LPS from Porphyromonas gingivalis increases the sensitivity of contractile response mediated by endothelin-B (ET(B)) receptors in cultured endothelium-intact rat coronary arteries

The purpose of our study was to examine if lipopolysaccharide (LPS) from Porphyromonas gingivalis (P.g.) modifies the vasomotor responses to Endothelin-1 (ET-1) and Sarafotoxin 6c (S6c) in rat coronary arteries. The arteries were studied directly or following organ culture for 24 h in absence and presence of 2.5EU/ml LPS. The contractile responses of coronary arteries were investigated by using the selective ETB receptor agonist S6c (1 pM-0.3 μM) and ET-1 (1 pM-0.3 μM). The functional studies demonstrated an augmented contractile response only to S6c in isolated rat coronary arteries after organ culture (with or without LPS). These contractile responses by S6c were blocked by the selective ETB receptor antagonist BQ788 in both vessel groups. The augmented contractile response to S6c was supported by immunohistochemistry, where a significant increase in fluorescence intensity for ETB receptors in smooth muscle cells was observed after organ culture. The presence of LPS in the culture medium significantly increased the sensitivity of endothelium-intact coronary artery to S6c as compared to endothelium-denuded segments. Our results showed a significant increase in both ETB receptor protein levels and S6c-induced maximal contraction in coronary arteries upon 24 h of organ culture, which was further sensitized by LPS.     

Importance of ERK1/2 in upregulation of endothelin type B receptors in cerebral arteries

This study examines the importance of mitogen-activated protein kinases (MAPKs) in upregulation of endothelin type B (ETB) receptors. Rat middle cerebral arteries (MCAs) were incubated for 24 h with or without kinase inhibitors. Vessel segments were mounted in myographs and the contractile responses to endothelin-1 (ET-1; ETA and ETB receptor agonist) and sarafotoxin 6c (S6c; ETB receptor agonist) were studied. We used real-time PCR to measure the receptor mRNA levels. An ELISA assay showed the activation of ERK1/2 kinases after 3 h. Immunohistochemistry revealed the presence of ETB receptors on the vessels. After organ culture, S6c induced vasoconstriction. Incubation with the MEK/ERK inhibitors U0126 and SB386023 diminished the contractile response to S6c. The p38 MAPK inhibitor SB239063 did not affect the S6c-induced contraction. The ET-1-induced vasoconstriction was increased after incubation with SB386023 or SB239063, while unaffected by U0126. The ETB receptor mRNA levels were diminished by SB386023 and U0126. The ETA receptor mRNA levels were unaffected. The levels of activated ERK1/2 kinases were significantly higher after 3 h of organ culture as compared to fresh vessels. The level of ETB receptor protein on the smooth muscle cells of the MCA, visualised by immunohistochemistry, was somewhat diminished by SB386023. Our results show that the ERK1/2 MAPK is important in the upregulation of contractile ETB receptors in MCA after organ culture. Since there is a similar upregulation in models of focal ischaemia and subarachnoid haemorrhage, this may be an important pathophysiological event.     

ERK1/2通路参与大鼠肠系膜动脉平滑肌细胞ETB受体上调表达

目的探讨细胞外信号调节激酶1/2(ERK1/2)信号转导通路在血管平滑肌细胞内皮素-1 B型受体(ET_B)上调中的作用。方法用大鼠肠系膜上动脉离体培养模型，以敏感的离体小血管张力描记技术记录血管张力变化，实时PCR定量ET_B受体mRNA，PhosphoELISA法测定细胞内磷酸化的ERK1/2蛋白水平。结果大鼠肠系膜上动脉培养3 h，细胞内ERK1/2蛋白磷酸化水平明显增高，培养24 h ET_B受体mRNA表达水平显著上调，选择性ET_B受体激动剂蛇毒类似物(sarafotoxin 6c，S6c)引起的收缩增强；与特异性ERK1/2通路阻滞剂SB386023共同孵育24 h，S6c引起的最大收缩E_max明显下降，ET_B受体mRNA水平也显著降低。结论ERK1/2信号转导通路参与大鼠肠系膜上动脉离体平滑肌细胞ET_B受体上调过程。     

