Enhanced G-protein coupled receptors-mediated contraction and reduced endothelium-dependent relaxation in hypertension

Doxorubicin alters G-protein coupled receptor-mediated vasocontraction in rat coronary arteries

Doxorubicin (Doxo)-associated cardio-and vasotoxicity has been recognised as a serious complication of cancer chemotherapy. The purpose of this novel paper was to determine the effect of Doxo on G-protein coupled receptor (GPCR)-mediated vasocontraction located on vascular smooth muscle cells. Rat left anterior descending artery segments were incubated for 24 h with 0.5 µM Doxo. The vasocontractile responses by activation of endothelin receptor type A (ETA) and type B (ETB), serotonin receptor 1B (5-HT1B) and thromboxane A2 prostanoid receptor (TP) were investigated by a sensitive myography using specific agonists, while the specificity of the GPCR agonists was verified by applying selective antagonists (i.e. ETA and ETB agonist = 10- 14-10- 7.5 M endothelin-1 (ET-1); ETA antagonist = 10 µM BQ123; ETB agonists = 10- 14-10- 7.5 M sarafotoxin 6c (S6c) and ET-1; ETB antagonist = 0.1 µM BQ788; 5-HT1B agonist = 10- 12-10- 5.5 M 5-carboxamidotryptamine (5-CT); 5-HT1B antagonist = 1 µM GR55562; TP agonist = 10- 12-10- 6.5 M U46619; TP antagonist = 1 µM Seratrodast). Our results show that 0.5 µM Doxo incubation of LAD segments leads to an increased VSMC vasocontraction through the ETB, 5-HT1B and TP GPCRs, with a 2.2-fold increase in ETB-mediated vasocontraction at 10- 10.5 M S6c, a 2.0-fold increase in 5-HT1B-mediated vasocontraction at 10- 5.5 M 5-CT, and a 1.3-fold increase in TP-mediated vasocontraction at 10- 6.5 M U46619. Further studies unravelling the involvement of intracellular GPCR signalling pathways will broaden our understanding of the Doxo-induced vasotoxicity, and thus pave the way to mitigate the adverse effects by potential implementation of adjunct therapy options.

Avocado Oil Prevents Kidney Injury and Normalizes Renal Vasodilation after Adrenergic Stimulation in Hypertensive Rats: Probable Role of Improvement in Mitochondrial Dysfunction and Oxidative Stress

Hypertension impairs the function of the kidney and its vasculature. Adrenergic activation is involved in these processes by promoting oxidative stress and mitochondrial dysfunction. Thus, the targeting of mitochondrial function and mitochondrial oxidative stress may be an approach to alleviate hypertensive kidney damage. Avocado oil, a source of oleic acid and antioxidants, improves mitochondrial dysfunction, decreases mitochondrial oxidative stress, and enhances vascular function in hypertensive rats. However, whether avocado oil improves the function of renal vasculature during the adrenergic stimulation, and if this is related to improvement in renal damage and enhancement of mitochondrial activity is unknown. Thus, the effects of avocado oil on renal vascular responses to adrenergic stimulation, mitochondrial dysfunction, oxidative stress, and renal damage were compared with prazosin, an antagonist of α₁-adrenoceptors, in hypertensive rats induced by L-NAME. Avocado oil or prazosin decreased blood pressure, improved endothelium-dependent renal vasodilation, prevented mitochondrial dysfunction and kidney damage in hypertensive rats. However, avocado oil, but not prazosin, decreased mitochondrial ROS generation and improved the redox state of mitochondrial glutathione. These results suggest that avocado oil and prazosin prevented hypertensive renal damage due to the improvement in mitochondrial function.

Role of the Purinergic P2Y2 Receptor in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH), group 1 pulmonary hypertension (PH), is a fatal disease that is characterized by vasoconstriction, increased pressure in the pulmonary arteries, and right heart failure. PAH can be described by abnormal vascular remodeling, hyperproliferation in the vasculature, endothelial cell dysfunction, and vascular tone dysregulation. The disease pathomechanisms, however, are as yet not fully understood at the molecular level. Purinergic receptors P2Y within the G-protein-coupled receptor family play a major role in fluid shear stress transduction, proliferation, migration, and vascular tone regulation in systemic circulation, but less is known about their contribution in PAH. Hence, studies that focus on purinergic signaling are of great importance for the identification of new therapeutic targets in PAH. Interestingly, the role of P2Y2 receptors has not yet been sufficiently studied in PAH, whereas the relevance of other P2Ys as drug targets for PAH was shown using specific agonists or antagonists. In this review, we will shed light on P2Y receptors and focus more on the P2Y2 receptor as a potential novel player in PAH and as a new therapeutic target for disease management.

Minimally modified low-density lipoprotein upregulates mouse mesenteric arterial 5-HT1B receptor in vivo via activation of the JAK2/STAT3 pathway

OBJECTIVES

To explore whether minimally modified low-density lipoprotein (mmLDL) upregulates mesenteric arterial 5-hydroxytryptamine 1B (5-HT_1B) receptor expression by activating the JAK2/STAT3 signaling pathway.

METHODS

Mice were randomly divided into the following groups: the normal saline (NS), LDL, mmLDL, mmLDL+galiellactone (GL, a JAK2/STAT3 pathway inhibitor), and mmLDL+DMSO groups. The dose-response curve of mesenteric arterial ring constriction after administration of 5-carboxamidotryptamine (5-CT), an agonist of 5-HT_1B, was recorded with a microvascular tensiometer. JAK2, p-JAK2, STAT3, p-STAT3, and 5-HT_1B receptor protein expression levels were determined by Western blotting. 5-HT_1B receptor mRNA levels were measured by RT-PCR. 5-HT_1B receptor protein expression was determined by immunofluorescence.

