Angiotensin II-induced Responses Research Articles

Repeated Amphetamine Exposure Blunted Angiotensin II-Induced Responses Mediated by AT1 Receptors.

Angiotensin II, is critical in regulating the sympathetic and neuroendocrine systems through angiotensin II type 1 receptors (AT1-R). Angiotensin II intracerebral administration increases water and sodium intake, as well as renal sodium excretion. Previously, our group has shown that AT1-R is involved in behavioral and neurochemical sensitization induced by amphetamine. We aimed to assess the physiological output, behavioral, and neurochemical responses to intracerebral angiotensin II administration, via the AT1-R, twenty-one days after amphetamine administration. Male Wistar rats received daily vehicle or AT1-R antagonist (oral) for 10 days, and amphetamine or saline intraperitoneal (i.p.) from day 6 to 10. On day 25 they were implanted with an intracerebral cannula. On day 32, the animals received intracerebral angiotensin II. First group: the animals were tested in a free choice paradigm for 2% NaCl and water intake, and sacrificed for neuronal activity assessment via c-Fos immunohistochemistry. Second group: urine samples were collected for electrolyte determination. Third group: the animals were tested in the plus maze or the hole board for anxiety and working memory evaluation, respectively, and sacrificed for c-Fos immunohistochemistry. Amphetamine exposure blunted the increase in sodium intake (p = 0.0022), and potentiated the natriuretic (p = 0.0043) and kaliuretic effect (p = 0.0002) induced by angiotensin II. Moreover, amphetamine exposure prevented the expression of the anxiogenic effect (drug effect p < 0.0001) and the memory deficit (p = 0.1314) induced by cerebral angiotensin II administration. Amph decreased c-Fos immunoreactivity in nucleus tractus solitarii (NTS) p = 0.0037; paraventricular nucleus (PVN) p = 0.0047; Central amygdala (CeA) p = 0.0008; Basolateral amygdala (BLA) p = 0.0018; increased in hippocampus region CA1 p = 0.0043; CA3 p = 0.026; and dentate gyrus (DG) p = 0.0057. The blockade of AT1-R prevented these alterations (sodium intake p = 0.0421 natriuresis p = 0.019; kaliuresis p = 0.196; working memory (p < 0.0001); but no the anxiogenic response to angiotensin II (drug effect p < 0.0001); as well as the c-Fos changes (NTS p = 0.0052; PVN p = 0.029; CeA p = 0.0002; BLA p = 0.0021; CA1 p = 0.0026; CA3 p = 0.022; and DG p = 0.0016). Most of the long-lasting AT1-R altered responses to brain angiotensin II administration induced by repeated amphetamine exposure could be prevented by AT1-R blockade.

Tumor Necrosis Factor-α-Induced Protein 8-Like 2 Ameliorates Cardiac Hypertrophy by Targeting TLR4 in Macrophages.

Background Tumor necrosis factor-α-induced protein 8-like 2 (TIPE2), a novel immunoregulatory protein, has been reported to regulate inflammation and apoptosis. The role of TIPE2 in cardiovascular disease, especially cardiac hypertrophy, has not been elucidated. Thus, the aim of the present study was to explore the role of TIPE2 in cardiac hypertrophy. Methods Mice were subjected to aortic banding (AB) to induce an adverse hypertrophic model. To overexpress TIPE2, mice were injected with a lentiviral vector expressing TIPE2. Echocardiographic and hemodynamic analyses were used to evaluate cardiac function. Neonatal rat cardiomyocytes (NRCMs) and mouse peritoneal macrophages (MPMs) were isolated and stimulated with angiotensin II. NRCMs and MPM were also cocultured and stimulated with angiotensin II. Cells were transfected with Lenti-TIPE2 to overexpress TIPE2. Results TIPE2 expression levels were downregulated in hypertrophic mouse hearts and in macrophages in heart tissue. TIPE2 overexpression attenuated pressure overload-induced cardiac hypertrophy, fibrosis, and cardiac dysfunction. Moreover, we found that TIPE2 overexpression in neonatal cardiomyocytes did not relieve the angiotensin II-induced hypertrophic response in vitro. Furthermore, TIPE2 overexpression downregulated TLR4 and NF-κB signaling in macrophages but not in cardiomyocytes, which led to diminished inflammation in macrophages and consequently reduced the activation of hypertrophic Akt signaling in cardiomyocytes. TLR4 inhibition by TAK-242 did not enhance the antihypertrophic effect of TIPE2 overexpression. Conclusions The present study indicated that TIPE2 represses macrophage activation by targeting TLR4, subsequently inhibiting cardiac hypertrophy.

