of breath, heart failure, liver and kidney damage, anosmia or hyposmia, and diarrhea. ACE2 exerts a chief role in the renin-angiotensin system (RAS) by converting angiotensin II to angiotensin-(1-7) that activates Mas receptor, inhibits ACE1, and modulates bradykinin (BK) receptor sensitivity, especially the BK type 2 receptor (BKB2R). ACE2 also hydrolizes des-Arg⁹-bradykinin (DABK), an active BK metabolite, agonist at BK type 1 receptors (BKB1R), which is upregulated by inflammation. In this opinion article, we conjecture a dialogue by the figure of Sérgio Ferreira which brought together basic science of classical pharmacology and clinical repercussions in COVID-19, then we propose that in the course of SARS-CoV-2 infection: i) downregulation of ACE2 impairs the angiotensin II and DABK inactivation; ii) BK and its metabolite DABK seems to be in elevated levels in tissues by interferences in kallikrein/kinin system; iii) BK1 receptor contributes to the outbreak and maintenance of the inflammatory response; iv) kallikrein/kinin system crosstalks to RAS and coagulation system, linking inflammation to thrombosis and organ injury. We hypothesize that targeting the kallikrein/kinin system and BKB1R pathway may be beneficial in SARS-CoV-2 infection, especially on early stages. This route of inference should be experimentally verified by SARS-CoV-2 infected mice.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Angiotensin III: a physiological relevant peptide of the renin angiotensin system

The renin angiotensin system (RAS) is a peptide hormone system that plays an important role in the pathophysiology of various diseases, including congestive heart failure, hypertension, myocardial infarction, and diabetic nephropathy. This has led researchers to focus extensively on this system, leading to the discovery of various peptides, peptidases, receptors and signal transduction mechanisms intrinsic to the RAS. Angiotensinogen (AGT), angiotensin (Ang) II, Ang III, Ang IV, and Ang-(1-7) are the main biologically active peptides of RAS. However, most of the available studies have focused on Ang II as the likely key peptide from the RAS that directly and indirectly regulates physiological functions leading to pathological conditions. However, data from recent studies suggest that Ang III may produce physiologically relevant effects that are similar to those produced by Ang II. Hence, this review focuses on Ang III and the myriad of physiological effects that it produces in the body.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Focus on Brain Angiotensin III and Aminopeptidase A in the Control of Hypertension

The classic renin-angiotensin system (RAS) was initially described as a hormone system designed to mediate cardiovascular and body water regulation. The discovery of a brain RAS composed of the necessary functional components (angiotensinogen, peptidases, angiotensins, and specific receptor proteins) independent of the peripheral system significantly expanded the possible physiological and pharmacological functions of this system. This paper first describes the enzymatic pathways resulting in active angiotensin ligands and their interaction with AT₁, AT₂, and mas receptor subtypes. Recent evidence points to important contributions by brain angiotensin III (AngIII) and aminopeptidases A (APA) and N (APN) in sustaining hypertension. Next, we discuss current approaches to the treatment of hypertension followed by novel strategies that focus on limiting the binding of AngII and AngIII to the AT₁ receptor subtype by influencing the activity of APA and APN. We conclude with thoughts concerning future treatment approaches to controlling hypertension and hypotension.

Translational success stories: angiotensin receptor 1 antagonists in heart failure

The title of the proposed series of reviews is Translational Success Stories. The definition of "translation" according to Webster is, "an act, process, or instance of translating as a rendering of one language into another." In the context of this inaugural review, it is the translation of Tigerstedt's and Bergman's(1) discovery in 1898 of the vasoconstrictive effects of an extract of rabbit kidney to the treatment of heart failure. As recounted by Marks and Maxwell,(2) their discovery was heavily influenced by the original experiments of the French physiologist Brown-Séquard, who was the author of the doctrine that "many organs dispense substances into the blood which are not ordinary waste products, but have specific functions." They were also influenced by Bright's(3) original observation that linked kidney disease with hypertension with the observation that patients dying with contracted kidneys often exhibited a hard, full pulse and cardiac hypertrophy. However, from Tigerstedt's initial discovery, there was a long and arduous transformation of ideas and paradigms that eventually translated to clinical applications. Although the role of the renin-angiotensin system in the pathophysiology of hypertension and heart failure was suspected through the years, beneficial effects from its blockade were not realized until the early 1970s. Thus, this story starts with a short historical perspective that provides the reader some insight and appreciation into the long delay in translation.

