Mesenteric Preparations Research Articles

Increased ATP and ADO Overflow From Sympathetic Nerve Endings and Mesentery Endothelial Cells Plus Reduced Nitric Oxide Are Involved in Diabetic Neurovascular Dysfunction.

Since the mechanism of human diabetic peripheral neuropathy and vascular disease in type 1 diabetes mellitus remains unknown, we assessed whether sympathetic transmitter overflow is altered by this disease and associated to vascular dysfunction. Diabetes was induced by streptozotocin (STZ)-treatment and compared to vehicle-treated rats. Aliquots of the ex vivo perfused rat arterial mesenteric preparation, denuded of the endothelial layer, were collected to quantify analytically sympathetic nerve co-transmitters overflow secreted by the isolated mesenteries of both groups of rats. Noradrenaline (NA), neuropeptide tyrosine (NPY), and ATP/metabolites were detected before, during, and after electrical field stimulation (EFS, 20 Hz) of the nerve terminals surrounding the mesenteric artery. NA overflow was comparable in both groups; however, basal or EFS-secreted ir-NPY was 26% reduced (p < 0.05) in diabetics. Basal and EFS-evoked ATP and adenosine (ADO) overflow to the arterial mesentery perfusate increased twofold and was longer lasting in diabetics; purine tissue content was 37.8% increased (p < 0.05) in the mesenteries from STZ-treated group of rats. Perfusion of the arterial mesentery vascular territory with 100 μM ATP, 100 nM 2-MeSADP, or 1 μM UTP elicited vasodilator responses of the same magnitude in controls or diabetics, but the increase in luminally accessible NO was 60–70% lower in diabetics (p < 0.05). Moreover, the concentration–response curve elicited by two NO donors was displaced downwards (p < 0.01) in diabetic rats. Parallel studies using primary cultures of endothelial cells from the arterial mesentery vasculature revealed that mechanical stimulation induced a rise in extracellular nucleotides, which in the cells from diabetic rats was larger and longer-lasting when comparing the extracellular release of ATP and ADO values to those of vehicle-treated controls. A 5 min challenge with purinergic agonists elicited a cell media NO rise, which was reduced in the endothelial cells from diabetic rats. Present findings provide neurochemical support for the diabetes-induced neuropathy and show that mesenteric endothelial cells alterations in response to mechanical stimulation are compatible with the endothelial dysfunction related to vascular disease progress.

Altered Calcium Handling in Peripheral Nerve Terminals and Blood Vessels in Spontaneously Hypertensive Rats

The present study was designed to clarify the roles of N-type and P/Q-type calcium channels in the increased sympathetic activity of spontaneously hypertensive rats (SHR/Izm). We also tested in SHR/Izm the contribution to increased vascular tone of α1A adrenoceptor-linked L-type calcium channels and α1B receptor-mediated calcium mobilization from the sarcoplasmic reticulum. Methods: Six-week-old SHR/Izm and Wistar-Kyoto rats (WKY/Izm) were used. A superior mesenteric arterial preparation was electrically stimulated before and after treatment with ω-conotoxin GVIa (N-type calcium channel blocker [CgTX]) and ω-agatoxinIVa (P/Q-type calcium channel blocker [AgaTX]). Pressor response to norepinephrine was measured before and after treatment with the α1A blocker WB-4101 and the α1B blocker chloroethyl clonidine (CEC). To determine the intracellular calcium store size, the effects of ryanodine on pressor response and caffeine-induced vascular contraction were also tested. Results: Norepinephrine overflow evoked by electrical stimulation was increased in SHR/Izm. CgTX but not AgaTX suppressed the increased NE overflow in SHR/Izm. WB-4101 suppressed the pressor response to norepinephrine in SHR/Izm but not WKY/Izm rats. CEC had no effects on pressor response to norepinephrine in both types of rats. Caffeine-induced contraction to a high potassium-induced maximal contraction ratio was reduced in SHR/Izm. The effect of ryanodine on pressor response was reduced in SHR/Izm. Conclusion: N-type calcium channels but not P/Q-type calcium channels play an important role in the increased sympathetic tone in SHR/ Izm. Although α1A adrenoceptor-linked L-type calcium channels contribute to the increased vascular tone, the intracellular calcium store size was reduced in SHR/Izm.

In focus: Fe3O4 nanoparticles and human mesenteric artery interaction in vitro.

