Regulatory role of brain angiotensins in the control of physiological and behavioral responses

Fetal Undernutrition Programming, Sympathetic Nerve Activity, and Arterial Hypertension Development

A wealth of evidence showed that low birth weight is associated with environmental disruption during gestation, triggering embryotic or fetal adaptations and increasing the susceptibility of progeny to non-communicable diseases, including metabolic and cardiovascular diseases, obesity, and arterial hypertension. In addition, dietary disturbance during pregnancy in animal models has highlighted mechanisms that involve the genesis of arterial hypertension, particularly severe maternal low-protein intake (LP). Functional studies demonstrated that maternal low-protein intake leads to the renal decrease of sodium excretion and the dysfunction of the renin-angiotensin-aldosterone system signaling of LP offspring. The antinatriuretic effect is accentuated by a reduced number of nephron units and glomerulosclerosis, which are critical in establishing arterial hypertension phenotype. Also, in this way, studies have shown that the overactivity of the central and peripheral sympathetic nervous system occurs due to reduced sensory (afferent) renal nerve activity. As a result of this reciprocal and abnormal renorenal reflex, there is an enhanced tubule sodium proximal sodium reabsorption, which, at least in part, contributes directly to arterial hypertension development in some of the programmed models. A recent study has observed that significant changes in adrenal medulla secretion could be involved in the pathophysiological process of increasing blood pressure. Thus, this review aims to compile studies that link the central and peripheral sympathetic system activity mechanisms on water and salt handle and blood pressure control in the maternal protein-restricted offspring. Besides, these pathophysiological mechanisms mainly may involve the modulation of neurokinins and catecholamines pathways.

Firibastat: A Novel Brain Aminopeptidase Inhibitor - A New Era of Antihypertensive therapy

Global incidence and prevalence of hypertension continues to increase and remains a significant challenge. The ever-increasing number of cases are due to comorbid conditions such as obesity and diabetes, as well as lifestyle indiscretions such as excessive salt intake. Hypertension, congestive heart failure, and kidney disease are all conditions resulting from abnormal Renin-Angiotensin-Aldosterone activation and adverse remodeling. Firibastat, a novel Brain Aminopeptidase inhibitor, may be able to help achieve blood pressure control in those with resistant hypertension. In this review article, we will discuss the biochemical pathway of firibastat and various trials assessing drug efficacy in animals and humans. This drug has the potential to curb the risk of uncontrolled hypertension and help improve long term cardiovascular morbidity and mortality.

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

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

Modulation of brain ACE and ACE2 may be a promising protective strategy against cerebral ischemia/reperfusion injury: an experimental trial in rats

The brain renin-angiotensin system (RAS) is considered a crucial regulator for physiological homeostasis and disease progression. We evaluated the protective effects of the angiotensin receptor blocker (ARB) telmisartan and the angiotensin-converting enzyme 2 (ACE2) activator xanthenone on experimental cerebral ischemia/reperfusion (I/R) injury. Rats were divided into a sham control, a cerebral I/R control, a standard treatment (nimodipine, 10 mg/kg/day, 15 days, p.o.), three telmisartan treatments (1, 3, and 10 mg/kg/day, 15 days, p.o.), and three xanthenone treatments (0.5, 1, and 2 mg/kg/day, 15 days, s.c.) groups. One hour after the last dose, all rats except the sham control group were exposed to 30-min cerebral ischemia followed by 24-h reperfusion. Brain ACE and ACE2 activities and the apoptotic marker caspase-3 levels were assessed. Glutathione (GSH), malondialdehyde (MDA), and nitric oxide end products (NOx) as oxidative markers and tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and IL-10 as immunological markers were assessed. Histopathological examination and immunohistochemical evaluation of glial fibrillary acidic protein (GFAP) were performed in cerebral cortex and hippocampus sections. Telmisartan and xanthenone in the higher doses restored MDA, NOx, TNF-α, IL-6, caspase-3, ACE, and GFAP back to normal levels and significantly increased GSH, IL-10, and ACE2 compared to I/R control values. Histopathologically, both agents showed mild degenerative changes and necrosis of neurons in cerebral cortex and hippocampus compared with I/R control group. Modulation of brain RAS, either through suppression of the classic ACE pathway or stimulation of its antagonist pathway ACE2, may be a promising strategy against cerebral I/R damage.

Advances in understanding the renin-angiotensin-aldosterone system (RAAS) in blood pressure control and recent pivotal trials of RAAS blockade in heart failure and diabetic nephropathy

The renin-angiotensin-aldosterone system (RAAS) plays a fundamental role in the physiology of blood pressure control and the pathophysiology of hypertension (HTN) with effects on vascular tone, sodium retention, oxidative stress, fibrosis, sympathetic tone, and inflammation. Fortunately, RAAS blocking agents have been available to treat HTN since the 1970s and newer medications are being developed. In this review, we will (1) examine new anti-hypertensive medications affecting the RAAS, (2) evaluate recent studies that help provide a better understanding of which patients may be more likely to benefit from RAAS blockade, and (3) review three recent pivotal randomized trials that involve newer RAAS blocking agents and inform clinical practice.

Losartan may prevent the elevation of plasma glucose, corticosterone and catecholamine levels induced by chronic stress

Introduction

Stress is a stimulus that activates the hypothalamic pituitary adrenal (HPA) axis and sympathetic nervous system (SNS). Increased activity of the SNS causes to increment or impairment in blood pressure, heart rate, body temperature and plasma glucose and adrenocorticotrophic hormone (ACTH) levels. Angiotensin II (Ang II), which is a product of the renin-angiotensin system (RAS), is an important factor affecting the activity of the SNS and responses to stress. We suggest that the blockade of Ang II may be worthwhile in the prevention and treatment of diabetes mellitus and cardiovascular diseases affected by stress. Therefore, we investigated the effects of immobilisation stress on blood glucose, norepinephrine (NE), epinephrine (E) and corticosterone levels and the effects of an Ang II receptor antagonist, losartan, on these parameters.

Materials and methods

The rats were kept in small cylindrical cages for 60 min/day for 10 consecutive days to perform chronic immobilisation stress. Losartan (10 mg/kg) was given daily by gavage to Losartan (L) and Losartan + Chronic Stress (L+CS) groups. Control (C) and Chronic Stress (CS) P groups received an equal volume of saline daily by gavage for 10 days. After the last stress regimen, blood samples were collected for plasma glucose, NE, E and corticosteroid measurements.

Results

Plasma glucose, NE, E and corticosterone levels in the CS Group increased significantly compared with the C group. In Group L+CS, the plasma glucose, NE, E and corticosterone levels decreased significantly vs. Group CS. In Group L there was no significant difference vs. Group C.

