Attenuation of angiotensin type 2 receptor function in the rostral ventrolateral medullary pressor area of the spontaneously hypertensive rat

We hypothesized that blockade of angiotensin II type 2 receptors (AT₂Rs) in the rostral ventrolateral medullary pressor area (RVLM) may elicit sympathoexcitatory responses which are smaller in hypertensive rats compared to normotensive rats. This hypothesis was tested in urethane-anesthetized, artificially ventilated male 14-week-old spontaneously hypertensive rats (SHR). Age-matched male Wistar–Kyoto rats (WKY) and Wistar rats were used as controls. PD123319 (AT₂R antagonist) was microinjected into the RVLM and mean arterial pressure (MAP), heart rate (HR) and greater splanchnic nerve activity (GSNA) were recorded. Increases in MAP, HR and GSNA elicited by unilateral microinjections of PD123319 into the RVLM were significantly smaller in SHR when compared with those in WKY and Wistar rats. Unilateral microinjections of l-glutamate (l-Glu) into the RVLM elicited greater increases in MAP and GSNA in SHR compared to those in WKY. AT₂R immunoreactivity was demonstrated in the RVLM neurons which were retrogradely labeled from the intermediolateral cell column (IML) of the spinal cord. These results indicate that AT₂Rs are present on the RVLM neurons projecting to the IML and their blockade results in sympathoexcitatory responses. Activation of AT₂Rs has an inhibitory influence in the RVLM and these receptors are tonically active. Attenuation of the function of AT₂Rs in the RVLM may play a role in genesis and/or maintenance of hypertension in SHR.     

Protective effect of Ferula gummosa hydroalcoholic extract against nitric oxide deficiency-induced oxidative stress and inflammation in rats renal tissues

Abstract

Nitric oxide (NO) synthase inhibition increases hypertension and causes renal injury. Ferula gummosa is used in Iranian traditional medicine for treatment of several diseases and has been reported to exert a potent anti-inflammatory and antioxidant action. The aim of this investigation was to evaluate the renoprotective effects of hydroalcoholic extract of Ferula gummosa (HEG) on Nω-nitro-l-arginine methyl ester (l-NAME)-induced oxidative stress and inflammation and explore the mechanisms that link NO deficiency with altered renal heat shock protein (HSP70). Rats were injected intraperitoneally with l-NAME (10?mg/kg) to induce renal injury. Simultaneously, HEG (90?mg/kg) was administered by gastric gavage to l-NAME-treated rats for 6 days/week during an 8-week period. Renal thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), HSP70, plasma NO and total antioxidant capacity (TAC) were evaluated. The administration of l-NAME significantly increased renal TBARS, TNF-α, IL-6, HSP70 levels and decreased renal SOD activity, that these changes were accompanied by the reduced plasma NO and TAC levels. HEG administration decreased TBARS, HSP70, TNF-α and IL-6 levels and increased SOD activity in the kidney tissues of l-NAME treated rats (p?<?0.05). Also, plasma TAC level and NO bioavailability have been elevated after administration of HEG (p?<?0.05). These findings support that NO deficiency induces renal stress oxidative and inflammation, which markedly increased renal HSP70 and HEG could protect kidney against these damaging effects via its anti-oxidative, anti-inflammatory action and modulate renal HSP70.     

Aldehyde dehydrogenase 2 partly mediates hypotensive effect of nitrite on l-NAME-induced hypertension in normoxic rat