RESULTS

Injection of mmLDL into the tail vein significantly increased the contractile dose-response curve after 5-CT stimulation, as the E_max was 82.15 ± 6.15% in the NS group and 171.88 ± 5.78% in the mmLDL group (P < 0.01); significantly elevated 5-HT_1B receptor mRNA and protein expression levels; and significantly increased p-JAK2 and p-STAT3 protein expression levels. After intraperitoneal injection of GL, the vasoconstrictive response was significantly reduced compared with that in the mmLDL group, as the E_max was decreased to 97.14 ± 1.20% (P < 0.01); 5-HT_1B receptor mRNA and protein expression levels were significantly reduced; STAT3 phosphorylation and p-JAK2 and p-STAT3 protein expression were not significantly changed; and 5-HT_1B receptor expression was altered via inhibition of p-STAT3 binding to DNA, which suppressed transcription.

CONCLUSIONS

mmLDL can upregulate 5-HT_1B receptor expression in mouse mesenteric arteries by activating the JAK2/STAT3 signaling pathway.

PM2.5 upregulates rat mesenteric arteries 5-HT2A receptor via inflammatory-mediated mitogen-activated protein kinases signaling pathway

Fine particulate matter (PM_2.5 ) is an important environmental risk factor for cardiovascular diseases. However, little is known about the effects of PM_2.5 on arteries. The present study investigated whether PM_2.5 alters 5-hydroxytryptamine (5-HT) receptor expression and inflammatory mediators on rat mesenteric arteries, and examined the underlying mechanisms. Isolated rat mesenteric arteries segments were cultured with PM_2.5 in the presence or absence of ERK1/2, JNK, and p38 pathway inhibitors. Contractile reactivity was monitored by a sensitive myograph. The expression of 5-HT_2A/1B receptors and inflammatory mediators were studied by a real-time polymerase chain reaction and/or by immunohistochemistry. The phosphorylation of mitogen-activated protein kinases (MAPK) pathway was detected by Western blot. Compared with the fresh or culture alone groups, 1.0 μg/mL PM_2.5 cultured for 16 hours significantly enhanced contractile response induced by 5-HT and increased 5-HT_2A receptor mRNA and protein expressions, indicating PM_2.5 upregulates 5-HT_2A receptor. SB203580 (p38 inhibitor) and U0126 (ERK1/2 inhibitor) significantly decreased PM_2.5 -induced elevated contraction and mRNA and protein expression of 5-HT_2A receptor. Cultured with PM_2.5 significantly increased the mRNA expression of inflammatory mediators (NOS2, IL-1β, and TNF-α), while SB203580 decreased mRNA expression level of NOS2, IL-1β, and TNF-α. SP600125 (JNK inhibitor) decreased mRNA expression level of TNF-α and IL-1β. After PM_2.5 exposure, the phosphorylation of p38 and ERK1/2 protein were increased. SB203580 and U0126 inhibited the PM_2.5 caused increased phosphorylation protein of p38 and ERK1/2. In conclusion, PM_2.5 induces inflammatory-mediated MAPK pathway in artery which subsequently results in enhanced vascular contraction responding to 5-HT via the upregulated 5-HT_2A receptors.

Minimally modified low-density lipoprotein upregulates the ETB and α1 receptors in mouse mesenteric arteries in vivo by activating the PI3K/Akt pathway

OBJECTIVES

The current study aimed to explore whether minimally modified low-density lipoprotein (mmLDL) via tail vein injection upregulates the ET_B and α₁ receptors in mouse mesenteric arteries by activating the PI3K/Akt pathway.

METHODS

The contraction curves of the mesenteric arteries caused by sarafotoxin 6c (S6c, ET_B receptor agonist) and phenylephrine (PE, α₁ receptor agonist) were measured by a myograph system. Serum oxLDL was detected using enzyme-linked immunosorbent assays. The levels of the ET_B receptor, the α₁ receptor, PI3K, p-PI3K and p-Akt were detected using real-time polymerase chain reaction and Western blot analyses.

KEY FINDINGS

Minimally modified low-density lipoprotein noticeably enhanced the contraction effect curves of S6c and PE, with significantly increased E_max values (P < 0.01), compared to those of the control group. This treatment significantly increased the mRNA expression and protein levels of the ET_B and α₁ receptors and the protein levels of p-PI3K and p-Akt in the vessel wall (P < 0.01). LY294002 inhibited the effect of mmLDL.

CONCLUSIONS

An increase in mmLDL activated the PI3K/Akt pathway, which upregulated the expression of the ET_B and α₁ receptors and enhanced the ET_B and α_1- receptor-mediated contractile function.

H2S Prevents Cyclosporine A-Induced Vasomotor Alteration in Rats

Cyclosporine A (CsA) induces hypertension after transplantation. Hydrogen sulfide (H₂S) was found to have hypotensive/vasoprotective effects in the cardiovascular system. The present study aims to investigate the role of H₂S on CsA-induced vascular function disorder in rats. Rats were subcutaneously injected with CsA 25 mg/kg for 21 days. Blood pressure was measured by the tail-cuff method. Vasomotion was determined using a sensitive myograph. Western blotting and immunohistochemistry were used to quantify the protein expression of endothelin type A (ET_A) receptor and essential MAPK pathway molecules. Vascular superoxide anion production and serum contents of malondialdehyde were determined. The results showed that sodium hydrosulfide (NaHS), a H₂S donor, significantly attenuated the increase of blood pressure and contractile responses, and the upregulation of ET_A receptor induced by CsA. In addition, NaHS could restore the CsA decreased acetylcholine-induced vasodilatation. Furthermore, NaHS blocked the CsA-induced elevation of reactive oxygen species level, extracellular signal-regulated kinase and p38 MAPK activities. In conclusion, H₂S prevents CsA-induced vasomotor dysfunction. H₂S attenuates CsA-induced ET_A receptor upregulation, which may be associated with MAPK signal pathways. H₂S ameliorates endothelial-dependent relaxation, which may be through antioxidant activity.