The growing implementation of iron oxide nanoparticles in medicine requires a thorough investigation of their physiological influence. Therefore, effects of Fe3O4 nanoparticles on isometric contractions of healthy human mesenteric artery in vitro were investigated. The effect of increasing concentrations (0.023, 0.069, 0.23, 0.69 and 2.31 μg/μl) of Fe3O4 nanoparticles (50-100 nm) on the contractility of mesenteric artery ring preparations was studied using wire myography technique. A lack of effects of Fe3O4 nanoparticles (50-100 nm) on isometric contractions of human mesenteric artery segments both in conditions of basal tension and precontraction was found. The observed unresponsiveness of human mesenteric arteries in vitro to Fe3O4 nanoparticles could be attributed to their safe mode of use in biomedicine.

Peritoneal Mast Cell Stabilization Potential of Ziziphus Xylopyrus (Retz) Wild Extract in Rat Mesenteric Model

Objective: To investigate the peritoneal mast cell stabilization activity of Ziziphus xylopyrus extracts. Materials and Methods: Ziziphus Xylopyrus L. (family- Rhamnaceae) stem part was successively extracted with ethanol and aqueous to prepare extract of the plant. The extracts of Ziziphus Xylopyrus (Z. xylopyrus) were evaluated for stabilization of mast cell in rat for the evaluation of Hypersensitivity type I allergic reaction in animal models. The extract of Z. xylopyrus ethanolic and aqueous (1, 10 and 100 μg/ml) was evaluated for peritoneal mast cell stabilization activity in rat mesenteric preparation induced by C 48/80. Result: Preliminary phytochemical analysis revealed the presence of carbohydrates, fixed oil, proteins, alkaloids, glycosides, flavonoids and phenolic compounds. The ethanolic and aqueous extracts of Z. xylopyrus showed dose dependent increase in the number of intact cells when compare with C 48/80 at the concentration of 10 and 100 μg/ml. It virtues further work towards the isolation of phyto constituents from this plant. Conclusion: This finding provides evidence that the Z. xylopyrus inhibits mast cell-derived immediate-type allergic reactions and mast cell degranulation. Z. xylopyrus has a potential as allergic anti-asthmatic agent.

Peritoneal Mast Cell Stabilization and Free radical Scavenging activity of Yucca gloriosa L

Objective: To investigate in vitro antioxidant and mast cell stabilization potential Yucca gloriosa L. Methods: The aerial parts of Yucca gloriosa L. (Family- Agavaceae ) were successively extracted with ethanol, 50% aqueous-ethanolic and aqueous to prepare an extract of the plant. Preliminary phytochemical tests, total phenol and flavonoid estimation were analyzed in Y. gloriosa L. extract. Furthermore, in vitro antioxidant activity was evaluated such as DPPH method, ABTS assay, superoxide assay, nitric oxide assay and lipid peroxidation inhibition assay. The extract of YGE, 50% YGE and YGA (1, 10 and 100µg/ml) was studied for peritoneal mast cell stabilization activity in rat mesenteric preparation induced by C 48/80. Result: The result revealed that YGE showed highest concentration of phenol and flavonoid compounds. Free radical scavenger activity and mast cell activity had been identified in YGE, 50%YGE and YGA extracts. The Free radical scavenger study revealed that the YGE, 50%YGE & YGA extracts of Y. gloriosa L. showed significant activity in DPPH method, Nitric oxide assay, ABTS cation decolorization assay, superoxide assay and lipid peroxidase assay. All the extracts showed ability to prevent oxidation when compare with standard markers. Upon further investigation for mast cell activity, of YGE extracts showed significant increase the number of intact cells when compared with C48/80 at the concentrations of 10 and 100 µg/mg when compare to other extracts. Conclusion: This finding provides suggested that Y. gloriosa L. is a potential candidate in herbal medicine for allergic asthma. Due to its ability to inhibit mast cell derived immediate-type I allergic reactions. It virtues further work towards the isolation of phytoconstituents from Y. gloriosa L. Key words: Compound 48/80, Free radicals, Mast cell, Yucca gloriosa L.