Nitrite has become a topic of interest in the field of medical research because of its potential therapeutic role as an alternative source of nitric oxide (NO). While the bioconversion of nitrite to NO occurs via either nonenzymatic or enzymatic reduction under acidic or hypoxic conditions, little is known about its conversion to NO under normoxic conditions. Because of a recent report of aldehyde dehydrogenase 2 (ALDH2)-catalyzed glyceryl trinitrate (GTN) vasorelaxation by denitration of GTN to 1,2-glyceryl dinitrate (1,2-GDN) and nitrite, we therefore investigated a catalytic activity of ALDH2 for nitrite reduction and subsequent effect on N^ω-nitro-l-arginine methyl ester (l-NAME)-induced hypertension in normoxic rat. Male Sprague–Dawley rats treated with l-NAME in drinking water for 3 weeks developed hypertension with significantly reduced plasma levels of nitrite and nitrate. The intravenous injection of sodium nitrite lowered the arterial pressure in a dose-dependent manner (17, 50 and 150?μmol/kg). Pretreatment with ALDH2 inhibitors (cyanamide and chloral hydrate) partially inhibited the hypotensive responses to sodium nitrite. In addition, cyanamide significantly delayed the nitrite clearance from plasma and most of the organs examined during the experimental period. These results suggest that ALDH2 may be at least in part involved in nitrite-mediated hypotensive effects and nitrite catalysis in many organs of normoxic rats.     

Nebivolol alleviates aortic remodeling through eNOS upregulation and inhibition of oxidative stress in l-NAME-induced hypertensive rats

Purpose: To investigate the effect and mechanism of nebivolol on aortic remodeling in N-nitro-l-arginine methyl ester (l-NAME)-induced hypertension. Methods: Male Sprague–Dawley rats were treated with equal volumes of drinking water or l-NAME (60 mg/kg/day), alone or in combination with nebivolol (8 mg/kg/day) or atenolol (80 mg/kg/day) by gavage for 8 weeks. Systolic blood pressure (SBP), aortic morphometry, plasma nitric oxide (NO) levels, nitric oxide synthase (NOS) activity, and relaxation of aorta to acetylcholine were determined. Protein expression of endothelial NOS (eNOS), Akt, and NADPH oxidase (Nox) was evaluated. Results: l-NAME-treated rats showed an elevated SBP associated with aortic remodeling. l-NAME-treated rats showed reduced plasma NO levels and NOS activity and increased reactive oxygen species (ROS). Protein expression of eNOS, eNOS phosphorylated at Ser¹¹⁷⁷ (p-eNOS), Akt, and Akt phosphorylated at Ser⁴⁷³ (p-Akt) decreased, whereas that of Nox2, Nox4, and p22^phox increased in the aortas from l-NAME-treated rats. Nebivolol treatment reduced SBP and ameliorated aortic remodeling. The effects of nebivolol were accompanied by increasing NO levels, NOS activity, and expression of eNOS, p-eNOS, Akt, and p-Akt, as well as reduction of ROS generation and Nox2, Nox4, and p22^phox expression. These effects of nebivolol were not reproduced by atenolol. Conclusion: Our data indicate a protective role of nebivolol on the high blood pressure and vascular remodeling induced by l-NAME. The beneficial vascular effect of nebivolol is mediated by the upregulation of eNOS and inhibition of oxidative stress.     

Role of propolis on biochemical parameters in kidney and heart tissues against l-NAME induced oxidative injury in rats

Nitric oxide (NO), produced by endothelial NO synthase, is recognised as a central antiinflammatory and antiatherogenic principle in the vasculature. Epidemiological and clinical studies have demonstrated that a growing list of natural products, as components of the daily diet or phytomedical preparations, may improve vascular function by enhancing NO bioavailability. In this article, we investigated antioxidant effects of propolis on biochemical parameters in kidney and heart tissues of acute NO synthase inhibited rats by Nω-nitro-l-arginine methyl ester (l-NAME). There was increase (p?l-NAME treatment groups when compared with control rats, but NO levels were decreased in both kidney and heart tissues. There were statistically significant changes (p?l-NAME?+?propolis treated rats as compared with l-NAME-treated group. In summary, propolis may influence endothelial NO production.     

