Isolated Rat Superior Mesenteric Arteries Research Articles

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.

Antioxidant and Antihypertensive Effects of a Chemically Defined Fraction of Syrah Red Wine on Spontaneously Hypertensive Rats.

A particularly phenolic-rich fraction extracted from red wine from the São Francisco valley (Northeastern Brazil) was chemically characterized and its hypotensive and antioxidant effects on spontaneously hypertensive rats were studied both in vitro and in vivo. The liquid-liquid pH dependent fractionation scheme afforded a fraction with high content of bioactive phenolics such as flavonols, flavonol glycosides, phenolic acids and anthocyanins, whose identities were confirmed by liquid chromatography coupled to mass spectrometry analysis. Pretreatment of spontaneously hypertensive rats with this wine fraction at doses of 50 and 100 mg/kg by gavage for 15 days was able to decrease mean arterial pressure and heart rate as well as decrease serum lipid peroxidation. The fraction at concentrations of 0.01–1000 µg/mL induced concentration-dependent relaxation of isolated rat superior mesenteric artery rings pre-contracted with phenylephrine and this effect was not attenuated by endothelium removal. Our results demonstrate it is possible for phenolic constituents of red wine that are orally bioavailable to exert in vivo hypotensive and antioxidant effects on intact endothelial function.

Levobupivacaine induces vasodilatation, but not vasoconstriction, in rat mesenteric artery

Abstract Introduction Levobupivacaine (LEVO) can replace analgesia because it exhibits low toxicity and causes minor vasoconstriction, enabling its use in patients in whom vasoconstrictors are contraindicated. Objective We aimed to evaluate the effects of LEVO in isolated rat superior mesenteric artery by using the vascular reactivity technique and compare its effect to that of lidocaine. Material and method Arterial rings were obtained from the mesenteric artery of male Wistar rats and kept in organ baths. For recording isometric contractions, each ring was suspended by cotton threads from a force transducer, which was connected to a data acquisition system. Result Both lidocaine and LEVO did not show a vasoconstrictor effect on the basal tone of the arterial rings with functional endothelium. However, when the rings were pre-contracted with phenylephrine, both drugs were able to induce concentration-dependent vasodilatation. The vasodilator effect induced by LEVO did not change after removal of the endothelium, or with the addition of tetraethylammonium (1 mM), a non-selective K+ channel blocker. In the rings without functional endothelium, which were pre-contracted with depolarizing Tyrode’s solution (KCl 80 mM), LEVO-induced vasodilatation was not significantly different from that observed in the rings pre-contracted with phenylephrine. Moreover, it did not show a significant additional vasodilator effect compared to the maximal vasodilator effect of nifedipine. Conclusion This study demonstrated that LEVO produces a vasodilator effect in the rat superior mesenteric artery in an endothelium-independent manner. This effect seems to be mediated via Ca2+ channel blockade in the vascular smooth muscle cells.

Ethanol attenuates vasorelaxation via inhibition of inducible nitric oxide synthase in rat artery exposed to interleukin-1β.

Nitric oxide produced by inducible nitric oxide synthase (iNOS) regulates sepsis-induced hypotension. During septic shock, interleukin (IL)-1β is synthesized in endothelial cells and smooth muscle cells by endotoxin. Ethanol (EtOH) suppresses endotoxin-induced hypotension. The present study aimed to elucidate the effect of EtOH on gradual relaxation and iNOS expression induced by IL-1β in isolated rat superior mesenteric arteries (SMAs). Exposure to IL-1β-induced contraction in SMA rings, followed by a gradual relaxation of phenylephrine precontracted tone. Contraction was abolished by indomethacin (IM), cycloheximide (Chx), and endothelium denudation. In contrast, the gradual relaxation was abolished by NOS inhibitors, Chx, endothelium denudation, and inhibited by EtOH (50 and 100 mM). However, IM had no effect on relaxation. Western blot analysis demonstrated that iNOS expression was induced by IL-1β and was inhibited by EtOH and endothelium denudation. Furthermore, messenger RNA expression of iNOS, but not endothelial NOS, was inhibited by EtOH. These data suggest that IL-1β-induced contraction is mediated by thromboxane A2, whereas IL-1β-induced relaxation occurs via NO derived from iNOS. The endothelium plays an important role in vasorelaxation. Taken together, EtOH inhibits IL-1β-mediated vasorelaxation by suppressing endothelium iNOS expression. This study provides the first evidence of EtOH -induced inhibition of IL-1β-mediated vasorelaxation.

The adipokine chemerin amplifies electrical field-stimulated contraction in the isolated rat superior mesenteric artery.

