Rat Thoracic Aortic Rings Research Articles

Twenty-four-hour variations in the effect of nitrodilators in rat aorta: lack of influence of the endothelium.

Time-dependent variations of the vasodilator effects of sodium nitroprusside and glyceryl trinitrate on isolated smooth muscle have been studied on rings of rat thoracic aorta, both endothelium-intact and endothelium-denuded. For most of the concentrations of sodium nitroprusside used the induced relaxations were significantly dependent on the time the tissues were obtained. However, significant temporal differences were obtained for glyceryl trinitrate-induced relaxations at lower concentrations only for both endothelium-intact and endothelium-denuded preparations. EC50 values of sodium nitroprusside and glyceryl trinitrate (i.e. the concentrations inducing half the maximum response) were also significantly different and they had quite similar rhythmic features both in endothelium-intact and in endothelium-denuded preparations. These results clearly show that the in-vitro sensitivity of rat thoracic aorta to nitrodilator agents varies over a 24-h period and thus depends on when the animals were killed; the presence of endothelium does not change the rhythm of nitrodilator activity. These variations might be a result of circadian rhythm in the guanylate cyclase-cGMP system which mediates responses to nitrodilator agents.

AICAR‐induced vasorelaxation is associated with the phosphorylation of HspB6 and VASP

AMP-activated protein kinase(AMPK) is a major regulator of metabolism and pharmacological regulation of this kinase has been widely used in the treatment of diabetes. Heat shock protein B6 (HspB6) and vasodilator-stimulated phosphoprotein (VASP) modulates thin filament regulation of vascular smooth muscle tone. This study examined the role of HspB6 in the AMPK-induced signaling pathways that lead to enhanced vasorelaxation in rat thoracic aorta (RA). Endothelium intact or denuded RA rings were either pre-contracted with phenylephrine (PE) and treated with 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) to induce relaxation, or incubated with AICAR prior to vasocontraction by PE. Force was measured in a muscle bath and tissues were frozen under tension. AICAR induced relaxation in PE pre-contracted tissues and pretreatment of RA rings with AICAR inhibited PE-induced contraction. Treatment with L-NAME prior to AICAR treatment partially abolished the effects of AICAR. Both AICAR-induced vasorelaxation and inhibition of contraction were associated with increased phosphorylation of HspB6 at Ser16 and VASP. These data show that activation of AMPK leads to vasorelaxation via endothelial and smooth muscle dependent mechanisms and is associated with the phosphorylation of HspB6 and VASP. This modulation may have potential implication in diabetic vascular disorders. Supported by NIH grant.

Macrophyllionium and Macrophyllines A and B, Oxindole Alkaloids from Uncaria macrophylla

An unusual oxindole alkaloid inner salt, macrophyllionium (1), and a pair of new tetracyclic oxindole alkaloids, macrophyllines A (2) and B (3), together with six known alkaloids, were isolated from the aerial parts of Uncaria macrophylla. Corynantheidine (8) exhibited moderate cytotoxicity against HL-60 and SW480 cells with IC(50) values of 13.96 and 23.28 μM, respectively. Dihydrocorynantheine (9) exhibited significant vasodilating activity against phenylephrine-induced contraction in rat thoracic aorta rings (IC(50) = 6.73 μg/mL). In addition, compounds 2, 6, and 9 showed weak inhibitory action on KCl-induced contraction.

Vasorelaxant Activities of Aqueous Extracts from Twenty Medicinal Plants Used in Oriental Medicines in Isolated Rat Aorta