Sodium hydrosulfide alleviates pulmonary artery collagen remodeling in rats with high pulmonary blood flow

This study aimed to explore the effect of sodium hydrosulfide (NaHS) on pulmonary artery collagen remodeling in rats with high pulmonary blood flow. Thirty-two Sprague-Dawley rats were randomly divided into a sham group, shunt group, sham + NaHS (an H₂S donor) group, and shunt + NaHS group. After 11 weeks of shunting, mean pulmonary artery pressure (MPAP), relative median area (RMA) of pulmonary arteries, H₂S concentration in lung tissues, plasma endothelin-1 (ET-1) levels, and ET-1 mRNA in lung tissues were investigated. Collagen I and collagen III were evaluated by immunohistochemistry. Hydroxyproline assay and Sirius-red staining were performed. Matrix metalloproteinase-13 (MMP-13), tissue inhibitor of metalloproteinase-1 (TIMP-1), and connective tissue growth factor (CTGF) were evaluated by immunohistochemistry. After 11 weeks of shunting, rats showed a significant pulmonary hypertension and pulmonary artery collagen remodeling in association with a decrease in lung tissue H₂S content. After NaHS treatment for 11 weeks, lung tissue H₂S content was increased, whereas MPAP was attenuated and RMA was reduced. Meanwhile, pulmonary artery collagen I and collagen III protein expressions of intra-acinar pulmonary arteries were inhibited, but MMP-13/TIMP-1 ratio was augmented with a decreased plasma ET-1 content and lung tissue ET-1mRNA and CTGF expressions. The downregulation of H₂S is involved in the development of pulmonary artery collagen remodeling induced by high pulmonary blood flow.     

Endogenous nitric oxide modulates small intestinal nutrient transit and activity in healthy adult humans

Objective. Nitric oxide (NO) mechanisms have been shown to modulate fasting small intestinal motility in humans, but a role in the regulation of human postprandial small intestinal motility has not been assessed. The aim of this study was to evaluate the effect of the NO synthase inhibitor NG-monomethyl-l-arginine (l-NMMA) on the regulation of small intestinal nutrient transit and postprandial small intestinal motility in healthy humans. Material and methods. Seven healthy male volunteers (18–27 years) underwent antroduodenal manometry recordings for 4 h on 2 occasions after intraduodenal instillation of a 500 KJ [120 Kcal] test meal. The meal was administered 15 min after the commencement of a 60-min intravenous infusion of l-NMMA (4 mg kg^?1 h^?1) or saline (0.9%). Studies were separated, performed in randomized order and >3 days apart. The frequency and amplitude of duodenal pressure waves together with time to return of fasting motility (phase III) was determined. On each day, small intestinal transit was measured using a lactulose breath test. Results. The test meal interrupted fasting small intestinal motility in all subjects. The time to recurrence of fasting motility following its postprandial disruption was similar (l-NMMA versus saline 1.6±0.2 h versus 1.9±0.1 h; p>0.05). Duodenocaecal transit was delayed by infusion of l-NMMA compared with saline (l-NMMA versus saline 92.1±3.9 min versus 66.4±6.4 min; p<0.005). Infusion of l-NMMA significantly increased the frequency (l-NMMA versus saline 50.4±6.6 versus 34.8±5.5 waves per 30 min; p<0.05) and amplitude (l-NMMA versus saline 20.4±1.5 versus 15.5±1.1 mmHg; p<0.01) of duodenal pressure waves. Conclusions. These data suggest that endogenous NO may play a role in the regulation of small intestinal nutrient transit by regulating small intestinal motility in healthy individuals.     

Nitric Oxide and Hydrogen Sulfide Interact When Modulating Gastric Physiological Functions in Rodents

Aim

The objective was to evaluate the effects of nitric oxide (NO) and hydrogen sulfide (H₂S) donors and possible interactions between these two systems in modulating gastric function.

Methods

Mice received saline, sodium nitroprusside (SNP), or sodium hydrosulfite (NaHS), and after 1 h, the animals were killed for immunofluorescence analysis of CSE or eNOS expressions, respectively. Other groups received saline, SNP, NaHS, Lawesson’s reagent (H₂S donor), PAG + SNP, l-NAME, l-NAME + NaHS, or l-NAME + Lawesson’s reagent. Then, the gastric secretions (mucous and acid), gastric blood flow, gastric defense against ethanol, and gastric motility (gastric emptying and gastric contractility) were evaluated.

