Contraction Of Rat Thoracic Aorta Research Articles

Fenfluramine-induced PVAT-dependent contraction depends on norepinephrine and not serotonin

Perivascular adipose tissue (PVAT) modulates vascular tone and altered PVAT function is observed in vascular diseases such as hypertension and atherosclerosis. We discovered that the PVAT surrounding rat thoracic aorta (RA) and the superior mesenteric artery (SMA) contain significant amounts of 5-hydroxytryptamine (5-HT). We hypothesized that the 5-HT contained within the PVAT is functional and vasoactive. Isolated tissue baths were used for isometric contractility studies and high performance liquid chromatography was used to quantitatively measure amines in the PVAT and release studies. The 5-HT releaser fenfluramine (10 nM–100 μM) was tested for its ability to contract arteries with and without PVAT. Contraction was reported as a percentage of the initial contraction to 10 μM phenylephrine. The RA with PVAT contracted to fenfluramine to a greater maximum (98 ± 10%) than RA without PVAT (24 ± 4%), while no difference in contraction of SMA to maximum fenfluramine with (78 ± 2%) and without (75 ± 6%) PVAT was observed. Contradicting our hypothesis, the maximum contraction of RA with PVAT to fenfluramine was diminished by the alpha-1 adrenoreceptor antagonist prazosin (100 nM; vehicle: 71 ± 4%, prazosin: 24 ± 2%) and the norepinephrine transporter (NET) inhibitor nisoxetine (1 μM; vehicle: 71 ± 4%, nisoxetine: 25 ± 4%) but not the 5-HT2A/2C receptor antagonist ketanserin (10 nM) or serotonin specific reuptake inhibitor fluoxetine (10 μM). To test if fenfluramine caused release of 5-HT or NE from PVAT, PVAT from RA was incubated with vehicle or fenfluramine (10 μM–10 mM), and amines released into the incubating buffer were quantified. A pronounced concentration-dependent NE-release (more than 5-HT) was observed. Collectively, this research illustrates the pharmacology of fenfluramine to primarily stimulate NE release (better than 5-HT) in a NET-dependent manner, leading to vasoconstriction. This adds additional support to PVAT as being an important reservoir of amines.

The Role of Cyclooxygenase Enzymes in the Effects of Losartan and Lisinopril on the Contractions of Rat Thoracic Aorta.

It was suggested that prostaglandins which are synthesized by cyclooxygenase (COX) enzymes contribute to the actions of angiotensin-converting enzyme (ACE) inhibition and angiotensin AT1 receptor antagonism and there is an interaction between ACE signaling pathway and COX enzymes. We aim to investigate the role of COX enzymes in the effects of losartan, an angiotensin II (Ang II) receptor antagonist or lisinopril, an ACE inhibitor, on the contractions of rat thoracic aorta in isolated tissue bath. Responses of losartan (10-6, 10-5, 10-4 M), lisinopril (10-6, 10-5, 10-4 M), and non-selective COX inhibitor dipyrone (10-4, 7 × 10-4, 2 × 10-3 M) alone to the contractions induced by phenylephrine (Phe) (10-7 M), potassium chloride (KCl) (6 × 10-2 M), Ang II (10-8 M) and responses of losartan or lisinopril in combination with dipyrone to the contractions induced by Phe or KCl were recorded. When used alone, dipyrone and losartan inhibited Phe, KCl, and Ang II-induced contractions, whereas lisinopril inhibited only Phe and Ang II-induced contractions. Inhibition of COX enzymes (COX-3, COX-3 + COX-1, COX-1+ COX-2 + COX-3 by dipyrone 10-4, 7 × 10-4, 2 × 10-3 M, respectively) augmented the relaxant effects of losartan or lisinopril. Also, dipyrone potentiated the effect of lisinopril on KCl-induced contractions. We suggest that dipyrone increases the smooth-muscle relaxing effects of losartan or lisinopril and that COX enzyme inhibition may have a role in the enhancement of this relaxation.