The adipokine chemerin causes arterial contraction and is implicated in blood pressure regulation, especially in obese subjects with elevated levels of circulating chemerin. Because chemerin is expressed in the perivascular adipose tissue (PVAT) that surrounds the sympathetic innervation of the blood vessel, we tested the hypothesis that chemerin (endogenous and exogenous) amplifies the sympathetic nervous system in mediating electrical field-stimulated (EFS) contraction. The superior mesenteric artery, with or without PVAT and with endothelium and sympathetic nerve intact, was mounted into isolated tissue baths and used for isometric contraction and stimulation. Immunohistochemistry validated a robust expression of chemerin in the PVAT surrounding the superior mesenteric artery. EFS (0.3-20 Hz) caused a frequency-dependent contraction in isolated arteries that was reduced by the chemerin receptor ChemR23 antagonist CCX832 alone (100 nM; with, but not without, PVAT), but not by the inactive congener CCX826 (100 nM). Exogenous chemerin-9 (1 μM)-amplified EFS-induced contraction in arteries (with and without PVAT) was blocked by CCX832 and the α-adrenergic receptor antagonist prazosin. CCX832 did not directly inhibit, nor did chemerin directly amplify, norepinephrine-induced contraction. Whole mount immunohistochemical experiments support colocalization of ChemR23 with the sympathetic nerve marker tyrosine hydroxylase in superior mesenteric PVAT and, to a lesser extent, in arteries and veins. These studies support the idea that exogenous chemerin modifies sympathetic nerve-mediated contraction through ChemR23 and that ChemR23 may be endogenously activated. This is significant because of the well-appreciated role of the sympathetic nervous system in blood pressure control.

Involvement of Na+-Ca 2+ exchanger in the endothelium-independent vasorelaxation induced by Curcuma longa L. in isolated rat superior mesenteric arteries

Previous studies confirmed that the methanolic extract from Curcuma longa L. (CLME) lowers arterial blood pressure and heart rate in rats due to the blockade of extracellular Ca(2+) influx. The aim of this study was to investigate the involvement of Na(+)-Ca (2+) exchanger in the vasorelaxant effects elicited by CLME in isolated rat superior mesenteric arteries. CLME (1-1,000 microg/ml) concentration-dependently relaxed phenylephrine (PHE) (10 microM) pre-contracted arterial rings with intact-endothelium (pD(2) and E(max) = 2.04 +/- 0.06 and 88.3 +/- 3.2%) or denuded-endothelium (pD(2) and E(max) = 2.06 +/- 0.03 and 91.4 +/- 1.0%), respectively, suggesting that the removal of endothelium has no significant effect (P>0.05) on the vasorelaxation induced by CLME. Furthermore, CLME (30, 100 and 300 microg/ml) inhibited the cumulative concentration-response curves to PHE (10(-8)-10(-5) M) in a concentration-dependent manner, whereas, treatment with ouabain 100 microM (selective blocker of Na(+)-K(+) ATPase) has no effect on the relaxant responses of CLME. However, treatment with nickel chloride (NiCl(2)) (100, 300 and 400 microM), a putative Na(+)-Ca(2+) exchanger inhibitor, concentration-dependently reduced the vasorelaxant responses of CLME. Precisely, NiCl(2) at 100, 300 and 400 microM significantly (P<0.05) decreased the pD(2) and E(max) values of CLME (1.86 +/- 0.03 and 81.3 +/- 1.2%, 1.77 +/- 0.03 and 60.2 +/- 0.8%, 1.69 +/- 0.04 and 55.3 +/- 1.6%, respectively). Also, CLME (100 microg/ml) produced less relaxant effect with decreasing extracellular Na(+) concentration. CLME-induced vasorelaxation was completely abolished in a Na(+)-free Tyrode's solution, a condition that eliminates the influence of the forward mode of the exchanger. The results provide indirect evidence that the stimulation of the forward mode of Na(+)-Ca (2+) exchanger may probably contribute to the vasorelaxation induced by CLME in endothelium-denuded arterial rings.

Distinct roles for protease-activated receptors 1 and 2 in vasomotor modulation in rat superior mesenteric artery.

