Localization of the angiotensin II and its receptor subtype expression in human endometrium and identification of a novel high-affinity angiotensin II binding site.

Angiotensin (ANG) II is not only a potent vasoconstrictor but may also be involved in the regeneration of new blood vessels. In proliferative endometrium, ANG II-like immunoreactivity was detected in glandular epithelium and stroma with negligible staining around the vascular endothelium. In contrast, in secretory endometrium intense immunostaining was seen in the perivascular stromal cells around the endometrial spiral arterioles with negligible staining of the other cell types. Quantitative receptor autoradiography using the nonselective radioligand [125I]-ANG II and subtype selective competing compounds showed that endometrium contained predominantly AT2 receptors, with relatively low expression of AT1 receptors and a novel non-AT1/non-AT2 angiotensin II recognition site that was insensitive to AT1 or AT2 selective ligands. Levels of specific [125I]-ANG II receptor binding displayed cyclic changes during the menstrual cycle, reaching a maximum in early secretory endometrium and then decreasing in mid to late secretory endometrium to levels seen in early to mid proliferative endometrium. In situ hybridization showed AT1 receptor mRNA expression in the glands and in the endometrial blood vessels. The cyclic changes in ANG II-like immunoreactivity together with expression of both the known and the novel AT receptor subtypes imply that this octopeptide may play a dual role both in the control of the uterine vascular bed and also in the regeneration of the endometrium after endometrial shedding, acting as an angiogenic and mitogenic mediator.     

Effects of angiotensin II type 1 and type 2 receptor on apoptosis

Apoptosis, a morphological form of programmed cell death required for control of cell populations, participates in reduced tissue volume associated with ventricular scarring. Prevention of apoptosis of excessive, damaged, or nonfunctioning cardiac or of infiltrating inflammatory cells is usually beneficial for the resolution of cardiac fibrosis. Angiotensin(Ang) II, the most important peptide that mediates the effects of the renin-angiotensin system, may play an important role in hypertension, hypertrophy, and interstitial fibrosis. Furthermore, AngII induced apoptosis of human venous endothelial cells, myocyte, and vascular smooth muscular cells by caspase cascade activation, and the both blockade of AngII type(AT)1 and AT2 receptor prevents AngII induced apoptosis, whereas selective agonistic stimulation of the AT2 receptor alone induces apoptosis. When AT1 or AT2 receptors are stimulated in vivo, apoptosis is enhanced in myocytes, myofibroblasts, and media smooth muscular cells. In the case of AT1 receptor stimulation, this may occur in cardiac myocytes secondary to ventricular hypertrophy. On the other hand, AT2 receptor stimulation induced apoptosis myofibroblasts associated with reduced interstitial fibrosis. Caspase-3 participates in the pathways of apoptosis triggered by in vivo AT1 and AT2 receptor stimulations.     

The angiotensin II type 2 receptor and improved adjacent region function post-MI.

Angiotensin II type 2 receptor (AT2-R) overexpression in the mouse heart preserves left ventricular (LV) size and global LV function during post-MI remodeling. We hypothesized that CMR tagging would localize regional improvements in myocardial function during post-MI remodeling in AT2-R cardiac overexpressed transgenic mice (TG), which could explain the preservation of global LV function post-MI. Six male wild-type (WT) C57BL/6 mice and 10 TG mice were studied by CMR at baseline (day 0) and days 1, 7, and 28 post-MI. MI was induced by 1 hour occlusion of the LAD followed by reperfusion. On day 1 post-MI, gadolinium-DTPA was injected to assess infarct size. LV size and function was assessed by cine CMR. Mean % circumferential shortening (%CS) was calculated within infarcted, adjacent, and remote regions at each time point in WT and TG mice. Quantitative interstitial collagen and mean myocyte cross-sectional area was measured postmortem at day 28 post-MI. LV end-systolic volume was lower and ejection fraction higher at baseline in the TG group and these differences were maintained post-MI. Within infarcted and remote zones, although %CS was higher in TG mice at day 0, there was no difference by day 28 between groups. Within adjacent regions, while there was no difference at day 0 or 1 in TG vs. WT, %CS was significantly higher in TG mice by day 7, and these changes persisted out to day 28 post-MI. Regional interstitial collagen and myocyte size were similar between groups. Thus, myocardial tagging can detect regional differences in contractile function post-MI in TG mice, and AT2-R overexpression is associated with improved contractile function in adjacent noninfarcted myocardium.     

