Rat Superior Mesenteric Artery Research Articles

Effects of Cold on Adrenoreactivity of the Rat Superior Mesenteric Artery

Effects of Cold on Adrenoreactivity of the Rat Superior Mesenteric Artery

Celastrol ameliorates energy metabolism dysfunction of hypertensive rats by dilating vessels to improve hemodynamics.

The impact of hypertension on tissue and organ damage is mediated through its influence on the structure and function of blood vessels. This study aimed to examine the potential of celastrol, a bioactive compound derived from Tripterygium wilfordii Hook F, in mitigating hypertension-induced energy metabolism disorder and enhancing blood perfusion and vasodilation. In order to investigate this phenomenon, we conducted in vivo experiments on renovascular hypertensive rats, employing indirect calorimetry to measure energy metabolism and laser speckle contrast imaging to evaluate hemodynamics. In vitro, we assessed the vasodilatory effects of celastrol on the basilar artery and superior mesenteric artery of rats using the Multi Wires Myograph System. Furthermore, we conducted preliminary investigations to elucidate the underlying mechanism. Moreover, administration of celastrol at doses of 1 and 2mg/kg yielded a notable enhancement in blood flow ranging from 6 to 31% across different cerebral and mesenteric vessels in hypertensive rats. Furthermore, celastrol demonstrated a concentration-dependent (1 × 10-7 to 1 × 10-5M) arterial dilation, independent of endothelial function. This vasodilatory effect could potentially be attributed to the inhibition of Ca2+ channels on vascular smooth muscle cells induced by celastrol. These findings imply that celastrol has the potential to ameliorate hemodynamics through vasodilation, thereby alleviating energy metabolism dysfunctions in hypertensive rats. Consequently, celastrol may hold promise as a novel therapeutic agent for the treatment of hypertension.

New paeonol derivative C302 reduces hypertension in spontaneously hypertensive rats through endothelium-dependent and endothelium-independent vasodilation

Hypertension is a major risk factor for cardiovascular disease and Chinese herb monomers could provide new structural skeletons for anti-hypertension new drug development. Paeonol is a Chinese herbal monomer extracted from Cortex moutan, exhibited some anti-hypertensive activity. The study focused on the structural optimization of paeonol to provide promising lead compounds for anti-hypertension new drug development. Herein, twelve new paeonol derivatives (PD) were designed and synthesized and their vasodilation activity was evaluated by in vitro vasodilation drug screening platform based on Myograph. Its anti-hypertension activity, PD-C302 (2-hydroxy-4-methoxyvalerophenone) as a representative with the optimal vasodilation activity, was determined by its response to blood pressure in spontaneously hypertensive rats (SHR) in vivo. Moreover, its molecular mechanism was probed by the vasodilation activity of rat superior mesenteric artery rings with or without endothelium pre-contracted by potassium chloride (KCl) or phenylephrine hydrochloride (PE). It was indicated that PD-C302 significantly reduced the blood pressure in SHR, which would involve in PD-C302-induced vasodilation. Furthermore, endothelium-dependent pathways and endothelium-independent pathways both contributed importantly to PD-C302-induced vasodilation at low concentration of PD-C302. Endothelium-independent pathways (vascular smooth muscle cell-mediated vasodilation), were mainly responsible for the PD-C302-induced vasodilation at high concentration of PD-C302, which involved in opening multiple K+ channels to restrain Ca2+ channels, and then triggered vasodilation to reduce blood pressure. PD-C302 has a simple structure and favorable anti-hypertensive activity in vivo, which could be a promising lead compound for anti-hypertension new drug development.

