Ginkgolide B caused the activation of the Akt/eNOS pathway through the antioxidant effect of SOD1 in the diabetic aorta.

Ginkgo biloba extract (GBE) helps lower cardiovascular disease risk. Diabetes mellitus (DM)-induced endothelial dysfunction is a critical and initiating factor in the beginning of diabetic vascular complications. It was reported that GBE causes an endothelial-dependent relaxation. This study was designed to figure out the molecular basis on which GBE protects from endothelial dysfunction in diabetes because the underlying mechanisms are unclear. Studies were performed in a normal control group and streptozotocin/nicotinamide-induced DM group. In aortas, notably diabetic aortas, GBE, and ginkgolide B (GB), a constituent of GBE, produced a dose-dependent relaxation. The relaxation by GB was abolished by prior incubation with L-NNA (an endothelial nitric oxide synthase (NOS) inhibitor), LY294002 (a phosphoinositide 3-kinase (PI3K) inhibitor), and Akt inhibitor, confirming the essential role of PI3K/Akt/eNOS signaling pathway. We also demonstrated that GB induced the phosphorylation of Akt and eNOS in aortas. The superoxide dismutase1 (SOD1) expression level decreased in DM aortas, but GB stimulation increased SOD activity and SOD1 expression in DM aortas. Our novel findings suggest that in DM aortas, endothelial-dependent relaxation induced by GB was mediated by activation of SOD1, resulting in activation of the Akt/eNOS signaling pathway.

Endothelial Dysfunction in Superior Mesenteric Arteries Isolated from Adenine-Induced Renal Failure in Model Rats.

Endothelial dysfunction-a hallmark of chronic kidney disease (CKD)-is one of the major risk factors for cardiovascular diseases (CVD). Imbalances in endothelium-derived relaxing factors (EDRFs) and contracting factors (EDCFs) specific to endothelial dysfunction in CKD are yet to be studied. Therefore, using adenine-treated rats-a CKD rat model-we investigated the responsiveness of superior mesenteric artery (SMA) endothelium to acetylcholine (ACh) stimulation under different experimental conditions. Nine-week-old male Wistar rats were treated daily with adenine (200 and 600 mg/kg body weight) by oral gavage, for 10 d; the two groups were named adenine-200 (200 mg/kg body weight) and adenine-600 (600 mg/kg body weight). The systolic blood pressure (measured 1-, 8-, and 15 d post-treatment) was significantly increased in the adenine-600 group compared with that in the control group; whereas that in the adenine-200 group showed only a slight increase. Moreover, in the adenine-600 group the serum creatinine and blood urea nitrogen (BUN) levels (measured at 18 d post-treatment) were significantly elevated when compared with those in control or adenine-200 groups. The ACh-mediated relaxation was slightly reduced in the adenine-200 group. The ACh- and sodium nitroprusside (SNP)-mediated relaxations were impaired in the adenine-600 group. Although no ACh-mediated contraction was observed in the presence of a nitric oxide (NO) synthase inhibitor, ACh-induced endothelium-derived hyperpolarizing factor-mediated relaxation was largely impaired in the adenine-600 mg/kg group. This study revealed that in the SMA of adenine-induced CKD model rats, EDCF signaling remained unaltered while the NO and EDHF signaling were impaired.

Indoxyl sulfate decreases uridine adenosine tetraphosphate-induced contraction in rat renal artery.

The protein-bound uremic toxin indoxyl sulfate has negative effects on a variety of physiological activities including vascular function. Uridine adenosine tetraphosphate (Up4A), a new dinucleotide molecule affects vascular function including induction of vasocontraction, and aberrant responsiveness to Up4A is evident in arteries from disorders such as hypertension and diabetes. The link between indoxyl sulfate and the Up4A-mediated response is, however, unknown. We used Wistar rat's renal arteries to see if indoxyl sulfate will affect Up4A-mediated vascular contraction. In renal arteries of indoxyl sulfate, the contractile response generated by Up4A was dramatically reduced compared to the non-treated control group. Indoxyl sulfate increased endothelin-1-induced contraction but had no effect on phenylephrine, thromboxane analog, or isotonic K+-induced renal arterial contractions. UTP, ATP, UDP, and ADP-produced contractions were reduced by indoxyl sulfate. CH223191, an aryl hydrocarbon receptor (AhR) antagonist, did not reverse Up4A, and UTP contraction decreases caused by indoxyl sulfate. The ectonucleotidase inhibitor ARL67156 prevents indoxyl sulfate from reducing Up4A- and UTP-mediated contractions. In conclusion, we discovered for the first time that indoxyl sulfate inhibits Up4A-mediated contraction in the renal artery, possibly through activating ectonucleotidase but not AhR. Indoxyl sulfate is thought to play a function in the pathophysiology of purinergic signaling.