Transactivation of epidermal growth factor receptor by enhanced levels of endogenous angiotensin II contributes to the overexpression of Giα proteins in vascular smooth muscle cells from SHR

We earlier showed that the increased expression of Gi proteins exhibited by vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) was attributed to the enhanced levels of endogenous endothelin. Since the levels of angiotensin II (Ang II) are also enhanced in VSMC from SHR, the present study was undertaken to examine the role of enhanced levels of endogenous Ang II in the overexpression of Giα proteins in VSMC from SHR and to further explore the underlying mechanisms responsible for this increase. The enhanced expression of Giα-2 and Giα-3 proteins in VSMC from SHR compared to WKY was attenuated by the captopril, losartan and AG1478, inhibitors of angiotensin converting enzyme, AT(1) receptor and epidermal growth factor receptor (EGFR) respectively as well as by the siRNAs of AT1, cSrc and EGFR. The enhanced inhibition of forskolin-stimulated adenylyl cyclase activity by low concentrations of GTPγS (receptor-independent functions) and of inhibitory responses of hormones on adenylyl cyclase activity (receptor-dependent functions) in VSMC from SHR was also attenuated by losartan. Furthermore, the enhanced phosphorylation of EGFR in VSMC from SHR was also restored to control levels by captopril, losartan, PP2, a c-Src inhibitor and N-acetyl-L-cysteine (NAC), superoxide anion (O(2)(-)) scavenger, whereas enhanced ERK1/2 phosphorylation was attenuated by captopril and losartan. Furthermore, NAC also restored the enhanced phosphorylation of c-Src in SHR to control levels. These results suggest that the enhanced levels of endogenous Ang II in VSMC from SHR, transactivate EGFR, which through MAP kinase signaling, enhance the expression of Giα proteins and associated adenylyl cyclase signaling.

Renin-angiotensin-aldosterone blockade for cardiovascular disease prevention

The renin-angiotensin-aldosterone system (RAAS) plays a significant role in pathophysiology of multiple disease states. RAAS blockade is beneficial in patients with hypertension, acute myocardial infarction, chronic heart failure, stroke, and diabetic renal disease. RAAS blockade with the combination angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) has demonstrated conflicting results in recent clinical trials. This article reviews the latest evidence of isolated ACEI or ARB use, their combination, and the role of aldosterone blockers and direct renin inhibitors in patients at risk, and makes recommendations for their use in the prevention of morbidity and mortality in cardiovascular disease.

Renin-angiotensin-aldosterone system blockade for cardiovascular diseases: current status

Activation of the renin-angiotensin-aldosterone system (RAAS) results in vasoconstriction, muscular (vascular and cardiac) hypertrophy and fibrosis. Established arterial stiffness and cardiac dysfunction are key factors contributing to subsequent cardiovascular and renal complications. Blockade of RAAS has been shown to be beneficial in patients with hypertension, acute myocardial infarction, chronic systolic heart failure, stroke and diabetic renal disease. An aggressive approach for more extensive RAAS blockade with combination of two commonly used RAAS blockers [ACE inhibitors (ACEIs) and angiotensin receptor blockers (ARBs)] yielded conflicting results in different patient populations. Combination therapy is also associated with more side effects, in particular hypotension, hyperkalaemia and renal impairment. Recently published ONTARGET study showed ACEI/ARB combination therapy was associated with more adverse effects without any increase in benefit. The Canadian Hypertension Education Program responded with a new warning: 'Do not use ACEI and ARB in combination'. However, the European Society of Cardiology in their updated heart failure treatment guidelines still recommended ACEI/ARB combo as a viable option. This apparent inconsistency among guidelines generates debate as to which approach of RAAS inhibition is the best. The current paper reviews the latest evidence of isolated ACEI or ARB use and their combination in cardiovascular diseases, and makes recommendations for their prescriptions in specific patient populations.