Inhibitors of the MAPK/ NF-κB pathway attenuate the upregulation of the ETB receptor mediated by high glucose in vascular smooth muscle cells

BackgroundIncreased vascular smooth muscle cell (VSMC) endothelin type B (ETB) receptor expression is involved in cardiovascular diseases. High glucose (HG) in diabetes is closely related to cardiovascular complications. Although diabetes upregulates VSMC endothelin subtype B (ETB) receptors, its mechanism is still unclear. Our aim is to investigate the mechanism of HG-induced ETB receptors in VSMCs. MethodsRat superior mesenteric arteries (SMAs) without endothelium were cultured in medium without serum for 24 h. HG with or without mitogen-activated protein kinase (MAPK) signaling pathway inhibitors and downstream nuclear factor-kappaB (NF-κB) inhibitors was coincubated with SMAs. A sensitive myograph detected the contractile responses to sarafotoxin 6c. Western blotting and immunofluorescence staining were used to determine protein expression. ResultsHG promoted the expression of VSMC ETB receptors in rat SMAs and enhanced the ETB receptor-induced contractile response. The results showed that HG increased vascular smooth muscle cell (VSMC) ETB receptor expression and ETB receptor-induced contractile responses in rat SMAs. Both extracellular signal-related kinase 1 and 2 (ERK1/2) inhibitors (U0126) and P38 inhibitors (SB203580) significantly inhibited HG-increased VSMC ETB receptors. However, a C-jun terminal kinase (p-JNK) inhibitor (SP600125) did not affect HG- upregulated VSMC ETB receptors. Further study showed that NF-κB using an IκB kinase inhibitor (wedelolactone) also significantly inhibited HG-increased VSMC ETB receptors. ConclusionIn conclusion, HG upregulated the VSMC ETB receptor by activating the ERK1/2- or P38- NF-κB signaling pathway.

Angiotensin II upregulates endothelin receptors through the adenosine monophosphate-activated protein kinase/sirtuin 1 pathway in vascular smooth muscle cells.

This study was designed to test our hypothesis that angiotensin II (Ang II) upregulates endothelin (ET) receptors in vascular smooth muscle cells (VSMCs). Rat superior mesenteric artery (SMA) without endothelium was cultured in serum-free medium for 24 h in the presence of Ang II with or without metformin or nicotinamide. In vivo, rats were implanted subcutaneously with a mini-osmotic pump infusing AngII (500 ng/kg/min) for 4 weeks. The level of protein expression was determined using Western blotting. The contractile response to ET receptor agonists was studied using sensitive myography. Caudal artery blood pressure (BP) was measured using non-invasive tail-cuff plethysmography. The results showed that Ang II significantly increased ET receptors and decreased phosphorylated-adenosine monophosphate-activated protein kinase α (p-AMPKα) in SMA. Furthermore, metformin significantly inhibited Ang II-upregulated ET receptors and upregulated Ang II-decreased sirtuin 1 (Sirt1). However, this effect was reversed by nicotinamide. Moreover, the in-vivo results showed that metformin not only inhibited Ang II-induced upregulation of ET receptors but also recovered Ang II-decreased p-AMPKα and Sirt1. In addition, metformin significantly inhibited Ang II-elevated BP. However, the effect was reversed by nicotinamide, except for p-AMPKα. Ang II upregulated ET receptors in VSMCs to elevate BP by inhibiting AMPK, thereby inhibiting Sirt1.

Trimethylamine-N-oxide (TMAO) Selectively Disrupts Endothelium-Dependent Hyperpolarization-Type Relaxations in a Time-Dependent Manner in Rat Superior Mesenteric Artery.

The vascular action of trimethylamine-N-oxide (TMAO)-the gut microbiota-derived metabolite-in contributing cardiovascular disease is a controversial topic. A recent study has shown that acute exposure of TMAO at moderate concentrations inhibits endothelium-dependent hyperpolarization (EDH)-type relaxations selectively in rat isolated femoral arteries, but not in mesenteric arteries. Here we determined the efficacy of higher TMAO concentrations with longer exposure times on vascular reactivity in rat isolated superior mesenteric arteries. Acetylcholine-induced EDH-type relaxations were examined before and after incubation with TMAO (0.1-10 mM) at increasing exposure times (1-24 h). One- and 4-h-incubations with TMAO at 0.1-3 mM did not cause any change in EDH-type relaxations. However, when the incubation time was increased to 24 h, responses to acetylcholine were reduced in arteries incubated with 1-3 mM TMAO. In addition, at higher TMAO concentration (10 mM) the decrease in EDH relaxations could be detected both in 4-h- and 24-h-incubations. The EDH-relaxations were preserved in rings incubated with 10 mM TMAO for 24 h in the presence of SKA-31 (10 µM), the small (SKCa)- and intermediate (IKCa)-conductance calcium-activated potassium channel activator. Contractile responses to phenylephrine increased in arteries exposed to 10 mM TMAO for 24 h. Interestingly, nitric oxide (NO)-mediated relaxations remained unchanged in arteries treated for 24 h at any TMAO concentration. Our study revealed that TMAO selectively disrupted EDH-type relaxations time-dependently without interfering with NO-induced vasodilation in rat isolated mesenteric arteries. Disruption of these relaxations may help explain the causal role of elevated TMAO levels in certain vascular diseases.