Autonomic Receptors and Nitric-Oxide Involvements in Mediating Vasorelaxation Effect Induced by Syzygium polyanthum Leaves Extract

Context:

Syzygium polyanthum (Wight) Walp leaves are traditionally used by Malays for treating hypertension. Our previous study showed that aqueous extract of S. polyanthum (AESP) and methanolic extract of S. polyanthum (MESP) extracts of S. polyanthum leaves significantly reduced blood pressure of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR).

Aims:

This study aimed to investigate their vasorelaxation potential and the possible involvement of autonomic receptors and nitric oxide in mediating their effect.

Settings and Design:

Both extracts will be tested on isolated thoracic aorta rings of WKY and SHR. The involvement of autonomic receptors and nitric oxide will be elucidated using respective blockers.

Materials and Methods:

Isolated thoracic aorta rings from WKY and SHR were mounted onto myograph chambers to measure changes in the aorta tension. Increasing concentrations of AESP and MESP, from 1 μg/ml to 10 mg/ml were added onto the myograph chambers. Blockers such as atropine (1 μM), phentolamine (1 μM), propranolol (1 μM), and Nω-nitro-l-arginine methyl ester (100 μM) were preincubated before addition of extracts to check for involvement of muscarinic, α- and β-adrenergic receptors (AR) as well as nitric oxide, respectively.

Statistical Analysis Used:

Two-way ANOVA, followed by post hoc Bonferroni test was used, where P < 0.05 (two-tailed) was considered statistically significant.

Results:

AESP and MESP caused significant vasorelaxations through nitric oxide pathway. The former was mediated through α-AR while the latter was mediated by β-adrenergic and muscarinic receptors.

Conclusion:

Vasorelaxation effect by AESP and MESP involved nitric oxide pathway which is possibly mediated by the autonomic receptors.

SUMMARY

This is the first study that reveals significant vasorelaxation effect induced by Syzygium polyanthum leaves extract. Vasorelaxation maybe one of the possible mechanisms for its ability to reduce blood pressure. This study also suggested that the vasorelaxation effect by this plant extract may involve nitric oxide pathway mediated by the autonomic receptors.

Abbreviations Used: AESP: Aqueous extract of Syzygium polyanthum leaves. MESP: Methanolic extract of Syzygium polyanthum leaves. SHR: spontaneously hypertensive rat, WKY: Wistar-Kyoto rat.

Tail vein injection of mmLDL upregulates mouse mesenteric artery ETB receptors via activation of the ERK1/2 pathway

Minimally modified low density lipoprotein (mmLDL) is a risk factor for cardiovascular disease. This study investigated the effect of mmLDL on mouse mesenteric artery endothelin type B (ET_B) receptors and its molecular mechanism. Mice were injected with normal saline (NS group), mmLDL in the tail vein (mmLDL group), or with both mmLDL and an intraperitoneal injection of the ERK1/2 pathway-specific inhibitor U0126 (mmLDL+U0126 group). The dose-response curve of mesenteric artery contraction induced by sarafotoxin 6c (S6c), the ET_B receptor agonist, was measured using a sensitive myograph system. ELISAs, RT-PCR and Western blot were used to determine the serum concentrations of mouse oxidized low density lipoprotein (oxLDL), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) as well as the expression of ET_B receptors, ICAM-1, VCAM-1 and phosphorylated-extracellular signal-regulated kinase 1/2 (p-ERK1/2). The S6c-induced contraction dose-response curve was significantly enhanced by mmLDL treatment and showed a significantly higher E_max value than in the NS group (P<0.001), and the ET_B receptor mRNA and protein expression in the vascular wall was significantly higher than in the NS group. The serum concentration and expression of ICAM-1 and VCAM-1 were also increased by mmLDL treatment, but intraperitoneal injection of U0126 inhibited these changes as well as the increase in p-ERK1/2 protein in the vessel wall caused by mmLDL. ICAM-1 and VCAM-1 serum concentrations were positively correlated with the S6c-induced maximum contraction of blood vessels. Increased in vivo levels of mmLDL increased the serum concentrations and expression of ICAM-1 and VCAM-1 by activating the ERK1/2 pathway, resulting in the expression of ET_B receptors and the enhancement of contractile function in vascular smooth muscle. Understanding the effect of mmLDL on ET_B receptors and its mechanism can provide ideas for cardiovascular disease prevention and treatment.

