Short-term insulin treatment and aortic expressions of IGF-1 receptor and VEGF mRNA in diabetic rats

We investigated the relationship between the changes in vascular responsiveness and growth factor mRNA expressions induced by 1-wk treatment with high-dose insulin in control and established streptozotocin (STZ)-induced diabetes. Aortas from diabetic rats, but not those from insulin-treated diabetic rats, showed impaired endothelium-dependent relaxation in response to ACh (vs. untreated controls). The ACh-induced nitrite plus nitrate (NOx) level showed no significant difference between controls and diabetics. Insulin treatment increased NOx only in diabetics. In diabetics, insulin treatment significantly increased the aortic expressions of endothelial nitric oxide synthase (eNOS) mRNA and VEGF mRNA. The expression of IGF-1 mRNA was unaffected by diabetes or by insulin treatment. In contrast, the mRNA for the aortic IGF-1 receptor was increased in diabetics and further increased in insulin-treated diabetics. In aortic strips from age-matched control rats, IGF-1 caused a concentration-dependent relaxation. This relaxation was significantly stronger in strips from STZ-induced diabetic rats. These results suggest that in STZ-diabetic rats, short-term insulin treatment can ameliorate endothelial dysfunction by inducing overexpression of eNOS and/or VEGF mRNAs possibly via IGF-1 receptors. These receptors were increased in diabetes, perhaps as result of insulin deficiency.     

Alterations in EDHF-type relaxation and phosphodiesterase activity in mesenteric arteries from diabetic rats

In isolated superior mesenteric artery rings from age-matched control rats and streptozotocin (STZ)-induced diabetic rats, we investigated the role of cAMP in endothelium-derived hyperpolarizing factor (EDHF)-type relaxation. The ACh-induced EDHF-type relaxation was significantly weaker in STZ-induced diabetic rats than in control rats, and in both groups of rats it was attenuated by 18alpha-glycyrrhetinic acid (18alpha-GA), an inhibitor of gap junctions, and enhanced by IBMX, a cAMP-phosphodiesterase (PDE) inhibitor. These enhanced EDHF-type responses were very similar in magnitude between diabetic and age-matched control rats. The EDHF-type relaxation was enhanced by cilostamide, a PDE3-selective inhibitor, but not by Ro 20-1724, a PDE4-selective inhibitor. The expression levels of the mRNAs and proteins for two cAMP PDEs (PDE3A, PDE3B) were significantly increased in STZ-induced diabetic rats, but those for PDE4D were not. We conclude that the impairment of EDHF-type relaxations in STZ-induced diabetic rats may be attributed to a reduction in the action of cAMP via increased PDE activity.     

Mechanisms underlying the chronic pioglitazone treatment-induced improvement in the impaired endothelium-dependent relaxation seen in aortas from diabetic rats

The objectives of this study were to determine the effects of chronic treatment with pioglitazone, a peroxisome proliferator-activated receptor gamma agonist, on the impaired endothelium-dependent relaxation seen in aortas from established streptozotocin (STZ)-induced diabetic rats, and to identify some of the molecular mechanisms involved. Starting at 8 weeks of diabetes, pioglitazone (10 mg/kg) was administered to STZ-induced diabetic rats for 4 weeks. In untreated STZ rats (vs age-matched control rats): (1) ACh-induced relaxation, cGMP accumulation, phosphorylation of the cGMP-dependent protein kinase substrate vasodilator-stimulated phosphoprotein at Ser-239 [an established biochemical end-point of nitric oxide (NO)/cGMP signaling], and Cu/Zn-superoxide dismutase (SOD) expression and SOD activity were all reduced; (2) aortic superoxide generation, nitrotyrosine expression, and NAD(P)H oxidase activity were increased; (3) plasma endothelin-1 (ET-1) and aortic c-Jun (AP-1 component) protein expressions were increased. Pioglitazone treatment markedly corrected the above abnormalities. Collectively, these results suggest that pioglitazone treatment improves endothelium-dependent relaxation by reducing oxidative stress via increased SOD activity, decreased NAD(P)H oxidase activity, and a decreased ET-1 level, and that this decreased ET-1 level may be attributable to an inhibition of the AP-1 signaling pathway.     

