Inhibition of acetylcholine-induced EDHF response by elevated glucose in rat mesenteric artery

Investigating the effect of some fluoroquinolones on C-reactive protein levels and ACh-Induced blood pressure reduction deviations after aging of diabetes in STZ-Induced diabetic wistar rats

The treatment of infections in diabetic patients by fluoroquinolone antibiotics is associated with a reduced risk of coronary artery disease, and may improve endothelium-derived hyperpolarizing factor (EDHF) efficacy. The inflammatory marker C-reactive protein (CRP) is an important predictor of cardiovascular events, and vascular endothelium dysfunction, which makes this marker a target for drug-based treatment. This study aims to investigate the relation between the treatment by fluoroquinolones with CRP plasma levels, as well as acetylecholine (ACh)-induced small conductance calcium-activated potassium channels (SKCa)-dependent blood pressure (BP) reduction deviations in wistar rats after inducing a type 2-like diabetes with aging state after four months of streptozotocin (STZ) injection. Experimental animals were divided into four groups, group 1: diabetic animals were treated with moxifloxacin (n = 15), group 2: diabetic animals were treated with levofloxacin (n = 15), group 3: diabetic control animals (n = 15), and group 4: non-diabetic control animals (n = 6). The levels of plasma CRP, as well as ACh-induced SKCa-dependent BP reduction deviations were compared four months after the development of diabetes, after that; two groups were treated with fluoroquinolones, four months after the treatment; CRP-plasma levels, as well as ACh-induced SKCa-dependent BP reduction deviations were also evaluated and compared for all groups. Sustained hyperglycemia after the induction of diabetes elevated CRP plasma levels, and reduced ACh-induced SKCa-dependent BP reduction, observed diabetes-induced variations were minimal in fluoroquinolones treated diabetic groups compared with diabetic control group, In conclusion, the treatment with fluoroquinolone antibiotics in diabetic wistars may be associated with a lowering in CRP levels progression, and improvement in SKCa vitality, which indicates the importance of treating infections in diabetics by fluoroquinolones to mitigate some vascular complications signs that lead to morbidity and mortality in diabetes.

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

Phosphodiesterase-3 inhibitor cilostazol reverses endothelial dysfunction with ageing in rat mesenteric resistance arteries

Ageing impairs endothelial function, which is considered a hallmark of the development of cardiovascular diseases in elderly. Cilostazol, a phosphodiesterase-3 inhibitor, has antiplatelet, antithrombotic and protective effects on endothelial cells. Here, we hypothesized that cilostazol could improve endothelial function in mesenteric resistance arteries (MRA) from old rats. Using eight-week cilostazol-treated (100mg/kg/day) or untreated 72-week-old Wistar rats, we evaluate the relaxation to acetylcholine, sodium nitroprusside (SNP), forskolin and isoproterenol and the noradrenaline-induced contraction in MRA. Superoxide anion and nitric oxide (NO) was measured by dihydroethidium- and diaminofluorescein-2-emitted fluorescence, respectively. Normotensive old rats had impaired acetylcholine-induced NO- and EDHF-mediated relaxation and increased noradrenaline vasoconstriction than young rats. This age-associated endothelial dysfunction was restored by cilostazol treatment. Relaxation to SNP, forskolin or isoproterenol remained unmodified by cilostazol. Diaminofluorescein-2-emitted fluorescence was increased while dihydroethidium-emitted was decreased by cilostazol, indicating increased NO and reduced superoxide generation, respectively. Cilostazol improves endothelial function in old MRA without affecting blood pressure. This protective effect of cilostazol could be attributed to reduced oxidative stress, increased NO bioavailability and EDHF-type relaxation. Although these results are preliminary, we believe that should stimulate further interest in cilostazol as an alternative for the treatment of age-related vascular disorders.