Abstract 624: Resolvin E1 Inhibits Thromboxane-Induced Contraction of Rat Aorta and Human Pulmonary Artery

Thromboxane is a vasoactive omega-6-derived lipid implicated in hypertension. Omega-3 fatty acid derivatives including resolvin (Rv) E1 have important roles in the resolution of inflammation, but their ability to mediate vasomotor activity is unknown. We assessed whether RvE1 modulates contraction of rat thoracic aorta and human pulmonary artery (HPA) in vitro. Rats were culled by CO2 inhalation and cervical dislocation, and the thoracic aorta was removed. HPA were obtained with informed consent from lung tissue of surgical patients at Southampton General Hospital. Segments of aorta or HPA were incubated in DMEM-F12 with or without RvE1 (10 nM, 100 nM or 300 nM) for 1 or 24 hours, and then mounted on a wire myograph. Mounted segments were bathed at 37[[Unable to Display Character: ]]C in Kreb’s buffer, gassed (95%/5% O2/CO2) and set to 1.5 g of baseline tension. Functional integrity was confirmed by a contractile response to 125 mM KPSS. After washing to restore baseline tension, a cumulative concentration-response curve was defined to the stable thromboxane A2 mimetic U46619 (1 nM - 1 μM). Contractions are expressed as percent of KPSS response and differences determined by two-way ANOVA and by pairwise comparisons. In rat aorta, treatment with RvE1 (10 nM) significantly shifted the U46619 curve rightwards, increasing the EC50 value 13-fold from 0.13 μM to 1.75 μM after 1 hour (n=5), and 4-fold from 0.093 μM to 0.41 μM after 24 hours (n=5). In contrast, 300 nM RvE1 caused no significant change in EC50 (1 hour 0.11 μM; 24 hours 0.097 μM, n=5). In HPA segments, RvE1 (10 nM, 1 hour) increased the U46619 EC50 value 7-fold from 0.0079 μM to 0.054 μM (n=3), with a preliminary experiment suggesting a similar outcome after 24 hours. Higher concentrations of RvE1 had no significant effect, suggesting the relaxant action of RVE1 has a bell-shaped response curve. In preliminary experiments, RvE1 inhibited U-46619 contractions of bronchiolar airways from the same human donors. Resolvin E1 is known for its immunomodulatory actions on leukocytes and also inhibits U46619-induced aggregation of platelets, but our results are the first evidence that this pro-resolution mediator can also inhibit contractions of intact vasculature from rat and human lung induced by a thromboxane mimetic.

Effect of interleukin-1 on contractile function of rat thoracic aorta

Objective To investigate the effect of interleukin-1(IL-1) on contractile function of rat thoracic aorta. Methods Forty male Sprague-Dawley rats, weighing 250-300 g, were sacrificed to obtain the thoracic aortic rings. The experiment was performed in 2 parts. PartⅠ The thoracic aortic rings were divided into 2 segments and randomly divided into 2 groups (n=20 each): control group and IL-1 group. In IL-1 group, the thoracic aortic rings were incubated with Kreb solution containing 20 ng/ml IL-1 for 2 h, and contracted with cumulative concentrations of phenylephrine, ranging from 10-9 to 10-5 mol/L. In control group, the thoracic aortic rings were incubated with Kreb solution for 2 h, and contracted with cumulative concentrations of phenylephrine, ranging from 10-9 to 10-5 mol/L. Part Ⅱ The thoracic aortic rings were divided into 3 segments and randomly divided into 3 groups (n=20 each): IL-1 group, IL-1+ L-NAME (the NOS inhibitor) group and IL-1+ cyclooxygenase inhibitor indomethacin group (IL-1+ I group). The thoracic aortic rings were incubated with Kreb solution containing 20 ng/ml IL-1 for 1.5 h in the three groups. In addition, in IL-1+ L-NAME and IL-1+ I groups, the thoracic aortic rings were incubated for 30 min with Kreb solution containing 100 μmol/L L-NAME and 2.5 mmol/L indomethacin, respectively. Contraction of the thoracic aorta was then induced with cumulative concentrations of phenylephrine, ranging from 10-9 to 10-5 mol/L. In group IL-1, the thoracic aortic rings were incubated with Kreb solution. The maximum contractile tension of the thoracic aortic rings was recorded at each concentration of phenylephrine, and the percentage of the maximum contractile tension at the concentration of 10-6mol/L in group C was obtained. Results PartⅠ The percentage of contractile tension at phenylephrine 10-8, 10-7, 10-6 and 10-5mol/L was significantly decreased in IL-1 group as compared with C group. Part Ⅱ The percentage of contractile tension at phenylephrine 10-7, 10-6 and 10-5mol/L was significantly increased in IL-1+ L-NAME and IL-1+ I groups as compared with IL-1 group. Conclusion IL-1 can inhibit the contraction of rat thoracic aorta, and promoted production of NO and prostacyclin may be involved in the mechanism. Key words: Interleukin-1; Thoracic aorta; Nitric oxide; Prostacyclin

Photoreleasable ligands to study intracrine angiotensin II signalling.

