Tissue renin-angiotensin system: a site of drug action?

An immunotherapeutic method for COVID-19 patients: a soluble ACE2-Anti-CD16 VHH to block SARS-CoV-2 Spike protein

The third outbreak of coronavirus (CoV) infection (after SARS-CoV and MERS-CoV) caused by a novel CoV (SARS-CoV-2) of the genus Beta-coronavirus has become a global pandemic. CoVs are enveloped viruses whose proteins include spike (S), membrane (M), and envelope (E) which are embedded in the viral envelope. The glycosylated S protein, which forms homo-trimeric spikes on the surface of the viral particle, mediates viral entry into host cells. SARS-CoV-2, like SARS-CoV, uses the Angiotensin-Converting Enzyme 2 (ACE2) cell surface protein for cellular entry. An attractive anti-viral approach is targeting virus entry into cells, for which three strategies are suggested: 1) direct targeting of the viral glycoprotein; 2) targeting the viral receptor on the cell surface; and 3) using soluble (s) ACE2 that binds to S protein thereby neutralizing the virus. In this article, the advantages and disadvantages of these strategies are explained. Moreover, we propose that fusion of the sACE2 to anti-CD16 to produce a bi-specific molecule could be a promising anti-viral strategy.

Effects of dual angiotensin type 1 receptor/neprilysin inhibition vs. angiotensin type 1 receptor inhibition on target organ injury in the stroke-prone spontaneously hypertensive rat

OBJECTIVES

The combination of AT1 blocker/neutroendopeptidase neprilysin inhibition (ARNi) represents an interesting approach to reduce cardiovascular risk in hypertension. We assessed the efficacy of ARNi, compared with angiotensin II type 1 receptor blockade alone, on blood pressure (BP) and on protection from target organ damage development in the stroke-prone spontaneously hypertensive rat (SHRSP).

METHODS

In high-salt fed SHRSP, we assessed plasma and tissue natriuretic peptides, urinary volume, BP and body weight over a short-term treatment (6 weeks) with either ARNi (sacubitril/valsartan 68 mg/kg per day) or valsartan (30 mg/kg per day), protection from stroke and renal damage (as documented by proteinuria) over 4 months of treatment with either sacubitril/valsartan or valsartan; the ability of either treatment to reduce progression of cerebrovascular and renal damage after 2 weeks of high-salt diet.

RESULTS

Higher levels of plasma and tissue atrial natriuretic peptide, of urinary cyclic guanosine 3'5'monophosphate and urine volumes, along with lower BP levels, were found upon sacubitril/valsartan as compared with valsartan over the short-term treatment. Sacubitril/valsartan caused a significant reduction of both BP and proteinuria levels and complete prevention of stroke over the long-term treatment. Once organ damage was established, a significant delay of its progression was observed with sacubitril/valsartan.

CONCLUSION

The dual angiotensin II type 1 receptor/neutroendopeptidase inhibition significantly increased atrial natriuretic peptide level and reduced BP. Complete prevention of stroke was achieved in this model. The ability of sacubitril/valsartan to reduce organ damage progression was superior to that of valsartan alone. ARNi may represent a highly effective therapeutic agent to protect from target organ damage development in hypertension.

The renin-angiotensin system in the breast and breast cancer

Much evidence now suggests that angiotensin II has roles in normal functions of the breast that may be altered or attenuated in cancer. Both angiotensin type 1 (AT1) and type 2 (AT2) receptors are present particularly in the secretory epithelium. Additionally, all the elements of a tissue renin-angiotensin system, angiotensinogen, prorenin and angiotensin-converting enzyme (ACE), are also present and distributed in different cell types in a manner suggesting a close relationship with sites of angiotensin II activity. These findings are consistent with the concept that stromal elements and myoepithelium are instrumental in maintaining normal epithelial structure and function. In disease, this system becomes disrupted, particularly in invasive carcinoma. Both AT1 and AT2 receptors are present in tumours and may be up-regulated in some. Experimentally, angiotensin II, acting via the AT1 receptor, increases tumour cell proliferation and angiogenesis, both these are inhibited by blocking its production or function. Epidemiological evidence on the effect of expression levels of ACE or the distribution of ACE or AT1 receptor variants in many types of cancer gives indirect support to these concepts. It is possible that there is a case for the therapeutic use of high doses of ACE inhibitors and AT1 receptor blockers in breast cancer, as there may be for AT2 receptor agonists, though this awaits full investigation. Attention is drawn to the possibility of blocking specific AT1-mediated intracellular signalling pathways, for example by AT1-directed antibodies, which exploit the possibility that the extracellular N-terminus of the AT1 receptor may have previously unsuspected signalling roles.

