Direct Vasorelaxant Effect Research Articles

Dapagliflozin prevents oxidative stress-induced endothelial dysfunction via sirtuin 1 activation

Recent studies have demonstrated that dapagliflozin, a sodium-glucose cotransporter type 2 (SGLT2) inhibitor, prevents endothelial dysfunction; however, direct effects of dapagliflozin on the endothelium under oxidative stress and the underlying mechanism of action are not completely understood. This study aimed to define the role and related mechanisms of dapagliflozin in hydrogen peroxide (H2O2)-induced endothelial dysfunction. The endothelium-dependent vasorelaxation effect of dapagliflozin was assessed in an organ bath study. Endothelial dysfunction was assessed using protein expression level and phosphorylation of endothelial nitric oxide synthase (eNOS), nitric oxide (NO), reactive oxygen species (ROS), senescence-associated beta-galactosidase (SA-β-gal) activity, and senescence marker proteins (p21, p53). Co-immunoprecipitation and protein acetylation were performed to detect protein interactions. Dapagliflozin exerted a direct vasorelaxant effect in the aortic rings of C57BL/6 J mice. Furthermore, there was a significant improvement in endothelium-dependent vasorelaxation in dapagliflozin-treated diabetic mice compared to vehicle controls. Moreover, intracellular ROS levels and ONOO- levels, increased by H2O2, were reduced by dapagliflozin. Importantly, dapagliflozin inhibited H2O2-induced senescence in the human umbilical vein endothelial cells (HUVECs), as indicated by reduced SA‐β‐gal, p21, and p53. Mechanistically, dapagliflozin reversed the H2O2-mediated inhibition of eNOS serine phosphorylation and sirtuin 1 (SIRT1) expression in endothelial cells. In particular, SIRT1-mediated eNOS deacetylation is reportedly involved in dapagliflozin-enhanced eNOS activity. These findings indicate that dapagliflozin ameliorates endothelial dysfunction by restoring eNOS activity, restoring NO bioavailability, and reducing ROS generation via SIRT1 activation in oxidative stress-stimulated endothelial cells.

Kynurenine Relaxes Arteries of Normotensive Women and Those With Preeclampsia.

[Figure: see text].

Benzodiazepines and non-benzodiazepine drugs have direct vasorelaxant effects

Benzodiazepines and non-benzodiazepine drugs have direct vasorelaxant effects

Detection of silent cerebral microcirculatory abnormalities in patients with manifest ischemic coronary disease: a perfusion brain MRI study combined with dipyridamole stress

Objectives Intravenous dipyridamole (DP) can induce transient perfusion abnormalities in the heart but also the brain indicated by brain SPECT. L-arginine can regulate the vascular tone via nitric oxide (NO). Therefore, we examined cerebral blood volume (CBV) by perfusion MRI and L-arginine level before and after DP stress in patients, who developed transient neurological signs, and compared these to unaffected patients. Design A total of nine patients with ischemic coronary disease after myocardial perfusion scintigraphy were selected for this prospective pilot study. Four had DP-induced transient mild neurologic signs during myocardial perfusion scintigraphy, while five had no neurological signs. By using perfusion MRI in both groups in a second stage, we examined CBV in identical areas of the two hemispheres before and during DP stress. Besides, pre-and post-stress L-arginine serum levels were also analyzed by high-performance liquid chromatography. Trial registration: NCT03688815. Results CBV in the sensory-motor area at baseline was significantly higher in patients with DP-induced transient neurological signs compared to patients without signs (p = 0.028). Intravenous DP normalized the higher perfusion by decreasing CBV, and also increased serum L-arginine level (p = 0.001). Conclusions Intravenous DP changed the CBV accompanied by a systemic elevation of L-arginine: this indicates a direct vasorelaxing effect on brain vessels, and an indirect vasodilator effect through L-arginine release presumably via NO. In areas with decreased CBV before DP, such double effects caused transient neurological symptoms presumably due to steal phenomenon. Therefore, intravenous DP may have a potential to identify patients with high risk for cerebral ischemia.

