Effects Of AT1 Receptor Blockade Research Articles

Effect of AT1 receptor blockade on cardiovascular outcome after cardiac arrest: an experimental study in rats

Angiotensin II receptor 1(AT1) antagonists are beneficial in focal ischemia/reperfusion (I/R). However, in cases of global I/R, such as cardiac arrest (CA), AT1 blocker's potential benefits are still unknown. Wistar male rats were allocated into four groups: Control group (CG)—animals submitted to CA by ventricular fibrillation induced by direct electrical stimulation for 3 min, and anoxia for 5 min; Group AT1 (GAT1)—animals subjected to CA and treated with 0.2 mg/kg of candesartan diluted in dimethylsulfoxide (DMSO) (0.1%); Vehicle Group (VG): animals subjected to CA and treated with 0.2 ml/kg of DMSO and Sham group (SG)—animals submitted to surgical interventions, without CA. Cardiopulmonary resuscitation consisted of group medications, chest compressions, ventilation, epinephrine (20 mcg/kg) and defibrillation. The animals were observed up to 4 h after spontaneous circulation (ROSC) return, and survival rates, hemodynamic variables, histopathology, and markers of tissue injury were analyzed. GAT1 group had a higher rate of ROSC (62.5% vs. 42.1%, p < 0.0001), survival (100% vs. 62.5%, p = 0.027), lower incidence of arrhythmia after 10 min of ROSC (10% vs. 62.5%, p = 0.000), and lower neuronal and cardiac injury scores on histology evaluation (p = 0.025 and p = 0.0052, respectively) than GC group. The groups did not differ regarding CA duration, number of adrenaline doses, or number of defibrillations. AT1 receptor blockade with candesartan yielded higher rates of ROSC and survival, in addition to neuronal and myocardial protection.

Inappropriate activation of the renin-angiotensin system improves cardiac tolerance to ischemia/reperfusion injury in rats with late angiotensin II-dependent hypertension.

The aim of the study was to clarify the role of the interplay between hypertension and the renin-angiotensin system (RAS) in the pathophysiology of myocardial ischemia/reperfusion (I/R) injury. We hypothesized that in the late phase of hypertension with already developed signs of end-organ damage, inappropriate RAS activation could impair cardiac tolerance to I/R injury. Experiments were performed in male Cyp1a1-Ren-2 transgenic rats with inducible hypertension. The early phase of ANG II-dependent hypertension was induced by 5days and the late phase by the 13days dietary indole-3-carbinol (I3C) administration. Noninduced rats served as controls. Echocardiography and pressure-volume analysis were performed, angiotensins' levels were measured and cardiac tolerance to ischemia/reperfusion injury was studied. The infarct size was significantly reduced (by 50%) in 13days I3C-induced hypertensive rats with marked cardiac hypertrophy, this reduction was abolished by losartan treatment. In the late phase of hypertension there are indications of a failing heart, mainly in reduced preload recruitable stroke work (PRSW), but only nonsignificant trends in worsening of some other parameters, showing that the myocardium is in a compensated phase. The influence of the RAS depends on the balance between the vasoconstrictive and the opposed vasodilatory axis. In the initial stage of hypertension, the vasodilatory axis of the RAS prevails, and with the development of hypertension the vasoconstrictive axis of the RAS becomes stronger. We observed a clear effect of AT1 receptor blockade on maximum pressure in left ventricle, cardiac hypertrophy and ANG II levels. In conclusion, we confirmed improved cardiac tolerance to I/R injury in hypertensive hypertrophied rats and showed that, in the late phase of hypertension, the myocardium is in a compensated phase.

The antiobese effect of AT1 receptor blockade is augmented in mice lacking Mas.