Results

SNP and NaHS increased the expression of CSE or eNOS, respectively. SNP or Lawesson’s reagent did not alter gastric acid secretion but increased mucus production, and these effects reverted with PAG and l-NAME treatment, respectively. SNP or NaHS increased gastric blood flow and protected the gastric mucosa against ethanol injury, and these effects reverted with PAG and l-NAME treatments, respectively. SNP delayed gastric emptying when compared with saline, and PAG partially reversed this effect. NaHS accelerate gastric emptying, and l-NAME partially reversed this effect. SNP and NaHS alone induced gastric fundus and pylorus relaxation. However, pretreatment with PAG or l-NAME reversed these relaxant effects only in the pylorus but not in the gastric fundus.

Conclusion

NO and H₂S interact in gastric physiological functions, and this “cross-talk” is important in the control of mucus secretion, gastric blood flow, gastric mucosal defense, and gastric motility, but not in the control of basal gastric acid secretion.

     

Inhibition of NADPH oxidase 4-related signaling by sodium hydrosulfide attenuates myocardial fibrotic response

Background

Myocardial fibrosis plays a pivotal role in the development of heart failure. Hydrogen sulfide (H₂S) is an endogenous gasotransmitter with potent cardioprotective properties; however, whether H₂S is involved in fibrotic process remains unknown. This study aimed to explore the role of H₂S in the process of cardiac fibrosis and the underlying mechanisms.

Methods

Myocardial infarction (MI) was established in rats by ligation of coronary artery. Activation of rat neonatal cardiac fibroblasts was induced by angiotensin II (Ang II). Fibrotic responses in ischemic myocardium and in Ang II-stimulated cardiac fibroblasts were examined. The effects of sodium hydrosulfide (NaHS, an exogenous H₂S donor) on NADPH oxidase 4 (Nox4), reactive oxygen species (ROS) production, extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, heme oxygenase-1 (HO-1), and cystathionine γ-lyase (CSE) were tested to elucidate the protective mechanisms of H₂S on fibrotic response.

Results

NaHS treatment inhibited Ang II-induced expression of α-smooth muscle actin, connective tissue growth factor (CTGF), and type I collagen and upregulated expression of HO-1 in cardiac fibroblasts. Ang II-induced Nox4 expression in cardiac fibroblasts was quenched by NaHS and this was associated with a decreased ROS production and reduced ERK1/2 phosphorylation and CTGF expression. In vivo studies using MI model indicated that NaHS administration attenuated Nox4 expression and fibrotic response. Moreover, NaHS therapy also prevented cardiac inflammatory response accompanied by increases in HO-1 and CSE expression.

Conclusions

The beneficial effect of H₂S, at least in part, was associated with a decrease of Nox4-ROS-ERK1/2 signaling axis and an increase in HO-1 expression.     

Maternal supplementation with citrulline increases renal nitric oxide in young spontaneously hypertensive rats and has long-term antihypertensive effects

NO deficiency is associated with development of hypertension. Defects in the renal citrulline-arginine pathway or arginine reabsorption potentially reduce renal NO in prehypertensive spontaneously hypertensive rats (SHRs). Hence, we investigated genes related to the citrulline-arginine pathway or arginine reabsorption, amino acid pools, and renal NO in 2-week-old prehypertensive SHRs. In addition, because perinatally supporting NO availability reduces blood pressure in SHRs, we supplemented SHR dams during pregnancy and lactation with citrulline, the rate-limiting amino acid for arginine synthesis. In female offspring, gene expression of argininosuccinate synthase (involved in renal arginine synthesis) and renal cationic amino acid Y-transporter (involved in arginine reabsorption) were both decreased in 2-day and 2-week SHRs compared with normotensive WKY, although no abnormalities in amino acid pools were observed. In addition, 2-week-old female SHRs had much less NO in their kidneys (0.46+/-0.01 versus 0.68+/-0.05 nmol/g of kidney weight, respectively; P<0.001) but not in their heart. Furthermore, perinatal supplementation with citrulline increased renal NO to 0.59+/-0.02 nmol/g of kidney weight (P<0.001) at 2 weeks and persistently ameliorated the development of hypertension in females and until 20 weeks in male SHR offspring. Defects in both the renal citrulline-arginine pathway and in arginine reabsorption precede hypertension in SHRs. We propose that the reduced cationic amino acid transporter disables the developing SHR kidney to use arginine reabsorption to compensate for reduced arginine synthesis, resulting in organ-specific NO deficiency. This early renal deficiency and its adverse sequels can be corrected by perinatal citrulline supplementation persistently in female and transiently in male SHRs.     