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Maternal nutrition, low nephron number and arterial hypertension in later life

A potential role of the intrauterine environment in the development of low nephron number and hypertension in later life has been recently recognized in experimental studies and is also postulated in certain conditions in human beings. Nephrogenesis is influenced by genetic as well as by environmental and in particular maternal factors. In man nephrogenesis, i.e. the formation of nephrons during embryogenesis, takes place from weeks 5 to 36 of gestation with the most rapid phase of nephrogenesis occurring from the mid-2nd trimester until 36 weeks. This 16 week period is a very vulnerable phase where genetic and environmental factors such as maternal diet or medication could influence and disturb nephron formation leading to lower nephron number. Given a constant rise in body mass until adulthood lower nephron number may become "nephron underdosing" and result in maladaptive glomerular changes, i.e. glomerular hyperfiltration and glomerular enlargement. These maladaptive changes may then eventually lead to the development of glomerular and systemic hypertension and renal disease in later life. It is the purpose of this review to discuss the currently available experimental and clinical evidence for factors and mechanisms that could interfere with nephrogenesis with particular emphasis on maternal nutrition. In addition, we discuss the emerging concept of low nephron number being a new cardiovascular risk factor in particular for essential hypertension in later life.

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.

AT2 receptors: functional relevance in cardiovascular disease

The renin angiotensin system (RAS) is intricately involved in normal cardiovascular homeostasis. Excessive stimulation by the octapeptide angiotensin II contributes to a range of cardiovascular pathologies and diseases via angiotensin type 1 receptor (AT₁R) activation. On the other hand, tElsevier Inc.he angiotensin type 2 receptor (AT₂R) is thought to counter-regulate AT₁R function. In this review, we describe the enhanced expression and function of AT₂R in various cardiovascular disease settings. In addition, we illustrate that the RAS consists of a family of angiotensin peptides that exert cardiovascular effects that are often distinct from those of Ang II. During cardiovascular disease, there is likely to be an increased functional importance of AT₂R, stimulated by Ang II, or even shorter angiotensin peptide fragments, to limit AT₁R-mediated overactivity and cardiovascular pathologies.

Angiotensin II Receptor Expression Following Intestinal Transplantation in Mice

BACKGROUND

To further improve the success rate of intestinal transplantation there is a need to find early appearing indicators of rejection. The specific aim of this study was to compare Angiotensin (Ang) II type 1 receptor and Ang II type 2 receptor expression in relation to histological signs of rejection.

METHODS

Mice of the C57BL6 strain with syngeneic intestinal grafts were compared to mice subjected to allogeneic intestinal transplantation with BalbC strain as donors. Local expression of Ang II type 1 and 2 receptor was evaluated using rt-PCR and Western blot and compared to histological picture in grafts and native intestine.

RESULTS

The Ang II type 2 receptor protein expression was markedly up-regulated in the allogeneically transplanted graft from day 1 postoperatively. Histological signs of rejection were not seen until day 6.

CONCLUSION

Intestinal allograft transplantation in mice is associated with a marked up-regulation of the Ang II type 2 receptor. However, the detailed role of the renin-angiotensin system in the immune rejection following intestinal transplantation remains to be clarified.

ANG II type 2 receptors and neural control of intrarenal blood flow

We tested the hypothesis that activation of angiotensin type 2 (AT(2)) receptors, by both exogenous and endogenous ANG II, modulates neurally mediated vasoconstriction in the renal cortical and medullary circulations. Under control conditions in pentobarbital-anesthetized rabbits, electrical stimulation of the renal nerves (RNS; 0.5-8 Hz) reduced renal blood flow (RBF; -88 +/- 3% at 8 Hz) and cortical perfusion (CBF; -92 +/- 2% at 8 Hz) more than medullary perfusion (MBF; -67 +/- 6% at 8 Hz). Renal arterial infusion of ANG II, at a dose titrated to reduce RBF by approximately 40-50% (5-50 ng.kg(-1).min(-1)) blunted responses of MBF to RNS, without significantly affecting responses of RBF or CBF. Subsequent administration of PD123319 (1 mg/kg plus 1 mg.kg(-1).h(-1)) during continued renal arterial infusion of ANG II did not significantly affect responses of RBF or CBF to RNS but enhanced responses of MBF, so that they were similar to those observed under control conditions. In contrast, administration of PD123319 alone blunted responses of CBF and MBF to RNS. Subsequent renal arterial infusion of ANG II in PD123319-pretreated rabbits restored CBF responses to RNS back to control levels. In contrast, ANG II infusion in PD123319-pretreated rabbits did not alter MBF responses to RNS. These data indicate that exogenous ANG II can blunt neurally mediated vasoconstriction in the medullary circulation through activation of AT(2) receptors. However, AT(2)-receptor activation by endogenous ANG II appears to enhance neurally mediated vasoconstriction in both the cortical and medullary circulations.