Upregulation of small GTPase RhoA in the basilar artery from diabetic (mellitus) rats

The goal of this study was to determine whether RhoA, a small GTPase, might be involved in the development of cerebral pathogenesis in diabetes. Male SD rats (n = 120) were divided into six groups: diabetic for 2, 4, 8 weeks, and an age-matched control group. Diabetes was induced by intravenous injection of streptozotocin (50 mg/kg). RhoA mRNA expression in basilar artery was measured by competitive RT-PCR. RhoA mRNA level was significantly increased in 4 weeks (184.1 +/- 28.5%, n = 7) and 8 weeks (218.7 +/- 24.5%, n = 7) after STZ injection compared to the age matched control basilar arteries (P < 0.05). Western blot was used to measure the membrane binding RhoA level to represent the activity of RhoA. We found that RhoA activity was strikingly increased in the diabetic basilar artery (n = 10 in each groups) compared to control basilar artery after STZ injection. Our data demonstrated that there was an upregulation of RhoA in the basilar artery of STZ induced diabetic rats, suggesting that RhoA might be involved in the cerebral vascular pathogenesis during diabetes mellitus.     

Angiotensin II and endothelin-1 augment the vascular complications of diabetes via JAK2 activation

The JAK/STAT pathway is activated in vitro by angiotensin II (ANG II) and endothelin-1 (ET-1), which are implicated in the development of diabetic complications. We hypothesized that ANG II and ET-1 activate the JAK/STAT pathway in vivo to participate in the development of diabetic vascular complications. Using male Sprague-Dawley rats, we performed a time course study [days 7, 14, and 28 after streptozotocin (STZ) injection] to determine changes in phosphorylation of JAK2, STAT1, and STAT3 in thoracic aorta using standard Western blot techniques. On day 7 there was no change in phosphorylation of JAK2, STAT1, and STAT3. Phosphorylation of JAK2, STAT1, and STAT3 was significantly increased on days 14 and 28 and was inhibited by treatment with candesartan (AT(1) receptor antagonist, 10 mg x kg(-1) x day(-1) orally in drinking water), atrasentan (ET(A) receptor antagonist, 10 mg x kg(-1) x day(-1) orally in drinking water), and AG-490 (JAK2 inhibitor, 5 mg x kg(-1) x day(-1) intraperitoneally). On day 28, treatment with all inhibitors prevented the significant increase in systolic blood pressure (SBP; tail cuff) of STZ-induced diabetic rats (SBP: 157 +/- 9.0, 130 +/- 3.3, 128 +/- 6.8, and 131 +/- 10.4 mmHg in STZ, STZ-candesartan, STZ-atrasentan, and STZ-AG-490 rats, respectively). In isolated tissue bath studies, diabetic rats displayed impaired endothelium-dependent relaxation in aorta (maximal relaxation: 95.3 +/- 3.0, 92.6 +/- 7.4, 76.9 +/- 12.1, and 38.3 +/- 13.1% in sham, sham + AG-490, STZ + AG-490, and STZ rats, respectively). Treatment of rats with AG-490 restored endothelium-dependent relaxation in aorta from diabetic rats at 14 and 28 days of treatment. These results demonstrate that JAK2 activation in vivo participates in the development of vascular complications associated with STZ-induced diabetes.     

The effect of systemic leptin administration on aorta smooth muscle responses in diabetic rats

Leptin produces effects in central nervous system and peripheral tissues via its specific receptors. Leptin also stimulates nitric oxide release in a concentration-dependent manner. In this study, our aim was to test the hypothesis that whether leptin has a modulatory role on endothelium or smooth muscle function in streptozotocin (STZ)-induced diabetic rats. Wistar-Albino rats were divided into four groups: 1 – Control, 2 – Diabetic, 3 – Control + leptin and 4 – Diabetic + leptin. Experimental diabetes was produced by intraperitoneal injection of a single dose of STZ (55 mg/kg). Diabetes was determined by increased fasting blood glucose level on the 7th day of the experiment. Leptin (0.1 mg/kg/day) was administered intraperitoneally for 5 days. At the end of the 5th day, thoracic aortas were isolated and phenylephrine (Phe)-induced contractions and acetylcholine (ACh)-induced relaxations of each group were estimated. In diabetic rats, Phe-induced contractility was increased (p < 0.05). Leptin pre-treatment increased the Phe-induced contractility significantly in aortic rings obtained from diabetic rats (p < 0.05). In normal rats, leptin administration produced only a slight and non-significant increase in Phe-induced contractions. Although the relaxant responses were decreased in diabetic rats, leptin administration enhanced the ACh-induced relaxation in both normal and diabetic animals significantly. As a conclusion; chronic leptin pre-treatment caused a significant increase both in Phe-induced contractions and ACh-induced Endothelial-Derived Relaxing Factor (EDRF)/Nitric oxide-mediated relaxations in the aortic rings isolated from streptozotocin-induced diabetic rats. This peptide hormone caused a significant increase in the relaxations obtained by ACh while not inducing a significant alteration in the contractile effect of Phe in control rats.     

