Aorta Of Streptozotocin-induced Diabetic Rats Research Articles

Effect of Topiroxostat on Reducing Oxidative Stress in the Aorta of Streptozotocin-Induced Diabetic Rats.

Xanthine oxidoreductase exists both intracellularly and extracellularly and induces vascular injury by producing reactive oxygen species (ROS). Here, we investigated the effects and mechanism of action of topiroxostat, a xanthine oxidase inhibitor, on ROS using an animal model of type 1 diabetes with persistent hyperglycemia. Six-week-old male Sprague-Dawley rats were administered 50 mg/kg streptozotocin to induce diabetes; at 8 weeks of age, animals were administered topiroxostat (0.3, 1, or 3 mg/kg) for 2 weeks through mixed feeding after which the aorta was sampled. The production of superoxide, a type of ROS, was measured by chemiluminescence and dihydroethidium staining. Cytotoxicity was evaluated by nitrotyrosine staining. Topiroxostat at 3 mg/kg significantly decreased blood urea nitrogen, e-selectin, urinary malondialdehyde, and the urinary albumin/creatinine ratio compared with the streptozotocin group. Superoxide production by xanthine oxidase anchored to the cell membrane was significantly decreased by topiroxostat at both 1 mg/kg and 3 mg/kg compared with the streptozotocin group. Dihydroethidium staining revealed no significant effect of topiroxostat administration on superoxide production. The fluorescence intensity of nitrotyrosine staining was significantly suppressed by 3 mg/kg topiroxostat. Topiroxostat was found to inhibit the production of ROS in the thoracic aorta and suppress vascular endothelial damage. The antioxidant effect of topiroxostat appears to be exerted via the inhibition of anchored xanthine oxidase.

Effects of Coenzyme Q10 on Some Blood Antioxidant System Parameters and Histological Changes in the Pancreas and Aorta of Streptozotocin-induced Diabetic Rats

Bu calismanin amaci diyabet olusturulan ratlarda koenzim Q10’un antioksidan parametreleri uzerine etkilerini degerlendirmektir. Calismada 38 yetiskin, erkek Wistar Abino rat (250-300 gr) kullanildi. Grup I’deki hayvanlara herhangi bir uygulama yapilmadi. Grup II’deki hayvanlara gunde 0.3 ml misir yagi dort hafta boyunca intraperitoneal olarak uygulandi. Grup III’deki hayvanlara gunde 0.3 ml misir yaginda cozdurulen 10 mg/kg CoQ10 dort hafta boyunca intraperitoneal olarak uygulandi. Grup IV’deki hayvanlarda, 40 mg/kg streptozotosinin gunde tek doz olmak uzere iki subkutan enjeksiyonu ile diyabet olusturuldu. Grup V’deki hayvanlarda ayni protokolle diyabet olusturuldu ve daha sonra bu hayvanlara dort hafta boyunca 0.3 ml misir yaginda cozdurulen 10 mg/kg CoQ10 intraperitoneal olarak uygulandi. Kan orneklerinde GSH, TBARS, SOD, NO seviyeleri ile GPx, CAT aktiviteleri belirlendi. Pankreas ve aorta doku ornekleri histolojik ve immunohistokimyasal yontemler kullanilarak incelendi. Diyabetik grupta plazma SOD, GPx, CAT ve GSH seviyeleri control grubuna gore onemli oranda dusuktu. Diyabetik ratlara CoQ10 uygulamasi ile bu parametreler diyabetik gruba gore onemli oranda artti. Diyabetle birlikte artan plazma TBARS seviyesi, CoQ10 uygulamasiyla azaldi. Calismanin histolojik bulgulari CoQ10 uygulamasi sonucunda enzim duzeylerindeki degisiklikleri desteklemektedir. Sonuc olarak, diyabetik ratlara CoQ10 uygulamasi diyabetin neden oldugu bazi olumsuz degisiklikler uzerine faydali etkilere sahip olabilir.

Glycine Suppresses AGE/RAGE Signaling Pathway and Subsequent Oxidative Stress by Restoring Glo1 Function in the Aorta of Diabetic Rats and in HUVECs.