Conclusion

It can be speculated that chronic blockade of RAS may decrease the excess sympathetic responses to stress in cardiovascular diseases and prevent the likely development of Type II diabetes mellitus.

Convergent evidences from human and animal studies implicate angiotensin I-converting enzyme activity in cognitive performance in schizophrenia

In schizophrenia (SCZ), higher angiotensin I-converting enzyme (ACE) levels have been reported in patient's blood and cerebrospinal fluid (CSF). Hereby, we propose to explore whether the ACE activity levels are associated to cognitive performance in SCZ. Seventy-two patients with SCZ or schizoaffective disorder diagnosis, and 69 healthy controls (HCs) underwent a cognitive battery with parallel collection of peripheral blood samples to measure ACE activity. Significant higher ACE activity levels were confirmed in the plasma of SCZ patients compared with HCs (Student's t=-5.216; P<0.001). ACE activity significantly correlated to Hopkins delayed recall measures (r=-0.247; P=0.004) and Hopkins total (r=-0.214; P=0.012). Subjects grouped as high ACE activity (above average) had worse performance compared with low ACE activity level group for Hopkins delayed recall measure, even after correction for clinical condition, age, gender and years of education (P=0.029). The adjusted R squared for this final model was 0.343. This result was evident only comparing extreme groups for ACE activity, when splitting the sample in three groups with similar number of subjects. To clarify this finding, we performed an evaluation of the cognitive performance of transgenic mice with three copies of ACE gene in novel object recognition (NOR) test, which showed that such animals presented impairment in NOR (P<0.05) compared with two copies of wild-type animals. The results observed in SCZ patients and animal model suggest both the association of ACE to cognitive deficits in SCZ. This finding may support the evaluation of novel treatment protocols and/or of innovative drugs for specific intervention of cognitive deficits in SCZ envisioning concomitant ACE activity and behavior evaluations.

Randomised, double-blind, placebo-controlled, dose-escalating phase I study of QGC001, a centrally acting aminopeptidase a inhibitor prodrug

BACKGROUND AND OBJECTIVES

Inhibition of brain aminopeptidase A (APA), which converts angiotensin II into angiotensin III, has emerged as a novel antihypertensive treatment, as demonstrated in several experimental animal models. QGC001 (originally named RB150) is a prodrug of the specific and selective APA inhibitor EC33, and as such it is the prototype of a new class of centrally acting antihypertensive agents. Given by the oral route in hypertensive rats, it enters the brain and generates EC33, which blocks the brain renin-angiotensin system activity and normalises blood pressure. The aim of the present study was to evaluate the safety, pharmacokinetics and pharmacodynamic effects of QGC001 in humans.

DESIGN AND METHODS

Fifty-six healthy male volunteers were randomly assigned to receive in double-blind and fasted conditions single oral doses of 10, 50, 125, 250, 500, 750, 1,000 and 1,250 mg of QGC001 (n = 6/dose) or placebo (n = 2/dose). We measured plasma and urine concentrations of both QGC001 and EC33 by liquid chromatography-tandem mass spectrometry, plasma renin concentrations (PRC), plasma and free urine aldosterone (PAldo and UAldo), plasma copeptine (PCop), and plasma and urine cortisol (PCort and UCort) concentrations, and supine systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) at various time points.

RESULTS

All doses of QGC001 were clinically and biologically well-tolerated. Peak plasma concentrations (Cmax) of QGC001 and EC33 increased linearly with the dose, with a median time to reach Cmax (tmax) of 1.5 h for QGC001 and 3.0 h for EC33. The median plasma elimination half-life of QGC001 was 1.6 h consistently throughout doses. Urinary excretion of QGC001 and EC33 was below 2% of the administered dose. When compared with placebo, QGC001 did not significantly change PRC, PAldo, UAldo, PCop, PCort or UCort. No significant change was observed for supine HR, SBP and DBP in any treatment group.

CONCLUSION

Single oral administration of QGC001 up to 1,250 mg in healthy volunteers was well-tolerated. Following oral administration, QGC001 is absorbed via the gastrointestinal tract and converted partially into its active metabolite EC33 in plasma. As in animal experiments, in normotensive subjects QGC001 had no effect on the systemic renin-angiotensin-aldosterone parameters and on PCop concentrations, a marker of vasopressin release. In normotensive subjects, a single dose of QCG001 had no effect on SBP, DBP or HR. These data support further evaluation of multiple oral doses of QGC001 in human volunteers and its clinical efficacy in hypertensive patients.

Enhancement of renal oxidative stress by injection of angiotensin II into the paraventricular nucleus in renal ischemia–reperfusion injury

This study was designed to investigate whether microinjection of angiotensin II (Ang II) into the hypothalamic paraventricular nucleus (PVN) in renal ischemia–reperfusion (IR) injury has any effect on renal oxidative stress and damage through renal sympathetic nerve activity (RSNA). One week before the induction of left renal IR injury, right nephrectomy was performed and a cannula was placed into the right PVN. Rats were then distributed among 4 groups (n = 6); Sham, IR, IR + Ang II, and IR + Ang II + losartan. Renal IR injury was induced by clamping the left renal artery for 45 min followed by 24 h reperfusion. Losartan (0.3 μg) and Ang II (3 ng) were microinjected into the PVN at 20 min and 10 min, respectively, before the induction of IR injury. Ang II increased plasma creatinine, urinary NAG activity, and histological changes, and enhanced RSNA compared with the IR group (p < 0.05). Ang II increased malondialdehyde (MDA) levels and reduced superoxide dismutase (SOD) activity in the kidney compared with IR injury. Losartan caused a reduction in plasma creatinine, urinary NAG activity, histological changes, renal sympathetic nerve activity (RSNA), and renal MDA levels, and increased renal SOD activity compared with the IR group (p < 0.05). These data demonstrated that increased RSNA activity, via microinjection of Ang II into the PVN, exaggerated renal IR injury by inducing oxidative stress in the kidney.