Effects of angiotensin II (AT1) receptor blockade on cardiac vagal control in heart failure.

The objective of the present study was to determine the autonomic effects of angiotensin II (AT(1)) receptor blocker therapy in heart failure. In a randomized double-blind cross-over study, we compared the effects of candesartan and placebo on baroreflex sensitivity and on heart rate variability at rest, during stress and during 24 h monitoring. Acute effects were assessed 4 h after oral candesartan (8 mg) and chronic effects after 4 weeks of treatment (dose titrated to 16 mg daily). The study group comprised 21 patients with heart failure [mean (S.E.M.) ejection fraction 33% (1%)], in the absence of angiotensin-converting enzyme (ACE) inhibitor therapy. We found that acute candesartan was not different from placebo in its effects on blood pressure or mean RR interval. Chronic candesartan significantly reduced blood pressure [placebo, 137 (3)/82 (3) mmHg; candesartan, 121 (4)/75 (2) mmHg; P<0.001; values are mean (S.E.M.)], but had no effect on mean RR interval [placebo, 857 (25) ms; candesartan, 857 (21) ms]. Compared with placebo there were no significant effects of acute or chronic candesartan on heart rate variability in the time domain and no consistent effects in the frequency domain. Baroreflex sensitivity assessed by the phenylephrine bolus method was significantly increased after chronic candesartan [placebo, 3.5 (0.5) ms/mmHg; candesartan, 4.8 (0.7) ms/mmHg; P<0.05], although there were no changes in cross-spectral baroreflex sensitivity. Thus, in contrast with previous results with ACE inhibitors, angiotensin II receptor blockade in heart failure did not increase heart rate variability, and there was no consistent effect on baroreflex sensitivity.     

Cardiac-specific overexpression of angiotensin II AT2 receptor causes attenuated response to AT1 receptor-mediated pressor and chronotropic effects.

Angiotensin (Ang) II has two major receptor isoforms, AT1 and AT2. Currently, AT1 antagonists are undergoing clinical trials in patients with cardiovascular diseases. Treatment with AT1 antagonists causes elevation of plasma Ang II which selectively binds to AT2 and exerts as yet undefined effects. Cardiac AT2 level is low in adult hearts, whereas its distribution ratio is increased during cardiac remodeling and its action is enhanced by application of AT1 antagonists. Although in AT2 knock-out mice sensitivity to the pressor action of Ang II was increased, underlying mechanisms remain undefined. Here, we report the unexpected finding that cardiac-specific overexpression of the AT2 gene using alpha-myosin heavy chain promoter resulted in decreased sensitivity to AT1-mediated pressor and chronotropic actions. AT2 protein undetectable in the hearts of wild-type mice was overexpressed in atria and ventricles of the AT2 transgenic (TG) mice and the proportions of AT2 relative to AT1 were 41% in atria and 45% in ventricles. No obvious morphological change was observed in the myocardium and there was no significant difference in cardiac development or heart to body weight ratio between wild-type and TG mice. Infusion of Ang II to AT2 TG mice caused a significantly attenuated increase in blood pressure response and the change was completely blocked by pretreatment with AT2 antagonist. This decreased sensitivity to Ang II-induced pressor action was mainly due to the AT2-mediated strong negative chronotropic effect and exerted by circulating Ang II in a physiological range that did not stimulate catecholamine release. Isolated hearts of AT2 transgenic mice perfused using a Langendorff apparatus also showed decreased chronotropic responses to Ang II with no effects on left ventricular dp/dt max values, and Ang II-induced activity of mitogen-activated protein kinase was inhibited in left ventricles in the transgenic mice. Although transient outward K+ current recorded in cardiomyocytes from AT2 TG mice was not influenced by AT2 activation, this study suggested that overexpression of AT2 decreases the sensitivity of pacemaker cells to Ang II. Our results demonstrate that stimulation of cardia AT2 exerts a novel antipressor action by inhibiting AT1-mediated chronotropic effects, and that application of AT1 antagonists to patients with cardiovascular diseases has beneficial pharmacotherapeutic effects of stimulating cardiac AT2.     

