Soluble Guanylate Cyclase-Mediated Relaxation in Aortas from Rats with Renovascular Hypertension.

Soluble guanylate cyclase (sGC) plays an important role in nitric oxide (NO)-mediated regulation of vascular tone; however, NO bioavailability is often reduced in diseased blood vessels. Accumulating evidence suggests that a shift of sGC from the NO-sensitive form to the NO-insensitive form could be an underlying cause contributing to this reduction. Herein, we investigated the impact of renovascular hypertension on NO-sensitive and NO-insensitive sGC-mediated relaxation in rat aortas. Renovascular hypertension was induced by partially clipping the left renal artery (2-kidneys, 1-clip; 2K1C) for 10 weeks. Systolic, diastolic, and mean arterial pressures were significantly increased in the 2K1C group when compared with the sham group. In addition, plasma thiobarbituric acid reactive substances and aortic superoxide generation were significantly enhanced in the 2K1C group when compared with those in the sham group. The vasorelaxant response of isolated aortas to the sGC stimulator BAY 41-2272 (NO-sensitive sGC agonist) was comparable between the sham and 2K1C groups. Likewise, the sGC activator BAY 60-2770 (NO-insensitive sGC agonist)-induced relaxation did not differ between the sham and 2K1C groups. In addition, the cGMP mimetic 8-Br-cGMP (protein kinase G agonist) induced similar relaxation in both groups. Furthermore, there were no differences in BAY 41-2272-stimulated and BAY 60-2770-stimulated cGMP generation between the groups. These findings suggest that the balance between NO-sensitive and NO-insensitive forms of sGC is maintained during renovascular hypertension. Therefore, sGC might not be responsible for the reduced NO bioavailability observed during renovascular hypertension.

Chronological Change of Vascular Reactivity to cGMP Generators in the Balloon-Injured Rat Carotid Artery.

BACKGROUND/AIMS: Soluble guanylate cyclase (sGC) exists as reduced, oxidized, and heme-free forms. Currently, it is unclear whether endovascular mechanical stenosis has an impact on vascular tone control by drugs targeting sGC, namely cGMP generators. METHODS: Pharmacological responses to acidified sodium nitrite (reduced sGC stimulant) and BAY 60-2770 (oxidized/heme-free sGC stimulant) were studied in balloon-injured rat carotid arteries at several time points. In addition, sGC expression was detected by immunohistochemistry. RESULTS: At 1 day after injury, acidified sodium nitrite-induced relaxation was attenuated in the injured artery, whereas BAY 60-2770-induced relaxation was augmented. Similar attenuation of response to acidified sodium nitrite was seen at 7 and 14 days after injury. On the other hand, the augmentation of response to BAY 60-2770 disappeared at 7 and 14 days after injury. At 1 day after injury, the immunohistochemical expression pattern of sGC in the smooth muscle layer of the injured artery was not different from that of the uninjured artery. However, in the injured artery, the intensity of sGC staining was weak at 7 and 14 days after injury. CONCLUSION: Balloon injury alters vascular responsiveness to cGMP generators, which seems to be associated with the form and/or expression of sGC.

Effects of Low-Dose Sacubitril/Valsartan on Different Stages of Cardiac Hypertrophy in Salt-Loaded Hypertensive Rats.

BACKGROUND: Sacubitril/valsartan was shown to attenuate the development of cardiac hypertrophy with enhanced blood pressure reduction compared with valsartan alone in animal models. We investigated whether a low-dose sacubitril/valsartan has blood pressure-independent effects on cardiac hypertrophy and pulmonary edema using a rat model of hypertension and obesity. METHODS AND RESULTS: In plan 1, male SHR/NDmcr-cp rats fed normal or phase-increased high salt were treated with vehicle, 6-mg/kg sacubitril/valsartan or 3-mg/kg valsartan, for 6 months. In plan 2, after high-salt loading for 6 months, drugs were administered for 4 months. Antihypertensive effects of the 2 drugs were similar during all study periods. In plan 1 with normal salt, there were no differences between treatments in the left ventricle weight/body weight (BW), or lung weight/BW as an index of cardiac hypertrophy or pulmonary edema, respectively. These indexes were smaller in high-salt-fed rats with sacubitril/valsartan than vehicle. In plan 2, both indexes did not differ between vehicle and sacubitril/valsartan. Ventricle weight/BW was lower in valsartan than sacubitril/valsartan. In plan 2, gene markers of cardiac dysfunction were upregulated by sacubitril/valsartan compared with the other groups. CONCLUSIONS: Low-dose sacubitril/valsartan may have different effects depending on the stage of cardiac hypertrophy in rats.