Impaired vascular dynamics in normotensive diabetic rats induced by streptozotocin: tapered T-tube model analysis

This study is to explore the changes of arterial mechanical properties in streptozotocin (STZ)-diabetic rats, based on the exponentially tapered T-tube model. Rats given STZ 65 mg kg(-1)i.v. are compared with untreated weight- and age-matched controls. A high-fidelity pressure sensor and electromagnetic flow probe measured pulsatile pressure and flow waves in the ascending aorta, respectively. Diabetic rats exhibit isobaric vasodilatation that is characterized by an increase in cardiac output and no significant changes in aortic pressure. Total peripheral resistance of diabetic rats is lower than that of weight- and age-matched controls. Diabetic rats have higher total peripheral compliance (2.86+/-0.70 microl mm Hg(-1)) than do weight- (1.77+/-0.34 microl mm Hg(-1)) and age-matched (1.87+/-0.69 microl mm Hg(-1)) controls. Aortic characteristic impedance is reduced from 0.017+/-0.003 mm Hg min kg ml(-1)in weight- and 0.020+/-0.004 mm Hg min kg ml(-1)in age-matched controls to 0.010+/-0.004 mm Hg min kg ml(-1)in diabetic rats. Moreover, diabetic rats show shorter wave transit time in lower body circulation (17.86+/-1.91 ms) than do weight- (20.45+/-1.91) and age-matched (23.05+/-2.04 ms) controls. Under isobaric vasodilatation, the decreased resistance and increased compliance in peripheral circulation suggest that the contractile dysfunction of the smooth muscle cells may occur in resistance arterioles in diabetes. With unaltered aortic pressure, an impairment in aortic distensibility of STZ-diabetic rats is manifest on the reduced wave transit time rather than on the diminished aortic characteristic impedance.     

Radiotelemetric monitoring of blood pressure and mesenteric arterial bed responsiveness in rats with streptozotocin-induced diabetes

We investigated the changes in arterial blood pressure (BP) and of mesenteric arterial bed (MAB) responsiveness that accompany streptozotocin (STZ)-induced diabetes. BP was recorded by radiotelemetry in conscious animals before and during a 4-week period following induction of the diabetic state with STZ. At the end of this period, the MAB was isolated and perfused under constant flow conditions: perfusion pressure (PP, mmHg) was taken as an index of arteriolar tone. BP was lower (P < 0.05) in STZ-treated diabetic rats (82.9+/-5.0 mmHg) than in vehicle-treated rats (108.9+/-6.3 mmHg). Basal perfusion pressure of the MAB was lower in STZ-treated rats than in control rats and inhibition of nitric oxide (NO) synthesis with N(G)-nitro-L-arginine-methyl-ester and N(G)-nitro-L-arginine (100 microM each) failed to change this relationship. Increases in PP of MAB to phenylephrine (Phe), norepinephrine (NE), and potassium chloride (KCl) were reduced in STZ-treated rats compared with control rats. Inhibition of NO synthesis reduced responses to Phe, NE, and KCL in both STZ and control rats. The reduced responsiveness of STZ rats to Phe, NE, and KCl persisted after inhibition of NO synthesis. Acetylcholine (ACh) evoked relaxation of the MAB in a dose-dependent fashion. Maximal responses to ACh, but not sodium nitroprusside, were lower in STZ rats than in vehicle treated rats. Inhibition of NO synthesis reduced responses to ACh in both STZ and control rats. The reduced responsiveness of STZ rats to ACh persisted after inhibition of NO synthesis. The data demonstrate that STZ-induced diabetes is associated with a fall in blood pressure when pressure is recorded with radiotelemetry. The fall in blood pressure may be related to a non-specific decrease in responsiveness to vasoconstrictor stimuli mediated at least in part by NO-independent mechanisms. A decrease in responsiveness to endothelial dependent vasodilator mechanisms appeared insufficient to restore responsiveness to vasoconstrictor stimuli.     