Water extracts from 20 medicinal plants, traditionally used for postmenopausal symptoms in Korea, were examined for their vasorelaxant activity in isolated rat thoracic aorta rings precontracted with norepinephrine (NE). Among the 20 medicinal plants, Cornus officinalis (CoEx, 0.3 ㎎/mL), Schisandra chinensis (ScEx, 0.3 ㎎/mL), Erythrina variegate (EvEx, 0.3 ㎎/mL), and Epimedium koreanum (EkEx, 0.3 ㎎/mL) showed rapid relaxation of endothelium-intact aorta (69±4%, 40±3%, 25±2%, and 23±3% of active tone induced by NE, respectively). In contrast, the extracts of Erythrina variegata (EvEx), Angelica gigas (AgEx), Pueraria thunbergiana (PtEx), and EkEx lead to gradual (i.e., long-term) relaxation to baseline in endothelium-intact vessels. The time to complete relaxation was 20～40 min. These 6 plant extracts were selected for the investigation of possible underlying mechanisms. The CoEx-, ScEx-, or EkEx-induced rapid relaxations were virtually abolished by endothelium denudation, and were significantly inhibited by pretreatment with nitric oxide (NO) synthase inhibitor N G -nitro-L-arginine (L-NNA, 10 μM), indicating that increased formation of NO might contribute to the endothelium-mediated relaxation. In long-term responses, the endothelium denudation did not affect PtEx-induced relaxation, whereas it delayed responses by EvEx and AgEx, and significantly inhibited the effect of EkEx. Among EvEx, AgEx, and PtEx, EvEx attenuated the CaCl₂-induced vasoconstriction in high-potassium depolarized medium, implying that EvEx is involved in inhibition of the extracellular calcium influx to smooth muscle through voltage dependent calcium channels. These results provide the scientific rationale for the interrelationships between the use of 20 medicinal plants and their effects on cardiovascular health in estrogen deficient conditions.

Identification of a New Natural Vasorelaxatant Compound, (+)-Osbeckic Acid, from Rutin-free Tartary Buckwheat Extract

The candidates responsible for vasorelaxation action of rutin-free tartary buckwheat extract (TBSP) were examined in this study. As a result of reversed-phase high-performance liquid chromatography (HPLC) separations, five prominent peaks in the acidic fraction of TBSP were obtained at 260 nm. Among the five collected peaks, we successfully identified four compounds by nuclear magnetic resonance (NMR) and mass spectrometry (MS) measurements: (+)-osbeckic acid as a dimer ([M - H](-) m/z: 371.2 > 184.9 > 140.9), 5-hydroxymethyl-2-furoic acid, protocatechuic acid, and p-hydroxybenzoic acid. A vascular contractive measurement in 1.0 μM phenylephrine-contracted Sprague-Dawley rat thoracic aorta rings revealed that (+)-osbeckic acid dimer evoked a potent vasorelaxant effect with an EC50 value of 887 μM compared to other isolates (EC50: 5-hydroxymethyl-2-furoic acid, 3610 μM; protocatechuic acid, 2160 μM; p-hydroxybenzoic acid, no inhibition). Dimeric (+)-osbeckic acid was stable in solutions and at high temperatures, while its degraded peak on the HPLC chromatogram was observed when it was dissolved in dimethyl sulfoxide.

Vascular relaxation by ethanol extract of Xanthoceras sorbifolia via Akt- and SOCE-eNOS-cGMP pathways

The aim of the present study was to define the effect of Xanthoceras sorbifolia extracts (XS) on vascular tension and responsible mechanisms in rat thoracic aortic rings. Ethanol extract of the leaves of XS (EXS) was examined for their vascular relaxant effects in isolated phenylephrine-precontracted rat thoracic aorta. EXS (0.1-100 μg/ml) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished EXS-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with N(G)-nitro-L-arginine methylester (L-NAME) and 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ) inhibited EXS-induced vasorelaxation. Inhibition of Ca(2+) entry via L-type Ca(2+) channels failed to block the EXS-induced vasorelaxation. Extracellular Ca(2+) depletion significantly attenuated EXS-induced vasorelaxation. Modulators of the store-operated Ca(2+) entry (SOCE), thapsigargin, 2-aminoethyl diphenylborinate (2-APB) and Gd(3+), and an inhibitor of Akt, wortmannin, markedly attenuated the EXS-induced vasorelaxation. EXS increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by L-NAME, ODQ, thapsigargin, Gd(3+), 2-APB, and wortmannin. Further, EXS-induced vasorelaxation was significantly attenuated by tetraethylammonium, a non-selective K(ca) channels blocker, but not by glibenclamide, an ATP-sensitive K(+) channels inhibitor. Inhibition of cyclooxygenase with indomethacin, and adrenergic and muscarinic receptors blockade had no effects on EXS-induced vasorelaxation. The present study suggests that EXS relaxes vascular smooth muscle via endothelium-dependent NO-cGMP signaling through activation of the Akt- and SOCE-eNOS-sGC pathways, which may, at least in part, be related to the function of K(+) channels.