A new strategy for treating hypertension by blocking the activity of the brain renin-angiotensin system with aminopeptidase A inhibitors

Hypertension affects one-third of the adult population and is a growing problem due to the increasing incidence of obesity and diabetes. Brain RAS (renin-angiotensin system) hyperactivity has been implicated in the development and maintenance of hypertension in several types of experimental and genetic hypertension animal models. We have identified in the brain RAS that APA (aminopeptidase A) and APN (aminopeptidase N), two membrane-bound zinc metalloproteases, are involved in the metabolism of AngII (angiotensin II) and AngIII (angiotensin III) respectively. The present review summarizes the main findings suggesting that AngIII plays a predominant role in the brain RAS in the control of BP (blood pressure). We first explored the organization of the APA active site by site-directed mutagenesis and molecular modelling. The development and the use in vivo of specific and selective APA and APN inhibitors EC33 and PC18 respectively, has allowed the demonstration that brain AngIII generated by APA is one of the main effector peptides of the brain RAS, exerting a tonic stimulatory control over BP in conscious hypertensive rats. This identified brain APA as a potential therapeutic target for the treatment of hypertension, which has led to the development of potent orally active APA inhibitors, such as RB150. RB150 administered orally in hypertensive DOCA (deoxycorticosteroneacetate)-salt rats or SHRs (spontaneously hypertensive rats) crosses the intestinal, hepatic and blood-brain barriers, enters the brain, generates two active molecules of EC33 which inhibit brain APA activity, block the formation of brain AngIII and normalize BP for several hours. The decrease in BP involves two different mechanisms: a decrease in vasopressin release into the bloodstream, which in turn increases diuresis resulting in a blood volume reduction that participates in the decrease in BP and/or a decrease in sympathetic tone, decreasing vascular resistance. RB150 constitutes the prototype of a new class of centrally acting antihypertensive agents and is currently being evaluated in a Phase Ib clinical trial.

Association between the angiotensin-converting enzyme gene insertion/deletion polymorphism and first-episode patients with schizophrenia in a Chinese Han population

BACKGROUND

Angiotensin-converting enzyme (ACE), a key enzyme of the renin-angiotensin system, can modulate dopamine turnover in the midbrain. Previous studies have revealed an association between ACE gene insertion/deletion (I/D) polymorphism and chronic schizophrenia, yet results are conflicting.

OBJECTIVE

The primary objective of this study was to examine whether the ACE gene I/D polymorphism is associated with first-episode patients with schizophrenia (FEP) in a Chinese Han population.

METHODS

The presence of the polymorphism was determined in 220 FEP and 538 healthy controls using a case-control design. We assessed the psychopathology in 212 FEP using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

The allelic and genotypic frequencies of the ACE gene I/D polymorphism did not significantly differ between FEP and healthy controls (both p>0.05). However, the negative PANSS symptom was significantly higher in FEP with the D/D genotype than those with I/D and I/I genotypes (all p<0.05) even after Bonferroni corrections (all p<0.05). Furthermore, the D allele of the ACE gene was associated with higher negative PANSS symptom score in FEP.

CONCLUSIONS

Our results indicated that even though the ACE gene I/D polymorphism did not associate with FEP, it may play a role in susceptibility to the negative PANSS symptom of FEP in a Chinese Han population.

Angiotensinergic neurotransmission in the paraventricular nucleus of the hypothalamus modulates the pressor response to acute restraint stress in rats

We tested the hypothesis that the angiotensinergic neurotransmission, specifically in the paraventricular nucleus of the hypothalamus (PVN), is involved in the cardiovascular modulation during acute restraint stress (RS) in rats. The intravenous pretreatment with the angiotensin AT1 receptor antagonist losartan (5mg/kg) inhibited the pressor response to RS, but did not affect the concomitant RS-evoked tachycardiac response. Because similar effects were observed after the PVN pretreatment with CoCl2, and considering the high density of angiotensin receptors reported in the PVN, we studied the effect of the pretreatment of the PVN with either losartan or the angiotensin-converting enzyme (ACE) inhibitor lisinopril on the RS-evoked cardiovascular response. The bilateral microinjection of losartan (0.5 nmol/100 nL) or lisinopril (0.5 nmol/100nL) into the PVN inhibited the RS-related pressor response without affecting the tachycardiac response, suggesting that the PVN angiotensinergic neurotransmission modulates the vascular component of the stress response. Finally, to exclude the possibility that centrally injected drugs could be leaking to the circulation and acting on peripheral vascular receptors, we tested the effect of the intravenous pretreatment with either losartan (0.5 nmol/animal) or lisinopril (0.5 nmol/animal), assuming the hypothesis of a total spread of drugs from the CNS to the peripheral circulation. When animals were pretreated with such doses of either losartan or lisinopril, the cardiovascular RS-evoked response was not affected, thus indicating that even if there were a complete leakage of the drug to the periphery, it would not affect the cardiovascular response to RS. This observation favors the idea that the effect of the intravenous injection of 5mg/kg of losartan on the RS-related cardiovascular response would be explained by an action across the blood-brain barrier, possibly in the PVN. In conclusion, the results suggest that an angiotensinergic neurotransmission in the PVN acting on AT1-receptors modulates the vascular component of the RS-evoked cardiovascular response.

Anti-stress and nootropic activity of drugs affecting the renin-angiotensin system in rats based on indirect biochemical evidence

INTRODUCTION

Various stress hormones are responsible for bringing out stress-related changes and are implicated in learning and memory processes. The extensive clinical experience of angiotensin receptor blockers (ARBs) and direct renin inhibitor as antihypertensive agents provides anecdotal evidence of improvements in cognition. The neurochemical basis underlying the anti-stress and nootropic effects are unclear. This study was aimed to determine the effects of aliskiren, valsartan and their combination on the neuromediators of the central nervous system (CNS) and periphery as well as on cognitive function.

MATERIALS AND METHODS

Groups of rats were subjected to a forced swim stress for one hour after daily treatment with aliskiren, valsartan and their combination. The 24 h urinary excretion of vanillylmandellic acid (VMA), 5-hydroxyindoleacetic acid (5-HIAA), 6-β-hydroxycortisol (6-β-OH) cortisol and homovanillic acid (HVA) was determined in all groups under normal and stressed conditions. Nootropic activity was studied using cook's pole climbing apparatus and acetylcholinesterase (AChE) inhibitory activity by Ellman's method.

RESULTS

Administration of aliskiren (10 mg/kg), valsartan (20 mg/kg) and their combination at a dose of 5 and 10 mg/kg respectively reduced the urinary metabolite levels. Further, all drugs showed significant improvement in scopolamine-impaired performance and produced inhibition of the AChE enzyme.

CONCLUSIONS

The present study provides scientific support for the anti-stress and nootropic activities of aliskiren, valsartan and their combination.