Occlusion of the Superior Mesenteric Artery in Rats Reversed by Collateral Pathways Activation: Gastric Pentadecapeptide BPC 157 Therapy Counteracts Multiple Organ Dysfunction Syndrome; Intracranial, Portal, and Caval Hypertension; and Aortal Hypotension.

Gastric pentadecapeptide BPC 157 therapy counteracts multiple organ dysfunction syndrome in rats, which have permanent occlusion of the superior mesenteric artery close to the abdominal aorta. Previously, when confronted with major vessel occlusion, its effect would rapidly activate collateral vessel pathways and resolve major venous occlusion syndromes (Pringle maneuver ischemia, reperfusion, Budd–Chiari syndrome) in rats. This would overwhelm superior mesenteric artery permanent occlusion, and result in local, peripheral, and central disturbances. Methods: Assessments, for 30 min (gross recording, angiography, ECG, pressure, microscopy, biochemistry, and oxidative stress), included the portal hypertension, caval hypertension, and aortal hypotension, and centrally, the superior sagittal sinus hypertension; systemic arterial and venous thrombosis; ECG disturbances; MDA-tissue increase; and multiple organ lesions and disturbances, including the heart, lung, liver, kidney, and gastrointestinal tract, in particular, as well as brain (cortex (cerebral, cerebellar), hypothalamus/thalamus, hippocampus). BPC 157 therapy (/kg, abdominal bath) (10 µg, 10 ng) was given for a 1-min ligation time. Results: BPC 157 rapidly recruits collateral vessels (inferior anterior pancreaticoduodenal artery and inferior mesenteric artery) that circumvent occlusion and ascertains blood flow distant from the occlusion in the superior mesenteric artery. Portal and caval hypertension, aortal hypotension, and, centrally, superior sagittal sinus hypertension were attenuated or eliminated, and ECG disturbances markedly mitigated. BPC 157 therapy almost annihilated venous and arterial thrombosis. Multiple organ lesions and disturbances (i.e., heart, lung, liver, and gastrointestinal tract, in particular, as well as brain) were largely attenuated. Conclusions: Rats with superior mesenteric artery occlusion may additionally undergo BPC 157 therapy as full counteraction of vascular occlusion-induced multiple organ dysfunction syndrome.

Регуляция тонуса артерий у крыс, длительно получавших высокосолевую диету

A high salt diet leads to a decrease in vascular dilatation to agonists, but the vascular mechanisms involved in this process are not extensively studied. A group of male Wistar rats at the age of 3 months was transferred to a diet containing 8% NaCl (HS) for 3 months, while the second group received a diet with a standard salt content (0.34%) (NS). At the end of the experiment, the rats were euthanized and the abdominal aorta and superior mesenteric artery (SMA) were extracted. The vascular segments were placed in a myograph and the acetylcholine (ACh) -induced relaxation of the vascular segments previously contracted with phenylephrine - was measured. A high salt diet led to a weakening of the relaxation of SMA in a calcium-free solution. In response to ACh and sodium nitroprusside, a pronounced relaxation of the vascular segments was observed, while the ACh-induced vascular relaxation of HS rats had a lower amplitude. K+ -channel blockers (TEA, TRAM-34, and apamine) weakened ACh-induced relaxation of the SMA, but not the aorta. In the SMA of HS rats the decrease in relaxation under the action of K+ -channel blockers was more significant. Inhibition of production of endogenous H2S also led to a weakening of the relaxation of the SMA segments on ACh. In SMA of HS rats, the degree of weakening of ACh-induced relaxation against the background of propargylglycine was greater than in NS rats. The data obtained in the study shows that a long-term high salt diet leads to a decrease in agonist-induced relaxation of the aorta segments and SMA. The relaxation weakening of the aorta segments and SMA occurs due to a decrease in the production of NO by the endothelium. In the SMA of HS rats, the decrease in NO-mediated relaxation is partially compensated by an increased role of EDHF in ACh-induced relaxation. The results of the study also show that one of the EDHFs in rat SMA is H2S, the role of which in SMA relaxation increases in HS rats.