Water extract of Zanthoxylum piperitum induces vascular relaxation via endothelium-dependent NO-cGMP signaling

Aim of the study The aim of the present study was to define the effects of extracts of leaves of Zanthoxylum piperitum (ZP) on the vascular tension and its mechanisms responsible in rat thoracic aortic rings. Materials and methods Methanol extract of ZP and aqueous fraction of the methanol extract (AZP) were examined for their vascular relaxant effects in isolated phenylephrine-precontracted aortic rings. Results Methanol extract of ZP and aqueous fraction of the methanol extract (AZP) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished the AZP-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with N G-nitro- l-arginine methylester (L-NAME) and 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ) inhibited the AZP-induced vasorelaxation. Inhibition of Ca 2+ entry via L-type Ca 2+ channels failed to block the AZP-induced vasorelaxation. Extracellular Ca 2+ depletion slightly but significantly attenuated the AZP-induced vasorelaxation. Thapsigargin significantly attenuated the AZP-induced vasorelaxation. Further, Gd 3+ and 2-aminoethyl diphenylborinate (2-APB), inhibitors of store-operated Ca 2+ entry (SOCE), markedly attenuated the AZP-induced vasorelaxation. Also, wortmannin, an inhibitor of Akt, an upstream signaling molecule of eNOS, attenuated the AZP-induced vasorelaxation. AZP increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by L-NAME, ODQ, thapsigargin, Gd 3+, 2-APB, and wortmannin. K + channel inhibition with glibenclamide and tetraethylammonium, cyclooxygenase inhibition with indomethacin, and adrenergic and muscarinic receptors blockade had no effects on the AZP-induced vasorelaxation. Conclusion Taken together, the present study suggests that AZP relaxes vascular smooth muscle via endothelium-dependent activation of NO-cGMP signaling through the Akt- and SOCE-eNOS pathways.

Nonlinear mixed effects models applied to cumulative concentration–response curves

In experimental pharmacology, drug effect studies currently establish and analyse cumulative concentration-response curves (CCRC) under repeated measurements designs. Usually the CCRC parameters are estimated using the Hill's function in a nonlinear regression for independent data. The two-way analysis of variance is generally used to identify a statistical difference between the responses for two treatments but that analysis does not take into account the nonlinearity of the model and the heteroscedasticity (uneven distribution) of the data. We presently tested the possibility of finding a statistical solution for the nonlinear response in repeated measurements data using the nonlinear mixed effects (nlme) models. Experimental data sets, originating from studies on beta-adrenoceptor-induced relaxation in rat thoracic aorta ring, were analysed using the nlme methods. Comparison with classical methods showed the superiority of the nlme models approach. For each pharmacological parameter (E(m), n, pD(2)), a point estimate, a standard error and a confidence interval are returned by the nlme procedures respecting the assumption of independency and normality of the residuals. Using the method presently described, it is now possible to detect significant differences for each pharmacological parameter estimated in different situations, even for designs with small samples size (i.e. at least six complete curves).