Mechanisms underlying the methylglyoxal-induced enhancement of uridine diphosphate-mediated contraction in rat femoral artery.

Although femoral artery dysfunctions, including aberrant vascular reactivity to vasoactive substances, are common in many chronic disorders, such as diabetes and hypertension, their inducible and/or progressive factors remain unclear. Methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of various chronic disorders. However, its direct correlation with extracellular nucleotides including uridine 5'-diphosphate (UDP) in the femoral artery function is currently unknown. Therefore, we investigated the acute effect of MGO on UDP-induced contraction in the rat femoral artery. MGO (4.2 × 10-4 M for 1 h) enhanced the UDP-induced contraction. This enhancement was not abolished in all conditions, including nitric oxide synthase inhibition, cyclooxygenase inhibition, or endothelial denudation. In the endothelium-denuded arteries, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 (10-5 M) suppressed the UDP-induced contraction in both control and MGO-treated groups, while MGO enhanced the p38 MAPK activation regardless of the UDP presence. Moreover, in the endothelium-denuded arteries, the Syk tyrosine kinase inhibitor piceatannol (10-5 M) suppressed the UDP-induced contraction. These results suggest that MGO augments UDP-induced contraction in rat femoral arteries and that this may be partly due to the alterations in the activities of Syk tyrosine kinase and p38 MAPK in the smooth muscle.

Effect of Nonsteroidal Mineralocorticoid Receptor Blocker Esaxerenone on Vasoreactivity to an Endothelial Stimulator in Superior Mesenteric Arteries of Type 2 Diabetic Goto-Kakizaki Rat.

Endothelial dysfunction contributes to cardiometabolic disorders, including hypertension, obesity, and type 2 diabetes. Esaxerenone is a selective, nonsteroidal, high-affinity mineralocorticoid receptor blocker recently approved in Japan for the treatment of hypertension. Although imbalanced signaling between vasorelaxant and vasocontractile factors induced by endothelial stimulation is often observed in type 2 diabetic vessels, the effects of esaxerenone on endothelium-dependent responses in type 2 diabetes remain unclear. The aim of this study was to investigate the effect of esaxerenone on endothelium-dependent responses in superior mesenteric arteries isolated from type 2 diabetic Goto-Kakizaki (GK) rats. It was found that esaxerenone (3 mg/kg/d for 4 weeks, per os (p.o.)) partially ameliorated acetylcholine (ACh)-induced endothelium-derived hyperpolarizing factor (EDHF)-type relaxation and NS309, a potent activator of small- and intermediate-conductance Ca2+-activated K+ channels, -induced relaxation, and reduced ACh-induced endothelium-derived contracting factor (EDCF)-mediated contraction. These results suggest that esaxerenone ameliorates endothelial function through increased EDHF signaling and suppressed EDCF signaling.

Indoxyl sulfate enhances endothelin-1-induced contraction via impairment of NO/cGMP signaling in rat aorta.