金耳菌丝体多糖对实验性2型糖尿病大鼠的降血糖作用研究

本文研究了金耳菌丝体多糖(TMP)对实验性2型糖尿病大鼠血糖、血脂、胰岛素敏感性和抗氧化能力的影响。采用烟酰胺,链脲佐菌素和高脂饲料诱导2型糖尿病大鼠模型,以50和100mg/(kg.d)剂量的TMP连续灌胃48d,监测血糖,测定血清胰岛素、体重、脂代谢及抗氧化系统部分相关指标,并进行口服糖耐量实验。结果显示,TMP可明显降低2型糖尿病大鼠的血清葡萄糖、总胆固醇、甘油三酯和丙二醛水平,并极显著提高受试模型鼠的胰岛素敏感指数,血清超氧化物歧化酶活性和肝脏过氧化氢酶活性。此外,TMP能显著降低糖耐量实验中糖负荷后120min时糖尿病大鼠的血糖含量。上述结果表明TMP可有效降低实验性2型糖尿病大鼠的血糖水平,纠正脂代谢紊乱,改善胰岛素抵抗,增强抗氧化能力。     

Effects of vitamin E on microsomal Ca(2+) -ATPase activity and calcium levels in streptozotocin-induced diabetic rat kidney

Vitamin E treatment has been found to be beneficial in preventing or reducing diabetic nephropathy. Increased tissue calcium and abnormal microsomal Ca(2+)-ATPase activity have been suggested as contributing factors in the development of diabetic nephropathy. This study was undertaken to test the hypothesis that vitamin E reduces lipid peroxidation and can prevent the abnormalities in microsomal Ca(2+)-ATPase activity and calcium levels in kidney of streptozotocin (STZ)-induced diabetic rats. Male rats were rendered diabetic by a single STZ injection (55 mg x kg(-1) i.p.). After diabetes was verified, diabetic and age-matched control rats were untreated or treated with vitamin E (400-500 IU kg(-1) x day(-1), orally) for 10 weeks. Ca(2+)-ATPase activity and lipid peroxidation (MDA) were determined spectrophotometrically. Blood glucose levels increased approximately five-fold (> 500 mg x dl(-1)) in untreated-diabetic rats but decreased to 340+/-27 mg x dl(-1) in the vitamin E treated-diabetic group. Kidney MDA levels did not significantly change in the diabetic state. However, vitamin E treatment markedly inhibited MDA levels in both control and diabetic animals. Ca(2+)-ATPase activity was 0.483+/-0.008 U l(-1) in the control group and significantly increased to 0.754+/-0.010 U l(-1) in the STZ-diabetic group (p < 0.001). Vitamin E treatment completely prevented the diabetes-induced increase in Ca(2+)-ATPase activity (0.307+/-0.025 U l(-1), p < 0.001) and also reduced the enzyme activity in normal control rats. STZ-diabetes resulted in approximately two-fold increase in total calcium content of kidney. Vitamin E treatment led to a significant reduction in kidney calcium levels of both control and diabetic animals (p < 0.001). Thus, vitamin E treatment can lower blood glucose and lipid peroxidation, which in turn prevents the abnormalities in kidney calcium metabolism of diabetic rats. This study describes a potential biochemical mechanism by which vitamin E supplementation may delay or inhibit the development of cellular damage and nephropathy in diabetes.     

Blunted nitric oxide-mediated inhibition of sympathetic nerve activity within the paraventricular nucleus in diabetic rats