The renin-angiotensin system plays a key role in cardiovascular physiology and its overactivation has been implicated in the pathogenesis of several major cardiovascular diseases. There is growing evidence that angiotensin II (Ang-II) may function as an intracellular peptide to activate intracellular/nuclear receptors and their downstream signalling effectors independently of cell surface receptors. Current methods used to study intracrine Ang-II signalling are limited to indirect approaches because of a lack of selective intracellularly-acting probes. Here, we present novel photoreleasable Ang-II analogues used to probe intracellular actions with spatial and temporal precision. The photorelease of intracellular Ang-II causes nuclear and cytosolic calcium mobilization and initiates the de novo synthesis of RNA in cardiac cells, demonstrating the application of the method. Several lines of evidence suggest that intracellular angiotensin II (Ang-II) contributes to the regulation of cardiac contractility, renal salt reabsorption, vascular tone and metabolism; however, work on intracrine Ang-II signalling has been limited to indirect approaches because of a lack of selective intracellularly-acting probes. Here, we aimed to synthesize and characterize cell-permeant Ang-II analogues that are inactive without uncaging, but release active Ang-II upon exposure to a flash of UV-light, and act as novel tools for use in the study of intracrine Ang-II physiology. We prepared three novel caged Ang-II analogues, [Tyr(DMNB)(4)]Ang-II, Ang-II-ODMNB and [Tyr(DMNB)(4)]Ang-II-ODMNB, based upon the incorporation of the photolabile moiety 4,5-dimethoxy-2-nitrobenzyl (DMNB). Compared to Ang-II, the caged Ang-II analogues showed 2-3 orders of magnitude reduced affinity toward both angiotensin type-1 (AT1R) and type-2 (AT2R) receptors in competition binding assays, and greatly-reduced potency in contraction assays of rat thoracic aorta. After receiving UV-irradiation, all three caged Ang-II analogues released Ang-II and potently induced the contraction of rat thoracic aorta. [Tyr(DMNB)(4)]Ang-II showed the most rapid photolysis upon UV-irradiation and was the focus of subsequent characterization. Whereas Ang-II and photolysed [Tyr(DMNB)(4)]Ang-II increased ERK1/2 phosphorylation (via AT1R) and cGMP production (AT2R), caged [Tyr(DMNB)(4)]Ang-II did not. Cellular uptake of [Tyr(DMNB)(4)]Ang-II was 4-fold greater than that of Ang-II and significantly greater than uptake driven by the positive-control HIV TAT(48-60) peptide. Intracellular photolysis of [Tyr(DMNB)(4)]Ang-II induced an increase in nucleoplasmic Ca(2+) ([Ca(2+)]n), and initiated 18S rRNA and nuclear factor kappa B mRNA synthesis in adult cardiac cells. We conclude that caged Ang-II analogues represent powerful new tools for use in the selective study of intracrine signalling via Ang-II.

Abstract P090: The Contractile Effect of Angiotensin II Type 1 Receptor Autoantibodies on Human Placental Vessels

Background: Decreased placental perfusion induced by abnormal placental vascular contraction is one of the pathological basis of preeclampsia. It has been reported that the sera titers of the autoantibody against the second extracellular loop of angiotensin II type 1 receptor (AT1-AA) were negatively correlated with placental blood flow in preeclampsia. Our previous study has found that AT1-AA could induce contraction of rat thoracic aorta and coronary rings by activing angiotensin II type 1 receptor (AT1R). However, there is no direct evidence for explaining whether AT1-AA might cause vasoconstriction on human placental blood vessels. Methods: The SD rats were immunized with the synthetic peptide corresponding to the sequence of the second extracellular loop of the human AT1 receptor (AT1R-EC II ), and anti-AT1R antibody (AT1R-Ab) was extracted. The expression of AT1R on human placental vessels was determined by immunohistochemistry. The effects of AT1R-Ab on placental vessels were measured with isolated vascular ring technique. Results: (1) AT1R was highly expressed in the human placental artery, vein and vascular endothelial cells. (2) AT1R-Ab (10 mmol/L) respectively enhanced the contraction of the placental arteries and veins (29.21% ± 3.7% vs . 21.35% ± 2.8%, P >0.05), which could be completely reversed when AT1R was blocked by AT1R inhibitor. (3) AT1R-Ab (0.1, 1 and 10 mmol/L) induced placental vasoconstriction of normal human. The percentage of maximal contraction was 2.73% ± 1.11%, 4.00% ± 3.2% and 33.30% ± 5.6%, respectively. There was significantly difference between the three groups for contraction amplitude induced by different concentrations of AT1R-Ab ( P <0.01). (4) AT1R-Ab (0.1, 1 and 10 mmol/L) induced placental vasoconstriction of preeclampsia. The percentage of maximal contraction was 1.74% ± 0.3%, 5.58% ± 1.41% and 3.73% ± 2.5%, respectively. There was significantly difference between the three groups for contraction amplitude induced by different concentrations of AT1R-Ab ( P <0.01). Conclusion: AT1R-Ab could induce human placental vasoconstriction in a concentration-dependent manner, which suggested that AT1-AA might be involved in the pathogenesis of preeclampsia by directly contracted placental blood vessles.

