AT1a Knockout Mice Research Articles

Lack of contribution of nitric oxide synthase to cholinergic vasodilation in murine renal afferent arterioles.

We have previously reported significant increases in neuronal nitric oxide synthase (NOS) immunostaining in renal arterioles of angiotensin type 1A receptor (AT1A) knockout mice, and in arterioles and macula densa cells of AT1A/AT1B knockout mice. The contribution of nitric oxide derived from endothelial and macula densa cells in the maintenance of afferent arteriolar tone and acetylcholine-induced vasodilation was functionally determined in kidneys of wild-type, AT1A, and AT1A/AT1B knockout mice. Acetylcholine-induced changes in arteriolar diameters of in vitro blood-perfused juxtamedullary nephrons were measured during control conditions, in the presence of the nonspecific NOS inhibitor, Nω-nitro-l-arginine methyl ester (NLA), or the highly selective neuronal NOS inhibitor, N5-(1-imino-3-butenyl)-l-ornithine (VNIO). Acetylcholine (0.1 mM) produced a significant vasoconstriction in afferent arterioles of AT1A/AT1B mice (-10.9 ± 5.1%) and no changes in afferent arteriolar diameters of AT1A knockout mice. NLA (0.01-1 mM) or VNIO (0.01-1 μM) induced significant dose-dependent vasoconstrictions (-19.8 ± 4.0% 1 mM NLA; -7.8 ± 3.5% 1 μM VNIO) in afferent arterioles of kidneys of wild-type mice. VNIO had no effect on afferent arteriole diameters of AT1A knockout or AT1A/AT1B knockout mice, suggesting nonfunctional neuronal nitric oxide synthase. These data indicate that acetylcholine produces a significant renal afferent arteriole vasodilation independently of nitric oxide synthases in wild-type mice. AT1A receptors are essential for the manifestation of renal afferent arteriole responses to neuronal nitric oxide synthase-mediated nitric oxide release.

Inhibition or deletion of angiotensin II type 1 receptor suppresses elastase-induced experimental abdominal aortic aneurysms

ObjectiveAngiotensin (Ang) II type 1 receptor (AT1) activation is essential for the development of exogenous Ang II-induced abdominal aortic aneurysms (AAAs) in hyperlipidemic animals. Experimental data derived from this modeling system, however, provide limited insight into the role of endogenous Ang II in aneurysm pathogenesis. Consequently, the potential translational value of AT1 inhibition in clinical AAA disease management remains incompletely understood on the basis of the existing literature. MethodsAAAs were created in wild-type (WT) and AT1a knockout (KO) mice by intra-aortic infusion of porcine pancreatic elastase (PPE). WT mice were treated with the AT1 receptor antagonist telmisartan, 10 mg/kg/d in chow, or the peroxisome proliferator-activated receptor γ (PPARγ) antagonist GW9662, 3 mg/kg/d through oral gavage, beginning 1 week before or 3 days after PPE infusion. Influences on aneurysm progression as well as mechanistic insights into AT1-mediated pathogenic processes were determined using noninvasive ultrasound imaging, histopathology, aortic gene expression profiling, and flow cytometric analysis. ResultsAfter PPE infusion, aortic enlargement was almost completely abrogated in AT1a KO mice compared with WT mice. As defined by a ≥50% increase in aortic diameter, no PPE-infused, AT1a KO mouse actually developed an AAA. On histologic evaluation, medial smooth muscle cellularity and elastic lamellae were preserved in AT1a KO mice compared with WT mice, with marked attenuation of mural angiogenesis and leukocyte infiltration. In WT mice, telmisartan administration effectively suppressed aneurysm pathogenesis after PPE infusion as well, regardless of whether treatment was initiated before or after aneurysm creation or continued for a limited or extended time. Telmisartan treatment was associated with reduced messenger RNA levels for CCL5 and matrix metalloproteinases 2 and 9 in aneurysmal aortae, with no apparent effect on PPARγ-regulated gene expression. Administration of the PPARγ antagonist GW9662 failed to “rescue” the aneurysm phenotype in telmisartan-treated, PPE-infused WT mice. Neither effector T-cell differentiation nor regulatory T-cell cellularity was affected by telmisartan treatment status. ConclusionsTelmisartan effectively suppresses the progression of elastase-induced AAAs without apparent effect on PPARγ activation or T-cell differentiation. These findings reinforce the critical importance of endogenous AT1 activation in experimental AAA pathogenesis and reinforce the translational potential of AT1 inhibition in medical aneurysm disease management.