Homocysteine up-regulates endothelin type A receptor in vascular smooth muscle cells through Sirt1/ERK1/2 signaling pathway

Sirtuin 1 (Sirt1) is a longevity gene that has protective effects in cardiovascular diseases (CVDs). The endothelin type A (ET_A) receptor is involved in pathogenesis of CVDs. The extracellular signal related kinases 1 and 2 (ERK1/2) signaling pathway is involved in regulation of the ET_A receptor induced by some CVD risk factors in vascular smooth muscle cells (VSMCs). Hyperhomocysteinemia (HHcy) is an independent risk factor for CVDs. The present study was designed to investigate the hypothesis that homocysteine up-regulates ET_A receptor through the Sirt1/ERK1/2 signaling pathway. In vitro experiments were performed in the rat superior mesenteric artery. The rat superior mesenteric artery was cultured with or without homocysteine (Hcy) in the presence and absence of Resveratrol (Res, a Sirt1 agonist), SRT1720 (a specific Sirt1 agonist) or U0126 (an ERK1/2 signaling pathway inhibitor) in serum-free medium for 24h. In vivo, the rats received subcutaneous injections of Hcy in the presence of or absence of Res or U0126 for 3weeks. The contractile response to ET-1 was studied using a sensitive myograph. In addition, the level of protein expression was determined using western blotting. Hcy significantly increased the expression of ET_A receptor and also increased the ET_A receptor-mediated contractile response induced by ET-1 in vitro. These effects were inhibited by Res, SRT1720 and U0126 treatment. In addition, Hcy down-regulated the level of Sirt1, and up-regulated the level of phosphorylated ERK1/2, which was reversed upon Res or SRT1720 treatment. In vivo results showed that HHcy results in the up-regulation of ET_A receptor expression, and elevated blood pressure in rats. However, Res and U0126 could block these effects, respectively. In conclusion, these results suggest that Hcy regulates ET_A receptor expression via the Sirt1/ERK1/2 signaling pathway in VSMCs.

Obesity, Inflammation, and Exercise Training: Relative Contribution of iNOS and eNOS in the Modulation of Vascular Function in the Mouse Aorta

Background: The understanding of obsesity-related vascular dysfunction remains controversial mainly because of the diseases associated with vascular injury. Exercise training is known to prevent vascular dysfunction. Using an obesity model without comorbidities, we aimed at investigating the underlying mechanism of vascular dysfunction and how exercise interferes with this process.

Methods: High-sugar diet was used to induce obesity in mice. Exercise training was performed 5 days/week. Body weight, energy intake, and adipose tissues were assessed; blood metabolic and hormonal parameters were determined; and serum TNFα was measured. Blood pressure and heart rate were assessed by plethysmography. Changes in aortic isometric tension were recorded on myograph. Western blot was used to analyze protein expression. Nitric oxide (NO) was evaluated using fluorescence microscopy. Antisense oligodeoxynucleotides were used for inducible nitric oxide synthase isoform (iNOS) knockdown.

Results: Body weight, fat mass, total cholesterol, low-density lipoprotein cholesterol fraction, insulin, and leptin were higher in the sedentary obese group (SD) than in the sedentary control animals (SS). Exercise training prevented these changes. No difference in glucose tolerance, insulin sensitivity, blood pressure, and heart rate was found. Decreased vascular relaxation and reduced endothelial nitric oxide synthase (eNOS) functioning in the SD group were prevented by exercise. Contractile response to phenylephrine was decreased in the aortas of the wild SD mice, compared with that of the SS group; however, no alteration was noted in the SD iNOS^−/− animals. The decreased contractility was endothelium-dependent, and was reverted by iNOS inhibition or iNOS silencing. The aortas from the SD group showed increased basal NO production, serum TNFα, TNF receptor-1, and phospho-IκB. Exercise training attenuated iNOS-dependent reduction in contractile response in high-sugar diet–fed animals, decreased iNOS expression, and increased eNOS expression.

Conclusion: Obesity caused endothelium dysfunction, TNFα, and iNOS pathway up-regulation, decreasing vascular contractility in the obese animals. Exercise training was an effective therapy to control iNOS-dependent NO production and to preserve endothelial function in obese individuals.

The ERK1/2 pathway participates in the upregulation of the expression of mesenteric artery α1 receptors by intravenous tail injections of mmLDL in mice

Minimally modified low density lipoprotein (mmLDL) is a risk factor for cardiovascular diseases. However, no studies examining the effect of mmLDL on vascular smooth muscle receptors have been released. The current study investigated the effect of mmLDL on the mesenteric artery α1 adrenoceptor and the molecular mechanisms. Mice were divided into the normal saline (NS), mmLDL, and mmLDL+U0126 groups. In the mmLDL+U0126 group, the animals were subjected to an intravenous tail injection of mmLDL and an intraperitoneal injection of U0126. Vascular tension caused by noradrenaline (NA) in mesenteric arteries was measured with a sensitive myograph system. The serum levels of oxLDL, TNF-α, and IL-1β were detected using enzyme-linked immunosorbent assays. The expressions of the α1 adrenoceptor, the α2 adrenoceptor, TNF-α, IL-1β, and pERK1/2 were detected using real-time polymerase chain reactions and Western blot analysis. Compared with the NS group, the mmLDL group exhibited a noticeably enhanced NA shrinkage dose-response curve and a significantly increased Emax value (P<0.01). Prazosin (α1 adrenoceptor antagonist) caused a noticeable right shift of the dose-response curve. U0126 inhibited the increases in the serum levels and vessel wall expression of IL-1β and TNF-α and enhanced the NA shrinkage dose-response curve caused by mmLDL, as observed by a significantly decreased Emax value (P<0.01). It inhibited the increased α1 adrenoceptor expression caused by mmLDL. The serum levels of IL-1β and TNF-α demonstrated a positive correlation with the NA-induced maximum shrinkage percentage. U0126 inhibited the mmLDL-induced increase in the pERK1/2 protein level in the vessel wall. In conclusion, mmLDL increased the serum levels of IL-1β and TNF-α in vivo by activating the ERK1/2 pathway, which resulted in α1 receptor-mediated vasoconstriction and an increase in the expression of α1 adrenoceptor. The results of this study may provide new ideas for the prevention and cure of cardiovascular diseases in the future.

