Renal angiotensin type 2 receptors mediate natriuresis via angiotensin III in the angiotensin II type 1 receptor-blocked rat

Whereas angiotensin (Ang) II is the major effector peptide of the renin-angiotensin system, its metabolite, des-aspartyl1-Ang II (Ang III), may also have biologic activity. We investigated the effects of renal interstitial (RI) administration of candesartan (CAND), a specific Ang II type 1 receptor (AT1) blocker, with and without coinfusion of PD-123319 (PD), a specific Ang II type 2 receptor (AT2) blocker, on Na+ excretion (UNaV) in uninephrectomized rats. We also studied the effects of unilateral RI infusion of Ang II or Ang III on UNaV with and without systemic infusion of CAND with the noninfused kidney as control. In rats receiving normal Na+ intake, RI CAND increased UNaV from 0.07+/-0.08 to 0.82+/-0.17 micromol/min (P<0.01); this response was abolished by PD. During Na+ restriction, CAND increased UNaV from 0.06+/-0.02 to 0.1+/-0.02 micromol/min (P<0.05); this response also was blocked by PD. In rats with both kidneys intact, in the absence of CAND, unilateral RI infusion of Ang III did not significantly alter UNaV. However, with systemic CAND infusion, RI Ang III increased U(Na)V from 0.08+/-0.01 micromol/min to 0.18+/-0.04 micromol/min (P<0.01) at 3.5 nmol/kg per minute, and UNaV remained elevated throughout the infusion; this response was abolished by PD. However, RI infusion of Ang II did not significantly alter UNaV at any infusion rate (3.5 to 80 nmol/kg per minute) with or without systemic CAND infusion. These results suggest that intrarenal AT1 receptor blockade engenders natriuresis by activation of AT2 receptors. AT2 receptor activation via Ang III, but not via Ang II, mediates the natriuretic response in the presence of systemic AT1 receptor blockade.     

Angiotensin II type 2 receptor gene transfer downregulates angiotensin II type 1a receptor in vascular smooth muscle cells

Two distinct subtypes of angiotensin (Ang) II receptors, type 1 (AT(1)) and type 2 (AT(2)), have been identified. Vascular smooth muscle cells (VSMCs) usually express AT(1) receptor. To elucidate the direct effects of the AT(2) receptor on the AT(1) receptor in VSMCs, we transfected AT(2) receptor gene into cultured rat VSMCs. Overexpression of AT(2) receptor significantly decreased expression of AT(1a) receptor at both the mRNA and protein levels in the presence and absence of Ang II in VSMCs. Overexpression of AT(2) receptor increased expression of bradykinin and inducible NO in the presence and absence of Ang II in VSMCs. Bradykinin B(2) receptor antagonist HOE-140 and NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) inhibited the decreases in AT(1a) receptor expression by the overexpression of AT(2) receptor in VSMCs. L-Arginine augmented the decrease in AT(1a) receptor expression. Overexpression of AT(2) receptor suppressed basal DNA synthesis and proliferation of VSMCs and abolished response of DNA synthesis to Ang II in VSMCs. Our results demonstrate that overexpression of the AT(2) receptor downregulates AT(1a) receptor expression in rat VSMCs in a ligand-independent manner that is mediated by the bradykinin/NO pathway. Downregulation of AT(1a) receptor is a novel mechanism by which the AT(2) receptor regulates growth and metabolism of VSMCs.     