Role of cyclic AMP response element binding protein (CREB) in angiotensin II-induced responses in vascular smooth muscle cells.

Cyclic AMP response element (CRE) binding protein (CREB) is a nuclear transcription factor that regulates the transcription of several genes containing the CRE sites on their promoters. CREB is activated by phosphorylation on a key serine residue, Ser311, in response to a wide variety of extracellular stimuli including angiotensin II (Ang II). Ang II is an important vasoactive peptide and mitogen for vascular smooth muscle cells (VSMC) that in addition to regulating the contractile response in VSMC also plays an important role in phenotypic switch of VSMC from contractile to a synthetic state. The synthetic VSMC are known to exhibit proliferative and migratory properties due to hyperactivation of Ang II-induced signaling events. Ang II has been shown to induce CREB phosphorylation/activation and transcription of genes implicated in proliferation, growth, and migration. Here, we have highlighted some key studies that have demonstrated an important role of CREB in Ang II-mediated gene transcription, proliferation, hypertrophy, and migration of VSMC.

Abstract P341: Melanocortin Receptor 4 Activation Mediates Leptin-Induced Sensitization of the Angiotensin II-Elicited Hypertensive Response in Mice

Obesity has been shown to promote the renin-angiotensin system (RAS) activity and inflammation in the hypothalamus that increase BP and sympathetic activity. Our previous studies using an Induction-Delay-Expression (IND-DEL-EXP) experimental design demonstrated that in the rats high-fat diet (HFD) or central leptin pretreatment resulted in an enhanced hypertensive response to subsequent treatment with angiotensin (ANG) II. The present study tested whether the leptin sensitization of ANG II-induced hypertension is mediated by activation of brain melanocortin receptor 4 (MC4R) in mice. The animals pretreated with either 3-week HFD or systemic leptin during IND responded with enhanced hypertension to ANG II (1000 ng/kg/min, sc.; HFD, Δ44.0±2.1 mmHg vs. Δ29.4±3.2 mmHg; leptin, Δ43.0±1.7 mmHg vs. Δ29.4±2.0 mmHg). This sensitized ANG II hypertensive response produced by systemic leptin given during IND was blocked by co-administration of icv SHU9119, a MCR4 antagonist (Δ24.0±2.9 mmHg). Moreover, a similar sensitization of the ANG II-induced hypertensive response was produced by icv pretreatment with MT II, a MC4R agonist (Δ39.6±2.1 mmHg). The results indicate that leptin-induced sensitization of ANG II-elicited hypertension is mediated by activation of brain MC4R.

Genetic and Pharmacologic Inhibition of the Chemokine Receptor CXCR2 Prevents Experimental Hypertension and Vascular Dysfunction.

The recruitment of leukocytes to the vascular wall is a key step in hypertension development. Chemokine receptor CXCR2 mediates inflammatory cell chemotaxis in several diseases. However, the role of CXCR2 in hypertension development and the underlying mechanisms remain unknown. Angiotensin II (490 ng·kg-1·min-1) or deoxycorticosterone acetate (DOCA) salt-induced mouse hypertensive models in genetic ablation, pharmacologic inhibition of CXCR2, and adoptive bone marrow transfer mice were used to determine the role of CXCR2 in hypertension (measured by radiotelemetry and tail-cuff system), inflammation (verified by flow cytometry and quantitative real-time polymerase chain reaction [PCR] analysis), vascular remodeling (studied by haematoxylin and eosin and Masson's trichrome staining), vascular dysfunction (assessed by aortic ring), and oxidative stress (indicated by nicotinamide adenine dinucleotide phosphate [NADPH] oxidase activity, dihydroethidium staining, and quantitative real-time PCR analysis). Moreover, the blood CXCR2+ cells in normotensive controls and hypertension patients were analyzed by flow cytometry. Angiotensin II significantly upregulated the expression of CXCR2 mRNA and protein and increased the number of CD45+ CXCR2+ cells in mouse aorta (n=8 per group). Selective CXCR2 knockout (CXCR2-/-) or pharmacological inhibition of CXCR2 markedly reduced angiotensin II- or DOCA-salt-induced blood pressure elevation, aortic thickness and collagen deposition, accumulation of proinflammatory cells into the vascular wall, and expression of cytokines (n=8 per group). CXCR2 inhibition also ameliorated angiotensin II-induced vascular dysfunction and reduced vascular superoxide formation, NADPH activity, and expression of NADPH oxidase subunits (n=6 per group). Bone marrow reconstitution of wild-type mice with CXCR2-/- bone marrow cells also significantly abolished angiotensin II-induced responses (n=6 per group). It is important to note that CXCR2 blockade reversed established hypertension induced by angiotensin II or DOCA-salt challenge (n=10 per group). Furthermore, we demonstrated that CXCR2+ proinflammatory cells were higher in hypertensive patients (n=30) compared with normotensive individuals (n=20). Infiltration of CXCR2+ cells plays a pathogenic role in arterial hypertension and vascular dysfunction. Inhibition of CXCR2 pathway may represent a novel therapeutic approach to treat hypertension.