Telmisartan ameliorates glutamate-induced neurotoxicity: Roles of AT1 receptor blockade and PPARγ activation

Sartans (Angiotensin II AT1 Receptor Blockers, ARBs) are powerful neuroprotective agents in vivo and protect against IL-1β neurotoxicity in vitro. The purpose of this research was to determine the extent of sartan neuroprotection against glutamate excitotoxicity, a common cause of neuronal injury and apoptosis. The results show that sartans are neuroprotective, significantly reducing glutamate-induced neuronal injury and apoptosis in cultured rat primary cerebellar granule cells (CGCs). Telmisartan was the most potent sartan studied, with an order of potency telmisartan > candesartan > losartan > valsartan. Mechanisms involved reduction of pro-apoptotic caspase-3 activation, protection of the survival PI3K/Akt/GSK-3β pathway and prevention of glutamate-induced ERK1/2 activation. NMDA receptor stimulation was essential for glutamate-induced cell injury and apoptosis. Participation of AT1A receptor was supported by glutamate-induced upregulation of AT1A gene expression and AT1 receptor binding. Conversely, AT1B or AT2 receptors played no role. Glutamate-induced neuronal injury and the neuroprotective effect of telmisartan were decreased, but not abolished, in CGCs obtained from AT1A knock-out mice. This indicates that although AT1 receptors are necessary for glutamate to exert its full neurotoxic potential, part of the neuroprotective effect of telmisartan is independent of AT1 receptor blockade. PPARγ activation was also involved in the neuroprotective effects of telmisartan, as telmisartan enhanced PPARγ nuclear translocation and the PPARγ antagonist GW9662 partially reversed the neuroprotective effects of telmisartan. The present results substantiate the therapeutic use of sartans, in particular telmisartan, in neurodegenerative diseases and traumatic brain disorders where glutamate neurotoxicity plays a significant role.

Six Commercially Available Angiotensin II AT1 Receptor Antibodies are Non-specific

Commercially available Angiotensin II AT1 receptor antibodies are widely employed for receptor localization and quantification, but they have not been adequately validated. In this study, six commercially available AT1 receptor antibodies were characterized by established criteria: sc-1173 and sc-579 from Santa Cruz Biotechnology, Inc., AAR-011 from Alomone Labs, Ltd., AB15552 from Millipore, and ab18801 and ab9391 from Abcam. The immunostaining patterns observed were different for every antibody tested, and were unrelated to the presence or absence of AT1 receptors. The antibodies detected a 43 kDa band in western blots, corresponding to the predicted size of the native AT1 receptor. However, identical bands were observed in wild-type mice and in AT1A knock-out mice not expressing the target protein. Moreover, immunoreactivity detected in rat hypothalamic 4B cells not expressing AT1 receptors or transfected with AT1A receptor construct was identical, as revealed by western blotting and immunocytochemistry in cultured 4B cells. Additional prominent immunoreactive bands above and below 43 kDa were observed by western blotting in extracts from tissues of AT1A knock-out and wild-type mice and in 4B cells with or without AT1 receptor expression. In all cases, the patterns of immunoreactivity were independent of the AT1 receptor expression and different for each antibody studied. We conclude that, in our experimental setup, none of the commercially available AT1 receptor antibodies tested met the criteria for specificity and that competitive radioligand binding remains the only reliable approach to study AT1 receptor physiology in the absence of full antibody characterization.