Tridax procumbens leaf extract elicits relaxation of rat mesenteric artery by activation of Na+ -K+ ATPase / Na+ - Ca2+ exchanger

Background: Tridax procumbens leaf extract has been reported to show antihypertensive actions through its vasodilatory effects. Although several mechanisms of action have been reported, the sub-cellular mechanism of action of the extract is yet to be fully elucidated. Aim and Objectives: In this study, we investigate the involvement of Na+ - K+ -pump and Na+- Ca2+ exchanger in the vasorelaxant activities of T. procumbens extract (TPE) in isolated rat superior mesenteric arteries. Materials and Methods: Superior mesenteric artery isolated from healthy, young adult Wistar rats (250–300 g) and pre-contracted with phenylephrine (PE) (10-7M) were treated with various concentrations of aqueous extract of TPE (0.5–9 mg/mL). The changes in arterial tension were recorded and interaction between TPE with the selective blocker of Na+ - K+ ATPase (ouabain) and putative Na+-Ca2+ exchanger inhibitor (NiCl2) was evaluated. Results: The result indicated that TPE significantly inhibit the cumulative concentration response curves to PE (10-9 - 10-5 M) in a concentration-dependent manner. Pre-treatment with both ouabain and nickel chloride (NiCl2), abolished the vasorelaxant responses of TPE. Furthermore, TPE reduced the relaxant effect with decreased extracellular Na+ concentration. TPE-induced vasorelaxation was completely abolished in a Na+ -free solution, a condition that eliminates the influence of the forward mode of the exchanger. Conclusion: The results provide direct hypothetical evidence that the activation of Na+ - K+ ATPase and stimulation of the forward mode of the Na+-Ca2+ exchanger contribute to the vasorelaxation induced by TPE in mesenteric artery.

Влияние нефрэктомии на реактивность артерий спонтанно гипертензивных крыс

The effect of nephrectomy on the SHR rat superior mesenteric artery (SMA) and internal carotid artery (ICA) segments constriction and dilatation ability was studied under isometric conditions using myograph. 5/6 nephrectomy (5/6 Nx) in the rats 3 months old was used as a model of the chronic kidney disease. Dilatation of the phenylephrine-precontracted segments was induced by acetylcholine (AСh) or sodium nitroprusside (SNP) in the absence and presence of potassium channels blockers (tetraethylammonium, glibenclamide) or methylene blue, a guanylyl-cyclase inhibitor. The phenylephrine-induced contraction was slightly reduced in the SMA from 5/6 Nx rats relative to the control ones and significantly decreased in the presence of methylene blue. This reaction in the ICA from 5/6 Nx rats was significantly less than in the control ones, both in the absence and in the presence of the blockers and the inhibitor. The effect of nephrectomy on the dilatatory reaction of both arteries caused by AСh or SNP was not found, but the constrictor reaction of ICA to AСh in the presence of glibenclamide significantly decreased in 5/6 Nx, but not in control rats. We conclude that the chronic kidney disease may weaken endothelium dependent and independent vasoconstriction in the ICA from SHR rats, as well as differently change the signaling pathways of this reaction in different types of arteries.

