摘要:

ObjectiveThe upregulation of left ventricular atrial natriuretic peptide (ANP) serves as a molecular marker of cardiac hypertrophy. The precise mechanisms underlying this gene induction are unclear, since the presently cloned 3.6 kilo base (kb) rat ANP promoter failed to substantially induce coupled reporter genes in chronically hypertrophied hearts. The aim of this study was to clone and to functionally analyse the upstream ANP promoter.DesignUpstream of the known ANP promoter, a 1.5 kb segment was cloned by the promoter walker method and found to harbour a putative CCAAT-binding site as well as multiple putative transcription factor binding sites. This newly cloned segment was ligated with a reporter gene,in vivotransfected into rat myocardium, and analysed under basal conditions or after stimulation with both acute (isovolumetric contractions in the Langendorff apparatus) and chronic wall stress (aortic banding).ResultsReporter gene constructs carrying the newly cloned segment conferred only little promoter activity. In hearts exposed to acute wall stress, the previously cloned 3.6 kb ANP promoter as well as a constitutive promoter (pGL3 promoter vector) were active but markedly suppressed after extension with the newly cloned upstream promoter (−88.1 and −85.5%;P<0.05 respectively). Site directed mutagenesis of two AP-2 transcription factor binding sites (base pairs –3946 to –3954 or –4192 to –4200) eliminated this silencing effect. In hearts with chronic pressure overload hypertrophy as well as in normal, unstimulated hearts the activity of the 3.6 kb ANP promoter was weak and also abolished after ligation with the 1.5 kb upstream segment. Moreover, both putative AP-2 binding sites within the upstream rat ANP promoter bound specifically to nuclear proteins of unstimulated, acute and chronic pressure overloaded hearts as demonstrated by electrophoresis mobility shift assays.ConclusionNovel silencer elements were cloned, localized to two AP-2 binding sites in the upstream ANP promoter, and functionally characterized. Given that the putative upregulation of left ventricular ANP by the extensively studied 3.6 kb proximal promoter region is substantially diminished by the newly cloned segment, the functional significance of regulatory elements within the proximal promoter region should be re-evaluated. The molecular mechanism causing ANP mRNA induction in left ventricular hypertrophy remains obscure.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectivesThe β2-adrenoceptor (ADRB2) plays a pivotal role in signalling in relation to hypertension and obesity. Polymorphisms of theADRB2gene have been shown to be potentially related to essential hypertension and other non-cardiovascular disease phenotypes. We investigated whether genetic variation of theADRB2gene might be related to essential hypertension or myocardial infarction (MI).MethodsFour ADRB2 gene polymorphisms C19R (T−47C), T−20C, G16R (G+46A), Q27E (C+79G) were investigated in two studies: PEGASE, a study of moderate to severe hypertension (707 cases) conducted in France, and ECTIM, a case-control study of MI (1178 cases, 1187 controls) conducted in France, Northern Ireland and Scotland. Genotyping was performed using allele-specific oligonucleotides.ResultsThe ADRB2 polymorphisms T−20C and Q27E were found to be completely concordant, generating the haplotypes [T−20–Q27] and [C−20–E27]. Three main haplotypes accounted for 94% of all haplotypes: [R19–G16–E27] (39%), [C19–R16–Q27] (35%) and [C19–G16–Q27] (20%). Haplotype frequencies were not significantly different between countries.Allele and genotype frequencies did not differ significantly between cases with essential hypertension or MI and control subjects. There was no association of the polymorphisms with early onset hypertension, blood pressure level, coronary artery stenosis or any other phenotype measured in these study populations. In the ECTIM Study, our calculation revealed that we could have detected an odds ratio (OR) for MI of 1.3 with 80% power at a 5% type I error probability, the corresponding value for the PEGASE Study being an OR of 1.6 for hypertension.ConclusionsFrom our present analysis we conclude that the ADRB2 gene polymorphisms studied do not contribute in any important way to the risk of essential hypertension or MI in subjects of European ancestry.