Effects of high glucose with or without other metabolic substrates on alpha-adrenergic contractions in rat mesenteric and femoral arteries

Hyperglycemia is associated with an increased risk of cardiovascular diseases. It has been demonstrated that chronic exposure to high glucose impaired endothelial functions. However, specific effects of short-term exposure to high glucose on vascular reactivity are controversial. Moreover, the combined effects of other metabolic substrates such as free fatty acids (FFA) on vascular reactivity remain poorly understood. Here we investigate the effects of short-term exposure to high glucose with or without other metabolic substrates including FFAs termed “nutrition full” (NF) solution, on mesenteric (MA) and deep femoral arteries (DFA) of rats. Arterial ring segments were mounted in a double-wire myograph. Contraction in response to phenylephrine (PhE) was determined in control (5 mM) and high glucose (23 mM, HG) environments over a 30 min period. In both arteries, PhE-inducedvasocontraction was enhanced by pre-incubation of HG solution. A combined incubation with HG and palmitic acid (100 µM) induced similar sensitization of PhE-contractions in both arteries. In contrast, high K⁺-induced contractions were not affected by HG. Interestingly, pre-incubation with NF solution decreased PhE-induced contraction in MA but increased the contraction in DFA. In NF solution, the HG-induced facilitation of PhE-contraction was not observed in MA. Furthermore, the PhE-induced contraction of DFA was attenuated by HG in NF solution. Our results demonstrate that the sensitization of PhE-induced arterial contraction by HG is differentially affected by other metabolic substrates. The conversation of skeletal arterial contractility by HG in NF solution requires careful interpretation of the previous in vitro studies where only glucose is included in physiological salt solutions. Further studies are required to elucidate the mechanism underlying the inconsistent effect of NF solution on MA and DFA.

Protective effect of resveratrol and quercetin on in vitro-induced diabetic mouse corpus cavernosum

BACKGROUND

Hyperglycemia and increased levels of methylglyoxal (MGO) can trigger the development of vascular complications in diabetes. Resveratrol and quercetin are red wine polyphenols with known beneficial cardiovascular properties, including an antioxidant capacity. This study evaluated whether resveratrol and/or quercetin could prevent in vitro-induced diabetic changes in neurogenic and vascular relaxant responses of mouse arteries and corpora cavernosa.

METHODS

Isometric tension of isolated aorta, mesenteric arteries and corpora cavernosa was measured using organ bath systems. Diabetic conditions were mimicked in vitro by co-incubating the tissues for 2 h with high glucose (HG, 30 mM) and MGO (120 µM).

RESULTS

The presence of HG and MGO significantly blunted acetylcholine (Ach)-induced relaxations in corpora cavernosa and mesenteric arteries but not in aorta. Electrical field stimulated (EFS) responses of corpora cavernosa were also significantly inhibited by these diabetic conditions. In corpora cavernosa 2 h co-incubation with resveratrol (30 µM) or quercetin (30 µM) significantly attenuated HG and MGO-induced deficits in Ach- and EFS-responses.

CONCLUSIONS

Our study demonstrates that in mouse arteries, HG and MGO rather affect endothelium derived hyperpolarizing factor-mediated than nitric oxide (NO)-mediated relaxations. In corpora cavernosa HG and MGO interfere with NO release. Resveratrol and quercetin protect mouse corpora cavernosa from diabetic-induced damage to NO-mediated relaxant responses. This might rely on their antioxidant capacity.