The microbiome-derived tryptophan metabolite, indoxyl sulfate, is considered a harmful vascular toxin. Here, we examined the effects of indoxyl sulfate on endothelin-1 (ET-1)-induced contraction in rat thoracic aortas. Indoxyl sulfate (10-3 M, 60 min) increased ET-1-induced contraction but did not affect isotonic high-K+-induced contraction. The ET-1-induced contraction was enhanced by endothelial denudation in both control and indoxyl sulfate-treated groups. BQ123 (10-6 M), an ETA receptor antagonist, reduced the ET-1-induced contraction in both control and indoxyl sulfate groups. BQ788 (10-6 M), an ETB receptor antagonist, increased the contraction in the control group but had no effect on the indoxyl sulfate group. Conversely, indoxyl sulfate inhibited relaxation induced by IRL1620, an ETB receptor agonist. L-NNA, an NO synthase (NOS) inhibitor, increased the ET-1-induced contractions in both the control and indoxyl sulfate groups, whereas L-NPA (10-6 M), a specific neuronal NOS inhibitor, did not affect the ET-1-induced contraction in both groups. However, ODQ, an inhibitor of soluble guanylyl cyclase, increased the ET-1-induced contraction in both groups. Organic anion transporter (OAT) inhibitor probenecid (10-3 M) and antioxidant N-acetyl-L-cysteine (NAC; 5 × 10-3 M) inhibited the effects of indoxyl sulfate. A cell-permeant superoxide scavenger reduced the ET-1-induced contraction in the indoxyl sulfate group. The aortic activity of SOD was reduced by indoxyl sulfate. The present study revealed that indoxyl sulfate augments ET-1-induced contraction in rat aortae. This enhancement may be due to the impairment of NO/cGMP signaling and may be attributed to impairment of the antioxidant systems via cellular uptake through OATs.

Reduced Relaxant Response to Adenine in the Superior Mesenteric Artery of Spontaneously Hypertensive Rats.

We investigated the vascular response to nucleobase adenine using freshly isolated superior mesenteric arteries of spontaneously hypertensive rats (SHR) and its control, Wistar Kyoto (WKY) rats. Endothelium-dependent and endothelium-independent relaxations were assessed in isolated segments in an organ bath. The releases of the metabolites of thromboxane A2 and prostaglandin I2 were also detected. Adenine induced vasorelaxation in both the endothelium-intact and endothelium-denuded arteries in a concentration-dependent manner. In the SHR group, the adenine-induced relaxation was slightly but significantly reduced in the endothelium-intact rings when compared with that in the WKY group. However, the relaxation in the endothelium-denuded rings were similar between the two groups. The difference in the adenine-mediated relaxation in the superior mesenteric arteries between the SHR and WKY groups was eliminated by endothelial denudation and a nitric oxide (NO) synthase inhibitor. In the absence and presence of adenine, SHR tended to have higher levels of metabolites of thromboxane A2 and prostaglandin I2 compared with WKY. However, adenine did not induce the release of these substances in the arteries in both the SHR and WKY groups. These results suggest that the reduced adenine-mediated relaxation in the superior mesenteric arteries in SHR is due to a lack of contribution from the endothelium-derived NO and not from the release of prostanoids.

Extracellular Uridine Nucleotides-Induced Contractions Were Increased in Femoral Arteries of Spontaneously Hypertensive Rats.

INTRODUCTION: Femoral arterial dysfunction including abnormal vascular responsiveness to endogenous ligands was often seen in arterial hypertension. Extracellular nucleotides including uridine 5'-diphosphate (UDP) and uridine 5'-triphosphate (UTP) play important roles for homeostasis in the vascular system including controlling the vascular tone. However, responsiveness to UDP and UTP in femoral arteries under arterial hypertension remains unclear. The aim of this study was to investigate if hypertension has an effect of vasoconstrictive responsiveness to UDP and UTP in femoral arteries of spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats (WKYs) after 7 and 12 months old. METHODS: Organ baths were conducted to determine vascular reactivity in isolated femoral arterial rings. RESULTS: In femoral arteries obtained from 12-month-old rats, augmented contractile responses to UDP and UTP were seen in femoral arteries of SHR than in those of WKY under situations not only intact but also nitric oxide synthase inhibition, whereas no difference of extracellular potassium-induced vasocontraction was seen in both SHR and WKY groups. Similar contraction trends occurred in femoral arteries obtained from 7-month-old rats. Moreover, contractions induced by UDP and UTP were increased in endothelium-denuded arteries. Cyclooxygenase inhibition decreased the contractions induced by these nucleotides and abolished the differences in responses between the SHR and WKY groups. CONCLUSIONS: This study demonstrates the importance of regulation of extracellular uridine nucleotides-induced contractions in hypertension-associated peripheral arterial diseases.