Oxidative stress plays a crucial role in the pathogenesis of diabetic vascular complications. It is known that the accumulation of advanced glycation end products (AGEs) and the activation of the receptor of AGEs (RAGE) induce sustained oxidative stress in the vascular tissue. Growing evidence indicates that glycine, the simplest amino acid, exerts antioxidant and antiglycation effects and also improves vascular function. However, the mechanism whereby glycine protects vascular tissue against oxidative stress in models with diabetes has not been investigated. In the present study, we evaluated whether glycine can attenuate oxidative stress by suppressing the AGE/RAGE signaling pathway in the aorta of streptozotocin-induced diabetic rats and in human umbilical vascular endothelial cells (HUVECs). Our results showed that oral glycine administration increased NO content and ameliorated oxidative stress in the serum and aorta of diabetic rats. The AGE/RAGE signaling pathway in the aorta of diabetic rats was significantly attenuated by glycine treatment as manifested by decreases in levels of AGEs, RAGE, Nox4, and NF-κB p65. The suppressive effect of glycine on the formation of AGEs was associated with increased activity and expression of aortic glyoxalase-1 (Glo1), a crucial enzyme that degrades methylglyoxal (MG), the major precursor of AGEs. In MG-treated HUVECs, glycine restored the function of Glo1, suppressed the AGE/RAGE signaling pathway, and inhibited the generation of reactive oxygen species. In addition, the reduction in the formation of AGEs in HUVECs caused by glycine treatment was inhibited by Glo1 inhibition. Taken together, our study provides evidence that glycine might inhibit the AGE/RAGE pathway and subsequent oxidative stress by improving Glo1 function, thus protecting against diabetic macrovascular complications.

Hibiscus sabdariffa (ROSELLE) POLYPHENOL-RICH EXTRACT PREVENTS THE AORTIC OXIDATIVE DAMAGE IN TYPE 1 DIABETIC RATS

Diabetes mellitus complications mainly occur due to the oxidative stress-related condition. Thus, this study aimed to investigate the protective effect of the polyphenol-rich extract of Hibiscus sabdariffa (roselle) (HPE) on the aorta of streptozotocin-induced diabetic rats. Twenty-four male Sprague-Dawley rats were divided into four groups (n=6/group); non-diabetes control (NDM), diabetes (DM), diabetes treated with HPE (DM+HPE) and metformin (DM+MET). HPE and metformin were given orally at the dose of 100mg/kg and 150mg/kg respectively for eight weeks duration. At the end of the experiment period, blood pressure was measured before the rats were sacrificed. Blood was taken for measurement of plasma glucose and lipid levels whilst aorta was excised for oxidative stress and histological evaluation. Results showed that HPE treatment reduced plasma glucose level, blood pressure and improved dyslipidemia significantly (p<0.05) in DM+HPE group compared to DM group. Malondialdehyde (MDA) and advanced oxidation protein product (AOPP) levels were significantly decreased (p<0.05) while GSH level was significantly increased (p<0.05) in DM+HPE group compared to DM group. No histological changes observed in the aorta of all diabetic groups compared to NDM group. In conclusion, HPE might have a potential in minimizing the risk of vascular damage in diabetic conditions.

Crocin attenuate Tumor Necrosis Factor-alpha (TNF-α) and interleukin-6 (IL-6) in streptozotocin-induced diabetic rat aorta