Glucocorticoid excess and hypertension

Cushing's syndrome is a rare disorder characterized by chronic, excess glucocorticoid exposure. Hypertension is one of the most discriminating features of the disease, as it is present in 80% of patients. Patients with Cushing's syndrome have a mortality rate four times that of the general population, most likely secondary to an increased number of cardiovascular risk factors, including hypertension. In this article, we review several pathogenetic mechanisms of glucocorticoid-induced hypertension, including the role of sodium/water and mineralocorticoid excess, as well as involvement of the vasculature and kidney. Although treatment of hypertension with available antihypertensive medications is only moderately successful, after cure of Cushing's syndrome, approximately 30% of patients have persistent hypertension.

ACE and non-ACE mediated effect of angiotensin I on intracellular calcium mobilization in rat glomerular arterioles

Because renin and angiotensin I (ANG I) level are high in the renal circulation, the conversion of ANG I is a critical step in the regulation of glomerular hemodynamics. We studied this conversion by investigating the effect of ANG I on intracellular Ca(2+) concentration ([Ca(2+)](i)) in rat juxtamedullary glomerular afferent and efferent arterioles (AA and EA, respectively). Two types of EA were considered, thin EA and muscular EA, terminating as peritubular capillaries and vasa rectae, respectively. In all arterioles, ANG I elicited [Ca(2+)](i) elevations. Maximal responses of 171 +/- 28 (AA), 183 +/- 7 (muscular EA), and 78 +/- 11 nM (thin EA) (n = 6), similar to those obtained with ANG II, were observed with 100 nM ANG I. The EC(50) values were 20 times higher for ANG I than for ANG II in AA (10.2 vs. 0.5) and muscular EA (6.8 vs. 0.4 nM) and 150 times higher in thin EA (15.2 vs. 0.1 nM). ANG I effect was blocked by losartan, indicating that AT(1) receptors were involved. The ANG-converting enyzme (ACE) inhibitor lisinopril inhibited the maximal response to ANG I in AA and muscular EA by 75 +/- 9% (n = 13) and 70 +/- 7% (n = 13), respectively, but had no effect in thin EA (n = 14). The serine protease inhibitor aprotinin, the chymase inhibitor chymostatin, and the cysteine protease inhibitors E64 and leupeptin had no effect on ANG I action. These data show that ANG I effects are mainly mediated by ACE in AA and muscular EA but not in thin EA. The lisinopril-insensitive response may be related to conversion by unknown enzyme(s) and/or to activation of AT(1) receptors by ANG I.

The angiotensin II receptor type 2 agonist CGP 42112A stimulates NO production in the porcine jejunal mucosa

BACKGROUND

This study was conducted to elucidate if nitric oxide is released by the porcine jejunal mucosa upon selective stimulation of AT2 receptors and the possible involvement of iNOS, and to investigate the presence of jejunal AT1 and AT2 receptors. Young landrace pigs were anaesthetized with ketamine and alpha-chloralose. Jejunal luminal NO output was assessed by intraluminal tonometry and analysed by chemiluminescense. Western blot analysis quantified mucosal iNOS and detected AT1 and AT2 receptor protein expression. AT1 and AT2 receptor RNA expression was detected by rtPCR.

RESULTS

Baseline luminal NO output correlated significantly to baseline mucosal iNOS-protein content. In animals treated with the AT2-receptor agonist CGP42112A (n = 11) luminal NO output increased significantly (at 0.1 micrograms kg(-1) min(-1) and 1.0 micrograms kg(-1) min(-1)), but not in animals simultaneously treated with the AT2-receptor antagonist PD123319 (bolus 0.3 mgkg-1, infusion 0.03 mg kg(-1) h(-1)) (n = 7). No differences in iNOS protein expression were found between groups or before/after the administration of drugs. Western blot and rtPCR recognised expression of the AT1 and AT2 receptors in jejunal tissue.