Mechanisms underlying suppression of noradrenaline-induced contraction by prolonged treatment with advanced glycation end-products in organ-cultured rat carotid artery.

We investigated the direct effects of prolonged exposure to advanced glycation end-products (AGEs) on noradrenaline-induced contraction of rat carotid artery smooth muscle. Noradrenaline-induced contraction of endothelium-denuded carotid artery rings was suppressed by AGE-bovine serum albumin (AGE-BSA) pretreatment (0.01 and 0.1 mg/mL for 23 ± 1 h) compared with vehicle pretreatment (control), whereas isotonic-K+-induced contraction was not significantly altered by AGE-BSA pretreatment. This reduction in noradrenaline-induced contraction by AGE-BSA (0.1 mg/mL) was reversed by iberiotoxin, an inhibitor of large-conductance calcium-activated potassium (BKCa) channels, but not by inhibitors of other K channels [4-AP (Kv inhibitor), TRAM-34 (IKCa inhibitor), or glibenclamide (KATP inhibitor)]. Acute incubation of carotid arterial rings with H2O2 had also reduced noradrenaline-induced contraction in control arteries, but it had no effect on noradrenaline-induced contraction in AGE-BSA-pretreated arteries. Alternatively, acute incubation with the H2O2 scavenger catalase increased noradrenaline-induced contraction of AGE-BSA-pretreated arteries but had no effect on noradrenaline-induced contraction of control arteries. Noradrenaline-induced contraction in the presence of H2O2 was increased by co-treatment with iberiotoxin. The AGE-BSA-mediated suppression of noradrenaline-induced contraction was prevented by the organic cation transporter 3 (OCT3) inhibitor corticosterone, whereas the expression of OCT3 protein was similar between control and AGE-BSA-treated endothelium-denuded carotid arteries. These findings suggest that noradrenaline-induced arterial contraction is reduced by prolonged AGE-BSA exposure due to activation of BKCa channels via H2O2 generation and increased OCT3-mediated noradrenaline transport activity.

Impaired UTP-induced relaxation in the carotid arteries of spontaneously hypertensive rats.

Uridine 5'-triphosphate (UTP) has an important role as an extracellular signaling molecule that regulates inflammation, angiogenesis, and vascular tone. While chronic hypertension has been shown to promote alterations in arterial vascular tone regulation, carotid artery responses to UTP under hypertensive conditions have remained unclear. The present study investigated carotid artery responses to UTP in spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY). Accordingly, our results found that although UTP promotes concentration-dependent relaxation in isolated carotid artery segments from both SHR and WKY after pretreatment with phenylephrine, SHR exhibited significantly lower arterial relaxation responses compared with WKY. Moreover, UTP-induced relaxation was substantially reduced by endothelial denudation and by the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine in both SHR and WKY. The difference in UTP-induced relaxation between both groups was abolished by the selective P2Y2 receptor antagonist AR-C118925XX and the cyclooxygenase (COX) inhibitor indomethacin but not by the thromboxane-prostanoid receptor antagonist SQ29548. Furthermore, we detected the release of PGE2, PGF2α, and PGI2 in the carotid arteries of SHR and WKY, both at baseline and in response to UTP. UTP administration also increased TXA2 levels in WKY but not SHR. Overall, our results suggest that UTP-induced relaxation in carotid arteries is impaired in SHR perhaps due to impaired P2Y2 receptor signaling, reductions in endothelial NO, and increases in the levels of COX-derived vasoconstrictor prostanoids.

Trimethylamine-N-oxide Specifically Impairs Endothelium-Derived Hyperpolarizing Factor-Type Relaxation in Rat Femoral Artery.