Cardiovascular effect of angiotensin-(1-12) in the caudal ventrolateral medullary depressor area of the rat

Angiotensin (ANG)-(1-12) excites neurons via ANG II type 1 receptors (AT1Rs), which are present in the caudal ventrolateral medullary depressor area (CVLM). We hypothesized that microinjections of ANG-(1-12) into the CVLM may elicit decreases in mean arterial pressure (MAP), heart rate (HR), and sympathetic nerve activity. This hypothesis was tested in urethane-anesthetized adult male Wistar rats. Microinjections of ANG-(1-12) into the CVLM elicited decreases in MAP, HR, and greater splanchnic nerve activity (GSNA). ANG-(1-12)-induced responses consisted of initial (first 1-8 min) and delayed (8-24 min) phases. Prior microinjections of losartan, A-779, and captopril into the CVLM blocked initial, delayed, and both phases of ANG-(1-12) responses, respectively. Blockade of GABA receptors in the rostral ventrolateral medullary pressor area (RVLM) attenuated cardiovascular responses elicited by microinjections of ANG-(1-12) into the ipsilateral CVLM. Microinjections of ANG-(1-12) into the CVLM potentiated the reflex decreases and attenuated the reflex increases in GSNA elicited by intravenous injections of phenylephrine and sodium nitroprusside, respectively. These results indicate that microinjections of ANG-(1-12) into the CVLM elicit decreases in MAP, HR, and GSNA. Initial and delayed phases of these responses are mediated via ANG II and ANG-(1-7), respectively; the effects of ANG II and ANG-(1-7) are mediated via AT1Rs and Mas receptors, respectively. Captopril blocked both phases of ANG-(1-12) responses, indicating that angiotensin-converting enzyme is important in mediating these responses. GABA receptors in the RVLM partly mediate the cardiovascular responses to microinjections of ANG-(1-12) into the CVLM. Microinjections of ANG-(1-12) into the CVLM modulate baroreflex responses.

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.

Effect of angiotensin II on spatial memory, cerebral blood flow, cholinergic neurotransmission, and brain derived neurotrophic factor in rats

RATIONAL

Studies have shown the involvement of angiotensin II (Ang II) in neurobehavioral aspects, but the exact role of Ang II in memory is still ambiguous.

OBJECTIVE

This study explored the effect of central Ang II on spatial memory along with cholinergic neurotransmission, brain energy metabolism, cerebral blood flow (CBF), and brain-derived neurotrophic factor (BDNF) in rats.

METHODS

Spatial memory was evaluated by Morris water maze (MWM) after Ang II (ICV) administration in male Sprague-Dawley rats. CBF was measured by laser Doppler flowmetry. Oxidative stress adenosine triphosphate (ATP), BDNF, acetylcholinesterase (AChE), and acetylcholine (ACh) were estimated in the cortex and hippocampus at 1, 24, and 48 h after Ang II administration. The effect of AT1 and AT2 receptor blocker (candesartan and PD123,319, respectively), AChE inhibitor (donepezil), and antioxidant melatonin was studied on memory, CBF, and biochemical parameters.

RESULTS

Ang II caused spatial memory impairment by affecting acquisition, consolidation, and recall in the MWM test along with a significant reduction in CBF. Ang II significantly reduced ACh level and caused oxidative stress in the rat brain 1 h post-injection. No significant change was observed in BDNF, AChE, and ATP level. Candesartan and donepezil prevented Ang II-induced memory impairment, reduction in CBF and ACh level. However, PD123,319 and melatonin failed to prevent Ang II-induced memory impairment but improved CBF partially.

CONCLUSION

This study suggests that Ang II, via the AT1 receptor, affects spatial memory formation, CBF, and ACh level while AT2 receptor has no significant role.

Genetics of age-related white matter lesions from linkage to genome wide association studies

White matter lesions are a frequent phenomenon in the elderly and contribute to the development of disability. The mechanisms underlying these brain lesions are still not fully understood with age and hypertension being the most well established risk factors. The heritability of white matter lesions is consistently high in different populations. Candidate gene studies strongly support the role of genes involved in the renin–angiotensin system, as well as Notch3 signaling. The recent genome wide association study by the CHARGE consortium identified a novel locus on chromosome 17q25 harboring several genes such as TRIM65 and TRIM47 which pinpoint to possible novel mechanisms leading to white matter lesions.

Hyponatremia in a patient with scleroderma renal crisis: a potential role of activated renin-angiotensin system

Background

Scleroderma renal crisis is an important complication of scleroderma (systemic sclerosis) that is associated with significant morbidity and mortality. On the other hand, hyponatremia has never been reported in patients with scleroderma renal crisis.

Case presentation

A 66-year-old man with scleroderma was admitted to our hospital for an evaluation of renal dysfunction and extreme hypertension. The laboratory evaluation revealed remarkably high plasma renin activity in association with microangiopathic hemolytic anemia, and the anti-RNA polymerase III antibody assessment was positive. The patient was diagnosed with scleroderma renal crisis and was started treatment with enalapril maleate, an angiotensin-converting enzyme inhibitor. During hospitalization, the patient developed symptomatic hyponatremia three times and each laboratory analysis revealed improperly high levels of antidiuretic hormone without signs of extracellular fluid volume depletion as well as remarkably high plasma renin activities and angiotensin levels. However, hyponatremia has not been demonstrated to occur as a result of combined therapy with candesartan cilexetil, an angiotensin II receptor blocker, and aliskiren fumarate, a direct renin inhibitor. The plasma renin activities and angiotensin levels were normalized and the renal function was maintained after treatment.

Conclusions

To our best knowledge, this is the first documented case of scleroderma renal crisis complicated with hyponatremia. This report also suggests that the activated renin-angiotensin system may play a role in the development of hyponatremia and that hyponatremia should be taken into consideration as a rare but possible complication associated with screloderma renal crisis.

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.

The role of the brain renin-angiotensin system in hypertension: implications for new treatment

Hypertension affects 26% of adults and is in constant progress related to increased incidence of obesity and diabetes. One-third of hypertensive patients may be successfully treated with one antihypertensive agent, one-third may require two agents and in the remaining patients will need three agents for effective blood pressure (BP) control. The development of new classes of antihypertensive agents with different mechanisms of action therefore remains an important goal. Brain renin-angiotensin system (RAS) hyperactivity has been implicated in hypertension development and maintenance in several types of experimental and genetic hypertension animal models. Among the main bioactive peptides of the brain RAS, angiotensin (Ang) II and Ang III have similar affinities for type 1 (AT1) and type 2 (AT2) Ang II receptors. Following intracerebroventricular (i.c.v.) injection, Ang II and Ang III similarly increase arginine-vasopressin (AVP) release and BP. Blocking the brain RAS may be advantageous as it simultaneously (1) decreases sympathetic tone and consequently vascular resistance, (2) decreases AVP release, reducing blood volume and vascular resistance and (3) blocks angiotensin-induced baroreflex inhibition, decreasing both vascular resistance and cardiac output. However, as Ang II is converted to Ang III in vivo, the exact nature of the active peptide is not precisely determined. We summarize here the main findings identifying AngIII as one of the major effector peptides of the brain RAS in the control of AVP release and BP. Brain AngIII exerts a tonic stimulatory effect on BP in hypertensive rats, identifying brain aminopeptidase A (APA), the enzyme generating brain Ang III, as a potentially candidate target for hypertension treatment. This has led to the development of potent orally active APA inhibitors, such as RB150--the prototype of a new class of centrally acting antihypertensive agents.