The Role of MAPK Pathways in Airborne Fine Particulate Matter-Induced Upregulation of Endothelin Receptors in Rat Basilar Arteries

Airborne fine particulate matter (PM(2.5)) increases the risk of cerebrovascular diseases. However, existing experimental data do not sufficiently explain how PM(2.5) affects cerebral vessels. This study sought to examine whether PM(2.5) alters endothelin (ET) receptor expression on rat cerebral arteries and the potential underlying mechanisms. Isolated rat basilar arteries were cultured with PM(2.5) aqueous suspension in the presence of mitogen-activated protein kinase (MAPK) pathway inhibitors. ET receptor-mediated vasomotor functions were recorded by a sensitive myograph. ET(A) and ET(B) receptor mRNA and protein expressions were assessed using quantitative real-time PCR, Western blotting, and immunohistochemistry, respectively. Compared with fresh and culture alone arteries, PM(2.5) significantly enhanced ET(A) and ET(B) receptor-mediated contractions and increased receptor mRNA and protein expressions in basilar arteries, indicating PM(2.5) upregulates ET(A) and ET(B) receptors. Culturing with SB386023 (MEK/ERK1/2 inhibitor), U0126 (ERK1/2 inhibitor), SP600125 [c-Jun N-terminal kinase (JNK) inhibitor], or SB203580 (p38 inhibitor) attenuated PM(2.5)-induced ETB receptor upregulation. PM(2.5)-induced enhancement of ET(A) receptor-mediated contraction and receptor expression was notably inhibited by SB386023 or U0126. However, neither SP600125 nor SB203580 had an effect on PM(2.5)-induced ET(A) receptor upregulation. In conclusion, PM(2.5) upregulates ET(A) and ET(B) receptors in rat basilar arteries. ET(B) receptor upregulation is involved in MEK/ERK1/2, JNK, and p38 MAPK pathways, and ET(A) receptors upregulation is associated with MEK/ERK1/2 pathway.

Enhanced vasoconstriction to α1 adrenoceptor autoantibody in spontaneously hypertensive rats

Autoimmune activities have been implicated in the pathogenesis of hypertension. High levels of autoantibodies against the second extracellular loop of α1-adrenoceptor (α1-AR autoantibody, α1-AA) are found in patients with hypertension, and α1-AA could exert a α1-AR agonist-like vasoconstrictive effect. However, whether the vasoconstrictive effect of α1-AA is enhanced in hypertension is unknown. Using aortic rings of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, we observed the vasoconstrictive responses to α1-AA with phenylephrine (α1-AR agonist) as a positive control drug. Aortic nitrotyrosine levels were also measured by ELISA and immunohistochemistry. The results showed that the aortic constrictive responses to α1-AA and phenylephrine (both 1 nmol L(-1)-10 μmol L(-1)) were greater in SHR than in WKY rats. Endothelial denudation or L-NAME (a non-selective NOS inhibitor) (100 μmol L(-1)) increased α1-AA- or phenylephrine-induced vasoconstrictions both in SHR and WKY. However, selective iNOS inhibitor 1400 W (10 μmol L(-1)) enhanced the α1-AA-induced aortic constriction in WKY, but not in SHR. The aortic nitrotyrosine level was significantly higher in SHR than WKY, as shown by both ELISA and immunohistochemistry. These results indicate that the vasoconstrictive response to α1-AA is enhanced in SHR, and this altered responsiveness is due to endothelial dysfunction and decreased NO bioavailability. The study suggests an important role of α1-AR autoimmunity in the pathogenesis and management of hypertension especially in those harboring high α1-AA levels.

Myeloperoxidase upregulates endothelin receptor type B expression

Neutrophil recruitment and activation are principal events in inflammation. Upon activation neutrophils release myeloperoxidase (MPO), a heme enzyme, which binds to and transcytoses endothelial cells. Whereas the significance of the subendothelial deposition of MPO has evolved as a critical prerequisite for the enzyme's suppression of nitric oxide (NO⋅) bioavailability, the functional consequences of MPO binding to and interaction with endothelial and smooth muscle cells remain poorly understood. Cultured human endothelial cells (HUVECs) were exposed to MPO. Gene expression of the endothelin receptor type B (ETRB), which is critically involved not only in endothelin-1 clearance, but also in endothelin-mediated vasoconstriction, was significantly increased. Real time PCR, Western blotting and immunofluorescence confirmed up-regulation of ETRB in MPO-treated endothelial cells. Inhibition of MPO's enzymatic activity blunted the increase in ETRB protein expression. Treatment of the cells with the MAP kinase inhibitors PD98059 or SB203580 indicates that MPO activates ETRB expression via MAP kinase pathways. On human smooth muscle cells (HAoSMCs), which not only express the endothelin receptor type B (ETRB) but also express the endothelin receptor type A (ETRA), MPO also stimulated ETRB expression as opposed to ETRA expression, which remained unchanged. Functional ex vivo organ bath chamber studies with MPO-incubated rat femoral artery sections revealed increased ETRB agonist dependent constriction. Binding of MPO to endothelial and vascular smooth muscle cells increases expression of the endothelin receptor type B (ETRB) via classical MAP kinase pathways. This suggests that MPO not only affects vasomotion by reducing the bioavailability of vasodilating molecules but also by increasing responsiveness to vasoconstrictors, further advocating for MPO as a central, leukocyte-derived regulator of vascular tone.

Altered endothelin receptor expression and affinity in spontaneously hypertensive rat cerebral and coronary arteries

Background

Hypertension is associated with arterial hyperreactivity, and endothelin (ET) receptors are involved in vascular pathogenesis. The present study was performed to examine the hypothesis that ET receptors were altered in cerebral and coronary arteries of spontaneously hypertensive rats (SHR).