Although substantial evidence suggests that an increase in the level of trimethylamine-N-oxide (TMAO) is associated with the risk of cardiovascular diseases, including atherosclerosis, chronic kidney diseases, and hypertension, the direct effect of TMAO on vascular endothelial function remains unclear. Therefore, we investigated the acute effects of TMAO on endothelium-dependent relaxation induced by acetylcholine (ACh) in the superior mesenteric arteries and femoral arteries of rat. In endothelium-intact preparations, it was observed that TMAO (300 µmol/L for 60 min) did not affect ACh-induced relaxation in either of the two arteries. In endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation under nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitions by Nω-nitro-L-arginine (L-NNA) and indomethacin, respectively, TMAO specifically impairs the relaxation in femoral arteries but not in the superior mesenteric arteries. Under the inhibitory actions of NOS and as well as blockade of intermediate-conductance calcium-activated potassium channel (IKCa) (by TRAM-34) and small-conductance calcium-activated potassium channel (SKCa) (by apamin), which are putative sources of EDHF, ACh-induced relaxation was low, and there were no differences between the control and TMAO-treated groups with respect to both arteries. In femoral arteries, TMAO slightly reduces ACh-induced relaxation in the presence of indomethacin (preserved NO and EDHF signals) but does not affect ACh-induced NO-mediated relaxation under the combined presence of indomethacin, TRAM-34, and apamin. These results suggest that acute treatment with TMAO specifically impairs EDHF-mediated relaxation in the femoral arteries but not in the superior mesenteric arteries. These novel observations show that TMAO is a causative factor in the development of peripheral arterial disease.

Toll-Like Receptor 4 Inhibitor TAK-242 Augments Acetylcholine-Induced Relaxation in Superior Mesenteric Arteries of the Streptozotocin-Induced Diabetic Rat.

Although vascular dysfunction is a key event in the development of diabetic complications, and abnormal toll-like receptor 4 (TLR4) may contribute to the pathophysiology of vascular diseases, the direct relationships between TLR4 and vascular function in diabetic arteries are still poorly understood. Thus, to investigate whether pharmacological blockade of TLR4 affects vascular function in the superior mesenteric artery (SMA) of streptozotocin (STZ)-induced diabetic rats, the SMA was isolated from male Wistar rat injected once with STZ (65 mg/kg, 27-34 weeks) which was treated with TAK-242 (10-6 M), a TLR4 inhibitor, for approximately 1 d using organ culture techniques. After incubation, functional and biochemical studies were performed. In the functional study, treatment with TAK-242 increased acetylcholine (ACh)-induced relaxation of the diabetic SMA in the intact condition. Sodium nitroprusside (SNP)-induced relaxation was also increased in the TAK-242-treated group compared with the vehicle-treated group. Under cyclooxygenase (COX) blockade by indomethacin (10-5 M), ACh-induced relaxation was similar in the vehicle- and TAK-242-treated groups. In addition, ACh-induced relaxation in the combined presence of the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine (L-NNA) (10-4 M), and indomethacin (10-5 M) was similar in the vehicle- and TAK-242-treated groups. The productions of thromboxane (TX) B2 in cultured medium in the presence of ACh (10-5 M) were lower in the TAK-242-treated group than in the vehicle-treated group. These data suggested that TAK-242 could augment endothelium-dependent relaxation by partly suppressing vasoconstrictor TXA2 or increasing NO signaling. TLR4 inhibition may be a novel therapeutic strategy to assist in the management of diabetes-associated vascular complications.

Differential Contractile Reactivity to Nucleotides in Femoral Arteries of OLETF and LETO Rats.

Extracellular nucleotides play an important role in the regulation of vascular function, and an abnormal vascular function is an important participant in the development and progression of diabetic vascular complications. The purpose of this study was to determine whether contractile responses induced by extracellular nucleotides and a dinucleotide, uridine adenosine tetraphosphate (Up4A), in femoral arteries would be altered at the chronic stage of type 2 diabetes. We determined the changes in contractile reactivity induced by ATP, uridine triphosphate (UTP), uridine diphosphate (UDP), and Up4A in the femoral arteries of Otsuka Long-Evans Tokushima Fatty (OLETF) rats (aged male type 2 diabetic rats) and, Long-Evans Tokushima Otsuka (LETO) rats (controls for OLETF rats). ATP-induced contractions were greater in OLETF rats than in LETO rats. UTP-induced contractions were lower in OLETF rats than in LETO rats. UDP- and Up4A-induced contractions were similar between OLETF and LETO rats. The femoral artery contractile changes induced by the extracellular nucleotides and dinucleotide were similar when nitric oxide synthase was inhibited. These results suggest that the extent of femoral artery contractile reactivity to nucleotides/dinucleotides differs during long-term duration of type 2 diabetes.