Effects of synthetic analogues of poly-APS on contractile response of porcine coronary arteries

APS12-2 and APS3 are synthetic analogues of polymeric alkylpyridinium salts (poly-APS) isolated from the marine sponge Reniera sarai. The aim of the present study was to determine the possible direct contractile effects of these two synthetic molecules on coronary arteries, in order partly to explain hemodynamic and cardiotoxic effects of APS12-2 previously observed in in vivo studies and to reveal possible adverse effects on the organism in the case of their clinical use. In contrast to APS3, APS12-2 caused a concentration-dependent vascular smooth muscle contraction of isolated porcine coronary ring preparations in a concentration-range from 1.36 to 13.60 μM. Lanthanum chloride (5 mM) and verapamil (10 μM) completely abolished the APS12-2 evoked contraction of the coronary rings. Pre-incubation with indomethacin (10 μM) had no effect on the contractile responses of coronary ring preparations. These results indicate that APS12-2 contracts vascular smooth muscle in a concentration-dependent manner, due to an increase of Ca²⁺ influx through the voltage-gated Ca²⁺ channels. Our data show for the first time that APS12-2 induces concentration-dependent contraction of coronary ring preparations, which may contribute to the cardiotoxic effects of APS12-2, in addition to hyperkalemia.     

Big ET-1 processing into vasoactive peptides in arteries and veins

The endothelin (ET) peptides are more potent in contracting veins than arteries. The precursor big ET-1 is metabolized by endothelin converting enzyme [ECE; to ET-1 (1–21)], matrix metalloproteases [MMPs; to ET-1 (1–32)] and chymase [to ET-1(1–31)]. We hypothesized that arteries and veins were differently dependent in conversion of big ET-1 to vasoconstrictors. Immunohistochemical, western, zymographic and isometric contractile assays in rat aorta and vena cava were used. Big ET-1 contracted aorta [60 ± 17% phenylephrine contraction] but was more efficacious in vena cava [478 ± 61% norepinephrine contraction]. ECE and its product ET-1(1–21) were detected in aorta and vena cava, and the ECE inhibitors phosphoramidon and CGS-26393 reduced big ET-1-induced contraction. ET-1 (1–32) contracted aorta and vena cava but inhibition of MMPs with minocycline or GM6001 did not reduce big ET-1-induced contraction; zymography confirmed active tissue MMPs. Aorta and vena cava contracted to the product of chymase, ET-1 (1–31). Chymase was detected in aorta and only weakly in vena cava. Inhibition of chymase (chymostatin, 100 μM) reduced arterial (19% control) but not venous constriction to big ET-1. These results suggest at least one potential significant difference — the role of chymase — in in vitro enzymatic processing of big ET-1 in arteries and veins.     

Preventive effects of interleukin-6 in lipopolysaccharide/d-galactosamine induced acute liver injury via regulating inflammatory response in hepatic macrophages

Lipopolysaccharide/d-Galactosamine (LPS/d-Gal)-induced acute liver injury is characterized by significant inflammatory responses including TNF-α and interleukin-6 (IL-6) and is a widely applied experimental model for inflammation research. TNF-α is critical in the progression of LPS/d-Gal-induced liver injury. However, the role of IL-6 in this model is still unknown. In the present study, we aim to elucidate the involvement of IL-6 in the pathogenesis of acute liver injury induced by LPS/d-Gal in mice and its underlying mechanism. To induce acute liver injury, LPS (50 μg/kg body weight) and d-Gal (400 mg/kg body weight) were injected intraperitoneally in the C57BL/6 mice. The vehicle (saline) or a single dose of recombinant IL-6 (200 μg/kg body weight) was administered 2 h prior to LPS/d-Gal injection. Mice were sacrificed 2 h and 6 h after LPS/d-Gal injection. The results indicated that IL-6 treatment could protect mice from LPS/d-Gal-induced tissue damage, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) elevation, as well as hepatocyte apoptosis and inflammation. Furthermore, in vitro study showed that IL-6 treatment could significantly suppress LPS-triggered expression of proinflammatory cytokines and chemokines, TNF-α, RANTES and MCP-1 in macrophages while promoting the expression of M2 markers, such as Arg-1 and Mrc-1 in macrophages. Taken together, these findings revealed a novel and unexpected role of IL-6 in ameliorating LPS/d-Gal-induced acute liver injury via regulating inflammatory responses in hepatic macrophages.     