CONCLUSION

The results suggest that activation of AT2 receptors increases jejunal luminal NO output. This response was not due to an increase in the expression of the iNOS protein in the mucosa.

Kidney development and the fetal programming of adult disease

Recent evidence, from both epidemiological and animal experimental studies, suggest that the very first environment, the intrauterine, is extremely important in determining the future health of the individual. Genetic and 'lifestyle' factors impinge on, and can exacerbate, a 'programming' effect of an adverse fetal environment. In this review, we present compelling evidence to suggest that one of the major organs affected by an unfavourable prenatal environment is the kidney. Many of the factors that can affect fetal renal development (i.e. exposure to excess glucocorticoids, insufficient vitamin A, protein/calorie malnutrition (in rats) and alterations in the intrarenal renin angiotensinogen system), also produce hypertension in the adult animal. When nephron number is compromised during kidney development, maladaptive functional changes occur and can lead, eventually, to hypertension and/or renal disease. Surprisingly, it is during the very earliest stages of kidney development that the vulnerability to these effects occurs.

Dissociation between the circulating renin-angiotensin system and angiotensin II receptors in central losartan-induced hypertension

Losartan, an AT1 angiotensin II (ANG II) receptor non-peptide antagonist, induces an increase in mean arterial pressure (MAP) when injected intracerebroventricularly (icv) into rats. The present study investigated possible effector mechanisms of the increase in MAP induced by icv losartan in unanesthetized rats. Male Holtzman rats (280-300 g, N = 6/group) with a cannula implanted into the anterior ventral third ventricle received an icv injection of losartan (90 micro g/2 micro l) that induced a typical peak pressor response within 5 min. In one group of animals, this response to icv losartan was completely reduced from 18 +/- 1 to 4 +/- 2 mmHg by intravenous (iv) injection of losartan (2.5-10 mg/kg), and in another group, it was partially reduced from 18 +/- 3 to 11 +/- 2 mmHg by iv prazosin (0.1-1.0 mg/kg), an alpha1-adrenergic antagonist (P<0.05). Captopril (10 mg/kg), a converting enzyme inhibitor, injected iv in a third group inhibited the pressor response to icv losartan from 24 +/- 3 to 7 +/- 2 mmHg (P<0.05). Propranolol (10 mg/kg), a beta-adrenoceptor antagonist, injected iv in a fourth group did not alter the pressor response to icv losartan. Plasma renin activity and serum angiotensin-converting enzyme activity were not altered by icv losartan in other animals. The results suggest that the pressor effect of icv losartan depends on angiotensinergic and alpha1-adrenoceptor activation, but not on increased circulating ANG II.

Targeting of captopril to the kidney reduces renal angiotensin-converting enzyme activity without affecting systemic blood pressure

We have synthesized a prodrug of the angiotensin-converting enzyme (ACE) inhibitor captopril by coupling this drug covalently to the low molecular weight protein (LMWP) lysozyme. Such drug-LMWP conjugates can be used for renal drug delivery, since LMWPs accumulate specifically in the proximal tubular cells of the kidney. In the present study, we compared the effects of captopril-lysozyme and free captopril in male Wistar rats. ACE activity in plasma and the kidney was measured after intravenous bolus injection of either the captopril-lysozyme conjugate (33 mg. kg(-1), corresponding to 0.2 mg. kg(-1) captopril) or equivalent dosages of free captopril and lysozyme. The administration of the captopril-lysozyme conjugate resulted in less plasma ACE inhibition and a longer-lasting renal ACE inhibition compared with the free drug. Effects on blood pressure and natriuresis were studied during intravenous infusion of captopril-lysozyme (275 mg. kg(-1). 6 h(-1) conjugate, corresponding to 5 mg. kg(-1). 6 h(-1) captopril) or an equimolar dosage of free captopril. Captopril-lysozyme did not affect systemic blood pressure, whereas free captopril lowered blood pressure significantly (-23 +/- 32% versus control after 6 h). Captopril-lysozyme increased natriuresis about 3-fold compared with control levels (260 +/- 32% after 6 h), whereas free captopril treatment resulted in a reduced sodium excretion (26 +/- 12%). Furthermore, captopril at a lower dose, which only moderately lowered blood pressure, showed an increased sodium excretion. We conclude that renal delivery of captopril using captopril-lysozyme results in reduced systemic activity and increased kidney-specific activity of the targeted drug.