Chronic exercise modulates RAS components and improves balance between pro- and anti-inflammatory cytokines in the brain of SHR

Recently, exercise has been recommended as a part of lifestyle modification for all hypertensive patients; however, the precise mechanisms of its effects on hypertension are largely unknown. Therefore, this study aimed to investigate the mechanisms within the brain that can influence exercise-induced effects in an animal model of human essential hypertension. Young normotensive WKY rats and SHR were given moderate-intensity exercise for 16 weeks. Blood pressure was measured bi-weekly by tail-cuff method. Animals were then euthanized; paraventricular nucleus (PVN) and rostral ventrolateral medulla (RVLM), important cardiovascular regulatory centers in the brain, were collected and analyzed by real-time RT-PCR, Western blot, EIA, and fluorescent microscopy. Exercise of 16-week duration attenuated systolic, diastolic, and mean arterial pressure in SHR. Sedentary SHR exhibited increased pro-inflammatory cytokines (PICs) and decreased anti-inflammatory IL-10 levels in the PVN and RVLM. Furthermore, SHR_sed rats exhibited elevated levels of ACE, AT1R, and decreased levels of ACE2 and receptor Mas in the PVN and RVLM. Chronic exercise not only prevented the increase in PICs (TNF-α, IL-1β), ACE, and AT1R protein expression in the brain of SHR, but also dramatically upregulated IL-10, ACE2, and Mas receptor expression in SHR. In addition, these changes were associated with reduced plasma AngII levels, reduced neuronal activity, reduced NADPH-oxidase subunit gp91^phox and inducible NO synthase in trained SHRs indicating reduced oxidative stress. These results suggest that chronic exercise not only attenuates PICs and the vasoconstrictor axis of the RAS but also improves the anti-inflammatory defense mechanisms and vasoprotective axis of the RAS in the brain, which, at least in part, explains the blood pressure-lowering effects of exercise in hypertension.     

Hydrogen sulfide ameliorates aging-associated changes in the kidney

Aging is associated with replacement of normal kidney parenchyma by fibrosis. Because hydrogen sulfide (H₂S) ameliorates kidney fibrosis in disease models, we examined its status in the aging kidney. In the first study, we examined kidney cortical H₂S metabolism and signaling pathways related to synthesis of proteins including matrix proteins in young and old male C57BL/6 mice. In old mice, increase in renal cortical content of matrix protein involved in fibrosis was associated with decreased H₂S generation and AMPK activity, and activation of insulin receptor (IR)/IRS-2-Akt-mTORC1-mRNA translation signaling axis that can lead to increase in protein synthesis. In the second study, we randomized 18–19 month-old male C57BL/6 mice to receive 30 μmol/L sodium hydrosulfide (NaHS) in drinking water vs. water alone (control) for 5 months. Administration of NaHS increased plasma free sulfide levels. NaHS inhibited the increase in kidney cortical content of matrix proteins involved in fibrosis and ameliorated glomerulosclerosis. NaHS restored AMPK activity and inhibited activation of IR/IRS-2-Akt-mTORC1-mRNA translation axis. NaHS inhibited age-related increase in kidney cortical content of p21, IL-1β, and IL-6, components of the senescence-associated secretory phenotype. NaHS abolished increase in urinary albumin excretion seen in control mice and reduced serum cystatin C levels suggesting improved glomerular clearance function. We conclude that aging-induced changes in the kidney are associated with H₂S deficiency. Administration of H₂S ameliorates aging-induced kidney changes probably by inhibiting signaling pathways leading to matrix protein synthesis.     