Effects of glucagon-like peptide-1 in diabetic rat small resistance arteries

We investigated the functional effects of glucagon-like peptide-1 [GLP-1(7-36)] and GLP-1(9-36) and the mechanism(s) playing a role in the effects of these agents in isolated small resistance arteries from control and diabetic rats. Cumulative concentrations of GLP-1(7-36) and GLP-1(9-36) produced concentration-dependent relaxations in endothelium-intact but not endothelium-denuded arteries that were significantly decreased in diabetic rats. GLP-1 receptor antagonist exendin(9-39) significantly inhibited responses to GLP-1 analogs. Nitric oxide/cyclic guanosine monophosphate pathway blockers, but not indomethacin, significantly decreased responses to GLP-1(7-36) or GLP-1(9-36) in control and diabetic rats. 4-Aminopyridine or glibenclamide incubation did not alter relaxations to GLP-1 analogs. GLP-1(7-36)- and GLP-1(9-36)-induced relaxations were blunted significantly and to similar extends by charybdotoxin and apamin combination in control and diabetic rats. Catalase did not affect, whereas superoxide dismutase (SOD) caused a significant increase in relaxations to GLP-1 analogs only in diabetic rats. We provided evidence about the relaxant effects of GLP-1(7-36) and GLP-1(9-36) in resistance arteries that were reduced in diabetic rats. Both calcium-activated potassium channels and endothelium played a major role in relaxations. Increment in certain reactive oxygen species and/or reduction in superoxide dismutase function might play a role in reduced relaxant responses of resistance arteries to GLP-1(7-36) and GLP-1(9-36) in diabetic rats.

The DPP-4 inhibitor linagliptin and the GLP-1 receptor agonist exendin-4 improve endothelium-dependent relaxation of rat mesenteric arteries in the presence of high glucose

The aim of the study was to investigate the effects of the DPP-4 inhibitors and GLP-1R agonist, exendin-4 on the mechanism(s) of endothelium-dependent relaxation in rat mesenteric arteries exposed to high glucose concentration (40 mM). Organ bath techniques were employed to investigate vascular endothelial function in rat mesenteric arteries in the presence of normal (11 mM) or high (40 mM) glucose concentrations. Pharmacological tools (1μM TRAM-34, 1μM apamin, 100 nM Ibtx, 100 μM l-NNA, 10 μM ODQ) were used to distinguish between NO and EDHF-mediated relaxation. Superoxide anion levels were assessed by L-012 and lucigenin enhanced-chemiluminescence techniques. Incubation of mesenteric rings with high glucose for 2 h caused a significant increase in superoxide anion generation and a significant impairment of endothelium-dependent relaxation. Exendin-4 and DPP-4 inhibitor linagliptin, but not sitagliptin or vildagliptin, significantly reduced vascular superoxide and improved endothelium-dependent relaxation in the presence of high glucose. The beneficial actions of exendin-4, but not linagliptin, were attenuated by the GLP-1R antagonist exendin fragment (9-39). Further experiments demonstrated that the presence of high glucose impaired the contribution of both nitric oxide and endothelium-dependent hyperpolarisation to relaxation and that linagliptin improved both mechanisms involved in endothelium-dependent relaxation. These findings demonstrate that high glucose impaired endothelium-dependent relaxation can be improved by exendin-4 and linagliptin, likely due to their antioxidant activity and independently of any glucose lowering effect.

Intraluminal hyperglycaemia causes conduit and resistance artery dilatation and inhibits vascular autoregulation in the anaesthetised pig

The effect of intraluminal hyperglycaemia was investigated in the iliac artery of 11 anaesthetised pigs. Following isolation of a test segment, hyperglycaemic blood (40 mmol·L–1) caused a significant dilatation of the artery of 167 ± 208 μm (mean ± SD; n = 6, P = 0.031). Dilatations were reduced by N(G)-nitro-l-arginine methyl esther (250 μg·mL–1) from 145 ± 199 to 38 ± 5 μm), but this was not statistically significant (n = 6, P = 0.18). Intra-arterial infusions of d-glucose (20–40 mmol·L–1·min–1), during graded constrictions, caused statistically significant increases in blood flow (n = 11, P = 0.0013). Vasodilatation was confirmed by measurements of the ratio of immediate pressure steps to flow steps (∂P/∂F) during the graded obstruction experiments, showing a decrease in instantaneous vascular resistance from a control of 0.62 ± 0.30 to 0.33 ± 0.34 mm Hg·mL–1·min–1 (n = 7, P = 0.016). Autoregulation was assessed from the slopes of the plots of steady-state flow versus pressure. There were significant increases in the slope from 2.32 ± 1.03 to 5.88 ± 5.60 mL·min–1·(mm Hg)–1 (n = 7, P = 0.0078), indicating significant impairment of autoregulation. In conclusion, luminal hyperglycaemia relaxes both arterial and resistance vessel smooth muscle.