Methodology/Principal Findings

Cerebral and coronary arteries were removed from SHR. Vascular contraction was recorded using a sensitive myograph system. Real-time PCR and Western blotting were used to quantify mRNA and protein expression of receptors and essential MAPK pathway molecules. The results demonstrated that both ET_A and ET_B receptor-mediated contractile responses in SHR cerebral arteries were shifted to the left in a nonparallel manner with increased maximum contraction compared with Wistar-Kyoto (WKY) rats. In SHR coronary arteries, the ET_A receptor-mediated contraction curve was shifted to the left in parallel with an increased pEC₅₀ compared with the arteries in WKY rats. There was no significant increase in ET_B receptor-mediated contraction in SHR coronary arteries. ET_A receptor mRNA and protein expression was increased in SHR cerebral arteries compared with the arteries in WKY rats. However, ET_A receptor mRNA and protein levels in coronary arteries and ET_B receptor protein levels in cerebral and coronary arteries remained unchanged in SHR compared with WKY rats. Meanwhile, phosphorylated ERK1/2 protein was significantly increased in SHR brain and heart vessels.

Conclusions/Significance

In SHR cerebral arteries, ET_A receptor expression was upregulated. ET_A receptor affinity was increased in coronary arteries, and ET_B receptor affinity was increased in cerebral arteries. The ERK1/2 activation may be involved in the receptor alterations.

Antihypertensive effect of formononetin through regulating the expressions of eNOS, 5-HT2A/1B receptors and α1-adrenoceptors in spontaneously rat arteries

One of the main pathological changes of hypertension is the dysfunction of blood vessels. We have found in our previous study that formononetin, one kind of phytoestrogens, has an acute antihypertensive effect. Therefore, we hypothesized that formononetin might produce a chronic antihypertensive effect through regulating the expressions of contractile receptors and endothelial nitric oxide synthase (eNOS) in artery. The present study was conducted to verify this effect. Male spontaneously hypertensive rats (SHRs) were divided into two groups, orally administrated formononetin (50mg/kg per day) and Tween 80 vehicle, respectively, for 8 weeks. The blood pressure was measured by tail-cuff method. Isometric tension of arterial rings was recorded by a myograph system. The mRNA and protein expression in arteries was determined with quantitative real-time polymerase chain reaction and immunohistochemistry, respectively. Results showed that the systolic blood pressure of SHRs decreased significantly in formononetin group compared to Tween 80 group. The vasoconstriction induced by phenylephrine or 5-hydroxytryptamine (5-HT) in the mesenteric artery segments in formononetin group was decreased, and the relaxation induced by acetylcholine was increased compared with that in Tween 80 group. In the mesenteric arteries of the formononetin-treated SHRs, the expressions of α(1)-adrenoceptors and 5-HT(2A/1B) receptors at both mRNA and protein levels decreased, while the mRNA and protein expressions of eNOS increased. In conclusion, formononetin has a chronic antihypertensive effect in SHRs. The antihypertensive mechanism may be associated with the down-regulation of α(1)-adrenoceptors and 5-HT(2A/1B) receptors, and the up-regulation of eNOS expression in arteries.

Up-regulation of G-protein-coupled receptors for endothelin and thromboxane by lipid-soluble smoke particles in renal artery of rat

Up-regulation of G-protein-coupled receptors (GPCR) plays key roles in renal hypertension and cardiovascular disease pathogenesis. The present study was designed to examine if lipid-soluble cigarette smoking particles (DSP), nicotine and endotoxin (LPS), induce GPCR up-regulation for thromboxane A(2) (TP), endothelin type A (ET(A) ) and type B (ET(B) ) receptors in renal artery, and if intracellular signal mechanisms are involved. Renal artery segments of rats were exposed to DSP, nicotine or LPS, in organ culture for up to 24 hr. The GPCR-mediated contractions were recorded by using a myograph system. Expression of the GPCR was examined by real-time PCR and immunohistochemistry at mRNA and protein levels. Sarafatoxin 6c (S6c, selective ET(B) receptor agonist), endothelin-1 (ET-1, non-selective ET(A) and ET(B) receptor agonist) and 9,11-Dideoxy-9a,11a-methanoepoxy prostaglandin F(2a) (U46619, a TP receptor agonist) induced contractions were significantly increased after the arterial segments exposed to DSP in a concentration-dependent (0.1-0.4 μl/ml) manner, and S6c also induced a time-dependent contraction, compared to control (dimethyl sulfoxide). This was in parallel with enhanced mRNA expression for ET(B) receptor but not ET(A) and TP receptors, while increased protein expression for ET(A) , ET(B) and TP receptors was seen. The specific nuclear factor-kappa B (NF-κB) signal pathway inhibitor BMS345541 was applied to link DSP effects to the GPCR up-regulation. It totally abolished ET(B) receptor up-regulation, but not ET(A) and TP receptor up-regulations. Our results suggest that DSP transcriptionally up-regulated ET(B) receptor expression in rat renal artery via NF-κB signal pathways, whereas up-regulation of ET(A) and TP receptor-mediated contraction may involve post-transcriptional mechanisms.

Regional variations of vasomotion to G-protein coupled receptor agonists following heat stress in rats

Objectives

This study was designed to compare vascular contractile and relaxing responses to G-protein coupled receptor agonists among the different regions of arteries following heat stress in rats.