Recent evidence suggests that a central mechanism may be contributing to the sympathetic abnormality in diabetes. Nitric oxide (NO) has been known as a neurotransmitter in the central nervous system. The goal of this study was to examine the role of the endogenous NO system of the paraventricular nucleus (PVN) in regulation of renal sympathetic nerve activity (RSNA) in streptozotocin (STZ)-induced diabetic rats. The change in number of NADPH-diaphorase-positive neurons [a marker for neuronal NO synthase (nNOS) activity] in the PVN was measured. Diabetic rats were found to have significantly fewer nNOS positive cells in the PVN than in the control group (120 +/- 11 vs. 149 +/- 13, P < 0.05). Using RT PCR, Western blotting and immunofluorescent staining, it was also found that nNOS mRNA expression and protein level in the PVN were significantly decreased in the diabetic rats. Furthermore, using an in vivo microdialysis technique, we found that there was a lower NO(x) release from the PVN perfusates in rats with diabetes compared with the control rats (142 +/- 33 nM vs. 228 +/- 29 nM, P < 0.05). In alpha-chloralose- and urethane-anesthetized rats, an inhibitor of NO synthase, l-NMMA, microinjected into the PVN produced a dose-dependent increase in RSNA, mean arterial pressure (MAP), and heart rate (HR) in both control and diabetic rats. These responses were significantly attenuated in rats with diabetes compared with control rats (RSNA: 11 +/- 3% vs. 35 +/- 3%, P < 0.05). On the other hand, an NO donor, sodium nitroprusside (SNP), microinjected into the PVN produced a dose-dependent decrease in RSNA, MAP, and HR in the control and diabetic rats. RSNA (17 +/- 3%, vs. 41 +/- 6%, P < 0.05) and MAP in response to SNP were significantly blunted in the diabetic group compared with the control group. In conclusion, these data indicate an altered NO mechanism in the PVN of diabetic rats. This altered mechanism may contribute to the increased renal sympathetic neural activity observed in diabetes.     

Diabetes-induced decrease in rat brain microsomal Ca2+-ATPase activity

The Ca(2+)-ATPase activity of rat brain microsomes was studied in streptozotocin (STZ)-induced diabetes. Male rats, 200-250 g, were rendered diabetic by injection of STZ (45 mg kg(-1) body weight) via the teil vein. Brain tissues were collected at 1, 4 and 10 weeks after diabetes was induced for determination of Ca(2+)-ATPase activity, lipid peroxidation and tissue calcium levels. Diabetic rats had significantly elevated blood glucose levels compared to controls. Blood glucose levels were 92.92 +/- 1.22 mg dl(-1) (mean +/- SEM) for the control group, 362.50 +/- 9.61 mg dl(-1) at 1 week and >500 mg dl(-1) at 4, 8 and 10 weeks for the diabetics. Enzyme activities were significantly decreased at 1, 4, 8 and 10 weeks of diabetes relative to the control group (p < 0.001). Ca(2+)-ATPase activity was 0.084 +/- 0.008 U l(-1), 0.029 +/- 0.005 U l(-1), 0.029 +/- 0.006 U l(-1), 0.033 +/- 0.003 U l(-1) and 0.058 +/- 0.006 U l(-1) (mean +/- SEM) at control, 1, 4, 8 and 10 week of diabetes respectively. The change in calcium levels in diabetic rat brain at 8 and 10 weeks of diabetes was significantly higher than that of the control group (p < 0.05). On the other hand lipid peroxidation measured as TBARS (thiobarbituric acid reactive substances) was significantly higher at 8 and 10 weeks of diabetes (p < 0.05). The increase in lipid peroxidation observed in diabetic rat brain may be partly responsible for the decrease in calcium ATPase activity.     

Effect of chromium picolinate on histopathological alterations in STZ and neonatal STZ diabetic rats

Earlier studies from our laboratory have indicated insulin sensitizing action of chromium picolinate as the mechanism of its anti-diabetic activity in experimental models of type I and type II diabetes. In the present investigation, we have evaluated the effects of chronic administration of chromium picolinate on the functional and histological alterations of streptozotocin (STZ)-induced diabetes in rats. Type I diabetes was induced by intravenous injection of STZ (40 mg/kg) in adult rats, whereas, type II diabetes was induced by intraperitoneal injection of STZ (90 mg/kg) in 2-day old rat pups which in adulthood develop abnormalities resembling type II diabetes. Chromium picolinate was administered at 8 μg/ml in drinking water for 6 weeks and was found to improve glucose tolerance and increase insulin sensitivity of STZ-diabetic rats. This treatment decrease elevated serum creatinine and urea levels as well as elevated serum levels of hepatic enzymes of both groups of diabetic rats. Histopathological studies of kidney and liver show decrease in the intensity and incidence of vacuolations, cellular infiltration and hypertrophy of STZ and nSTZ (neonatal STZ) diabetic rats. Chronic treatment with chromium picolinate however, did not alter the normal function or morphology of control rats. Chronic chromium picolinate at the therapeutic doses that improved glucose tolerance, was observed to have no hepatotoxic or nephrotoxic potential. It was rather found to improve renal and hepatic function and to reduce abnormalities associated with STZ-diabetes. Chromium picolinate could play an important role in the long term management of diabetes mellitus.     