Toll-like receptor 4 mutation protects obese mice against endothelial dysfunction by decreasing NADPH oxidase isoforms 1 and 4

OBJECTIVE

To analyze the role of toll-like receptor 4 in modulating metabolism and endothelial function.

APPROACH AND RESULTS

Type 2 diabetic mice with mutated toll-like receptor 4 (DWM) were protected from hyperglycemia and hypertension, despite an increased body weight. Isometric tension was measured in arterial rings with endothelium. Relaxations to acetylcholine were blunted in aortae and mesenteric arteries of Lepr(db/db) mice, but not in DWM mice; the endothelial NO synthase dimer/monomer ratio and endothelial NO synthase phosphorylation levels were higher in DWM preparations. These differences were abolished by apocynin. Contractions to acetylcholine (in the presence of L-NAME) were larger in carotid arteries from Lepr(db/db) mice than from DWM mice and were inhibited by indomethacin and SC560, demonstrating involvement of cyclooxygenase-1. The release of 6-ketoprostaglandin F1α was lower in DWM mice arteries, implying lower cyclooxygenase-1 activity. Apocynin, manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin, catalase, and diethyldithiocarbamate inhibited endothelium-dependent contractions. The mRNA and protein levels of NADPH oxidase isoforms NOX1 and NOX4 were downregulated in DWM mice arteries. The in vivo and in vitro administration of lipopolysaccharide caused endothelial dysfunction in the arteries of wild-type, but not toll-like receptor 4-mutated mice.

CONCLUSIONS

Toll-like receptor 4 plays a key role in obesity and diabetes-associated endothelial dysfunction by increasing oxidative stress.

Total flavonoids of Flos Chrysanthemi protect arterial endothelial cells against oxidative stress

ETHNOPHARMACOLOGICAL RELEVANCE

Total flavonoids of Flos Chrysanthemi (TFFC) are known to modulate vascular functions, but their effect on endothelial cells injured by oxidative stress is unknown. Our objective was to investigate the vasoprotective effect and mechanism of action of TFFC on rat mesenteric artery exposed to superoxide anions produced by pyrogallol.

MATERIALS AND METHODS

The vasoprotective effect and mechanism of action of TFFC on primary cultured rat mesenteric arterial endothelial cells and small mesenteric arteries was investigated using small-vessel myography, fluorescent Ca(2+) measurement, fluorescent membrane potential measurement and oxidative fluorescent studies.

RESULTS

Experiments using small-vessel myography of third-order rat mesenteric arterial rings showed that pretreatment with pyrogallol (10-1000μM), an auto-oxidizing source of superoxide anions, dose-dependently decreased ACh-induced endothelium-dependent relaxation. TFFC (2.5-320mg/L) evoked a concentration-dependent dilation (pD(2): 29.6±0.276mg/L), which was weakened by ChTX plus apamin. TFFC markedly attenuated the inhibition of vasorelaxation induced by pyrogallol (E(max) elevated from 50.4±7.36% to 86.2±3.61%, and pD(2) increased from 6.74±0.06 to 7.28±0.12). Furthermore, in primary cultured endothelial cells, fluorescent Ca(2+) measurement, fluorescent membrane potential measurement and oxidative fluorescent studies demonstrated that ACh-induced endothelial Ca(2+) influx and hyperpolarization were significantly weakened by the increased basal superoxide level induced by pyrogallol. When the endothelial cells were concurrently exposed to TFFC, the impairment effect of oxidative stress on ACh-induced Ca(2+) influx, hyperpolarization and vasorelaxation were attenuated due to its superoxide-lowering activity.

CONCLUSION

This study shows that oxidative stress has a pronounced deleterious effect on EDHF-mediated vasorelaxation to ACh in rat mesenteric artery. TFFC has vasodilating effect and protects EDHF-mediated vasodilator reactivity from oxidative stress. Thus, our experiments suggest that TFFC is potentially useful for the development of therapeutic treatments for cardiovascular diseases associated with oxidative stress.