硫化氢对自发性高血压大鼠血管炎症反应的调节作用

目的 探讨新型气体信号分子硫化氢(H2S)对自发性高血压大鼠(SHR)血管炎症反应的调节作用.方法 4周龄Wistar-Kyoto(WKY)雄性大鼠和SHR雄性大鼠分为4组:WKY大鼠对照组、SHR对照组、SHR+硫氢化钠(NaHS,H2S供体)组及SHR+炔丙基甘氨酸(PPG,H2S生成关键酶抑制剂)组,饲养至9周.尾容积法测清醒时大鼠血压,免疫组织化学方法检测主动脉内皮细胞膜细胞间黏附分子-1(ICAM-1)、核转录因子-κB p65(NF-κB p65)和核转录因子抑制因子-α(IκB-α)的蛋白表达,原位杂交分析检测主动脉内皮细胞ICAM-1 mRNA的表达.结果 SHR对照组血压显著高于WKY对照组(P<0.05),主动脉内皮细胞ICAM-1、ICAM-1 mRNA、胞核NF-κB p65明显高(P均<0.01),胞浆IκB-α蛋白表达明显低(P<0.01).SHR+NaHS组血压显著低于SHR对照组,主动脉内皮细胞ICAM-1、ICAM-1 mRNA、胞核NF-κB p65蛋白表达明显低(P<0.05),胞浆IκB-α蛋白表达明显增高(P<0.05),SHR+PPG组主动脉内皮细胞ICAM-1、ICAM-1mRNA、胞核NF-κB p65蛋白表达更高(P<0.05),胞浆IκB-α蛋白表达显著低(P<0.05).结论 H2S可通过抑制SHR血管炎症发挥抗高血压效应.H2S的抗血管炎症效应可能通过上调IκB-α的表达,降低NF-κB p65的表达,抑制ICAM-1 mRNA的转录和蛋白表达实现.     

Renal Nerve-Mediated Proximal Tubule Solute Reabsorption Contributes to Hypertension in Spontaneously Hypertensive Rats

Renal nerve activity increases (Na⁺, K⁺)-ATPase activity and contributes to the development of hypertension in young SHR. The present study was designed to examine the effect of sodium intake on blood pressure and proximal tubule solute reabsorption in sham-operated or renal denervated, 5-week old SHR and WKY. Three-week old SHR and WKY rats underwent sham surgery or renal denervation with 10% phenol and were maintained for 10 days on either a 0.6% or 2.2% NaCl diet. Blood pressure was obtained by indirect tail cuff measurements during this interval. Of the eight groups, only sham-operated SHR on a high sodium diet had hypertension, 122.0 × 4.2 mm Hg vs. 98.7 × 3.3 mm Hg (mean for remaining groups). Renal plasma flow (RPF), glomerular filtration rate (GFR), and the fractional excretion of lithium (FE_Lj) were determined in rats maintained on a 2.2% sodium diet at 5 weeks of age. FE_li was less in sham-operated SHR, 5.3 × 0.7%, compared to WKY, 9.4 × 2.8% (P>0.02). Furthermore, denervation ameliorated the reduced FE_Li in SHR, 10.2 × 1.2%, without affecting FE_Li in WKY. RPF and GFR were similar between sham-operated and renal denervated SHR and WKY. No significant difference could be detected in net sodium balance between WKY and SHR during this period. These findings demonstrate 1) from the basis of FE_Li, young SHR, of this strain, exhibit enhanced proximal tubule solute reabsorption and hypertension while on a high sodium diet and, 2) renal denervation ameliorates both the enhanced proximal tubule solute reabsorption and the early development of hypertension. These data support the concept that renal nerve activity of young SHR is augmented and contributes to the development of hypertension by enhancing salt retention.     