Abstract P146: Transient Neonatal High Oxygen Exposure Accelerates Adult Cardiac Baseline and Ang Ii-induced Prooxidative and Proinflammatory Responses

Objective: Preterm birth is associated with disequilibrated early life oxidant-antioxidant and proinflammatory conditions that can be carried into adulthood and contribute to the development of organ dysfunction. Neonatally high O 2 -exposed rats, a model of prematurity-related prooxidative conditions, exhibit adult hypertension, early cardiac dysfunction and fibrosis, and premature angiotensin (ANG) II-induced heart failure. We hypothesized that neonatal high O 2 exposure will exaggerate baseline and ANG II-induced cardiac prooxidative and proinflammatory gene expression in adult rats. Design and Methods: Sprague-Dawley pups were kept in 80% O 2 (H group) or room air (NNI group) from day 3-10 of life. Twelve-weeks-old H and NNI rats were infused with ANG II (100 ng.kg -1 .min -1 ) or saline (NaCl) for 4 weeks (n = 4 per group). RNA extracted from hearts was used in arrays to assess expression of oxidative stress and inflammatory genes. Data is expressed as fold change (F.C.) compared to control NNI+NaCl. Results: H+NaCl exhibited increased baseline Cd68 expression (F.C: 1.47; P&lt;0.05 vs control), tendancy of increased Nfkb1 and Tnf expression (1.52 and 1.48), and a tendancy of decreased Il1b and Il18 expression (0.72 and 0.78). H+ANGII versus NNI+ANGII exhibited similar increase in Tnf ( 2.12 vs 2.13; P&lt;0.05 vs control), greater increase in Cd14 , Cd68 , and Nfkb1 (2.5 vs 1.78, 2.13 vs 1.94, 2.0 vs 1.7; P&lt;0.05 vs controls), and a greater tendancy of increase in Tgfb1 , Myd88 , Cybb , and Gstp1 (2.68 vs 1.82, 2.37 vs 1.31, 1.91 vs 0.98, 2.45 vs 1.61) expression. NNI+ANGII versus H+ANGII exhibited greater increase in expression of genes involved in early inflammatory process, including Ccl2 , Icam1 , and Vcam1 (2.07 vs 1.56, 1.88 vs 1.36, 2.34 vs 1.29; P&lt;0.05 vs control). Conclusions: Neonatal high O 2 exposure accelerates baseline and ANG II-induced cardiac prooxidative and proinflammatory responses in adult rats, which could account for early cardiac abnormalities and premature ANG II-induced heart failure in this model.

Effects of thromboxane A2 synthetase inhibitor, DP-1904 on the action of vasoactive substances in rabbit blood vessel smooth muscle preparations

Thromboxane A2 (TxA2) is a potent platelet aggregator as well as a vascular and bronchial constrictor. DP-1904, a newly synthesized imidazol TxA2 synthetase inhibitor, is a potent and long-acting agent. The present investigation was conducted to explore the effect of DP-1904 on the contractile responses in rabbit pulmonary artery and descending aorta strips induced by various vasoactive substances. Fourteen Japanese albino rabbits, weighing about 3 kg, were sacrificed. Rabbit pulmonary artery and descending aorta were removed, cut spirally, set up in bioassay glass jackets and superfused with Krebs-Henseleit solution at 37 degrees C, saturated with oxygen and carbon dioxide. Contraction of tissues was detected by an isotonic transducer and displayed on a polyrecorder. Arachidonic acid-induced contractile responses in rabbit pulmonary artery and descending aorta strips were attenuated significantly by the continuous infusion of DP-1904 in a dose-dependent fashion. Prostaglandin F2 alpha-induced contractile responses in rabbit pulmonary artery and descending aorta strips were attenuated significantly by the continuous infusion of DP-1904, dose-dependently. Angiotensin II-induced contractile responses in rabbit pulmonary artery and descending aorta strips were attenuated significantly by the continuous infusion of DP-1904, dose-dependently. Norepinephrine-induced contractile responses in rabbit pulmonary artery and descending aorta strips were attenuated significantly by the continuous infusion of DP-1904, dose-dependently. The above results suggest that DP-1904 might be a useful therapeutic agent for treatment of pulmonary hypertension in patients with chronic obstructive lung diseases.