Vasorelaxant Effect Induced by the Essential Oil of Ocotea duckei Vattimo Leaves and Its Main Constituent, Trans-caryophyllene, in Rat Mesenteric Artery

Aims: To evaluate the vasorelaxant effect induced by the essential oil of the leaves of O. duckei Vattimo (ODEO) and its main constituent, trans-caryophyllene, in rat superior mesenteric arteries.
 Methodology: Isolated rat superior mesenteric rings were suspended by cotton threads for isometric tension recordings in Tyrode’s solution at 37ºC, gassed with 95% O2 and 5% CO2 and different ODEO concentrations (0.1-300 μg/mL) or trans-caryophyllene (1-1000 μg/mL) were added cumulatively to the organ baths.
 Results: Vasorelaxant effect induced by the essential oil of Ocotea duckei leaves (ODEO) and its main constituent, trans-caryophyllene (60.54 %), was evaluated in this work. In intact isolated rat superior mesenteric rings ODEO (0.1-300 μg/mL, n=6) induced concentration-dependent relaxation of tonus induced by phenylephrine (10 µM) or K+-depolarizing solution (KCl 80 mM) (IC50=31±5, 5±0.4 µg/mL, respectively, n=6). The relaxations of phenylephrine-induced contractions were not significantly attenuated after removal of the vascular endothelium (IC50=25±5 µg/mL). ODEO antagonized the concentration-response curves to CaCl2 (10-6-3x10-2 M) and Bay K 8644 (10-10-3x10-6 M). Furthermore, in nominally without calcium solution, ODEO significantly inhibited, in a concentration-dependent manner, transient contractions induced by 10 µM phenylephrine or 20 µM caffeine. Trans-caryophyllene induced vasorelaxations, however, this effect was 18.6 times less potent when compared to ODEO-induced vasorelaxations.
 Conclusion: The relaxant effect induced by ODEO in rat superior mesenteric artery rings is endothelium-independent and seems to be related to both, inhibition of Ca2+ influx through L-type voltage-gated Ca2+-channels sensitive to dihydropyridines and inhibition of the calcium release from intracellular IP3-and caffeine-sensitive stores.

Inhibition of intracellular Ca2+ mobilization and potassium channels activation are involved in the vasorelaxation induced by 7-hydroxycoumarin

Coumarins exhibit a wide variety of biological effects, including activities in the cardiovascular system and the aim of this study was to evaluate the vascular therapeutic potential of 7-Hydroxicoumarin (7-HC). The vascular effects induced by 7-HC (0.001 μM–300 μM), were investigated by in vitro approaches using isometric tension measurements in rat superior mesenteric arteries and by in silico assays using Ligand-based analysis. Our results suggest that the vasorelaxant effect of 7-HC seems to rely on potassium channels, notably through large conductance Ca2+-activated K+ (BKCa) channels activation. In fact, 7-HC (300 μM) significantly reduced CaCl2-induced contraction as well as the reduction of intracellular calcium mobilization. However, the relaxation induced by 7-HC was independent of store-operated calcium entry (SOCE). Moreover, in silico analysis suggests that potassium channels have a common binding pocket, where 7-HC may bind and hint that its binding profile is more similar to quinine's than verapamil's. These results are compatible with the inhibition of Ca2+ release from intracellular stores, which is prompted by phenylephrine and caffeine. Taken together, these results demonstrate a therapeutic potential of 7-HC on the cardiovascular system, making it a promising lead compound for the development of drugs useful in the treatment of cardiovascular diseases.

Abstract P071: Transglutaminases Are Active In Perivascular Adipose Tissue

Transglutaminases (TGs) are crosslinking enzymes best known for their vascular remodeling in hypertension. They require calcium to form an isopeptide bond, connecting a glutamine to a protein bound lysine residue or a free amine donor such as norepinephrine (NE) or serotonin (5-HT). We discovered that perivascular adipose tissue (PVAT) contains significant amounts of these amines, making PVAT an ideal model in which to test interactions of amines and TGs. We hypothesized that TG2 and FXIII are active in PVAT. Sprague-Dawley rat aortic, superior mesenteric (SMA), and mesenteric resistance artery (MR) PVAT express TG2 and blood coagulation factor XIII (FXIII) mRNA (Figure 1A). Consistent with this, immunohistochemical analyses support that PVATs all express TG2 and FXIII protein. The activity of TG2 and FXIII was investigated in tissue sections using substrate peptides that label active TGs and a catalyzing calcium solution, visualized with TRITC fluorescence (Figure 1B,C). Both TG2 and FXIII are active in rat aortic PVAT, SMAPVAT, and MRPVAT. Western blot analysis determined that the known TG inhibitor cystamine reduced incorporation of experimentally added amine donor 5-(biotinamido)pentylamine (BAP) into MRPVAT by 6.14% of total normalized signal (p<0.0001, N=7). Further Western blot analysis proved that experimentally added 5-HT competitively inhibits incorporation of experimentally added BAP into MRPVAT adipocytes, reducing total normalized signal by 10.75% (p=0.001, N=4). Further studies to determine what proteins TGs are amidating will give insight into how these enzymes contribute to the development of hypertension.