Amplification of the COX/TXS/TP receptor pathway enhances uridine diphosphate-induced contraction by advanced glycation end products in rat carotid arteries.

Advanced glycation end products (AGEs) play a pivotal role in vascular functions under various pathophysiological conditions. Although uridine diphosphate (UDP) is an important extracellular nucleotide, the relationship between AGEs and UDP regarding their effect on vascular functions remains unclear. Therefore, we investigated the effects of AGE-bovine serum albumin (AGE-BSA) on UDP-mediated responses in rat thoracic aorta and carotid arteries. In rat thoracic aorta, UDP-induced relaxation was observed and this relaxation was similar between control (1.0 v/v% PBS) and AGE-BSA-treated (0.1 mg/mL for 60 min) groups. In contrast, contraction but not relaxation was obtained following UDP application to carotid arteries with and without endothelia; contraction was greater in the AGE-BSA-treated group than in the control group. The difference in UDP-induced contraction between the two groups was not abolished by the use of a nitric oxide synthase (NOS) inhibitor, whereas it was abolished by the use of cyclooxygenase (COX), thromboxane synthase (TXS), and thromboxane-prostanoid (TP) receptor antagonist. Further, the difference in UDP-induced contraction was not abolished by the use of a cPLA2 inhibitor, whereas it was abolished by the use of an iPLA2 inhibitor. UDP increased TXA2 release in both groups, and its level was similar in both groups. Moreover, the release of PGE2, PGF2α, and PGI2 was similar among the groups. Under NOS inhibition, TP receptor agonist-induced contraction increased in the AGE-BSA-treated group (vs. control group). In conclusion, the increase in UDP-induced carotid arterial contraction by AGE-BSA can be attributed to an increase in the COX/TXS/TP receptor pathway, particularly, TP receptor signaling.

Effect of Equol on Vasocontractions in Rat Carotid Arteries Treated with High Insulin.

Previous research has indicated that high insulin affects vascular function. Equol is an active metabolite of daidzein, an isoflavone produced from soy by intestinal microbial flora, with beneficial effects on the vascular system. This study investigated whether equol was beneficial for vascular function under high insulin conditions. Using organ culture techniques, rat carotid arteries were treated for 23 ± 1 h with a vehicle, high insulin (100 nM), or equol (100 µM) plus high insulin (100 nM). Vascular isometric forces were measured by the organ bath technique. In each endothelium-intact ring, the contractions induced by high-K+, noradrenaline, or by serotonin (5-HT) were similar for the vehicle, insulin, and equol + insulin treatments. Contractions induced by a selective 5-HT2A receptor agonist (TCB2) increased with insulin treatment (vs. vehicle), but less so with equol + insulin. Under basal conditions, a selective 5-HT2B receptor agonist (BW723C86) did not induce contraction; following precontraction by a thromboxane analog, it induced contraction but not relaxation. These responses were similar across the three treatments. Acetylcholine-induced relaxations were also similar for the three treatments. In the endothelium-denuded preparations, 5-HT-induced contraction was augmented with insulin treatment (vs. vehicle) but less so by equol + insulin treatment. These differences in 5-HT-induced contractions were eliminated by iberiotoxin, a large-conductance calcium-activated K+ channel (BKCa) inhibitor. These results suggest that equol exerts a preventive effect on the enhancement of 5-HT-induced contraction by high insulin (possibly mediated by the 5-HT2A receptor), and that these effects may be attributed to the activation of BKCa channels in vascular smooth muscle.

Direct Impairment of the Endothelial Function by Acute Indoxyl Sulfate through Declined Nitric Oxide and Not Endothelium-Derived Hyperpolarizing Factor or Vasodilator Prostaglandins in the Rat Superior Mesenteric Artery.