Central injection of galanin inhibits angiotensin II-induced responses in rats

Galanin inhibits electrical activation of angiotensin II-sensitive neurons in the subfornical organ, which is related to angiotensin II-induced drinking behavior and pressor responses. In this study, the authors investigated whether intracerebroventricular injection of galanin in conscious rats inhibits the responses. Water intake following intracerebroventricular injection of angiotensin II at 100 pmol was inhibited significantly by coinjection of galanin at over 25 pmol, although galanin alone did not affect water intake. Furthermore, angiotensin II-induced pressor responses were inhibited significantly by coinjection of galanin at 50 pmol while galanin alone elicited slight pressor responses. These results suggest that galanin inhibits angiotensin II-induced physiological responses.

Novel Regulatory Effect of Angiotensin II Type 1 Receptor-Interacting Molecule on Vascular Smooth Muscle Cells

We have recently cloned a novel molecule that interacts with the angiotensin II type 1 receptor (AT1R)-associated protein (ATRAP). In this study, we tested the hypothesis that ATRAP modulates angiotensin II-induced responses in vascular smooth muscle cells. The results of immunoprecipitation and bioluminescence resonance energy transfer assay demonstrated a direct interaction between ATRAP and AT1R at baseline and showed that angiotensin II enhanced the interaction of these proteins >2-fold. The results of immunofluorescence analysis also demonstrated that >65% of ATRAP constitutively colocalized with an endosome marker. Although only 36% of ATRAP colocalized with AT1R at baseline, angiotensin II enhanced the colocalization of these molecules and made 92% of ATRAP colocalize with AT1R on a quantitative fluorescence analysis. Overexpression of ATRAP by adenoviral transfer decreased the cell surface AT1R number from 4.33 to 2.13 fmol/10(6) cells at baseline and from 3.04 to 1.26 fmol/10(6) cells even after removal of angiotensin II. ATRAP also suppressed angiotensin II-mediated increases in c-fos gene transcription and transforming growth factor-beta production. Furthermore, this suppression was accompanied by inhibition of angiotensin II-induced activation of 5-bromodeoxyuridine incorporation. Finally, ATRAP knockdown by small-interference RNA activated angiotensin II-induced c-fos gene expression, which was effectively inhibited by valsartan, an AT1R-specific antagonist. These results indicate that ATRAP promotes internalization of AT1R and attenuates the angiotensin II-mediated c-fos-transforming growth factor-beta pathway and proliferative response in vascular smooth muscle cells, suggesting a novel strategy to inhibit vascular fibrosis and remodeling through a novel and specific blockade of AT1R signaling.

HMG-CoA reductase inhibitors up-regulate anti-aging klotho mRNA via RhoA inactivation in IMCD3 cells.

Klotho is thought to play a critical role in the development of age-related disorders including arteriosclerosis. Statins may exert vascular protective effects, independent of the lowering of plasma cholesterol levels. We investigated the impact of statins on mRNA expression of the age-suppressor gene, klotho in mIMCD3 cells. Klotho mRNA levels were evaluated with real-time RT-PCR. Atorvastatin and pitavastatin increased the expression of klotho mRNA in a dose-dependent manner. This stimulatory effect was abolished by the addition of mevalonate, GGPP and FPP, essential molecules for isoprenylation of the small GTPase Rho. As was the case with the statin treatment, inhibition of Rho-kinase by Y27632 up-regulated klotho mRNA. In contrast to the statin treatment, stimulation with angiotensin II down-regulated klotho mRNA expression without obvious morphological changes. Furthermore, pretreatment with atorvastatin blunted the angiotensin II-induced response and ameliorated the decrease in klotho mRNA expression towards basal levels. RhoA activity was further evaluated by detection of its translocation. Angiotensin II activated RhoA, whereas statins potently inactivated RhoA and blocked RhoA activation by angiotensin II. Statins inactivate the RhoA pathway, resulting in over-expression of klotho mRNA, which may contribute to the novel pleiotropic effects of statins towards vascular protection.