Hypotensive and vasorelaxant effects induced by the ethanolic extract of the Mimosa caesalpiniifolia Benth. (Mimosaceae) inflorescences in normotensive rats

Ethnopharmacological relevanceCaatinga is highly influenced by its seasonality. This species is endemic in the northeastern region, which is rich in plants with pharmacological potential. Many of these plants are used by the population and some of them have confirmed pharmacological properties. Mimosa caesalpiniifolia Benth. (Mimosaceae) is a native plant from northeastern Brazil׳s caatinga, popularly known as sabiá and cascudo. The tea from the inflorescence of this species is used by the population of the semi-arid for the treatment of hypertension, and the utilization of the plant bark for the staunching of bleedings and wound washing in order to prevent inflammation; also, the ingestion of the bark infusion is used in the treatment of bronchitis. However, its pharmacological effects and mechanisms of action have not yet been studied. The aim of the present study was to determine the effect of the ethanolic extract of M. caesalpiniifolia on the cardiovascular system in rats. Material and methodsIn a study for the assessment of the hypotensive effect of the extract, the polyethylene catheters were inserted in the aorta artery and inferior vena cava for the measurement of the arterial pressure and heart rate. When intragastric administration was performed, only one catheter was implanted in the abdominal aorta. In studies for the vasorelaxant activity, mesenteric arterial rings (1–2mm) were used: they were kept in Tyrode׳s solution (95% O2 and 5% CO2) and submitted to tension of 0.75g/f for 1h. The results were expressed as mean±S.E.M., significant to the values of p<0.05. ResultsThe administration of the doses through venous pathway (6.25; 12.5 and 25mg/kg, i.v.) promoted hypotension followed by bradycardia in the higher doses. The pre-treatment with atropine (2mg/kg, i.v.) interrupted both the hypotension and the bradycardia; with hexamethonium, hypotension was reverted and bradycardia was attenuated. While the administration of tea/flowers (25mg/kg i.v.) also promoted a following section of hypotension, a slight increase in heart rate was observed. When administered orally, MC-EtOH/flowers (100mg/kg, v.o.) promoted a decrease in the arterial pressure from 90min on, without a significant alteration in the heart rate in relation to the control. In the in vitro study, a pharmacological trial was performed with the extracts obtained from parts of the species M. caesalpiifolia (leaves, bark, fruit and inflorescences). Among all extracts tested, the ethanolic extract from the inflorescences (MC-EtOH/flowers) presented higher vasorelaxant potency in relation to the other parts of the plant. Henceforth, MC-EtOH/flowers was used in the sequence. In mesenteric preparations pre-contracted with phenylephrine (10−5M), the MC-EtOH/flowers (0.1–750µg/ml) promoted vasorelaxant effect regardless of the vascular endothelium. MC-EtOH/flowers inhibited the contractions induced by the cumulative addition of phenylephrine (10−9–10−5mol/l) or CaCl2 (10−6–3×10−2M), in a concentration-dependent way. In contractions induced by S(-)Bay K 8644, a Cav-L activator, the MC-EtOH/flowers promoted concentration-dependent relaxation, corroborating previous results. ConclusionThe tea of flowers of M. caesalpiniifolia promotes hypotension and tachycardia, whereas ethanolic extract (MC-EtOH) promotes hypotension and bradycardia involving the participation of the muscarinic and ganglionic pathways, as well as vasorelaxant action involving the Ca2+ influx inhibition blockade.

Peritoneal mast cell stabilization potential of Pothos scandens L.

Objective:To investigate the peritoneal mast cell stabilization activity of Pothos scandens extractsMaterials and Methods:Pothos scandens L. (family- Araceae) aerial part was successively extracted with ethanol and aqueous to prepare extract of the plant. The extracts of P. scandens were evaluated for stabilization of mast cell in rat allergic models. The extract of P. scandens ethanolic, 50% aqueous ethanolic and aqueous (1, 10 and 100 μg/ml) was studied for peritoneal mast cell stabilization activity in rat mesenteric preparation induced by C 48/80.Result:Preliminary phytochemical analysis revealed the presence of carbohydrates, fixed oil, proteins, alkaloids, glycosides, flavonoids and phenolic compounds. The ethanolic, 50% aqueous ethanolic and aqueous extracts of P. scandens L. showed dose dependent increase in the number of intact cells when compare with C48/80 at the concentration of 10 and 100 μg/ml. It virtues further work towards the isolation of phytoconstituents from this plant.Conclusion:This finding provides evidence that the P. scandens L. inhibits mast cell-derived immediate-type allergic reactions and mast cell degranulation. P. scandens has a potential as allergic anti- asthmatic agent.