Involvement of the angiotensin II type 2 receptor in apoptosis during human fetal adrenal gland development

The aim of this study was to establish a link between the highly expressed angiotensin II (Ang II) type 2 receptor (AT2) in human fetal adrenal cells and the proposed apoptotic activity in the center of the gland. There was an important increase in apoptotic DNA fragmentation with age in adrenal glands of fetuses from 15-20 weeks gestation. Adrenal cells showing the characteristic apoptotic internucleosomal DNA fragmentation were localized in the central portion of the fetal zone. In cells cultured for 24 h, Ang II, via the AT2 receptor, induced DNA fragmentation and cleavage of the DNA repair enzyme, poly-(ADP-ribose) polymerase. Furthermore, characteristic membrane blebbing was observed specifically on cells of the fetal zone. Immunofluorescence studies demonstrated that stimulation with Ang II or CGP 42112 (an agonist of the AT2 receptor) strongly modified the actin network, now localized exclusively along the plasma membrane, with a predominance of labeling at the base of the bleb formation. This rearrangement of actin distribution was different in cells from the definitive zone, corroborating the observation that these cells express many more Ang II type 1 receptors (AT1) than AT2 receptors. Taken together, our data indicate that the AT2 receptor is involved in the apoptotic process observed in the human fetal adrenal gland and could participate in the morphological changes occurring after birth, leading to involution of the fetal zone.     

Angiotensin II type 1 receptor antibodies and increased angiotensin II sensitivity in pregnant rats

Pregnant women who subsequently develop preeclampsia are highly sensitive to infused angiotensin (Ang) II; the sensitivity persists postpartum. Activating autoantibodies against the Ang II type 1 (AT(1)) receptor are present in preeclampsia. In vitro and in vivo data suggest that they could be involved in the disease process. We generated and purified activating antibodies against the AT(1) receptor (AT(1)-AB) by immunizing rabbits against the AFHYESQ epitope of the second extracellular loop, which is the binding epitope of endogenous activating autoantibodies against AT(1) from patients with preeclampsia. We then purified AT(1)-AB using affinity chromatography with the AFHYESQ peptide. We were able to detect AT(1)-AB both by ELISA and a functional bioassay. We then passively transferred AT(1)-AB into pregnant rats, alone or combined with Ang II. AT(1)-AB activated protein kinase C-α and extracellular-related kinase 1/2. Passive transfer of AT(1)-AB alone or Ang II (435 ng/kg per minute) infused alone did not induce a preeclampsia-like syndrome in pregnant rats. However, the combination (AT(1)-AB plus Ang II) induced hypertension, proteinuria, intrauterine growth retardation, and arteriolosclerosis in the uteroplacental unit. We next performed gene-array profiling of the uteroplacental unit and found that hypoxia-inducible factor 1α was upregulated by Ang II plus AT(1)-AB, which we then confirmed by Western blotting in villous explants. Furthermore, endothelin 1 was upregulated in endothelial cells by Ang II plus AT(1)-AB. We show that AT(1)-AB induces Ang II sensitivity. Our mechanistic study supports the existence of an "autoimmune-activating receptor" that could contribute to Ang II sensitivity and possible to preeclampsia.     

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

AIMS: 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. METHODS AND RESULTS: 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. CONCLUSION: Aldosterone produces a non-genomic, endothelium-independent vasoconstrictor effect by enhancing intracellular transglutaminase activity and presumably inducing AT1 dimer formation in mesenteric arterioles.     

Angiotensin II and angiotensin converting enzyme binding in human adrenal gland and pheochromocytomas

Binding sites for angiotensin II (Ang II) and angiotensin converting enzyme (ACE) were studied by autoradiography in human, rat and bovine adrenals and human pheochromocytomas. In human and rat adrenals, binding sites for both Ang II and ACE were found in the medulla and zona glomerulosa. In bovine adrenals, ACE binding sites were not detectable, while Ang II binding was higher in the zona glomerulosa, lower in the rest of the cortex and undetectable in the medulla. In pheochromocytomas, ACE binding was homogeneously distributed, but no Ang II binding was detected. These results suggest that circulating and/or locally formed Ang II could regulate adrenomedullary and zona glomerulosa functions in man, and show that chromaffin cells in tumors retain ACE binding sites but lose Ang II binding sites. Thus, there are alterations in the regulation of the renin-angiotensin system in chromaffin tumors.     

