DIRECT EFFECT OF DEXMEDETOMIDINE ON RAT ISOLATED AORTA INVOLVES ENDOTHELIAL NITRIC OXIDE SYNTHESIS AND ACTIVATION OF THE LIPOXYGENASE PATHWAY

• 1 The aims of the present in vitro study were to examine the roles of pathways associated with arachidonic acid metabolism in dexmedetomidine‐induced contraction and to determine which endothelium‐derived vasodilators are involved in the endothelium‐dependent attenuation of vasoconstriction elicited by dexmedetomidine.
• 2 Dexmedetomidine (10^?9–10^?6 mol/L) concentration–response curves were constructed in: (i) aortic rings with no drug pretreatment; (ii) endothelium‐denuded aortic rings pretreated with either 2 × 10^?5 mol/L quinacrine dihydrochloride, 10^?5 mol/L nordihydroguaiaretic acid (NDGA), 3 × 10^?5 mol/L indomethacin or 10^?5 mol/L fluconazole; and (iii) endothelium‐intact aortic rings pretreated with either 5 × 10^?5 mol/L N^G‐nitro‐l‐ arginine methyl ester (l ‐NAME), 10^?5 mol/L fluconazole, 10^?5 mol/L indomethacin, 10^?5 mol/L glibenclamide, 5 × 10^?3 mol/L tetraethylammonium or 5 × 10^?5 mol/L l ‐NAME plus rauwolscine (10^?5, 10^?6 mol/L). The production of nitric oxide (NO) metabolites was determined in human umbilical vein endothelial cells treated with dexmedetomidine.
• 3 Quinacrine dihydrochloride, NDGA and indomethacin attenuated the dexmedetomidine‐induced contraction of endothelium‐denuded rings. Dexmedetomidine (10^?7–10^?6 mol/L)‐induced contractions of endothelium‐denuded rings were enhanced compared with those of endothelium‐intact rings, as were dexmedetomidine‐induced contractions of endothelium‐intact rings pretreated with l ‐NAME or tetraethylammonium. Rauwolscine attenuated dexmedetomidine‐induced contractions in endothelium‐intact rings pretreated with l ‐NAME. Dexmedetomidine (10^?6 mol/L) was found to activate NO production.
• 4 Taken together, the results indicate that dexmedetomidine‐induced contraction of aortic rings involves activation of the lipoxygenase and cyclo‐oxygenase pathways and is attenuated by increased NO production following stimulation of endothelial α₂‐adrenoceptors by dexmedetomidine.

     

Exogenous L‐arginine attenuates the effects of angiotensin II on renal hemodynamics and the pressure natriuresis–diuresis relationship

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Inhibitory effect of 1,8-cineole on guinea-pig airway challenged with ovalbumin involves a preferential action on electromechanical coupling

• 1 1,8‐Cineole is a terpenoid constituent of essential oils with anti‐inflammatory properties. It reduces the neural excitability, functions as an antinociceptive agent and has myorelaxant actions in guinea‐pig airways. The aim of the present study was to investigate the mechanism underlying the myorelaxant effects of 1,8‐cineole in guinea‐pig isolated trachea from either naïve guinea‐pigs or ovalbumin (OVA)‐sensitized animals subjected to antigenic challenge.
• 2 Isometric recordings were made of the tone of isolated tracheal rings. Rings with an intact epithelium relaxed beyond basal tone in the presence of 1,8‐cineole (6.5 × 10^?6 to 2 × 10^?2 mol/L) in a concentration‐dependent manner (P < 0.001, anova ) with a pD₂ value of 2.23 (95% confidence interval 2.10–2.37). Removal of the epithelium or pretreatment of intact tissue for 15 min with 50 µmol/L N^G‐nitro‐l ‐arginine methyl ester, 5 mmol/L tetraethylammonium, 0.5 µmol/L tetrodotoxin or 5 µmol/L propranolol did not alter the potency (pD₂) or the maximal myorelaxant effect (E_max) of 1,8‐cineole.
• 3 1,8‐Cineole also significantly decreased the Schultz‐Dale contraction induced by OVA, mainly in preparations from OVA‐sensitized animals submitted to antigen challenge. 1,8‐Cineole decreased tracheal hyperresponsiveness to KCl and carbachol caused by antigen challenge and almost abolished the concentration–response curves to KCl, whereas it had little effect on the concentration–response curves to carbachol. Under Ca²⁺‐free conditions and in the presence of 10^?4 mol/L acetylcholine, neither 1,8‐cineole (6.5 × 10^?3 mol/L) nor verapamil (1 × 10^?5 mol/L) affected Ca²⁺‐induced contractions, but they almost abolished Ba²⁺‐induced contractions.
• 4 In conclusion, the findings of the present study show that 1,8‐cineole is a tracheal myorelaxant that acts preferentially on contractile responses elicited electromechanically.