Effects of cilostazol, a cyclic AMP phosphodiesterase inhibitor, on pulmonary vascular tone

We examined the effect of Cilostazol, a cyclic AMP phosphodiesterase inhibitor, rat isolated pulmonary arterial ring tone. Cilostazol dilated pulmonary arterial rings pre-contracted with 10(-6) M phenylephrine in a dose-dependent manner (ED50 3.00 x 10(-6) M). This vasodilatory effect of Cilostazol was not affected by pretreatment with meclofenamate (10(-5) M), mechanical endothelium denudation, methylene blue (10(-5) M) or nitro-L-arginine (2 x 10(-4) M). The vasodilatory effect of Cilostazol on rat thoracic aortic rings was stronger than that on rat pulmonary arterial ring (ED50 1.89 x 10(-6) M). Cilostazol (10(-6) M-10(-4) M) inhibited hypoxic contraction of rat pulmonary rings in a dose-dependent manner. Our experimental data indicated that Cilostazol caused vasodilation regardless of vascular endothelium function and inhibited hypoxic contraction due to inhibition of cyclic AMP phosphodiesterase.

Synthesis and biological activity of n-butylphthalide derivatives

A series of n-butylphthalide derivatives were designed and synthesized. The in vitro activities of these compounds were evaluated by a resting tension of isolated rat thoracic aorta ring assay. Compounds 4g and 4i were found to be more active than n-butylphthalide.

Vasorelaxant Effects of Clearfil SE Bond and Clearfil S3 Bond Mediated by Calcium Antagonistic Action

Dental adhesives can alter the contractility of vascular tissue via different mechanisms. The aim of this study was to investigate and compare the vascular action of two self-etch adhesive systems, Clearfil SE Bond (CSEB) and Clearfil S3 Bond (CS3B). Responses of isolated rat thoracic aorta rings were recorded isometrically by force displacement transducers. Following pre-contraction of aorta rings, relaxations to the independent and mixed components of CSEB and CS3B were recorded in the absence and presence of nitric oxide synthase (NOS) inhibitor (N ω -nitro-L-arginine methyl ester (N-LAME)), cyclooxygenase (COX) inhibitor (indomethacin) and K+ channel inhibitors (tetraethylammonium, glibenclamide and 4-aminopyridine). We also tested the effects of CSEB and CS3B in endothelium-intact and -denuded rat thoracic aorta rings. To investigate the Ca2+-channel antagonistic effect of adhesive components, concentration–response curves to CaCl2 were obtained in the absence and presence of the components. The primer, the bond, and the mixture of CSEB and CS3B elicited concentration-dependent relaxations. Mechanical rubbing of the endothelium did not significantly modify the extent of vasorelaxation induced by the test materials. The vasorelaxant effect was mediated neither by NOS and COX inhibition nor by the tested K+ channel antagonists. Mechanical removal of the endothelium did not alter the vasodilatory effect induced by the self-etch adhesives. Both CSEB and CS3B significantly inhibited the contractions induced by CaCl2. These results demonstrate the vasodilatory effect induced by the self-etch adhesive systems through a Ca2+-antagonistic effect.

Vasorelaxant Effect of Gangwhal in Korean and Chinese on Rat Thoracic Aorta Rings

Vasorelaxant Effect of Gangwhal in Korean and Chinese on Rat Thoracic Aorta Rings

Relative Roles of Heme-Irons and Globin-Thiols in the Genesis of Acellular Hemoglobin Mediated Vasoconstriction