Mechanism of action of angiotensin II in human isolated subcutaneous resistance arteries

1. Human isolated subcutaneous arteries were mounted in a myograph and isometric tension measured. In some experiments, intracellular calcium [Ca(2+)]i was also measured using fura-2. 2. Angiotensin II (100 pM - 1 microM) increased [Ca(2+)]i and tone in a concentration-dependent manner. The effects of angiotensin II (100 nM) were inhibited by an AT1-receptor antagonist, candesartan (100 pM). 3. Ryanodine (10 microM), had no effect on angiotensin II-induced responses, but removal of extracellular Ca(2+) abolished angiotensin II-induced rise in [Ca(2+)]i and tone. Inhibition of Ca(2+) entry by Ni(2+) (2 mM), also inhibited angiotensin II responses. The dihydropyridine, L-type calcium channel antagonist, amlodipine (10 microM), only partially attenuated angiotensin II responses. 4. Inhibition of protein kinase C (PKC) by chelerythrine (1 microM), or by overnight exposure to a phorbol ester (PDBu; 500 nM) had no effect on angiotensin II-induced contraction. 5. Genistein (10 microM), a tyrosine kinase inhibitor, inhibited angiotensin II-induced contraction, but did not inhibit the rise in [Ca(2+)]i, suggesting that at this concentration it affected the calcium sensitivity of the contractile apparatus. Genistein did not affect responses to norepinephrine (NE) or high potassium (KPSS). 6. A selective MEK inhibitor, PD98059 (30 microM), inhibited both the angiotensin II-induced contraction and rise in [Ca(2+)]i, but had no effect on responses to NE or KPSS. 7. AT1 activation causes Ca(2+) influx via L-type calcium channels and a dihydropyridine-insensitive route, but does not release Ca(2+) from intracellular sites. Activation of tyrosine kinase(s) and the ERK 1/2 pathway, but not classical or novel PKC, also play a role in angiotensin II-induced contraction in human subcutaneous resistance arteries.

Cardiovascular responses of the taurine-depleted rat to vasoactive agents.

The objective of this study was to assess the effect of taurine-depletion on cardiovascular responses of rat to vasoactive agents. Male Wistar-Kyoto (WKY) rats were given either tap water (control) or 3% beta-alanine (taurine-depleted) for three weeks. Thereafter, mean arterial pressure (MAP) and heart rate of the freely moving animal were measured in response to vasoactive agents. Administration of phenylephine (5-40 microg/kg/min; i.v.) resulted in a similar and significant increase in MAP but a reduction in heart rate in both control and taurine-depleted groups. On the other hand, administration of sodium nitroprusside (15-300 microg/kg/min; i.v.) elicited a similar and significant reduction in MAP but increased heart rate in both groups. Lack of a differential response to phenylephrine and sodium nitroprusside between the two groups suggests that baroreflex regulation of cardiovascular function is not adversely affected by taurine-depletion. Administration of angiotensin II (0.1-3.0 microg/kg/min; i.v.) resulted in a dose-related increase in the pressor response and a decrease in heart rate in both groups. However, angiotensin II-induced pressor response was reduced in the taurine-depleted compared to the control rats (p < 0.05); heart rate was similarly reduced in both groups. Acute exposure to beta-alanine (3 g/kg; i.v., 30-minutes) did not alter angiotensin II-induced hemodynamic responses. Similarly, incubation of aortic rings with beta-alanine (40mM, 30 minutes) did not affect the contractile responses to angiotensin II. The results suggest that beta-alanine, per se, does not affect angiotensin II-induced responses in rat. However, beta-alanine-induced taurine depletion is associated with a reduction in the pressor response to angiotensin II without impairing baroreflex function.

Cytochrome P450 metabolites of arachidonic acid may be important mediators in angiotensin II-induced vasoconstriction in the rat mesentery in vivo