     

Puerarin protects against high glucose-induced acute vascular dysfunction: Role of heme oxygenase-1 in rat thoracic aorta

ObjectiveTo investigate the antioxidant and vascular protective effect of puerarin, an isoflavone glycoside known in traditional Chinese medicine on vascular reactivity subsequent to high glucose stress.MethodsThe thoracic aortic rings with or without endothelium from male SD rats were mounted in an organ bath. Isometric contraction of aortic rings was measured. HO-1 protein expression and HO activity were also evaluated.Results(1) After incubation with 44 mmol/L of high glucose for 2 or 4 h, the vascular contraction responses to phenylephrine (PE) and relaxation response to acetylcholine (Ach) decreased in an endothelium-dependent manner; (2) Coincubation with puerarin (10^? 10–10^? 8 mol/L) and high glucose, the high glucose-induced vasoconstriction and vasodilation dysfunction was partly inhibited in a dose-dependent manner; (3) Puerarin increased the HO-1 protein expression and HO activity of thoracic aorta. ZnPP (an inhibitor of heme oxygenase-1) offset the protective effect of puerarin.ConclusionPuerarin could alleviate the high glucose-induced acute endothelium-dependent vascular dysfunction in rat aortic rings. HO-1 activity was proposed as a mechanism to account for the protection of vascular responses by puerarin.     

CILOSTAMIDE PRODUCES HYPERPOLARIZATION ASSOCIATED WITH KATP CHANNEL ACTIVATION, BUT DOES NOT AUGMENT ENDOTHELIUM-DERIVED HYPERPOLARIZATION IN RAT MESENTERIC ARTERIES

• 1 Non‐nitric oxide/prostaglandin‐mediated endothelium‐derived hyperpolarization (EDH) is considered to be mediated, in part, by gap junctions and it has been suggested that cAMP increases endothelium‐derived hyperpolarizing factor (EDHF)‐mediated relaxation through the modulation of gap junctions. Cilostamide, which inhibits phosphodiesterase III, has been suggested to augment EDHF‐type relaxation by increasing the concentration of cAMP.
• 2 In the present study, we investigated the effect of cilostamide on EDH per se in mesenteric arteries of Wistar rats using a conventional microelectrode technique.
• 3 The resting membrane potential of the mesenteric arteries was significantly more negative in the presence of 10^?6 mol/L cilostamide compared with control conditions. Furthermore, EDH in response to 10^?6 mol/L acetylcholine (ACh) in the presence of 10^?5 mol/L indomethacin and 10^?4 mol/L N^G‐nitro‐L‐arginine was decreased in the presence of 10^?6 mol/L cilostamide by approximately 5 and 3.5 mV in proximal and distal arteries, respectively.
• 4 Glibenclamide (10^?5 mol/L), an ATP‐sensitive potassium channel (K_ATP) inhibitor, abolished the hyperpolarization to 10^?6 mol/L cilostamide. Furthermore, in the presence of glibenclamide, ACh‐induced EDH was unaffected by cilostamide, suggesting that the inhibition of ACh‐induced hyperpolarization by cilostamide in the absence of glibenclamide may be due to the smaller driving force for hyperpolarization because of the more negative membrane potential under such conditions.
• 5 The findings of the present study suggest that cilostamide produces hyperpolarization by activating K_ATP channels, presumably by increasing cAMP. However, cilostamide alone may not directly affect EDH.

