Effect of hyperoxia acclimation on catalase and glutathione peroxidase activities and in vivo peroxidation products in various tissues of the frog Rana ridibunda perezi

Among vertebrates, adult amphibians are known to be especially tolerant to exposure to high environmental oxygen tensions. To clarify the basis for this high O2 tolerance, adult Rana ridibunda perezi frogs were acclimated for 15 days to water-air phases with either 149 mm Hg O2 (normoxia) or 710 mm Hg O2 (hyperoxia). At the end of the acclimation, various morphometric and biochemical parameters related to oxidative stress were measured in seven organs and tissues. Hyperoxia acclimation did not change either the total weight of the animals or the total and relative wet weights of the organs studied, except for the brain, which showed weight increases in the hyperoxic group. In vivo tissue peroxidation increased in the kidney; decreased in the skeletal muscle and skin; and did not change in the liver, lung, brain, and heart after hyperoxic exposures. Whereas liver, lung, and skin showed glutathione peroxidase (GSH-Px) activities with both cumene hydroperoxide (cumene-OOH) and H2O2 as substrates, skeletal muscle only showed H2O2 GSH-Px activity. Hyperoxia acclimation did not change either catalase (CAT) or GSH-Px activities in any organ, except for the liver in which CAT activity was induced by hyperoxia. Thus hyperoxia tolerance in this species does not need the induction of H2O2-detoxifying enzymes in the majority of the organs. It is suggested that the high O2 tolerance of this amphibian species is related to its comparatively high constitutive GSH-Px activities.     

Different levels of hyperoxia reversibly induce catalase activity in amphibian tadpoles

Studies about the proposed antioxidant physiological role of the catalase (CAT) enzyme in relation to different environmental oxygen tensions are reported for the first time in amphibian larvae of Discoglossus pictus and Rana ridibunda perezi during their development. The CAT levels of whole tadpoles increased constantly in both species during the larval period, reaching a maximum during the metamorphic climax. All through development, CAT activity levels were always greater in D. pictus than in R. ridibunda perezi. This correlates well with the already reported higher SOD activity and hyperoxia resistance of the D. pictus species when compared to R. ridibunda perezi. Long-term acclimation to different levels of hyperoxia (40, 60, and 100% O2) showed dose-related increases in the CAT activity of D. pictus tadpoles. These increases did not take place when the animals were subjected to acute hyperoxia (24 h). The increase in CAT activity observed after 15 days of acclimation to acute hyperoxia (710 mm Hg: 100% O2) was reversed after 15 additional days of postacclimation to normal air (149 mm Hg O2). When recently metamorphosed frogs were acclimated to acute hyperoxia, significant increases in CAT activity were observed after 15 days, but not after 7 days. The results are interpreted as supporting a protective role for the CAT enzyme in amphibian larvae and froglets against oxygen toxicity.     

Hyperoxia decreases lung size of amphibian tadpoles without changing GSH-peroxidases or tissue peroxidation

1. During the development of D. pictus larvae (Amphibia) in normoxia, selenium (Se) GSH-Px increased whereas non-Se GSH-Px did not change. 2. Acclimation to 60 or 100% O2 did not change Se GSH-Px or non-Se GSH-Px. 3. Hyperoxia did not change tissue peroxidation (TBA-RS) confirming the good capacity of D. pictus tadpoles for O2-adaptation. 4. Since hyperoxic induction of catalase (CAT) has been previously described in D. pictus tadpoles, it is concluded that CAT is more important than both GSH-Px for the establishment of O2-adaptation. 5. Increases of Se GSH-Px, SOD and CAT, are probably important for adaptation to the change from aquatic to aerial environment during metamorphosis in normoxia. 6. Chronic exposure to 100% O2 enormously reduced the lung size of D. pictus larvae.     

mRNA expression of antioxidant enzymes (SOD, CAT and GSH-Px) and lipid peroxidative stress in liver of Atlantic salmon (Salmo salar) exposed to hyperoxic water during smoltification