Responsiveness of Coronary Arteries to Nitroglycerin under Hypoxia: The Importance of the Endothelium.

BACKGROUND/AIMS: Nitroglycerin is widely used as a coronary vasodilator in the treatment of ischemic heart diseases. This study investigated the influence of hypoxia on nitroglycerin-induced relaxation in endothelium-intact and -denuded rabbit, monkey, and porcine coronary arteries. METHODS: Helically cut strips of coronary arteries were suspended in organ chambers, and isometric tension was recorded. RESULTS: Nitroglycerin concentration dependently relaxed endothelium-intact rabbit coronary arteries, which were not different under normoxic and hypoxic conditions. On the other hand, nitroglycerin-induced relaxation of endothelium-denuded arteries was significantly attenuated by hypoxia. Similarly, the relaxant response of endothelium-intact monkey coronary arteries to nitroglycerin was not affected by hypoxia, whereas that of endothelium-denuded arteries was impaired. As is the case with rabbit and monkey coronary arteries, exposure to hypoxia resulted in impaired relaxation by nitroglycerin in endothelium-denuded but not endothelium-intact porcine coronary arteries. CONCLUSION: These findings suggest that coronary endothelium plays a pivotal role in preventing the hypoxia-induced impairment of nitroglycerin responsiveness, regardless of the animal species.

Aging does not affect soluble guanylate cyclase redox state in mouse aortas.

Aging is associated with endothelial dysfunction, defined as a reduction in nitric oxide (NO) bioavailability. Although the redox state of the NO acceptor soluble guanylate cyclase (sGC) is another determinant factor for its bioavailability and is disturbed by reactive oxygen species (ROS) known to be increased with age, it is unclear whether aging actually has an impact on vascular sGC redox equilibrium. Therefore, this study investigated this issue using two different types of compounds, the sGC stimulator BAY 41-2272 and the sGC activator BAY 60-2770. Plasma thiobarbituric acid-reactive substances (TBARS) levels were markedly higher in aged (19-20 months old) mice than in young (2-3 months old) mice, whereas superoxide levels in endothelium-denuded aortas were not different between the groups. The relaxant response of endothelium-denuded aortas to either BAY 41-2272 or BAY 60-2770 was identical in aged and young mice. In addition, the vascular cGMP production stimulated with BAY 41-2272 or BAY 60-2770 in aged mice was the same level as that in young mice. These findings suggest that aging accompanied by an increase in systemic oxidative stress does not affect vascular smooth muscle ROS generation and sGC redox equilibrium. Unless ROS are increased in vascular smooth muscle, the sGC redox equilibrium might remain unchanged.

MicroRNA-494 plays a role in fiber type-specific skeletal myogenesis in human induced pluripotent stem cells.

Mitochondrial oxidative capacity in skeletal muscle is known to decrease in diabetic patients, and sarcopenia is a risk factor for diabetes, particularly in elderly people. We previously revealed that microRNA (miR)-494 inhibits mitochondrial biogenesis during myogenic differentiation in murine C2C12 cells and others reported that exercise regulates miR-494 levels in obese sedentary individuals with increased risk of type 2 diabetes. In this study, to investigate the therapeutic potential of miR-494, we first investigated the role of miR-494 during human skeletal myogenesis. Using human induced pluripotent stem (hiPS) cells stably transfected with the Tet/ON-myogenic differentiation 1(MYOD1) gene (MyoD-hiPS cells), we found that miR-494 expression transiently increased and was downregulated after myogenic induction. In miR-494 transfected MyoD-hiPS cells, the level of high oxidative fiber (type IIa) marker proteins specifically decreased, while no change in the total number of cells was observed. In contrast, the expression of both type I and type IIx markers was unaffected by miR-494 overexpression. Furthermore, miR-494 overexpression suppressed basal oxygen consumption rate concomitant with the inhibition of myotube formation and without significant effects on the mitochondrial content. These results suggest that miR-494 plays a novel role in the fiber type-specific skeletal myogenesis in MyoD-hiPS cells, distinct from murine C2C12 myogenesis.