     

Warifteine,a bisbenzylisoquinoline alkaloid,induces relaxation by activating potassium channels in vascular myocytes

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Trimebutine maleate relaxes the isolated rat thoracic aorta: The role of nitric oxide and L‐type calcium channels

Trimebutine maleate (TMB), a widely prescribed drug for functional gastrointestinal disorders, has been reported to regulate smooth muscle contractility by modulating multiple ion channel activities in the gastrointestinal tract. However, its action on isolated aorta has not yet been reported. The aim of the present study was to evaluate in vitro vasorelaxant properties and the underlying pharmacological mechanisms of TMB in isolated rat thoracic aortic rings. Vascular activity experiments were performed on thoracic aorta isolated from Sprague‐Dawley rats in vitro, including endothelium‐intact and endothelium‐denuded aortic rings. TMB (10^?10‐10^?5 mol/L) induced relaxation in endothelium‐intact aortic rings precontracted by phenylephrine with a potency similar to that of carbachol. TMB‐induced relaxation was not altered by glibenclamide and atropine in endothelium‐intact aortic rings. However, L‐NAME and endothelium denudation significantly reduced but not completely reversed the vasorelaxant effect of TMB. Also, TMB‐induced relaxation wasn't affected by diclofenac in endothelium‐intact aortic rings. TMB at 10^?5 mol/L significantly reduced the CaCl₂‐induced contractions in endothelium‐intact aortic rings stimulated with KCl, but not stimulated with phenylephrine under Ca²⁺free conditions. Moreover, TMB at 10^?5 mol/L effectively attenuated Bay‐K8644‐induced contractions in aortic rings. These results suggest that TMB‐induced relaxation was mediated by both endothelium‐dependent and endothelium‐independent manner in isolated rat thoracic aorta. The mechanism of TMB‐induced relaxation at low concentrations is partially related to NO‐ and endothelium‐dependent but unrelated to prostanoids formation. However, inhibition of Ca²⁺ influx through voltage‐operated calcium channels and L‐type Ca²⁺channel blocking effect appears to be involved in the mechanism of vasorelaxant effect of TMB at high concentrations.     

CALCITONIN GENE-RELATED PEPTIDE MEDIATES THE CARDIOPROTECTIVE EFFECTS OF RUTAECARPINE AGAINST ISCHAEMIA–REPERFUSION INJURY IN SPONTANEOUSLY HYPERTENSIVE RATS

• 1 It has been shown that calcitonin gene‐related peptide (CGRP) plays an important role in mediating the cardioprotection exerted by rutaecarpine in normal animals. The aim of the present study was to determine whether rutaecarpine is able to decrease the susceptibility of hypertensive animals to ischaemia–reperfusion injury by stimulating CGRP release.
• 2 Spontaneously hypertensive rats (SHR) were pretreated with rutaecarpine (20 or 40 mg/kg per day, i.g.) for 18 days and then the heart and thoracic aorta were isolated for cardiac function and vascular relaxation analysis. Blood samples and coronary effluent were collected to measure CGRP levels and creatine kinase activity, respectively. The effect of 10 or 30 µmol/L rutaecarpine on CGRP release was also examined in isolated aortic rings set up in a homeothermal organ bath.
• 3 Rutaecarpine treatment resulted in a hypotensive effect in SHR concomitant with increases in plasma CGRP levels. In addition, rutaecarpine significantly stimulated the release of CGRP from aortic rings. Twenty minutes ischaemia and 30 min reperfusion resulted in a marked decrease in myocardial function and a significant increase in the release of creatine kinase in normal control (Wistar‐Kyoto) rats, an effect that was exacerbated in SHR. Similarly, the decreased vasodilator response to acetylcholine (3 ? 10^?9 to 10^?6 mol/L) in isolated aortic rings from Wistar‐Kyoto rats was also aggravated in SHR. Both cardiac function and vasodilator responses were significantly improved in SHR after pretreatment with rutaecarpine.
• 4 The results of the present study suggest that the increased cardiac susceptibility to ischaemia–reperfusion injury in SHR is related to decreased plasma CGRP levels and that antihypertensive therapy with rutaecarpine reverses cardiac susceptibility to reperfusion injury by stimulating CGRP release.