A Review of the Phytochemistry and Biological Activities of Hibiscus sabdariffa (Zobo) Plant

Hibiscus sabdariffa (HS) is a plant from the Malvaceae family that is grown widely in most of Asia and tropical Africa. The various parts of the plant are used traditionally as food in form of beverages or salads and as medicine. In folklore, HS has been used to treat many ailments including cardiac and nerve ailments, induction of diuresis and lactation among others. Scientific studies have also demonstrated the antihypertensive, antidiabetic, anti-obesity and anti-hyperlipidaemic properties of HS. These biological activities are thought to be as a result of the battery of phytochemicals in HS that have strong antioxidant activity and that inhibit α-amylase, α-glucosidase, angiotensin converting enzyme, calcium channel blockage and direct vasorelaxant effects. Some of the phytochemicals that are thought to be responsible for these biological effects include anthocyanins, flavonoids and organic acids.There is however the need for more robust researches including controlled clinical trials to validate these biological activities with a view to bringing the benefits closer to the bedside.

In Vitro Effects of Eicosapentaenoic and Docosahexaenoic Acid on the Vascular Tone of a Human Saphenous Vein: Influence of Precontractile Agents

Cardiovascular effects of omega-3 polyunsaturated fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been widely reported. However, there are limited studies concerning their effects on human blood vessels. Therefore, the aim of this study was to investigate the direct vascular effects of EPA and DHA on the human saphenous vein (SV) precontracted with either prostaglandin F2α (PGF2α), or thromboxane A2 analogue (U46619), or norepinephrine (NE). Moreover, we aimed to investigate the protein expression of free fatty acid receptor 4 (FFAR4) in human SV. Pretreatment of human SV rings with EPA and DHA (100μM, 30min) was tested on vascular reactivity induced by PGF2α (10 nM to 5 μM), NE (10 nM to 100 μM), and U46619 (1nM to 100 nM). In addition, direct relaxant effects of EPA/DHA (1-100μM) were tested in human SV rings precontracted by PGF2α, NE, and U46619. Furthermore, the involvement of potassium channels on their vascular effects was investigated in the presence of the nonselective K+ channel inhibitor tetraethylammonium chloride. Pretreatment with EPA and DHA resulted in a significant decrease in vascular reactivity induced by U46619 and PGF2α compared to NE. In the presence of TEA, the relaxant effects of EPA and DHA were significantly decreased in SV preparations precontracted by U46619 and PGF2α for DHA. Furthermore, FFAR-4 protein was expressed in tissue extracts of humanSV. Our study demonstrates that both EPA and DHA reduce the increased vascular tone elicited by contractile agents on the human SV and that the direct vasorelaxant effect is likely to involve potassium channels.

Erucin exhibits vasorelaxing effects and antihypertensive activity by H2S‐releasing properties

Hydrogen sulfide (H2 S)-releasing agents are viewed as potential antihypertensive drugs. Recently, natural isothiocyanates emerged as original H2 S-donor agents. Among them, erucin, present in some edible cruciferous plants, shows suitable H2 S-releasing properties and features of "druggability." The aim of this work was to investigate the erucin-mediated release of H2 S inside vascular cells, its vasorelaxing effects, and activity on BP of normo and hypertensive animals. Intracellular H2 S-release and the hyperpolarizing effect of erucin were tested using fluorescent dye, in human aortic smooth muscle cells (HASMCs). Its direct vasorelaxing effect and ability to inhibit noradrenaline-induced vasoconstriction were evaluated on endothelium-intact or -denuded rat aortic rings. Its vasodilator properties were tested in coronary arteries using Langendorff-perfused rat hearts. Finally, erucin's antihypertensive activity was evaluated in vivo in normotensive and spontaneously hypertensive rats (SHRs) by recording systolic BP using the tail-cuff method. Erucin induced the release of H2 S inside HASMCs. Moreover, erucin hyperpolarized the membrane of HASMCs membrane in a concentration-dependent manner. It induced vasodilatation of rat aortic rings, in endothelium-denuded vessels. This effect was further improved by the presence of endothelial NO. When pre-incubated with rat aortic rings, erucin induced concentration-dependent inhibition of noradrenaline-induced vasoconstriction. Erucin did not affect basal coronary flow but restored the flow to normal in pre-contracted coronary vessels. Finally, in vivo, erucin decreased systolic BP in SHRs by about 25%, and restored the BP to values observed in normotensive rats. Erucin is an H2 S donor endowed with vasorelaxing and antihypertensive effects. This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