Effects of hydrogen peroxide on relaxation through the NO/sGC/cGMP pathway in isolated rat iliac arteries.

The production of reactive oxygen species, including hydrogen peroxide (H(2)O(2)), is increased in diseased blood vessels. Although H(2)O(2) leads to impairment of the nitric oxide (NO)/soluble guanylate cyclase (sGC)/cGMP signaling pathway, it is not clear whether this reactive molecule affects the redox state of sGC, a key determinant of NO bioavailability. To clarify this issue, mechanical responses of endothelium-denuded rat external iliac arteries to BAY 41-2272 (sGC stimulator), BAY 60-2770 (sGC activator), nitroglycerin (NO donor), acidified NaNO(2) (exogenous NO) and 8-Br-cGMP (cGMP analog) were studied under exposure to H(2)O(2). The relaxant response to BAY 41-2272 (pD2: 6.79 ± 0.10 and 6.62 ± 0.17), BAY 60-2770 (pD2: 9.57 ± 0.06 and 9.34 ± 0.15) or 8-Br-cGMP (pD2: 5.19 ± 0.06 and 5.24 ± 0.08) was not apparently affected by exposure to H(2)O(2). In addition, vascular cGMP production stimulated with BAY 41-2272 or BAY 60-2770 in the presence of H(2)O(2) was identical to that in its absence. On the other hand, nitroglycerin-induced relaxation was markedly attenuated by exposing the arteries to H(2)O(2) (pD2: 8.73 ± 0.05 and 8.30 ± 0.05), which was normalized in the presence of catalase (pD2: 8.59 ± 0.05). Likewise, H(2)O(2) exposure impaired the relaxant response to acidified NaNO(2) (pD2: 6.52 ± 0.17 and 6.09 ± 0.16). These findings suggest that H(2)O(2) interferes with the NO-mediated action, but the sGC redox equilibrium and the downstream target(s) of cGMP are unlikely to be affected in the vasculature.

Vasorelaxing effects of the soluble guanylyl cyclase activator BAY 60-2770 in nitrate-tolerant monkey and canine coronary arteries.

Nitrate tolerance is an important problem in the treatment of ischemic heart diseases. The present study investigated whether or not a soluble guanylyl cyclase (sGC) activator can be used as a coronary vasodilator under nitrate-tolerant conditions. Helically cut strips of endothelium-denuded monkey and canine coronary arteries were suspended in organ chambers for isometric tension recording. Nitrate tolerance was induced by a 1-h treatment with nitroglycerin (0.1 mM) followed by 1-h washout of the agent. Control strips were not exposed previously to nitroglycerin, but otherwise were treated identically. The relaxant response to nitroglycerin was dramatically impaired by previous exposure to the drug for 1 h in either monkey or canine coronary arteries, indicating the development of nitrate tolerance. In contrast, development of nitrate tolerance did not affect the relaxant potency and efficacy of the sGC activator BAY 60-2770 in either the monkey or canine coronary arteries. These findings suggest that it may be possible to use sGC activators as substitute drugs for nitroglycerin if tolerance is developed during the treatment of ischemic heart diseases.

Different influences of extracellular and intracellular superoxide on relaxation through the NO/sGC/cGMP pathway in isolated rat iliac arteries.