     

Angiotensin‐(1–7) treatment ameliorates angiotensin II‐induced apoptosis of human umbilical vein endothelial cells

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Pharmacological characterization of mechanisms involved in the vasorelaxation produced by rosuvastatin in aortic rings from rats with a cafeteria‐style diet

The present study aimed to investigate the possible influence of several inhibitors and blockers on the vascular effect produced by the acute in vitro application of rosuvastatin to phenylephrine‐precontracted aortic rings from rats with a semi‐solid, cafeteria‐style (CAF) diet. It also aimed to examine the effects of rosuvastatin on the expression of endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase, constitutive cyclooxygenase, and inducible cyclooxygenase in aortic rings from rats with a CAF diet. From comparisons of the effect on phenylephrine‐precontracted aortic rings extracted from rats with two different diets (a standard and a CAF diet), it was found that 10^?9–10^?5‐mol/L rosuvastatin produced lower concentration‐dependent vasorelaxation on rings from the CAF diet group. The vasorelaxant effect was unaffected by the vehicle, but it was significantly attenuated by 10^?5‐mol/L N^G‐nitro‐l ‐arginine methyl ester, 10^?2‐mol/L tetraethylammonium, 10^?3‐mol/L 4‐aminopyridine, 10^?7‐mol/L apamin plus 10^?7‐mol/L charybdotoxin, 10^?5‐mol/L indomethacin, or 10^?5‐mol/L cycloheximide. Moreover, in aortic rings from rats with a CAF diet, rosuvastatin enhanced the expression of eNOS, inducible nitric oxide synthase, constitutive cyclooxygenase, and inducible cyclooxygenase. The acute in vitro application of rosuvastatin to phenylephrine‐precontracted aortic rings from rats with a CAF diet had a vasorelaxant effect. Overall, the present results suggest that the stimulation of eNOS, the opening of Ca²⁺‐activated and voltage‐activated K⁺ channels, the stimulation of prostaglandin synthesis and enhanced protein levels of eNOS, inducible nitric oxide synthase, constitutive cyclooxygenase, and inducible cyclooxygenase are involved in this relaxant effect.     

Characterization of relaxant mechanism of H2S in mouse corpus cavernosum

The aim of this study was to investigate the mechanism of H₂S‐induced relaxation in mouse corpus cavernosal tissue. l ‐cysteine (10^?6 × 10^?3 mol/L) and exogenous H₂S (NaHS; 10^?6 to 10^?3 mol/L) induced concentration‐dependent relaxation. l ‐cysteine‐induced relaxations was reduced by d,l ‐propargylglycine, a cystathionine gamma lyase (CSE) inhibitor but not influenced by aminooxyacetic acid, a cystathionine beta synthase (CBS) inhibitor. l ‐cysteine induced relaxations, but not of those of H₂S diminished in endothelium‐denuded tissues. N^ω‐nitro‐l ‐arginine (l ‐NA; 10^?4 mol/L), a nitric oxide synthase inhibitor, and ODQ (10^?4 mol/L), a guanylyl cyclase inhibitor, increased the H₂S‐induced relaxation. Zaprinast (5 × 10^?6 mol/L) and sildenafil (10^?6 mol/L), phosphodiesterase inhibitors, inhibited H₂S‐induced relaxation. Adenylyl cyclase inhibitors N‐ethylmaleimide (2.5 × 10^?5 mol/L) and SQ22536 (10^?4 mol/L) reduced relaxation to H₂S. Also, H₂S‐induced relaxation was reduced by KCl (50 mmol/L), 4‐aminopyridine (10^?3 mol/L), a K_v inhibitor, glibenclamide (10^?5 mol/L), a K_ATP inhibitor or barium chloride (10^?5 mol/L), a K_IR inhibitor. However, H₂S‐induced relaxation was not influenced by apamin (10^?6 mol/L), a SK_Ca²⁺ inhibitor, charybdotoxin (10^?7 mol/L), an IK_Ca²⁺ and BK_Ca²⁺ inhibitor or combination of apamin and charybdotoxin. Nifedipine (10^?6 mol/L), an L‐type calcium channel blocker and atropine (10^?6 mol/L), a muscarinic receptor blocker, inhibited H₂S‐induced relaxation. However, H₂S‐induced relaxation was not influenced by ouabain (10^?4 mol/L), a Na⁺/K⁺‐ATPase inhibitor. This study suggests that H₂S endogenously synthesizes from l ‐cysteine by CSE endothelium‐dependent in mouse corpus cavernosum tissue, and exogenous H₂S may cause endothelium‐independent relaxations via activation of K channels (K_ATP channel, K_V channels, K_IR channels), L‐type voltage‐gated Ca²⁺ channels, adenylyl cyclase/cAMP pathway and muscarinic receptor, and there is the interaction between H₂S and NO/cGMP.     