We recently showed that the antiobese efficacy of the AT1 receptor blocker telmisartan (TEL) is at least partially related to an Ang(1-7)-dependent mechanism. Ang(1-7) acts via Mas, thus raising the question of whether Mas-deficient (Mas-ko) mice are likewise predisposed to develop diet-induced obesity and, further, whether this can be prevented by TEL treatment. Mas-ko mice and FVB/N wild-type (wt) animals were treated with TEL (8mg/kg/day) or vehicle while they were fed with high-fat diet (HFD) or chow. Mice were phenotyped regarding body weight, fat mass, insulin sensitivity, and leptin sensitivity. In response to HFD feeding, gain in body weight and impairment of leptin sensitivity were similar between wt and Mas-ko mice. TEL reduced body weight in both strains but effects were stronger in Mas-ko mice. TEL diminished fat mass and restored leptin sensitivity only in Mas-ko mice. Blood glucose was higher in wt than Mas-ko mice fed with HFD while not differing when they were fed with chow. Insulin challenge confirmed that wt mice became insulin resistant when fed with HFD while HFD feeding did not impair insulin sensitivity in Mas-ko mice. TEL had no further effect. Our findings on the influence of TEL on growth and metabolism in Mas-ko mice conflict with our previous findings in rats. We assume that the FVB/N background of the mice may partly explain these inconsistent data. Moreover, it also seems feasible that the MrgD receptor compensates for Mas deficiency.

Angiotensin Receptor Blockade Modulates NFκB and STAT3 Signaling and Inhibits Glial Activation and Neuroinflammation Better than Angiotensin-Converting Enzyme Inhibition.

Neuroinflammation, sustained by astroglial and microglial activation, is the preceding event in neurodegeneration. Various clinical reports showed better neuroprotection by AT1 receptor blockade (ARB) than angiotensin-converting enzyme inhibition (ACEi), but experimental evidences and associated mechanism for this observation are lacking. Therefore, we investigated the effect of ARB, using Candesartan, and ACEi, using Perindopril, in equimolar concentrations in astroglial (C6) and microglial (BV2) cells employing lipopolysaccharide (LPS) to induce neuroinflammation. Further, Candesartan (0.1mg/kg) and Perindopril (0.1mg/kg) were orally administered in male SD rats for five consecutive days, and on the fifth day, rats were challenged with LPS (i.p.; 250μg/kg) and sacrificed after 24h. LPS-induced neuroinflammation (increased astroglial and microglial activation, IκBα degradation, NFкB nuclear translocation, STAT3 activation, and TNF-α release) was more efficiently prevented by Candesartan (even at lower concentration of 1nM) than by Perindopril (1μM) in both the cell types and in rat model of neuroinflammation. In addition, increased AT1 receptor (AT1R) and decreased AT2 receptor (AT2R) expression was observed in LPS-induced neuroinflammation in both in vitro and in vivo studies. Candesartan, as compared to Perindopril, increased the expression of AT2R in both the experimental conditions. Interestingly, concomitant blockade of AT2R by PD123319 significantly reversed the beneficial effects of Candesartan in both the cell types and in rat model of neuroinflammation. Finally, our data emphasize that superiority of Candesartan as compared to Perindopril is due to better activation of AT2R which results in PP2A activation, IκBα stabilization, and suppression of NFкB and STAT3 inflammatory signaling.

Beneficial Effects of the Activation of the Angiotensin-(1–7) Mas Receptor in a Murine Model of Adriamycin-Induced Nephropathy

Angiotensin-(1–7) [Ang-(1–7)] is a biologically active heptapeptide that may counterbalance the physiological actions of angiotensin II (Ang II) within the renin-angiotensin system (RAS). Here, we evaluated whether activation of the Mas receptor with the oral agonist, AVE 0991, would have renoprotective effects in a model of adriamycin (ADR)-induced nephropathy. We also evaluated whether the Mas receptor contributed for the protective effects of treatment with AT1 receptor blockers. ADR (10 mg/kg) induced significant renal injury and dysfunction that was maximal at day 14 after injection. Treatment with the Mas receptor agonist AVE 0991 improved renal function parameters, reduced urinary protein loss and attenuated histological changes. Renoprotection was associated with reduction in urinary levels of TGF-β. Similar renoprotection was observed after treatment with the AT1 receptor antagonist, Losartan. AT1 and Mas receptor mRNA levels dropped after ADR administration and treatment with losartan reestablished the expression of Mas receptor and increased the expression of ACE2. ADR-induced nephropathy was similar in wild type (Mas+/+) and Mas knockout (Mas −/−) mice, suggesting there was no endogenous role for Mas receptor activation. However, treatment with Losartan was able to reduce renal injury only in Mas+/+, but not in Mas −/− mice. Therefore, these findings suggest that exogenous activation of the Mas receptor protects from ADR-induced nephropathy and contributes to the beneficial effects of AT1 receptor blockade. Medications which target specifically the ACE2/Ang-(1–7)/Mas axis may offer new therapeutic opportunities to treat human nephropathies.