ObjectiveCrocin, a bioactive component of saffron, has many biological effects such as antioxidant property. The present study investigated the anti-hyperglycemic, anti oxidant and immunomodulatory effects of crocin on streptozotocin-induced diabetic rats. MethodIn this study, the rats were divided into the following groups of 9 animals each: control, untreated diabetic, three crocin (10, 20, 30mg/kg/day)-treated diabetic groups. Diabetes was induced by streptozotocin in rats. Streptozotocin was injected intraperitoneally at a single dose of 60mg/kg for diabetes induction. Crocin (intraperitoneal injection) was administered 3days after streptozotocin administration; these injections were continued to the end of the study (4weeks). At the end of the 4-week period, blood was drawn for biochemical assays and abdominal aorta was removed for detecting the inflammatory cytokines expression. ResultsOurs results showed that the crocin decreased blood glucose, malondialdehyde, nitric oxide, total lipids, triglycerides, cholesterol levels significantly (p<0.01) and increased glutathione level, catalase and superoxide dismutases activities in the crocin–treated diabetic groups compared with the untreated groups, in a dose dependent manner (p<0.05, p<0.01, p<0.001). On the other hand, crocin-treated diabetic rats inhibited the expression of inflammatory cytokines in abdominal aorta, with respect to the untreated diabetic rats. ConclusionsThese results validate the use of crocin as a treatment against diabetes mellitus and its complications and suggest it is suitable to continue studies for its safe therapeutic use.

Nigella sativa seed decreases endothelial dysfunction in streptozotocin-induced diabetic rat aorta.

Diabetes is an important risk factor for cardiovascular events. The great percent of morbidity in patients with diabetes is due to endothelial dysfunction. The present study investigated the effects of hydroalcholic extract of Nigella sativa (N. sativa) on contractile and dilatation response of isolated aorta in streptozotocin (STZ)-induced diabetic rat. Rats were divided into six experimental groups (control, untreated STZ-diabetic, and N. sativa hydroalcholic extract or metformin-treated diabetic rats). Treated rats received N. sativa extract (100, 200, and 400 mg/kg) or metformin (300 mg/kg) by gavage, daily for 6 weeks. Isolated rat thoracic rings were mounted in an organ bath system then contractile and dilatation responses induced by phenylephrine (PE), acetylcholine (ACh), potassium chloride (KCl), and sodium nitroprusside (SNP) were evaluated in different situations. The lower concentrations of N. sativa seed extract (DE 100 and DE 200) and metformin significantly reduced the contractile responses to higher concentrations of PE (10(-6) - 10(-5) M) compared to diabetic group (p<0.05 to p<0.01). The relaxation response to Ach 10(-8) M, was increased in DE 200 and metformin groups compared to diabetic group (p<0.05). The relaxation responses to Ach 10(-7) - 10(-5) M were significantly higher in all treated groups compared to diabetic group (p<0.05 to p<0.001). Chronic administration of N. sativa seed extract has a significant hypoglycemic effect and improves aortic reactivity to vasoconstrictor and vasodilator agents in STZ-induced diabetic rats.

Endothelial Dysfunction, Macrophage Infiltration and NADPH Oxidase-Dependent Superoxide Production Were Attenuated by Erythropoietin in Streptozotocin-Induced Diabetic Rat Aorta

Erythropoietin (EPO) has been used for the management of renal anemia. Recent studies suggest the pleiotropic properties of EPO in various tissues such as brain, kidney and vasculature. Diabetes mellitus is a major risk for development of vascular impairment. The aim of the present study was to investigate the hypothesis that EPO would be beneficial in inhibiting diabetic macroangiopathy. Recombinant human EPO (rHuEPO; 150 U/kg, 3 times/week, s.c.) was administered to streptozotocin-induced diabetic rats for 4 weeks. Streptozotocin (65 mg/kg, i.v.) significantly increased macrophage infiltration and adhesion molecules, monocyte chemoattractant protein-1 and osteopontin mRNA levels in the aorta. These inflammatory changes were suppressed by rHuEPO. Vasodilation in response to acetylcholine in the aortic ring was impaired in the diabetic rats, and improved by rHuEPO. rHuEPO inhibited the aortic expression of mRNA for nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and the NADPH oxidase-dependent superoxide production and the increase in plasma malondialdehyde concentration in diabetic rats. rHuEPO also decreased the level of the receptor for advanced glycation end products in the aorta. We also found an increased expression of phospho-Akt and endothelial nitric oxide synthase and plasma NOx level in the rHuEPO-treated group. On the other hand, rHuEPO did not affect blood glucose levels, hemoglobin A_1c, blood pressure or hematocrit in diabetic rats. These results indicate that rHuEPO exerts pleiotropic antioxidant and anti-inflammatory properties in diabetic rat aorta.