Involvement of perivascular nerves and transient receptor potential vanilloid 1 (TRPV1) in vascular responses to histamine in rat mesenteric resistance arteries

A previous report showed that histamine in denuded mesenteric vascular beds produced a triphasic response; an initial small histamine H2 receptor-mediated vasodilation, a transient histamine H1 receptor-mediated vasoconstriction, and finally a long-lasting vasodilation. We further investigated the vascular effect of histamine in mesenteric preparations without an endothelium to clarify the possible involvement of perivascular nerves. Male Wistar rat mesenteric vascular beds without an endothelium were perfused with Krebs solution containing methoxamine to produce active tone and lafutidine to block histamine H2 receptor-mediated vasodilation. Histamine (1–100μM) was perfused for 1min and perfusion pressure was measured with a pressure transducer. Histamine caused a biphasic vascular response; initial vasoconstriction followed vasodilation. Tetrodotoxin (a neurotoxin, 1μM) and procaine (a local anesthetic, 100μM) significantly inhibited the vasoconstriction and vasodilation. Ruthenium red (a transient receptor potential vanilloid 1 (TRPV1) antagonist, 1μM) also significantly inhibited both phases of the response. Pretreatment with capsaicin (a depletor of calcitonin gene-related peptide (CGRP)-containing nerves, 5μM) significantly inhibited the vasodilation without affecting the initial vasoconstriction. Both indomethacin (a cyclooxygenase inhibitor, 0.5μM) and seratrodast (a thromboxane A2 receptor antagonist, 0.1μM) abolished the histamine-induced vasoconstriction and subsequent vasodilation. These results suggest that histamine-induced vasoconstriction and long-lasting vasodilation are mediated by activation of TRPV1 on capsaicin-sensitive and capsaicin-insensitive nerves. They also suggest that perivascular nerves and prostanoids, probably thromboxane A2, are responsible for the vascular response to histamine.

Inhibitory effects of sertraline in rat isolated perfused kidneys and in isolated ring preparations of rat arteries

Sertraline is often prescribed to patients suffering with end stage renal disease, but its action on kidney has not been investigated. We aimed to investigate the pharmacological action of sertraline on rat kidney with emphasis on the underlying mechanisms involved in the vascular actions of the drug. The effects of sertraline were evaluated in rat isolated perfused kidneys and on ring preparations of mesenteric or segmental rat renal artery. In kidneys, sertraline prevented the effects of phenylephrine on perfusion pressure, glomerular filtration rate, urinary flow and renal vascular resistance. In mesenteric rings sertraline inhibited phenylephrine-induced contractions with potency 30-times lower than verapamil. Sertraline reversed sustained contractions induced by phenylephrine or 60mm K(+) within a similar concentration range. In segmental isolated rings, sertraline also reversed contractions induced by phenylephrine or 60mm K(+) with the same concentration range, but with higher potency compared with mesenteric preparations. Under Ca(2+) -free conditions, sertraline did not change the intracellularly-mediated phasic contractions induced by phenylephrine or caffeine. Sertraline was ineffective against contractions induced by extracellular Ca(2+) restoration after thapsigargin treatment and Ca(2+) store depletion with phenylephrine. Conversely, sertraline decreased the contractions induced by Ca(2+) addition in tissues under high K(+) solution or phenylephrine plus verapamil. In rat isolated kidneys and in rat ring preparations of mesenteric or renal vessels, sertraline had antispasmodic effects that appeared to be caused by a direct action on vascular smooth muscle cells. Its actions were ineffective against Ca(2+) -releasing intracellular pathways, but appeared to interfere with sarcolemmal Ca(2+) influx with reduced permeability of both receptor- and voltage-gated Ca(2+) channels.

Cardiovascular effects of 1-nitro-2-phenylethane, the main constituent of the essential oil of Aniba canelilla, in spontaneously hypertensive rats