Enhancement of phosphatidylcholine biosynthesis by angiotensin-(1-7) in the rat renal cortex

In the present paper, we investigated the effect of angiotensin-(1-7) (Ang-(1-7)) on phospholipid biosynthesis in the rat renal cortex. A significant increase in phosphatidylcholine (PC) labeling was observed when cortical slices, prelabeled with [32P]orthophosphate, were incubated for 30 min in the presence of Ang-(1-7) (1 pM to 100 nM). Neither the phospholipase C inhibitors, neomycin or db-cAMP nor the protein kinase C inhibitors, chelerythrine or H7, modified the stimulatory effect induced by 0.1 nM Ang-(1-7). The enhancement of PC biosynthesis caused by 0.1 nM Ang-(1-7) was unmodified by either losartan, an AT(1) receptor antagonist, or (1-[[4-(dimethylamino)-3-methylphenyl]methyl]-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazol[4,5-c]pyridine-6-carboxylic acid ditrifluoroacetate) (PD 123319), an AT(2) receptor antagonist, but was partially blocked by [D-Ala(7)]Ang-(1-7), an Ang-(1-7) specific antagonist. However, losartan potentiated the effect of 100 nM Ang-(1-7) on PC biosynthesis. Losartan by itself increased the de novo synthesis of PC. These results suggest that the Ang-(1-7)-mediated increase in PC biosynthesis is independent of AT(1) and AT(2) receptor activation but mediated by a specific Ang-(1-7) receptor. This mechanism is independent of phospholipase C and PKC activation.

Angiotensin II-responsive element is the insulin-responsive element in the adipocyte fatty acid synthase gene: role of adipocyte determination and differentiation factor 1/sterol-regulatory-element-binding protein 1c

We have previously shown that angiotensin II (Ang II) increases the expression of the gene encoding adipocyte fatty acid synthase (FAS). Here we investigate the mechanism responsible for increased FAS gene transcription by Ang II. We demonstrate that Ang II increased luciferase activity by 3-fold in 3T3-L1 adipocytes transfected with fusion constructs linking the FAS promoter to the luciferase reporter gene. Interestingly, we mapped the Ang II regulatory sequences to the insulin-responsive region (E box) in the proximal FAS promoter. The E box alone was able to mediate Ang II responsiveness when linked to a heterologous promoter. However, this response was lost when mutations that abolished the binding of the E box to its transcription factors were introduced. Using adenoviral overexpression of a dominant-negative form of adipocyte determination and differentiation factor 1 (ADD1), a transcription factor that binds to the insulin-responsive E box, we demonstrated that ADD1 was required for Ang II regulation of the FAS gene in 3T3-L1 adipocytes. Furthermore, ADD1 expression was also up-regulated by Ang II. With the use of transfections as well as glucose transport assays, we further demonstrated that Ang II stimulation of the FAS gene was dependent on glucose. In conclusion, this is the first report that Ang II regulates adipocyte FAS gene transcription via insulin response sequences in a glucose-dependent manner and that this regulation is mediated at least in part via the ADD1 transcription factor.

Protective effect of agiotensin II type I receptor antagonist, CV-11974, on ischemia and reperfusion injury of the liver

BACKGROUND

Microcirculatory disturbance has been shown to play a critical role in hepatic ischemia and reperfusion (I/R) injury. Angiotensin II (AngII) is one of the most potent endogenous vasoconstrictors. Angiotensin II type I (AT1) receptor antagonist has been reported to have protective effects on I/R injury of the heart and kidney. However, effect on hepatic I/R injury has not been determined. In this study, we investigate our hypothesis that AT1 receptor antagonist, CV-11974, attenuates hepatic I/R injury.

METHODS

Twelve beagle dogs underwent a 2-hr total hepatic vascular exclusion with veno-venous bypass. CV-11974 was given to animals at a dose of 0.002 mg/ kg/min for 5 min followed by 0.001 mg/kg/min for 25 min via portal vein before ischemia (group II, n=6). Nontreated animals were used as the control (group I, n=6). Animal survival, hemodynamics, hepatic tissue blood flow (HTBF), liver function, platelet count, renin activity, and AngII concentration of hepatic vein, energy metabolism, and histopathology were analyzed.