Increase in caveolae and caveolin-1 expression modulates agonist-induced contraction and store- and receptor-operated Ca2 + entry in pulmonary arteries of pulmonary hypertensive rats

Caveolin-1 (Cav-1) is a major component protein associated with caveolae in the plasma membrane and has been identified as a regulator of store-operated Ca^2 + entry (SOCE) and receptor-operated Ca^2 + entry (ROCE). However, the contributions of caveolae/Cav-1 of pulmonary arterial smooth muscle cells (PASMCs) to the altered Ca^2 + signaling pathways in pulmonary arteries (PAs) during pulmonary hypertension (PH) have not been fully characterized. The present study quantified caveolae number and Cav-1 expression, and determined the effects of caveolae disruption on ET-1, cyclopiazonic acid (CPA) and 1-Oleoyl-2-acetyl-glycerol (OAG)-induced contraction in PAs and Ca^2 + influx in PASMCs of chronic hypoxia (CH)- and monocrotaline (MCT)-induced PH rats. We found that the number of caveolae, and the Cav-1 mRNA and protein levels were increased significantly in PASMCs in both PH models. Disruption of caveolae by cholesterol depletion with methyl-β-cyclodextrin (MβCD) significantly inhibited the contractile response to ET-1, CPA and OAG in PAs of control rats. ET-1, SOCE and ROCE-mediated contractile responses were enhanced, and their susceptibility to MβCD suppression was potentiated in the two PH models. MβCD-induced inhibition was reversed by cholesterol repletion. Introduction of Cav-1 scaffolding domain peptide to mimic Cav-1 upregulation caused significant increase in CPA- and OAG-induced Ca^2 + entry in PASMCs of control, CH and MCT-treated groups. Our results suggest that the increase in caveolae and Cav-1 expression in PH contributes to the enhanced agonist-induced contraction of PA via modulation of SOCE and ROCE; and targeting caveolae/Cav-1 in PASMCs may provide a novel therapeutic strategy for the treatment of PH.     

Human urotensin II in internal mammary and radial arteries of patients undergoing coronary surgery

AimsInternal mammary (IMA) and radial artery (RA) have different incidence of vasospasm and long-term patency rates in arterial grafting. We compared the vasoreactivity of human urotensin II (hU-II) and its receptor with mechanism investigations in IMA and RA.MethodsIMA and RA taken from patients undergoing coronary bypass surgery were studied in organ baths. Urotensin receptor expression was determined by RT-PCR.ResultshU-II contracted IMA with pD₂ of 8.57 ± 0.41 and 45.4 ± 9.1% E_max of contraction to 100 mM KCl, whereas caused less contractile responses in RA (pD₂:8.30 ± 0.79, E_max:20.4 ± 4.8%, p < 0.05). Nifedipine inhibited hU-II-contraction in IMA. In U₄₆₆₁₉-precontraction, hU-II elicited comparable relaxation in IMA (pD₂:8.39 ± 0.43, E_max:56.1 ± 4.0%) and RA (pD₂:9.03 ± 0.46, E_max:65.2 ± 7.1%). The relaxation was abolished by endothelium denudation and by indomethacin, oxadiazoloquinoxalinone or N^ω-nitro-l-arginine, oxyhemoglobin, and Ca²⁺-activated K⁺ channel (K_Ca) blockers. Urotensin receptor mRNA was detected in both arteries.ConclusionshU-II is an important spasmogen in arterial grafts with receptors expressed in IMA and RA. hU-II elicits stronger contraction in IMA than in RA and a moderate endothelium-dependent relaxation attributable to nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor with involvement of K_Ca activation. The relaxant response of endothelium-intact IMA and RA to hU-II demonstrates the importance of preservation of endothelium in these grafts.     