Altered insulin-like growth factor-1 and nitric oxide sensitivities in hypertension contribute to vascular hyperplasia

Vascular medial thickening, a hallmark of hypertension, is associated with vascular smooth muscle cell (VSMC) hypertrophy and hyperplasia. Although the precise mechanisms responsible are elusive, we have shown that strain induced regulation of autocrine insulin-like growth factor-1 (IGF-1) and nitric oxide (NO) reciprocally modulate VSMC proliferation. Therefore, we investigated potential IGF-1 and NO abnormalities in young (10-week-old) spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) and their respective VSMC ex vivo. The SHR had increased mean arterial pressure (173 ± 2 v 128 ± 3 mm Hg, n = 24, P < .05) but similar pulse pressures (31 ± 2 v 30 ± 3 mm Hg; P > .05) v WKY. The SHR exhibited increased aortic wall thickness in comparison with WKY (523 ± 16 v 355 ± 17μm; P < .05). No differences were seen in plasma combined NO₂ and NO₃ (NO_x) (0.48 ± 0.11 mmol/L for WKY v 0.58 ± 0.18 mmol/L for SHR) or plasma IGF-1 (1007 ± 28 ng/mL for WKY v 953 ± 26 ng/mL for SHR). Aortic VSMC from SHR displayed enhanced proliferation in comparison with WKY (P < .05). Underlying this enhanced proliferation was altered SHR VSMC sensitivity to the antiproliferative NO donor 2,2"[Hydroxynitrosohydrazono] bis-ethanimine (DETA-NO) (ID₅₀: 270 ± 20 mmol/L for SHR; 150 ± 11 mmol/L for WKY; P < .05). Basal cyclic guanosine monophosphate (cGMP) secretion from SHR VSMC was 65-fold greater than that seen from WKY (P < .001). In response to DETA-NO, cGMP secretion from SHR VSMC increased modestly (1.5-fold; P < .01), whereas treatment of WKY VSMC resulted in a 26-fold (P < .001) increase in cGMP. The SHR VSMC did not respond to exogenous IGF-1, whereas WKY VSMC exhibited a dose dependent increase in proliferation with IGF-1 (10⁻¹⁰ to 10⁻⁷ mol/L). These data suggest that VSMC hyperplasia in early hypertension is not reflected by imbalances in plasma IGF-1 or NO. Rather, altered SHR VSMC sensitivity to NO is likely responsible in part for the observed hyperproliferation seen in early stages of hypertension.     

Cardiovascular responses to microinjections of endomorphin-2 into the nucleus of the solitary tract are attenuated in the spontaneously hypertensive rat

Abstract

Stimulation of µ₁-opioid receptors (M1ORs) in the medial nucleus solitarius (mNTS) by endomorphin-2 (EM2) elicits decreases in mean arterial pressure (MAP), heart rate (HR) and greater splanchnic nerve activity (GSNA) in Wistar rats. We tested the hypothesis that EM2-induced responses in the mNTS may be attenuated in the spontaneously hypertensive rat (SHR). Experiments were carried out in urethane-anesthetized, artificially ventilated, adult male SHR and Wistar-Kyoto rats (WKY). Alterations in responses to chemical stimulation of the hypothalamic arcuate nucleus (ARCN) after bilateral blockade of M1ORs in the mNTS were also studied. In SHR, microinjections of EM2 into the mNTS elicited smaller decreases in MAP, HR and GSNA compared to those elicited in WKY; smaller cardiovascular responses in SHR can be explained by lower expression of M1OR mRNA in the NTS of SHR compared to WKY. Decreases in MAP and GSNA and increases in HR were elicited by microinjections of N-methyl-d-aspartic acid (NMDA) into the ARCN of WKY. Bilateral blockade of M1ORs in the mNTS attenuated the decreases in MAP and GSNA and exaggerated the increases in HR elicited by the ARCN stimulation in WKY but not in SHR. Tonic inhibitory activity of neuropeptide Y/gamma-aminobutyric acid (NPY/GABA) neurons in the ARCN is attenuated in SHR; this observation may explain increases in MAP, GSNA and HR elicited by microinjections of NMDA into the ARCN of SHR. These results demonstrate that attenuation of EM2-induced responses in the mNTS of SHR may contribute to the excitatory responses elicited by ARCN stimulation in SHR.     