Unravelling the cardiovascular effects induced by α‐terpineol: A role for the nitric oxide–cGMP pathway

1. α‐Terpineol is a monoterpene found in the essential oils of several aromatic plant species. In the present study, we investigated the mechanisms underlying the cardiovascular changes induced by α‐terpineol in rats. 2. In normotensive rats, administration of α‐terpineol (1, 5, 10, 20 and 30 mg/kg, i.v.) produced a dose‐dependent hypotension (?10 ± 3, ?20 ± 8, ?39 ± 16, ?52 ± 21 and ?57 ± 23 mmHg, respectively; n = 5) followed by tachycardia. The hypotensive responses to 1, 5, 10, 20 and 30 mg/kg, i.v., α‐terpineol were significantly attenuated following the administration of N^G‐nitro‐l‐ arginine methyl ester (l ‐NAME; 20 mg/kg, i.v.; ?2 ± 1, ?5 ± 2, ?7 ± 3, ?22 ± 9 and ?22 ± 10 mmHg, respectively; P < 0.05; n = 5). 3. In 10 μmol/L phenylephrine (PE)‐precontracted mesenteric artery rings, α‐terpineol (10^?12 to 10^?5 mol/L) caused a concentration‐dependent relaxation (maximum relaxation 61 ± 6%; n = 7). After removal of the endothelium, the vasorelaxation elicited by α‐terpineol was attenuated (maximum relaxation 20 ± 1%; P < 0.05; n = 7). In addition, vasorelaxation induced by α‐terpineol in rings pretreated with 100 or 300 μmol/L l ‐NAME, 30 μmol/L hydroxocobalamin or 10 μmol/L 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one was attenuated (maximum relaxation 18 ± 3, 23 ± 3, 24 ± 7 and 21 ± 1%, respectively; n = 6; P < 0.05). 4. Furthermore, in a rabbit aortic endothelial cell line, 10^?6, 10^?5 and 10^?4 mol/L α‐terpineol induced concentration‐dependent increases in nitric oxide (NO) levels (12 ± 6, 18 ± 9 and 34 ± 12%Δ fluorescence, respectively; n = 3). 5. In conclusion, using combined functional and biochemical approaches in the present study, we were able to demonstrate that α‐terpineol‐induced hypotension and vasorelaxation are mediated, at least in part, by the endothelium, most likely via NO release and activation of the NO–cGMP pathway.     

ROLE OF EXTRACELLULAR Na+, Ca2+-ACTIVATED Cl- CHANNELS AND BK CHANNELS IN THE CONTRACTION OF Ca2+ STORE-DEPLETED TRACHEAL SMOOTH MUSCLE

• 1 In the present study, we investigated the series of events involved in the contraction of tracheal smooth muscle induced by the re‐addition of Ca²⁺ in an in vitro experimental model in which Ca²⁺ stores had been depleted and their refilling had been blocked by thapsigargin.
• 2 Mean (±SEM) contraction was diminished by: (i) inhibitors of store‐operated calcium channels (SOCC), namely 100  µ mol/L SKF‐96365 and 100  µ mol/L 1‐(2‐trifluoromethylphenyl) imidazole (to 66.3 ± 4.4 and 41.3 ± 5.2% of control, respectively); (ii) inhibitors of voltage‐gated Ca²⁺ channels Ca_V1.2 channels, namely 1  µ mol/L nifedipine and 10  µ mol/L verapamil (to 86.2 ± 3.4 and 76.9 ± 5.9% of control, respectively); and (iii) 20  µ mol/L niflumic acid, a non‐selective inhibitor of Ca²⁺‐dependent Cl^? channels (to 41.1 ± 9.8% of control). In contrast, contraction was increased 2.3‐fold by 100 nmol/L iberiotoxin, a blocker of the large‐conductance Ca²⁺‐activated K⁺ (BK) channels.
• 3 Furthermore, contraction was significantly inhibited when Na⁺ in the bathing solution was replaced by N‐methyl–d ‐glucamine (NMDG⁺) to 39.9 ± 7.2% of control, but not when it was replaced by Li⁺ (114.5 ± 24.4% of control). In addition, when Na⁺ had been replaced by NMDG⁺, contractions were further inhibited by both nifedipine and niflumic acid (to 3.0 ± 1.8 and 24.4 ± 8.1% of control, respectively). Nifedipine also reduced contractions when Na⁺ had been replaced by Li⁺ (to 10.7 ± 3.4% to control), the niflumic acid had no effect (116.0 ± 4.5% of control).
• 4 In conclusion, the data of the present study demonstrate the roles of SOCC, BK channels and Ca_V1.2 channels in the contractions induced by the re‐addition of Ca²⁺ to the solution bathing guinea‐pig tracheal rings under conditions of Ca²⁺‐depleted sacroplasmic reticulum and inhibition of sarcoplasmic/endoplasmic reticulum calcium ATPase. The contractions were highly dependent on extracellular Na⁺, suggesting a role for SOCC in mediating the Na⁺ influx.