Influence of specific endothelin-1 receptor blockers on hemodynamic parameters and antioxidant status of plasma in LPS-induced endotoxemia

BackgroundThe potent vasoconstrictor endothelin-1 has been implicated in the pathogenesis of plasma oxidative stress seen in sepsis. The selective endothelin receptor blockers BQ123 andBQ788 were used to investigate the importance of selective endothelin receptor blockage in modulating oxidative stress during endotoxemia.MethodsThe study was performed on male Wistar rats (n = 6 per group) divided into groups: (1) saline, (2) lipopolysaccharide (LPS) (15 mg\kg)-saline, (3) BQ123 (0.5 mg\kg)-LPS, (4) BQ123 (1 mg\kg)-LPS, (5) BQ788 (3 mg\kg)-LPS. The endothelin receptor type A (ETA-R) or type B (ETB-R) antagonist was injected intravenously 30 min before LPS administration. Blood pressure was monitored and blood was taken before, 90 min and 300 min after saline or LPS administration.ResultsInjection of LPS alone resulted in a decrease in mean arterial pressure (MAP) (p < 0.05), a decrease in ferric reducing ability of plasma (FRAP) value (p < 0.01) and a marked increase in plasma tumor necrosis factor α (TNF-α) and thiobarbituric acid reactive substances (TBARS) (p < 0.001, p < 0.001, respectively). Administration of BQ123 before LPS administration deteriorated MAP in a dose dependent way. Moreover, BQ123 (1 mg\kg) decreased plasma level of TBARS and TNF-α (p < 0.01 and p < 0.05, respectively) and increased FRAP value (p < 0.001). On the contrary, BQ788 prevented LPS-induced decrease in MAP (p < 0.001) and led to a significant reduction in plasma TBARS concentration (p < 0.01).ConclusionOur study showed that blockage of ETB-R during endotoxemia improved blood hemodynamics and decreased plasma lipid peroxidation. Blockage of ETA-R improved plasma antioxidant status and decreased lipid peroxidation and TNF-a production, but it deteriorated hemodynamic conditions.     

Impact of type 2 diabetes on vascular reactivity to cGMP generators in human internal thoracic arteries

ObjectiveThe balance between nitric oxide (NO)-sensitive and -insensitive forms of soluble guanylate cyclase (sGC) has been demonstrated to be disrupted in certain lifestyle-related diseases. However, it remains unclear whether type 2 diabetes results in a shift of sGC to the NO-insensitive form. This study addressed this issue in the human blood vessel.MethodsInternal thoracic arteries were obtained from patients undergoing coronary artery bypass grafting. Helically cut strips of the arteries were suspended in organ chambers, and relaxant responses to nitroglycerin (NO-sensitive sGC stimulant) and BAY 60-2770 (NO-insensitive sGC stimulant) were assessed.ResultsThe patients were divided into two groups according to the presence of type 2 diabetes (HbA1c: 7.0 ± 0.3%) or its absence (HbA1c: 5.6 ± 0.1%). Nitroglycerin-induced relaxation was not different in the arteries obtained from type 2 diabetic and non-diabetic patients. In addition, the relaxant response to BAY 60-2770 in type 2 diabetics was comparable to that observed in non-diabetics. Although the patients enrolled often had vascular risk factors other than type 2 diabetes, the relaxant responses were still in the same range in a comparison based on the number of risk factors. However, in separate experiments, the relaxant response to nitroglycerin was attenuated by pre-incubation of the arteries with ODQ (sGC imbalance inducer), whereas the relaxant response to BAY-60-2770 was augmented.ConclusionsThese findings suggest that type 2 diabetes does not affect the balance between NO-sensitive and -insensitive sGC in human internal thoracic artery grafts.     

