A lack of synergistic interaction between insulin and pioglitazone on reactivity of rat aorta from chronically high dose insulin-treated diabetic rats.

Our goal was to determine whether hyperinsulinaemic and diabetic state can affect vaso-depressor effects of insulin and pioglitazone (PIO), an insulin-sensitizing thiazolidinedione drug. For this purpose, we established an experimental type 2 diabetic model (streptozotocin-nicotinamide model) in adult male rats (DIA group) and some of them were treated with chronically high-dose insulin for 14 weeks (INS-T DIA group). Blood pressure, glucose, HbA(1C), triglyceride, cholesterol, plasma insulin levels and body weight were measured. Endothelium-denuded aortic rings were suspended in tissue baths for reactivity studies. Cumulative concentration-response curves of serotonin (5-hydroxytryptamine; 5-HT) were evaluated before and after 1 h incubations with insulin (10(-7) or 10(-4) U/l), or PIO (10 micromol/l) or insulin plus PIO. PIO or higher concentration of insulin (10(-4) U/l), each alone, attenuated 5-HT induced contractions in both groups of aortae. Vasodepressor effect of insulin was diminished by 12% +/- 4% in aortae from INS-T DIA group. The presence of PIO in the bath did not affect impaired vasodepressor response of insulin. Contractions induced by KCl, or Bay K 8644 were partly inhibited after PIO incubations, with similar E(max) and pD(2) values in both groups of aortae. The results indicate that PIO does not modulate directly vasodepressor effect of insulin in hyperinsulinaemic/diabetic state. But, the direct vasodepressor effect of PIO, partly by Ca(2+) channel inhibition, may be beneficial by improving insulin utilization due to increasing blood flow to the insulin-sensitive tissues in hyperinsulinaemic/diabetic state.

Simvastatin treatment restores vasoconstriction and the inhibitory effect of LPC on endothelial relaxation via affecting oxidizing metabolism in diabetic rats.

Oxidative stress and dyslipidaemia play an important role in the development of diabetes-induced vascular complications. The aim of this study was to examine the reversal effects of simvastatin on some metabolic and oxidative parameters, and vascular functions in diabetic rats. Diabetes was induced by a single injection of streptozotocin (STZ, 45 mg/kg, i.p.). Eight weeks after STZ induction, some of the diabetic and control rats were treated with simvastatin (10 mg/kg rat/d) for 4 weeks. Plasma glucose, triglyceride and total cholesterol concentrations were significantly increased in 12-week diabetic rats. Simvastatin treatment stopped the loss of body weight, completely normalized the increase of plasma lipids and partially reduced the hyperglycaemia in diabetic rats. Increased malondialdehyde levels, catalase and glutathione peroxidase activities were normalised by simvastatin treatment in diabetic aorta. Phenylephrine (PE)-induced contractility in aorta rings was unaffected by diabetes, but was markedly decreased after simvastatin treatment in both control and diabetic rats. Reduction of endothelium-dependent vasorelaxation in diabetes was significantly ameliorated by simvastatin treatment. Incubation of aorta rings with lysophosphatidylcholine, a component of the oxidized LDL, did not significantly affect PE-induced contractions, but reduced endothelium-dependent relaxations more in untreated-diabetic rats than in other experimental groups. The endothelium-independent vasorelaxations were similar in all ring preparations. These results indicate that simvastatin treatment may ameliorate diabetes-induced abnormal vasoconstriction and endothelial dysfunction via affecting general and oxidizing metabolism, nitric oxide disability and intracellular calcium mobilisation.

Effects of gemfibrozil treatment on vascular reactivity of streptozotocin-diabetic rat aorta.

The effects of gemfibrozil treatment on plasma lipids, lipid peroxides and vascular reactivity of aorta were investigated in diabetic rats. Rats were divided randomly into two groups: control and diabetic. Diabetes was induced by a single intraperitoneal injection of streptozotocin (45 mg kg(-1)). Twelve weeks after the induction of diabetes, some of the control and diabetic rats were started treatment with gemfibrozil (100 mg kg(-1) daily; gavage) for 2 weeks. Blood glucose, plasma triglyceride, cholesterol, low-density lipoprotein (LDL) cholesterol and thiobarbituric acid reactive substances (TBARS) levels were markedly increased and gemfibrozil treatment restored these parameters in diabetic rats. However high-density lipoprotein (HDL) cholesterol levels did not differ in all experimental groups. In diabetic rats, the endothelium-dependent relaxations to acetylcholine were decreased when compared with control rats. Gemfibrozil treatment restored the endothelium-dependent responses to acetylcholine in diabetic rats. The endothelium-independent relaxation responses to sodium nitroprusside were not altered in all groups. These findings suggest that gemfibrozil treatment has beneficial effects against cardiovascular and metabolic complications of diabetes via its hypolipidaemic and antioxidant properties.