Superoxide production is increased in diseased blood vessels, which is considered to lead to impairment of the nitric oxide (NO)/soluble guanylate cyclase (sGC)/cGMP pathway. To investigate the respective influence of extracellular and intracellular superoxide on vascular function through the NO/sGC/cGMP pathway, mechanical responses of rat external iliac arteries without endothelium were studied under exposure to a superoxide-generating agent, pyrogallol, or menadione. Exposure to pyrogallol impaired the relaxation induced by acidified NaNO2 (exogenous NO) but not that by nitroglycerin (organic nitrate), BAY 41-2272 (sGC stimulator), BAY 60-2770 (sGC activator), or 8-Br-cGMP (cGMP analog). Superoxide dismutase (SOD) and tempol restored the impaired relaxation by acidified NaNO2. Superoxide production in the bathing solution, but not in artery segments, was significantly increased by exposure to pyrogallol, which was abolished in the presence of SOD or tempol. However, exposure to menadione impaired the relaxant response to acidified NaNO2, nitroglycerin, or BAY 41-2272, whereas it augmented that to BAY 60-2770. Also, this exposure had no effect on the 8-Br-cGMP-induced vasorelxation. Superoxide production in artery segments was dramatically enhanced by exposure to menadione, whereas that in the bathing solution was not affected. This increase in vascular superoxide production was normalized by tempol but not by SOD. These findings suggest that extracellular superoxide reacts with NO only outside the cell, whereas intracellular superoxide not only scavenges NO inside the cell but also shifts the sGC redox equilibrium.

Soluble guanylate cyclase redox state under hypoxia or hypoxia/reoxygenation in isolated monkey coronary arteries.

Hypoxia or hypoxia/reoxygenation impairs nitric oxide (NO)-mediated relaxation through the increase in superoxide generation in monkey coronary arteries. Soluble guanylate cyclase (sGC), the target enzyme of NO, has been shown to change from the NO-sensitive reduced form to the NO-insensitive oxidized/heme-free form under substantial oxidative stress, so the present study investigated whether hypoxia or hypoxia/reoxygenation influences sGC redox equilibrium. In isolated monkey coronary arteries without endothelium, the relaxation caused by the sGC stimulator BAY 41-2272 (Emax: 93.3% ± 2.2%) was somewhat impaired under hypoxia (Emax: 86.3% ± 2.6%) or hypoxia/reoxygenation (Emax: 86.1% ± 3.2%), whereas that by the sGC activator BAY 60-2770 (Emax: 86.0% ± 3.2%) was significantly augmented under hypoxia (Emax: 94.4% ± 1.3%) or hypoxia/reoxygenation (Emax: 95.5% ± 1.1%). In addition, cGMP formation in response to BAY 41-2272 and BAY 60-2770 was inhibited and stimulated, respectively, under hypoxia or hypoxia/reoxygenation. The effects of hypoxia or hypoxia/reoxygenation on BAY 41-2272- and BAY 60-2770-induced vasorelaxation were completely canceled by the treatment with the superoxide dismutase mimetic tempol. These findings suggest that sGC redox equilibrium in the coronary artery is shifted towards the NO-insensitive form under hypoxia or hypoxia/reoxygenation and that superoxide seems to play an important role in this shift.

The dipeptidyl peptidase-4 inhibitor teneligliptin improved endothelial dysfunction and insulin resistance in the SHR/NDmcr-cp rat model of metabolic syndrome.

Diabetes mellitus, hypertension and metabolic syndrome are major risk factors for the occurrence of cardiovascular events. In this study, we used spontaneous hypertensive rat (SHR)/NDmcr-cp (cp/cp) (SHRcp) rats as a model for metabolic syndrome to examine the effects of dipeptidyl peptidase (DPP)-4 inhibition on hypertension, glucose metabolism and endothelial dysfunction. First, we confirmed that SHRcp rats showed very severe obesity, hypertension and endothelial dysfunction phenotypes from 14 to 54 weeks of age. Next, we examined whether the DPP-4 inhibitor teneligliptin (10 mg kg(-1) per day per os for 12 weeks) could modify any of these phenotypes. Treatment with teneligliptin significantly improved hyperglycemia and insulin resistance, as evidenced by an oral glucose tolerance test and homeostasis model assessment for insulin resistance, respectively. Teneligliptin showed no effects on systolic blood pressure or heart rate. In regard to endothelial function, the vasodilator response to acetylcholine was significantly impaired in SHRcp rats when compared with WKY rats. Long-term treatment with teneligliptin significantly attenuated endothelial dysfunction through the upregulation of endothelium-derived nitric oxide synthase mRNA. These results demonstrate that long-term treatment with teneligliptin significantly improved endothelial dysfunction and glucose metabolism in a rat model of metabolic syndrome, suggesting that teneligliptin treatment might be beneficial for patients with hypertension and/or diabetes.