Apple procyanidins induced vascular relaxation in isolated rat aorta through NO/cGMP pathway in combination with hyperpolarization by multiple K+ channel activations

Apple (Malus pumila) procyanidins led to a potent vasorelaxation effect in 1.0 microM phenylephrine-contractive rat thoracic aorta. Relaxation was greatly reduced by 70 mM KCl as well as by removal of the endothelium, suggesting that it was associated with endothelium-dependent hyperpolarization. Neither cAMP synthesis inhibition nor NAD(P)H oxidase inhibition abolished the effect. In contrast, complete abolition by a soluble guanylyl cyclase inhibitor revealed that apple procyanidins were mainly involved in the cGMP production pathways. In the presence of N(G)-monoethyl-L-arginine or tetraethylammonium chloride, the effect was still observed at higher concentrations (>25 microg/ml), while their combination completely diminished the effect. Vasorelaxation was to some extent affected by paxillin, apamin and glybenclamide, and was greatly affected by 4-aminopyridine and by BaCl(2). These results indicate that procyanidin-induced vasorelaxation is associated with NO-cGMP pathway in combination with hyperpolarization due to multiple activation of Ca(2+)-dependent and -independent K(+) channels.

Cilostazol improves endothelial dysfunction by increasing endothelium-derived hyperpolarizing factor response in mesenteric arteries from Type 2 diabetic rats

Diabetes mellitus impairs endothelial function, an effect that can be considered a hallmark of the development of cardiovascular diseases in diabetics. Cilostazol, a selective phosphodiesterase 3 inhibitor, is currently used to treat patients with diabetic vascular complications. However, the effects of cilostazol on responses mediated by endothelium-derived relaxing [in particular, nitric oxide (NO) and hyperpolarizing factors (EDHF)] and contracting factors remain unclear. Here, we hypothesized that cilostazol could improve endothelial dysfunctions in mesenteric arteries isolated from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Using cilostazol-treated (100 mg/kg/day for 4 weeks) or -untreated OLETF and control (Long Evans Tokushima Otsuka) rats, we examined the acetylcholine-induced endothelium-dependent responses and the cell-permeant cyclic adenosine monophosphate (cAMP) analog-induced relaxations in the superior mesenteric artery. We also determined blood parameters in these animals. In OLETF rats, chronic treatment with cilostazol reduced the blood levels of triglyceride, non-esterified fatty acids, and leptin, and increased antioxidant capacity, but did not alter the blood glucose or insulin levels. In studies on mesenteric arteries from cilostazol-treated OLETF animals, the cilostazol treatment improved: (a) the acetylcholine-induced EDHF-mediated relaxation and (b) the cAMP-mediated relaxation. However, cilostazol did not alter the NO-mediated relaxation or the endothelium-derived contracting factor-mediated contraction. These results suggest that cilostazol improves endothelial functions in OLETF mesenteric arteries by increasing EDHF signaling, and that it normalizes some metabolic abnormalities in OLETF rats. On that basis, cilostazol may prove to be a potent drug for the clinical treatment of diabetic vasculopathy.

Differential effects of glucose on agonist-induced relaxations in human mesenteric and subcutaneous arteries

BACKGROUND AND PURPOSE

Acute periods of hyperglycaemia are strongly associated with vascular disorder, yet the specific effects of high glucose on human blood vessel function are not fully understood. In this study we (1) characterized the endothelial-dependent relaxation of two similarly sized but anatomically distinct human arteries to two different agonists and (2) determined how these responses are modified by acute exposure to high glucose.

EXPERIMENTAL APPROACH

Ring segments of human mesenteric and subcutaneous arteries were mounted in a wire myograph. Relaxations to acetylcholine and bradykinin were determined in a control (5 mM) and high glucose (20 mM) environment over a 2 and 6 h incubation period.