This study investigated the cardiovascular responses to the essential oil of Aniba canelilla (EOAC) and its main constituent 1-nitro-2-phenylethane (NP) in spontaneously hypertensive rats (SHRs). In anesthetized SHRs, intravenous (i.v.) bolus injections of EOAC (1-20 mg/kg) or NP (1-10 mg/kg) elicited dose-dependent hypotensive and bradycardiac effects, which were characterized in two periods (phases 1 and 2). The first rapid component (phase 1) evoked by EOAC and NP both at 10 mg/kg was absent after left ventricle injection, fully abolished by bilateral vagotomy and perineural treatment of both cervical vagus nerves with capsaicin (250 μg/mL) while remained unaltered by i.v. pretreatment with capsazepine (1 mg/kg) or ondansetron (30 μg/kg). In conscious SHRs, NP (5 and 10 mg/kg, i.v.) evoked rapid hypotensive and bradycardiac effects (phase 1) that were fully abolished by methylatropine (1 mg/kg, i.v.) pretreatment. In rat endothelium-containing mesenteric preparations, increasing concentrations (0.1-1000 μg/mL) of EOAC and NP relaxed the phenylephrine-induced contraction in a concentration-dependent manner. It is concluded that NP induces a vago-vagal bradycardiac and depressor reflex (phase 1) that apparently results from the stimulation of vagal pulmonary rather than cardiac C-fiber afferents. This effect does not appear to involve activation of either vanilloid TPRV(1) or 5-HT(3) receptors located on vagal sensory nerves. The phase 2 hypotensive response to i.v. NP seems to result, at least in part, from its direct vasodilatory effect on the peripheral smooth muscle. All in vivo and in vitro effects of EOAC are mostly attributed to the actions of its main constituent NP.

A ketolide antibiotic, telithromycin, inhibits vascular adrenergic neurotransmission in the rat mesenteric vascular bed

A ketolide antibiotic, telithromycin, has side effects including temporary loss of consciousness in clinical use, but the underlying mechanisms remain unclear. This study investigated the effects of telithromycin on perivascular nerve function in rat mesenteric arteries, in comparison with those of macrolide (erythromycin and clarithromycin) and new quinolone antibiotics (levofloxacin and gatifloxacin). In vitro, vascular responses and release of noradrenaline induced by periarterial nerve stimulation (PNS) of rat perfused mesenteric vascular beds were measured in the presence of each antibiotic. In vivo blood pressure measurement was performed in Wistar rats. In mesenteric preparations with resting tone, telithromycin (10 nM-10 microM) markedly inhibited PNS (4-12 Hz)-induced adrenergic nerve- and exogenous noradrenaline-mediated vasoconstriction, whereas the other antibiotics slightly inhibited PNS-induced responses without affecting noradrenaline-induced responses. Telithromycin significantly reduced PNS (12 Hz)-evoked noradrenaline release in the perfusate. In pre-constricted preparations with or without endothelium, telithromycin (0.1 nM-10 microM) caused a concentration-dependent vasodilation. Telithromycin (10 nM) inhibited calcium-induced vasoconstriction in high KCl and calcium-free medium. None of the antibiotics used affected PNS (0.5-2 Hz)-induced calcitonin gene-related peptide (CGRP) nerve- and exogenous CGRP-mediated vasodilation. Intravenous injection of telithromycin significantly lowered blood pressure in anaesthetized rats. These results suggest that telithromycin causes not only strong inhibition of perivascular adrenergic neurotransmission but also a vasodilator action in mesenteric vascular beds and hypotension. It is thus possible that telithromycin increases visceral blood flow, consequently reducing cerebral blood flow and resulting in a temporary loss of consciousness.

Oxidative stress attenuates NO-induced modulation of sympathetic neurotransmission in the mesenteric arterial bed of spontaneously hypertensive rats

Current evidence suggests that hyperactivity of the sympathetic nervous system and endothelial dysfunction are important factors in the development and maintenance of hypertension. Under normal conditions the endothelial mediator nitric oxide (NO) negatively modulates the activity of the norepinephrine portion of sympathetic neurotransmission, thereby placing a "brake" on the vasoconstrictor ability of this transmitter. This property of NO is diminished in the isolated, perfused mesenteric arterial bed taken from the spontaneously hypertensive rat (SHR), resulting in greater nerve-stimulated norepinephrine and lower neuropeptide Y (NPY) overflow from this mesenteric preparation compared with that of the normotensive Wistar-Kyoto rat (WKY). We hypothesized that increased oxidative stress in the SHR contributes to the dysfunction in the NO modulation of sympathetic neurotransmission. Here we demonstrate that the antioxidant N-acetylcysteine reduced nerve-stimulated norepinephrine and increased NPY overflow in the mesenteric arterial bed taken from the SHR. Furthermore, this property of N-acetylcysteine was prevented by inhibiting nitric oxide synthase with N(omega)-nitro-l-arginine methyl ester, demonstrating that the effect of N-acetylcysteine was due to the preservation of NO from oxidation. Despite a reduction in norepinephrine overflow, the nerve-stimulated perfusion pressure response in the SHR mesenteric bed was not altered by the inclusion of N-acetylcysteine. Studies including the Y(1) antagonist BIBO 3304 with N-acetylcysteine demonstrated that this preservation of the perfusion pressure response was due to elevated NPY overflow. These results demonstrate that the reduction in the bioavailability of NO as a result of elevated oxidative stress contributes to the increase in norepinephrine overflow from the SHR mesenteric sympathetic neuroeffector junction.