We have investigated the role of cytochrome P450 (CYP-450) metabolites of arachidonic acid in the modulation of vascular reactivity to angiotensin II in vivo using an in situ blood-perfused mesenteric preparation in anaesthetized spontaneously hypertensive rats (SHR). Miconazole, a non-selective inhibitor of CYP-450 that inhibits both hydroxylation and epoxidation, substantially suppressed mesenteric vasoconstrictor responses to angiotensin II in SHR, but had no effect on responses to noradrenaline or sympathetic nerve stimulation. In normotensive Wistar–Kyoto (WKY) rats, miconazole caused only a modest suppression of vasoconstrictor responses to angiotensin II. N-Methylsulphonyl-12,12-dibromododec-11-enamide (DDMS), a new selective inhibitor of CYP-450 ω-hydroxylase activity, decreased mean intra-arterial blood pressure and significantly attenuated mesenteric angiotensin II-induced vasoconstrictor responses in SHR. Isolated mesenteric vessels were able to metabolize 14C-labelled arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) in vitro, and this was substantially inhibited by DDMS. The results from the present studies combined with the existing evidence that angiotensin II stimulates the release of 20-HETE, a CYP-450 metabolite of arachidonic acid, suggest that CYP-450-derived HETEs may be important mediators in angiotensin II-induced vasoconstriction. However, the development of more sensitive assays for the detection in vivo of 20-HETE in mesenteric vessels would be required to confirm these findings.

Angiotensin II type 1 receptor-mediated increase in cytosolic Ca 2+ and proliferation in mesothelial cells

We investigated the Ca 2+ signaling pathways of the response to angiotensin II in pleural mesothelial cells and the role of these Ca 2+ signaling pathways in mesothelial cell proliferation. Rat pleural mesothelial cells were maintained in vitro, and the Ca 2+ movement to angiotensin II was evaluated using the fluorescent Ca 2+ indicator fura 2. Furthermore, proliferation of mesothelial cells was assessed using a spectrophotometric 3-(4,5-dimethylthazol-2-yl)-2,5-diphenyl-2 H-tetrasodium bromide (MTT) assay. Angiotensin II (1 pM–100 μM) induced in mesothelial cells a biphasic elevation of intracellular Ca 2+ concentration ([Ca 2+] i) that consisted of a transient initial component, followed by a sustained component. Neither removal of extracellular Ca 2+ nor inhibition of Ca 2+ influx by 1 μM nifedipine affected the angiotensin II-induced initial transient elevation of [Ca 2+] i in mesothelial cells. Nifedipine did not block angiotensin II-induced sustained elevation of [Ca 2+] i. Angiotensin II (1 pM–100 μM) had a proliferative effect on mesothelial cells in a dose-dependent manner. Angiotensin II type 1 (AT 1) receptor antagonist ([Sar 1, Ile 8]angiotensin II) inhibited both angiotensin II-induced elevation of [Ca 2+] i and proliferation of mesothelial cells. Pertussis toxin did not affect angiotensin II-induced responses. These results suggest that angiotensin II-induced responses to mesothelial cells are extremely dependent on the angiotensin AT 1 receptor coupled with pertussis toxin-insensitive G protein.

Modulatory effect of insulin on release of calcium from human fibroblasts by angiotensin II.

Angiotensin II stimulates synthesis and deposition of collagen and might contribute to the vascular and cardiac dysfunction associated with arterial hypertension. Insulin attenuates angiotensin II-induced responses of intracellular Ca2+ concentration ([Ca2+]) in many cell types but this effect is less in insulin-resistant states. The mechanisms of the interaction between insulin and angiotensin II are still not known. To characterize the effects of angiotensin II on intracellular [Ca2+] and the effects of insulin on the angiotensin II-induced response of intracellular [Ca2+] in human skin fibroblasts. Spectrofluorophotometric measurements of intracellular [Ca2+] in monolayers of cultured human skin fibroblasts from 15 normotensive patients were performed using Fura-2 at 510 nm emission with excitation wavelengths of 340 and 380 nm. Basal intracellular [Ca2+] in quiescent (24 h serum-deprived) human fibroblasts was 75 +/- 3 nmol/l (n = 20). Administration of angiotensin II elevated intracellular [Ca2+] dose-dependently with a concentration for half-maximal effect of 20 nmol/l. Administration of 100 nmol/l angiotensin II stimulated a rapid and transient increase in intracellular [Ca2+] (from 75 +/- 3 to 130 +/- 2 nmol/l, n = 20). Removal of extracellular calcium did not change peak intracellular [Ca2+], but it did reduce the time to recovery of [Ca2+] (from 64 +/- 4 to 48 +/- 2 s, n = 10, P < 0.01), suggesting that an angiotensin II-induced transmembrane calcium influx had occurred. This hypothesis was confirmed by quenching studies with manganese. The angiotensin II-induced changes in intracellular [Ca2+] were completely blocked by administration of 100 nmol/l of the angiotensin II type 1 receptor inhibitor losartan but not by administration of 100 nmol/l of the angiotensin II type 2 receptor blocker CGP42112A. Acute (20 min) exposure to 100 nmol/l insulin did not alter basal intracellular [Ca2+] in quiescent fibroblasts, but significantly blunted angiotensin II-stimulated peak of [Ca2+] (to 101 +/- 3 nmol/l, P < 0.01, n = 18) and delayed recovery of [Ca2+] (to 99 +/- 5 s, P < 0.01). The inhibitory effect of insulin was observed both with and without extracellular Ca2+. Our results demonstrate that administration of angiotensin II increases intracellular [Ca2+] in human skin fibroblasts by release of Ca2+ from intracellular Ca2+ stores and by influx of Ca2+ and that administration of insulin attenuates the response of [Ca2+] to angiotensin II but prolongs the time to recovery of [Ca2+].