Physiological function of the angiotensin AT1a receptor in bone remodeling

In order to determine whether the renin-angiotensin system (RAS) has any physiologic function in bone metabolism, mice lacking the gene encoding the major angiotensin II receptor isoform, AT1a, were studied using micro CT scanning, histomorphometric, and biochemical techniques. Three-dimensional (3D) micro CT analysis of the tibial metaphysis revealed that both male and female AT1a knockout mice exhibited an increased trabecular bone volume along with increased trabecular number and connectivity. Histomorphometric analysis of the tibial metaphysis indicated that the parameters of bone formation as well as resorption were increased, which was also supported by elevated serum osteocalcin and carboxy-terminal collagen crosslink (CTX) concentrations in the AT1a-deficient mice. Osteoclastogenesis and osteoblastogenesis assays in ex vivo cultures, however, did not reveal any intrinsic alterations in the differentiation potential of AT1a-deficient cells. Quantitative RT-PCR using RNA isolated from the tibia and femur revealed that the receptor activator of NF-κB ligand (RANKL)/osteoprotegerin (OPG) ratio and the expression of stromal cell-derived factor (SDF)1α were increased, whereas that of SOST was decreased in AT1a-deficient bone, which may account for the increased bone resorption and formation, respectively. AT1a-deficient mice also displayed a lean phenotype with reduced serum leptin levels. They maintained high bone mass with advancing age, and were protected from bone loss induced by ovariectomy. Collectively, the data suggest that RAS has a physiologic function in bone remodeling, and that signaling through AT1a negatively regulates bone turnover and bone mass.

Angiotensin type 1 receptor modulates macrophage polarization and renal injury in obesity

The mechanisms for increased risk of chronic kidney disease (CKD) in obesity remain unclear. The renin-angiotensin system is implicated in the pathogenesis of both adiposity and CKD. We investigated whether the angiotensin type 1 (AT(1)) receptor, composed of dominant AT(1a) and less expressed AT(1b) in wild-type (WT) mice, modulates development and progression of kidney injury in a high-fat diet (HFD)-induced obesity model. WT mice had increased body weight, body fat, and insulin levels and decreased adiponectin levels after 24 wk of a high-fat diet. Identically fed AT(1a) knockout (AT1aKO) mice gained weight similarly to WT mice, but had lower body fat and higher plasma cholesterol. Both obese AT1aKO and obese WT mice had increased visceral fat and kidney macrophage infiltration, with more proinflammatory M1 macrophage markers as well as increased mesangial expansion and tubular vacuolization, compared with lean mice. These abnormalities were heightened in the obese AT1aKO mice, with downregulated M2 macrophage markers and increased macrophage AT(1b) receptor. Treatment with an AT(1) receptor blocker, which affects both AT(1a) and AT(1b), abolished renal macrophage infiltration with inhibition of renal M1 and upregulation of M2 macrophage markers in obese WT mice. Our data suggest obesity accelerates kidney injury, linked to augmented inflammation in adipose and kidney tissues and a proinflammatory shift in macrophage and M1/M2 balance.

Trapping intracellular ANG II to the proximal tubule: powerful in vivo effects on sodium handling and blood pressure

destined for secretion out of the cells, ECFP/ANG II protein is thus trapped within the cytoplasm of the proximal tubule cell and is unable to act on cell surface AT1 receptors. Confirmation of the expression pattern of ECFP/ANG II was performed by fluorescent immunohistochemical localization using CFP- and ANG II-specific antibodies to cortical proximal tubules with limited expression in glomeruli, cortical connecting tubules, and medullary tissues. Ectopic ECFP/ ANG II expression was very low to undetectable in extrarenal tissues. Most interesting was the demonstration of a significantly elevated renal sodium reabsorption and ultimately increased blood pressure in the animals injected with the ECFP/ANG II adenovirus compared with animals injected with the scrambled version of the fusion protein construct. Two weeks following the introduction of the ECFP/ANG II vector, peptide levels of ANG II were significantly increased in the injected kidney and freshly isolated proximal tubules without alterations in the plasma or urinary levels of the peptide, suggesting that the blood pressure effects reflect the intracellular expression of the peptide. These hypertensive effects were observed in both

Intrarenal transfer of an intracellular fluorescent fusion of angiotensin II selectively in proximal tubules increases blood pressure in rats and mice.