KEY RESULTS

Bradykinin-induced relaxation in both sets of vessels was mediated entirely by EDHF whilst that generated by acetylcholine, though principally generated by EDHF, also had contribution from prostacyclin and possibly nitric oxide in mesenteric and subcutaneous vessels, respectively. A 2-h incubation of high glucose impaired bradykinin-induced relaxation of subcutaneous vessels whilst, in contrast, the relaxation generated by bradykinin in mesenteric vessels was enhanced at the same time point. High glucose significantly augmented the relaxation generated by acetylcholine in mesenteric and subcutaneous vessels at a 2 and 6 h incubation point, respectively.

CONCLUSIONS AND IMPLICATIONS

Short periods of high glucose exert a variable influence on endothelial function in human isolated blood vessels that is dependent on factors of time, agonist-used and vessel studied. This has implications for how we view the effects of acute hyperglycaemia found in patients with diabetes mellitus as well as other conditions.

Selective resistance to vasoactive effects of insulin in muscle resistance arteries of obese Zucker (fa/fa) rats

Obesity is related to insulin resistance and hypertension, but the underlying mechanisms are unclear. Insulin exerts both vasodilator and vasoconstrictor effects on muscle resistance arteries, which may be differentially impaired in obesity.

OBJECTIVES

To investigate whether vasodilator and vasoconstrictor effects of insulin are impaired in muscle resistance arteries of obese rats and the roles of Akt and endothelial NO synthase (eNOS).

METHODS/RESULTS

Effects of insulin were studied in resistance arteries isolated from cremaster muscles of lean and obese Zucker rats. In arteries of lean rats, insulin increased activity of both NO and endothelin (ET-1), resulting in a neutral effect under basal conditions. In arteries of obese rats, insulin induced endothelin-mediated vasoconstriction (-15 +/- 5% at 1 nM, P < 0.05 vs. lean). Insulin induced vasodilatation during endothelin receptor blockade in arteries of lean rats (20 +/- 5% at 1 nM) but not in those of obese rats. Inhibition of NO synthesis increased vascular tone (by 12 +/- 2%) and shifted insulin-mediated vasoreactivity to vasoconstriction (-25 +/- 1% at 1 nM) in lean rats but had no effect in arteries of obese rats, indicating reduced NO activity. Protein analysis of resistance arteries revealed that insulin-mediated activation of Akt was preserved in obese rats, whereas expression of eNOS was markedly decreased.

CONCLUSIONS

Vasodilator but not vasoconstrictor effects of insulin are impaired in muscle resistance arteries of obese rats, and this selective impairment is associated with decreased protein levels of eNOS. These findings provide a new mechanism linking obesity to insulin resistance and hypertension.

Disruption of endothelial caveolae is associated with impairment of both NO- as well as EDHF in acetylcholine-induced relaxation depending on their relative contribution in different vascular beds

Caveolae represent an important structural element involved in endothelial signal-transduction. The present study was designed to investigate the role of caveolae in endothelium-dependent relaxation of different vascular beds. Caveolae were disrupted by cholesterol depletion with filipin (4x10(-6) g L(-1)) or methyl-beta-cyclodextrin (MCD; 1x10(-3) mol L(-1)) and the effect on endothelium-dependent relaxation was studied in rat aorta, small renal arteries and mesenteric arteries in the absence and presence of L-NMMA. The contribution of NO and EDHF, respectively, to total relaxation in response to acetylcholine (ACh) gradually changed from aorta (71.2+/-6.1% and 28.8+/-6.1%), to renal arteries (48.6+/-6.4% and 51.4+/-6.4%) and to mesenteric arteries (9.1+/-4.0% and 90.9+/-4.1%). Electron microscopy confirmed filipin to decrease the number of endothelial caveolae in all vessels studied. Incubation with filipin inhibited endothelium-dependent relaxation induced by cumulative doses of ACh (3x10(-9)-10(-4) mol L(-1)) in all three vascular beds. In aorta, treatment with either filipin or MCD only inhibited the NO component, whereas in renal artery both NO and EDHF formation were affected. In contrast, in mesenteric arteries, filipin treatment only reduced EDHF formation. Disruption of endothelial caveolae is associated with the impairment of both NO and EDHF in acetylcholine-induced relaxation.