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveTo determine whether estrogen rapidly affects endothelium-derived contracting factor (EDCF) in the renal artery of hypertensive Dahl rats, and whether factors other than nitric oxide (NO) contribute to the effect of estrogen.DesignAcute effects of estrogen on the acetylcholine-induced vasomotor responses and on prostaglandin H2/thromboxane A2mimetic, U46619,-induced contraction were examined in isolated arterial rings.Methods and resultsDahl salt-sensitive male and female rats were fed an 8% NaCl diet for 4 weeks. The blood pressure increased more rapidly and to a greater extent in males than in females. Renal arterial rings were prepared for isometric tension recording. 17β-Estradiol, but not the biologically less active stereoisomer, 17α-estradiol, improved the relaxation response to acetylcholine in renal arteries from females. Estrogen also rapidly decreased the contraction evoked by acetylcholine (10−6to∼10−4mol/l) in renal arteries from females and it was effective at a physiological concentration (10−9mol/l) in the presence ofNω-nitro-l-arginine methyl ester (an NO synthase inhibitor). The estrogen receptor antagonist, ICI 182,780, abolished the effect of estrogen, whereas the cytochrome P450 inhibitor, miconazole, had no effect. The contraction induced by U46619 was also suppressed by estrogen, without any contribution from NO. Estrogen had no effect on either relaxation or contraction responses in renal arteries from males.Conclusion17β-Estradiol antagonizes increases in vascular tone in hypertensive females by enhancing NO-dependent relaxation, and by suppressing EDCF-mediated mechanisms in an NO-independent manner.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectivesHypertension is accompanied by endothelial dysfunction. The present study has investigated endothelial cell morphology and connexin expression in the caudal artery of the rat during the development of hypertension.MethodsA significant increase in systolic blood pressure was detected from 9 weeks of age in spontaneously hypertensive male rats (SHR) compared to normotensive Wistar–Kyoto (WKY) rats, reaching a maximum by 11–12 weeks of age. Immunohistochemistry was used to quantify cell size and expression of connexins (Cxs) 37, 40 and 43 in the endothelium of prehypertensive (3-week-old) and hypertensive (12-week-old) rats.ResultsAt 12 weeks, the size of endothelial cells and the expression of all three Cxs per endothelial cell were significantly less in SHR than WKY rats. At 3 weeks, there was no significant difference in cell size nor in the expression of Cxs 37 or 43; however, expression of Cx40 was significantly lower in SHR than in WKY rats. Between 3 and 12 weeks in WKY rats, there was no change in endothelial cell size, nor in the expression of Cxs 37, 40 and 43. In SHR, both cell size and Cx expression per endothelial cell were significantly decreased during the same developmental period, with a significant decrease in the density of Cx40 plaques.ConclusionThe development of hypertension in the SHR is accompanied by significant decreases in endothelial cell size and expression of Cx40, which may contribute to the endothelial dysfunction present in hypertension.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveThe pregnant spontaneously hypertensive rat (SHR) exhibits a decrease in arterial blood pressure shortly before delivery; however, the mechanisms are unknown. Nitric oxide may be involved.DesignBlood pressure in stroke-prone SHR (SHRSP) and Wistar–Kyoto control rats (WKY) was telemetrically measured. Four groups were studied: pregnant and non-pregnant WKY and SHRSP rats, respectively. Mean blood pressure in pregnant SHRSP rats decreased from 148±2 mmHg at conception to 120±4 mmHg at day 15, compared to 112±1 mmHg in pregnant WKY rats. At delivery, we determined the vasodilatory responses of isolated preconstricted aortic strips.ResultsVasodilatory responses from late-term SHRSP rats were significantly greater following acetylcholine than either those from non-pregnant SHRSP or pregnant and non-pregnant WKY rats (acetylcholine IC50: 5, 22.8, 398, 1000 nmol/l, respectively), while contractile responses to increasing doses of norepinephrine were not different. Similar results were obtained with substance P. Indomethacin had no effect on the relaxation responses. Relaxation in response to sodium nitroprusside was not different in the groups. Western blot analysis showed that endothelial nitric oxide synthase (eNOS) levels were significantly increased in the pregnant SHRSP vessels compared to non-pregnant SHRSP, pregnant WKY, and non-pregnant WKY vessels.ConclusionIncreased NOS may explain the blood pressure decrease during late pregnancy in genetically hypertensive rats.