A11957 Irisin Lowers Blood Pressure by Improvement of Endothelial Dysfunction via AMPK-Akt-eNOS-NO Pathway in the Spontaneously Hypertensive Rat

Objectives: Exercise is a major nonpharmacological treatment for hypertension, but its underlying mechanisms are still not completely elucidated. Irisin, a polypeptide containing 112 amino acids, which is secreted mainly by skeletal muscle cells during exercise, exerts a protective role in metabolic diseases, such as diabetes and obesity. Due to the close relationship between irisin and metabolic diseases, we hypothesized that irisin may play a role in the regulation of blood pressure. Methods: Blood pressures of male WKY rats and SHRs were monitored via the carotid artery. The vascular response was checked by tension measurement of the artery rings. Protein expression was tested by immunoblot. Results: Our study found that the acute intravenous injection of irisin reduced blood pressure in SHRs but not WKY rats. Irisin, by itself, had no direct vasorelaxing effect in phenylephrine-pre-constricted mesenteric arteries from SHRs. However, irisin augmented the acetylcholine-induced vasorelaxation in mesenteric arteries from SHRs that could be reversed by Nω-nitro-L-arginine-methyl ester (L-NAME, 100 μM), indicating a role of NO in this action. Indeed, irisin increased NO production and phosphorylation of eNOS in endothelial cells. 5¢-AMP-activated protein kinase (AMPK) was involved in the vasorelaxing effect of irisin because compound C (20 μM), an AMPK inhibitor, blocked the irisin-mediated increase in phosphorylation of eNOS and Akt in endothelial cells and vasodilation in mesenteric arteries. Conclusion: We conclude that acute administration of irisin lowers blood pressure of SHRs by amelioration of endothelial dysfunction of the mesenteric artery via AMPK-Akt-eNOS-NO signaling pathway.

Possible mechanisms involved in the vasorelaxant effect produced by clobenzorex in aortic segments of rats.

Clobenzorex is a metabolic precursor of amphetamine indicated for the treatment of obesity. Amphetamines have been involved with cardiovascular side effects such as hypertension and pulmonary arterial hypertension. The aim of the present study was to investigate whether the direct application of 10–9–10–5 M clobenzorex on isolated phenylephrine-precontracted rat aortic rings produces vascular effects, and if so, what mechanisms may be involved. Clobenzorex produced an immediate concentration-dependent vasorelaxant effect at the higher concentrations (10–7.5–10–5 M). The present outcome was not modified by 10–6 M atropine (an antagonist of muscarinic acetylcholine receptors), 3.1×10–7 M glibenclamide (an ATP-sensitive K+ channel blocker), 10–3 M 4-aminopyridine (4-AP; a voltage-activated K+ channel blocker), 10–5 M indomethacin (a prostaglandin synthesis inhibitor), 10–5 M clotrimazole (a cytochrome P450 inhibitor) or 10–5 M cycloheximide (a general protein synthesis inhibitor). Contrarily, the clobenzorex-induced vasorelaxation was significantly attenuated (P<0.05) by 10–5 M L-NAME (a direct inhibitor of nitric oxide synthase), 10–7 M ODQ (an inhibitor of nitric oxide-sensitive guanylyl cyclase), 10–6 M KT 5823 (an inhibitor of protein kinase G), 10–2 M TEA (a Ca2+-activated K+ channel blocker and non-specific voltage-activated K+ channel blocker) and 10–7 M apamin plus 10–7 M charybdotoxin (blockers of small- and large-conductance Ca2+-activated K+ channels, respectively), and was blocked by 8×10–2 M potassium (a high concentration) and removal of the vascular endothelium. These results suggest that the direct vasorelaxant effect by clobenzorex on phenylephrine-precontracted rat aortic rings involved stimulation of the NO/cGMP/PKG/Ca2+-activated K+ channel pathway.