Mast Cell Degranulation Alters Lymphatic Contractile Activity Through Action of Histamine

Mast cells reside in most tissues and in close association with blood vessels and nerves, areas where lymphatic vessels are also present. Mast cells and lymphatic vessels are two important players in the development of the inflammatory process. This study was designed to examine the effects of mast cell degranulation on the contractile activity of mesenteric lymphatic vessels. Lymphatic vessel contractile activity was assessed in vitro by video microscopy of the mesentery of cow's milk-sensitized guinea pigs upon application of beta-lactoglobulin and compared to the response measured in sham animals. Application of 5-10 microM beta-lactoglobulin increased lymphatic vessel constriction frequency and decreased constriction amplitude (n = 12). This effect was not seen in sham-treated animals (n = 16) and was not due to an increased number of mast cells in the mesentery of the milk-sensitized animals, as revealed by histological examination. Two known mast cell-derived mediators, histamine and thromboxane A2, via stable mimetic U46619 also altered lymphatic pumping in a similar manner, but only pretreatment with the histamine H1 receptor antagonist pyrilamine (1 microM) could reduce the beta-lactoglobulin-induced response. The thromboxane A2 receptor antagonist, SQ 29548, and the 5-lipoxygenase inhibitor, caffeic acid, were without significant effect. In the in vitro mesenteric preparation, mast cell degranulation altered lymphatic contractile activity via the release of a mediator suggested to be histamine and the subsequent activation of H1 receptors. This action could potentially interfere with the expected ability of lymphatic vessels to reduce edema during inflammation.

Impaired alpha‐adrenergic autoreceptor modulation of purinergic transmission in mesenteric arteries of DOCA‐salt rats

Hypertension is associated with an increase in NE and ATP release from sympathetic nerves associated with mesenteric arteries where ATP is the principal constrictor transmitter. Prejunctional α 2-adrenoreceptors (ARs), regulate ATP and NE release. It is hypothesized that impairment of α 2-AR function may cause increased ATP release contributing to arterial constriction and hypertension. Our goal was to determine whether impaired α 2-AR function contributes to increased ATP release in mesenteric arteries of DOCA-salt hypertensive rats. Mesenteric preparations were maintained in vitro and intracellular recordings of excitatory junction potentials (EJPs) from smooth muscle cells were recorded. EJPs, mediated by ATP acting at P2X1 receptors, were evoked using single electrical stimuli (10–100V). There were no differences in peak EJP amplitude recorded at any voltage from sham or DOCA-salt arteries, nor were there differences in resting membrane potential or EJP rise/decay time. Clonidine (α 2-AR agonist) caused a concentration dependent inhibition of EJPs in sham and DOCA-salt arteries but EJPs in DOCA-salt arteries was less sensitive to inhibition by clonidine (P < 0.05). Clonidine did not change ATP-induced constrictions of sham arteries. However, clonidine caused direct constrictions of DOCA-salt arteries. We conclude that DOCA-salt hypertension does not modify the properties of arterial P2X1 receptors. In addition, α 2-ARs modulate ATP release and their function is impaired in DOCA-salt hypertension. DOCA-salt arteries are sensitized to the contractile effects of clonidine through an unidentified mechanism.

Effects of the Dietary Flavonoid Chrysin in Isolated Rat Mesenteric Vascular Bed

In the present study, the effects of the bioflavonoid chrysin (5,7-dihydroxyflavone) were analyzed on the perfusion pressure of isolated mesenteric vascular bed. The vasorelaxant effects of chrysin were more potent on intact endothelium than on denuded vessels. This endothelium-dependent response induced by chrysin was inhibited in the presence of N^G-nitro-L-arginine methyl ester (L-NAME), KCl, tetraethylammonium (TEA), BaCl₂, TEA plus L-NAME, and ouabain plus BaCl₂, while incubations with indomethacin and glibenclamide did not modify the response induced by this bioflavonoid. Neither gap junction inhibition with carbenoxolone nor epoxyeicosatrieconic acid synthesis inhibition with sulfaphenazole (selective CYP 2C/3A inhibitor) or 7-ethoxyresorufin (selective CYP 1A inhibitor) inhibited the chrysin-induced relaxation. Moreover, chrysin increased L-NAME-sensitive cGMP accumulation in intact vascular mesenteric preparation. In conclusion, chrysin shows vasodilator effects on resistance vessels, which depend partially on the functional endothelium and appear to be related to the NO/cGMP pathway and, possibly to the release of endothelium-derived hyperpolarizing factor.