Angiotensin II AT1 receptor blockade decreases lipopolysaccharide-induced inflammation in the rat adrenal gland

Peripheral administration of bacterial endotoxin [lipopolysaccharide (LPS)] to rodents produces an innate immune response and hypothalamic-pituitary-adrenal axis stimulation. Renin-angiotensin-aldosterone system inhibition by angiotensin II AT1 receptor blockade has antiinflammatory effects in the vasculature. We studied whether angiotensin II receptor blockers (ARBs) prevent the LPS response. We focused on the adrenal gland, one organ responsive to LPS and expressing a local renin-angiotensin-aldosterone system. LPS (50 microg/kg, ip) produced a generalized inflammatory response with increased release of TNF-alpha and IL-6 to the circulation, enhanced adrenal aldosterone synthesis and release, and enhanced adrenal cyclooxygenase-2, IL-6, and TNF-alpha gene expression. ACTH and corticosterone release were also increased by LPS. Pretreatment with the ARB candesartan (1 mg/kg.d, sc for 3 d before the LPS administration) decreased LPS-induced cytokine release to the circulation, adrenal aldosterone synthesis and release, and cyclooxygenase-2 and IL-6 gene expression. Candesartan did not prevent the LPS-induced ACTH and corticosterone release. Our results suggest that AT1 receptors are essential for the development of the full innate immune and stress responses to bacterial endotoxin. The ARB decreased the general peripheral inflammatory response to LPS, partially decreased the inflammatory response in the adrenal gland, prevented the release of the pro-inflammatory hormone aldosterone, and protected the antiinflammatory effects of glucocorticoid release. An unrestricted innate immune response to the bacterial endotoxin may have deleterious effects for the organism and may lead to development of chronic inflammatory disease. We postulate that the ARBs may have therapeutic effects on inflammatory conditions.     

Control of aldosterone secretion during sodium restriction: Adrenal receptor regulation and increased adrenal sensitivity to angiotensin II

The mechanism of increased adrenal sensitivity to angiotensin II during the aldosterone response to sodium restriction was investigated in the rat. Sodium restriction for 36 hr markedly increased the aldosterone-stimulating effect of low-dose (1 ng/min) infusion of angiotensin II and caused enhanced binding of (125)I-labeled angiotensin II to the zona glomerulosa in vivo. Conversely, in vivo binding of (125)I-labeled angiotensin II was significantly decreased after 36 hr of high-sodium intake. In isolated glomerulosa cells, the increased binding of angiotensin II after sodium restriction was shown to result from a significant increase in receptor affinity (+80%) and a smaller increase in receptor concentration (+25%). The corresponding aldosterone responses in dispersed cells showed an increase in sensitivity to angiotensin II, commensurate with the increased receptor affinity. More prolonged sodium restriction (4 days) caused a further increase in angiotensin receptor concentration (+70%) and maximal aldosterone response (+50%), whereas the binding affinity of adrenal receptors and the sensitivity of the in vitro aldosterone response had returned to normal. During sodium loading for 36 hr and 4 days, the converse effects on adrenal angiotensin II receptors and aldosterone production were observed. Also, in contrast to the consistent increase in angiotensin II receptors in the adrenal glands of sodium-restricted animals, the angiotensin II binding capacity of uterine smooth muscle was decreased by 40% after 7 days of sodium restriction.The rapid regulation of receptor affinity and concentration during changes in sodium intake provides a basis for the dynamic modulation of aldosterone responses by dietary sodium content. During sodium restriction, the sequential changes in receptor affinity and concentration account for the enhanced binding and steroidogenic actions of angiotensin II in vivo and in vitro. These receptor changes, and the converse effects of sodium loading, serve as a local regulatory mechanism in the physiological control of adrenal sensitivity and aldosterone secretion. The opposite finding in smooth muscle-that sodium restriction decreases the concentration of angiotensin II receptors-is consistent with the divergent effects of changing sodium balance upon vascular and adrenal responses to angiotensin II.     

Angiotensin II type 2 receptor blockade partially negates antihypertrophic effects of type 1 receptor blockade on pressure-overload rat cardiac hypertrophy.