     

Bitter tastants induce relaxation of rat thoracic aorta precontracted with high K+

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INVOLVEMENT OF PROTEIN KINASE C IN THE REGULATION OF Na+/Ca2+ EXCHANGER IN BOVINE ADRENAL CHROMAFFIN CELLS

• 1 The Na⁺/Ca²⁺ exchanger (NCX) exchanges Na+ and Ca²⁺ bidirectionally through the forward mode (Ca²⁺ extrusion) or the reverse mode (Ca²⁺ influx). The present study was undertaken to clarify the role of protein kinase C (PKC) in the regulation of NCX in bovine adrenal chromaffin cells. The Na⁺‐loaded cells were prepared by treatment with 100 µmol/L ouabain and 50 µmol/L veratridine. Incubation of Na⁺‐loaded cells with Na⁺‐free solution in the presence of the Ca²⁺ channel blockers nicardipine (3 µmol/L) and ω‐conotoxin MVIIC (0.3 µmol/L) caused Ca²⁺ uptake and catecholamine release.
• 2 The Na⁺‐dependent Ca²⁺ uptake and catecholamine release were inhibited by 2‐[4‐[(2,5‐difluorophenyl)methoxy]phenoxy]‐5‐ethoxyaniline (SEA0400; 1 µmol/L) and 2‐[2‐[4‐(4‐nitrobenzyloxy)phenyl]isothiourea (KB‐R7943; 10 µmol/L), both NCX inhibitors. These results indicate that the Na⁺‐dependent responses are mostly due to activation of the NCX working in the reverse mode.
• 3 In addition, we examined the effects of PKC inhibitors and an activator on the NCX‐mediated Ca²⁺ uptake and catecholamine release. Bisindolylmaleimide I (0.3–10 µmol/L) and chelerythrine (3–100 µmol/L), both PKC inhibitors, inhibited NCX‐mediated responses. In contrast, phorbol 12,13‐dibutyrate (0.1–10 µmol/L), a PKC activator, enhanced the responses. Bisindolylmaleimide I and chelerythrine, at effective concentrations for inhibition of Na⁺‐dependent catecholamine release, had a little or no effect on high K⁺‐induced catecholamine release in intact cells or on Ca²⁺‐induced catecholamine release in β‐escin‐permeabilized cells.
• 4 These results suggest that PKC is involved in the activation of NCX in bovine adrenal chromaffin cells.

     