Apocynin normalizes hyperreactivity to phenylephrine in mesenteric arteries from cholesterol-fed mice by improving endothelium-derived hyperpolarizing factor response

We studied the relationship among endothelial function, oxidative stress, and phenylephrine (PE; alpha(1)-adrenoceptor agonist)-induced contraction in mesenteric arteries from high-cholesterol (HC)-diet-fed mice. In HC mice (vs age-matched normal-diet-fed mice): (1) PE-induced contraction in endothelium-intact rings was enhanced (endothelial denudation increased contraction in "normal-diet" rings, but did not enhance it further in "HC" rings); (2) the enhanced PE-induced contraction was further enhanced in the presence of N(G)-nitro-L-arginine (L-NNA; nitric oxide synthase inhibitor) or L-NNA plus indomethacin (cyclooxygenase inhibitor) [to preserve endothelium-derived hyperpolarizing factor (EDHF)], but unchanged in the presence of charybdotoxin plus apamin (to block EDHF); (3) ACh-induced EDHF-type relaxation was reduced; and (4) oxidative stress [indicated by the plasma 8-isoprostane level (reliable systemic marker) and aortic superoxide production] was greater. In HC mice, PE-induced contraction was normalized by apocynin [NAD(P)H oxidase inhibitor] or tempol (superoxide dismutase mimetic), but enhanced by NADH [NAD(P)H oxidase substrate]. Oral dietary supplementation with apocynin (30 mg/kg/day for 4 weeks) corrected the above abnormalities. Hence: (1) PE-induced contraction is modulated by the endothelium, and the enhanced contractility in HC mice results from defective EDHF signaling and elevated oxidative stress, and (2) apocynin normalizes PE-induced contraction in HC mice by improving EDHF signaling.

Acetylcholine stimulated dilatation and stretch induced myogenic constriction in mesenteric artery of rats with chronic heart failure

Rats with chronic heart failure (CHF) develop increased myogenic constriction in mesenteric resistance arteries. Here we investigated increased myogenic constriction in relation to alterations in EDHF- and NO-mediated dilatation in CHF-rats. Male Spraque-Dawley rats were subjected to myocardial-infarction or sham-surgery. At 9-10 weeks after surgery, isolated mesenteric artery ring preparations were studied in a wire-myograph. Stretch-induced myogenic constriction was obtained by stepwise increase of the internal circumference diameter (0.5-1.2 L100). Cyclooxygenase- and eNOS-inhibitors were employed to study NO- and EDHF-mediated dilatation in response to acetylcholine. Rats with CHF (n=8), but not sham-rats (n=6), developed significant myogenic constriction. In addition, the contribution of endothelial dilator mediators was significantly altered in CHF-rats, with increased dependency on NO and decreased EDHF-mediated dilatation. Moreover, EDHF-mediated dilatation was inversely correlated with myogenic constriction in individual CHF-rats (r=-0.74, p=0.04). These data demonstrate increased myogenic constriction in mesenteric arteries of rats with CHF post-MI to be correlated to decreased EDHF-mediated dilatation. These findings extend the previous observation that myogenic constriction antagonizes EDHF-mediated dilatation in rat coronary artery under normal conditions, and suggests this relationship also to become functional in mesenteric arteries under pathophysiological conditions of CHF.

Specific impairment of endothelium-derived hyperpolarizing factor-type relaxation in mesenteric arteries from streptozotocin-induced diabetic mice