Some nonylphenol isomers show antiestrogenic potency in the MVLN cell assay

It has been shown that nonylphenol (NP) isomers vary in their estrogenic potency. These differences may be due to varieties in receptor affinity, receptor activation, or activation/deactivation of non-receptor mediated side paths of reporter gene translation. In the present study we investigated the underlying mechanism of the different estrogenic potency of seven nonylphenol isomers. An estrogen receptor binding assay was conducted with the human estrogen receptor alpha (hERα). Additionally we co-incubated the nonylphenol isomers with two concentrations of 17β-estradiol (E2) in the MVLN cell assay to measure the potency of the isomers to compete with E2. No significant differences were found between the nonylphenol isomer binding affinities for the hERα. The IC₅₀ were in the range of 2.1–8.1 × 10⁻⁶ M and the binding affinity relative to estradiol (set to 1) were between 2.6 and 6.7 × 10⁻³. Only two test items (p353-NP and p-NP) were able to increase the estrogenic response of 100 pM estradiol. The response of the other isomers co-incubated with 100 pM E2 showed varying degrees of inhibition of the response in the MVLN reporter gene assay. Thus, it appears that all isomers bind to the ER but some are partial agonists while others are antagonists in the MVLN reporter gene assay.     

Influence of NADPH oxidase inhibition on oxidative stress parameters in rat hearts

BackgroundThe aim of this study was to assess whether apocynin, an nicotinamide adenine dinucleotide phosphate (NADPH) oxidase blocker, influences lipid peroxidation TBARS, hydrogen peroxide (H₂O₂) content, protein level, heart edema, tumor necrosis factor a (TNF-α) concentration or the glutathione redox system in heart homogenates obtained from endothelin 1 (ET-1)-induced oxidative stress rats.MethodsExperiments were carried out on adult male Wistar-Kyoto rats. The animals were divided into 4 groups: Group I: saline-treated control; Group II: saline followed by ET-1 (3 μg/kg b.w., iv); Group III: apocynin (5 mg/kg b.w., iv) administered half an hour before saline; Group IV: apocynin (5 mg/kg b.w., iv) administered half an hour before ET-1 (3 μg/kg b.w., iv).ResultsInjection of ET-1 alone showed a significant (p < 0.001) increase in thiobarbituric acid reactive substances (TBARS) and the hydrogen peroxide level (p < 0.01) vs. control, as well as a decrease (p < 0.001) in the GSH level. Apocynin significantly decreased TBARS (p < 0.001) and H₂O₂ (p < 0.05) level (vs. control) as well as improved protein level (p < 0.001) in the heart. Apocynin also prevented ET-1-induced heart edema (p < 0.05). The presence of ET-1 increased the concentration of TNF-α (p < 0.05) while apocynin decreased it (p < 0.05). Our results indicate that ET-1 may induce oxidative stress in heart tissue by reducing the GSH/GSSG ratio, stimulating lipid peroxidation and increasing TNF-α concentration. Apocynin diminished these measures of oxidative stress and TNF-α.ConclusionET-1-induced formation of ROS in the heart is at least partially regulated via NADPH oxidase.     

Alterations in acetylcholine,PGE2 and IL6 release from urothelial cells following treatment with pyocyanin and lipopolysaccharide