Effects of atorvastatin, amlodipine, and their combination on vascular dysfunction in insulin-resistant rats.

Deficiency of tetrahydrobiopterin (BH4) in the vascular tissue contributes to endothelial dysfunction through reduced eNOS activity and increased superoxide anion (O2(-)) generation in the insulin-resistant state. We investigated the effects of atorvastatin, a 3-hydroxyl-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitor; amlodipine, a calcium antagonist; and their combination on blood pressure, arterial relaxation and contraction, and vascular oxidative stress in aortas of high fructose-fed rats. Oral administration of atorvastatin for 8 weeks did not significantly lower blood pressure, but normalized angiotensin II-induced vasoconstriction and endothelial function in the fructose-fed rats. Atorvastatin treatment of fructose-fed rats increased vascular BH4 content, which was associated with an increase in endothelial NO synthase activity as well as a reduction in endothelial O2(-) production. On the other hand, administration of amlodipine did not affect the angiotensin II-induced vasoconstriction and endothelial function, but normalized the elevated blood pressure in the fructose-fed rats. The combined treatment did not show synergistic but additive beneficial effects. The present study suggests that combined therapy of HMG-CoA reductase inhibitors and calcium antagonists prevents functional vascular disorders in the insulin-resistant state, possibly resulting in the protection against or delay of development of hypertension, vascular dysfunction in diabetes, and thereafter atherosclerosis.

Effects of peroxynitrite on relaxation through the NO/sGC/cGMP pathway in isolated rat iliac arteries.

BACKGROUND/AIMS: The present study investigated the mechanism by which peroxynitrite impairs vascular function through the nitric oxide (NO)/soluble guanylate cyclase (sGC)/cGMP pathway. METHODS: Mechanical responses of rat external iliac arteries without endothelium were studied under exposure to peroxynitrite. cGMP concentrations were determined by enzyme immunoassay. RESULTS: Relaxation induced by BAY 41-2272 (sGC stimulator) was impaired under exposure to peroxynitrite, whereas that by BAY 60-2770 (sGC activator) was enhanced. These responses were correlated with tissue levels of cGMP. Effects of peroxynitrite on the relaxant responses to BAY compounds were also observed in the presence of superoxide dismutase (SOD) or tempol, both of which scavenge a certain kind of reactive molecules other than peroxynitrite. As is the case with the relaxant response to BAY 41-2272, acidified NaNO2- and nitroglycerin-induced relaxations were markedly attenuated by exposing the arteries to peroxynitrite, which was not abolished by preincubation with SOD or tempol. On the other hand, peroxynitrite exposure had no effect on the 8-Br-cGMP-induced vasorelxation. CONCLUSION: These findings suggest that peroxynitrite interferes with the NO/sGC/cGMP pathway by altering the redox state of sGC. It is likely that peroxynitrite can shift the sGC redox equilibrium to the NO-insensitive state in the vasculature.

Influence of hypoxia on endothelium-derived NO-mediated relaxation in rat carotid, mesenteric and iliac arteries.

Individual vascular beds exhibit differences in vascular reactivity. The present study examined the influence of hypoxia on endothelium-dependent, especially nitric oxide (NO)-mediated, relaxation in the isolated rat common carotid, superior mesenteric and external iliac arteries. Hypoxia for 1 and 3 h had no effects on the relaxations caused by acetylcholine (ACh) and sodium nitroprusside (SNP) in common carotid and external iliac arteries. In addition, NO synthase inhibitor N(G)-nitro-L-arginine (L-NA, 10 µmol/l)-resistant, endothelium-dependent relaxations by ACh were also unaffected by hypoxia in these arteries. On the other hand, ACh-induced relaxation in superior mesenteric arteries was significantly impaired by exposure to hypoxia, while this condition did not affect the relaxation induced by SNP or ACh in the presence of L-NA. This impairment was partially prevented by treatment with tempol (3 mmol/l), a superoxide scavenger. These findings demonstrate a marked heterogeneity in response to hypoxia in rat arteries. Briefly, acute hypoxia induces impairment of endothelium-derived NO-mediated relaxation through the decrease in its bioavailability in the superior mesenteric, but not in common carotid or external iliac, arteries. Furthermore, superoxide seems to be one causal factor responsible for the undesirable effect of hypoxia.