Upon stimulation, endothelial cells release various factors to regulate the vascular tone. In particular, vasorelaxing factors, called endothelium-derived relaxing factors (EDRFs), are altered in the production and/or release, as well as their signaling every vessel and under pathophysiological states, including cardiovascular, kidney, and metabolic diseases. Although indoxyl sulfate is known as a protein-bound uremic toxin and circulating levels are elevated in the impaired kidney functions, direct impact on the vascular function, especially EDRF's signaling, remains unclear. In this study, we hypothesize that acute exposure to indoxyl sulfate could alter vascular relaxation in the rat superior mesenteric artery. Accordingly, we measured acetylcholine (ACh)-induced endothelium-dependent relaxation in the absence and presence of several inhibitors to divide into each EDRF, including nitric oxide (NO), vasodilator prostaglandins (PGs), and endothelium-derived hyperpolarizing factor (EDHF). Indoxyl sulfate reduced the sensitivity to ACh but not sodium nitroprusside. Under cyclooxygenase (COX) inhibition or inhibitions of COX plus source of EDHF, such as small (SKCa)- and intermediate (IKCa)-conductance calcium-activated K+ channels, the decreased sensitivity to ACh in indoxyl sulfate exposed vessel was still preserved. However, under inhibition of NO synthase (NOS) or inhibitions of NOS and COX, the difference of sensitivity to ACh between vehicle and indoxyl sulfate was eliminated. These findings indicated that acute exposure of indoxyl sulfate in the rat superior mesenteric artery specifically explicitly impaired NO signaling but not EDHF or vasodilator PGs.

Acute Exposure to Indoxyl Sulfate Impairs Endothelium-Dependent Vasorelaxation in Rat Aorta.

Gut microbiota are emerging as potential contributors to the regulation of host homeostasis. Dysbiosis of the gut microbiota associated with increased intestinal permeability facilitates the passage of endotoxins and other microbial products, including indoxyl sulfate in the circulation. Although an emerging body of evidence has suggested that indoxyl sulfate is a key substance for the development of chronic kidney disease, few studies have investigated the direct association of indoxyl sulfate with vascular function. We hypothesized that indoxyl sulfate adversely affects vascular function. Aortas isolated from male Wistar rat were examined in the presence or absence of indoxyl sulfate to assess the vascular function, including vasorelaxation and vasocontraction. Indoxyl sulfate (vs. vehicle) (1) decreased vasorelaxation induced by acetylcholine (ACh) but not by sodium nitroprusside; (2) had no significant alterations of noradrenaline-induced vasocontraction in the absence and presence of endothelium; (3) decreased adenylyl cyclase activator (forskolin)-induced vasorelaxation, while such a difference was eliminated by endothelial denudation; and (4) decreased vasorelaxations induced by calcium ionophore (A23187) and transient receptor potential vanilloid 4 agonist (GSK1016790A). The indoxyl sulfate-induced decrease in the vasorelaxations induced by ACh and A23187 increased by cell-permeant superoxide dismutase or by organic anion transporter inhibitor. However, apocynin, an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, had no effects on vasorelaxations induced by ACh, A23187, forskolin, and GSK1016790A in the presence of indoxyl sulfate. These results suggest that indoxyl sulfate directly affects the vascular function, particularly, endothelium-dependent vasorelaxation, and this effect may be attributable to increased oxidative stress after cell transportion via organic anion transporter, and such increased oxidative stress may not be attributable to activation of NADPH oxidase activation.

UDP-induced relaxation is enhanced in aorta from female obese Otsuka Long-Evans Tokushima Fatty rats.