Diabetes abolishes the vascular protective effects of estrogen in female rats

Estrogen is known to exert a protective effect against cardiovascular disease. However, women with diabetes have three times the risk as compared with age-matched non-diabetic women. Our previous study on aortic rings of ovariectomized (OVX) female rats treated with 17-beta-estradiol (E2) demonstrated that the beneficial effect of estrogen is related to the basal release of NO from endothelial cells. In the present study, in order to understand why estrogen protection is abolished in diabetes, we tested vascular responses in OVX, streptozotocin-diabetic female rats and their non-diabetic controls receiving or not E2 replacement. Concentration-response curves to norepinephrine (NE) showed attenuation of the contractile response in E2-treated diabetic, with respect to non-diabetic preparations. This response was further impaired in diabetic, E2-deprived rats. The basal release of NO, as evaluated by concentration-related responses to N(G)-methyl-L-arginine acetate in NE-precontracted aortic rings, was found to be impaired in E2-treated diabetic rats, no further effect being induced by E2 deprivation. The endothelium-dependent relaxation produced by carbachol did not change between groups, whereas the relaxation produced by histamine was enhanced by both diabetes and E2 deprivation. However, E2 treatment counteracted the response to histamine only in preparations from non-diabetic animals. Finally, the relaxation induced by sodium nitroprusside, an endothelium-independent relaxant agent, was comparable between groups. These findings suggest that the lack of protective effects of estrogen in diabetes may be mainly ascribed to the failure of estrogen to reverse the impaired basal release of NO and the abnormal relaxation to histamine, which are observed in the aorta of diabetic rats.     

The rat model of type 2 diabetic mellitus and its glycometabolism characters.

To develop a rat model of type 2 diabetic mellitus that simulated the common manifestation of the metabolic abnormalities and resembled the natural history of a certain type 2 diabetes in human population, male Sprague-Dawley rats (4 months old) were injected with low-dose (15 mg/kg) STZ after high fat diet (30% of calories as fat) for two months (L-STZ/2HF). The functional and histochemical changes in the pancreatic islets were examined. Insulin-glucose tolerance test, islet immunohistochemistry and other corresponding tests were performed and the data in L-STZ/2HF group were compared with that of other groups, such as the model of type 1 diabetes (given 50 mg/kg STZ) and the model of obesity (high fat diet). The body weight of rats in the group of rats given 15 mg/kg STZ after high fat diet for two months increased significantly more than that of rats in the group of rats given 50 mg/kg STZ (the model of type 1 diabetes) (595 +/- 33 g vs. 352 +/- 32 g, p<0.05). Fast blood glucose levels for L-STZ/2HF group were 16.92 +/- 1.68 mmol/l, versus 5.17 +/- 0.55 mmol/l in normal control and 5.59 +/- 0.61 mmol/l in rats given high fat diet only. Corresponding values for fast serum insulin were 0.66 +/- 0.15 ng/ml, 0.52 +/- 0.13 ng/ml, 0.29 +/- 0.11 ng/ml, respectively. Rats of type 2 diabetes (L-STZ/2HF) had elevated levels of triglyceride (TG, 3.82 +/- 0.88 mmol/l), and cholesterol(Ch, 2.38 +/- 0.55 mmol/l) compared with control (0.95 +/- 0.15 mmol/l and 1.31 +/- 0.3 mmol/l, respectively) (p<0.05). The islet morphology as examined by immunocytochemistry using insulin antibodies in the L-STZ/2HF group was affected and quantitative analysis showed the islet insulin content was higher than that of rats with type 1 diabetes (P<0.05). We concluded that the new rat model of type 2 diabetes established with conjunctive treatment of low dose of STZ and high fat diet was characterized by hyperglycemia and light impaired insulin secretion function accompanied by insulin resistance, which resembles the clinical manifestation of type 2 diabetes. Such a model, easily attainable and inexpensive, would help further elucidation of the underlying mechanisms of diabetes and its complications.     