A018 Tumor necrosis factor-alpha attenuates angiotensin II-induced responses in vascular smooth muscle via an eicosanoid-dependent mechanism

A018 Tumor necrosis factor-alpha attenuates angiotensin II-induced responses in vascular smooth muscle via an eicosanoid-dependent mechanism

Ability of angiotensin II to modulate striatal dopamine release via the AT1 receptor in vitro and in vivo.

1. The ability of angiotensin II to modulate dopamine release from rat striatal slices in vitro and in the intact rat striatum in vivo was assessed by the microdialysis technique. 2. In slices of rat striatum, angiotensin II (0.1-1.0 microM) induced a concentration-related increase in endogenous dopamine release which was maximal (approximately 250% above basal levels) within the first 2-4 min of agonist application and subsequently declined to near basal values. The angiotensin II-induced increase in dopamine release was Ca(2+)-dependent and was completely antagonized by the selective AT1 receptor antagonist, losartan (1.0 microM). In contrast, the AT2 receptor antagonist, PD123177 (1.0 microM) failed to modify the angiotensin II-induced response. Neither antagonist alone modified basal dopamine release from striatal slices. 3. In freely moving rats, angiotensin II (1.0-10 microM; administered via the microdialysis probe) induced a concentration-related increase in extracellular levels of dopamine which was maximal (approximately 150% above basal levels) within 20-40 min of agonist application and subsequently declined. The angiotensin II (10 microM)-induced increase in extracellular levels of dopamine was completely antagonized by the AT1 receptor antagonist, losartan (0.1-1.0 microM; administered via the microdialysis probe) but not by the AT2 receptor antagonist, PD123177 (1.0 microM; administered via the microdialysis probe). Neither antagonist alone modified basal extracellular levels of dopamine. 4. Homogenate radioligand binding studies with [125I]-angiotensin II (0.1 nm) identified relatively low levels of specific binding sites in rat striatal homogenates compared to homogenates of pyriform cortex (51.3 +/- 9.2 and 651.3 +/- 55.1 fmol g-1 wet weight, respectively, mean +/- s.e.mean, n = 3; non-specific binding defined by unlabelled angiotensin II). The majority of the specific [125I]-angiotensin II (0.1 nM) binding in the striatal and pyriform cortex homogenates was sensitive to the selective AT1 receptor antagonist, losartan (1.0 microM). 5. In conclusions the present study provides direct evidence that angiotensin II acting via the AT1 receptor subtype facilitates the release of dopamine in the rat striatum in vitro and in vivo. This receptor-mediated response may account for the modulation of dopamine-mediated behavioural responses by antagonists of the AT1 receptor and inhibitors of angiotensin converting enzyme.

Atrial Natriuretic Factor and Angiotensin Ii Stimulate Nitric Oxide Release from Human Proximal Tubular Cells

1. It has been recently reported that angiotensin II can enhance atrial natriuretic factor-stimulated cyclic GMP release from brain capillary endothelial cells and stimulate directly the release of cyclic GMP by Neuro 2a cells. A possible mechanism mediating such cyclic GMP release could be via the production of nitric oxide and the resultant stimulation of soluble guanylate cyclase. 2. The ability of angiotensin II, atrial natriuretic factor and c(4-23) atrial natriuretic factor to stimulate nitric oxide production was investigated in primary cultures of human proximal tubular cells. 3. Freshly prepared human proximal tubular cells were seeded onto 6-well plates and allowed to reach confluence. Cells were then incubated with incremental concentrations of either angiotensin II, atrial natriuretic factor or c(4-23) atrial natriuretic factor alone for 1, 4, 12 or 24h or in the presence of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine. Angiotensin II was also incubated with human proximal tubular cells in the presence of the AT1 and AT2 receptor antagonists DuP 753 and PD 123319. 4. Incubation of human proximal tubular cells with angiotensin II, atrial natriuretic factor or c(4-23) atrial natriuretic factor produced a dose- and time-dependent increase in nitric oxide production, which was inhibited in the presence of NG-monomethyl-L-arginine. A similar increase in nitric oxide production was observed after incubation with atrial natriuretic factor or c(4-23) atrial natriuretic factor. 5. The angiotensin-induced increase in nitric oxide production was not inhibited in the presence of either the angiotensin AT1 or AT2 receptor antagonists DuP 753 or PD 123319. 6. This study demonstrates that primary cultures of human proximal tubular cells can be stimulated to produce nitric oxide by both atrial natriuretic factor and angiotensin II. Furthermore, the atrial natriuretic factor-induced response appears to be mediated via the atrial natriuretic factor-C receptor, while the angiotensin II-induced response appears to be mediated by a novel, as yet unidentified, angiotensin II receptor.