Ang (1–7) Has a Greater Contribution to the Blood Pressure Lowering Effects of AT1 Receptor Blockade in Female Spontaneously Hypertensive Rats (SHR) Compared to Males

Ang (1–7) contributes to the blood pressure (BP) lowering effects of renin angiotensin system inhibitors in male SHR. We have previously published that female SHR have greater Ang (1–7) levels than males, however, the functional implications of this with regards to BP control remains largely unknown. Therefore, the goal of this study was to test the hypothesis that female SHR have a larger Ang (1–7) contribution to the BP lowering effects of the angiotensin receptor blocker (ARB) candesartan than male SHR. BP was measured via telemetry in 12 week old male and female SHR (n=4–8). Animals were pre‐treated with either the Ang (1–7) antagonist A‐779 (4 days; 48 μg/kg/hr via osmotic minipump) or vehicle. Candesartan was then co‐administered (0.5 mg/kg/day via drinking water) for a week. A‐779 alone did not alter basal BP in either sex. In male SHR, candesartan‐mediated decreases in BP were comparable in vehicle (15% decrease: 143±2 to 122±3 mmHg; p&lt;0.05) and A‐779 treated (12% decrease: 147±3 to 129±4 mmHg; p&lt;0.05). In contrast, A‐779 attenuated candesartan‐mediated decreases in BP (5% decrease: 127±1 to 121±2 mmHg; NS) in female SHR compared to vehicle treatment (10% decrease: 128±1 to 115±1 mmHg; p&lt;0.05). In conclusion, female SHR have a greater Ang (1–7) contribution to ARB‐mediated decreases in BP than males. This study was funded by National Institutes of Health grant 1R01 HL093271–01A1 to J.C.S.

Effect of AT1 receptor blockade on intermittent hypoxia-induced endothelial dysfunction

Chronic intermittent hypoxia (CIH) raises arterial pressure, impairs vasodilator responsiveness, and increases circulating angiotensin II (Ang II); however, the role of Ang II in CIH-induced vascular dysfunction is unknown. Rats were exposed to CIH or room air (NORM), and a subset of these animals was treated with losartan (Los) during the exposure period. After 28 days, vasodilatory responses to acetylcholine or nitroprusside were measured in isolated gracilis arteries. Superoxide levels and Ang II receptor protein expression were measured in saphenous arteries. After 28 days, arterial pressure was increased and acetylcholine-induced vasodilation was blunted in CIH vs. NORM, and this was prevented by Los. Responses to nitroprusside and superoxide levels did not differ between CIH and NORM. Expression of AT2R was decreased and the AT1R:AT2R ratio was increased in CIH vs. NORM, but this was unaffected by Los. These results indicate that the blood pressure elevation and endothelial dysfunction associated with CIH is dependent, at least in part, on RAS signaling.

Angiotensin II receptor type 1 blockade decreases CTGF/CCN2‐mediated damage and fibrosis in normal and dystrophic skeletal muscles