Novel angiotensin II AT(1) receptor antagonist irbesartan prevents thromboxane A(2)-induced vasoconstriction in canine coronary arteries and human platelet aggregation

This study was conducted to investigate whether the novel orally active nonpeptide angiotensin II (Ang II) AT(1) receptor antagonist irbesartan interacts with the thromboxane A(2)/prostaglandin endoperoxide H(2) (TxA(2)/PGH(2)) receptor in canine coronary arteries and human platelets. Coronary artery rings were isolated from male dog hearts (n = 18) and isometric tension of vascular rings was measured continuously at optimal basal tension in organ chambers. Autoradiographic binding of [(3)H]SQ29,548, a TxA(2) receptor antagonist, in canine coronary sections was determined. Blood for platelet aggregation studies was collected by venous puncture from healthy human volunteers (n = 6) who were free of aspirin-like agents for at least 2 weeks. Vascular reactivity and platelet aggregation in response to the TxA(2) analogs U46619 and autoradioagraphic receptor binding to the TxA(2) receptor antagonist [(3)H]SQ29,548 were studied with and without irbesartan. The TxA(2) analog U46619 produced dose-dependent vasoconstriction in coronary rings (EC(50) = 11.6 +/- 1.5 nM). Pretreatment with irbesartan inhibited U46619-induced vasoconstriction, and the dose-response curve was shifted to the right in a dose-dependent manner. The EC(50) of U46619 was increased 6- and 35-fold in the presence of 1 and 10 microM of irbesartan without a change of maximal contraction. At 1 microM, irbesartan is 2-fold more potent than the AT(1) receptor antagonist losartan in the inhibition of U46619-induced vasoconstriction in canine coronary arteries. In contrast, neither AT(1) receptor antagonists (CV11974 and valsartan), the AT(2) receptor antagonist PD123319, nor the angiotensin converting enzyme inhibitor lisinopril had any effect on U46619-induced coronary vasoconstriction. Irbesartan did not change potassium chloride-induced vasoconstriction; however, irbesartan did inhibit the vasoconstriction mediated by another TxA(2)/PGH(2) receptor agonist prostaglandin F(2alpha) (PGF(2alpha)). Neither the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester nor the cyclooxygenase inhibitor indomethacin had any effect on irbesartan's attenuation of U46619-induced vasoconstriction. Irbesartan specifically reversed U46619-preconstricted coronary artery rings with and without endothelium in a dose-dependent manner. Irbesartan at high concentrations significantly competed for [(3)H]SQ29,548 binding in canine coronary sections. U46619 stimulated dose-dependent human platelet aggregation of platelet-rich plasma. Preincubation with irbesartan significantly inhibited platelet aggregation in a concentration-dependent manner. In conclusion, the dual antagonistic actions of irbesartan by acting at both the AT(1) and TxA(2) receptors in blood vessels and platelets may overall enhance its therapeutic profile in the treatment of hypertension, atherosclerosis, and arterial thrombosis.     

Protective effects of the angiotensin II type 1 (AT1) receptor blockade in low-renin deoxycorticosterone acetate (DOCA)-treated spontaneously hypertensive rats

The present study evaluates the participation of oxidative stress, tissue angiotensin II (Ang II) and endothelin (ET) in the effects of losartan on blood pressure (BP), ventricular hypertrophy and renal injury in spontaneously hypertensive rats (SHRs), and explores how these effects are modified when spontaneous hypertension is transformed in a low-renin model by the administration of deoxycorticosterone acetate (DOCA). The following groups were used: SHR-control, SHR+DOCA, SHR+losartan and SHR+DOCA+losartan. Tail systolic BP was measured once a week. After 9 weeks of treatment, direct BP and metabolic, morphological, biochemical and renal variables were measured. DOCA administration to SHRs produced an increase in BP, ventricular hypertrophy, renal weight, proteinuria, renal histopathological lesions, urinary excretion of isoprostane F2alpha and ET levels in the renal cortex. Losartan reduced BP, plasma malondialdehyde levels, urinary excretion of isoprostane F2alpha, renal Ang II and renal and urinary levels of ET in the SHR and DOCA-treated SHR groups. Losartan increased plasma nitrite/nitrate in SHRs, but not in low-renin DOCA-treated SHRs. Losartan reduced ventricular hypertrophy and ventricular Ang II in SHRs, but not in DOCA-treated SHRs. Losartan significantly decreased proteinuria and renal injury in DOCA-treated SHRs. We conclude that (i) the DOCA-induced aggravation of hypertension, ventricular hypertrophy and renal injury in SHRs is accompanied by augmented oxidative stress and increased levels of ET in the renal cortex, which could contribute to their development; and (ii) losartan reduced oxidative stress and renal Ang II and ET in SHRs and DOCA-treated SHRs, which might contribute to its antihypertensive and renoprotective effects, regardless of renin status.     