We investigated the effects of angiotensin II type 2 (AT2) receptor blockade on the antihypertrophic effects of type 1 receptor (AT1) blockade in pressure-overload cardiac hypertrophy in adult rats. Cardiac hypertrophy was induced by banding the abdominal aorta above the renal arteries. The rats were treated with either an AT1 receptor antagonist TCV-116 (TCV, 10 mg/kg/day), an AT2 receptor antagonist PD123319 (PD, 20 mg/kg/day), or both for 4 weeks after the aortic banding. We measured systolic and diastolic blood pressure (BP), body weight (BW), left ventricular weight (LVW), and serum and cardiac angiotensin converting enzyme (ACE) activities. Aortic banding increased BP and LVW/BW, and TCV reversed both these increases. PD affected neither BP nor LVW/BW. TCV+PD reversed the increase in BP but not LVW/BW. Thus, PD was considered to counteract the antihypertrophic effect of TCV without affecting BP. All three treatments reduced cardiac ACE activity without affecting serum ACE activity. Our data demonstrated that AT2 receptor blockade negates the antihypertrophic effects of AT1 receptor blockade in an adult rat model of pressure-overload cardiac hypertrophy. AT2 receptors may mediate the signaling pathways involved in growth inhibition, which could counteract mediation of the cellular growth signaling pathways by AT1 receptors.     

The angiotensin II type 2 receptor causes constitutive growth of cardiomyocytes and does not antagonize angiotensin II type 1 receptor-mediated hypertrophy

Angiotensin II (Ang II) has important actions on the heart via type 1 (AT1) and type 2 (AT2) receptors. The link between AT1 receptor activation and the hypertrophy of cardiomyocytes is accepted, whereas the contribution of the AT2 receptor, which reportedly antagonizes the AT1 receptor, is contentious. This ambiguity is primarily based on in vivo approaches, in which the direct effect of the AT2 receptor and its modulation of the AT1 receptor (at the level of the cardiomyocyte) are difficult to establish. In this study, we used adenoviruses encoding AT1 and AT2 to coexpress these receptors in isolated cardiomyocytes, allowing a direct examination of the consequence of varying AT1/AT2 stoichiometry on cardiomyocyte hypertrophy. In myocytes expressing only the AT1 receptor, Ang II stimulation promoted robust hypertrophy (increased protein:DNA ratio and phenotypic changes) via activation of mitogen-activated protein kinases (MAPKs). Titration of the AT2 receptor against the AT1 receptor did not inhibit Ang II-mediated cardiomyocyte hypertrophy. Instead, basal and Ang II-mediated hypertrophy was increased in line with the amplified expression of the AT2 receptor, indicating a capacity for the AT2 receptor to enhance basal cardiomyocyte growth. Indeed, expression of the AT2 receptor alone resulted in hypertrophy; remarkably, this was unaffected by Ang II stimulation or the AT2 receptor-specific ligands PD123319 and CGP42112. Although previous studies have indicated that the AT2 receptor can antagonize MAPK activation via the AT1 receptor, we found no evidence for this in cardiomyocytes. Thus, the AT2 receptor promotes ligand-independent, constitutive cardiomyocyte hypertrophy and does not directly antagonize the AT1 receptor in this setting.     

Chronic estradiol treatment decreases angiotensin II receptor density in the anterior pituitary gland and adrenal cortex but not in the mesenteric artery

Chronic estrogen treatment has been shown to produce a marked reduction in anterior pituitary angiotensin II (AII) receptor density. In order to determine whether this effect is generalized, we studied the effect of chronic estradiol treatment on AII receptor density in the anterior pituitary gland, adrenal cortex and mesenteric artery of ovariectomized (OVX) rats. Treated rats were injected daily with 25 micrograms of estradiol valerate while controls received only the vehicle. Binding affinity and density of AII receptors were measured using the AII antagonist [125I]-Sar1Ile8 AII ([125I]-SARILE). Following 7-, 14- or 28-day treatments, AII receptor density decreased by approximately 80% in the anterior pituitary; 30% in the adrenal cortex and remained the same in mesenteric artery particulate fractions. In all 3 target tissues, dissociation constants (KD) for binding of [125I]-SARILE were in the nanomolar range and were the same between control and treated rats. Using conscious rats, estradiol treatment for 7 days was also shown to block the release of aldosterone by low dose infusions of AII (10 ng/min, 30 min). Plasma AII and plasma renin activity were also the same or slightly decreased following estradiol treatments. This study suggests that estrogens may be important modulators of the AII receptor and may be directly involved in modulating target cell responsiveness to AII as expressed through differential down-regulation of AII receptors.     