Renin-angiotensin-aldosterone system blockade for cardiovascular diseases: current status

Activation of the renin-angiotensin-aldosterone system (RAAS) results in vasoconstriction, muscular (vascular and cardiac) hypertrophy and fibrosis. Established arterial stiffness and cardiac dysfunction are key factors contributing to subsequent cardiovascular and renal complications. Blockade of RAAS has been shown to be beneficial in patients with hypertension, acute myocardial infarction, chronic systolic heart failure, stroke and diabetic renal disease. An aggressive approach for more extensive RAAS blockade with combination of two commonly used RAAS blockers [ACE inhibitors (ACEIs) and angiotensin receptor blockers (ARBs)] yielded conflicting results in different patient populations. Combination therapy is also associated with more side effects, in particular hypotension, hyperkalaemia and renal impairment. Recently published ONTARGET study showed ACEI/ARB combination therapy was associated with more adverse effects without any increase in benefit. The Canadian Hypertension Education Program responded with a new warning: 'Do not use ACEI and ARB in combination'. However, the European Society of Cardiology in their updated heart failure treatment guidelines still recommended ACEI/ARB combo as a viable option. This apparent inconsistency among guidelines generates debate as to which approach of RAAS inhibition is the best. The current paper reviews the latest evidence of isolated ACEI or ARB use and their combination in cardiovascular diseases, and makes recommendations for their prescriptions in specific patient populations.

Fragmentomics of natural peptide structures

Natural fragmentation of peptide and other chemical structures is well known. They are a significant object of biochemical investigations. In this connection, the bases and determination are given for the notion of the "fragmentome" as a set of all fragments of a single substance, as well as for global fragmentome of all chemical components of living organisms. It is described how protein-peptide fragments are formed in nature, what experimental and theoretical methods are used for their investigation, as well as mathematical characteristics of fragmentomes. Individual fragmentomes of all subunits and of complete casein fragmentome are considered in detail. Structural and functional variety of its possible fragments was revealed by computer analysis. Formation in an organism of an exogenous-endogenous pool of oligopeptides and correlation of these data with concepts of structure-functional continuum of regulatory molecules is shown on an example of food protein fragments. Possible practical importance of the use of natural fragments in dietology, therapy, as well as in sanitary hygiene and cosmetics is noted.

Angiotensin converting enzyme insertion/deletion polymorphism and renoprotection in diabetic and nondiabetic nephropathies

Despite the huge amount of studies looking for candidate genes, the ACE gene remains the unique, well-characterized locus clearly associated with pathogenesis and progression of chronic kidney disease, and with response to treatment with drugs that directly interfere with the renin angiotensin system (RAS), such as angiotensin converting enzyme (ACE) inhibitors and angiotensin II receptor antagonists (ARA). The II genotype is protective against development and progression of type I and type II nephropathy and is associated with a slower progression of nondiabetic proteinuric kidney disease. ACE inhibitors are particularly effective at the stage of normoalbuminuria or microalbuminuria in both type I and type II diabetics with the II genotype, whereas the DD genotype is associated with a better response to ARA therapy in overt nephropathy of type II diabetes and to ACE inhibitors in male patients with nondiabetic proteinuric nephropathies. The role of other RAS or non-RAS polymorphisms and their possible interactions with different ACE I/D genotypes are less clearly defined. Thus, evaluating the ACE I/D polymorphism is a reliable tool to identify patients at risk and those who may benefit the most of renoprotective therapy with ACE inhibitors or ARA. This may guide pharmacologic therapy in individual patients and help design clinical trials in progressive nephropathies. Moreover, it might help optimize prevention and intervention strategies at population levels, in particular, in countries where resources are extremely limited and 1 million patients continue to die every year of cardiovascular or renal disease.

Urinary albumin excretion and the renin-angiotensin system in cardiovascular risk management

Microalbuminuria has been shown to be a strong predictor of cardiovascular morbidity and mortality in diabetic and hypertensive patients, but also in the general population. Moreover, several reports suggest that reduction of urinary albumin excretion (UAE) is associated with improvement of cardiovascular prognosis. Reduction of UAE can be achieved by lowering arterial blood pressure, but blockers of the renin-angiotensin system (RAS) with their specific renal actions have demonstrated to be able to reduce UAE more than might be expected from reduction of blood pressure alone. Consequently, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may also provide superior cardiovascular protection, especially in subjects with higher levels of albuminuria, but evidence is still scarce. The ability of both angiotensin-converting enzyme inhibitors and angiotensin receptor blockers to reduce UAE and provide cardiovascular protection suggests that the RAS may play a central role. New developments in this area include the use of aldosterone antagonists in albuminuric/proteinuric subjects, and the development of oral renin inhibitors. Combinations of the aforementioned drugs may have the ability to fully block the RAS, potentially avoiding all detrimental effects of this hormonal cascade. However, combination therapy is expected to also increase the incidence of side effects, such as hyperkalaemia and acute renal insufficiency. The current knowledge of microalbuminuria represents the proverbial tip of the iceberg, and future studies should focus on the underlying pathophysiological mechanism of urinary albumin excretion in relation to cardiovascular protection. Only then can a better understanding of the problem be achieved and the optimal pharmacological approach be ascertained.