Changed salt appetite and central angiotensin II-induced cellular activation in rat offspring following hypoxia during fetal stages

Hypoxia in pregnancy may induce fetal growth restriction and cause functional abnormalities during development. The present study determined the long-term influence of hypoxia in fetal life on dipsogenic behavior linked to central angiotensin (Ang) network in the offspring rats. Fetal blood pO(2) and body weight were decreased by hypoxia during pregnancy, followed by a postnatal "catch-up" growth. Subcutaneous hypertonic saline or intracerebroventricular Ang II significantly increased salt intake in the offspring prenatally exposed to hypoxia, while water intake was the same between the two groups. Ang II-induced c-fos expression was detected in the paraventricular nuclei, median preoptic nuclei, supraoptic nuclei, and subfornical organ in the brain, in association with reduced forebrain AT(2) receptor protein abundance in the offspring prenatally exposed to hypoxia. Levels of central AT(1) receptor protein were not changed between the two groups. Hypoxia during pregnancy could be linked to developmental problems related to behavioral dysfunctions in body fluid regulations in later life, in association with the change in central angiotensin II-mediated neural activation and expression of the Ang II receptor in the brain.

Candesartan improves memory decline in mice: involvement of AT1 receptors in memory deficit induced by intracerebral streptozotocin

The Renin-angiotensin system, besides blood pressure regulation, affects learning and memory as evidenced by improvement of cognition in hypertensive patients being treated with AT1 receptor blockers like candesartan. The present study examined the influence of candesartan on memory impairment induced by intracerebral streptozotocin (IC STZ 0.5 mg/kg) in mice. Candesartan (0.05 mg/kg and 0.1 mg/kg, i.p.) was given for 14 days following IC STZ administration. The dose of 0.1 mg/kg significantly improved latency period in passive avoidance test. Further, treatment with 0.1 mg/kg candesartan for 14 days significantly improved spatial memory in mice in water maze test also. In another group, after memory impairment in mice following IC STZ administration, memory improving effect of a 7 days treatment with 0.1 mg/kg candesartan lasted only for 3 subsequent days in water maze task. IC STZ increased oxidative stress but pretreatment with 0.1 mg/kg candesartan decreased oxidative stress as indicated by a decrease in MDA and increase in GSH. Further, candesartan decreased free radicals as evidenced by flow cytometry. IC STZ affected cholinergic system also by increasing acetylcholine esterase activity that was restored by pretreatment with 0.1 mg/kg candesartan. Locomotor activity and serum glucose level remained unaffected by candesartan treatment. These results suggest that AT1 receptors play a facilitatory role in STZ induced memory deficit and corroborate number of human studies that AT1 receptor blockers can be used therapeutically against cognitive decline in hypertensive patients.

The effect of long-term lactobacilli (lactic acid bacteria) enteral treatment on the central nervous system of growing rats

The aim of this study was to explore the relationship between consumption of large doses of lactic acid bacteria (LAB) and the behaviour and brain morphobiochemistry of normal growing rats. Four groups of rats were treated with LAB cultures twice daily for 6 months. The control group received 1 ml of saline per treatment, while two experimental groups received 1 ml of living bacteria (Lactobacillus plantarum and Lactobacillus fermentum, respectively) and the remaining group received a heat-treated (inactivated) L. fermentum culture. After 2 and 6 months of treatment, respectively, eight animals from each group were sacrificed, and specimens were taken for further analyses. The behaviour of the rats was evaluated five times in an open-field test at monthly intervals throughout the study. Lactobacilli treatment for 2 months induced changes in the motoric behaviour of the rats. The concentration of the astrocytesoluble and filament glial fibrillary acidic protein (GFAP) decreased in the posterior part of the hemispheres, including the thalamus, hippocampus and cortex of the rats treated with L. fermentum. A greater decrease in filament GFAP (up to 50%) was shown in the group receiving the live form of L. fermentum. In contrast, the GFAP in the live L. plantarum-treated group increased, showing elevated levels of the soluble and filament forms of GFAP in the posterior part of the hemispheres. A 60-66% decrease in the amount of the astrocyte-specific Ca-binding protein S-100b was shown in the posterior parts of the hemispheres and in the hindbrain of rats given LAB for 2 months. Prolonged feeding with LAB for 4 months up to full adulthood led to a further decrease in astrocyte reaction, reflected as an additional decrease in the amount of soluble GFAP and locomotor activity in all experimental groups. The changes in filament GFAP and S-100b appeared to disappear after prolonged feeding (total of 6 months) with LAB. In summary, LAB dietary treatment affected the ontogenetic development of the astrocytes, with the highest intensity observed in the early stages of rat development. It can be postulated that LAB treatment may play a preventive role in neurological diseases by decreasing astrocyte reaction and, consequently, lowering locomotor activity.

New insights into the importance of aminopeptidase A in hypertension

The renin-angiotensin system (RAS) plays an important role in the maintenance of normal blood pressure and the etiology of hypertension; however, minimal attention has been paid to the degradation of the effector peptide, angiotensin II (AngII). Since aminopeptidase A (APA)-deficient mice develop hypertension APA appears to be an essential enzyme in the control of blood pressure via degradation of AngII. The robust hypertension seen in the spontaneously hypertensive rat (SHR) is due to activation of the RAS, and an accompanying decrease in kidney APA. Changes in APA have also been measured during the activation of the RAS in the Goldblatt hypertension model and Dahl salt-sensitive (DSS) rat. The DSS rat shows an elevation in renal APA activity at the onset of hypertension suggesting a protective role against elevations in circulating AngII, followed by decreased APA activity with advancing hypertension. Changes seen in human maternal serum APA activity during preeclampsia are similar to changes measured in renal APA in the DSS rat model. APA activity is higher than during normal pregnancy at the onset of preeclampsia, and with advancing preeclampsia (severe preeclampsia) declines below that seen during normal pregnancy. Serum APA activity is also increased during hormone replacement therapy (HRT), perhaps in reaction to elevated levels of AngII. Thus, it appears important to consider the relationship among activation of the RAS, circulating levels of AngII, and the availability of APA in hypertensive disorders.