Connective tissue growth factor (CTGF/CCN-2) is mainly involved in the induction of extracellular matrix (ECM) proteins. The levels of CTGF correlate with the degree and severity of fibrosis in many tissues, including dystrophic skeletal muscle. The CTGF overexpression in tibialis anterior skeletal muscle using an adenoviral vector reproduced many of the features observed in dystrophic muscles including muscle damage and regeneration, fibrotic response and decrease in the skeletal muscle strength. The renin–angiotensin system is involved in the genesis and progression of fibrotic diseases through its main fibrotic components angiotensin-II and its transducer receptor AT-1. The use of AT-1 receptor blockers (ARB) has been shown to decrease fibrosis. In this paper, we show the effect of AT-1 receptor blockade on CTGF-dependent biological activity in skeletal muscle cells as well as the response to CTGF overexpression in normal skeletal muscle. Our results show that in myoblasts ARB decreased CTGF-mediated increase of ECM protein levels, extracellular signal regulated kinases 1/2 (ERK-1/2) phosphorylation and stress fibres formation. In tibialis anterior muscle overexpressing CTGF using an adenovirus, ARB treatment decreased CTGF-mediated increase of ECM molecules, α-SMA and ERK-1/2 phosphorylation levels. Quite remarkable, ARB was able to prevent the loss of contractile force of tibialis anterior muscles overexpressing CTGF. Finally, we show that ARB decreased the levels of fibrotic proteins, CTGF and ERK-1/2 phosphorylation augmented in a dystrophic skeletal muscle from mdx mice. We propose that ARB is a novel pharmacological tool that can be used to decrease the fibrosis induced by CTGF in skeletal muscle associated with muscular dystrophies.

Metabolic and cardiovascular effects of AT1 receptor blockade in rats with diet‐induced obesity

Causes of metabolic and cardiovascular disturbances in obesity are poorly understood. This study analyzed whether the angiotensin II receptor blockade reverses abnormalities in diet‐induced obesity. Wistar‐Kyoto rats (n=40) were subjected to control (C) or hypercaloric diet (OB) for 30 weeks and then assigned to four groups: C, C+Los, OB, and OB+Los. Los‐groups received losartan (30mg/kg/day) during five weeks. Subsequently, cardiac structures and function were assessed by echocardiography. Glycemia was studied by tolerance glycemic curve. OB‐groups presented higher body mass and adiposity. Other results are in the table.ConclusionLosartan improves metabolic and cardiovascular profile in diet‐induced obesity.

Effect of mechanical stretch on rat neonatal cardiomyocyte somatostatin receptor subtype 1 expression

Somatostatin receptors (SSTRs) have been proven to be involved in cardioprotection, but the effects of mechanical stress on their expression remain to be elucidated. To investigate whether mechanical stretch is associated with increased expression of the SSTR in cardiomyocytes and if the phenomenon is mediated via an angiotensin II signaling pathway. Using a well established cyclic mechanical stretch model exerting strain on primary cultured neonatal Wistar rat cardiomyocytes, we studied the expression of major SSTRs of cardiomyocyte under such stress. Western blot and immunoprecipitation were used to demonstrate the related changes. The role of endogenous angiotensin II and the effects of AT-1 receptor blockade were studied by pre-administration of losartan. Northern and western blotting revealed progressive increase of SSTR-1 mRNA and protein expression as the duration of stretch increased up to 48 hours. The maximal increases of SSTR-1 mRNA and protein were observed at 24 hours. The mechanical stretch significantly increased the angiotensin II in cardiomyocytes concomitantly. Losartan and PD98059 had a significant inhibitory effect on the expression of SSTR-1, indicating the angiotensin II and p42/p44 MAP kinases-related pathways were involved in the expression of SSTR-1 under mechanical stress. By contrast, tyrosine kinases, protein kinase A, protein kinase C, JAK-2, JNK and phosphoinositol-3-kinases had no effect. This study demonstrated that accentuating the expression of SSTR-1mechanical stretch is angiontensin II and p42/p44 MAP kinases-dependent.

AT1 receptor‐mediated augmentation of urinary excretion of endogenous Ang II in Val5‐Ang II infused rats