Isolation and identification of a pepsitensin

1. From ox plasma incubated with pepsin a highly purified pepsitensin has been isolated by fractional precipitation, solvent extraction, column chromatography, countercurrent distribution and paper chromatography. 2. Comparison of the properties of this substance with those of synthetic valyl-5 angiotensin I showed: (a) the same specific pressor activity; (b) the same amino acid composition; (c) identical paper-electrophoretic mobilities at various pH values. 3. N- and C-Terminal studies carried out on the intact polypeptide and on the products of chymotrypsin digestion established the following sequence for the amino acids present in the molecule: Asp-Arg-Val-Tyr-Val-His-Pro-Phe-His-Leu. This structure is identical with that of valyl-5 angiotensin I.

The EROP-Moscow oligopeptide database

Natural oligopeptides may regulate nearly all vital processes. To date, the chemical structures of nearly 6000 oligopeptides have been identified from >1000 organisms representing all the biological kingdoms. We have compiled the known physical, chemical and biological properties of these oligopeptides—whether synthesized on ribosomes or by non-ribosomal enzymes—and have constructed an internet-accessible database, EROP-Moscow (Endogenous Regulatory OligoPeptides), which resides at . This database enables users to perform rapid searches via many key features of the oligopeptides, and to carry out statistical analysis of all the available information. The database lists only those oligopeptides whose chemical structures have been completely determined (directly or by translation from nucleotide sequences). It provides extensive links with the Swiss-Prot-TrEMBL peptide-protein database, as well as with the PubMed biomedical bibliographic database. EROP-Moscow also contains data on many oligopeptides that are absent from other convenient databases, and is designed for extended use in classifying new natural oligopeptides and for production of novel peptide pharmaceuticals.

Biochemical problems of regulation by oligopeptides

Some problems are considered which arise in biochemical studies on structure and function of natural oligopeptides consisting of 2-50 amino acid residues. The problems under consideration include the generation of oligopeptides from precursors, chemical structure, the role of functionally important radicals and spatial configuration, and structure-function relationships. Different types of regulation are shown mainly for oligopeptides involved in muscle contraction.

Historical perspective of the renin-angiotensin system

Researchers continue to be fascinated with the renin-angiotensin system (RAS) more than 100 yr after its discovery because of its powerful role in controlling sodium balance, body fluid volumes, and arterial pressure. Development of drugs that block different components of this system has led to powerful treatments for hypertension, heart failure, diabetes, and other diseases. Molecular approaches to studying this system offer new possibilities for better understanding the physiology and pathophysiology of the RAS, and for developing new therapeutic paradigms. Our challenge in the future will be to effectively utilize the technological advances that are taking place in virtually all areas of science, including the RAS, and to translate them into a better understanding of the pathophysiology and treatment of human diseases.

The synthesis of a tetradecapeptide renin substrate

A tetradecapeptide renin substrate having a biological activity comparable to the natural product and similar chemical properties has been synthesized by means of the carbobenzyloxyl azide and mixed anhydride methods.

Contractile effects by intracellular angiotensin II via receptors with a distinct pharmacological profile in rat aorta