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectivesWe have previously reported that 5-lipoxygenase-derived products, and particularly the cysteinyl leukotrienes (CysLTs), were involved in angiotensin II (Ang II)-induced contractions in isolated aortas from spontaneously hypertensive rats.DesignThe aim of this study was to assess the role of CysLTs in the vascular response to Ang II in an Ang II-dependent model of hypertension, the (mRen-2)27 transgenic rats (TGs).MethodsIntact aortic rings from TG and normotensive Sprague–Dawley rats (SDs) were suspended in organ chambers for isometric tension development in response to Ang II. In addition, the release of CysLTs in response to Ang II (0.3 μmol/l) was measured by enzyme immunoassay.ResultsIn isolated aortas from TG rats, pretreatment with the 5-lipoxygenase inhibitor (AA861, 10 μmol/l) or the CysLT1receptor antagonist (MK571, 1 μmol/l) significantly (P<0.05) reduced Ang II-induced contractions by 52 and 42%, respectively. In addition, Ang II induced a 2.6-fold increase in CysLT release (pg/mg dry weight tissue: 58.3±17.9 (Ang II,n= 7) versus 22.5±5.9 (basal,n= 7)P<0.05), which was inhibited by the AT1receptor antagonist losartan (1 μmol/l). In contrast, in aortas from SD rats, pretreatment with AA861 or MK571 did not alter Ang II-induced contraction and CysLT production remained unchanged after exposure to Ang II.ConclusionThese data suggest that CysLTs are involved in the contractile responses to Ang II in isolated aortas from TG but not from SD rats.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

BackgroundHypertension in endothelial nitric oxide synthase knockout (eNOS−/−) mice is believed to be partly due to altered vasodilatation. However, nitric oxide (NO) is also known to play an important part in angiogenesis.ObjectiveTo investigate whether capillary and arteriolar density were impaired in eNOS−/−mice, as this could account for increased vascular resistance and hypertension.MethodsUsing immunohistochemistry with mouse monoclonal smooth muscle α-actin antibody to detect arterioles and rabbit polyclonal fibronectin antibody to detect capillaries, we quantified arteriolar and capillary density in the left ventricle and in the gracilis muscle from eNOS−/−mice compared with those in C57BL6J littermates (n= 6–8) in 8- and in 12-week-old mice. In a second set of experiments, we treated 8-week-old normotensive eNOS−/−mice with the antihypertensive vasodilator, hydralazine, for 1 month.ResultsEight-week-old eNOS−/−mice were normotensive and presented similar arteriolar and capillary densities in cardiac and skeletal mucles compared with those in eNOS+/+mice. Twelve-week-old eNOS−/−mice were hypertensive (mean arterial pressure 118±21 mmHg compared with 64±2 mmHg;P<0.05). Capillary densities were similar in eNOS−/−mice and eNOS+/+mice in the heart (4154±123 and 4051±247/mm2, respectively) and in skeletal muscle (961±40 and 1025±41/mm2, respectively). Arteriolar densities were 15% lower in skeletal muscle and in the heart in eNOS−/−mice than in the eNOS+/+control group (P<0.05). Hydralazine prevented hypertension and arteriolar rarefaction in eNOS−/−mice, whereas capillary density was unaffected by treatment with the vasodilator.ConclusionIn young non-hypertensive eNOS−/−mice, the lack of eNOS did not affect microvascular densities in either of the muscles studied. In adult hypertensive eNOS−/−mice, we observed a lower arteriolar density, but a similar capillary density compared with controls. Hydralazine prevented hypertension and arteriolar rarefaction in adult mice, suggesting a non-NO-dependent pathway. Capillary density was not affected by hydralazine.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveTo determine the effects of the angiotensin II receptor antagonist irbesartan, the calcium-channel blocker amlodipine, and hydrochlorothiazide/hydralazine on superoxide, NAD(P)H oxidase and nitric oxide bioavailability in spontaneously hypertensive stroke-prone rats (SHRSP).MethodsDrugs or vehicle were administered for 8 weeks to SHRSP and blood pressure was measured weekly by tail-cuff plethysmography. After 8 weeks, superoxide levels in carotid arteries and aortas were measured by lucigenin chemiluminescence and p22phox expression quantified by immunohistochemistry.In vitrothe effects of exposure to drugs and vehicle