We hypothesized that the contribution made by endothelium-derived hyperpolarizing factor (EDHF) to acetylcholine (ACh)-induced endothelium-dependent relaxation (EDR) might be altered in mesenteric arteries from streptozotocin (STZ)-induced diabetic mice. In endothelium-intact preparations, the ACh-induced EDR (but not the sodium nitroprusside-induced relaxation) was weaker in the STZ group than in age-matched controls. Indomethacin (10 muM) had no significant effect on EDR in either group, indicating that cyclooxygenase products, including prostacyclin, are not involved. This indomethacin-resistant EDR was weaker in the STZ group than in the controls. To isolate the EDHF-resistant component of EDR, charybdotoxin (100 nM) and apamin (100 nM) were present in the bath solution throughout the next experiment. This EDHF-resistant relaxation did not differ significantly between the two groups. On the other hand, the EDHF-mediated relaxation was significantly weaker in the STZ group than in the controls, and it was completely blocked by lysophosphatidylcholine (LPC, 10 microM) in each group. The eNOS protein expression was similar between the two groups. These results suggest that (a) the endothelial dysfunction present in mesenteric arteries from type 1 diabetic mice is largely attributable to reduced EDHF signaling, and (b) LPC may be involved in this attenuation of EDHF-mediated relaxation.

Mechanisms underlying the impaired EDHF-type relaxation response in mesenteric arteries from Otsuka Long-Evans Tokushima Fatty (OLETF) rats

We previously reported that in mesenteric arteries from streptozotocin-induced diabetic rats, the endothelium-derived hyperpolarizing factor (EDHF)-type relaxation is impaired, possibly due to a reduced action of cAMP. Here, we observed an impairment of acetylcholine-induced EDHF-type relaxation in mesenteric arteries from a type 2 diabetic model, Otsuka Long-Evans Tokushima Fatty (OLETF) rats [vs. age-matched control Long-Evans Tokushima Otsuka (LETO) rats], and we investigated the mechanism underlying this impairment. In the LETO group, this EDHF-type relaxation was attenuated by 18alpha-glycyrrhetinic acid (a gap-junction inhibitor) and by a protein kinase A (PKA) inhibitor. In both groups (OLETF and LETO), it was enhanced by 3-isobutyl-1-methylxanthine, a cAMP-phosphodiesterase (PDE) inhibitor, but following these enhancements it was still weaker in OLETF rats than in LETO rats. The relaxations induced by cilostamide (a selective PDE3 inhibitor) and 8-bromo-cAMP (a cell-permeant cAMP analog) were reduced in OLETF rats, as was PKA activity. The relaxations induced by two activators of Ca(2+)-activated K(+) channels (K(Ca)) [1-ethyl-2-benzimidazolinone (1-EBIO), intermediate-conductance K(Ca) channel (IK(Ca)) activator, and riluzole, small-conductance K(Ca) channel (SK(Ca)) activator] were also impaired in OLETF rats. We conclude that the impairment of EDHF-type relaxation seen in OLETF rats may be attributable not only to a reduction in cAMP/PKA signaling, but also to reduced endothelial K(Ca) channel activities.

Role of nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) in the regulation of blood pressure by leptin in lean and obese rats

We investigated the role of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in hemodynamic action of leptin. The effect of leptin (1 mg/kg i.p.) on systolic blood pressure (SBP) was examined in lean rats and in rats made obese by feeding highly palatable diet for either 1 or 3 months. Separate groups received NO synthase inhibitor, L-NAME, or EDHF inhibitors, the mixture of apamin+charybdotoxin or sulfaphenazole, before leptin administration. Leptin increased NO production, as evidenced by increase in plasma and urinary NO metabolites and cyclic GMP. This effect was impaired in both obese groups. In lean rats either leptin or EDHF inhibitors had no effect on blood pressure. L-NAME increased blood pressure in lean animals and this effect was prevented by leptin. However, when leptin was administered to animals pretreated with both L-NAME and EDHF inhibitors, blood pressure increased even more than after L-NAME alone. In the 1-month obese group leptin had no effect on SBP, however, pressor effect of leptin was observed in animals pretreated with EDHF inhibitors. In the 3-month obese group leptin alone increased SBP, and EDHF inhibitors did not augment its pressor effect. The results suggest that leptin may stimulate EDHF when NO becomes deficient, e.g. after NOS blockade or in short-term obesity. Although the effect of leptin on NO production is impaired in the 1-month obese group, BP does not increase, probably because EDHF compensates for NO deficiency. In contrast, leptin increases BP in 3-month obesity because its effect on EDHF is also attenuated.