1. We studied the effect of intracellular angiotensin II (Ang II) and related peptides on rat aortic contraction, whether this effect is pharmacologically distinguishable from that induced by extracellular stimulation, and determined the Ca2+ source involved. 2. Compounds were delivered into the cytoplasm of de-endothelized aorta rings using multilamellar liposomes. Contractions were normalized to the maximum obtained with phenylephrine (10(-5) M). 3. Intracellular administration of Ang II (incorporation range: 0.01-300 nmol mg(-1)) resulted in a dose-dependent contraction, insensitive to extracellular administration (10(-6) M) of the AT1 receptor antagonist CV11947, the AT2 receptor antagonist PD 123319, or the non-selective AT receptor antagonist and partial agonist saralasin ([Sar1,Val5,Ala8]-Ang II (P<0.05). 4. Intracellular administration of CV11947 or PD 123319 right shifted the dose-response curve about 1000 fold or 20 fold, respectively. PD 123319 was only effective if less than 30 nmol mg(-1) Ang II was incorporated. 5. Contraction was partially desensitized to a second intracellular Ang II addition after 45 min (P<0.05). 6. Intracellular administration of Ang I and saralasin also induced contraction (P<0.05). Both responses were sensitive to intracellular CV11947 (P<0.05), but insensitive to PD 123319. The response to Ang I was independent of intracellular captopril. 7. Contraction induced by extracellular application of Ang II and of Ang I was abolished by extracellular pre-treatment with saralasin or CV11947 (P<0.05), but not with PD 123319. Extracellular saralasin induced no contraction. 8. Intracellular Ang II induced contraction was not affected by pre-treatment with heparin filled liposomes, but completely abolished in Ca2+-free external medium. 9. These results support the existence of an intracellular binding site for Ang II in rat aorta. Intracellular stimulation induces contraction dependent on Ca2+-influx but not on Ins(1,4,5)P3 mediated release from intracellular Ca2+-stores. Intracellular Ang I and saralasin induce contraction, possibly via the same binding site. Pharmacological properties of this putative intracellular receptor are clearly different from extracellular stimulated AT1 receptors or intracellular angiotensin receptors postulated in other tissue.

Some pharmacological actions of synthetic analogues of angiotensinamide

In order to evaluate the importance of some structural features of asparagyl(1)-Valyl(5)-angiotensin II (angiotensinamide) for its pharmacological actions, the relative potencies of angiotensinamide and five peptide analogues were studied on the blood pressure of the rat, the isolated rat uterus and the isolated guinea-pig ileum. All the modifications of the angiotensinamide structure that were studied led to a decrease of potency which, however, was not the same on all three preparations. The importance of the guanido group, the phenolic group and the length of the peptide chain for the pharmacological activities of these peptides is discussed.

The purification and partial characterization of several forms of hog renin substrate

Hog renin substrate has been separated into three major (A, B, and C) and two minor forms (D and E) by DEAE cellulose chromatography. Two of the major forms (B and C) have been further fractionated into two additional types (1 and 2) by countercurrent distribution. The purification of substrates A, C₁, and C₂ has been completed. Analysis shows that all three are glycoproteins with molecular weights of about 57,000, and have similar amino acid compositions. Differences exist in the sialic acid, glucosamine, and neutral hexose content, which may account for different physical properties. All the forms of the substrates are attacked by renin at similar rates, and appear to yield the same angiotensin I.

Immunologic production of antiangiotensin. I. Preparation of angiotensin-protein complex antigen

Angiotensin II was coupled with bovine γ-globulin (BGG) through the following series of reactions. See PDF for Structure By determinations of the aromatic amine and tyrosine contents of p-aminobenzoylangiotensin II, the number of p-aminobenzoyl residues introduced per molecule of angiotensin II was calculated. Absorption spectra (between 250 and 500 mµ) of BGG complexes of p-aminobenzoylangiotensin II and six different para substituted aromatic amines were compared. Specific activities (dog units/millimicromole) of the different intermediate products were determined. Presence of a terminal, free amino group does not appear to be an absolute requirement for the biological activity of angiotensin II, since substitution of a p-aminobenzoyl radical in this group yields a product with 40 to 50 per cent of the activity of the parent compound. Angiotensin I, on the other hand, is completely inactivated under identical circumstances. Possible implication of this finding has been discussed.