Protease-activated receptors (PARs) 1 and 2 are expressed in various blood vessels including rat aorta, modulating vascular tone. We investigated the roles of PAR-1 and PAR-2 in vasomotor modulation in rat superior mesenteric artery. Effects of the PAR-2-activating peptide Ser-Leu-Ile-Gly-Arg-Leu-amide (SLIGRL-amide) and the PAR-1-activating peptide Thr-Phe-Leu-Leu-Arg-amide (TFLLR-amide) on isometric tension were examined in isolated rat superior mesenteric artery or aorta. Both SLIGRL-amide and TFLLR-amide caused relaxation in the precontracted rat aortic rings. The latter peptide, but not the former, produced contraction in the resting rings. NG-nitro-L-arginine methyl ester (L-NAME), but not apamin/charybdotoxin known to block the endothelium-derived hyperpolarizing factor (EDHF) pathway, abolished the relaxation and facilitated the contraction. In the precontracted rat superior mesenteric artery, SLIGRL-amide, but not TFLLR-amide, elicited endothelium-dependent relaxation, which was only partially inhibited by L-NAME with and without indomethacin. The residual relaxation was abolished by apamin/charybdotoxin. Carbenoxolone, a gap junction inhibitor, significantly attenuated the SLIGRL-amide-evoked, EDHF-dependent relaxation, although neither 17-octadecynoic acid, a P450 epoxygenase inhibitor, nor catalase, a hydrogen peroxide scavenger, revealed inhibitory effects. The residual response resistant to carbenoxolone was unaffected by ouabain/BaCl2. In the resting artery, TFLLR-amide, but not SLIGRL-amide, produced only slight contraction, which was dramatically facilitated by combination of L-NAME and apamin/charybdotoxin or by removal of the endothelium. Our data suggest that, in rat superior mesenteric artery, endothelial PAR-2, upon activation, causes relaxation via both NO and EDHF pathways, and that activation of muscular PAR-1 exhibits potential contractile activity that is largely masked by NO and EDHFs pathways triggered by endothelial PAR-1. Gap junctions might be involved in the EDHF mechanisms in this artery.

Pharmacological Evaluation of a Novel Oxime Derived from Isosorbide‐5‐mononitrate on Isolated Rat Superior Mesenteric Artery.

AbstractFor Abstract see ChemInform Abstract in Full Text.

In vitro simultaneous measurements of relaxation and nitric oxide concentration in rat superior mesenteric artery.

1. The relationship between nitric oxide (NO) concentration measured with an NO-specific microelectrode and endothelium-dependent relaxation was investigated in isolated rat superior mesenteric artery contracted with 1 microM noradrenaline. 2. Acetylcholine (10 microM) induced endothelium-dependent simultaneous increases in luminal NO concentration of 21 +/- 6 nM, and relaxations with pD2 values and maximum of 6.95 +/- 0.32 and 97.5 +/- 0.7 % (n = 7), respectively. An inhibitor of NO synthase, N G-nitro-L-arginine (L-NOARG, 100 microM) inhibited the relaxations and increases in NO concentration induced by acetylcholine. 3. Oxyhaemoglobin (10 microM) reversed the relaxations and increases in NO concentrations induced by acetylcholine, S-nitroso-N-acetylpenicillamine (SNAP) and S-morpholino-sydnonimine (SIN-1), but not the relaxations induced with forskolin. Oxyhaemoglobin also decreased the NO concentration below baseline level. 4. In the presence of L-NOARG (100 microM), a small relaxation to acetylcholine (10 microM) of noradrenaline-contracted segments was still seen; oxyhaemogobin inhibited this relaxation and decreased the NO concentration by 14 +/- 4 nM (n = 4). 5. The NO concentration-relaxation relationship for acetylcholine resembled that for SNAP and SIN-1 more than for authentic NO. Thus while 7-17 nM NO induced half-maximal relaxations in response to SNAP or SIN-1, 378 +/- 129 nM NO (n = 4) was needed for half-maximal relaxation to authentic NO. 6. The present study provides direct evidence that the relaxation of the rat superior mesenteric artery with the endothelium-dependent vasodilator acetylcholine is correlated to the endogeneous release of NO. The study also suggests that NO mediates the L-NOARG-resistant relaxations in this artery, and that there is a basal NO release.

Lipid hydroperoxides potentiate mesenteric artery vasoconstrictor responses

The aim of this study was to investigate the effects of lipid and organic hydroperoxides on vasomotor activity of isolated rat superior mesenteric arteries. Hydroperoxides did not elicit measurable responses in unstimulated (quiescent) mesenteric arteries. Contractile responses to potassium, however, were significantly potentiated by 13-(s)-hydroperoxylinoleic acid (range 3–54 μM). Potentiation of potassium responses by linoleic acid (18:2) and linolenic acid (18:3) was increased by pretreatment of the fatty acids with lipoxygenase ( p < .01). Lipoxygenase alone had no contractile effects. Lipoxygenase-treated 18:2, tert-butyl hydroperoxide, and hydrogen peroxide augmented contractile responses to phenylephrine, but to a lesser degree than corresponding augmentation of potassium responses. Contractile responses to lipoxygenase-treated 18:3 were blunted by vitamin E ( p < .02) and by nitroblue tetrazolium ( p < .02), whereas catalase and mannitol had no effects, implicating lipid free radicals in the contractile response. Responses to lipid hydroperoxides were not significantly altered by prostaglandin inhibitors. Endothelial cell denudation significantly enhanced the contractile responses elicited by 13-(s)-hydroperoxylinoleic acid ( p < .05), indicating that lipid hydroperoxides enhance agonist-induced contractions by a direct effect on the smooth muscle. These results support a hypothesized link between lipid peroxidation and development of altered vascular function. They further suggest that the vascular endothelium may play an important role in regulation of vasomotor responses to lipid hydroperoxides.