The present study tested the hypothesis that intrarenal adenoviral transfer of an intracellular cyan fluorescent fusion of angiotensin II (ECFP/ANG II) selectively in proximal tubules of the kidney increases blood pressure by activating AT(1) (AT(1a)) receptors. Intrarenal transfer of ECFP/ANG II was induced in the superficial cortex of rat and mouse kidneys, and the sodium and glucose cotransporter 2 (sglt2) promoter was used to drive ECFP/ANG II expression selectively in proximal tubules. Intrarenal transfer of ECFP/ANG II induced a time-dependent, proximal tubule-selective expression of ECFP/ANG II in the cortex, which peaked at 2 wk and was sustained for 4 wk. ECFP/ANG II expression was low in the glomeruli and the entire medulla and was absent in the contralateral kidney or extrarenal tissues. At its peak of expression in proximal tubules at day 14, ANG II was increased by twofold in the kidney (P < 0.01) and more than threefold in proximal tubules (P < 0.01), but remained unchanged in plasma or urine. Systolic blood pressure was increased in ECFP/ANG II-transferred rats by 28 ± 6 mmHg (P < 0.01), whereas fractional sodium excretion was decreased by 20% (P < 0.01) and fractional lithium excretion was reduced by 24% (P < 0.01). These effects were blocked by losartan and prevented in AT(1a) knockout mice. Transfer of a scrambled ECFP/ANG IIc had no effects on blood pressure, kidney, and proximal tubule ANG II, or sodium excretion. These results provide evidence that proximal tubule-selective transfer of an intracellular ANG II fusion protein increases blood pressure by activating AT(1a) receptors and increasing sodium reabsorption in proximal tubules.

Angiotensin II Type 1a–Deficient Bone Marrow–Derived Dendritic Cells Produce Higher Levels of Monocyte Chemoattractant Protein 1

To the Editor: We read with interest the article from Crowley et al,1 who studied the role of angiotensin II type 1 (AT1) receptors (AT1aR) on immune cells in the pathogenesis of angiotensin II–induced hypertension by generating bone marrow chimeras with wild-type (WT) donors or donors lacking AT1aR. Interestingly, they found that the group of donors lacking AT1aR had more albuminuria and higher expression of a number of inflammatory mediators, including monocyte chemoattractant protein 1 (MCP-1), with persistent infiltration of macrophages in the kidney, concluding that AT1aR on bone marrow–derived cells had protective actions. The absence of a functional renin-angiotensin system, like in mice genetically lacking renin, angiotensinogen, angiotensin-converting enzyme, or AT1aR, is associated with microvascular disease and tubulointerstitial inflammation. Ouyang et al2 described that AT1a knockout (KO) mice spontaneously develop glomerular and tubulointerstitial diseases. They observed increased …

Vasoconstrictor effect of aldosterone via angiotensin II type 1 (AT1) receptor: possible role of AT1 receptor dimerization

We recently demonstrated that aldosterone induces a non-genomic vasoconstrictor effect on rat coronary arterioles and that this effect was blocked by angiotensin II type 1 receptor (AT1) blockers. Intracellular transglutaminase enhances AT1 signalling by cross-linking AT1 homodimers. The purpose of this study was to confirm the AT1-dependency of the vasoconstrictor effect of aldosterone using AT1a knockout (AT1aKO) mice and to investigate the role of intracellular transglutaminase and AT1 dimerization in this effect. The mesenteric arterioles (60-160 microm) were isolated from C57BL/6J (wild-type, WT) and AT1aKO mice, and the internal diameter was measured by video microscopy. Aldosterone (10(-13) to 10(-6) M), but not hydrocortisone, produced a dose-dependent vasoconstriction in WT mice; the maximal diameter change was -8.6 +/- 0.3% from the baseline (P < 0.001). This vasoconstrictor effect was unaffected by the mineralocorticoid receptor antagonist spironolactone or eplerenone, the AT2 antagonist PD123319, the glucocorticoid receptor antagonist RU486, or endothelium denudation. Aldosterone's vasoconstrictor effect was negligible in AT1aKO mice. The AT1 blockers valsartan or candesartan suppressed aldosterone-induced vasoconstriction in WT mice. The transglutaminase inhibitors cystamine and monodansyl cadaverine also suppressed the vasoconstrictor effect of aldosterone, without affecting the vasoconstrictor effect of angiotensin II in WT mice. AT1 dimer protein levels were increased in WT mesenteric arterioles treated with 10(-7) M aldosterone, and the transglutaminase inhibitor and AT1 blocker blocked this aldosterone-induced formation of AT1 dimer. Treatment with 10(-7) M aldosterone for 10 min increased the transglutaminase activity by 2.5 +/- 0.2-fold in cultured vascular smooth muscle cells and by 1.2 +/- 0.1-fold in the mesenteric arterioles. These increases were abolished by transglutaminase inhibitors. Aldosterone produces a non-genomic, endothelium-independent vasoconstrictor effect by enhancing intracellular transglutaminase activity and presumably inducing AT1 dimer formation in mesenteric arterioles.