Irisin Lowers Blood Pressure by Improvement of Endothelial Dysfunction via AMPK-Akt-eNOS-NO Pathway in the Spontaneously Hypertensive Rat.

BackgroundExercise is a major nonpharmacological treatment for hypertension, but its underlying mechanisms are still not completely elucidated. Irisin, a polypeptide containing 112 amino acids, which is secreted mainly by skeletal muscle cells during exercise, exerts a protective role in metabolic diseases, such as diabetes mellitus and obesity. Because of the close relationship between irisin and metabolic diseases, we hypothesized that irisin may play a role in the regulation of blood pressure.Methods and ResultsBlood pressures of male Wistar‐Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) were monitored through the carotid artery. Our study found that acute intravenous injection of irisin reduced blood pressure in SHRs, but not WKY rats. Irisin, by itself, had no direct vasorelaxing effect in phenylephrine‐preconstricted mesenteric arteries from SHRs. However, irisin augmented the acetylcholine‐induced vasorelaxation in mesenteric arteries from SHRs that could be reversed by Nω‐nitro‐l‐arginine‐methyl ester (L‐NAME; 100 μmol/L), indicating a role of nitric oxide (NO) in this action. Indeed, irisin increased NO production and phosphorylation of endothelial nirtic oxide synthase (eNOS) in endothelial cells. 5′‐AMP‐activated protein kinase (AMPK) was involved in the vasorelaxing effect of irisin because compound C (20 μmol/L), an AMPK inhibitor, blocked the irisin‐mediated increase in phosphorylation of eNOS and protein kinase B (Akt) in endothelial cells and vasodilation in mesenteric arteries.ConclusionsWe conclude that acute administration of irisin lowers blood pressure of SHRs by amelioration of endothelial dysfunction of the mesenteric artery through the AMPK‐Akt‐eNOS‐NO signaling pathway.

6-Gingerol alleviates exaggerated vasoconstriction in diabetic rat aorta through direct vasodilation and nitric oxide generation.

The aim of the present study is to investigate the effect and potential mechanism of action of 6-gingerol on alterations of vascular reactivity in the isolated aorta from diabetic rats. Male Wistar rats were divided into two experimental groups, control and diabetics. Diabetes was induced by a single intraperitoneal injection of streptozotocin (50 mg kg−1), and the rats were left for 10 weeks to develop vascular complications. The effect of in vitro incubation with 6-gingerol (0.3–3 μM) on the vasoconstrictor response of the isolated diabetic aortae to phenylephrine and the vasodilator response to acetylcholine was examined. Effect of 6-gingerol was also examined on aortae incubated with methylglyoxal as an advanced glycation end product (AGE). To investigate the mechanism of action of 6-gingerol, the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester hydrochloride (100 μM), guanylate cyclase inhibitor methylene blue (5 μM), calcium-activated potassium channel blocker tetraethylammonium chloride (10 mM), and cyclooxygenase inhibitor indomethacin (5 μM) were added 30 minutes before assessing the direct vasorelaxant effect of 6-gingerol. Moreover, in vitro effects of 6-gingerol on NO release and the effect of 6-gingerol on AGE production were examined. Results showed that incubation of aortae with 6-gingerol (0.3–10 μM) alleviated the exaggerated vasoconstriction of diabetic aortae to phenylephrine in a concentration-dependent manner with no significant effect on the impaired relaxatory response to acetylcholine. Similar results were seen in the aortae exposed to methylglyoxal. In addition, 6-gingerol induced a direct vasodilation effect that was significantly inhibited by Nω-nitro-l-arginine methyl ester hydrochloride and methylene blue. Furthermore, 6-gingerol stimulated aortic NO generation but had no effect on AGE formation. In conclusion, 6-gingerol ameliorates enhanced vascular contraction in diabetic aortae, which may be partially attributed to its ability to increase the production of NO and stimulation of cyclic guanosine monophosphate.

Investigation of the vasorelaxant effects of moxonidine and its relaxation mechanism on the human radial artery when used as a coronary bypass graft.