Methods

Heat exposure was performed by increasing the internal temperature of the rats to 42°C for 15 min. After heat stress for 48 h, a myograph system was used to monitor the contractile responses in rat renal, femoral and mesenteric arteries to agonists of endothelin type B (ETB) receptor, endothelin type A (ETA) receptor, serotonin receptor and α-adrenoceptor, respectively. In addition, calcitonin gene-related peptide (CGRP)-induced vasodilation was studied.

Key findings

The results showed that heat stress induced decreased contractions mediated by α-adrenoceptors and serotonin receptors (at lower concentration), while it increased contraction mediated by endothelin ETB receptors and enhanced relaxation mediated by CGRP receptors in the renal artery. Heat stress increased contractions mediated by endothelin ETB receptors, endothelin ETA receptors and α-adrenoceptors in the femoral artery. In the mesenteric artery, heat stress increased contractions mediated by endothelin ETB and serotonin receptors and relaxation mediated by CGRP receptors.

Conclusions

The vasomotor responses to the G-protein coupled receptor agonists with altered vascular contractions and relaxations were different in rat renal, femoral and mesenteric arteries after heat stress. This might have contributed to the redistribution of blood flow and aids understanding of the preconditioning phenomenon.

Increased perfusion pressure enhances the expression of endothelin (ETB) and angiotensin II (AT1, AT2) receptors in rat mesenteric artery smooth muscle cells

In the present study, we hypothesized that changes in perfusion pressure result in altered expression of mRNA and protein encoding for the ETA-, ETB-, AT1- and AT2-receptors in rat mesenteric vessels. Segments of the rat mesenteric artery were cannulated with glass micropipettes, pressurized and luminally perfused in a perfusion chamber. After either exposure to no ("organ culture" (0 mmHg)), normal (85/75 mmHg) or high pressure (160/150 mmHg) at constant flow for 1-17 h, the vessel segments were snap frozen and real-time polymerase chain reaction was performed to quantify the ET- and AT-receptor mRNA content, or immersed in a fixative solution, dehydrated, frozen, cut in a cryostat and immunohistology stained for ET- and AT-receptor protein. The mRNA expressions of ETB and of AT2 were significantly enhanced in vessels exposed to high perfusion pressure, compared with normal and no perfusion pressure at 4 h. In concordance, AT1-, AT2- and ETB-receptor proteins were up-regulated at 17 h of high perfusion pressure. In conclusion, the results from our rat perfusion model suggest a more important role of shear stress than pure pressure alone and may serve as a surrogate model for studies designed to investigate hypertension mechanisms.

Alteration of airway responsiveness mediated by receptors in ovalbumin-induced asthmatic E3 rats

AIM

Airway hyperresponsiveness is a constant feature of asthma. The aim of the present study was to investigate airway hyperreactivity mediated by contractile and dilative receptors in an ovalbumin (OVA)-induced model of rat asthma.

METHODS

Asthmatic E3 rats were prepared by intraperitoneal injection with OVA/aluminum hydroxide and then challenged with intranasal instillation of OVA-PBS two weeks later. The myograph method was used to measure the responses of constriction and dilatation in the trachea, main bronchi and lobar bronchi.

RESULTS

In asthmatic E3 rats, beta(2) adrenoceptor-mediated relaxation of airway smooth muscle pre-contracted with 5-HT was inhibited, and there were no obvious difference in relaxation compared with normal E3 rats. Contraction of lobar bronchi mediated by 5-HT and sarafotoxin 6c was more potent than in the trachea or main bronchi. Airway contractions mediated by the endothelin (ET)(A) receptor, ET(B) receptor and M(3) muscarinic receptor were augmented, and the augmented contraction was most obvious in lobar bronchi. The order of efficacy of contraction for lobar bronchi induced by agonists was ET-1, sarafotoxin 6c>ACh>5-HT. OX8 (an antibody against CD8(+) T cells) strongly shifted and OX35 (an antibody against CD4(+) T cells) modestly shifted isoprenaline-induced concentration-relaxation curves in a nonparallel fashion to the left with an increased R(max) in asthmatic rats and sarafotoxin 6c-induced concentration-contractile curves to the right with a decreased E(max).

CONCLUSION

The inhibition of airway relaxation and the augmentation of contraction mediated by receptors contribute to airway hyperresponsiveness and involve CD8(+) and CD4(+) T cells.Acta Pharmacologica Sinica (2009) 30: 965-972; doi: 10.1038/aps.2009.61.

The Raf-1 inhibitor GW5074 and dexamethasone suppress sidestream smoke-induced airway hyperresponsiveness in mice

BACKGROUND

Sidestream smoke is closely associated with airway inflammation and hyperreactivity. The present study was designed to investigate if the Raf-1 inhibitor GW5074 and the anti-inflammatory drug dexamethasone suppress airway hyperreactivity in a mouse model of sidestream smoke exposure.

METHODS

Mice were repeatedly exposed to smoke from four cigarettes each day for four weeks. After the first week of the smoke exposure, the mice received either dexamethasone intraperitoneally every other day or GW5074 intraperitoneally every day for three weeks. The tone of the tracheal ring segments was recorded with a myograph system and concentration-response curves were obtained by cumulative administration of agonists. Histopathology was examined by light microscopy.

RESULTS

Four weeks of exposure to cigarette smoke significantly increased the mouse airway contractile response to carbachol, endothelin-1 and potassium. Intraperitoneal administration of GW5074 or dexamethasone significantly suppressed the enhanced airway contractile responses, while airway epithelium-dependent relaxation was not affected. In addition, the smoke-induced infiltration of inflammatory cells and mucous gland hypertrophy were attenuated by the administration of GW5074 or dexamethasone.