Itaconimides derivatives induce relaxation in mesenteric artery and negative inotropism by inhibition of CA2+ influx.

The aim of this study was to evaluate the cardiovascular effects of N-phenyl-itaconimide (Imide-1), N-4-methyl-phenyl-itaconimide (Imide-2), N-4-methoxy-phenyl-itaconimide (Imide-3) and N-4-chloro-phenyl-itaconimide (Imide-4), and investigate the mechanisms of action involved in the observed responses. The relaxant effect was investigated in rat superior mesenteric arteries by using isometric tension measurements. Additionally, in isolated atria were evaluated the heart rate and force of cardiac contraction and in vivo experiments was evaluated blood pressure and heart rate. Cumulative administration of itaconimides (3 × 10-8 to 3 × 10-4M) in pre-contracted mesenteric artery rings with phenylephrine, 1μM, induced endothelium-independent vasorelaxation. The itaconimides showed similar maximum efficacies. Additionally, Imide-3 induced vasorelaxation in rings exposed to a depolarizing-tyrode solution containing 60mM KCl or 20mM KCl similar to the control, suggesting the non-participation of K+ channels. Imide-3 attenuated Ca2+ influx in a concentration-dependent manner. As well, imide-3 reduced CaCl2-induced contraction in nominally calcium-free medium, in the presence of cyclopiazonic acid (20μM), phenylephrine (1μM) and nifedipine (1μM), indicating a reduction of Ca2+ influx by receptor-operated channels (ROC) and store-operated channels (SOC). The presence of SKF 96365 (10-5M), SOC blocker, did not significantly alter the vasorelaxant effect induced by imide-3. Moreover, imide-3 induced a negative inotropic effect. In vivo studies, in non-anesthetized normotensive rats, imide-3 lowered blood pressure and induced bradycardia. These results suggest that itaconimides have concentration-dependent vascular effects and the vasorelaxation seems to be endothelium-independent. The vasodilatory effect induced by imide-3 may be due to a possible influence on the CaV and ROC. In addition, imide-3 is able to reduce force of cardiac contraction, blood pressure and promote bradycardia.

Влияние нефрэктомии на реактивность артерий крыс линии Wistar-Kyoto

The effect of nephrectomy on the Wistar Kyoto rat superior mesenteric artery (SMA) and internal carotid artery (ICA) segments constriction and dilatation ability was studied under isometric conditions using myograph. 5/6 nephrectomy (5/6 Nx) in the rats 3 months old was used as a model of the chronic kidney disease. Dilatation of the phenylephrine-precontracted segments was induced by acetylcholine (AСh) or sodium nitroprusside (SNP) in the absence and presence of potassium channels blockers (tetraethylammonium, glibenclamide) or methylene blue, a guanylyl-cyclase inhibitor. The phenylephrine-induced contraction was increased in the SMA but not in the ICA from 5/6 Nx rats. This reaction was not changed by the blockers and by inhibitor. The AСh-evoked reaction often had two phases. AСh-evoked dilatation phase of the reaction of the both arteries from 5/6 Nx rats have shown no difference from control (C) and was diminished by tetraethylammonium (in С and 5/6 Nx rats) and by methylene blue (in С rats). In 5/6 Nx rats, AСh-evoked constriction phase of the reaction in the absence of the blockers and inhibitor was significantly larger compared to С rats only in SMA, but in the absence of tetraethylammonium, it was significantly larger in both arteries. Glibenclamide diminished AСh-induced constriction of SMA from 5/6 Nx rats, while methylene blue diminished this constriction of ICA from control rats only. We conclude that the chronic kidney disease may increase endothelium dependent and independent vasoconstriction and may change signal pathways of this constriction, which may differ in the arteries of different types.