RESULTS

Two-week survival was 33% in group I, in contrast, 100% in group II. Mean arterial blood pressure during early reperfusion was maintained, and HTBF after reperfusion was significantly higher in group II. Treatment attenuated liver enzyme release and decrease of platelet count, increased renin and AngII, suppressed ATP degradation during ischemia and enhanced ATP resynthesis after reperfusion. Neutrophil infiltration and histopathological damages were lessened in group II.

CONCLUSIONS

Our data demonstrated that the local renin-angiotensin system might play a role in hepatic microcirculation. AT1 receptor blockade with CV-11974 attenuated hepatic microcirculatory disturbance and ameliorated I/R injury.

Involvement of angiotensin II and endothelin-1 in the development of submandibular gland hypertrophy in response to isoproterenol in rats

We investigated whether angiotensin II (Ang II) and endothelin-1(ET-1) are involved in submandibular hypertrophy in response to repeated treatment with isoproterenol (ISO) in rats. The immunoreactive Ang II (IRAng II) and immunoreactive ET-1 (IRET-1) contents of ISO-induced hypertrophy were significantly higher than those of control glands. Treatment of isolated gland tissues with ISO (1 microM) or dobutamine (1 microM) caused significant increases in the IRAng II and IRET- 1 contents of the glands compared with controls. These increases were suppressed by pretreatment with enalapril (3 microM) or captopril (3 microM). Treatment with Ang II (10 microM) also caused an increase in IRET-1 content. Our findings suggest that Ang II and ET-1 are involved in the submandibular gland hypertrophy that develops in rats repeatedly treated with ISO, and that these biologically active peptides may act as growth factors. They also imply that the tissue renin-angiotensin system and Ang II specific receptors are present in the submandibular glands.

Novel mechanisms linking angiotensin II and early atherogenesis

We propose that Ang II exerts an as yet uncharacterized immunomodulatory effect on monocyte maturation, differentiation, or extravasation, which may depend on the myelomonocytic phenotype. Since the myelopoietic process originating at stem cells and culminating in release to the blood is at least 6 days, it is conceivable that the observation of reduced monocyte CD11b expression two weeks after completion of losartan treatment indicates a suppression of the CD11b phenotype in newly released CD14(+)/CD45(+) monocytes. Other studies employing suppression of AT(1)-receptors with deoxy-oligonucleotides have reported effects on blood pressure that surpass those predicted by the duration of the treatment.(87) These data would suggest that it is possible to interrupt a stimulatory signal by Ang II through a gene-related mechanism that in our experiments may reside in the mechanisms that regulate myelopoiesis. While our knowledge of the role of Ang II in the regulation of monocyte formation and function is incomplete, we have taken a first step in attempting to synthesize the data described above into a comprehensive hypothesis for further evaluation of the factors that initiate atherogenesis. Such effects may crucially contribute to the clinical benefit of AT(1)-receptor antagonists, independent of depressor effects, and may represent a paradigm for novel, anti-inflammatory actions by this class of drugs.

Activation of local renin-angiotensin system by chronic hypoxia in rat pancreas

Previous studies have provided evidence that several key elements of renin-angiotensin system (RAS) are present in the rat pancreas, notably angiotensinogen, which is mandatory for intracellular generation of physiologically active angiotensin II. The data support the existence of an intrinsic RAS, which may be important for pancreatic blood flow and ductal anion secretion. In the present study, the effect of chronic hypoxia on the expression of RAS components, particularly at the levels of its precursor angiotensinogen and its receptor subtypes AT(1) and AT(2), were investigated in the rat pancreas. Results from western blot and semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) analyses unequivocally showed that chronic hypoxia caused a marked increase in angiotensinogen both at the protein and gene levels when compared with that in the normoxic pancreas. However, results from RT-PCR showed that there was a differential effect of chronic hypoxia on the expression of AT(1) and AT(2) receptor subtypes, which exhibited subtype-specific changes in gene expression. For AT(1), chronic hypoxia did not cause a significant change in mRNA expression for AT(1a) but a significant increase in mRNA expression for AT(1b). For AT(2), chronic hypoxia caused a marked increase in its mRNA expression. The increased expression of RAS component genes by chronic hypoxia and its significance of changes may be important for physiological and pathophysiological aspects of the pancreas.