Parathyroid hormone modulates angiotensin II-induced aldosterone secretion from the adrenal glomerulosa cell.

The effect of PTH on aldosterone secretion from isolated bovine adrenal glomerulosa cells was examined. PTH binding was autoradiographically localized to the adrenal cortex, suggesting a specific effect. This binding of PTH was displaceable by cold PTH, but not by ACTH. No binding was observed in the adrenal medulla. In addition, PTH was shown to stimulate aldosterone secretion in a dose-dependent manner and to potentiate aldosterone secretion in response to angiotensin-II, such that PTH (10(-9)M) elevated the secretory rate from 58.6 +/- 6.8 to 110.9 +/- 19 pg/min.million cells in the presence of 10 nM angiotensin-II. The magnitude of the synergism between the two hormones depended on the concentrations of PTH and angiotensin-II as well as the time during which aldosterone secretion was measured. Within the first 15 min of stimulation, PTH increased the sensitivity to angiotensin-II, shifting the Ka for activation from 1.0 to 0.3 nM. In contrast, between 30-45 min of angiotensin-II stimulation, PTH elevated the maximal secretory response to angiotensin-II from 109 +/- 3.4 to 219 +/- 13.3 pg/min.million cells. By itself PTH elicited only a small increase in the intracellular Ca2+ concentration, as measured by aequorin luminescence in glomerulosa cells. In cells pretreated with angiotensin-II or 15 mM potassium, the intracellular calcium response to PTH was markedly potentiated. PTH was also found to cause a small increase in the cellular cAMP content. Thus, PTH stimulates aldosterone secretion from adrenal glomerulosa cells, both alone and in combination with angiotensin-II.     

Angiotensin II type 1 and type 2 receptors bind angiotensin II through different types of epitope recognition

OBJECTIVE: This study was designed to demonstrate that the principle of molecular recognition underlying high-affinity binding of angiotensin II to the type 2 (AT2) receptor is distinct from that of the type 1 (AT1) receptor. In general, the same functional pharmacophores in hormones are used to bind and activate different subtypes of cell surface receptors. However, the binding of angiotensin II to the AT2 receptor is distinct from that of the AT1 receptor. DESIGN AND METHODS: To systematically evaluate the effect of modification of angiotensin II side chains on binding to both the receptors, several analogs of angiotensin II were synthesized. Rat AT1 or AT2 receptors expressed in COS1 cell membranes were used to determine the affinity of analogs using radioligand competition binding experiments under equilibrium conditions. RESULTS: Modifications of all angiotensin II side chains affected binding to the AT2 receptor to nearly similar extents. In contrast, binding to the AT1 receptor was significantly affected by modifications at side chain positions 2, 4, 6 and 7. In accordance with previous observations that Tyr4- or Phe8-modified angiotensin II analogs antagonized vasoconstriction mediated exclusively by the AT1 receptor, binding to the AT1 receptor was significantly dependent on Tyr4 or Phe8 of angiotensin II whereas binding to the AT2 receptor was not. Rather surprisingly, the affinity profile of several angiotensin II analogs towards the AT2 receptor was similar to the measured affinity of the constitutively active N111G mutant AT1 receptor. CONCLUSIONS: These results suggest that the AT2-receptor pharmacophore is very distinct from that of the AT1 receptor. The AT1 receptor is in a constrained conformation and is activated only when bound to angiotensin II. In contrast, the AT2 receptor is 'relaxed' in that no single interaction is critical for binding, like the N111G mutant AT1 receptor, which is constitutively active.     