The effects of pseudomonal virulence factor pyocyanin, and LPS from Pseudomonas aeruginosa and Escherichia coli on urothelial mediator release and cytokine production were examined. RT4 urothelial cells were treated with pyocyanin (1–100 μM) or LPS (1–100 ng/mL) for 24-h. Effects were measured in terms of changes in cell viability, basal and stretch-induced acetylcholine (Ach) and PGE₂ release, and inflammatory cytokines (IL-6 and IL-12) production. Twenty-four hour pyocyanin (100 μM) treatment significantly decreased urothelial cell viability, while stretch-induced Ach release response was inhibited. E. coli LPS (100 ng/mL) produced a similar response with an additional significant increase in basal Ach release. All three virulence factors significantly increased urothelial PGE₂ release; under basal release for pyocyanin (100 μM), stretch-induced release for pseudomonal LPS (?10 ng/mL) and both basal and stimulated release for E. coli LPS (?10 ng/mL). IL-6 and IL-12 were not detected in control samples, however 24 h treatment with pyocyanin (100 μM) or LPS (100 ng/mL) resulted in IL-6 release from urothelial cells. The changes in urothelial Ach and PGE₂, and release of inflammatory cytokine IL-6 induced by exposure to the bacterial virulence factors may play a role in the symptoms of pain and urinary urgency experienced with urinary tract infections.     

Further preliminary assessment of three human glioma cell lines as models of human astrocytic toxicity in vitro

Three human astroglioma lines U251-MG, U373-MG and CCF-STTG1 have been evaluated further as possible models for astrocytotoxicity (GFAP and IL-6 release). The effects of bacterial lipopolysaccharide, chloroquine diphosphate and acrylamide were studied on GFAP expression and LPS, chloroquine diphosphate, ethanol, trimethyltin chloride (TMTC) and acrylamide were examined on interleukin-6 (IL-6) release in the U373-MG line only. At 4-h LPS elevated GFAP (17.0 ± 5.0% P < 0.05) above control in the U251-MG cell line only. Chloroquine diphosphate over 4 h in the U251-MG line resulted in an increase in GFAP-IR to 20.3 ± 4.2% and 21.1 ± 4.1% above control levels 0.1 μM (P < 0.05) and 1 μM (P < 0.05) respectively. CQD was associated with decreases in MTT turnover, particularly after 24 h incubation. With the U373-MG line, LPS (0.5 μg/ml) increased IL-6 expression 640% above control (P < 0.001), whilst chloroquine diphosphate (100 μM), ethanol (10 mM) and TMTC chloride (1 μM) also increased IL-6. It is possible that batteries of astrocytic human glioma cell lines may be applicable to the sensitive evaluation of toxicants on astrogliotic expression markers such as GFAP and IL-6.     

Comparison of endothelin B (ETB) receptors in rabbit isolated pulmonary artery and bronchus.