The Importance of Angiotensin II Subtype Receptors for Blood Pressure Control During Mouse Pregnancy

Pregnancy is characterized by a progressive increase in the different components of the renin angiotensin system (RAS) including angiotensin II, a potent vasoconstrictor. Pregnant women and experimental animals are resistant to the pressor effect of increased angiotensin II concentrations during pregnancy. In normal pregnancy, maternal blood pressure (BP) begins to fall in early gestation, reaches a nadir in midgestation, and then gradually increases to nonpregnant levels before term in both humans and C57BL/6J mice. The mechanism producing these changes is unknown. The present study investigates the roles of angiotensin II subtype receptors (AT1a and AT2) in hemodynamic regulation during pregnancy in mice. Female mice genetically or pharmacologically manipulated to alter angiotensin receptor stimulation were bred to 2 strains of males. Maternal BP was measured daily throughout pregnancy. Pup weight and number were determined. Pregnancy-induced hypertension was apparent in transgenic female mice expressing the human angiotensin gene bred with males expressing human renin. This effect was not apparent in the absence of the AT1a receptor (ie, in AT1a knockout mice). The midgestation BP decline in both C56BL/6J and AT1a(-/-) females was abolished by AT2 receptor antagonism. There was a linear, inverse relationship between average BP throughout pregnancy and the average pup weight and number per litter. In summary, these findings suggest that activation of the AT2 receptor may be an important factor in promoting the midgestation BP decline that occurs in several mammalian species and, furthermore, that angiotensin is an important modulator of BP during pregnancy.

The involvement of type 1a angiotensin II receptors in the regulation of airway inflammation in a murine model of allergic asthma

There has been increasing evidence suggesting the involvement of angiotensin II (Ang II) and type 1 Ang II receptors (AT1) in the pathogenesis of bronchial asthma. However, whether such an involvement would promote or suppress the pathophysiology of asthma is controversial. The aim of this study was to investigate the role of AT1 in the development of allergic airway inflammation. Agtr1a+/+ [wild-type C57BL/6 mice (WT)] and Agtr1a-/- mice [AT1a knockout mice (AT1aKO)] with a genetic background of C57BL/6 were systemically sensitized to ovalbumin (OVA), followed by OVA inhalation. OVA-specific IgE in serum obtained just before the inhalation was measured. Bronchoalveolar lavage (BAL) fluid and lung tissues were obtained at various time-points. Cell numbers and differentiation, and cytokine contents in BAL fluids were determined. Peribronchial accumulation of eosinophils and mucus inclusions in the bronchial epithelium were evaluated in lung tissues stained histochemically. Cell numbers and differentiation in BAL fluids of the mice were also determined after lipopolysaccharide (LPS) inhalation. The levels of OVA-specific IgE in AT1aKO were significantly higher than those in WT. The numbers of total cell, eosinophils and lymphocytes in BAL fluids 7 days after OVA inhalation in AT1aKO were significantly higher than those in WT. Airway inflammation in bronchial tissues in terms of eosinophil accumulation and mucus hypersecretion in AT1aKO was also stronger than in WT. The contents of IL-4, IL-5 and IL-13, but not IFN-gamma, in BAL fluids of AT1aKO were significantly higher than those of WT. In contrast, neutrophil accumulation in BAL fluids after LPS inhalation was significantly higher in WT than in AT1aKO. AT1a might be involved in the negative regulation of the development of allergic airway inflammation through polarizing the T-helper (Th) balance towards Th1 predominance. Therefore, it would be of clinical importance to investigate the effects of long-term administration of AT1 blockers on the Th1/Th2 balance in hypertensive patients with bronchial asthma.