Histological changes in the heart and the proximal aorta in experimental diabetic rats fed with &lt;i&gt;Piper sarmentsoum&lt;/i&gt;

Cardiovascular complications are one of the major causes of death in diabetes mellitus. Piper sarmentosum (P.s) is an herb that possesses antihyperglycaemic effects. The main aim of the study was to observe the histological changes in the heart and the proximal aorta of streptozotocin-induced diabetic rats following P.s administration. Twenty-four male Sprague-Dawley rats (n=24) were equally randomized into four groups: control group supplemented with normal saline (C); control group supplemented with P.s (CTx) ; diabetic group supplemented with normal saline (D) and, diabetic group supplemented with P.s (DTx). Diabetes was induced by STZ (50mg/kg body weight) intramuscularly. P.s extract (0.125g/kg) was administered orally for 28 days, following four weeks of STZ induction. The cardiac and aortic tissues were collected and processed under different stains: Haematoxylin and Eosin (H & E), Verhoeff-Van Gieson (VVG), Masson's Trichome (MT) and Periodic Acid- Schiff (PAS). There were abnormal cardiomyocytes nuclei, disarray of myofibres and increase in connective tissue deposits in cardiac tissues of the diabetic untreated group. The thickness of tunica media and ratio of tunica intima to media were found to be significantly increased in the aorta of diabetic untreated group (P < 0.05) compared to the control group. There were degenerative changes in the proximal aorta in diabetic untreated groups. All the histological damages of cardiac and aortic tissues were found to be lesser in the diabetic treated groups. Supplementation with P.s extract prevented the oxidative damage arising from diabetes mellitus, and reduced its complications.

Prevention of endothelial dysfunction in streptozotocin-induced diabetic rats by &lt;em&gt;Sargassum echinocarpum&lt;/em&gt; extract

Aim This study aimed to elicit the protective effect of Sargassum echinocarpum extract on endothelial dysfunction in thoracic aorta of streptozotocin-induced diabetic rats. Methods The animals were divided into 5 groups. The first was normal, the second was diabetic non treated animals. The third to fifth groups were the diabetic animals which given Sorgassum echinocarpum extract (150; 300, and 450 mg kg-l body weight, respectively) by oral gavage and extract treatment was given for 12 weeks. Diabetes was induced by single administration of streptozotocin (45 mg kg-I, i.p.), dissolved in freshly prepared 0.1 M citrate buffer, pH 4.5. Diabetes was ctnfirmed ten days latter in streptozotocin induced animals showing blood glucose levels> 200 mg dL-I (11.1 mmol L-I) as monitored in the blood from tail vein using glucometer. After the treatment period, the blood serum acquired was used for antioxidant enzymes assays and the thoracic aorta was used for vasorelaxation assay. Results There was a significant decrease in the activity of super oxide dismu1ase (SOD), catalase (CAT) and glutathione peroxidase (GSH-px) in diabetic rats (3.31± 0.12,-67.17 ± 0.62,-35.10 ± 0.83) comaped to control rats (9.97 ± 0.12,-185.31 ± 0.23;1I6.38 ± 0.88). Administration of Sargassum extract increased the activity of SOD, CAT, and GSH-px. The diabetic rats exhibit endothelial dysfunction as shown by loss of vasodilatory response to acethylcholine (ACH). This was restored by administration ofSargassum extract. Conclusion Sargassum echinocarpum extract ameliorates oxidative stress and reverses the endothelial dysfunction associated with diabetes. This effect appears to be due to its antioxidant properties.