Effects of angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor antagonists in rats with heart failure. Role of kinins and angiotensin II type 2 receptors.

Angiotensin-converting enzyme inhibitors (ACEi) improve cardiac function and remodeling and prolong survival in patients with heart failure (HF). Blockade of the renin-angiotensin system (RAS) with an angiotensin II type 1 receptor antagonist (AT1-ant) may have a similar beneficial effect. In addition to inhibition of the RAS, ACEi may also act by inhibiting kinin destruction, whereas AT1-ant may block the RAS at the level of the AT1 receptor and activate the angiotensin II type 2 (AT2) receptor. Using a model of HF induced by myocardial infarction (MI) in rats, we studied the role of kinins in the cardioprotective effect of ACEi. We also investigated whether an AT1-ant has a similar effect and whether these effects are partly due to activation of the AT2 receptor. Two months after MI, rats were treated for 2 mo with: (a) vehicle; (b) the ACEi ramipril, with and without the B2 receptor antagonist icatibant (B2-ant); or (c) an AT1-ant with and without an AT2-antagonist (AT2-ant) or B2-ant. Vehicle-treated rats had a significant increase in left ventricular end-diastolic (LVEDV) and end-systolic volume (LVESV) as well as interstitial collagen deposition and cardiomyocyte size, whereas ejection fraction was decreased. Left ventricular remodeling and cardiac function were improved by the ACEi and AT1-ant. The B2-ant blocked most of the cardioprotective effect of the ACEi, whereas the effect of the AT1-ant was blocked by the AT2-ant. The decreases in LVEDV and LVESV caused by the AT1-ant were also partially blocked by the B2-ant. We concluded that (a) in HF both ACEi and AT1-ant have a cardioprotective effect, which could be due to either a direct action on the heart or secondary to altered hemodynamics, or both; and (b) the effect of the ACEi is mediated in part by kinins, whereas that of the AT1-ant is triggered by activation of the AT2 receptor and is also mediated in part by kinins. We speculate that in HF, blockade of AT1 receptors increases both renin and angiotensins; these angiotensins stimulate the AT2 receptor, which in turn may play an important role in the therapeutic effect of the AT1-ant via kinins and other autacoids.     

Angiogenesis and angiotensin II: differential postnatal angiogenic activities unmasked by gene-engineered mouse models of angiotensin AT1 and AT2 receptor subtypes

We tested angiogenic activities of angiotensin II(Ang II) in ischemic hindlimbs using AT1 receptor(AT1R)-knock out(KO), AT2R-KO, wild-type(WT) mice. METHODS AND RESULTS: Angiogenesis was evaluated three weeks after unilateral hindlimb ischemia by laser Doppler perfusion(LDP) and capillary density. The ischemia/normal LDP ratio was markedly(p < 0.001) decreased in AT1R-KO(54 +/- 5% recovery) and AngII infusion-AT1R-KO(43 +/- 3%) than in WT(71 +/- 6%). In contrast, ischemia/normal LDP ratio was significantly(p < 0.01) increased in AT2R-KO(82 +/- 5%) and AngII infusion-AT2R-KO(96 +/- 6%) than in WT(71 +/- 6%). AT1R-KO and AngII infusion -AT1R-KO mice displayed lower capillary densities than WT(15 +/- 3, 11 +/- 3 vs 24 +/- 3 per field; p < 0.001). CONCLUSION: Ischemia in skeletal muscle causes upregulation of AT1R and AT2R expression, which positively and negatively modulates VEGF expression. This VEGF regulation via AngII receptor subtypes is closely involved in postnatal angiogenesis in ischemic limbs.     

The subtype 2 (AT2) angiotensin receptor mediates renal production of nitric oxide in conscious rats.