Physiological regulation of brain angiotensin receptor mRNA in AT1a deficient mice

Experiments were performed to study the physiological regulation of angiotensin (Ang) AT1b receptors using Ang AT1a knockout mice (AT1aKO). Ang AT1b mRNA was analyzed in forebrain, hypothalamus, and brainstem using in situ hybridization (ISH) under baseline and water-restricted conditions. Plasma was analyzed for osmolality, vasopressin, and corticosterone. Dehydration (24 h) increased osmolality and corticosterone and decreased body weight with no difference between groups. Plasma vasopressin was not different between the groups and was not stimulated by dehydration. Under water ad libitum conditions, there were no differences in AT1b mRNA expression in medial periventricular, anterior third ventricle (AV3V), and subfornical organ (SFO) between controls and AT1aKO. In contrast, there was higher expression in the dorsal motor nucleus of the vagus (DMV) of AT1aKO vs. Controls (0.6 ± 0.1 vs. 0.9 ± 0.1 μCi/g, Control vs. AT1aKO in water ad libitum group). Dehydration increased AT1b expression in SFO in AT1aKO, but not in controls (0.6 ± 0.07 vs. 0.9 ± 0.06 μCi/g; water ad libitum vs. dehydrated). Emulsion autoradiography documents the detailed pattern of AT1b expression in brainstem of controls and AT1aKO. There was labeling in DMV, locus coeruleus, inferior olive, lateral reticular nucleus, and caudalis spinal trigemius. In conclusion, deletion of AT1a receptors produces a compensatory increase in AT1b receptor mRNA expression in brainstem, but not in hypothalamus or rostral forebrain. In addition, AT1aKO mice showed an enhanced response to dehydration in terms of AT1b mRNA expression in SFO.

Phosphatidylinositol 3-kinase/Akt regulates angiotensin II-induced inhibition of apoptosis in microvascular endothelial cells by governing survivin expression and suppression of caspase-3 activity.

Angiotensin II (Ang II) plays essential roles in vascular homeostasis, neointimal formation, and postinfarct remodeling. Although Ang II has been shown to regulate apoptosis in cardiomyocytes and vascular smooth muscle cells, its role in vascular endothelial cells (ECs) remains elusive. To address this issue, we first performed TUNEL and caspase-3 activity assays with porcine microvascular ECs challenged by serum deprivation. Ang II significantly reduced the ratio of apoptotic cells and caspase-3 activity. The Ang II type 1 receptor (AT1) was responsible for these effects. Among the signaling molecules downstream of AT1, we revealed that PI3-kinase/Akt pathway plays a predominant role in the antiapoptotic effect of Ang II. Interestingly, the expression of survivin, a central molecule of cell survival, increased after Ang II stimulation. Overexpression of a dominant-negative form of Akt abolished both Ang II-induced antiapoptosis and survivin protein expression. In a murine model of hyperoxygen-induced retinal vascular regression, AT1a knockout mice showed a significant increase in retinal avascular areas. Our data indicate that Ang II plays a critical antiapoptotic role in vascular ECs by a mechanism involving PI3-kinase/Akt activation, subsequent upregulation of survivin, and suppression of caspase-3 activity.

Renal vascular reactivity in mice: AngII-induced vasoconstriction in AT1A receptor null mice.