In both low- and high-risk patients undergoing coronary artery bypass grafting, the internal mammary artery is the first choice of arterial graft, and the second choice is the radial artery (RA). Unfortunately, RA spasms are a significant problem for a surgical team to overcome in the perioperative and postoperative period. In current surgical practice, the use of vasodilator agents perioperatively in the pending graft preparation is generally accepted and these may be implemented topically, endoluminally or both ways. Moxonidine is the latest second-generation, centrally acting antihypertensive agent, and the intention in this paper is to investigate its direct vasorelaxant effects and relaxation mechanisms on the human radial artery in vitro. RA rings were mounted in an organ bath and tested for changes in isometric tension in its relaxation response to moxonidine in the presence and absence of NG-nitro-L-arginine methyl ester (L-NAME, non-specific inhibitor of nitric oxide synthase), idazoxan (non-selective I1 and α2-antagonist) and yohimbine (selective α2-antagonist). Moxonidine induced concentration-dependent relaxations on the RA rings precontracted with phenylephrine (P < 0.05). L-NAME and idazoxan significantly reduced the relaxation caused by moxonidine (P < 0.05), while yohimbine significantly increased the relaxation by moxonidine (P < 0.05). In the presence of L-NAME + idazoxan, the relaxation by moxonidine was eliminated completely (P < 0.05). We speculate that the relaxant effect of moxonidine may be attributed partly to the synthesis and/or release of nitric oxide, and partly to the stimulation of imidazoline I1 receptors. We suggest that moxonidine may help to prevent RA spasms during the preparation period in operation when used topically or/and endoluminally.

Effects of Resveratrol on Contractions of the Rat Tail Artery

In 2000, Naderali et. al. reported in Clinical Science (98:537-43) that resveratrol's direct vasorelaxant effect in vitro (on either adrenergic receptor-induced or high potassium-induced vascular smooth muscle contractions) was significantly greater in ring segments cut from mesenteric resistance arteries than from the main uterine conductance artery of female guinea pigs. Since then this important difference has not been confirmed in any other resistance versus conductance arterial tissues, and isolated from the same vasculature perfusing the same organ rather than different vessels perfusing different organs. The most distal and most proximal portions of the notably long ventral tail artery of the laboratory rat are commonly known for their unique structural and functional similarities to other resistance and conductance arteries (respectively) found throughout the rest of the body. Accordingly, we tested for relaxant effects of resveratrol in vitro in adrenergically pre-contracted rings cut from short segments of the distal and proximal portions of the tail artery from male rats. Its half-maximally effective concentration values were essentially identical (25±3 versus 27±3 micromolar) in distal versus proximal segments; results which do not confirm a greater relaxant effect of resveratrol in resistance versus conductance arterial tissues. Therefore, what Naderali et. al. previously observed may have been due to some other property that differed between their mesenteric and uterine arterial preparations. Support: MWU Master's Program.

Comparison of the Intrinsic Vasorelaxant and Inotropic Effects of the Antiarrhythmic Agents Vernakalant and Flecainide in Human Isolated Vascular and Cardiac Tissues

This study explored the intrinsic vasorelaxant and inotropic effects of the mixed potassium and sodium channel blocker atrial antiarrhythmic vernakalant and the class IC antiarrhythmic agent flecainide in human isolated subcutaneous resistance artery and in ventricular trabecular muscle preparations. At test concentrations encompassing free plasma concentrations associated with clinical efficacy for conversion of atrial fibrillation, vernakalant (1-10 μM) displayed no significant direct effects on human resistance artery tone or ventricular contractility. In contrast, tested at equimolar concentrations, flecainide significantly reduced peak isometric contractile force (10 μM) and maximal rates of force development and decline (3 and 10 μM) in the human ventricular muscle preparation while displaying no significant effect on human resistance artery tone. The lack of effects of vernakalant on human resistance artery tone and ventricular muscle contractile function suggests that direct vasorelaxant and inotropic effects do not underlie the rare hypotensive events observed clinically with vernakalant, raising the possibility that secondary (eg, reflex) effects may mediate these events. The demonstration of negative inotropic effects with flecainide in the human ventricular muscle preparations in the absence of an effect on resistance artery tone suggests that the hemodynamic effects of flecainide observed clinically result primarily from direct negative inotropic effects.