In addition to heme-irons, reactive (beta-globin thiols (betaCys93s) of hemoglobin (Hb) also have been shown to interact with endogenous nitric oxide (NO) thereby contributing to vascular tone regulation. What relative roles do these NO binding sites contribute to the overall Hb-mediated vasoactivity? Several test Hbs with either or both the NO binding sites preliganded or blocked were prepared and tested in a rat thoracic aortic ring model. Hbs tested were: NEM-Hb (ferrous Hb with masked thiols), HbNO (ferrous Hb preliganded with NO), Hb(+)CN (ferric Hb liganded with CN(-)), NEM-HbNO and NEM-Hb(+)CN (Hbs with both heme-iron and cysteine sites preliganded or blocked). Typically, >0.2 microM control Hb significantly increased isometric tension in agonist stimulated vessel rings (58.1 +/-7.0% over baseline). At comparable concentrations, NEM-Hb also caused a significant contraction (50.7+/-9.5%) while HbNO and Hb(+)CN did not (-5.5+/-6.0% and -3.7+/-4.6%, respectively). For these Hbs, masking thiols as well did not significantly alter respective vascular effects. Ferrous sperm whale myoglobin (Mb), which has no reactive thiol, elicited a significant contraction (55.1+/-13.2%) while metMb did not (-0.8+/-3.2%), suggesting the relative importance of heme-iron ligand and oxidation state in Hb vasoactivity. Additionally, ferrous or ferric equine heart cytochrome-C, a heme protein with no readily available heme-iron and cysteine binding sites, did not elicit notable contraction. Human Hb variants in which (betaCys93s are deleted or substituted with non-cysteine residues did not reveal any documented significant hemodynamic abnormalities. These results indicate that reactive globin-thiols do not appear to play a prominent role relative to heme-irons in Hb-mediated vasoconstriction.

Vasodilator effect of gaseous sulfur dioxide and regulation of its level by Ach in rat vascular tissues

To explore the toxicological and physiological role of gaseous SO2 on vascular contractility and its level in vascular tissues, a vasodilation study of isolated rat thoracic aortic rings by gaseous SO2 was carried out. The level of SO2 in vascular tissue was assayed using a modified high-performance liquid chromatographic method with fluorescence detection (HPLC-FD). The results show that gaseous SO2 (from 1 μM to 2000 μM) relaxed rat thoracic aortic rings in a dose-dependent manner. The physiological concentrations of SO2 in thoracic aortic tissues and plasma in rats were 127.76 ± 31.34 μM and 16.77±8.24 μM, respectively; The vasorelaxant effect of gaseous SO2 at physiological and low concentrations (<450 μM) was endothelium dependent, and at high concentrations (>500 μM) was endothelium independent. The results also show that SO2 could be endogenously generated in vascular tissues, and mainly in vascular endothelial cells; acetylcholine (Ach) increased the SO2 level in vascular tissue, and noradrenaline (NE) decreased the SO2 level. These findings demonstrate that gaseous SO2 is a vasorelaxant substance, and the vasorelaxant effect of gaseous SO2 is much stronger than that of its derivatives sulfite and bisulfite, which result from the inactivation process of SO2 gas transmitter by which SO2 is hydrated to form sulfite, and the latter is enzymatically oxidized to form sulfate. These findings also demonstrate that endogenous SO2 level in vascular tissue may be regulated by Ach and NE.

Echinacoside Elicits Endothelium-Dependent Relaxation in Rat Aortic Rings via an NO-cGMP Pathway

The aim of this study was to identify and elucidate the vasorelaxant activity of echinacoside, a phenylethanoid glycoside isolated from the medicinal herb Cistanche tubulosa, and its possible underlying mechanism on isolated rat thoracic aortic rings pre-contracted with phenylephrine (PE, 1 microM) and KCl (60 mM). Echinacoside (30-300 microM) exhibited an acute relaxation in endothelium-intact rings in a concentration-dependent manner, while this relaxation was significantly inhibited in endothelium-denuded condition and in the presence of the endothelial nitric oxide synthase (eNOS) inhibitor, N(W)-nitro-L-arginine methyl ester (L-NNA, 100 microM), an unselective soluble guanylate cyclase blocker, methylene blue (10 microM), the selective sGC inhibitor 1 H-[1, 2, 4]oxadiazolo[4,3- A]quinoxalin-1-one (ODQ, 1 microM); in addition, atropine (1 microM), a selective muscarinic receptor antagonist, partially affected the relaxation. However, the cyclooxygenase inhibitor indomethacin (5 microM) had no influence on the action. Echinacoside enhanced the cyclic guanosine monophosphate (cGMP) production in aortic rings contracted with PE. These results indicate for the first time that echinacoside mediates the endothelium-dependent vasodilator action in rat thoracic aortic rings through nitric oxide (NO)-cGMP pathway.