Release of angiotensin-(1-7) from the rat hindlimb: influence of angiotensin-converting enzyme inhibition

The results of recent studies have demonstrated that angiotensin (Ang)-(1-7) contributes to the antihypertensive actions of either combined ACE/Ang II type 1 receptor blockade or ACE inhibition alone. The vasculature is a key site of action for either drug regimen, and evidence favors a local Ang system within these tissues. Because ACE may degrade Ang-(1-7), we determined whether ACE inhibition alters Ang-(1-7) release from the rat hindlimb perfused with Krebs-Ringer buffer containing Ficoll. Ang-(1-7) release averaged 36+/-13 fmol (period 1, 15-minute collection) and 44+/-11 fmol (period 2) in the control buffer. The addition of the ACE inhibitor lisinopril to the perfusion buffer augmented levels of Ang-(1-7) in periods 3 (144+/-39 fmol) and 4 (163+/-35 fmol; P<0.05 versus 1 or 2, n=8). HPLC and radioimmunoassay of effluent from control or lisinopril treatment demonstrated a single immunoreactive peak with a retention time identical to that of Ang-(1-7). The addition of the neprilysin inhibitor SCH 39370 reduced Ang-(1-7) release in the lisinopril buffer from 177+/-32 (period 1) and 173+/-39 (period 2) fmol to 112+/-24 (period 3) and 87+/-23 fmol (period 4; P<0.05 versus 1 or 2, n=6). Ang I metabolism in the collected perfusate revealed the formation of Ang-(1-7) that was sensitive only to thimet oligopeptidase inhibition; Ang II generation was not detected. The present study demonstrates the recovery of endogenous Ang-(1-7) from the perfused hindlimb. The release of Ang-(1-7) is significantly influenced by inhibition of ACE, which may reflect both increased substrate (Ang I) levels and reduced metabolism of the peptide. Neprilysin inhibition reduced but did not abolish Ang-(1-7) release, which suggests that other endopeptidases may contribute to the release of the peptide.

Dynamic Ca2+ signalling in rat arterial smooth muscle cells under the control of local renin-angiotensin system

1. We visualized the changes in intracellular Ca2+ concentration ([Ca2+]i), using fluo-3 as an indicator, in individual smooth muscle cells within intact rat tail artery preparations. 2. On average in about 45 % of the vascular smooth muscle cells we found spontaneous Ca2+ waves and oscillations ( approximately 0.13 Hz), which we refer to here as Ca2+ ripples because the peak amplitude of [Ca2+]i was about one-seventh of that of Ca2+ oscillations evoked by noradrenaline. 3. We also found another pattern of spontaneous Ca2+ transients often in groups of two to three cells. They were rarely observed and are referred to as Ca2+ flashes because their peak amplitude was nearly twice as large as that in noradrenaline-evoked responses. 4. Sympathetic nerve activity was not considered responsible for the Ca2+ ripples, and they were abolished by inhibitors of either the Ca2+ pump in the sarcoplasmic reticulum (cyclopiazonic acid) or phospholipase C (U-73122). 5. Both angiotensin antagonists ([Sar1,Ile8]-angiotensin II and losartan) and an angiotensin converting enzyme inhibitor (captopril) inhibited the Ca2+ ripples. 6. The extracellular Ca2+-dependent tension borne by unstimulated arterial rings was reduced by the angiotensin antagonist by approximately 50 %. 7. These results indicate that the Ca2+ ripples are generated via inositol 1,4, 5-trisphosphate-induced Ca2+ release from the intracellular Ca2+ stores in response to locally produced angiotensin II, which contributes to the maintenance of vascular tone.

Delayed recovery of hypertension after single dose losartan in angiotensin II-infused conscious rats

OBJECTIVE

In a conscious unrestrained rat model, it takes approximately 1 week for angiotensin II to increase blood pressure to maximum levels. We investigated the time required for hypertension to fully recover after acute angiotensin II receptor blockade in this angiotensin II dependent hypertensive model.

DESIGN

Conscious unrestrained rats (n = 8) infused with 10 ng/kg per min angiotensin II for 21 days received losartan (10 mg/kg) on day 17 of angiotensin II infusion. Mean arterial pressure (MAP) and heart rate were monitored continuously. The acute pressor response to 50 ng/kg per min angiotensin II was monitored for 2 h on days 15, 17, 18, 19 and 20 of angiotensin II infusion. Plasma renin concentration (PRC) was measured daily.