The vascular effects of different arginase inhibitors in rat isolated aorta and mesenteric arteries

Arginase and nitric oxide (NO) synthase share the common substrate L-arginine, and arginase inhibition is proposed to increase NO production by increasing intracellular levels of L-arginine. Many different inhibitors are used, and here we have examined the effects of these inhibitors on vascular tissue. Each arginase inhibitor was assessed by its effects on isolated rings of aorta and mesenteric arteries from rats by: (i) their ability to preserve the tolerance to repeated applications of the endothelium-dependent agonist acetylcholine (ACh); and (ii) their direct vasorelaxant effect. In both vessel types, tolerance (defined as a reduced response upon second application) to ACh was reversed with addition of L-arginine, (S)-(2-boronethyl)-L-cysteine HCl (BEC) or N(G)-Hydroxy-L-arginine (L-NOHA). On the other hand, N(omega)-hydroxy-nor-L-arginine (nor-NOHA) significantly augmented the response to ACh, an effect that was partially reversed with L-arginine. No effect on tolerance to ACh was observed with L-valine, nor-valine or D,L, alpha-difluoromethylornithine (DFMO). BEC, L-NOHA and nor-NOHA elicited endothelium-independent vasorelaxation in both endothelium intact and denuded aorta while L-valine, DFMO and nor-valine did not. BEC and L-NOHA, but not nor-NOHA, L-valine, DFMO or nor-valine, significantly reversed tolerance to ACh possibly conserving L-arginine levels and therefore increasing NO bioavailability. However, both BEC and L-NOHA caused endothelium-independent vasorelaxation in rat aorta, suggesting that these inhibitors have a role beyond arginase inhibition alone. Our data thus questions the interpretation of many studies using these antagonists as specific arginase inhibitors in the vasculature, without verification with other methods.

Glucuronidated and sulfated metabolites of the flavonoid quercetin prevent endothelial dysfunction but lack direct vasorelaxant effects in rat aorta

Epidemiological studies have reported an inverse association between dietary flavonoid intake and mortality for ischemic heart disease. Quercetin reduces blood pressure and restores endothelial dysfunction in hypertensive animals. However, quercetin (aglycone) is usually not present in plasma, but it is rapidly metabolized during absorption by methylation, glucuronidation and sulfation. We have analyzed the vasorelaxant effects and the role on NO bioavailability and endothelial function of quercetin and its conjugated metabolites (quercetin-3-glucuronide, isorhamnetin-3-glucuronide and quercetin-3′-sulfate) in rat aorta. Thoracic aortic rings isolated from Wistar rats were mounted for isometric force recording and endothelial function was tested by measuring the vasorelaxant response to acetylcholine. NADPH-enhanced O 2 − release was quantified in homogenates from cultured aortic smooth muscle cells using lucigenin chemiluminescence. Unlike quercetin, the conjugated metabolites had no direct vasorelaxant effect, and did not modify endothelial function or the biological activity of NO. However, all metabolites (at 10 μmol/L) prevented, at least partially, the impairment of endothelial-derived NO response under conditions of high oxidative stress induced by the SOD inhibitor DETCA. Furthermore, they protected the biological activity of exogenous NO when impaired by DETCA. Quercetin and quercetin-3′-sulfate (≥10 μmol/L) or quercetin-3-glucuronide (100 μmol/L) inhibited NADPH oxidase-derived O 2 − release. Quercetin and quercetin-3-glucuronide (1 μmol/L) prevented the endothelial dysfunction induced by incubation with ET-1. These data indicate, for the first time, that the conjugated metabolites could be responsible for the in vivo protective activity of quercetin on endothelial dysfunction.