Comprehensive Study of Evodia rutaecarpa-induced Contraction on Blood Vascular in Vivo and in Vitro

Aim Evodiae Fructus (fruit of Evodia rutaecarpa), a blood vessel activator, has been used, with headache, migraine, shock etc., for a long history in Chinese medical practice. However, previous studies supported the vessel relaxation and the potential action on cardiac and cerebral blood circulation of vessel contraction. The present study was designed to explore it effects on contraction and the relative mechanism. Methods Evodiae Fructus was extracted by dialysis tubing (in diameter of 100 Dalton cutoff) and the effect of the evodia dialyzed (ED) (> 100 D) was studied in vivo and in vitro. Results ED could dose-dependently promote the micro-cerebral blood flow in mice and induced the contraction of rat thoracic aorta at rest and phenylephrine pre-evoked state. Compared with the vasocontraction under 50 mmol·L −1 KCl, 250 mg·L −1 ED increased by 113%. The effect was inhibited by a-adrenergic receptor blocker phentolamine, instead of β-adrenergic receptor blocker propranolol, M-adrenaline receptor blocker atropine, and angiotensin II receptor blocker losartan. The depletion of extracellular calcium decreased the contraction induced by ED and the addition of L-type calcium ion channel antagonist (nicardipine), calcium ion channel activator (BAY-K8644) and potassium ion channel opener (pinacidil) significantly affected the contraction induced by ED. Selected inhibitors were used to investigate the possible mechanism of ED-induced vasocontraction. Inhibitors of myosin light chain kinase (MLCK), Rho-kinase (ROK) and inositol 1, 4, 5-triphosphate (IP 3) receptor suppressed the effect of ED. Conclusion ED induced Ca 2+-dependent and Ca 2+-independent contraction, the Ca 2+ influx, a-adrenoceptor, ROK and IP 3 receptor signal pathways and MLCK activation might be involved in the contractile process. These results suggested that Evodiae Fructus could increase the blood vessel contraction by the effect on calcium channel on the membrane.

α1‐Adrenoceptor‐mediated contraction of rat aorta is partly mediated via transactivation of the epidermal growth factor receptor

High level of plasma catecholamines is a risk factor for vascular diseases such as hypertension and atherosclerosis. Catecholamines induce hypertrophy of vascular smooth muscle through α(1) -adrenoceptors, which in cell culture involves the transactivation of epidermal growth factor receptor (EGFR). We hypothesized that EGFR transactivation was also involved in contractions of rat aorta mediated by α(1) -adrenoceptors. Thoracic aorta was isolated from 12-14 week old male Wistar rats. In vitro aortic contractile responses to cumulative doses of phenylephrine were characterized in the absence and presence of the EGFR kinase inhibitors, AG1478 and DAPH, in intact and endothelium-denuded rings. Involvement of signal transduction pathways was investigated by using heparin and inhibitors of Src, matrix metalloproteinase (MMP), extracellular signal-regulated kinase (ERK)1/2 and phosphatidyl inositol 3-kinase (PI3K). Phosphorylation of EGFR and ERK1/2 was measured after short-term phenylephrine or EGF stimulation in aorta segments in the presence of AG1478 and the PI3K inhibitor, wortmannin. AG1478 and DAPH concentration dependently attenuated phenylephrine-induced contractile responses in intact or endothelium-denuded aortic rings. Inhibition of PI3K (wortmannin and LY294002) but not heparin or inhibitors of Src or MMP, prevented the effect of AG1478 on the responses to phenylephrine. Phenylephrine induced phosphorylation of EGFR, which was partially blocked by AG1478. Phenylephrine also increased phosphorylation of ERK1/2, time-dependently and was blocked by AG1478 and wortmannin. Contractions of rat thoracic aorta mediated by α(1) -adrenoceptors involved transactivation of EGFR, mediated via a PI3K and ERK1/2 dependent pathway.