The mRNA levels of three antioxidant genes, Cu/Zn superoxide dismutase (SOD), catalase (CAT) and phospholipid hydroperoxide glutathione peroxidase (GSH-Px), were quantified with real-time qRT-PCR in liver of Atlantic salmon Salmo salar exposed to 80% (normoxia), 105% and 130% O2 saturation for 54 days. The salmon were then translocated and exposed to 90% and 130% O2 saturation for additional 72 days during smoltification. TBARS and vitamin E levels in liver and the levels of oxidized glutathione (GSSG), total glutathione (GSH) and the resulting oxidative stress index (OSI) in blood were quantified as traditional oxidative stress markers. No significant mean normalized expression (MNE) differences of SOD, CAT or GSH-Px were found in liver after hyperoxia exposure at the two sampling times. Significantly decreased OSI was found in smolt exposed to 130% O2 saturation after 126 days (n = 18, P < 0.0001), indicating hyperoxia-induced oxidative stress. No effects were seen on growth, or on the levels of thiobarbituric reactive substances (TBARS) and vitamin E in liver after the exposure experiment. Overall, the mRNA expression of SOD, CAT and GSH-Px in liver related poorly with the hyperoxic exposure regimes, and more knowledge are needed before the expressed levels of these antioxidant genes can be applied as biomarkers of hyperoxia in Atlantic salmon.     

Effect of oxygen and endotoxin on lactate dehydrogenase release, 5-hydroxytryptamine uptake, and antioxidant enzyme activities in endothelial cells

We compared the effects of 95% O2 (hyperoxia) alone, endotoxin (20 ng/ml) alone, and 95% O2 plus endotoxin on the release of lactate dehydrogenase (LDH), uptake of 5-hydroxytryptamine (5-HT), and antioxidant enzyme activities in porcine pulmonary arterial and aortic endothelial cells in monolayer culture. Hyperoxia increased LDH release and decreased 5-HT in both endothelial cell types. Hyperoxia also caused a decrease in catalase (CAT) activity and an increase in total superoxide dismutase (SOD) and glutathione reductase (GSH-Red) activities in both cell types. Endotoxin alone had no effect on LDH release, 5-HT uptake, or antioxidant enzyme activities. However, endotoxin prevented the hyperoxic increase in LDH release and the hyperoxic decrease in 5-HT uptake. Endotoxin plus 95% O2 had no consistent effect on the antioxidant enzyme profile in pulmonary artery or aortic endothelial cells. These results indicate that (1) hyperoxia injures both pulmonary artery and aortic endothelial cells in culture and causes changes in the antioxidant enzyme profile that are similar in the two cell types; (2) hyperoxia-induced decreases in CAT activity and increases in SOD activity may be responsible for increased sensitivity of endothelial cells to O2 toxicity; and (3) endotoxin protects against hyperoxic injury to endothelial cells in vitro, but increases in antioxidant enzyme activities are not the mechanism for this protection.     

辐射所致小鼠肾脏氧化损伤及川芎嗪的保护作用

目的:研究川芎嗪对辐射所致小鼠肾脏氧化损伤的预防和治疗作用。方法:采用60Co-γ射线5 Gy全身单次照射小鼠造模,在照射前和照射后分别于每天腹腔注射川芎嗪130 mg/kg,连续给药10 d,进行预防和治疗,并设对照组,观察肾组织中丙二醛(MDA)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、还原型谷胱甘肽(GSH)、谷胱甘肽过氧化物酶(GSH-Px)及总抗氧化力(T-AOC)的变化。结果:与阴性对照组比较,照射可显著增加肾组织中MDA的含量(P<0.05),降低SOD、CAT的活性(P<0.05),升高GSH-Px活性(P<0.05),降低GSH含量(P<0.05),使肾组织T-AOC下降(P<0.05),。与照射组比较,给予川芎嗪预防和治疗后,均可降低肾组织MDA含量(P<0.05),升高肾组织T-AOC(P<0.05),且治疗组优于预防组,与阴性对照组无显著性差异。同时,预防组可使SOD活性和GSH含量升高(P<0.05),治疗组可使SOD和CAT活性增高(P<0.05),但均对GSH-Px活性无显著影响(P>0.05)。结论:川芎嗪具有很好的抗氧化作用,无论预防和治疗均可降低辐射所致小鼠肾脏的氧化应激损伤,并且治疗效果优于预防效果。     