Disodium cromoglycate stabilizes mast cell degranulation while reducing the number of hemoglobin-induced microvascular leaks in rat mesentery.

Blood substitutes, such as diaspirin cross-linked Hb (DBBF-Hb), have been considered for use during blood transfusions. Unfortunately, bolus injection of modified Hb has been shown to rapidly increase the leakage of microvessels to plasma albumin. This effect may result from production of excess reactive oxygen species (ROS) and could be linked to the observed increase in degranulated mast cells (DMC). Disodium cromoglycate (cromolyn) stabilizes mast cells and therefore might minimize the venular permeability in the rat mesentery. In 10 anesthetized Sprague-Dawley rats, the mesenteric preparation was continuously suffused with cromolyn while the microvasculature was filled with DBBF-Hb solution (10 mg/ml) for 10 min. Six animals received cromolyn pretreatment [two intravascular injections over 30 min (experiment A)] and four animals received pretreatment with 2% HEPES-buffered saline (HBS)-BSA (experiment B). Two more animals were pretreated with HBS-BSA without DBBF-Hb infusion but with cromolyn suffusion (experiment C). Another set of experiments was performed on five animals without cromolyn suffusion or any pretreatment but with DBBF-Hb infusion (experiment D). All groups then received a 1-min perfusion of FITC-albumin, fixation for 60 min, and microscopic examination. Experiments A and B demonstrated a significant reduction in the number of venular leaks and DMC compared with experiment D, but not in the area of venular leaks. These results suggest mast cell degranulation is not a major contributor to microvascular leakage induced by DBBF-Hb.

Octreotide in Intestinal Lymphangiectasia: Lack of a Clinical Response and Failure to Alter Lymphatic Function in a Guinea Pig Model

Intestinal lymphangiectasia, which can be classified as primary or secondary, is an unusual cause of protein-losing enteropathy. The main clinical features include edema, fat malabsorption, lymphopenia and hypoalbuminemia. Clinical management generally includes a low-fat diet and supplementation with medium chain triglycerides. A small number of recent reports advocate the use of octreotide in intestinal lymphangiectasia. It is unclear why octreotide was used in these studies; although octreotide can alter splanchnic blood flow and intestinal motility, its actions on lymphatic function has never been investigated. A case of a patient with intestinal lymphangiectasia who required a shunt procedure after failing medium chain triglycerides and octreotide therapy is presented. During the management of this case, all existing literature on intestinal lymphangiectasia and all the known actions of octreotide were reviewed. Because some of the case reports suggested that octreotide may improve the clinical course of intestinal lymphangiectasia by altering lymphatic function, a series of experiments were undertaken to assess this. In an established guinea pig model, the role of octreotide in lymphatic function was examined. In this model system, the mesenteric lymphatic vessels responded to 5-hydroxytryptamine with a decrease in constriction frequency, while histamine administration markedly increased lymphatic constriction frequency. Octreotide failed to produce any change in lymphatic function when a wide range of concentrations were applied to the mesenteric lymphatic vessel preparation. In conclusion, in this case, octreotide failed to induce a clinical response and laboratory studies showed that octreotide did not alter lymphatic function. Thus, the mechanisms by which octreotide induced clinical responses in the cases reported elsewhere in the literature remain unclear, but the present study suggests that it does not appear to act via increasing lymphatic pumping.

Polyphenol-enriched extract of oil palm fronds (Elaeis guineensis) promotes vascular relaxation via endothelium-dependent mechanisms.