We previously demonstrated that rats infused chronically with Val5‐Ang II exhibited increased urinary excretion of endogenous Ile5‐Ang II by the 12th day of infusion suggesting the stimulation of endogenous Ang II formation by Val5‐Ang II infusion. To determine the time course of increased urinary Ang II excretion and the effects of AT1 receptor blockade (candesartan, 0.69 ± 0.04 mg/day) on the urinary excretion rates of Ile5‐Ang II in Val5‐Ang II infused rats, Sham (6), Val5‐Ang II infused (5), and Val5‐Ang II infused rats treated with candesartan (6) were evaluated. Val5‐Ang II was infused for 13 days, and Ile5‐Ang II was separated from Val5‐Ang II in urine by HPLC and measured by RIA. SBP increased progressively (206 ± 3.8 mmHg) in Val5‐Ang II infused rats while the candesartan treated group remained normotensive (129.5 ± 6.0 mmHg). Urinary endogenous Ile5‐Ang II excretion rates were elevated by day 9 (2185.7 ± 283.2 fmol/24hr) in Val5‐Ang II infused rats but not in candesartan treated rats (740.6 ± 110.3 fmol/24hr). Thus, AT1 receptor blockade prevented the increase in urinary excretion of endogenous Ang II. These data indicate that the increased urinary endogenous Ang II excretion in Val5‐Ang II infused rats is not due to filtration but is due to secretion into and/or de novo formation of Ang II within the tubular lumen, which is mediated by AT1 receptors.

Effect of AT1 receptor blockade on intermittent hypoxia‐induced endothelial dysfunction

Exposure of rats to chronic intermittent hypoxia (CIH) impairs vasodilator responsiveness and raises arterial pressure. CIH‐induced increases in arterial pressure are prevented by blockade of the angiotensin type 1 receptor (AT1R); however, it is unknown if renin‐angiotensin system (RAS) activity plays a role in CIH‐induced vascular dysfunction. Sprague Dawley rats were exposed to CIH, while control rats (NORM) were housed under normoxic conditions. A subset of animals from each group was treated with an AT1R blocker, losartan (Los), during the exposure period. Arterial pressure was monitored by telemetry. After 4 weeks, gracilis arteries (GA) were isolated and cannulated with glass micropipettes, and pressurized to 80 mmHg. Diameters were measured using video microscopy before and after exposure to acetylcholine (10−6 M) or sodium nitroprusside (10−4 M) in the superfusate. CIH caused elevations in arterial pressure when intermittent hypoxia cycles were administered and also when the animals were unperturbed. Los attenuated both increases. Acetylcholine‐induced vasodilation was blunted in CIH vs. NORM, and this was prevented by Los treatment. Responses to nitroprusside were not different between CIH‐exposed and control animals. These results suggest that vascular dysfunction associated with CIH is dependent in part on RAS signaling through the AT1R. Funded by #HL074072.

Short Communication: Angiotensin II Type 1 Receptor–Mediated Upregulation of Calcineurin Activity Underlies Impairment of Cardioprotective Signaling in Diabetic Hearts

The diabetic heart is resistant to ischemic preconditioning because of diabetes-associated impairment of phosphatidylinositol 3-kinase (PI3K)-Akt signaling. The mechanism by which PI3K-Akt signaling is impaired by diabetes remains unclear. Here, we examined the hypothesis that phosphorylation of Jak2 upstream of PI3K is impaired in diabetic hearts by an angiotensin II type 1 (AT1) receptor-mediated mechanism. Infarct size (as percentage of risk area) after 20-minute ischemia/2-hour reperfusion was larger in a rat model of type 2 diabetes (Otsuka-Long-Evans-Tokushima fatty [OLETF] rat) than in its control (Long-Evans-Tokushima-Otsuka [LETO] rat) (60.4+/-1.6% versus 48.4+/-1.3%). Activation of Jak2-mediated signaling by erythropoietin or DADLE ([D-Ala2, D-Leu5]-enkephalin acetate), a delta-opioid receptor agonist, limited infarct size in LETO rats (27.7+/-3.4% and 24.8+/-5.0%) but not in OLETF rats (53.9+/-5.3% and 55.0+/-2.2%). Blockade of the AT1 receptor by valsartan or losartan for 2 weeks restored the myocardial response of OLETF rats to erythropoietin-induced infarct size limitation (39.4+/-4.9% and 31.2+/-7.5). In OLETF rats, erythropoietin failed to phosphorylate both Jak2 and Akt, and calcineurin activity was significantly higher than in LETO rats. Two-week treatment with valsartan normalized calcineurin activity in OLETF rats and restored the response of Jak2 to erythropoietin. This effect of AT1 receptor blockade was mimicked by inhibition of calcineurin by FK506. These results suggest that the diabetic heart is refractory to protection by Jak2-activating ligands because of AT1 receptor-mediated upregulation of calcineurin activity.