Angiotensin II-induced responses in vascular smooth muscle cells: inhibition by non-peptide receptor antagonists

The present study investigates the effect of angiotensin II and LR-B/081 (-methyl 2-[[4-butyl-2-methyl-6-oxo-5-[[2′-(1 H-tetra-zol-5-yl) [1,1′-biphenyl]-4-yl] methyl]-1(6 H)-pyrimidinyl] methyl]-3-thiophenecarboxylate), a novel non-peptide angiotensin II receptor antagonist, on both early and late responses in rat vascular smooth muscle cells. Angiotensin II induced a rapid and transient elevation of inositol trisphosphate intracellular levels, triggered the release of both prostaglandin E 2 and prostaglandin I 2 (EC 50 = 21 ± 3 and 16 ± 2 nM, respectively), and, in long-term studies, increased leucine and thymidine incorporation. All angiotensin II effects were antagonized by LR-B/081 and losartan, the reference non-peptide angiotensin AT 1-selective receptor antagonist, whereas they were unaffected by PD123177 (1-(4-amino-3-methylphenyl)methyl-5-diphenylacetyl-4,5,6,7-tetrahydro-1 H-imidazo[4,5- c]pyridine carboxylic acid), a non-peptide angiotensin AT 2-selective receptor antagonist. LR-B/081 displayed a much higher potency than losartan in inhibiting angiotensin II-induced prostaglandin E 2 (IC 50 = 0.15 ± 0.02 and 39 ± 9 nM, respectively) and prostaglandin I 2 release (IC 50 = 0.18 ± 0.04 and 134 ± 40 nM, respectively) and was also more potent in blocking the increase in protein synthesis (IC 50 = 242 ± 119 nM and 1221 ± 687 nM, respectively). Moreover, LR-B/081 and losartan blocked the response to angiotensin III but failed to inhibit the prostaglandin release stimulated by vasopressin or the mitogenic effect of serum. LR-B/081 and losartan were devoid of intrinsinc agonistic properties in the experimental conditions employed. The present results describe LR-B/081 as a novel, highly specific and potent, non-peptide angiotensin AT 1-selective receptor antagonist, that is capable of blocking angiotensin II-proliferative responses, which may be of relevance for cardiovascular diseases.

Effects of TCV-116 and CV-11974 on angiotensin II-induced responses in vascular smooth muscle cells

(±)-1-(Cyclohexyloxycarbonyloxy)ethyl 2-ethoxy-1-[[2′-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]-1H-benzimidazole-7-carboxylate (TCV-116, Candesartan) and its active metabolite 2-ethoxy-1-[[2′-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]-1H-benzimidazole-7-carboxylic acid (CV-11974) are specific nonpeptide angiotensin AT 1 receptor antagonists. In the present study, the inhibitory potency of these two antagonists on the angiotensin II-induced responses in aortic vascular smooth muscle cells from Wystar Kyoto rats was investigated. The specific binding of 125I-angiotensin II to cells was inhibited by CV-11974 and TCV-116 with a half-maximal inhibitory concentration (IC 50) of 3 × 10 −11 M and 1 × 10 −9 M, respectively. CV-11974 and TCV-116 inhibited the angiotensin II-induced increase in [ 3H]thymidine incorporation with an IC 50 of 3 × 10 −10 and 5 × 10 −9 M, respectively. Both CV-11974 and TCV-116 (10 −7 M) completely blocked the angiotensin II-induced increase in c- fos mRNA. The inhibitory potency of the metabolite CV-11974 was about 30–100-fold higher than that of the prodrug TCV-116.