Influence of 6-week exercise training on erythrocyte and liver antioxidant defense in hyperinsulinemic rats.

High dosage of fructose in rats causes insulin resistance and hyperinsulinemia. This study investigates the effect of physical exercise on oxidant-antioxidant balance in rats fed a high fructose diet, which show characteristic features of insulin resistance. Products of lipid peroxidation and the activity of enzymic antioxidants namely superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase, in red blood cells (RBCs) and liver were assayed. Levels of non-enzymic antioxidants alpha-tocopherol and ascorbic acid and of protein and non-protein thiols were also determined. The levels of lipid peroxides, diene conjugates, lipofuscin and hydroperoxides were significantly higher in the liver of fructose-fed rats. The RBCs showed significantly higher susceptibility to H(2)O(2)-induced stress compared to control rats. Inadequate antioxidant system was noted in high fructose-fed rats. Physical training to these rats reversed the adverse effects, which could be important in alleviating the pathological consequences of insulin resistance.

Taurine modulates antioxidant potential and controls lipid peroxidation in the aorta of high fructose-fed rats.

High dosage of fructose induces insulin resistance, glucose intolerance and alterations in plasma lipid profile in normal rats. Recently, it has been shown that these rats also develop oxidative stress, which plays a prominent role in diabetic pathology. We now report the effect of taurine on the susceptibility of the aorta to lipid peroxidation and also on the activities of enzymic and non-enzymic antioxidants in rats fed a high fructose-diet for 4 weeks. Fructose-fed rats were more susceptible to lipid peroxidation as measured by thiobarbituric acid reactivity, and antioxidant status was significantly lower. Taurine supplementation caused a significant reduction in the production of thiobarbituric acid--reactive substances and significant rises in antioxidant enzyme activities. The levels of lipid peroxides, diene conjugates, lipofuscin and hydroperoxides were significantly higher in fructose-fed rats. When these rats received taurine in drinking water, no peroxidative changes were observed. Increased aorta lipid peroxidation could play a role in the pathology associated with fructose-feeding, and taurine reduces the lipid peroxidation by inducing antioxidant enzymes.

Response of liver antioxidant system to taurine in rats fed high fructose diet.

Fructose-fed rats were more susceptible to peroxidative damage as measured by thiobarbituric acid reactive species. The concentrations of lipid peroxides, diene conjugates, lipofuscin and hydroperoxides were significantly higher. The levels of enzymic antioxidants such as vitamin C, vitamin E and glutathione and activities of antioxidant enzymes were significantly lower in fructose-fed rats. When these rats received taurine in drinking water, peroxidative damage was minimal in both plasma and liver. Taurine was effective in inducing the antioxidant potential in fructose-fed rats. Increased peroxidative damage in liver is likely to be associated with fructose dependent pathology, which could be reduced by taurine by enhancing the antioxidant potential.

Taurine attenuates hypertension and improves insulin sensitivity in the fructose-fed rat, an animal model of insulin resistance.

Fructose feeding induces moderate increases in blood pressure levels in normal rats, which is associated with hyperinsulinemia, insulin resistance, and impaired glucose tolerance. Increased vascular resistance, sodium retention, and sympathetic overactivity have been proposed to contribute to the blood pressure elevation in this model. Taurine, a sulphur-containing amino acid, has been reported to have antihypertensive and sympatholytic actions. In the present study, the effects of taurine on blood pressure, plasma levels of glucose and insulin, glucose tolerance, and renal function were studied in fructose-fed rats. Fructose-fed rats had higher blood pressure and elevated plasma levels of insulin and glucose. The plasma glucose levels were higher in fructose-fed rats than in controls at 15, 30, and 60 min after the oral glucose load. Treatment with 2% taurine in drinking water prevented the blood pressure elevation and attenuated the hyperinsulinemia in fructose-fed rats. The exaggerated glucose levels in response to the oral glucose load was also prevented by taurine administration. Thus, taurine supplementation could be beneficial in circumventing metabolic alterations in insulin resistance.

Exercise, depletion of antioxidants and antioxidant manipulation.

Strenuous physical activity is known to increase the production of reactive oxygen species (ROS), associated with depletion of antioxidant defence. In the present work we evaluated the level of lipid peroxidation and antioxidant components in blood of sportsmen under resting conditions and compared the data obtained with those in age- and sex-matched sedentary controls. A significant increase was noted in the levels of thiobarbituric acid reactive substances (TBARS) and conjugated dienes while a decrease was observed in ascorbic acid and glutathione levels in sportsmen. alpha-Tocopherol was unaltered in plasma of sportsmen as compared to controls. The activity of superoxide dismutase was increased (52 per cent) and glutathione peroxidase was decreased (43 per cent) in the erythrocytes of sportsmen compared to controls. Basal glutathione levels were negatively correlated with conjugated dienes and maximal oxygen uptake (VO2max) of the subjects. Dietary supplementation with antioxidant vitamins has been shown to be beneficial in combating oxidative stress without enhancing performance while exogenous glutathione was found to influence the endurance capacity of athletes. Such studies demonstrate the critical role played by glutathione and suggest that intervention trials should include a mixture of antioxidants rather than a single antioxidant.

Effect of training on lipid peroxidation, thiol status and antioxidant enzymes in tissues of rats.

The effect of training on lipid peroxidation, thiol-status and certain antioxidant enzymes of glutathione system was studied in blood and tissues such as liver and skeletal muscle of rats. Exercise training was given by subjecting the rats to treadmill running. Training for a period of 6 weeks resulted in increased lipid peroxidation (P < 0.001) as indicated by thiobarbituric acid test and conjugated diene measurement in liver and muscle. Thiol levels (total and non-protein) were reduced. However, glutathione level in blood was increased and blood lipid peroxides were unaltered as a result of training compared to sedentary controls. Adaptive increases in three antioxidant enzyme activities were observed. The study indicates that training induces adaptation in the glutathione system.