AT 1-receptor blockade by telmisartan upregulates GTP-cyclohydrolase I and protects eNOS in diabetic rats

Several enzymatic sources of reactive oxygen species (ROS) were described as potential reasons of eNOS uncoupling in diabetes mellitus. In the present study, we investigated the effects of AT 1-receptor blockade with chronic telmisartan (25 mg/kg/day, 6.5 weeks) therapy on expression of the BH 4-synthesizing enzyme GTP-cyclohydrolase I (GCH-I), eNOS uncoupling, and endothelial dysfunction in streptozotocin (STZ, 60 mg/kg iv, 7 weeks)-induced diabetes mellitus (type I). Telmisartan therapy did not modify blood glucose and body weight. Aortas from diabetic animals had vascular dysfunction as revealed by isometric tension studies (acetylcholine and nitroglycerin potency). Vascular and cardiac ROS produced by NADPH oxidase, mitochondria, eNOS, and xanthine oxidase were increased in the diabetic group as was the expression of NADPH oxidase subunits at the protein level. The expression of GCH-I and the phosphorylation of eNOS at Ser1177 was decreased by STZ treatment. Therapy with telmisartan normalized these parameters. The present study demonstrates for the first time that AT 1-receptor blockade by telmisartan prevents downregulation of the BH 4 synthase GCH-I and thereby eNOS uncoupling in experimental diabetes. In addition, telmisartan inhibits activation of superoxide sources like NADPH oxidase, mitochondria, and xanthine oxidase. These effects may explain the beneficial effects of telmisartan on endothelial dysfunction in diabetes.

Modulation of kinin B1 receptor expression by endogenous angiotensin II in hypertensive rats

We investigated the expression and localization of B1 receptor in tissues of rats submitted to a renin-dependent model of hypertension (2K-1C), and analyzed the influence of endogenous Ang II in modulating the in vivo expression of these receptors. B1 mRNA levels in the heart, kidney and thoracic aorta were quantified by real time PCR, B1 receptor protein expression was assessed by immunohistochemistry, plasma Ang II levels were analyzed by radioimmunoassay and the effects of AT1 receptor blockade were determined after losartan treatment. 2K-1C rats presented a marked increase in Ang II levels when compared to sham-operated rats. In parallel, cardiac- (but not renal and aortic) B1 mRNA levels were 15-fold higher in 2K-1C than in sham rats. In 2K-1C, B1 expression was detected in the endothelium of small cardiac arteries and in cardiomyocytes. Losartan completely reverted the increased B1 mRNA levels and significantly decreased the protein expression observed in 2K-1C rats, despite reducing, but not normalizing blood pressure. We conclude that in the 2K-1C rat, induction of cardiac B1 receptor might be tightly linked to AT1 receptor activation. These data suggest the existence of a new site of interaction between kinins and angiotensins, and might provide important contributions for a better understanding of the pathophysiology of hypertension.

AT 1 Receptor Blockade Regulates the Local Angiotensin II System in Cerebral Microvessels From Spontaneously Hypertensive Rats

Blockade of angiotensin II AT1 receptors in cerebral microvessels protects against brain ischemia and inflammation. In this study, we tried to clarify the presence and regulation of the local renin-angiotensin system (RAS) in brain microvessels in hypertension. Spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) controls were treated with an AT1 receptor antagonist (candesartan, 0.3 mg/kg per day) via subcutaneous osmotic minipumps for 4 weeks. The expression and localization of RAS components and the effect of AT1 receptor blockade were assessed by Affymetrix microarray, qRT-PCR, Western blots, immunohistochemistry and immunofluorescence. We found transcripts of most of RAS components in our microarray database, and confirmed their expression by qRT-PCR. Angiotensinogen (Aogen), angiotensin-converting enzyme (ACE) and AT1 receptors were localized to the endothelium. There was no evidence of AT2 receptor localization in the microvascular endothelium. In SHR, (pro)renin receptor mRNA and AT1 receptor mRNA and protein expression were higher, whereas Aogen, ACE mRNA and AT2 receptor mRNA and protein expression were lower than in WKY rats. Candesartan treatment increased Aogen, ACE and AT2 receptor in SHR, and increased ACE and decreased Aogen in WKY rats, without affecting the (pro)renin and AT1 receptors. Increased (pro)renin and AT1 receptor expression in SHR substantiates the importance of the local RAS overdrive in the cerebrovascular pathophysiology in hypertension. AT1 receptor blockade and increased AT2 receptor stimulation after administration of candesartan may contribute to the protection against brain ischemia and inflammation.