Differential expression of alpha2D-adrenoceptor and eNOS in aortas from early and later stages of diabetes in Goto-Kakizaki rats

The aim of the present study was to compare vascular dysfunction between the early (12 wk old) and later (36 wk old) stages of spontaneous diabetes in Goto-Kakizaki (GK) rats. We also evaluated the aortic expression of the alpha(2D)-adrenoceptor and endothelial nitric oxide synthase (eNOS). Vascular reactivity was assessed in thoracic aortas from age-matched control rats and 12- and 36-wk GK rats. Using RT-PCR and immunoblots, we also examined the changes in expression of the alpha(2D-)adrenoceptor and eNOS. In aortas from GK rats (vs. those from age-matched control rats): 1) the relaxation response to ACh was enhanced at 12 wk but decreased at 36 wk; 2) the relaxation response to sodium nitroprusside was decreased at both 12 and 36 wk, 3) norepinephrine (NE)-induced contractility was decreased at 12 wk but not at 36 wk, 4) the expressions of alpha(1B)- and alpha(1D)-adrenoceptors were unaffected, whereas those of alpha(2D)-adrenoceptor and eNOS mRNAs were increased at both 12 and 36 wk; and 5) NE- and ACh-stimulated NO(x) (nitrite and nitrate) levels were increased at 12 wk, although at 36 wk ACh-stimulated NO(x) was lower, whereas NE-stimulated NO(x) showed no change. These results clearly demonstrate that enhanced ACh-induced relaxation and impaired NE-induced contraction, due to NO overproduction via eNOS and increased alpha(2D)-adrenoceptor expression, occur in early-stage GK rats and that the impaired ACh-induced relaxation in later-stage GK rats is due to reductions in both NO production and NO responsiveness (but not in eNOS expression).     

α-亚麻酸对糖尿病大鼠炎症介质和氧化应激的影响

目的:观察α-亚麻酸(ALA)对糖尿病大鼠体内炎症介质和氧化应激的影响,探讨ALA在糖尿病防治中的作用。方法:雄性SD大鼠高脂饮食喂养4周后,腹腔注射链脲佐菌素(STZ)30 mg/kg建立2型糖尿病(T2DM)模型。将大鼠随机分为3组(n=10):正常对照组、糖尿病模型组和ALA治疗组(500μg/kg.d)。4周后测定大鼠血清中肿瘤坏死因子(TNF-α)、可溶性P-选择素(sP-selectin)、可溶性细胞间黏附分子(sICAM-1)、一氧化氮(NO)、丙二醛(MDA)的含量以及超氧化物岐化酶(SOD)和过氧化氢酶(CAT)的活性。结果:与正常对照组相比,糖尿病大鼠血清中炎症介质TNF-α、sP-selectin和sICAM-1的含量增加,血清NO含量下降而MDA升高,同时抗氧化酶SOD和CAT的活性降低;ALA治疗可显著降低糖尿病大鼠血清中TNF-α、sP-selectin和sICAM-1的含量(与STZ+vehicle组相比,P<0.01),增加血清NO水平并减少MDA含量,升高抗氧化酶SOD和CAT的活性(与STZ+vehicle组相比,均P<0.05)。结论:ALA可显著降低糖尿病大鼠血清炎症介质的生成,减轻氧化应激水平,具有抗炎和抗氧化作用。提示ALA对糖尿病及糖尿病并发症的发生发展可能具有一定的防治作用。     

Mechanisms underlying enhanced vasorelaxant response to protease-activated receptor 2-activating peptide in type 2 diabetic Goto–Kakizaki rat mesenteric artery