CONCLUSION

Sidestream smoke induces airway contractile hyperresponsiveness. Inhibition of Raf-1 activity and airway inflammation suppresses smoking-associated airway hyperresponsiveness.

Lipid-soluble smoke particles upregulate vascular smooth muscle ETB receptors via activation of mitogen-activating protein kinases and NF-kappaB pathways

Cigarette smoke is a strong risk factor for cardiovascular disease. However, the underlying molecular mechanisms that lead to cigarette smoke-associated cardiovascular disease remain elusive. With functional and molecular methods, we demonstrate for the first time that lipid-soluble cigarette smoke particles (dimethylsulfoxide-soluble cigarette smoke particles; DSP) increased the expression of endothelin type B (ET(B)) receptors in arterial smooth muscle cells. The increased ET(B) receptors in arterial smooth muscle cells was documented as enhanced contractility (sensitive myograph technique), elevated levels of ET(B) receptor mRNA (quantitative real-time PCR), and protein expressions (immunohistochemistry and Western blotting). Intracellular signaling was studied with Western blotting and phosphoELISA; this revealed that DSP induced extracellular-regulated protein kinases 1 and 2 (ERK1/2), p38, and nuclear factor-kappaB (NF-kappaB) phosphorylation within 3 h. Blocking ERK1/2, p38, or NF-kappaB activation by their specific inhibitors significantly attenuated the DSP-induced upregulation of ET(B) receptor-mediated contraction and both ET(B) receptor mRNA and protein expression. In addition, dexamethasone abolished the DSP-induced upregulation of ET(B) receptor-mediated contraction. In conclusion, upregulation of ET(B) receptors by DSP in arterial smooth muscle cells involves activation of mitogen-activating protein kinases (ERK1/2 and p38) and the downstream transcriptional factor NF-kappaB pathways.

c-Src tyrosine kinase, a critical component for 5-HT2A receptor-mediated contraction in rat aorta

Serotonin (5-hydroxytryptamine, 5-HT) receptors (5-HTRs) play critical roles in brain and cardiovascular functions. In the vasculature, 5-HT induces potent vasoconstrictions, which in aorta are mainly mediated by activation of the 5-HT(2A)R subtype. We previously proposed that one signalling mechanism of 5-HT-induced vasoconstriction could be c-Src, a member of the Src tyrosine kinase family. We now provide evidence for a central role of c-Src in 5-HT(2A)R-mediated contraction. Inhibition of Src kinase activity with 10 mum 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) prior to contraction resulted in approximately 90-99% inhibition of contractions induced by 5-HT or by alpha-methyl-5-HT (5-HT(2)R agonist). In contrast, PP2 pretreatment only partly inhibited contractions induced by angiotensin II and the thromboxane A(2) mimetic, U46619, and had no significant action on phenylephrine-induced contractions. 5-Hydroxytryptamine increased Src kinase activity and PP2-sensitive tyrosine-phosphorylated proteins. As expected for c-Src identity, PP2 pretreatment inhibited 5-HT-induced contraction with an IC(50) of approximately 1 mum. Ketanserin (10 nm), a 5-HT(2A) antagonist, but not antagonists of 5-HT(2B)R (100 nm SB204741) or 5-HT(2C)R (20 nm RS102221), prevented 5-HT-induced contractions, mimicking PP2 and implicating 5-HT(2A)R as the major receptor subtype coupled to c-Src. In HEK 293T cells, c-Src and 5-HT(2A)R were reciprocally co-immunoprecipitated and co-localized at the cell periphery. Finally, 5-HT-induced Src activity was unaffected by inhibition of Rho kinase, supporting a role of c-Src upstream of Rho kinase. Together, the results highlight c-Src activation as one of the early and pivotal mechanisms in 5-HT(2A)R contractile signalling in aorta.

Heat stress alters G-protein coupled receptor-mediated function and endothelium-dependent relaxation in rat mesenteric artery

Heat stress has been demonstrated to have strong cardiovascular effects. However, the underlying mechanism-mediated cardiovascular effects are still not fully understood. The present study was designed to examine if heat stress alters vascular G-protein coupled receptor-mediated vasomotion and endothelium function in rat mesenteric artery. Rats were divided into two groups, heat stress rats and control. The G-protein coupled receptors of endothelin type B (ETB) receptor-, endothelin type A (ETA) receptor-, 5-hydroxytryptamine (5-HT) receptor-, calcitonin gene-related peptide (CGRP) receptor-, alpha-adrenoceptor-mediated vosoactivity and endothelium-dependent relaxation on rat mesenteric artery ring segments were monitored by a myograph system. The plasma level of CGRP was determined by radioimmunological assay. Compared with control arterial segments, the contractile response curves of sarafotoxin 6c, a selective ETB receptor agonist and 5-HT in the arterial segments from heat stress rats were shifted towards left. An increased maximum contraction (Emax) induced by sarafotoxin 6c, but not 5-HT, was seen in the arterial segments from heat stress rats. CGRP-induced relaxation in endothelium-denuded arterial segments from heat stress rats was enhanced. The relaxation in endothelium-intact arterial segments induced by acetylcholine was significantly decreased in heat stress rats. In addition, the plasma concentration of CGRP was increased in heat stress rats. The endothelium-dependent relaxation was characterized and shown there was a decrease in nitric oxide and endothelium-derived hyperpolarizing factor-mediated relaxation in the arterial segments from heat stress rats. In conclusion, heat stress induces an enhanced vascular endothelin ETB-, 5-HT-receptors-mediated contraction, an enhanced CGRP-receptor-induced relaxation and damage to endothelium-dependent relaxation.