Elucidating the Structure-Activity Relationships of the Vasorelaxation and Antioxidation Properties of Thionicotinic Acid Derivatives

Nicotinic acid, known as vitamin B3, is an effective lipid lowering drug and intense cutaneous vasodilator. This study reports the effect of 2-(1-adamantylthio)nicotinic acid (6) and its amide 7 and nitrile analog 8 on phenylephrine-induced contraction of rat thoracic aorta as well as antioxidative activity. It was found that the tested thionicotinic acid analogs 6-8 exerted maximal vasorelaxation in a dose-dependent manner, but their effects were less than acetylcholine (ACh)-induced nitric oxide (NO) vasorelaxation. The vasorelaxations were reduced, apparently, in both NG-nitro-L-arginine methyl ester (L-NAME) and indomethacin (INDO). Synergistic effects were observed in the presence of L-NAME plus INDO, leading to loss of vasorelaxation of both the ACh and the tested nicotinic acids. Complete loss of the vasorelaxation was noted under removal of endothelial cells. This infers that the vasorelaxations are mediated partially by endothelium-induced NO and prostacyclin. The thionicotinic acid analogs all exhibited antioxidant properties in both 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide dismutase (SOD) assays. Significantly, the thionicotinic acid 6 is the most potent vasorelaxant with ED50 of 21.3 nM and is the most potent antioxidant (as discerned from DPPH assay). Molecular modeling was also used to provide mechanistic insights into the vasorelaxant and antioxidative activities. The findings reveal that the thionicotinic acid analogs are a novel class of vasorelaxant and antioxidant compounds which have potential to be further developed as promising therapeutics.

Endothelin ETBReceptors in Arteries and Veins: Multiple Actions in the Vein

Endothelin receptors (ET(A) and ET(B)) mediate responses to ET-1. ET(B) receptor function seems to differ between a similarly sized arterial and venous pair, the rat vena cava (RVC) and rat thoracic aorta (RA). ET(B) receptors mediate RVC contraction directly, but it is unclear whether ET(B) receptors mediate contraction in RA. Because of these apparent differences in ET(B) receptor-mediated vascular contraction, we hypothesize that relaxant ET(B)-receptor mechanisms in RVC would be different from those in RA. RA and RVC rings were isolated from rats for measurement of isometric contraction. When contracted with prostaglandin F-2alpha (PGF-2alpha) (20 microM), the ET(B) receptor agonist sarafotoxin-6c (S6c) (100 nM) significantly relaxed RA and RVC. N(omega)-Nitro-L-arginine (LNNA) (100 microM) or endothelial denudation abolished relaxation to S6c in RA. By contrast, S6c-induced relaxation of RVC was attenuated but not abolished by LNNA and endothelial denudation. RVC (PGF-2alpha-contracted) relaxed to low concentrations of ET-1, whereas under the same conditions RA responded with contraction. ET-1-induced relaxation in RA was observed only with ET(A) receptor blockade. Vessels from dopamine-beta-hydroxylase-ET(B) transgenic rats, which lack functional ET(B) receptors in the vasculature, were also used. RVC (PGF-2alpha-contracted) from these rats did not relax to ET-1. Thus, although both RA and RVC possess endothelial relaxant ET(B) receptors, RA and RVC differ in that relaxant ET(B) receptors may also be present in smooth muscle of RVC. Moreover, the mechanisms of endothelial cell ET(B) receptor-mediated relaxation in RA and RVC are not the same.

Prolonged Cold Storage Diminishes the 5-Hydroxytryptamine- and Potassium Chloride-Mediated Contractions of Rat Thoracic Aorta

Hypothermic preservation of the organ for transplantation causes vascular damage; therefore, the preservation of vascular function is important for the organs to function correctly after transplantation. The aim of the present study is to evaluate the influence of prolonged cold storage (72 hours) on vascular responses to 5-hydroxytryptamine (5-HT) and potassium chloride (KCl), each of which causes receptor-dependent and receptor-independent contractions, respectively. We also examined the protective roles of superoxide dismutase (SOD), L-arginine, the precursor of nitric oxide, iloprost, a synthetic analogue of prostaglandin I(2) with vasodilator functions, or endothelium removal for vascular responses. Endothelium-intact rings were prepared from the rat thoracic aorta, and stored at 4 degrees C for up to 72 hours in Krebs solution alone or Krebs solution that contains SOD, L-arginine or iloprost. The vascular responses were investigated daily. The Analysis of Variance (ANOVA) followed by Dunn test was used for statistical analysis. Being kept in cold in Krebs solution diminished the vascular responses to 5-HT and KCl. The presence of SOD in Krebs solution successfully prevented the decline in these responses, while iloprost or L-arginine partially restored them. In the endothelium-denuded rings, the 5-HT-induced contraction remained protected after 72 hours, whereas the KCl-induced contraction was partially restored. These results indicate that cold preservation declines the 5-HT and KCl-induced vascular responses, which can be partially prevented by iloprost or L-arginine, and can be restored by endothelium removal or SOD. Therefore, superoxide anion and endothelium-derived factors contribute to the decline in the contracting function of the aorta during prolonged cold storage.