AT2 receptors contribute to acute blood pressure-lowering and vasodilator effects of AT1 receptor antagonism in conscious normotensive but not hypertensive rats

The aims of this study were to determine the contribution of the AT2 receptor to the antihypertensive and regional vasodilatory effects of AT1 receptor blockade in adult spontaneously hypertensive rats (SHR), 2-kidney, 1-clip hypertensive (2K1C) rats, and sham-operated normotensive rats. Several studies have provided evidence to support the notion that the AT2 receptor may have opposing effects to those mediated by the AT1 receptor. We therefore tested the hypothesis that the depressor and vasodilator effects of acute AT1 receptor blockade are dependent on AT2 receptor activation. Heart rate, mean arterial pressure, and regional hemodynamics were measured over a 4-day protocol in rats that received the following treatments in randomized order: saline vehicle, the AT1 receptor antagonist candesartan (0.1 mg/kg iv bolus), the AT2 receptor antagonist PD-123319 (50 microg.kg(-1).min(-1)), or both antagonists. Intravenous candesartan reduced mean arterial pressure in all groups of rats, and this was accompanied by renal and mesenteric vasodilation. Neither saline nor PD-123319 significantly affected these variables. Concomitant PD-123319 administration partially reversed the depressor and mesenteric vasodilator effects of candesartan in sham-operated normotensive rats but not in SHR or 2K1C rats. These data indicate that the AT2 receptor contributes to the blood pressure-lowering and mesenteric vasodilator effects of AT1 receptor blockade in the acute setting in conscious normotensive but not hypertensive rats.

Angiotensin II type 1 receptor blockers reduce tissue factor activity and plasminogen activator inhibitor type-1 antigen in hypertensive patients: a randomized, double-blind, placebo-controlled study

Angiotensin II stimulates the expression of tissue factor (TF) and plasminogen activator inhibitor type-1 (PAI-1), and AT1 receptor blockade (ARB) reduces PAI-1 and TF activities in experimental studies. We investigated the effects of ARBs on TF activity, tissue plasminogen activator (tPA), PAI-1 antigen levels, plasma renin activity (PRA) and aldosterone levels in hypertensive patients. Placebo, losartan 100 mg, irbesartan 300 mg, and candesartan 16 mg daily were administered to 122 patients for 2 months. Compared with placebo, ARBs significantly reduced TF activity ( P < 0.001 by ANOVA), and candesartan was the most potent. Compared with placebo or losartan, irbesartan and candesartan significantly lowered plasma levels of PAI-1 antigen ( P < 0.001 by ANOVA) with no differences between the two. Compared with placebo, all ARBs lowered plasma levels of aldosterone ( P = 0.012 by ANOVA) and increased PRA ( P = 0.005 by ANOVA). There were significant correlations between the degree of change in TF activity and PAI-1 antigen levels ( r = 0.458, P < 0.0001) and between the change in TF activity and PRA ( r = −0.296, P = 0.006), but not with the magnitude of reduction in blood pressure following ARB therapy. ARBs significantly reduced TF activity, PAI-1 antigen levels, and aldosterone levels in hypertensive patients. The clinical significance of the varying potency of some ARBs needs to be further investigated.