Characterizing the Mechanisms of Insulin Vasodilatation of Normal and Streptozotocin-induced Diabetic Rat Aorta

The mechanism by which insulin causes vasodilatation remains unclear, so we explored this in aortic rings from normal Wistar Kyoto and streptozotocin-induced diabetic rats. Insulin-induced relaxation of phenylephrine-contracted [endothelium (ED) intact or denuded] aortic rings was recorded in the presence or absence of various drug probes. Insulin relaxant effect was more in ED-intact than in-denuded tissues from normal or diabetic rats. l-NAME or methylene blue partially inhibited insulin effect in ED-intact but not the ED-denuded tissues, whereas indomethacin (cyclooxygenase inhibitor) had no effect on any of the tissues, indicating that insulin induces relaxation by ED-dependent and -independent mechanisms, the former via the NOS-cyclic guanosine monophosphate but not the cyclooxygenase pathway. The voltage-dependent K channel (KV) blocker (4-aminopyridine) inhibited insulin action in all the tissues (normal or diabetic, with or without ED), whereas the selective BKCa blocker, tetraethylammonium, inhibited it in normal (ED intact or denuded) but not in diabetic tissues, indicating that KV mediates insulin action in normal and diabetic tissues, whereas the BKCa mediates it only in normal tissues, with possible pathophysiologic absence in diabetic tissues. The inward rectifier K channel (Kir) blocker (barium chloride) significantly inhibited insulin effect only in ED-intact or -denuded diabetic tissues, whereas the KATP channel blocker, glibenclamide, inhibited it only in the ED-denuded diabetic tissues, suggesting that Kir channels mediate insulin-induced relaxation in ED-intact or -denuded diabetic tissues, whereas the KATP channel mediates it in ED-denuded diabetic tissues. All the agents combined did not abolish insulin action, suggestive of a direct vasodilatory effect. In conclusion, insulin causes vasodilatation in normal and diabetic tissues via ED-dependent and -independent mechanisms differentially modulated by K channels, some of which functions are altered in diabetes and thus are potential therapeutic targets.

The direct antioxidative and anti-inflammatory effects of peroxisome proliferator-activated receptors ligands are associated with the inhibition of angiotensin converting enzyme expression in streptozotocin-induced diabetic rat aorta

Peroxisome proliferator-activated receptors (PPARs) are expressed on vascular tissue. To investigate the direct vasoprotective effects of PPARγ and PPARα ligands, pioglitazone (3 mg/kg/day) and bezafibrate (10 mg/kg/day) were given by gavage to streptozotocin-induced diabetic rats for 4 weeks. Streptozotocin (65 mg/kg, i.p.) significantly increased NADPH oxidase, vascular call adhesion molecule-1 (VCAM-1), and osteopontin mRNA levels in the aorta, as determined by reverse transcription (RT)-polymerase chain reaction (PCR). Immunohistochemical analysis revealed that the expression of osteopontin protein was also enhanced in the streptozotocin-injected rat aorta. Pioglitazone or bezafibrate attenuated the streptozotocin-induced increase in the expression of NADPH oxidase and VCAM-1 mRNA. The enhanced expression of osteopontin gene and protein induced by streptozotocin was suppressed by pioglitazone, whereas treatment with bezafibrate had no effect on the expression of osteopontin. We also demonstrated that pioglitazone or bezafibrate prevented the streptozotocin-induced increase in angiotensin converting enzyme (ACE) gene and protein content, by the means of RT-PCR and Western blotting. On the other hand, the treatment of pioglitazone or bezafibrate in the present study did not affect glucose tolerance, serum insulin or lipid level in streptozotocin-induced diabetic rats. These results suggest that the direct anti-oxidant and anti-inflammatory effects of PPARs ligands in the aorta of streptozotocin-induced diabetic rats were not likely to have been mediated by the normalization of glucose or lipid metabolism, but instead these salutary effects appear to have been associated with the inhibition of the expression of ACE. In addition, pioglitazone appeared to be more effective on the suppression of osteopontin expression compared with bezafibrate.

Metformin reduces blood pressure and restores endothelial function in aorta of streptozotocin-induced diabetic rats