Angiotensin, thirst, and sodium appetite

Angiotensin (ANG) II is a powerful and phylogenetically widespread stimulus to thirst and sodium appetite. When it is injected directly into sensitive areas of the brain, it causes an immediate increase in water intake followed by a slower increase in NaCl intake. Drinking is vigorous, highly motivated, and rapidly completed. The amounts of water taken within 15 min or so of injection can exceed what the animal would spontaneously drink in the course of its normal activities over 24 h. The increase in NaCl intake is slower in onset, more persistent, and affected by experience. Increases in circulating ANG II have similar effects on drinking, although these may be partly obscured by accompanying rises in blood pressure. The circumventricular organs, median preoptic nucleus, and tissue surrounding the anteroventral third ventricle in the lamina terminalis (AV3V region) provide the neuroanatomic focus for thirst, sodium appetite, and cardiovascular control, making extensive connections with the hypothalamus, limbic system, and brain stem. The AV3V region is well provided with angiotensinergic nerve endings and angiotensin AT1 receptors, the receptor type responsible for acute responses to ANG II, and it responds vigorously to the dipsogenic action of ANG II. The nucleus tractus solitarius and other structures in the brain stem form part of a negative-feedback system for blood volume control, responding to baroreceptor and volume receptor information from the circulation and sending ascending noradrenergic and other projections to the AV3V region. The subfornical organ, organum vasculosum of the lamina terminalis and area postrema contain ANG II-sensitive receptors that allow circulating ANG II to interact with central nervous structures involved in hypovolemic thirst and sodium appetite and blood pressure control. Angiotensin peptides generated inside the blood-brain barrier may act as conventional neurotransmitters or, in view of the many instances of anatomic separation between sites of production and receptors, they may act as paracrine agents at a distance from their point of release. An attractive speculation is that some are responsible for long-term changes in neuronal organization, especially of sodium appetite. Anatomic mismatches between sites of production and receptors are less evident in limbic and brain stem structures responsible for body fluid homeostasis and blood pressure control. Limbic structures are rich in other neuroactive peptides, some of which have powerful effects on drinking, and they and many of the classical nonpeptide neurotransmitters may interact with ANG II to augment or inhibit drinking behavior. Because ANG II immunoreactivity and binding are so widely distributed in the central nervous system, brain ANG II is unlikely to have a role as circumscribed as that of circulating ANG II. Angiotensin peptides generated from brain precursors may also be involved in functions that have little immediate effect on body fluid homeostasis and blood pressure control, such as cell differentiation, regeneration and remodeling, or learning and memory. Analysis of the mechanisms of increased drinking caused by drugs and experimental procedures that activate the renal renin-angiotensin system, and clinical conditions in which renal renin secretion is increased, have provided evidence that endogenously released renal renin can generate enough circulating ANG II to stimulate drinking. But it is also certain that other mechanisms of thirst and sodium appetite still operate when the effects of circulating ANG II are blocked or absent, although it is not known whether this is also true for angiotensin peptides formed in the brain. Whether ANG II should be regarded primarily as a hormone released in hypovolemia helping to defend the blood volume, a neurotransmitter or paracrine agent with a privileged role in the neural pathways for thirst and sodium appetite of all kinds, a neural organizer especially in sodium appetit

Use of angiotensin-converting enzyme inhibitors as monotherapy and in combination with diuretics and calcium channel blockers

Angiotensin-converting enzyme (ACE) inhibitors have earned an important place in medical therapy since their discovery about two decades ago. This family of drug has grown tremendously since the introduction of captopril in 1981. There are currently more than 14 ACE inhibitors in the world and 9 are available in the United States. Although these agents share many similarities, they differ in their pharmacokinetic properties, approved indications, and cost. This paper provides guidance for selection of ACE inhibitors by examining the pharmacokinetics, pharmacodynamics, drug interactions, adverse effects, and cost of these agents. Combination products of ACE inhibitors with either diuretics or calcium channel blockers also are reviewed.

Angiotensin II: biosynthesis, molecular recognition, and signal transduction

1. Angiotensin II is a well-known vasopressive octapeptide that is the principal end-product of the renin-angiotensin system. In addition to its tonic effect on vascular smooth muscle cells, it also stimulates aldosterone secretion from the adrenals and promotes sodium reabsorption through renal tubular cells. 2. These physiological functions have been appreciated for some time, but as details of the molecular and cell biology of the angiotensin response mechanism become understood, it is increasingly apparent that the hormone has a much broader repertoire. Its functional variability is made possible by (i) different enzymatic routes for its generation, (ii) different receptors distributed in different tissues, (iii) different mechanisms for receptor regulation, and (iv) different signal transduction pathways. 3. This insight is the direct consequence of advances in pharmacology that led first to inhibitors of angiotensin converting enzyme and later to angiotensin II receptor antagonists. This review looks at the current status of angiotensin biochemistry and physiology and provides a basis for anticipation of future developments.

Angiotensin and the brain

A brief account for the renal renin-angiotensin system (RAS), its inhibitors and receptors, as for the presence of an intrinsic cerebral RAS is initially provided. The review is then focused upon the circumventricular organs as cerebral targets for blood-borne angiotensin II (Ang II) and on centrally mediated Ang II effects. These concern influences upon the cardiovascular system, water balance, sodium balance, and ACTH-cortisol secretion.