Chronic administration of nicotine-free cigarette smoke extract impaired endothelium-dependent vascular relaxation in rats via increased vascular oxidative stress.

Cigarette smoking has been implicated in the initiation and progression of cardiovascular disorders and atherosclerosis. Here, we examined the effects of nicotine-free cigarette smoke extract (CSE) on the regulation of cardiovascular function. Rats were subcutaneously administered PBS or nicotine-free CSE at 0.05 to 1.5 mL/day per rat for 4 weeks. Blood pressure, cardiac function, and vascular responsiveness were measured at 4 weeks after administration. Furthermore, acute effects of nicotine-free CSE were also studied in the aorta isolated from normal rats. Blood pressure and left ventricular systolic pressure (LVSP) were significantly increased in the nicotine-free CSE-administered rats, but heart rate, dP/dt(max), and dP/dt(min) were not affected. Endothelium-dependent relaxation by acetylcholine (ACh) in the nicotine-free CSE-treated rats was significantly attenuated compared to PBS-treated rats, but endothelium-independent relaxation by sodium nitroprusside (SNP) did not differ. Pretreatment with superoxide dismutase restored the attenuated ACh-induced relaxation. Contractions by phenylephrine, angiotensin II, and KCl did not differ between two groups. In vitro acute nicotine-free CSE treatment did not alter the response to ACh or SNP. These results suggest that chronic nicotine-free CSE administration impairs endothelial function by increased production of superoxide derived from the vascular wall components other than smooth muscles and induces slight hypertension accompanied with LVSP elevation.

Modification of a novel angiogenic peptide, AG30, for the development of novel therapeutic agents.

We previously identified a novel angiogenic peptide, AG30, with antibacterial effects that could serve as a foundation molecule for the design of wound-healing drugs. Toward clinical application, in this study we have developed a modified version of the AG30 peptide characterized by improved antibacterial and angiogenic action, thus establishing a lead compound for a feasibility study. Because AG30 has an α-helix structure with a number of hydrophobic and cationic amino acids, we designed a modified AG30 peptide by replacing several of the amino acids. The replacement of cationic amino acids (yielding a new molecule, AG30/5C), but not hydrophobic amino acids, increased both the angiogenic and the antimicrobial properties of the peptide. AG30/5C was also effective against methicillin-resistant Staphylococcus aureus (MRSA) and antibiotic-resistant Pseudomonas aeruginosa. In a diabetic mouse wound-healing model, the topical application of AG30/5C accelerated wound healing with increased angiogenesis and attenuated MRSA infection. To facilitate the eventual clinical investigation/application of these compounds, we developed a large-scale procedure for the synthesis of AG30/5C that employed the conventional solution method and met Good Manufacturing Practice guidelines. In the evaluation of stability of this peptide in saline solution, RP-HPLC analysis revealed that AG30/5C was fairly stable under 5°C for 12 months. Therefore, we propose the use of AG30/5C as a wound-healing drug with antibacterial and angiogenic actions.

Nifedipine prevents hepatic fibrosis in a non-alcoholic steatohepatitis model induced by an L-methionine-and choline-deficient diet.

Recent reports have shown that nifedipine, a calcium channel blocker, increases peroxisome proliferator-activated receptor-γ (PPARγ) activity. Since PPARγ agonists, such as pioglitazone and rosiglitazone, are effective in reducing non-alcoholic steatohepatitis (NASH) and cirrhosis in animal models, we examined the protective effects of nifedipine, as compared with bezafibrate, a PPARα agonist, in a NASH model induced by an L-methionine- and choline-deficient (MCD) diet. An MCD diet for 20 weeks changed the color of the rat liver to yellow with an irregular surface, whereas the color of the liver in both the bezafibrate and nifedipine treatment groups was markedly changed to yellow-brown with a smooth surface. Furthermore, nifedipine, as well as bezafibrate, significantly prevented liver fibrosis induced by an MCD diet, as assessed by Masson's trichrome staining, accompanied by a significant decrease in serum AST. Overall, nifedipine treatment resulted in an improvement in NASH, similar to bezafibrate, in a rat model. In hypertensive patients with metabolic syndrome, nifedipine may provide additional benefits, beyond its blood pressure-lowering effects, to prevent NASH and fatty liver disease.