Angiotensin II stimulates endothelial NO synthase phosphorylation in thoracic aorta of mice with abdominal aortic banding via type 2 receptor

Abdominal aortic banding in mice induces upregulation of angiotensin II (Ang II) type 2 (AT2) receptors in the pressure-overloaded thoracic aorta. To clarify mechanisms underlying the vascular AT2 receptor-dependent NO production, we measured aortic levels of endothelial NO synthase (eNOS), eNOS phosphorylated at Ser633 and Ser1177, protein kinase B (Akt), and Akt phosphorylated at Ser473 in thoracic aortas of mice after banding. Total eNOS, both forms of phosphorylated eNOS, Akt, and phosphorylated Akt levels, as well as cGMP contents, were significantly increased 4 days after banding. The administration of PD123319 (an AT2 receptor antagonist) or icatibant (a bradykinin B2 receptor antagonist) abolished the banding-induced upregulation of both forms of phosphorylated eNOS, as well as elevation of cGMP, but did not affect the upregulation of eNOS, Akt, and phosphorylated Akt. In the in vitro experiments using aortic rings prepared from banded mice, Ang II produced significant increases in both forms of phosphorylated eNOS, as well as cGMP, and these effects were blocked by PD123319 and icatibant. Ang II-induced eNOS phosphorylation and cGMP elevation in aortic rings were inhibited by protein kinase A (PKA) inhibitors H89 and KT5720 but not by phosphatidylinositol 3-kinase inhibitors wortmannin and LY24002. The contractile response to Ang II was attenuated in aortic rings from banded mice via AT2 receptor, and this attenuation was blocked by PKA inhibitors. These results suggest that the activation of AT2 receptor by Ang II induces phosphorylation of eNOS at Ser633 and Ser1177 via a PKA-mediated signaling pathway, resulting in sustained activation of eNOS.     

Angiotensin II type 1 receptor, but no type 2 receptor, interferes with the insulin-induced nitric oxide production in HUVECs

Objective

Two subtypes of angiotensin II (ATII) receptor have been defined on the basis of their differential pharmacological and biochemical properties: ATII-type1 receptors (AT₁-R) and ATII-type2 receptors (AT₂-R). It has been hypothesized that part of the protective effects on the cardiovascular system of AT₁-R blockers is mediated by an ATII-mediated overstimulation of AT₂-R.We hypothesized that the inhibition of AT₁-R has a stronger impact on insulin-induced nitric oxide (NO) production than ATII-mediated overstimulation of AT₂-R. Therefore we studied the effect of the inhibition of AT₁-R and AT₂-R on ATII-mediated actions in Human Umbilical Vein Endothelial Cells (HUVECs).

Methods

We analyzed the phosphorylation state of IRS1 at Ser⁶¹⁶ and Ser³¹² and on tyrosines after preincubation with PD123319, an inhibitor of AT₂-R, alone and in combination whit losartan, an inhibitor of AT₁-R. In addition we measured eNOS and Akt activation through the evaluation of their phosphorylation at Ser¹¹⁷⁷ and Ser⁴⁷³ sites respectively.

Results

ATII induces IRS-1 phosphorylation at Ser³¹² and Ser⁶¹⁶ through the activation of JNK and ERK 1/2, resulting in the inhibition of the insulin-induced phosphorylation of IRS1 tyrosines, Akt and eNOS. Treatment of HUVECs with AT₁-R inhibitor restored the insulin signaling leading to NO production, whereas AT₂-R inhibitor did not have effects on NO production in presence of ATII.

Conclusion

Our results demonstrate that in presence of AT₁-R antagonist, the AT₂-R blockage does not modify the effect obtained with the AT₁-R inhibition alone. Therefore, a possible positive role of an AT₂-R overstimulation in condition of AT₁-R antagonism seems to be irrelevant.