Atorvastatin improves function of vascular endothelium by decreasing oxidative stress

Vascular oxidative injury is involved in numerous cardiovascular diseases, particularly in hypertension and atherosclerosis. Statins ‐‐ a family of lipid lowering drugs ‐‐ appear to display non‐lipid modifying abilities. The aim of this study was to investigate the effect of atorvastatin on vascular tone and its vasoprotection against oxidative stress injury. The tension of the isolated rat thoracic aortic rings was measured using organ bath technique and superoxide arterial injury was induced by pyrogallol (which produces superoxide anions) incubation. We found that atorvastatin (10−7 M ‐ 10−4 M) caused a concentration‐dependent relaxation in endothelium‐intact aortic rings precontracted by phenylephrine (PE, 10−6 M), which was abolished by L‐NAME (10−4 M), a nitric oxide synthase inhibitor. However, atorvastatin did not relax endothelium‐denuded aortic rings. Exposure to pyrogallol (3 ?10−4 M) for 15 min inhibited the acetylcholine (ACh, 10−9 M ‐ 10−5 M)‐induced relaxation in aortic rings precontracted by PE. This superoxide anion‐induced impairment was attenuated by pre‐incubation of atorvastatin (10−5 M) for 30 min. Atorvastatin administration (2, 10, 50 mg·kg−1·d−1, respectively) by gavage for 14 days did not alter the body weight of the rats, but showed improvement of ACh‐induced relaxation in aortic rings exposure to pyrogallol. These results indicate that atorvastatin has an endothelium‐dependent vasodilating effect on rat aorta, mediated by nitric oxide. Both acute and chronic administration of atorvastatin protect aorta from oxidative stress injury.

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.

Un effet direct de la ropivacaïne implique l’activation des voies de la lipoxygénase dans le muscle lisse de l’aorte du rat

Ropivacaine is a long-acting amino-amide local anesthetic that induces vasoconstriction in vitro and in vivo. The aim of this study was to investigate the pathways involved in arachidonic acid metabolism associated with S-ropivacaine-induced contraction of rat aortic smooth muscle in vitro. Rat thoracic aortic rings without endothelium were isolated and suspended for isometric tension recording. Cumulative dose-response curves were generated with concentrations of 10(-5) to 10(-3) M ropivacaine enantiomer in the presence or absence of quinacrine dihydrochloride, nordihydroguaiaretic acid, quinacrine dihydrochloride plus nordihydroguaiaretic acid, indomethacin, fluconazole, AA-861, and verapamil. The maximal S-ropivacaine-induced contractile response achieved at 3x10(-4) M was also assessed in aortic rings pretreated with normal or calcium-free Krebs solution. Ropivacaine enantiomers induced dose-dependent biphasic contractions in aortic rings. S-ropivacaine (10(-4), 3x10(-4) M) induced a stronger contraction than R-ropivacaine. Quinacrine dihydrochloride (2x10(-5), 4x10(-5) M) attenuated the S-ropivacaine-induced biphasic contraction in a dose-dependent manner. Indomethacin (3x10(-5), 6x10(-5) M), nordihydroguaiaretic acid (10(-5) M), and AA-861 (10(-5) M) also attenuated the S-ropivacaine-induced dose-dependent biphasic contraction, whereas fluconazole (3x10(-5)) had no effect. Combined pretreatment with quinacrine dihydrochloride and nordihydroguaiaretic acid almost completely abolished the S-ropivacaine-induced contraction. S-ropivacaine-induced contractile responses were attenuated by verapamil (10(-5) M) and calcium-free Krebs solution. S-ropivacaine induces dose-dependent biphasic contractions in rat aortic smooth muscle through a mechanism requiring extracellular calcium that is mediated by activation of the lipoxygenase pathway and, to a lesser extent, the cyclooxygenase pathway.