Impairment by hypoxia or hypoxia/reoxygenation of nitric oxide-mediated relaxation in isolated monkey coronary artery: the role of intracellular superoxide.

To investigate the effect of hypoxia or hypoxia/reoxygenation on vascular smooth muscle function, mechanical response of monkey coronary artery without endothelium was studied under normoxia, hypoxia, and hypoxia/reoxygenation. Hypoxia or hypoxia/reoxygenation impaired the relaxation by nitroglycerin or isosorbide dinitrate but not that by 8-bromoguanosine-3',5'-cyclic monophosphate or isoproterenol. Tempol restored the impaired relaxation by nitroglycerin or isosorbide dinitrate, but superoxide dismutase had no effect. Apocynin, an NADPH oxidase inhibitor, improved the nitroglycerin-induced relaxation under hypoxia, but not under reoxygenation. Under combined treatment of apocynin with oxypurinol (xanthine oxidase inhibitor), rotenone (mitochondria electron transport inhibitor), or both, hypoxic impairment of vasorelaxation was restored more effectively. Similarly, impairment of the nitroglycerin-induced vasorelaxation under hypoxia/reoxygenation was restored by combined treatment with three inhibitors, apocynin, oxypurinol, and rotenone. Increase in superoxide production under hypoxia tended to be inhibited by apocynin and that under hypoxia/reoxygenation was abolished by combined treatment with three inhibitors. These findings suggest that increased intracellular superoxide production under hypoxia or hypoxia/reoxygenation attenuates vasodilation mediated with a nitric oxide/soluble guanylyl cyclase, but not adenylyl cyclase, signaling pathway. The main source of superoxide production under hypoxia seems to be different from that under reoxygenation: superoxide is produced by NADPH oxidase during hypoxia, whereas it is produced by xanthine oxidase, mitochondria, or both during reoxygenation.[Supplementary Figure: available only at http://dx.doi.org/10.1254/jphs.11031FP].

Candesartan and amlodipine combination therapy provides powerful vascular protection in stroke-prone spontaneously hypertensive rats.

The vascular protective effects of placebo, candesartan (1 mg kg(-1) per day) monotherapy, candesartan (1 mg kg(-1) per day) and amlodipine (1 mg kg(-1) per day) combination therapy, and candesartan (1 mg kg(-1) per day) and hydrochlorothiazide (HCTZ) (10 mg kg(-1) per day) combination therapy for 2 weeks were compared in stroke-prone, spontaneously hypertensive rats. Candesartan monotherapy significantly reduced blood pressure, and both combination therapies were equally and significantly lower than the monotherapy. Acetylcholine-induced vascular relaxation was significantly stronger in all therapeutic groups than in the placebo-treated group. Furthermore, the relaxation was significantly stronger in the candesartan plus amlodipine-treated group than in the candesartan-treated group; however, there was no significant difference between the candesartan- and candesartan plus HCTZ-treated groups. Vascular gene expressions of the NADPH oxidase subunits p22(phox), gp91(phox), NOX1 and NOX4 were significantly attenuated in all therapeutic groups compared with the placebo-treated group, and there were no significant differences among those groups. However, a significant augmentation of vascular superoxide dismutase activity was observed in the candesartan plus amlodipine-treated group, but not in other groups. Malondialdehyde levels in the vascular tissues were significantly attenuated in all therapeutic groups. Compared with the candesartan-treated group, significant attenuation was observed in the candesartan plus amlodipine-treated group, but not in the candesartan plus HCTZ-treated group. Immunohistological analysis showed that areas positive for 4-hydroxy-2-nonenal were significantly reduced in all therapeutic groups, but this reduction was significantly greater for the candesartan plus amlodipine-treated group than for the candesartan-treated group. Thus, candesartan and amlodipine combination therapy could have a powerful protective effect in vascular tissues via the reduction of oxidative stress.