Plant-based polyphenolic compounds have been reported to possess cardiovascular health benefits. Several dietary sources, including herbs and spices, fruits and vegetables, and tea and wine, contain an array of biologically active compounds that have been shown to be effective in retarding oxidation of low-density lipoproteins (LDL) and promoting vascular relaxation. In the present study four different plant sources, both edible and non-edible, were evaluated for potential activity. Organic extracts enriched in polyphenols were prepared from palm fronds (Elaesis guineensis); lemongrass (Cymbopogon citrates); papaya shoots (Carica papaya) and green chilli (Capsicum frutescenes) and tested for their ability to prevent in vitro oxidation of LDL, and for potential vascular relaxation actions. Rings of rat thoracic aorta and isolated perfused mesenteric vascular beds were mounted in organ baths, contracted using a half-maximal dose of noradrenaline and exposed to cumulative additions of test extracts. Palm frond extract resulted in considerable relaxation (>75%) in both preparations and was found to be endothelium-dependent as removal of endothelium or inhibition of endogenous nitric oxide (NO) led to a total loss in relaxant activity. Lemongrass extract caused a greater relaxation action in the mesenteric preparation compared to aortic rings, and appears to be mediated via NO-independent and non-prostanoid mechanisms. Of the extracts tested, palm fronds also demonstrated the highest antioxidant capacity, as determined by the ferric reducing activity/potential assay, and resulted in a significant delay (P < 0.05) in the oxidation of LDL. Collectively, these preliminary findings lend further support to the potential cardiovascular actions of plant polyphenols and also identify oil palm fronds as containing constituents that promote vascular relaxation via endothelium-dependent mechanisms.

Cytochrome P450 metabolites of arachidonic acid may be important mediators in angiotensin II-induced vasoconstriction in the rat mesentery in vivo

We have investigated the role of cytochrome P450 (CYP-450) metabolites of arachidonic acid in the modulation of vascular reactivity to angiotensin II in vivo using an in situ blood-perfused mesenteric preparation in anaesthetized spontaneously hypertensive rats (SHR). Miconazole, a non-selective inhibitor of CYP-450 that inhibits both hydroxylation and epoxidation, substantially suppressed mesenteric vasoconstrictor responses to angiotensin II in SHR, but had no effect on responses to noradrenaline or sympathetic nerve stimulation. In normotensive Wistar–Kyoto (WKY) rats, miconazole caused only a modest suppression of vasoconstrictor responses to angiotensin II. N-Methylsulphonyl-12,12-dibromododec-11-enamide (DDMS), a new selective inhibitor of CYP-450 ω-hydroxylase activity, decreased mean intra-arterial blood pressure and significantly attenuated mesenteric angiotensin II-induced vasoconstrictor responses in SHR. Isolated mesenteric vessels were able to metabolize 14C-labelled arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) in vitro, and this was substantially inhibited by DDMS. The results from the present studies combined with the existing evidence that angiotensin II stimulates the release of 20-HETE, a CYP-450 metabolite of arachidonic acid, suggest that CYP-450-derived HETEs may be important mediators in angiotensin II-induced vasoconstriction. However, the development of more sensitive assays for the detection in vivo of 20-HETE in mesenteric vessels would be required to confirm these findings.

Cytochrome P450 metabolites of arachidonic acid may be important mediators in angiotensin II-induced vasoconstriction in the rat mesentery in vivo

We have investigated the role of cytochrome P450 (CYP-450) metabolites of arachidonic acid in the modulation of vascular reactivity to angiotensin II in vivo using an in situ blood-perfused mesenteric preparation in anaesthetized spontaneously hypertensive rats (SHR). Miconazole, a non-selective inhibitor of CYP-450 that inhibits both hydroxylation and epoxidation, substantially suppressed mesenteric vasoconstrictor responses to angiotensin II in SHR, but had no effect on responses to noradrenaline or sympathetic nerve stimulation. In normotensive Wistar-Kyoto (WKY) rats, miconazole caused only a modest suppression of vasoconstrictor responses to angiotensin II. N-Methylsulphonyl-12, 12-dibromododec-11-enamide (DDMS), a new selective inhibitor of CYP-450 omega-hydroxylase activity, decreased mean intra-arterial blood pressure and significantly attenuated mesenteric angiotensin II-induced vasoconstrictor responses in SHR. Isolated mesenteric vessels were able to metabolize (14)C-labelled arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) in vitro, and this was substantially inhibited by DDMS. The results from the present studies combined with the existing evidence that angiotensin II stimulates the release of 20-HETE, a CYP-450 metabolite of arachidonic acid, suggest that CYP-450-derived HETEs may be important mediators in angiotensin II-induced vasoconstriction. However, the development of more sensitive assays for the detection in vivo of 20-HETE in mesenteric vessels would be required to confirm these findings.