Effect of metformin treatment on blood pressure, endothelial function and oxidative stress in streptozotocin (STZ)-induced diabetes in rats was studied. In vitro effect of metformin on vascular reactivity to various agonist in the presence of metformin in untreated nondiabetic and STZ-diabetic rats were also studied. Sprague-Dawley rats were randomized into nondiabetic and STZ-diabetic groups. Rats were further randomized to receive metformin (150 mg/kg) or vehicle for 4 weeks. Metformin treatment reduced blood pressure without having any significant effect on blood glucose level in STZ-diabetic rats. Enhanced phenylephrine (PE)-induced contraction and impaired acetylcholine (Ach)-induced relaxation in STZ-diabetic rats were restored to normal by metformin treatment. Enhanced Ach-induced relaxation in metformin-treated STZ-diabetic rats was blocked due to pretreatment with 100 μM of Nω-nitro- l-arginine-methyl ester ( l-NAME) or 10 μM of methylene blue but not 10 μM of indomethacin. Metformin treatment significantly increased antioxidant enzymes and reduced lipid peroxidation in STZ-diabetic rats. In vitro studies in aortic rings of untreated nondiabetic and STZ-diabetic rats showed that the presence of higher concentration of metformin (1 mM and 10 mM) significantly reduced PE-induced contraction and increased Ach-induced relaxation. Metformin per se relaxed precontracted aortic rings of untreated nondiabetic and STZ-diabetic rats in a dose-dependent manner. Pretreatment with l-NAME or removal of endothelium blocked metformin-induced relaxation at lower concentration (up to 30 μM) but not at higher concentration (above 30 μM). Metformin-induced relaxation was blocked in the presence of 1 mM of 4-aminopyridine, or 1 mM of tetraethylammonium but not in the presence of 100 μM of barium ion or 10 μM of glybenclamide. The restored endothelial function along with direct effect of metformin on aortic rings and reduced oxidative stress contributes to reduced blood pressure in STZ-diabetic rats. From the present study, it can be concluded that metformin administration to STZ-diabetic rats lowers blood pressure, and restores endothelial function.

Pioglitazone, a PPAR? agonist, restores endothelial function in aorta of streptozotocin-induced diabetic rats

To study the effect of pioglitazone (a PPAR gamma agonist) treatment on blood pressure, endothelial function, and oxidative stress in streptozotocin (STZ)-induced diabetic rats. Sprague-Dawley rats were randomized into control (n=32) and STZ-diabetic (n=32) groups. Rats were further randomized to receive pioglitazone (10 mg/kg) or placebo for 4 weeks, and the following protocols were carried out. Blood pressure, blood glucose level, and body weight were measured. Thoracic aorta was isolated and the dose-response curve of phenylephrine (PE) in the presence or absence of Nomega-nitro-L-arginine-methyl ester (L-NAME) was recorded. The dose-response curve of acetylcholine (Ach) in the presence or absence of indomethacin, L-NAME, and methylene blue was recorded. Tone-related basal nitric oxide release experiments were carried out. Lipid peroxidation, superoxide dismutase, catalase, and reduced glutathione were estimated in liver, kidney, and aorta. Aortic nitrite levels were also measured. Further, in vitro effects of PE and Ach in the presence of pioglitazone (0.1 M-10 mM) were measured in aortic rings of nondiabetic and STZ-diabetic rats. Pioglitazone-induced relaxations were recorded in PE-contracted rings (with intact and denuded endothelium) in the presence of L-NAME and in KCl-contracted rings. Pioglitazone treatment reduced blood pressure without having any significant effect on blood glucose level and body weight of STZ-diabetic rats. Enhanced PE-induced contraction and impaired Ach-induced relaxations in STZ-diabetic rats were restored to normal by pioglitazone treatment. The presence of L-NAME but not indomethacin blocked Ach-induced relaxation in pioglitazone-treated STZ-diabetic rats. Basal nitric oxide release was significantly higher in pioglitazone-treated STZ-diabetic rats. Oxidative stress was significantly higher in STZ-diabetic rats and pioglitazone treatment significantly reduced it. High aortic nitrite levels of STZ-diabetic rats were significantly reduced by pioglitazone treatment. The presence of pioglitazone at higher concentrations (>10 muM), but not at lower concentrations, significantly changed the dose-response curve of PE or Ach. Pioglitazone relaxations at lower concentrations but not at higher concentrations were blocked by endothelium removal or by the presence of L-NAME. Pioglitazone administration reduced oxidative stress, which prevented the breakdown of nitric oxide and increased nitric oxide levels, thereby restoring the endothelial function in aorta of STZ-diabetic rat. Hence, from the present study it can be concluded that pioglitazone administration in STZ-diabetic rats lowers blood pressure, protects against oxidative stress, and restores endothelial function.