Effects of trans- and cis-resveratrol on Ca 2+ handling in A7r5 vascular myocytes

Although the natural polyphenol resveratrol posses a direct vasorelaxant effect, its effects on cytoplasmic Ca 2+ concentration ([Ca 2+] i) in vascular cells remain still unclear. Here, we have investigated the effects of the isomers trans- and cis-resveratrol on agonist- and high-K +-induced [Ca 2+] i increases and on voltage-activated transmembrane Ca 2+ fluxes using imaging and patch-clamp techniques in vascular A7r5 myocytes. Arginine vasopressin (AVP) or angiotensin II caused a biphasic increase in [Ca 2+] i that was reduced by preincubation with trans-resveratrol and cis-resveratrol. Both isomers also reduced the agonist-induced increase in [Ca 2+] i in absence of extracellular Ca 2+. In high-K + Ca 2+-free solution, reintroduction of Ca 2+ caused a sustained rise in [Ca 2+] i that was reduced by preincubation with trans-resveratrol or cis-resveratrol. When the isomers were applied during the plateau phase of the agonist- or the high-K +-induced response, a biphasic change in [Ca 2+] i was observed: a transient reduction of the plateau (< 5 min) followed by an increase (> 10 min). Finally, trans-resveratrol and cis-resveratrol inhibited voltage-dependent L-type Ca 2+ currents ( I Ca(L)). In conclusion, resveratrol isomers exert a dual effect on [Ca 2+] i handling in A7r5 myocytes: 1) a blockade of I Ca(L) and 2) an increase in [Ca 2+] i by depletion of intracellular Ca 2+ stores (which interferes with the agonist-induced release of intracellular Ca 2+) and influx of Ca 2+, mainly due to activation of capacitative Ca 2+ entry, although other Ca 2+-permeable channels are also involved. Taken together, these effects may explain, in part, the endothelium-independent vasorelaxant effects of resveratrol in rat aorta.

Mechanisms of Hypoxic Erythrovasodilation.

Red blood cells (RBC) have the unique ability to relax blood vessels under low oxygen conditions (Pawloski et al. Nature 409:622, 2001), an activity now termed hypoxic erythrovasodilation (HEV). With human erythrocytes, HEV appears to be mediated, in part, by the export of nitric oxide (NO) bioequivalents formed in the RBC membrane by nitric oxide (NO) group transfer from S-nitrosohemoglobin (SNO-Hb) to cysteine thiols in the cytoplasmic domain of the anion exchanger-1 (AE1 or band 3) protein. Alternatively, HEV has been proposed to be mediated via the nitrite reductase activity of deoxy Hb, resulting in the formation of heme-bound or nitrosyl Hb (HbNO), with subsequent export of NO from the RBC. For both paradigms, downstream export mechanisms, and a precise chemical identity of the discharged specie(s), have yet to be resolved. Interactions between RBCs and vascular tissue (i.e. endothelium and smooth muscle) involved in the HEV response remain undefined, and are the focus of the current study.Rabbit aortic rings were suspended in jacketed organ chambers filled with Krebs-bicarbonate buffer at 37°C, and bubbled continuously with either 21% O2/5% CO2 or 95% argon/5% CO2. Basal tension was maintained at 2 grams, and active tension induced with phenylephrine (PE) or prostaglandin F2a (PGF2a). Fresh (<4 days) or old (>60 days) RBCs were washed and resuspended in phosphate-buffered saline at 50% hematocrit prior to use. Following induction of active tension with PE or PGF2a, changing the aeration gas from O2 to argon resulted in a brisk increase in vascular tone (hypoxic vasoconstriction, HVC). At the peak of this contractile response, RBCs were added to the tissue chambers, causing a dose-dependent relaxation of the rings. There was no correlation between the magnitude of the HVC and that of the ensuing HEV. Following physical removal of the endothelium (confirmed by loss of relaxation to acetylcholine), HVC was unaffected, but HEV was reduced about 20%. In contrast, pretreating the rings with the NO scavenger Hb (100 uM), the NOS inhibitor L-NAME (10 uM), or the soluble guanylate cyclase inhibitor ODQ (10 uM), virtually abolished HVC, while augmenting the HEV response. Deoxygenating RBCs prior to use reduced HEV ~ 50% versus oxyRBCs, while treating the RBCs with carbon monoxide (CO-RBC) abolished HEV. Adding a molar equivalent of purified oxyHb (10 uM), instead of RBCs, at the peak of HVC, resulted in a comparable relaxation response. HEV activity was markedly attenuated using old RBCs, but could be fully restored by pretreating the old RBCs with aqueous NO (1:250 NO:heme) or 1 mM N-acetylcysteine (NAC). NO and NAC treatment did not enhance the HEV of fresh RBCs. In contrast, treating old RBCs with nitrite (100 or 500 nM), or adding nitrite to the tissue bath (100 or 500 nM) had no effect on the HEV response.These results demonstrate that hypoxic erythrovasodilation is a multi-mechanistic biologic response involving the vascular endothelium, oxygen transfer to substrate-limited smooth muscle inducible NOS (iNOS), and possibly a direct vasorelaxant effect on the vascular smooth muscle. Further, we have shown that hypoxic vasoconstriction can occur in non-pulmonary vascular tissue, an effect likely mediated by increased iNOS expression.