Repetitive 50 Hz pulsed electromagnetic field ameliorates the diabetes-induced impairments in the relaxation response of rat thoracic aorta rings

Purpose: To evaluate the characteristic features of mechanical responses and the membrane potential changes induced by repetitive pulsed electromagnetic field (PEMF, 50 Hz, 5 mT) in thoracic aorta rings obtained from streptozotocin-induced diabetic and healthy control rats to determine if PEMF could ameliorate problems associated with diabetes.Methods: Sixty male Wistar rats weighing 250–290 g were randomly divided into two experimental groups, each containing 30 animals. Streptozotocin was given via tail vein to produce diabetes mellitus (DM) in the first group rats. The second group rats were treated only with % 0.9 saline and considered as non-DM group. Both groups were also divided into two subgroups as DM + PEMF, DM + sham, PEMF and sham, each containing 15 animals. Although the DM + PEMF and PEMF groups were treated, the DM + sham and sham groups were not treated with PEMF. The PEMF treatment occurred four times daily for 30 min at 15-min intervals repeated daily for 30 days. Thoracic aorta rings from both DM and non-DM rats exposed to PEMF were evaluated for contraction and relaxation responses and membrane potential changes in the presence or absence of chemical agents that were selected to test various modes of action.Results: Relaxation response of thoracic aorta rings was significantly reduced in DM than non-DM group. PEMF treatment significantly increased the relaxation response of the diabetic rings to acetylcholine, and reduced the concentration response to phenylephrine. Resting membrane potential was significantly higher in DM than in non-DM group. Inhibitors of nitric oxide (NO), both nitro-L-arginine (L-NO-ARG) and L-NO-ARG + indometacin combination, produced a significant transient hyperpolarisation in all groups. Inhibitors of potassium channel activity, charybdotoxin or apamine, produced a membrane depolarisation. However, PEMF did not induce any significant effect on the membrane potential in DM group.Conclusions: Diabetes reduced the relaxation response of thoracic aorta rings. It also affected the membrane potentials of the rings. Treatment with PEMF ameliorated the diabetes-induced impairments in the relaxation response of these rings.

The role of sulfur dioxide as an endogenous gaseous vasoactive factor in synergy with nitric oxide

To explore the physiological role of endogenous gaseous sulfur dioxide (SO 2) on vascular contractility and its underlying cellular and molecular mechanisms, vasodilation experiment of isolated rat thoracic aortic rings by gaseous SO 2 was carried out and the signal transduction pathways involved in the vascular effects of SO 2 were investigated. In the present study, SO 2 gas and SO 2 gas-bubbled solution (SO 2 stock solution) were first used to relax vascular tissues. The results show: (1) Gaseous SO 2 relaxed rat thoracic aortic rings in a dose-dependent manner (from 1 to 2000 μM). The vasorelaxant effect of SO 2 at physiological relevant and low concentrations (<450 μM) was endothelium-dependent, and at high concentrations (>500 μM) was endothelium-independent. (2) The vasorelaxation by addition of SO 2 stock solution (final concentrations ⩽2 mM) was actually caused by SO 2 molecules, not by sulfite or bisulfite, and the characteristic of vasorelaxation by SO 2 was different from that of sulfite and bisulfite. (3) The vasorelaxant effect of SO 2 was not due to the altered neurotransmitter release from the autonomous or nonadrenergic and noncholinergic (NANC) nerve endings, also not due to superoxide and hydrogen peroxide produced in the vascular tissues, also disapproving the involvement of prostaglandin, PKC, β-adrenoceptor and cAMP pathways. (4) The vasorelaxant effect of SO 2 at the physiological relevant and low concentrations was mediated by the cGMP pathway. (5) There was the synergistic effect on smooth muscle relaxation between much lower concentrations of SO 2 (3 μM) and NO (3 or 5 nM). These findings led to the conclusions: endogenous gaseous SO 2 was a vasoactive factor, which might regulate vascular smooth muscle tone in synergy with NO.