Protease-activated receptor 2 (PAR2) is a G-protein-coupled receptor that is proteolytically activated by certain endogenous proteases, such as trypsin, tryptase, and factor Xa. PAR2 can also be activated by synthetic peptides if their sequence mimics the tethered ligand exposed after receptor cleavage. Although it is known that PAR2 modulates vascular reactivity, it is unclear whether at the chronic stage of type 2 diabetes there are alterations in PAR2-mediated vascular responses. We investigated this issue by exposing mesenteric artery rings to PAR2-activating peptide (PAR2-AP; SLIGRL-NH₂), the arteries used being obtained from later-stage (32–40-week-old) type 2 diabetic Goto–Kakizaki (GK) rats. The PAR2-AP-induced relaxation was enhanced in GK rats (vs. age-matched Wistar rats), whereas the ACh-induced relaxation was weaker in GK than in Wistar rats. In both groups, the PAR2-AP-induced relaxation was largely blocked by endothelial denudation or by N^G-nitro-l-arginine [nitric oxide (NO) synthase inhibitor] treatment, but it was unaffected by indomethacin (cyclooxygenase inhibitor) treatment. Both the NO production induced by PAR2-AP and the PAR2 protein expression were significantly increased in mesenteric arteries from GK rats (vs. Wistar rats). These data are the first to indicate that the PAR2-AP-induced endothelium-dependent relaxation is enhanced in mesenteric arteries isolated from type 2 diabetic GK rats at the chronic stage, and they further suggest that the enhancement may be due to an increased expression of PAR2 receptors in this artery.     

Pomegranate (Punica granatum L.) flower improves learning and memory performances impaired by diabetes mellitus in rats

Oxidative stress induced by diabetes mellitus leads to damages in the brain, as a consequence of which cognitive functions is impaired. Therefore, for the treatment of diabetes mellitus, in addition to antidiabetics, antioxidants are used to cope with oxidative stress. The antioxidant ability of pomegranate flowers (PGF) to cope with the oxidative stress was investigated. Rats were divided into five groups with 12 animals in each group as given below: control, diabetes (STZ), STZ + the PGF I (300 mg/kg/day), STZ + PGF II (400 mg/kg/day) and STZ + PGF III (500 mg/kg/day).The findings from Morris water maze and probe tests showed that the animals in STZ group had impairments in learning and memory performances compared to the control group. Supplementation of PGF led to improvements in learning and memory performances of diabetic rats.While lipid peroxidation (LPO) was increased (P<0.001), glutathione (GSH) content was decreased (P<0.001) in hippocampal tissue of STZ-induced diabetic rats when compared with control values. Supplementation of PGF restored the levels of LPO and GSH towards their control values. Daily PGF supplementation to diabetic rats reduced the increase in glial-fibrilar acidic protein (GFAP) contents induced by diabetes in the hippocampus, which was significant in STZ + PGF III in comparison to STZ group (p<0.05).In conclusion, these observations suggest that PGF supplementation decreases oxidative stress and ameliorates impairment in learning and memory performances in diabetic rats. Therefore, we suggest that PGF supplementation may be clinically useful in treating neuronal deficit in diabetic patients.     

Chronic tempol treatment attenuates the renal hemodynamic effects induced by a heme oxygenase inhibitor in streptozotocin diabetic rats

Heme oxygenase-1 (HO-1) is induced by oxidative stress and plays an important role in protecting the kidney from oxidant-mediated damage in the streptozotocin (STZ) rat model of type-1 diabetes mellitus (DM-1). HO-derived metabolites, presumably carbon monoxide (CO), mediate vasodilatory influences in the renal circulation, particularly in conditions linked to elevated HO-1 protein expression or diminished nitric oxide (NO) levels. We tested the hypothesis that diabetes increases oxidative stress and induces HO-1 protein expression, which contributes to regulate renal hemodynamics in conditions of low NO bioavailability. Two weeks after the induction of diabetes with STZ (65 mg/kg iv), Sprague-Dawley rats exhibited higher renal HO-1 protein expression, hyperglycemia, and elevated renal nitrotyrosine levels than control normoglycemic animals. In anesthetized diabetic rats, renal vascular resistance (RVR) was increased, and in vivo cortical NO levels were reduced (P < 0.05) compared with control animals. Acute administration of the HO inhibitor Stannous mesoporphyrin (SnMP; 40 μmol/kg iv) did not alter renal hemodynamics in control rats, but greatly decreased glomerular filtration rate and renal blood flow, markedly increasing RVR in hyperglycemic diabetic rats. Chronic oral treatment with the SOD mimetic tempol prevented the elevation of nitrotyrosine, the HO-1 protein induction, and the increases in RVR induced by SnMP in the diabetic group, without altering basal NO concentrations or RVR. Increasing concentrations of a CO donor (CO-releasing molecule-A1) on pressurized renal interlobar arteries elicited a comparable relaxation in vessels taken from control or diabetic animals. These results suggest that oxidative stress-induced HO-1 exerts vasodilatory actions that partially maintain renal hemodynamics in uncontrolled DM-1.