Brain angiotensin-converting enzymes: role of angiotensin-converting enzyme 2 in processing angiotensin II in mice

Angiotensin (Ang)‐converting enzyme 2 (ACE2) metabolizes Ang II to the vasodilatory peptide Ang(1–7), while neprilysin (NEP) generates Ang(1–7) from Ang I. Experiments used novel Surface Enhanced Laser Desorption Ionization‐Time of Flight (SELDI‐TOF) mass spectroscopic (MS) assays to study Ang processing. Mass spectroscopy was used to measure proteolytic conversion of Ang peptide substrates to their specific peptide products. We compared ACE/ACE2 activity in plasma, brain and kidney from C57BL/6 and NEP^−/− mice. Plasma or tissue extracts were incubated with Ang I or Ang II (1296 or 1045, m/z, respectively), and generated peptides were monitored with MS. Angiotensin‐converting enzyme 2 activity was detected in kidney and brain, but not in plasma. Brain ACE2 activity was highest in hypothalamus. Angiotensin‐converting enzyme 2 activity was inhibited by the specific ACE2 inhibitor, DX600 (10 μm, 99% inhibition), but not by the ACE inhibitor, captopril (10 μm). Both MS and colorimetric assays showed high ACE activity in plasma and kidney with low levels in brain. To extend these findings, ACE measurements were made in ACE overexpressing mice. Angiotensin‐converting enzyme four‐copy mice showed higher ACE activity in kidney and plasma with low levels in hypothalamus. In hypothalamus from NEP^−/− mice, generation of Ang(1–7) from Ang I was decreased, suggesting a role for NEP in Ang metabolism. With Ang II as substrate, there was no difference between NEP^−/− and wild‐type control mice, indicating that other enzymes may contribute to generation of Ang(1–7). The data suggest a predominant role of hypothalamic ACE2 in the processing of Ang II, in contrast to ACE, which is most active in plasma.

Angiotensin receptor subtype mediated physiologies and behaviors: new discoveries and clinical targets

The renin-angiotensin system (RAS) mediates several classic physiologies including body water and electrolyte homeostasis, blood pressure, cyclicity of reproductive hormones and sexual behaviors, and the regulation of pituitary gland hormones. These functions appear to be mediated by the angiotensin II (AngII)/AT(1) receptor subtype system. More recently, the angiotensin IV (AngIV)/AT(4) receptor subtype system has been implicated in cognitive processing, cerebroprotection, local blood flow, stress, anxiety and depression. There is accumulating evidence to suggest an inhibitory influence by AngII acting at the AT(1) subtype, and a facilitory role by AngIV acting at the AT(4) subtype, on neuronal firing rate, long-term potentiation, associative and spatial learning, and memory. This review initially describes the biochemical pathways that permit synthesis and degradation of active angiotensin peptides and three receptor subtypes (AT(1), AT(2) and AT(4)) thus far characterized. There is vigorous debate concerning the identity of the most recently discovered receptor subtype, AT(4). Descriptions of classic and novel physiologies and behaviors controlled by the RAS are presented. This review concludes with a consideration of the emerging therapeutic applications suggested by these newly discovered functions of the RAS.

Angiotensin type 1 receptor antagonist inhibits lipopolysaccharide-induced stimulation of rat microglial cells by suppressing nuclear factor kappaB and activator protein-1 activation

We investigated whether angiotensin (ANG) II and its receptors contribute to lipopolysaccharide (LPS)-induced microglial activation through activation of the proinflammatory transcription factors nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1). Using primary microglial cell cultures, we examined whether losartan [ANG type 1 receptor (AT(1)) antagonist] alters the effects of LPS on: the production of interleukin-1 (IL-1) and nitric oxide, cell morphology, and NF-kappaB and AP-1 activities. Reverse transcription-polymerase chain reaction revealed that LPS-stimulated microglial cells exhibited marked mRNA expression for AT(1), ANG type 2 receptor (AT(2)) and the ANG II precursor angiotensinogen, whereas non-stimulated microglial cells expressed only those for AT(2) and angiotensinogen. We further demonstrated marked peptide/protein expression for AT(1) and ANG II in LPS-activated microglial cells. LPS (100 ng/mL)-stimulated microglial cells showed increased concentrations of IL-1 and nitrite (a relatively stable metabolite of nitric oxide), and increased expression of IL-1 mRNA as well as a morphological change from an amoeboid shape to a multipolar (mostly bipolar but sometimes tripolar) rod shape. These effects were all significantly inhibited by losartan treatment (10(-5) M or less). NF-kappaB and AP-1 activities were enhanced in LPS-stimulated microglial cells, effects that were significantly suppressed by losartan (10(-5) M). ANG II application enhanced the LPS-induced increases in IL-1 and nitrite concentrations, as well as the LPS-induced morphological changes and AP-1 activation, and these enhancements were inhibited by losartan (10(-5) M). These results suggest that endogenous ANG II enhances LPS-induced microglial activities through stimulation of the microglial AT(1), which itself evokes activation of the transcription factors NF-kappaB and AP-1.

Angiotensin II increases evoked release at the frog neuromuscular junction through a receptor sensitive to A779

Receptor mediated presynaptic modulation is a ubiquitous mechanism involved in synaptic plasticity. Here we show that angiotensin II increased quantal content at the frog neuromuscular junction. This presynaptic effect of angiotensin II was insensitive to losartan and PD123319, but was antagonized by a more potent partial agonist of the amphibian angiotensin receptor, L162313. In addition, A779, a blocker of the angiotensin-[1-7] receptor, also abolished the effect of angiotensin II. These results indicate that the effect of angiotensin II on evoked release is mediated through an angiotensin receptor. L162313 alone increased quantal content, and A779 also antagonized this effect of L162313. We conclude that the neuromuscular junction possesses angiotensin receptors involved in presynaptic modulation.

Intracerebroventricular injection of losartan inhibits angiotensin II-sensitive neurons via GABA inputs in the anterior hypothalamic area of rats

Previously, we have demonstrated that pressure-ejected application of angiotensin II and losartan, an angiotensin AT1 receptor antagonist, onto some neurons in the anterior hypothalamic area (AHA) of the rat increases and decreases, respectively, the basal firing rate of the neurons. To investigate possible participation of these AHA neurons in the brain angiotensin system, we examined whether intracerebroventricular injection of the angiotensin AT1 receptor antagonist losartan inhibits the neuronal activity of angiotensin II-sensitive neurons via GABA inputs in the AHA of rats. Intracerebroventricular injection of losartan decreased the firing rate of AHA angiotensin II-sensitive neurons. However, the intracerebroventricular injection of losartan did not affect the increase in firing rate of AHA angiotensin II-sensitive neurons induced by pressure application of angiotensin II onto the same neurons, although losartan similarly injected abolished the increase in firing rate of AHA angiotensin II-sensitive neurons induced by intracerebroventricular injection of angiotensin II. The losartan-induced decrease of unit firing in AHA neurons was abolished by pressure application of the GABAA receptor antagonist bicuculline onto the same neurons. Bicuculline itself did not affect the basal firing rate of AHA neurons. These findings suggest that intracerebroventricular injection of losartan inhibits AHA angiotensin II-sensitive neurons via GABA inputs to the neurons.