The angiotensin AT2 receptor modulates renal production of cyclic guanosine 3',5'-monophosphate (cGMP; J. Clin. Invest. 1996. 97:1978-1982). In the present study, we hypothesized that angiotensin II (Ang II) acts at the AT2 receptor to stimulate renal production of nitric oxide leading to the previously observed increase in cGMP. Using a microdialysis technique, we monitored changes in renal interstitial fluid (RIF) cGMP in response to intravenous infusion of the AT2 receptor antagonist PD 123319 (PD), the AT1 receptor antagonist Losartan, the nitric oxide synthase (NOS) inhibitor nitro--arginine-methyl-ester (-NAME), the specific neural NOS inhibitor 7-nitroindazole (7-NI), or Ang II individually or combined in conscious rats during low or normal sodium balance. Sodium depletion significantly increased RIF cGMP. During sodium depletion, both PD and -NAME caused a similar decrease in RIF cGMP. Combined administration of PD and -NAME decreased RIF cGMP to levels observed with PD or -NAME alone or during normal sodium intake. During normal sodium intake, Ang II caused a twofold increase in RIF cGMP. Neither PD nor -NAME, individually or combined, changed RIF cGMP. Combined administration of Ang II and either PD or -NAME produced a significant decrease in RIF cGMP compared with that induced by Ang II alone. Combined administration of Ang II, PD, and -NAME blocked the increase in RIF cGMP produced by Ang II alone. During sodium depletion, 7-NI decreased RIF cGMP, but the reduction of cGMP in response to PD alone or PD combined with 7-NI was greater than with 7-NI alone. During normal sodium intake, 7-NI blocked the Ang II-induced increase in RIF cGMP. PD alone or combined with 7-NI produced a greater inhibition of cGMP than did 7-NI alone. During sodium depletion, 7-NI (partially) and -NAME (completely) inhibited RIF cGMP responses to -arginine. These data demonstrate that activation of the renin- angiotensin system during sodium depletion increases renal nitric oxide production through stimulation by Ang II at the angiotensin AT2 receptor. This response is partially mediated by neural NOS, but other NOS isoforms also contribute to nitric oxide production by this pathway.     

A1166C polymorphism of the angiotensin AT1 receptor (AT1R) gene alters endothelial response to statin treatment.

BACKGROUND: The function of vascular endothelium is influenced by several factors: low-density lipoprotein (LDL) cholesterol, oxidative stress and the reninangiotensin system. METHODS: We tested the hypothesis that polymorphisms A1166C of the angiotensin AT1 receptor (AT1R) gene, C242T and A640G of the pphox22 gene (p22 phox is an essential component of NADH/NADPH oxidases) and G894T of the endothelial nitric oxide (NO) synthase (eNOS) gene influence endothelial function and its reaction to statin treatment. In 44 patients with coronary artery disease or hypercholesterolemia (not on lipid-lowering treatment), lipid profile and endothelial function (brachial artery flow-mediated dilation, FMD) were measured at baseline and after treatment with statins for 8-12 weeks. All subjects were genotyped for the above-mentioned polymorphisms. RESULTS: None of the polymorphisms significantly predicted baseline FMD. Patients with the C allele of A1166C showed smaller changes in FMD in comparison with patients with the AA genotype (-0.044+/-0.439% vs. 0.386+/-0.599%; p=0.016). None of the other polymorphisms significantly influenced changes in FMD. CONCLUSIONS: The C allele of AT1R A1166C is associated with significantly lower endothelial response to statin treatment.     

Effects of AT1 and AT2 receptor blockade on angiotensin II induced apoptosis of human renal proximal tubular epithelial cells

BACKGROUND: Tubular atrophy is a common histological feature of chronic renal failure, and epithelial cell death by apoptosis might play an important role in its pathogenesis. Angiotensin II contributes to the progressive nature of many kidney diseases and treatment with angiotensin converting enzyme inhibitors preserves the structure of the tubulointerstitial compartment in human and experimental renal diseases. METHODS: Primary cultures of human renal proximal tubular epithelial cells were co-incubated with angiotensin II alone or in combination with the angiotensin II AT1 receptor antagonist losartan or/and the AT2 antagonist PD123319. Apoptosis was determined after 20 hours by TUNEL staining and flow cytometry. RESULTS: Angiotensin II at concentrations of 10(-9) M induced apoptosis (control vs. angiotensin II 4 +/- 3% vs. 73 +/- 11%; p < 0.05). This effect was completely offset by co-incubation with the angiotensin II AT2 receptor blocker at concentrations 10(-7) M (control vs. PD123319 4 +/- 3% vs. 8 +/- 3%; p < 0.05); AT1 blockade was ineffective in apoptosis inhibition. When both angiotensin receptors were blocked, no additional effect on apoptosis inhibition could be detected. CONCLUSION: We provided evidence, that physiological concentrations of angiotensin II can induce apoptosis of human renal proximal tubule epithelial cells. This effect is mediated via AT2 receptors.     