Effects of magnolol on vascular contraction in rat aortic rings

1. Magnolol (5,5′‐diallyl‐2,2′‐dihydroxybiphenyl) is a major phenolic compound purified from Magnolia officinalis. The aim of the present study was to elucidate the effects of magnolol on vascular contractions. 2. Rat aortic rings were mounted in organ baths. Magnolol was added cumulatively (0.3–30 μmol/L) to elicit relaxation in endothelium‐intact and ‐denuded rat aortic rings precontracted with U46619 (30 nmol/L, 20 min), NaF (8.0 mmol/L, 40 min), phenylephrine (1.0 or 0.1 μmol/L, 15 min) or phorbol‐12,13‐dibutyrate (PDBu, 0.3 or 0.1 μmol/L, 40 min). In separate experiments, cumulative concentration?response curves were obtained for NaF (2.0–12 mmol/L), U46619 (1.0 nmol/L?1.0 μmol/L) or PDBu (1.0 nmol/L?1.0 μmol/L) after pretreatment with either magnolol or vehicle for 30 min in endothelium‐denuded aortic rings. After completion of the functional study, we measured the amount of guanosine triphosphate (GTP) RhoA by using a G‐LISA RhoA Activation Assay, as well as the phosphorylation of 20 kDa myosin light chain (MLC₂₀), myosin phosphatase‐targeting subunit 1 (MYPT1) and protein kinase C‐potentiated inhibitory protein for heterotrimeric myosin light‐chain phosphatase of 17 kDa (CPI‐17) by immunobloting. 3. Magnolol (0.3–30 μmol/L) reduced vascular tension induced by the thromboxane A₂ agonist U46619 (30 nmol/L), sodium fluoride (NaF) (8.0 mmol/L) and the α₁‐adrenoceptor agonist phenylephrine (1.0 or 0.1 μmol/L) in both endothelium‐intact and ‐denuded rings. The magnitude of the relaxation effects of magnolol on the contraction induced by each of the drugs were similar. The magnitude of the effect of magnolol in endothelium‐intact and ‐denuded rings were similar. 4. Pretreatment of rat aortic rings with 1.0, 3.0 or 10 μmol/L magnolol for 30 min dose‐dependently inhibited the maximum response on the concentration–response curves to NaF and U46619, but not to phorbol‐12,13‐dibutyrate (PDBu). 5. Magnolol (3.0 or 10 μmol/L) decreased RhoA activation, as well as the phosphorylation of MLC₂₀, MYPT1_Thr855 and CPI‐17_Thr38 induced by either 8.0 mmol/L NaF or 30 nmol/L U46619. In contrast, magnolol did not affect PDBu (0.1 μmol/L)‐induced phosphorylation of CPI‐17_Thr38. 6. In conclusion, magnolol reduces vascular contraction by inhibiting the RhoA/Rho kinase pathway in endothelium‐denuded rat aorta.     

SUFENTANIL AND ALFENTANIL CAUSE VASORELAXATION BY MECHANISMS INDEPENDENT OF THE ENDOTHELIUM

1. The aim of these experiments was to determine if the vasorelaxation of the rat isolated aorta induced by sufentanil or alfentanil is mediated by the endothelium, and, if not, by α-adrenoceptor blockade, or a direct effect on the smooth muscle. 2. Both sufentanil (from 10^?7 mol/L to 10^?4 mol/ L) and alfentanil (from 10^?7 mol/ L to 3 × 10^?4 mol/L) relaxed rings, where endothelium was intact and precontracted with 40 mmol/L KC1, in a concentration-related manner. Similarly, sufentanil and alfentanil relaxed rings, in the presence or absence of endothelium, which had been precontracted with phenylephrine. 3. Naloxone (10^?4 mol/L) had no significant effect on the relaxation induced by either sufentanil or alfentanil. 4. In a similar manner as phentolamine, pretreatment with sufentanil protected α-adrenoceptors from blockade by phenoxybenzamine (PBZ) in both endothelium intact and denuded rings, but the estimated potency of sufentanil was approximately 100-fold less than that of phentolamine in α-adrenoceptor protection. Treatment with alfentanil did not produce any receptor protection. 5. We concluded that, in the rat aorta, vascular relaxation induced by sufentanil is mediated by both α-adrenoceptor blockade and a direct effect on smooth muscle, whilst the relaxant effect of alfentanil is caused by direct effects alone. We also concluded that the endothelium has little role in relaxation produced by either drug.     