Tempol augments angiotensin II-induced AT2 receptor-mediated relaxation in diabetic rat thoracic aorta.

To assess angiotensin II type 2 receptor-mediated responses in thoracic aorta of streptozotocin-induced diabetic rats. The concentration-dependent relaxation response (in the presence of an AT1 receptor blocker) to angiotensin II (Ang II) was studied in phenylephrine (PE) or potassium chloride (KCl) precontracted rat thoracic aortic rings isolated from male Sprague-Dawley rats pretreated with streptozotocin (65 mg/kg i.p.) or vehicle 8 weeks prior to the study. Ang II-induced relaxation response (% relaxation), evident only in the presence of an AT1 receptor blocker, was significantly enhanced in aortic rings isolated from diabetic (55%) compared to control (25%) rats. Tempol (100 micromol/l) augmented the relaxation response in aortic rings isolated from diabetic (80%) but not control (28%) rats. N-nitro-l-arginine methyl ester (L-NAME) (100-300 micromol/l) [a nitric oxide (NO) synthase inhibitor] partially inhibited the relaxation response in diabetic (25%) and control (15%) rats. However, l-NAME (100 micromol/l) and glipizide or butanedione monoxime (1 micromol/l) (ATP-sensitive K channel blockers) together completely blocked the relaxation response. [H]Ang II saturation binding at the AT2 receptor was enhanced in aortic membranes from diabetic [maximum binding capacity, (Bmax)=1.14 +/- 0.06 fmol/mg protein] compared to control rats (Bmax=0.75 +/- 0.03 fmol/mg protein), with no change in the dissociation equilibrium constant (Kd) value (2.55 +/- 0.12 versus 2.22 +/- 0.15 nmol/l). The results suggest enhanced AT2-receptor density and function [mediated by a nitric oxide and ATP-sensitive K channel-dependent relaxation response (in presence of an AT1 receptor blocker)] in thoracic aorta isolated from diabetic rats. This could be a compensatory mechanism, which may be therapeutically exploited.

Effect of cobalt on the oxidative status in heart and aorta of streptozotocin-induced diabetic rats.

Effects of cobalt on the antioxidant status of control and streptozotocin diabetic rat heart and aorta were examined at the second, fourth and sixth week of treatment. Rats were divided into four groups: control, diabetic, control treated with cobalt chloride and diabetic treated with cobalt chloride. Diabetes was induced by tail vein injection of streptozotocin (STZ). Cobalt treatment groups were given 0.5 mM of CoCl(2) in drinking water. The rats in both groups were further subdivided into three groups of six rats each. Rats in these subgroups were studied at 2-week intervals up to 6 weeks. At the end of the experiment, all animals were sacrificed by decapitation, heart and aorta samples were removed for determination of thiobarbituric acid reactive substance (TBARS) level and superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities. It was found that lipid peroxidation levels and antioxidant enzyme activities were increased in the streptozotocin-induced diabetic rats at all times studied. Cobalt treatment of diabetic rats (0.5 mM in drinking water) resulted in attenuation of the increased levels of TBARS and antioxidant enzyme activities in heart and aorta. Thus, the effect of oral administration of cobalt at this dose during the early stage of experimental diabetes can be considered as a consequence of altered endogenous defence mechanisms in heart and aorta.

Hyper-reactivity of diacylglycerol kinase is involved in the dysfunction of aortic smooth muscle contractility in streptozotocin-induced diabetic rats.