Ketamine enantiomers differentially relax isolated coronary artery rings

Background and objective: It has been shown that racemic ketamine increases coronary blood flow and that this effect is at least in part due to a direct vasorelaxing effect of this substance. This study was designed to determine whether ketamine might stereoselectively relax isolated porcine coronary arteries. Methods: Using the model of isolated vessels we studied the effects of S(+) ketamine, R(−) ketamine, and racemic ketamine (5-500 μg mL−1) on artery strips pre-contracted by either potassium chloride (KCl) or prostaglandin F2α (PGF2α). To elucidate possible mechanisms of action these experiments were repeated in the presence of one of the following compounds: Nω-nitro-L-arginine (L-NNA), indomethacin, glibenclamide, and tetraethylammonium (TEA) chloride, an inhibitor of the BKCa K+ channel. Results: Both isoforms and racemic ketamine relaxed isolated coronary arteries in a concentration-dependent manner in concentrations beyond those used in clinical practice. S(+) ketamine exerted the strongest vasorelaxing effect, followed by racemic ketamine and R(−) ketamine. Pretreatment with L-NNA, indomethacin, or glibenclamide did not alter the vasodilating properties of ketamine, whereas TEA chloride significantly attenuated the vasorelaxing effects of all the three forms of ketamine. Conclusions: Ketamine dilates coronary arteries in vitro when administered in high concentrations. There is a stereoselective difference with a stronger vasorelaxing effect of S(+) ketamine compared to racemic and R(−) ketamine. The impact of TEA chloride suggests that the activation of the BKCa channel may contribute to the vasodilating effect of ketamine.

Ketamine enantiomers differentially relax isolated coronary artery rings

It has been shown that racemic ketamine increases coronary blood flow and that this effect is at least in part due to a direct vasorelaxing effect of this substance. This study was designed to determine whether ketamine might stereoselectively relax isolated porcine coronary arteries. Using the model of isolated vessels we studied the effects of S(+) ketamine, R(-) ketamine, and racemic ketamine (5-500 microg mL(-1)) on artery strips pre-contracted by either potassium chloride (KCl) or prostaglandin F2alpha (PGF2alpha). To elucidate possible mechanisms of action these experiments were repeated in the presence of one of the following compounds: N(omega)-nitro-L-arginine (L-NNA), indomethacin, glibenclamide, and tetraethylammonium (TEA) chloride, an inhibitor of the BK(Ca) K+ channel. Both isoforms and racemic ketamine relaxed isolated coronary arteries in a concentration-dependent manner in concentrations beyond those used in clinical practice. S(+) ketamine exerted the strongest vasorelaxing effect, followed by racemic ketamine and R(-) ketamine. Pretreatment with L-NNA, indomethacin, or glibenclamide did not alter the vasodilating properties of ketamine, whereas TEA chloride significantly attenuated the vasorelaxing effects of all the three forms of ketamine. Ketamine dilates coronary arteries in vitro when administered in high concentrations. There is a stereoselective difference with a stronger vasorelaxing effect of S(+) ketamine compared to racemic and R(-) ketamine. The impact of TEA chloride suggests that the activation of the BK(Ca) channel may contribute to the vasodilating effect of ketamine.