Vasorelaxation induced by methyl cinnamate,the major constituent of the essential oil of Ocimum micranthum,in rat isolated aorta

The aim of the present study was to investigate the vascular effects of the E‐isomer of methyl cinnamate (E‐MC) in rat isolated aortic rings and the putative mechanisms underlying these effects. At 1–3000 μmol/L, E‐MC concentration‐dependently relaxed endothelium‐intact aortic preparations that had been precontracted with phenylephrine (PHE; 1 μmol/L), with an IC₅₀ value (geometric mean) of 877.6 μmol/L (95% confidence interval (CI) 784.1–982.2 μmol/L). These vasorelaxant effects of E‐MC remained unchanged after removal of the vascular endothelium (IC₅₀ 725.5 μmol/L; 95% CI 546.4–963.6 μmol/L) and pretreatment with 100 μmol/L N^G‐nitro‐l ‐arginine methyl ester (IC₅₀ 749.0 μmol/L; 95% CI 557.8–1005.7 μmol/L) or 10 μmol/L 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (IC₅₀ 837.2 μmol/L; 95% CI 511.4–1370.5 μmol/L). Over the concentration range 1–3000 μmol/L, E‐MC relaxed K⁺‐induced contractions in mesenteric artery preparations (IC₅₀ 314.5 μmol/L; 95% CI 141.9–697.0 μmol/L) with greater potency than in aortic preparations (IC₅₀ 1144.7 μmol/L; 95% CI 823.2–1591.9 μmol/L). In the presence of a saturating contractile concentration of K⁺ (150 mmol/L) in Ca²⁺‐containing medium combined with 3 μmol/L PHE, 1000 μmol/L E‐MC only partially reversed the contractile response. In contrast, under similar conditions, E‐MC nearly fully relaxed PHE‐induced contractions in aortic rings in a Ba²⁺‐containing medium. In preparations that were maintained under Ca²⁺‐free conditions, 600 and 1000 μmol/L E‐MC significantly reduced the contractions induced by exogenous Ca²⁺ or Ba²⁺ in KCl‐precontracted preparations, but not in PHE‐precontracted preparations (in the presence of 1 μmol/L verapamil). In addition, E‐MC (1–3000 μmol/L) concentration‐dependently relaxed the contractions induced by 2 mmol/L sodium orthovanadate. Based on these observations, E‐MC‐induced endothelium‐independent vasorelaxant effects appear to be preferentially mediated by inhibition of plasmalemmal Ca²⁺ influx through voltage‐dependent Ca²⁺ channels. However, the involvement of a myogenic mechanism in the effects of E‐MC is also possible.     

ENDOTHELIUM-DERIVED RELAXING FACTOR, HYPERTENSION AND CHRONIC PARATHYROIDECTOMY IN SPONTANEOUSLY HYPERTENSIVE AND WISTAR-KYOTO RATS

• 1 Parathyroidectomy (PTX) lessens the development of hypertension in young spontaneously hypertensive rats (SHR) and the involved mechanisms remain to be elucidated. We have studied here the aortic vascular reactivity to both norepinephrine (NE) and acetylcholine in 10 week old male PTX SHR and Wistar-Kyoto (WKY) rats.
• 2 Depolarized (KCl 100 mmol/L) and NE (1 μmol/L or cumulative 10^-9-10^--⁵ mol/L) precontracted intact aortic rings from PTX rats show a significant and unexpected increase of maximal contractile responses in normotensive and hypertensive animals. These results are also obtained with low extracellular ionized calcium levels (0.625 and 0.9 mmol/L) similar to PTX ionized plasma calcium. N^ω-Nitro-L-arginine methyl ester (l-NAME, 20 μmol/L) potentiates the NE response in SHR and WKY rats, more significantly in control than in PTX animals.
• 3 In the presence of indomethacin (10 μmol/L) in SHR the potentiating effect of PTX on NE contraction is still observed, ruling out a specific production of vasoconstrictors from the arachidonic cascade by the PTX rat aortic endothelium.
• 4 After PTX a moderate impairment of acetylcholine relaxant responses is observed in SHR and WKY rat aortas and basal aortic cyclic guanosine 3′-4′ monophosphate (cGMP) content is also decreased; nevertheless sodium nitroprusside causes a similar relaxation. Furthermore in l-NAME-treated aortas and in the presence of l-arginine (100 μmol/L), acetylcholine (1 μmol/L) produces a significantly less pronounced relaxation in PTX rats.
• 5 In conclusion, the enhancement of NE contractile response in PTX rat aortas is not linked to the strain but probably related to a decrease in endothelial nitric oxide (NO) release or activity. Enhancement of force generation that we describe does not directly participate in the attenuated hypertension observed in SHR after parathyroidectomy.

     

Quantitative changes in pharmacodynamic parameters of noradrenaline in different rat aorta preparation: influence of endogenous EDRF

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