Cross-talk between AT(1) and AT(2) angiotensin receptors in rat anococcygeus smooth muscle

Schild regressions for the selective AT(1) and AT(2) receptor antagonists, losartan and PD123319 (S-[+]-1-[(4-dimethylamino]-3-methylphenyl)methyl]-5-[diphenylacetyl]-4,5,6,7-tetrahydro-1H-imidazol[4,5-c]pyridine-6-carboxilic acid), respectively, were calculated to analyze the heterogeneity of receptor populations in the rat anococcygeus muscle. For a one-receptor system, the Schild regression has a slope of unity and an intercept of K(B) for competitive antagonists. However, in a two-receptor system, a deviation from the single-receptor plot will occur. This is predicated on the assumption that the secondary receptor is less sensitive to the antagonist than the primary receptor. Results showed that the Schild regression for losartan did not produce a slope of unity, and PD123319 did not produce any effect. However, tissue incubation with losartan plus PD123319 resulted in a Schild regression that has a slope of unity and a pK(B) of 9.32. In the presence of prazosin, an alpha(1)-adrenoceptor antagonist, losartan did not produce any effect. Conversely, PD123319 enhanced the angiotensin II (Ang II)-induced contraction in a concentration-dependent fashion, suggesting an inhibitory AT(2)-mediated effect. This effect was confirmed with assays that showed a relaxant response induced by Ang II on precontracted tissues incubated with prazosin. PD123319 and N(G)-nitro-L-arginine methyl ester [nitric-oxide (NO) synthase inhibitor)] markedly inhibited the relaxant response of Ang II. In contrast, losartan did not produce any significant effect. Consequently, results show that the mechanism underlying the AT(2)-mediated effect is highly dependent on NO generation. Results indicate the presence of a heterogeneous angiotensin receptor population in the rat anococcygeus muscle following a negative cross-talk relationship between the AT(1) and AT(2) subtypes.     

血管紧张素II1型受体基因多态性与原发性高血压的关系

目的探讨血管紧张素Ⅱ1型受体（AT1R）基因多态性与原发性高血压（EH）之间的关系。方法应用聚合酶链反应-限制性片段长度多态性（PCR—RFLP）对200例汉族EH患者（EH组）和192例正常血压者（对照组）的ATlR基因1166A／C及-810A／T多态性进行检测,测定空腹血糖、甘油三酯（TG）、总胆固醇（TC）、低密度脂蛋白胆固醇（LDL—C）及高密度脂蛋白胆固醇（HDL—C）等生物化学指标,分析各基因型和等位基因频率与EH的关系。结果1166A／C等位基因和基因型频率在EH组和对照组的分布无统计学差异（P均〉0．05）,-810A／T各基因型在EH组和对照组间差异有统计学意义（χ^2=10．862,P=0．004）,-810T等位基因频率在EH组显著增高[22．5％（102／400）与11．5％（44／384）,χ^2=12．745,P=0．000],用Logistic回归模型校正了传统危险因素的影响后,-810AT和TT基因型的携带者患高血压的危险性显著增加（P=0．003,OR值为2．57,95％CI：1．37～4．84）。结论AT1R-810A／T多态性与EH发病相关,-810T等位基因可能是EH发病的风险因子。     

Ontogeny of type 1 angiotensin II receptor gene expression in the rat.