Effects of AT1 receptor blockade on renal injury and mitogen-activated protein activity in Dahl salt-sensitive rats

The mitogen-activated protein kinase (MAPK) cascade is an important intracellular mediator of angiotensin II (Ang II)-induced cell growth and differentiation. Here, we examined the effect of angiotensin II type 1 receptor (AT1) receptor blockade on renal injury and MAPK activity in Dahl salt-sensitive (DS) rats. DS rats were maintained on a high (H: 8.0%NaCl, N= 8) or low (L: 0.3%NaCl, N= 7) salt diet, or H + candesartan cilexetil (10 to 15 mg/kg/day, N= 8). Urinary protein excretion (UproteinV), renal cortical collagen content, and glomerular injury (assessed by semiquantitative morphometric analysis) were determined after 4-week treatments. Plasma and kidney Ang II levels were measured by radioimmunoassay. Protein levels of AT1 and AT2 receptors in the renal cortical tissues were analyzed by Western-blotting analyses. MAPKs activities, including extracellular signal-regulated kinases (ERK)1/2, c-Jun NH2-terminal kinases (JNK), p38 MAPK, and Big-MAPK-1 (BMK1), were measured by Western-blotting analyses or in vitro kinase assays. DS/H rats showed higher mean blood pressure (MBP), UproteinV, and renal cortical collagen content than DS/L rats. Increased ERK1/2, JNK, and BMK1 activities were observed in renal cortical tissues of DS/H rats (approximately 6.3-, 4.5-, and 2.5-fold, respectively), whereas p38 MAPK activity was unchanged. Plasma Ang II levels were significantly reduced in DS/H rats compared with DS/L rats, whereas kidney Ang II contents and AT1 receptor protein levels were similar. Candesartan did not alter MBP, but significantly reduced UproteinV and collagen content, and ameliorated progressive sclerotic and proliferative glomerular changes. Furthermore, candesartan decreased renal tissue Ang II contents (from 216 +/- 19 to 46 +/- 3 fmol/mL) and ERK1/2, JNK, and BMK1 activities (-45%, -60%, and -70%, respectively) in DS/H rats. In DS hypertensive rats, some of the renoprotective effects of AT1 receptor blockade are accompanied by reductions in intrarenal Ang II contents and MAPK activity, which might not be mediated through arterial pressure changes.

Elevation of sympathetic activity by eprosartan in young male subjects

Background Selective blockade of the type 1 angiotensin II receptors (AT1 receptors) reduced blood pressure (BP) elevation caused by sympathetic stimulation in the pithed rat model. This has been attributed to blockade of AT1 receptors located presynaptically on sympathetic nerve endings normally facilitating norepinephrine release. We examined the effects of AT1 receptor blockade on the sympathetic nervous system in humans. Methods Twenty-nine young white men with normal to mildly hypertensive BP values participated in a double-blind, placebo-controlled, randomized cross-over protocol receiving 600 mg/d of eprosartan or placebo for 1 week. At the last day of intake we measured hemodynamic parameters, muscle sympathetic nerve activity by microneurography, and plasma levels of norepinephrine, epinephrine, and angiotensin II during rest and cardiovascular stress. Results Eprosartan lowered resting mean arterial pressure (73.6 ± 11.0 v 78.0 ± 10.3 mm Hg, P < .05; Finapres, Ohmeda, Englewood, CO), and elevated heart rate (64.4 ± 7.6 v 61.1 ± 6.8 beats/min, P = .01), muscle sympathetic nerve activity (14.1 ± 10.4 v 9.8 ± 6.3 bursts/min, P < .05) and plasma angiotensin II (37.0 ± 33.7 v 6.9 ± 2.8 ng/L, P < .01), as well as norepinephrine levels (234.2 ± 87.6 v 187.8 ± 59.3 ng/L, P < .01). Eprosartan did not blunt sympathetic activation caused by lower body negative pressure or mental stress. Conclusions These results contrast with animal data showing antiadrenergic properties of this drug. If any, it appeared, that eprosartan causes augmented central neural vasoconstrictor outflow paralleled by increased plasma levels of norepinephrine, which casts doubt on its ability to dampen norepinephrine release from peripheral sympathetic nerve endings in humans. We hypothesize that eprosartan leads to a resetting of the baroreflex, presumably by the markedly elevated circulating angiotensin II.