Protein Phosphatase 2A B56α During Development in the Spontaneously Hypertensive Rat

Mistargeting of the regulatory subunit of protein phosphatase 2A (PP2A), B56α is involved in the hyperphosphorylation and desensitization of the D₁ dopamine receptor in renal proximal tubules of spontaneously hypertensive rats (SHRs). However, the renal expression of B56α before hypertension develops is not known. Therefore, we studied the expression of B56α and PP2A activity in the kidney during development in the SHR and its normotensive control, the Wistar‐Kyoto (WKY) rat. PP2A B56α was expressed in proximal and distal tubules with no differences in the pattern of expression in WKY and SHRs at any age. In brush border membranes of renal proximal tubules, PP2A B56α protein was greatest in the immature rats and decreased with development. However, PP2A activity did not change with age. PP2A B56α protein and PP2A activity were similar in WKY and SHRs except at 2 weeks when both PP2A B56α protein and PP2A activity were higher in SHRs than in WKY rats. The PP2A catalytic subunit co‐immunoprecipitated with the D₁ receptor in renal proximal tubule cells. It is possible that the increased expression of PP2A B56α and increased basal PP2A activity in the young, especially in the SHRs, may serve as a compensatory mechanism in the increased phosphorylation and decreased renal D₁ receptor function, including D₁‐receptor mediated stimulation in renal proximal tubules of SHRs.     

Endothelial Dysfunction in the Human Umbilical Artery due to Preeclampsia Can Be Prevented by Sildenafil

Abstract

Objectives. We aimed to determine the effects of sildenafil in human umbilical artery preparation taken from preeclamptic or normal pregnant women, also to investigate underlying mechanisms in these effects. Study design. Eighteen pregnant women with preeclampsia and 18 healthy pregnant women were involved. Relaxation responses of sildenafil in presence and absence of nitric oxide (NO) synthase inhibitor, N-[omega]-nitro-l-arginine methyl ester (l-NAME), and soluble guanylyl cyclase inhibitor, 1H-[1,2,4] oxadiazolo [4,3-a]quinoxalin-1-one (ODQ), were compared between the preeclampsia group and control group. Results. Sildenafil-induced relaxation responses were significantly attenuated in the presence of preeclampsia, l-NAME or ODQ, but not totally abolished. Interestingly, except with ODQ incubation, in all set of experiments maximal relaxation response was achieved by sildenafil. Conclusion. These data indicate that sildenafil might effect vascular responsiveness of human umbilical artery through the involvement of NO/cyclic guanosine monophosphate (cGMP)-dependent and -independent pathways. Further investigations are needed to clarify the exact mechanisms.     

Effect of Treadmill Exercise and Ferula gummosa on Myocardial HSP72, Vascular Function,and Antioxidant Defenses in Spontaneously Hypertensive Rats

This study evaluates the effect of treadmill exercise and Ferula gummosa (FG) on heat shock protein (HSP72), biomarkers related to vascular function, and oxidant/antioxidant system in the heart tissue of spontaneously hypertensive rats treated with N(ω)-nitro-l–arginine-methyl ester (l–NAME). Fifty adult male Wistar rats are randomly classified into five groups: treadmill exercise, FG, combination of treadmill exercise + FG, l–NAME, and saline. Treadmill exercise was performed between 25 and 64 minutes at the speed of 15–22 m per minute for 8 weeks and five sessions a week. The FG will be fed through gavage with 90 mg/kg dosage. Hypertension was induced by l–NAME (10 mg/kg) for 8 weeks and six sessions a week. Administration of l–NAME for 8 weeks caused significant increase in HSP72, angiotensin-converting enzyme (ACE), and protein carbonyl (PC), and significant decrease in glutathione peroxidase (GPx) and nitric oxide (NO) level, when compared with the saline group. In contrast, both treadmill exercise and/or FG protocols, in particular, the combined protocol, led to the improvement in HSP72 and balance in oxidant/antioxidant process and inhibited vascular dysfunction, when compared with the l–NAME group. Moreover, no significant differences were detected in the HSP72 level between rats in the treadmill exercise and FG groups. These results provide a rationale for an inhibitory role and a cardioprotective effect of lifestyle related to the health in the attenuation of hypertension-induced cardiotoxicity.