To determine whether the expression of the type 1 angiotensin II receptor (AT1) gene is developmentally regulated and whether the regulation is tissue specific, AT1 mRNA levels were determined by Northern blot analysis in livers and kidneys from fetal, newborn, and adult rats, using a 1133-bp rat AT1 cDNA. In the liver, AT1 mRNA levels increased fivefold from 15 d gestation to 5 d of age. Liver AT1 mRNA levels at 5 d of age were similar to those of adult rats. In the kidney, AT1 mRNA levels were higher in immature than in adult animals. The intrarenal distribution of AT1 mRNA was assessed by in situ hybridization to a 35S-labeled 24 residues oligonucleotide complementary to rat AT1 mRNA. In the adult, AT1 mRNA was present in glomeruli, arteries, and vasa recta, whereas in the newborn AT1 mRNA was observed also over the nephrogenic area of the cortex. We conclude that: (a) fetal kidney and liver express the AT1 gene; (b) the AT1 gene expression is developmentally regulated in a tissue-specific manner; (c) during maturation, localization of AT1 mRNA in the kidney shifts from a widespread distribution in the nephrogenic cortex to specific sites in glomeruli, arteries, and vasa recta, suggesting a role for the angiotensin receptor in nephron growth and development.     

Association of angiotensin II type 1 receptor gene polymorphism with carotid atherosclerosis.

BACKGROUND: Polymorphisms of the angiotensin II type 1 receptor (AGTR1) gene are associated with essential hypertension and cardiovascular disease, but the correlation between AGTR1 A1166C polymorphism and carotid intima-media thickness (IMT) remains unclear. We sought to demonstrate correlation between AGTR1 gene polymorphism and carotid atherosclerosis in a Chinese population. METHOD: A total of 150 patients diagnosed with essential hypertension were included in this study. The AGTR1 A1166C polymorphism was detected by restriction analysis of the polymerase chain reaction product with Ddel digestion. Carotid IMT was measured by B-mode ultrasonography. RESULTS: The AC genotype frequency and the C1166 allele frequency of the AGTR1 gene in essential hypertensive patients were significantly higher than in controls (22.00% vs. 6.00% for AC, p < 0.01; 18.67% vs. 8.00% for the C allele, p < 0.05). Hypertensive subjects with the AC genotype had increased carotid artery IMT and IMT/D (common carotid artery diameter) ratio compared with the AA genotype (IMT 1.14 +/- 0.39 vs. 0.88 +/- 0.16, p < 0.05; IMT/D 14.08 +/- 2.88 vs. 10.51 +/- 1.94, p < 0.01). CONCLUSION: These results suggest that the AGTR1 A1166C polymorphism is associated with essential hypertension and carotid atherosclerosis in a Chinese population.     

Histamine 3 receptor activation reduces the expression of neuronal angiotensin II type 1 receptors in the heart

In severe myocardial ischemia, histamine 3 (H?) receptor activation affords cardioprotection by preventing excessive norepinephrine release and arrhythmias; pivotal to this action is the inhibition of neuronal Na?/H? exchanger (NHE). Conversely, angiotensin II, formed locally by mast cell-derived renin, stimulates NHE via angiotensin II type 1 (AT?) receptors, facilitating norepinephrine release and arrhythmias. Thus, ischemic dysfunction may depend on a balance between the NHE-modulating effects of H? receptors and AT? receptors. The purpose of this investigation was therefore to elucidate the H?/AT? receptor interaction in myocardial ischemia/reperfusion. We found that H? receptor blockade with clobenpropit increased norepinephrine overflow and arrhythmias in Langendorff-perfused guinea pig hearts subjected to ischemia/reperfusion. This coincided with increased neuronal AT? receptor expression. NHE inhibition with cariporide prevented both increases in norepinephrine release and AT? receptor expression. Moreover, norepinephrine release and AT? receptor expression were increased by the nitric oxide (NO) synthase inhibitor N(G)-methyl-L-arginine and the protein kinase C activator phorbol myristate acetate. H? receptor activation in differentiated sympathetic neuron-like PC12 cells permanently transfected with H? receptor cDNA caused a decrease in protein kinase C activity and AT? receptor protein abundance. Collectively, our findings suggest that neuronal H? receptor activation inhibits NHE by diminishing protein kinase C activity. Reduced NHE activity sequentially causes intracellular acidification, increased NO synthesis, and diminished AT? receptor expression. Thus, H? receptor-mediated NHE inhibition in ischemia/reperfusion not only opposes the angiotensin II-induced stimulation of NHE in cardiac sympathetic neurons, but also down-regulates AT? receptor expression. Cardioprotection ultimately results from the combined attenuation of angiotensin II and norepinephrine effects and alleviation of arrhythmias.