Effects of simvastatin treatment on oxidant/antioxidant state and ultrastructure of diabetic rat myocardium.

In the present study we investigated the effects of simvastatin treatment on lipid metabolism and peroxidation, antioxidant enzyme activities and ultrastructure of the diabetic rat myocardium. Diabetes was induced by single injection of streptozotocin (45 mg/kg i.p.). Eight weeks after induction of diabetes, a subgroup of control and of diabetic rats was treated with simvastatin for 4 weeks (10 mg/kg/day, orally). Blood glucose, plasma cholesterol and triacylglycerol, as well as levels of cardiac thiobarbituric acid reactive substances (TBARS) were significantly increased in diabetic rats. The activities of antioxidant enzymes, catalase (CAT) and glutathione peroxidase (GSHPx), were also elevated in the diabetic myocardium. Treatment with simvastatin markedly reduced serum triacylglycerol and cholesterol, and partially controlled hyperglycemia in diabetic animals. The increased activation of antioxidant enzymes and the excess of lipid peroxidation measured by TBARS were completely reversed by simvastatin treatment. Diabetic rats displayed ultrastructural ischemia-like alterations of cardiomyocytes and capillaries, which support oxidative stress-induced tissue remodelling. In the diabetic myocardium simvastatin treatment partly attenuated angiopathic and atherogenic processes, detected by electron microscopy. These results suggest that simvastatin, known as a lipid-lowering drug, may positively affect diabetes induced cardiovascular complications via reducing risks of atherosclerotic pathological processes, such as imbalance between oxidant and antioxidant state.

Short-term gemfibrozil treatment reverses lipid profile and peroxidation but does not alter blood glucose and tissue antioxidant enzymes in chronically diabetic rats.

In this study, we investigated the efficiency of short-term treatment with gemfibrozil in the reversal of diabetes-induced changes on carbohydrate and lipid metabolism, and antioxidant status of aorta. Diabetes was induced by a single injection of streptozotocin (45 mg/kg, i.p.). After 12 weeks of induction of diabetes, the control and diabetic rats were orally gavaged daily with a dosing vehicle alone or with 100 mg/kg of gemfibrozil for 2 weeks. At 14 weeks, there was a significant increase in blood glucose, plasma cholesterol and triglyceride levels of untreated-diabetic animals. Diabetes was associated with a significant increase in thiobarbituric acid reactive substances (TBARS) in both plasma and aortic homogenates, indicating increased lipid peroxidation. Diabetes caused an increase in vascular antioxidant enzyme activity, catalase, indicating existence of excess hydrogen peroxide (H2O2). However, superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) activities in aortas did not significantly change in untreated-diabetic rats. In diabetic plus gemfibrozil group both plasma lipids and lipid peroxides showed a significant recovery. Gemfibrozil treatment had no effect on blood glucose, plasma insulin and vessel antioxidant enzyme activity of diabetic animals. Our findings suggest that the beneficial effect of short-term gemfibrozil treatment in reducing lipid peroxidation in diabetic animals does not depend on a change of glucose metabolism and antioxidant status of aorta, but this may be attributed to its decreasing effect on circulating lipids. The ability of short-term gemfibrozil treatment to recovery of metabolism and peroxidation of lipids may be an effective strategy to minimize increased oxidative stress in diabetic plasma and vasculature.

Changes in isoprenaline-induced endothelium-dependent and -independent relaxations of aorta in long-term STZ-diabetic rats: reversal effect of dietary vitamin E.

1. The present study concerns in vitro isoprenaline (ISO)-induced relaxation of aortic rings of long-term streptozotocin (STZ)-diabetic and nondiabetic rats, both with and without dietary vitamin E supplementation. 2. Incubation with propranolol, NG-nitro-L-arginine methyl ester and methylene blue, as well as absence of endothelium, all negatively affect the ISO-induced relaxations. 3. Thiobarbituric acid reactivity levels used as an index of lipid peroxidation are elevated in the aorta by diabetes. Four months of STZ-diabetes results in a significant increase in the ISO-induced relaxations together with endothelial dysfunction in the rat aorta. Diabetes also causes the loss of vascular integrity. 4. Dietary vitamin E supplementation during the last 2 months of diabetes allows normalization of the levels of lipid peroxides. This vitamin also completely reverses the increased sensitivity (pD2 value) of the aorta to ISO, whereas the maximum ISO-induced relaxations are partially restored after the treatment in diabetic rats. 5. The results suggest that ISO-induced relaxation in the aorta partially depends on the intact endothelium and that the endothelium-dependent relaxant effect of ISO is mediated by endothelium-derived relaxing factor. Results also indicate that abnormal vascular reactivity and structure of the diabetic rat aorta may be related to the increased lipid peroxidation. In conclusion, vitamin E can protect the arterial wall from oxidative stress-induced injury associated with chronic STZ-diabetes and allows normalization of the response to ISO and the structure of the aorta in diabetic rats.