Pharmacological properties of β-adrenoceptors mediating rat superior mesenteric artery relaxation and the effects of chemical sympathetic denervation

Aimsβ-Adrenoceptors (β-ADRs) mediating the relaxation of rat superior mesenteric arteries (SMAs) were pharmacologically identified, and the effects of chemical sympathetic denervation on β-ADR-mediated relaxation were examined. Main methodsThe tension changes of endothelium-denuded SMAs were isometrically recorded and the mRNA of endothelium-denuded SMA β-ADR was detected using RT-PCR. Key findingsIn endothelium-denuded SMAs contracted with ≥10−7 M phenylephrine (an α1-ADR agonist), isoprenaline (a β-ADR agonist)-induced relaxation was competitively inhibited by 3 × 10−9–10−8 M propranolol (a β1,2-ADR antagonist), but not further affected by ≥10−8 M propranolol. Although isoprenaline-induced relaxation was not affected by ICI-118,551 (10−9–10−8 M; a β2-ADR antagonist), it was competitively inhibited by atenolol (10−7–3 × 10−7 M; a β1-ADR antagonist) in the presence of ICI-118,551. In the presence of 10−7 M propranolol, isoprenaline- and CGP-12177A (a β3-ADR partial agonist)-induced relaxation was competitively inhibited by high concentrations of bupranolol (a β1,2,3-ADR antagonist), with pA2 values of 6.49 and 5.76, respectively. We detected the mRNA of β1- and β3-ADRs in endothelium-denuded SMAs. Treatment with 6-hydroxydopamine (a catecholaminergic neurotoxin) reduced maximal isoprenaline-induced relaxation in the presence and absence of 10−7 M propranolol, but not CGP-12177A-induced relaxation. SignificanceIsoprenaline-induced relaxation of rat SMAs is mediated by β1- and β3-ADRs. β-ADR-mediated relaxation of rat SMAs is shown to be attenuated by chemical sympathetic denervation. The differences in the effects of bupranolol and chemical sympathetic denervation on the responses to isoprenaline and CGP-12177A in rat SMAs might be explained by the possible presence of multiple β3-ADRs with different pharmacological properties.

Metformin inhibited homocysteine-induced upregulation of endothelin receptors through the Sirt1/NF-κB signaling pathway in vascular smooth muscle cells

Metformin (Met) can improve atherosclerosis (As). Abnormal endothelin receptors [including endothelin type A (ETA) or type B (ETB) receptor] in vascular smooth muscle cells (VSMCs) are involved in As. Hyperhomocysteinemia (HHcy) is an independent risk factor for As. The present study was designed to test our hypothesis that Met inhibits the upregulation of endothelin receptors induced by homocysteine (Hcy) in VSMCs. Rat superior mesenteric artery (SMA) without endothelium, as an in vitro model, was cultured in serum-free medium for 24 h in the presence of Hcy with or without Met or nicotinamide (Nic). In vivo, rats received subcutaneous injections of Hcy in the presence or absence of Met or Nic for 3 weeks. Levels of protein expression were determined by Western blotting. The contractile responses to sarafotoxin 6c (an ETB receptor agonist) or ET-1 (an ETA/ ETB receptor agonist) were studied using a sensitive myograph. The blood pressure of rats was measured using a noninvasive tail-cuff plethysmography method. The results showed that Met could significantly inhibit the Hcy-induced upregulation of endothelin receptors (including ETA and ETB receptor) protein expression and endothelin receptor-mediated vasoconstriction, and it recovered the Hcy-induced decrease in silent information regulator 1 (Sirt1) in a dosage-dependent manner in SMA. However, Nic (a Sirt1 inhibitor) recovered the levels of Met-inhibited endothelin receptors and acetylated p65. Furthermore, the in vivo results showed that Met not only significantly the inhibited HHcy-induced upregulation of endothelin receptors and acetylated p65 but also recovered the HHcy-induced decrease in Sirt1 in a dosage-dependent manner in SMA. In addition, Met significantly inhibited the HHcy-induced blood pressure elevation. However, these effects were reverted by Nic. In conclusion, these data demonstrated that Met inhibited the Hcy-induced increase in endothelin receptor expression by activating Sirt1 and then inhibiting NF-κB in VSMCs. These findings may provide insights into the mechanism underlying of Met-treated cardiovascular diseases induced by Hcy.