1. To explore potential differences between endothelin (ET) receptors in airway versus vascular smooth muscle from the same species, the ETB receptors mediating contractions produced by ET-1, ET-3 and the selective ETB ligands, sarafotoxin S6c (S6c) and BQ-3020, in rabbit bronchus and pulmonary artery were investigated by use of peptide and non-peptide ET receptor antagonists. 2. In rabbit pulmonary artery SB 209670 (10 microM), a mixed ETA/ETB receptor antagonist, was a more potent antagonist of contractions produced by S6c (pKB = 7.7; n = 9; P < 0.05), than those elicited by ET-1 (pKB = 6.7; n = 6) or ET-3 (pKB = 6.7; n = 5). BQ-788 (10 microM), an ETB receptor antagonist, inhibited responses produced by ET-3 (pKB = 5.1; n = 8), BQ-3020 (pKB = 5.2; n = 4) or S6c (pKB = 6.2; n = 9; P < 0.05 compared to potency versus ET-3- or BQ-3020-induced contractions), but was without inhibitory effect on ET-1-induced contractions (n = 5). RES-701 (10 microM), another selective ETB receptor antagonist, was without effect on contractions produced by S6c (n = 4) or ET-1 (n = 4), and potentiated ET-3- (n = 5) or BQ-3020-induced responses (n = 4). 3. The combination of BQ-788 (10 microM) and BQ-123 (10 microM), an ETA-selective receptor antagonist, antagonized contractions produced by lower concentrations of ET-1 (1 and 3 nM) in rabbit pulmonary artery, but was without effect on responses elicited by higher concentrations of ET-1 (n = 5). The combination of RES-701 (10 microM) and BQ-123 (10 microM) potentiated responses elicited by ET-1, producing a 3.7 fold shift to the left in the agonist concentration-response curve (n = 5). 4. In rabbit bronchus SB 209670 (3 microM) had similar potency for antagonism of contractions produced by ET-1 (pKB = 6.3; n = 6), ET-3 (pKB = 6.5; n = 6) or S6c (pKB = 6.1; n = 8). BQ-788 (3 microM) was without effect on responses elicited by ET-1, ET-3 or S6c (n = 6) but antagonized BQ-3020-induced contractions (pKB = 6.4; n = 4). RES-701 (3 microM) was without effect on contractions produced by S6c (n = 6) or BQ-3020 (n = 4), and potentiated rather than antagonized ET-1- or ET-3-induced responses (n = 6), reflected by a significant (about 6 fold) shift to the left in ET-1 or ET-3 concentration-response curves. The combination of BQ-788 (3 microM) and BQ-123 (3 microM) was without effect on contractions produced by ET-1 in rabbit bronchus (n = 6). The combination of RES-701 (3 microM) and BQ-123 (3 microM) potentiated responses elicited by ET-1, producing a 5.2 fold shift to the left in the agonist concentration-response curve (n = 5). 5. BQ-123 (3 or 10 microM), an ETA-selective receptor antagonist, was without effect on ET-1, ET-3 or S6c concentration-response curves (n = 3-6) in rabbit pulmonary artery or rabbit bronchus. 6. These data indicate that contractions induced by ET-1, ET-3, S6c and BQ-3020 in rabbit pulmonary artery or rabbit bronchus appear to be mediated predominantly via stimulation of ETB receptors. However, the qualitative and quantitative differences in the relative profiles of the various structurally diverse peptide and non-peptide antagonists examined suggests that responses produced by the ET ligands may not be mediated by a homogeneous ETB receptor population. In addition, the results suggest that differences exist in the ETB receptors mediating contraction in pulmonary vascular versus airway tissues in the same species. These receptors are not very sensitive to the standard ETB receptor antagonists, BQ-788 and RES-701. Furthermore, the results also provide further evidence that the potencies of ET receptor antagonists depend upon the ET agonist.     

Different endothelin receptors involved in endothelin-1- and sarafotoxin S6B-induced contractions of the human isolated coronary artery.

1. Endothelin receptors, that mediate contraction of the human isolated coronary artery, were characterized by use of a number of agonists and antagonists. Contraction induced by the non-selective agonists, endothelin (ET)-1 and sarafotoxin S6b, was compared in endothelium-intact and endothelium-denuded ring segments. The effects of ET-1 and BQ-123 (an ETA receptor antagonist) were investigated both in ring segments and in spirally cut strips. Lastly, the effect of phosphoramidon was studied on contraction induced by big-ET-1. 2. The order of agonist potency (pD2) in endothelium-intact coronary artery ring segments was: ET-1 (8.27) approximately sarafotoxin S6b (8.16) > big-ET-1 (< 7.1) approximately ET-3 (< 6.9). [Ala1,3,11,15]ET-1 (ETB receptor agonist) caused significant contraction only at 1 microM, whereas 0.3 microM big-ET-3 had no effect. Removal of the endothelium in ring segments did not affect the contractile response to ET-1 or to sarafotoxin S6b. 3. After a full concentration-response curve had been obtained to ET-1 or sarafotoxin S6b, further contractions of the endothelium-intact coronary artery segments could only be achieved by applying ET-1 in segments exposed to sarafotoxin S6b, and not the reverse. 4. BQ-123 (0.1 microM) antagonized contractions of endothelium-intact ring segments induced by sarafotoxin S6b (pKB 7.86). Only 10 microM BQ-123 antagonized contractions induced by ET-1 (pKB 5.75). FR139317 was also more potent against sarafotoxin S6b (pKB 8.24-8.47) than against ET-1 (pKB 6.11). [Ala1,3,11,15]ET-1 (1 microM) had no effect on the contractile response to ET-1 or to sarafotoxin S6b.(ABSTRACT TRUNCATED AT 250 WORDS)     

EndothelinB receptor-mediated contraction in human pulmonary resistance arteries.