1. Dysfunction of vascular contraction in diabetes has been reported; however, the mechanisms are poorly understood. In this study, calcium sensitization involving increases in contraction in streptozotocin-induced diabetic rat aorta was detected. We hypothesize that an alteration in the intracellular signalling system plays a role in the dysfunction of vascular contractility in diabetes. Therefore, diacylglycerol (DG) kinase as a key enzyme of phosphatidylinositol (PI) turnover was investigated. 2. Treatment with norepinephrine (NE) caused time- and dose-dependent activation of DG kinase in control rats. This activation required simultaneous increases in intracellular calcium concentration ([Ca2+]i) and protein kinase C (PKC) activation. I3. n diabetic rats, hyper-reactivity of DG kinase involving inactivation in the resting state and over-activation in NE stimulation was observed. During hyper-reactivity, [Ca2+]i dependency of DG kinase was enhanced. Treatment with 50 mM KCl induced significant escalation in activity; moreover, basal activation of PKC was detected only in diabetes. These results suggested that PKC had been activated in the resting state. In contrast, these conditions were insufficient for DG kinase activation due to the absence of [Ca2+]i elevation. 4. During NE-stimulation, PKC activation was maintained and [Ca2+]i increased. Therefore, DG kinase was activated and an elevation in calcium dependency enhanced this activation. 5. The present study suggested that DG kinase hyper-reactivity in diabetes involved both an increase in [Ca2+]i and basal activation of PKC. This phenomenon may be associated with increased vascular contraction in diabetes mediated by acceleration of PI-turnover.

Effect and regulatory mechanism of heat shock on the vascular reactivity in isolated aorta of streptozotocin-induced diabetic rats

Effect and regulatory mechanism of heat shock on the vascular reactivity in isolated aorta of streptozotocin-induced diabetic rats

Erigeron breviscapus prevents defective endothelium-dependent relaxation in diabetic rat aorta

We examined the endothelium-dependent relaxation response to acetylcholine (Ach) in streptozotocin-induced diabetic rat aorta at the stages of 2- and 6-wks' duration in vitro, and compared with another two groups which were treated with dietary supplement of 0.1% Aminoquanidine (AG) and 0.5% Erigeron breviscapus(EB) from 1-week of diabetes induction. At the stage of 2-wks' duration of diabetes, relaxation responses to lower concentrations of Ach in 0.3uM phenylepherine-precontracted aortas were diminished significantly (P < 0.05) compared with age-matched control, but the maximal relaxation of Ach remained unchanged. At the stage of 6-wks' duration, diabetes caused an approximately 60% (P < 0.001) deficit in maximum relaxation, and this was significantly (P < 0.001) prevented in AG and EB treated groups. There was an approximately 40% enhancement in the maximum contractile response to phenylepherine with diabetes (P < 0.05), which was unaffected significantly by AG and EB treatments. The data suggest that the defective endothelium-dependent relaxation in diabetic rat aorta occurred as early as 2-wks' duration of diabetes, and the treatments of AG and EB could protect vascular endothelium although the deficits in vascular smooth muscle contractile responses were not protected.

Existence of Oxidative Stress and Alteration of Antioxidative Enzymes in Aorta of Streptozotocin-induced Diabetic Rats

Existence of Oxidative Stress and Alteration of Antioxidative Enzymes in Aorta of Streptozotocin-induced Diabetic Rats

Endothelium-derived hyperpolarizing factor does not contribute to the decrease in endothelium-dependent relaxation in the aorta of streptozotocin-induced diabetic rats

1. 1. We examined the contribution of endothelium-derived hyperpolarizing factor (EDHF) to the impairment of endothelium-dependent relaxation caused by acetylcholine (ACh) in the aorta of streptozotocin-induced diabetic rats, by using N ω-nitro- l-arginine methylester (L-NAME) and tetraethylammonium chloride (TEA) to inhibit nitric oxide (NO) and EDHF, respectively. 2. 2. ACh-induced relaxation of the aorta decreased in diabetic rats. In contrast, sodium nitroprusside-induced relaxation was the same in diabetic rats and control rats. 3. 3. Treatment with 5 × 10 −7 M L-NAME resulted in a right shift of the dose-response curves of ACh-induced relaxation in the aorta. The shift was greater in the control aorta. 4. 4. Treatment with 5 × 10 −4 M TEA resulted in a similar right shift in both the control and diabetic aorta. 5. 5. Therefore, while endothelium-derived NO appears to contribute to the impairment of ACh-induced endothelium-dependent relaxation in the aorta of diabetic rats, EDHF does not .