Direct Impairment of the Endothelial Function by Acute Indoxyl Sulfate through Declined Nitric Oxide and Not Endothelium-Derived Hyperpolarizing Factor or Vasodilator Prostaglandins in the Rat Superior Mesenteric Artery.

Upon stimulation, endothelial cells release various factors to regulate the vascular tone. In particular, vasorelaxing factors, called endothelium-derived relaxing factors (EDRFs), are altered in the production and/or release, as well as their signaling every vessel and under pathophysiological states, including cardiovascular, kidney, and metabolic diseases. Although indoxyl sulfate is known as a protein-bound uremic toxin and circulating levels are elevated in the impaired kidney functions, direct impact on the vascular function, especially EDRF's signaling, remains unclear. In this study, we hypothesize that acute exposure to indoxyl sulfate could alter vascular relaxation in the rat superior mesenteric artery. Accordingly, we measured acetylcholine (ACh)-induced endothelium-dependent relaxation in the absence and presence of several inhibitors to divide into each EDRF, including nitric oxide (NO), vasodilator prostaglandins (PGs), and endothelium-derived hyperpolarizing factor (EDHF). Indoxyl sulfate reduced the sensitivity to ACh but not sodium nitroprusside. Under cyclooxygenase (COX) inhibition or inhibitions of COX plus source of EDHF, such as small (SKCa)- and intermediate (IKCa)-conductance calcium-activated K+ channels, the decreased sensitivity to ACh in indoxyl sulfate exposed vessel was still preserved. However, under inhibition of NO synthase (NOS) or inhibitions of NOS and COX, the difference of sensitivity to ACh between vehicle and indoxyl sulfate was eliminated. These findings indicated that acute exposure of indoxyl sulfate in the rat superior mesenteric artery specifically explicitly impaired NO signaling but not EDHF or vasodilator PGs.

In Vitro Measurement of H2S-Mediated Vasoactive Responses.

Isolated tissue chamber bath system and wire myograph were developed for "in vitro" investigation of vasoactive responses on isolated arteries from a variety of animal species and vascular beds. The chapter characterizes the main principles of mechanical measurement of the changes in isometric tension of vascular smooth muscles in isolated rat thoracic aorta and superior mesenteric artery and describes several protocols on how to investigate vasoactive properties of hydrogen sulfide (H2S) from the point of view of its mutual interaction with NO. Several methodological advances, results, and their interpretations in the context of the general knowledge are described. In the protocols the approach on how to study the vasoactive modulatory as well as direct action of H2S and mutual interaction of H2S with nitroso compounds, lipids, and endogenously produced NO is described.

Tetrahydroxystilbene glucoside-induced relaxation of the superior mesenteric artery via both endothelium-dependent and endothelium-independent mechanisms

Tetrahydroxystilbene glucoside (TSG) is the main water-soluble component in Polygonum multiflorum Thunb, and it has many cardioprotective effects. Although TSG is able to relax blood vessels, its relaxation of rat superior mesenteric arteries and the underlying mechanism of this process are not clearly understood. The aim of the present study was to use in vivo and in vitro models to investigate the arterial relaxation effect of TSG on rat superior mesenteric arteries and the mechanisms involved. We found that TSG concentration-dependently relaxed the superior mesenteric artery with or without endothelium. The vasorelaxation induced by TSG is not related to the vasodilator derived factor NO but is rather by the inhibition of COX-2 activity and decreased TXA2. We also found that the vasorelaxation induced by TSG was attenuated by 4‑AP. Moreover, TSG also inhibited the contraction induced by an increase in external calcium concentration in Ca2+-free medium plus KCl (60 mM). These results suggest that TSG induces relaxation in mesenteric arterial rings through an endothelium-dependent pathway that involves the inhibition of COX-2 activity and decreased in TXA2 and through an endothelium-independent pathway via opening of a voltage-dependent K+ channel, blockade of Ca2+ influx and release of intracellular Ca2+.