Vasorelaxant and Antioxidant Activities of Spilanthes acmella Murr.

This study reports the effect of Spilanthes acmella Murr. extracts on phenylephrine-induced contraction of rat thoracic aorta as well as their antioxidant activity. Results show that the extracts exert maximal vasorelaxations in a dose-dependent manner, but their effects are less than acetylcholine-induced nitric oxide (NO) vasorelaxation. Significant reduction of vasorelaxations is observed in both NG-nitro-l-arginine methyl ester (l-NAME) and indomethacin (INDO). In the presence of l-NAME plus INDO, synergistic effects are observed, leading to loss of vasorelaxation of both acetylcholine and the extracts. Similarly, the vasorelaxations of the extracts are completely abolished upon the removal of endothelial cells. This demonstrates that the extracts exhibit vasorelaxation via partially endothelium-induced NO and prostacyclin in a dose-dependent manner. Significantly, the ethyl acetate extract exerts immediate vasorelaxation (ED50 76.1 ng/mL) and is the most potent antioxidant (DPPH assay). The chloroform extract shows the highest vasorelaxation and antioxidation (SOD assay). These reveal a potential source of vasodilators and antioxidants.

Brazilein-induced contraction of rat arterial smooth muscle involves activation of Ca2+ entry and ROK, ERK pathways

Brazilein (6a,7-dihydro-3,6a,10-trihydroxy-benz[b]indeno[1,2-d]pyran-9(6H)-one) is a compound isolated from Caesalpinia sappan. The vasoactivities of brazilein were evaluated in isolated rat thoracic aorta. The results showed that brazilein can dose-dependently induce contraction of rat thoracic aorta in the resting and phenylephrine pre-evoked state. The average response to 100 μM of brazilein was 30% of the 50 mM KCl contraction, 26% of the 10 μM phenylephrine and 116% of the 20 mM caffeine contraction in comparison. The effects of vasocontraction were proved not to be endothelial dependent and could not be inhibited by α-adrenergic receptor blocker phentolamine, β-adrenergic receptor blocker propranolol, M-adrenaline receptor blocker atropine, angiotensin II receptor blocker losartan or the non-selective nitric oxide synthase (NOS) inhibitor NG-Nitro-l-Arginine Methyl Ester (l-NAME). However the influx of extracellular calcium seemed to be required for this action, because depletion of extracellular calcium and the addition of L-type calcium ion channel antagonist (nimodipine and diltiazem), calcium ion channel activator (BAY-K8644) and potassium ion channel opener (pinacidil) could significantly affect the contraction induced by brazilein. We also investigated the possible signal mechanisms underlying brazilein-induced contraction using selective inhibitors. The inhibitors of myosin light chain kinase (MLCK), Rho-kinase (ROK) and extracellular signal regulated kinase (ERK) can suppress the effect of brazilein respectively, whereas inhibitors of other signaling or receptor molecules such as protein kinase C (PKC) and inositol 1,4,5-triphosphate (IP3) receptor had no effect. All these results demonstrated that brazilein can induce contraction of rat aorta, that the Ca2+ influx, ROK and ERK signal pathways and MLCK activation must be involved in the contractile processes.

The Effect of Mineral Trioxide Aggregate on the Contractility of the Rat Thoracic Aorta

Mineral trioxide aggregate (MTA) is being advocated for vital pulp therapy. In the case of direct pulp capping, hemorrhage control is an important step on success, but little is known about the effect of MTA on pulpal bleeding. In addition, there has been a lack of information on the effect of MTA on smooth muscle contraction, such as can occur in the blood vessels of dental pulp. The present study assessed the vascular effects of MTA, using the rat aortic ring preparations as a tissue model. MTA (100-500 mg) induced dose-dependent contraction in rat thoracic aorta. The contractile effect of MTA was blocked by calcium channel blocker nifedipine (1 muM). These data suggest that the vasoconstrictor property of MTA is related to calcium influx and it may allow proper control of hemorrhage which is critical for the success of any pulp-capping treatment.