Uridine 5'-diphosphate (UDP) plays an important role in controlling vascular tone; however, UDP-mediated response in metabolic syndromes, including obesity and type 2 diabetes in females, remains unclear. In this study, we investigated UDP-mediated response in the aorta of female obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats and control Long-Evans Tokushima Otsuka (LETO) rats. In OLETF rat aortas precontracted by phenylephrine (PE) (vs. LETO), (1) UDP-induced relaxation was increased, whereas acetylcholine (ACh)-induced relaxation was decreased; (2) no UDP- or ACh-induced relaxations were observed in endothelial denudation, whereas UDP-induced small contraction was observed; and (3) NG-nitro-L-arginine [L-NNA, a nitric oxide (NO) synthase inhibitor] eliminated UDP-induced relaxation and small contraction, whereas caused contrasting responses by ACh, including slight relaxations (LETO) and contractions (OLETF). Indomethacin, a cyclooxygenase inhibitor, eliminated the difference in UDP- and ACh-induced relaxations between the groups by increased UDP-induced relaxation in the LETO group and increased ACh-induced relaxation in the OLETF group. MRS2578, a P2Y6 receptor antagonist, eliminated the difference in UDP-induced relaxations between the groups by decreasing UDP-induced relaxation in the OLETF group. MRS2578 had no effect on UDP-induced contraction in endothelium-denuded aortas. Therefore, these findings demonstrate opposite trends of relaxations by UDP and ACh in OLETF and LETO rat aortas. These differences may be attributed to the imbalance between NO and vasoconstrictor prostanoids upon stimulations. Increased UDP-induced relaxation in OLETF rat aorta may be caused by the activation of endothelial MRS2578-sensitive P2Y6 receptor.

Impairment of Protease-Activated Receptor 2-Induced Relaxation of Aortas of Aged Spontaneously Hypertensive Rat.

Hypertension is one of the most prevalent diseases worldwide and can cause harmful complications within the vascular system. Further research on vascular responsiveness to different ligands and diverse receptors in various arteries is required to understand the mechanisms underlying the development of these vascular complications. Here, we investigated the vasorelaxant effect of the protease-activated receptor 2 (PAR2) agonist 2-furoyl-LIGRLO-amide (2-Fly) and two commonest agents, namely endothelium-dependent dilator acetylcholine (ACh) and endothelium-independent dilator sodium nitroprusside (SNP), on the thoracic aorta isolated from aged spontaneously hypertensive rats (SHR) (age, 52±1 weeks). The effects of these agents were compared between aortas isolated from SHR and age-matched normotensive Wistar Kyoto (WKY) rats. Compared with the WKY group, in the SHR group, 2-Fly-induced relaxation was impaired, ACh-induced relaxation was slightly decreased at low concentrations, and SNP-induced relaxation was similar. In addition, 2-Fly-induced aortic relaxation was largely decreased by a PAR2 antagonist (FSLLRY), endothelial denudation, and a nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) but not by an Akt inhibitor. These results suggested that PAR2-induced relaxations of aortas of aged SHR was impaired, and this impaired aortic relaxation may be attributed to decreased NO bioavailability rather than altered NO sensitivity unrelated to the Akt activity.

Differential participation of calcium-activated potassium channel in endothelium-dependent hyperpolarization-type relaxation in superior mesenteric arteries of spontaneously hypertensive rats.

The purpose of this study was to determine the relationship of KCa channels to endothelium-dependent hyperpolarizing factor (EDHF)-mediated relaxation induced by acetylcholine (ACh) in the superior mesenteric arteries of 7-month-old spontaneously hypertensive rats (SHR). Upon inhibition of nitric oxide synthase and cyclooxygenase, ACh-induced EDHF-mediated relaxation was found to be weaker in SHR than in age-matched Wistar Kyoto rats (WKY). These relaxations in both group were attenuated by combined treatment with small-conductance and intermediate-conductance Ca2+-activated K+ channels (SKCa and IKCa) inhibitors, with the exception of relaxation resistant to inhibition of these channels in SHR (vs. WKY). Treatment with large-conductance Ca2+-activated K+ channels (BKCa) inhibitor specifically attenuated relaxation in SHR, but not in WKY. Protein expression of IKCa and SKCa in the arteries did not differ between the 2 groups, whereas ratio of sloß1 subunit to α subunit of BKCa was increased in SHR (vs. WKY). These results suggest that EDHF-mediated relaxations in superior mesenteric arteries are impaired in SHR, and utilize components of BKCa in addition to SKCa/IKCa channel activities, that the increased participation of BKCa may be attributable to alterations in α and sloß1 subunit ratio, and that components unrelated to KCa activity may also contribute to the difference between SHR and WKY arteries.