Antioxidant and triglyceride-lowering effects of vitamin E associated with the prevention of abnormalities in the reactivity and morphology of aorta from streptozotocin-diabetic rats. Antioxidants in Diabetes-Induced Complications (ADIC) Study Group.

In this study, we evaluated the effects of vitamin E on the vascular reactivity and structure of thoracic aorta from streptozotocin (STZ)-diabetic rats. Plasma glucose, cholesterol, and triglyceride concentrations in rats were increased markedly by STZ-diabetes. The thiobarbituric acid (TBA) reactivity level as an index of lipid peroxidation was higher in both plasma and aorta of STZ-diabetic rats compared with controls. The rings of thoracic aorta with or without endothelium were mounted in organ chambers for measurement of isometric tension and were contracted by a single dose (10-5 mol/L) and then cumulative doses of noradrenaline ([NA] 10(-9) to 10(-5) mol/L). Pretreatment with methylene blue (MB) or removal of the endothelium resulted in a similar degree of enhancement in NA-induced contraction of control rings. STZ-diabetes increased the fast and slow components of NA-induced contraction in all experiments. The maximal contractile response of aorta to NA was also augmented by STZ-diabetes, whereas the sensitivity (pD2) remained unaltered. STZ-diabetes resulted in significant increases in the maximum contractile response and sensitivity of aorta to KCl. STZ-diabetic rats showed a significant reduction in the percentage of endothelial response (PER). A group of diabetic rats was treated from the time of diabetes induction with a 0.5% dietary supplement of vitamin E. Vitamin E supplementation of STZ-diabetic rats eliminated accumulation of lipid peroxides and returned plasma triglycerides toward normal levels. Diabetes-induced abnormal contractility and endothelial dysfunction were significantly but not completely prevented by vitamin E treatment. The endothelium-independent relaxation response to sodium nitroprusside (SNP) was not affected by diabetes or vitamin E treatment. Electron microscopic examination of thoracic aorta revealed that normal tissue organization was disrupted in STZ-diabetic rats, and that vitamin E treatment can protect the morphological integrity of aorta against STZ-diabetes. The results suggest the following: (1) The increased triglycerides/lipid peroxides may be an important reason for morphological or functional disruption of endothelium and enhanced activation of contractile mechanisms of vascular smooth muscle in STZ-diabetic rats. Both contribute to an increased responsiveness of diabetic aorta to vasoconstrictor agents. (2) Vitamin E treatment of STZ-diabetic rats can prevent the development of abnormal contractility and structure and endothelial dysfunction in aorta. (3) The triglyceride- and/or lipid peroxidation-lowering effect of vitamin E may be crucial for the protective effect of this vitamin on the vasculature.

The effect of oral vanadyl treatment on the reactivity of tracheal smooth muscle obtained from insulin-dependent diabetic rats.

1. In this study, we investigated the contractile effects of acetylcholine (ACh) and KCl in tracheas obtained from 12-13 wk insulin-dependent (ID)-diabetic rats. 2. The maximum contractile responses to ACh and KCl were significantly increased in ID-diabetic rat tracheas compared with those from controls. But the sensitivity (pD2 values) of ID-diabetic tracheas to these agents were not significantly altered relative to controls. 3. The alterations which occurred in ID-diabetic rats were prevented with oral vanadyl treatment during a 10 wk period.

The effects of acetylcholine on insulin-dependent and non-insulin-dependent diabetic rat tracheal segments.

1. In the present study, the contractile effects of acetylcholine (Ach) were investigated in isolated tracheal strips obtained from insulin-dependent (ID) and non-insulin-dependent (NID) diabetic rats. 2. The maximum responses to Ach were significantly decreased in 5-6 week ID diabetic rat tracheal segments compared with those from controls but, the sensitivity (pD2 values) of ID diabetic tracheas to Ach were not significantly altered relative to corresponding controls. 3. Tracheas isolated from 11-12 week NID diabetic rats exhibited reduced maximal contractile effect of Ach and also sensitivity (pD2 values) of NID diabetic tracheas to Ach were significantly decreased when compared to control rat tracheas. 4. Insulin treatment of both group of diabetic rats for 10 days corrected the changes observed in diabetic tracheas.