Effects of Propofol on Phenylephrine Induced Vascular Smooth Muscle Contraction in Rat Thoracic Aorta

Propofol decreases arterial blood pressure. This has been ascribed to vasodilation and decreased cardiac output occuring separately or in combination. The goal of the present study was to assess the effects of propofol on the phenylephrine induced vasoconstriction in rat thoracic aortic rings. Methods: All aortic rings were removed endothelium and isometric tension was recorded under a resting tension of 3 g. Isolated aortic rings were precontracted with phenylephrine (0.3μM) and propofol (1 to 100μM) was added cumulatively. We induced the phenylephrine preconstriction after treatment of verapamil 10μM in the other vascular rings. Results: Propofol (1 to 100μM) attenuated phenylephrine (0.3μM) induced preconstriction dose-dependently. The administration of propofol (1 and 10μM) did not change the tonic constriction. The contractile response were significantly attenuated in verapamil pretreated rings but propofol did not affect on constriction in all dose range. Conclusions: Propofol attenuated phenylephrine precontracted rat thoracic aortic rings with inhibition of Ca2+ movement through the L-type calcium channel in the sarcolemmal membrane.

Cyclooxygenase, p38 Mitogen-Activated Protein Kinase (MAPK), Extracellular Signal-Regulated Kinase MAPK, Rho Kinase, and Src Mediate Hydrogen Peroxide-Induced Contraction of Rat Thoracic Aorta and Vena Cava

In hypertension, blood vessels exhibit increased reactive oxygen species production that may alter vascular tone. We previously observed that H2O2 contracted rat thoracic vena cava under resting tone and aorta contracted with KCl. In arteries but not veins, H2O2-induced contraction required extracellular Ca2+ influx. Because of this difference in Ca2+ utilization, we hypothesized that signaling pathways mediating H2O2-induced contraction in vena cava under resting tone differed from those mediating H2O2-induced contraction in aorta contracted with KCl. Inhibitors of cyclooxygenase (COX) 1 and 2 (indomethacin, 10 microM), thromboxane A2 (TXA2) receptors [ICI185282 (2RS,4RS,5SR-4-o-hydroxyphenyl-2-trifluoromethyl-1,3-dioxan-5-yl heptenoic acid), 10 microM], p38 mitogen-activated protein kinase (MAPK) [SB203580 (4-[5-(4-fluorophenyl)-2-[4-(methylsulfonyl)phenyl]-1H-imidazol-4-yl]pyridine), 10 microM], extracellular signal-regulated kinase (Erk) [PD98059 (2'-amino-3'-methoxyflavone), 10 microM], src [PP1 (4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine, 10 microM], and rho kinase [Y27632 (trans-4-[(1R)-1-aminoethyl]-N-4-pyridinylcyclohexanecarboxamide dihydrochloride), 10 microM], significantly reduced H2O2-induced contraction in vena cava under resting tone and aorta after KCl (30 mM) contraction. In contrast, the phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one, 20 microM] did not reduce aortic or venous H2O2-induced contraction. p38 MAPK, Erk MAPK, and src inhibition did not reduce aortic or venous contraction to the TXA2 receptor agonist U46619 (9,11-dideoxy-9alpha,11alpha-methanoepoxy PGF(2alpha), 1 microM), whereas rho kinase inhibition significantly reduced aortic and venous contraction to U46619, and PI3-K inhibition reduced venous contraction to U46619. Our data suggest that, in rat thoracic aorta and vena cava, a COX-derived metabolite is one important mediator of H2O2 contraction, possibly via rho kinase activation, and that H2O2-induced contraction via p38 and Erk MAPK probably occurs independently of TXA2 receptor activation.

Inhibitory effects of <I>Musanga cecropioides</I> on noradrenaline and potassium-induced contractions in rat thoracic aorta

The pharmacological effects of Musanga cecropioides on rat thoracic aorta were examined in high K,SUP>+ medium (55mM), Ca 2+ 3mM) induced vasoconstriction was inhibited by Musanga cecropioides in a concentration-dependent manner. The tonic contra ctions elicited by KCI 55mM were relaxed by Musanga and were more marked in 0.45mM Ca 2+ than 1.8mM Ca 2+ medium. NA -induced responses were antagonized non competitively by Musanga. NA- sustained contraction was relaxed, the relaxing effect of Musanga was not antagonized by indomethacin or methylene blue. It is concluded that Musanga relaxation of the rat aorta does not involve cyclo-oxygenase, nor cAMP pathway, but unique, unlike those of known classical vasodilators. African Journal of Biomedical Research Vol. 8(1) 2005: 59-61