Angiotensin-(3-7) pressor effect at the rostral ventrolateral medulla

Ang-(3-7) is a fragment of the renin-angiotensin system that can be derived both from Ang II or Ang-(1-7). In the present study we determined the cardiovascular effects produced by angiotensin-(3-7) [Ang-(3-7)] microinjection into the rostral ventrolateral medulla (RVLM), a key region for the control of sympathetic drive to the periphery. RVLM microinjection of Ang-(3-7) (20, 40 or 80 ng) in male Wistar rats anesthetized with urethane produced significant increases in MAP (19+/-3.8 mm Hg, n=5; 16+/-1.6 mm Hg, n=15 and 11+/-1.2 mm Hg, n=4, respectively) as compared to saline (4+/-0.7 mm Hg, n=6). These alterations were similar to that induced by Ang-(1-7) (14+/-1.3 mm Hg, 40 ng; n=12) and Ang II (17+/-2.3 mm Hg, 40 ng; n=7). Microinjection of losartan (AT(1) receptor antagonist, 100 pmol) or A779 (selective Mas receptor antagonist, 100 pmol) did not alter the pressor effect caused by Ang-(3-7). Microinjection of an Ang-(3-7) analogue, d-Ala(7)-Ang-(3-7) (100 pmol), completely abolished the pressor effect caused by Ang-(3-7). These results suggest that Ang-(3-7) may be an additional peptide of the RAS to act as neuromodulator, at least at the RVLM. Further, the Ang-(3-7) pressor effect is not mediated by the interaction with AT(1) or the Ang-(1-7), Mas, receptors.

Cognitive effects attributed to angiotensin II may result from its conversion to angiotensin IV

This study tests the hypothesis that the facilitation of learning and improvement of memory observed after an intracerebroventricular (i.c.v.) injection of angiotensin II (Ang II) is, in fact, caused by its derivative angiotensin IV (Ang IV). We ran two memory tests as well as an auxiliary test assessing motor performance in rats injected (i.c.v., 1 nmol in 2 microl saline) with Ang II or Ang IV. There were separate groups receiving peptide or saline five, 10 and 15 minutes before testing. Ang IV significantly increased step-through latencies in a passive avoidance paradigm as well as improved discrimination between familiar and unfamiliar objects in an object recognition test in all groups showing better retrieval of memory of aversive as well as appetitive stimuli in the peptide-treated groups regardless of the time of its injection. In contrast, rats treated with Ang II demonstrated significant improvement of memory of aversive and appetitive stimuli in the same tests only 15 minutes after its i.c.v. injection, with no effect in the groups injected five minutes before testing and slight efficacy in those injected 10 minutes before the test. Numbers of crossings, rearings and bar approaches in an open field were similar both in the peptide-treated and control groups making it unlikely that changes in motor performance affected the memory tests. In line with the present views on the intracellular metabolism of Ang II, these results suggest degradation to Ang IV by aminopeptidases A and N is necessary before the cognitive effects can occur.

Genetic polymorphism of the angiotensin converting enzyme and L-dopa-induced adverse effects in Parkinson's disease

There was increasing evidence suggesting that angiotensin I-converting enzyme may play an important role in the pathogenesis of PD. Our former study has shown that angiotensin I-converting enzyme gene (ACE) may confer a susceptibility for the risk of Parkinson's disease (PD). Meanwhile, recent studies have emphasized that genetic factors may involve in the occurrence of the adverse effects of chronic L-dopa therapy in PD patients. This study was designed to assess whether genetic polymorphism of the ACE could be a predictor of L-dopa-induced adverse effects in PD. There were 251 patients included in this study and their mean age at onset of disease was 63.3+/-11.4 years. The duration of disease and the treatment with L-dopa was 6.3+/-5.1 and 5.0+/-4.3 years, respectively. The frequency of the homozygote ACE-II genotype of the ACE in PD patients with L-dopa-induced psychosis was significantly higher than that in PD patients without the adverse effect (63.3% vs 43.0%; chi(2)=6.347, OR=1.435, 95%CI=1.105-1.864, p=0.012). However, the ACE polymorphism was not associated with the risk to develop dyskinesia or motor fluctuation induced by L-dopa. Furthermore, a logistic regression analysis confirmed that the ACE-II genotype was an independent risk factor for L-dopa-induced psychosis in PD patients (OR=2.542, p=0.012). In conclusion, results of the study showed that ACE-II genotype might confer a primary predictor for the occurrence of psychosis in L-dopa-treated PD.

The participation of brain NO synthase in blood pressure control of adult spontaneously hypertensive rats

Increased blood pressure (BP) in genetic hypertension is usually caused by high activity of sympathetic nervous system (SNS) which is enhanced by central angiotensin II but lowered by central nitric oxide (NO). We have therefore evaluated NO synthase (NOS) activity as well as neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS) protein expression in brainstem and midbrain of adult spontaneously hypertensive rats (SHR) characterized by enhanced sympathetic vasoconstriction. We also studied possible participation of brain NO in antihypertensive effects of chronic captopril treatment of adult SHR. NOS activity was increased in midbrain of SHR compared to Wistar-Kyoto (WKY) rats. This could be ascribed to enhanced iNOS expression, whereas nNOS expression was unchanged and eNOS expression was reduced in this brain region. In contrast, no significant changes of NOS activity were found in brainstem of SHR in which nNOS and iNOS expression was unchanged, but eNOS expression was increased. Chronic captopril administration lowered BP of adult SHR mainly by attenuation of sympathetic tone, whereas the reduction of angiotensin II-dependent vasoconstriction and the decrease of residual BP (amelioration of structural remodeling of resistance vessels) were less important. This treatment did not affect significantly either NOS activity or expression of any NOS isoform in the two brain regions. Our data do not support the hypothesis that altered brain NO formation contributes to sympathetic hyperactivity and high BP of adult SHR with established hypertension.