for 30 min and 4 h on superoxide levels and nitric oxide bioavailability were examined. The latter was expressed as the increase in contractile responses of carotid arteries to phenylephrine in the presence of the nitric oxide synthase inhibitorNG-nitro-l-arginine methyl ester (l-NAME).ResultsIn vivoirbesartan, amlodipine and hydrochlorothiazide/hydralazine produced similar falls in blood pressure, from 162±4 to 125±5, 132±4 and 131±6 mmHg, respectively, but irbesartan caused a greater reduction in superoxide and p22phox; superoxide levels in carotid arteries being 3.1±0.3, 1.1±0.2, 1.9±0.3 and 2.0±0.3 nmoles/mg per min, respectively.In vitro4 h exposure to irbesartan decreased superoxide levels in the aorta from 2.08±0.68 to 1.48±0.62 nmoles/mg per min and increased nitric oxide bioavailability in carotid arteries. Neither 30 min incubation with irbesartan nor 4 h with amlodipine or hydrochlorothiazide/hydralazine altered superoxide levels.ConclusionsThese studies support the hypothesis that AT1receptor blockade has beneficial effects on superoxide production and nitric oxide bioavailability above that of other classes of antihypertensive agents. Reduced expression of components of the NAD(P)H oxidase may contribute to these effects.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveThe sympathetic nervous system (SNS) is commonly activated in hypertension; however, the role of SNS activation in the pathogenesis of cardiovascular structural changes remains poorly defined. In particular, the effect of adrenergic stimulation on extracellular matrix (ECM) protein production by human cardiovascular cells is unknown. The present study thus investigated the direct effect of adrenergic stimulation on ECM protein production by cultured human vascular smooth muscle (VSM) cells.Methods and resultsExposing human VSM cells to norepinephrine increased collagen protein production by 42%,P<0.01, when compared to control (unstimulated) cells. This effect was mediated by the α1-adrenoceptor, since it was inhibited by the selective α1-adrenoceptor antagonist; prazosin (2 μmol/l) and reproduced by the selective α1-adrenoceptor agonist; phenylephrine (10 μmol/l). In contrast, β-adrenoceptor stimulation – isoprenaline (1 μmol/l) or norepinephrine (10 μmol/l) + prazosin (2 μmol/l) – inhibited collagen production by 12%,P<0.01. This inhibitory effect was mediated via the β1-adrenoceptor, since it was blocked by atenolol (β1-adrenoceptor antagonist) but not butoxamine (β2-adrenoceptor antagonist). Fibronectin, another ECM protein, was similarly regulated by α- and β-adrenoceptor stimulation. Transforming growth factor β1 (TGFβ1) mRNA expression by human VSM cells was also significantly influenced by adrenergic stimulation, being increased by phenylephrine (α-agonist) and inhibited by isoprenaline (β-agonist).ConclusionsThese results uniquely demonstrate the capacity for adrenergic stimulation to directly modulate TGFβ1 expression and ECM protein synthesis by the human cardiovascular system.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveIn this study we aimed to characterize and clarify the mechanisms involved in the acute blood pressure increase observed concomitantly with water intake in moderately dehydrated rats.DesignShort-term water deprivation was employed as a model to induce controlled water intake to study concomitant cardiovascular responses in the rat.MethodsMale Wistar rats were deprived of water for 18–24 h before the experiments and were allowed to drink for 20 s periods during the experimental session. During these periods water intake was accompanied by steady arterial pressure increases. This pressor response was unaffected by topical anesthesia of the oral cavity. Direct administration of water into the stomach did not cause pressor responses. The pressor response was not affected by bilateral adrenal demedullation or by pretreatment with diazepam, homatropine methyl bromide, d(CH2)5Tyr(Me)AVP, losartan or RX821002. The pressor response was significantly reduced by ganglionic blockade with mecamylamine or pretreatment with the α1-adrenoceptor antagonist, prazosin.ConclusionsOur results show that: (1) short-term dehydration can be used as a model to study cardiovascular responses associated with water intake in rats; and (2) the sympathetic nervous system and vascular smooth muscle α1-adrenoceptors are involved in the pressor response to water intake by dehydrated rats.

ISSN:0263-6352    

出版商:OVID    

年代:2002

数据来源: OVID