RESULTS

Angiotensin II increased MAP acutely by 26 +/- 2 mmHg and by a further 23 +/- 4 mmHg between days 4 and 8. Losartan acutely reduced MAP by 75 +/- 2 mmHg; 24 h later MAP had partially recovered but remained suppressed by 47 +/- 3 mmHg. MAP had not fully recovered 4 days later. Some 2 h after losartan, the acute pressor response to angiotensin II had fallen from 24 +/- 2 mmHg to zero. This recovered to 13 +/- 5 and 28 +/- 2 mmHg 24 and 48 h post losartan. After losartan PRC rose from 0.1 +/- 0.05 to above 1 ng/ml per h for less than 24 h.

CONCLUSION

A single dose of losartan reverses both the fast and slow pressor effects of continuous angiotensin II infusions. While losartan is metabolized, the fast vasoconstrictor effect recovers quickly but the slow pressor effect takes almost a week to build up again to maximum levels. Since the slow pressor effect is mediated via the AT1 receptor, any means of blocking the renin-angiotensin system is likely to keep blood pressure below maximum hypertensive levels for several days after the drug has disappeared from the circulation.

Intrarenal angiotensin converting enzyme inhibition in spontaneously hypertensive rats

We examined the hypotensive effect of enalapril in relation to the local renin-angiotensin system of the kidney in spontaneously hypertensive rats (SHR). Oral administration of enalapril for 7 days decreased mean arterial blood pressure and renal tissue angiotensin II concentration without affecting plasma angiotensin II concentration in SHR. The enalapril treatment did not affect maximum binding of angiotensin II to renal tubules and glomeruli in SHR. In normotensive Wistar-Kyoto rats, no significant changes in mean arterial blood pressure, renal and plasma angiotensin levels were observed with enalapril treatment. Direct infusion of enalapril into the renal medullary interstitium decreased mean arterial blood pressure in association with the reduction of renal tissue angiotensin II concentration without changes in plasma angiotensin II concentration in SHR. These observations suggest that the inhibition of angiotensin conversion in the kidney is important for the hypotensive action of enalapril.

Cross-over study comparing effects of treatment with an angiotensin converting enzyme inhibitor and an angiotensin II type 1 receptor antagonist on cardiovascular changes in hypertension

OBJECTIVE

To compare the blood-pressure-lowering effects of an angiotensin converting enzyme inhibitor, perindopril, with those of an angiotensin II type 1 receptor antagonist, L-158,809, for adult spontaneously hypertensive rats.

DESIGN

A cross-over design was used, to treat adult spontaneously hypertensive rats with one drug for 10 weeks, and then with the other for 5 weeks.

METHODS

Adult, male spontaneously hypertensive rats (aged 15 weeks) were treated daily by gavage for 10 weeks with perindopril (P group) or L-158,809 (L group), then treatment was crossed over so that rats in the P group were treated with L-158,809 (P/L group) and rats in the L group were treated with perindopril (L/P group) for 5 weeks. Blood pressure was measured weekly. Plasma angiotensin converting enzyme activity, renal angiotensin receptor density, and arterial structure and functioning were measured after the single and crossover treatment periods.

RESULTS

Treatment lowered the blood pressure from 206 +/- 2 mmHg in rats in the control group, to 126 +/- 2 in rats in the P group and 150 +/- 2 in rats in the L group. After the cross-over period, blood pressure decreased further from 150 +/- 2 to 129 +/- 3 mmHg in rats in the L/P group, whereas blood pressure of spontaneously hypertensive rats in the P/L group increased from 126 +/- 2 to 148 +/- 2 mmHg. Perindopril treatment almost abolished plasma angiotensin converting enzyme activity, whereas L-158,809 treatment had no effect. Renal angiotensin II receptor density was decreased versus baseline in rats in the P and L groups. The affinity of binding was decreased versus baseline in rats in the L group. A positive correlation to blood pressure was found for mesenteric artery wall thickness and wall: lumen ratio. Concentration for half-maximal effect for the response of mesenteric arteries from rats in the P group to norepinephrine was lower than that of the control group rats. Angiotensin II potentiated the norepinephrine-stimulated contraction of arteries from rats in the control and P groups, but not that of arteries from rats in the groups treated with L-158,809.

CONCLUSION

Perindopril was more effective than was L-158,809 at lowering the blood pressure of adult spontaneously hypertensive rats, and at altering the structure and functioning of the arteries.