Endothelium‐dependent contraction of rat thoracic aorta induced by gallic acid

The vascular effect of a component of hydrolysable tannins, gallic acid, was examined in isolated rat thoracic aorta. Gallic acid exerted a contractile effect on the phenylephrine- or prostaglandin F(2/alpha)-precontracted endothelium-intact arteries. In endothelium-denuded arteries, the contractile response to-gallic acid was absent. Pretreatment with N(G)-nitro-L-arginine methyl ester (30 microM) abolished the gallic acid-induced contraction. Pretreatment with indomethacin (10 microM) or BQ610 (100 nM) had no observed effect. Pretreatment with gallic acid (1-10 microM) significantly attenuated the relaxation induced by acetylcholine, and that with 10 microM gallic acid also reduced the potency of sodium nitroprusside in the relaxation, without a reduction in efficacy, in endothelium-denuded arteries. These findings indicate that gallic acid induced endothelium-dependent contraction and strongly inhibited the endothelium-dependent relaxation rather than the endothelium-independent relaxation, probably through inhibition of endothelial nitric oxide (NO) production. Since NO plays an important role in vasodilative regulation and inflammatory disorders, these findings may also indicate that gallic acid interferes with the inflammatory responses.

Ca2+ entry channels involved in contractions of rat aorta induced by endothelin-1, noradrenaline, and vasopressin.

Endothelin-1 (ET-1) has been shown to activate three types of Ca2+ channel, namely two Ca2+-permeable nonselective cation channels (designated NSCC-1 and NSCC-2) and a store-operated Ca2+ channel (SOCC), and that these channels can be discriminated by Ca2+ channel blockers such as LOE 908 (a blocker of NSCC-1 and NSCC-2) and SK&F 96365 (a blocker of NSCC-2 and SOCC). This study pharmacologically compared Ca2+ entry channels involved in contractions of rat thoracic aorta without endothelium induced by ET-1, noradrenaline (NA), or arginine-vasopressin (AVP). These agonists-induced contractions of aortic rings without endothelium and increases in the intracellular free Ca2+ concentration ([Ca2+]i) of cultured aortic smooth muscle cells were abolished by removal of extracellular Ca2+. A blocker of L-type voltage-operated Ca2+ channel (VOCC), nifedipine had no effect on the responses to ET-1, but it suppressed the responses to NA and AVP to 70% and 65% of control responses, respectively. LOE 908 partially suppressed the nifedipine-resistant responses to ET-1 and AVP, but not those to NA. SK&F 96365 also partially suppressed the nifedipine-resistant responses to ET-1 and AVP, whereas it abolished the responses to NA. LOE 908 in combination with SK&F 96365 abolished the nifedipine-resistant responses to either of the agonists. These results show that the contraction of rat aorta involves different Ca2+ entry channel depending on agonists: (a) NSCC-1, NSCC-2, and SOCC for ET-1; (b) VOCC and SOCC for NA; and (c) VOCC, NSCC-1, NSCC-2, and SOCC for AVP.

Involvement of p44/42 mitogen-activated protein kinases in regulating angiotensin II- and endothelin-1-induced contraction of rat thoracic aorta

In order to elucidate the signal transduction pathway of vascular smooth muscle contraction induced by the activation of receptors for angiotensin II and endothelin-1, we examined whether tyrosine kinases and mitogen-activated protein (MAP) kinases are involved in the development of force of contraction in the rat aorta. Isolated aortic smooth muscles without endothelium were incubated in a modified Krebs–Henseleit solution and stimulated with angiotensin II (100 nM) or endothelin-1 (10 nM). A tyrosine kinase inhibitor genistein (10 μM) reduced the angiotensin II- and endothelin-1-induced aortic contraction, while 10 μM of daidzein (an inactive analogue of genistein) did not. The K + depolarization-induced contraction was not attenuated by 10 μM of genistein. Selective inhibitors of MAP kinase/extracellular signal-regulated kinase (Erk) kinase (MEK) such as PD98059 [2-(2-amino-3-methoxyphenyl)-4 H-1-benzopyran-4-one] and U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] inhibited the angiotensin II- and endothelin-1-induced vasocontraction. The p44/42 MAP kinases were phosphorylated in cultured aortic smooth muscle cells and in physiologically contracted aortic vessels stimulated with angiotensin II and endothelin-1 for 5 min. The angiotensin II- and endothelin-1-induced phosphorylations of p44/42 MAP kinases were inhibited by PD98059 as well as U0126 in the intact aorta. These results suggest that the activation of genistein-sensitive tyrosine kinases and p44/42 MAP kinases is involved in the angiotensin II- and endothelin-1-induced rat aortic contraction.