1. Using wire myography, we have examined the endothelin (ET) receptor subtypes mediating vasoconstriction to ET peptides in human pulmonary resistance arteries (150-200 microns, i.d.). 2. Cumulative concentration-response curves to ET-1, sarafotoxin 6c (SX6c) and ET-3 were constructed in the presence and absence of the selective antagonists FR 139317 (ETA-selective), BMS 182874 (ETA-selective) and BQ-788 (ETB-selective). 3. All agonists induced concentration-dependent contractions. However, the response curves to ET-1 were biphasic in nature. The first component demonstrated a shallow slope up to 1 nM ET-1. Above 1 nM ET-1 the response curve was markedly steeper. Maximum responses to ET-3 and SX6c were the same as those to 1 nM ET-1 and 30% of those to 0.1 microM ET-1. The order of potency, taking 0.3 microM as a maximum concentration was SX6c >> ET-3 > ET-1 (pEC50 values of: 10.75 +/- 0.27, 9.05 +/- 0.19, 8.32 +/- 0.08 respectively). Taking 1 nM ET-1 as a maximum, the EC50 for ET-1 was 10.08 +/- 0.13 and therefore ET-1 was equipotent to ET-3 and SX6c over the first component of the response curve. 4. Responses to ET-1 up to 1 nM were resistant to the effects of the ETA receptor antagonists, FR 139317 and BMS 182874 but were inhibited by the ETB receptor antagonist, BQ-788. Conversely, responses to ET-1 over 1 nM were inhibited by the ETA receptor antagonists, FR 139317 and BMS 182874 but unaffected by the ETB receptor antagonist, BQ-788. 5. The results suggest that at concentrations up to 1 nM, responses to ET-1 are mediated via the ETB receptor, whilst the responses to higher concentrations are mediated by ETA receptors.     

Propargylglycine aggravates liver damage in LPS-treated rats: Possible relation of nitrosative stress with the inhibition of H2S formation

BackgroundHydrogen sulfide (H₂S) is a naturally occurring gaseous transmitter, which may play important roles in normal physiology and disease. Here, we investigated the effect of endogenously formed H₂S in the endotoxemic organ injury.MethodsMale Wistar rats were subjected to acute endotoxemia [Escherichia coli lipopolysaccharide (LPS) 20 mg kg⁻¹, intraperitoneally (ip)]. A group of animals was injected d,l-propargylglycine (PAG, 50 mg kg⁻¹, ip), an inhibitor of the H₂S-synthesizing enzyme cystathionine-γ-lyase (CSE), 60 min before LPS administration. Six hours after the LPS treatment, animals were sacrificed. Myeloperoxidase (MPO), dimethylarginine dimethylaminohydrolase (DDAH) activities and levels of nitrotyrosine and GSH were measured in the liver. Asymmetric dimethylarginine (ADMA) and arginine levels in both liver and plasma were determined using HPLC.ResultsLPS injections caused liver injury, as evidenced by the activities of serum aspartate aminotransferase and arginase. After LPS injections, increased arginine content and arginine/ADMA ratio were observed in the liver, together with significant decrements in both DDAH activity and GSH levels. Despite the accumulation of ADMA in the plasma, its level remained unchanged in the liver. PAG pretreatment aggravated the LPS-induced increase in the activities of MPO and serum enzymes. The most profound effect of PAG pretreatment was observed in nitrotyrosine levels in the liver, which were increased significantly as compared with the control and LPS-injected groups.ConclusionThese findings support the view that the suppression of nitrosative stress by endogenous H₂S is one of the mechanisms to protect liver against endotoxemic injury.