The present study describes methodology and its application to evaluate renal reactivity in acute studies on anesthetized mice. Renal blood flow (RBF) was measured using an ultrasonic transit-time flowmeter and a non-cannulating V-shaped probe. An intrarenal artery injection technique established feasibility and reproducibility of studies of renal vascular reactivity to angiotensin II (AngII) in adult wild-type mice. The study also examined whether AngII would affect RBF in mice lacking AT1A receptors due to gene targeting. Mean arterial pressure averaged 83 and 62 mmHg, respectively, in mice with and without AT1A receptors. The RBF was similar in both groups, averaging 7 ml/min per g kidney wt. AngII injection (10-microl bolus) into the renal artery produced transient, dose-dependent, selective reductions in RBF in AT1A knockout mice as well as wild-type mice. The response was considerably greater in mice with AT1A receptors: 10% for 0.1 ng, 30% for 1 ng, and 45% for 5 ng AngII in control animals versus respective decreases of 6, 15, and 17% in knockout mice. In other studies, angiotensin-converting enzyme (captopril) or renin (CP-71362-14) was inhibited. During inhibition of AngII formation, renal vascular reactivity to AngII increased twofold in both groups. Coadministration of the AT1 receptor antagonist losartan (1 to 1000 ng) elicited dose-dependent inhibition of AngII effects, with near maximum blockage of 80 to 90% in both groups of mice. The putative AT2 receptor antagonist PD 123319 inhibited 30 to 40% of AngII-induced vasoconstriction, whereas CGP 42112 had no effect in either group. In conclusion, AngII can elicit renal vasoconstriction, albeit attenuated, in AT1A knockout mice. The weaker RBF effects are most likely due to the absence of the AT1A receptor. Inhibition of the response by AT1 receptor antagonist suggests mediation by the AT1B receptor in these animals. The residual constrictor effect observed during AT1 receptor blockade and sensitive to PD 123319 appears to be mediated by a non-AT1 receptor.

Pressure overload induces cardiac hypertrophy in angiotensin II type 1A receptor knockout mice.

Many studies have suggested that the renin-angiotensin system plays an important role in the development of pressure overload-induced cardiac hypertrophy. Moreover, it has been reported that pressure overload-induced cardiac hypertrophy is completely prevented by ACE inhibitors in vivo and that the stored angiotensin II (Ang II) is released from cardiac myocytes in response to mechanical stretch and induces cardiomyocyte hypertrophy through the Ang II type 1 receptor (AT1) in vitro. These results suggest that the AT1-mediated signaling is critical for the development of mechanical stress-induced cardiac hypertrophy. To determine whether AT1-mediated signaling is indispensable for the development of pressure overload-induced cardiac hypertrophy, pressure overload was produced by constricting the abdominal aorta of AT1A knockout (KO) mice. Quantitative reverse transcriptase-polymerase chain reaction revealed that the cardiac AT1 (probably AT1B) mRNA levels in AT1A KO mice were <10% of those of wild-type (WT) mice and were not affected by pressure overload. Chronic treatment with subpressor doses of Ang II increased left ventricular mass in WT mice but not in KO mice. Pressure overload, however, fully induced cardiac hypertrophy in KO as well as WT mice. There were no significant differences between WT and KO mice in expression levels of fetal-type cardiac genes, in the left ventricular wall thickness and systolic function as revealed by the transthoracic echocardiogram, or in the histological changes such as myocyte hypertrophy and fibrosis. AT1-mediated Ang II signaling is not essential for the development of pressure overload-induced cardiac hypertrophy.

Pressure-overload hypertrophy is unabated in mice devoid of AT1A receptors.

Mechanisms controlling cardiac growth are under intense investigation. Among these, the renin-angiotensin system has received great interest. In the current study, we tested the hypothesis that the renin-angiotensin system was not an obligate factor in cardiac hypertrophy. We examined the left ventricular hypertrophic response to a pressure overload in mice devoid of the AT1A receptor, the putative major effector of the growth response of the renin-angiotensin system. Aortic banding produced similar transband gradients in wild-type and AT1A knockout mice. The left ventricular mass-to-body weight ratio increased from 3.44 +/- 0.08 to 5.62 +/- 0.25 in wild-type ascending aortic-banded mice. The response in the knockout mice was not different (from 2.97 +/- 0.13 to 5.24 +/- 0.37). We conclude that the magnitude of cardiac hypertrophy is not affected by the absence of the AT1A receptor and its signaling pathway and that this component of the renin-angiotensin system is not necessary in cardiac hypertrophy.