Effects of i.c.v. losartan on the angiotensin II-mediated vasopressin release and hypothalamic fos expression in near-term ovine fetuses

Our previous studies have shown that central administration of angiotensin (ANG II) causes arginine vasopressin (AVP) release in the fetus at 70-90% gestation. This is evidence that the hypothalamic-neurohypophysial system is relatively mature before birth. However, few data exist regarding central ANG receptor mechanisms-mediated AVP response during fetal life. To determine roles of brain ANG receptor subtypes in this response, AT1 and AT2 receptor antagonists, losartan and PD123319, were investigated in the brain in chronically prepared ovine fetuses at the last third of gestation. Application of losartan intracerebroventricularly (i.c.v.) at 0.5 mg/kg suppressed central ANG II-stimulated plasma AVP release. Losartan at 5 mg/kg (i.c.v.) demonstrated a significant enhancement of AVP increase to i.c.v. ANG II. Associated with the increase of plasma vasopressin levels, c-fos expression in the hypothalamic neurons was significantly different between the low and high doses of losartan. The low dose losartan markedly reduced the dual immunoreactivity for FOS and AVP in the supraoptic nuclei and paraventricular nuclei after i.c.v. ANG II, whereas the high dose losartan together with ANG II, significantly increased the co-localization of positive FOS in the AVP-containing neurons than that induced by i.c.v. ANG II alone. Central ANG II induced fetal plasma vasopressin increase was not altered by PD123319. The data suggest that losartan in the fetal brain has remarkably different effects based on the doses administrated on central ANG II-related neuroendocrine effects at the late gestation, and that the AT1 mechanism is critical in the regulation of fetal body fluid homeostasis related to plasma AVP levels.

Time course analysis of tyrosine hydroxylase and angiotensinogen mRNA expression in central nervous system of rats submitted to experimental hypertension

Catecholaminergic and angiotensinergic systems are involved in the neural control of blood pressure. The present study analysed the expression of tyrosine hydroxylase (TH), a key enzyme for catecholamine synthesis and of angiotensinogen (AGT), the precursor of angiotensin II (Ang II), in areas of the central nervous system (CNS) involved with cardiovascular regulation such as nucleus tractus solitarius (NTS), ventrolateral medulla (VLM), locus coeruleus (LC) and hypothalamic paraventricular nucleus (PVN) 2 h, 3 and 7 days after aortic coarctated hypertensive rats. In situ hybridization, was employed for the analysis of messenger RNA (mRNA) expression with anatomical resolution. No changes were seen in TH and AGT mRNA expression in the analysed areas 2 h and 3 days after aortic coarctation when compared to the respective sham group. TH mRNA expression was increased in the NTS and LC of rats 7 days after coarctation hypertension when compared to sham rats. Time course analysis, showed an increase in TH mRNA expression in the NTS 7 days after aortic coarctation when compared to 2 h and 3 days groups, as well as an increase in LC 3 days and 7 days following coarctation hypertension in comparison with the 2 h group. Analysis of AGT mRNA in the NTS expression revealed a decrease at 3 days, followed by an increase in mRNA expression 7 days following coarctation hypertension when compared to the sham group. Time course analysis, showed an increase in AGT mRNA expression in the NTS 7 days after coarctation when compared to 2 h and 3 days groups. The results show that TH and AGT mRNA expression changes during the different phases of experimental hypertension, suggesting that the noradrenaline (NOR) and angiotensin II (Ang II) might participate in the modulation/maintenance of coarctation hypertension.

Effects of central injection of angiotensin-converting-enzyme inhibitor and angiotensin type 1 receptor antagonist on the brain NF-kappaB and AP-1 activities of rats given LPS

Angiotensin II (ANG II) activation of the angiotensin type 1 (AT1) receptor facilitates the production of brain interleukin-1beta (IL-1beta) and contributes to the induction of the fever following the intracerebroventricular (i.c.v.) injection of lipopolysaccharide (LPS). The purpose of the present study was to investigate whether proinflammatory transcription factors [nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1)] contribute to the ANG II-dependent production of cytokines within the brain. Interestingly, we found that a single i.c.v. injection of LPS had no effect on NF-kappaB and AP-1 activities in the hypothalamus, hippocampus, and cerebellum at either 1 or 3 h post-injection (except for a decrease in hypothalamic AP-1 activity at 1 h). Furthermore, both an angiotensin-converting-enzyme (ACE) inhibitor and an AT1 receptor antagonist enhanced (rather than reduced) the NF-kappaB and AP-1 activities in the hippocampus and/or cerebellum of rats given LPS. In contrast, an i.c.v. injection of ANG II increased the NF-kappaB activity in the hypothalamus. These results suggest that while "endogenous" ANG II exerts (via AT1 receptors) inhibitory effects on the activation of transcription factors in the brain of rats given LPS, a large dose of exogenous ANG II produces effects opposite to those induced by the presumably small amount of endogenous ANG II released locally by LPS. Our results seem not to support the idea that NF-kappaB and AP-1 play key roles in the ANG II-induced enhancement of the production of proinflammatory cytokines that is induced by LPS in the rat's brain.

Evidence suggesting that angiotensins released not via synaptic inputs are involved in the basal activity of anterior hypothalamic neurons in rats

Previously, we have demonstrated that angiotensin II-sensitive neurons exist in the anterior hypothalamic area (AHA) and that these neurons are tonically activated by endogenous angiotensins in rats. Chemical stimulation of the lateral septal area (LSV) and medial amygdaloid nucleus (MeA), and intracerebroventricular injection of hypertonic saline, activated AHA angiotensin II-sensitive neurons. To investigate mechanisms of the basal activity of AHA angiotensin II-sensitive neurons, we examined the effect of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W7), a calmodulin inhibitor, applied onto AHA neurons on the basal activity and the stimulus-evoked activation of these neurons. Male Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Microinjections of carbachol into the LSV and corticotropin-releasing factor into the MeA, and intracerebroventricular injection of hypertonic saline, activated AHA angiotensin II-sensitive neurons. These three kinds of injection-induced activations of AHA neurons were abolished by pressure application of W7 onto the same neurons, while the calmodulin inhibitor did not affect the increase in firing of AHA neurons induced by pressure application of angiotensin II onto the same neurons. The pressure application of W7 did not affect the basal activity of AHA angiotensin II-sensitive neurons, whereas the angiotensin AT1 receptor antagonist losartan similarly applied inhibited it. These findings suggest that the basal activity of AHA angiotensin II-sensitive neurons is mediated by angiotensins released not via synaptic inputs.

Effects of valsartan on stress-induced changes of serum vascular endothelial growth factor and nitric oxide in mice

This study investigated the effects of renin-angiotensin system (RAS) blockade on stress-induced changes of serum vascular endothelial growth factor (VEGF) and nitric oxide (NO) in mice. Chronic stress increased the serum NO levels significantly compared to control group (p = .0172). Valsartan, an angiotensin II receptor antagonist, alone, did not make significant difference versus control group. In chronic stress + valsartan group, serum NO levels decreased nonsignificantly compared to chronic stress group. There was a nonsignificant increase in serum VEGF levels after chronic stress. Valsartan alone or with chronic stress did not significantly affect the serum VEGF levels. In conclusion, there was no correlation between NO and VEGF changes during the stress response. In this respect, there may be other mechanisms to explain the stress-induced NO increase.