17β-Estradiol and Vitamin E Modulates Oxidative Stress-Induced Kidney Toxicity in Diabetic Ovariectomized Rat

The aim of this study was to investigate the effects of vitamin E (alpha-tocopherol) and 17β-estradiol (E(2)) supplementation on malondialdehyde (MDA), glutathione (GSH), vitamin A, beta carotene, selenium-dependent glutathione peroxidase (GSH-Px), zinc-dependent superoxide dismutase (SOD), and copper/zinc-dependent catalase (CAT) values in the kidney of ovariectomized (OVX) diabetic rats. Forty-two female rats were randomly divided into seven equal groups as follows: group I, control; group II, OVX; group III, OVX+E(2); group IV, OVX+E(2)+alpha-tocopherol; group V, OVX+diabetic; group VI, OVX+diabetic+E(2); and group VII, OVX+diabetic+E(2)+alpha-tocopherol. E(2) (40?μg?kg(-1)/day) and alpha-tocopherol (100?μg?kg(-1)/day) were given. Bilateral ovariectomy was performed in all groups except group I. After 4?weeks, antioxidant and MDA levels in the kidney for all groups were analyzed. GSH-Px, CAT, SOD, GSH levels, vitamin A, and beta carotene levels were decreased in OVX group compared to those in the control group but MDA level was elevated via ovariectomy. However, E(2) and E(2)+alpha-tocopherol supplementations in OVX group was associated with an increase in the GSH-Px, GSH, CAT and Zn-SOD values, vitamin A, and beta carotene levels but a decrease in MDA levels in kidney. The MDA levels in the kidney of diabetic OVX rats were found higher than those in the control and OVX groups. However, GSH, GSH-Px, CAT, SOD, vitamin A, and beta carotene levels in kidney were lower in OVX diabetic rats. On the other hand, E(2) and E(2)+alpha-tocopherol supplementations to OVX diabetic rats have caused an increase in GSH-Px, CAT and SOD, GSH, vitamin A, and beta carotene levels but a decrease in MDA levels. In conclusion, the E(2) and E(2)+alpha-tocopherol supplementations to diabetic OVX and OVX rats may strengthen the antioxidant defense system by reducing lipid peroxidation, and therefore they may play a role in preventing renal disorders.     

Protective effect of chelerythrine on gentamicin-induced nephrotoxicity

Despite their beneficial effects, aminoglycosides including gentamicin (GEN) have considerable nephrotoxic side-effects. The toxicity of GEN at the level of the kidney seems to relate to the generation of reactive oxygen species (ROS). ROS have been reported to be involved in the activation of protein kinase C (PKC). The unique structural aspects of PKC cause it to function as a sensor for oxidative stress. It seems likely that the increased NAD(P)H oxidase-derived superoxide (O2) production is at least in part mediated by PKC. We investigated the effects of chelerythrine, a commonly used PKC inhibitor, on GEN-induced changes of renal malondialdehyde (MDA), nitric oxide (NO) generation, catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) activities, glutathione (GSH) content, and serum creatinine (Cr), blood urea nitrogen (BUN) levels. Morphological changes in the kidney were also examined. GEN administration to control rats increased MDA and NO generation but decreased CAT, SOD and GSH-Px activities, and GSH content. Chelerythrine administration with GEN caused significantly decreased MDA, NO generation and increased CAT, SOD and GSH-Px activities, and GSH content when compared with GEN alone. Chelerythrine also significantly decreased serum Cr and BUN levels. Morphological changes in the kidney including tubular necrosis were evaluated qualitatively. Both biochemical findings and histopathological evidence showed that administration of chelerythrine reduced the GEN-induced kidney damage. We propose that chelerythrine acts in the kidney as a potent scavenger of free radicals to prevent the toxic effects of GEN via the inhibition of a PKC pathway.     

Physiological significance of catalase and glutathione peroxidases,and in vivo peroxidation,in selected tissues of the toadDiscoglossus pictus (Amphibia) during acclimation to normobaric hyperoxia

1. Various parameters related to oxidative stress were measured in adult Discoglossus pictus acclimated for 15 days to either normoxia or hyperoxia (PO2 = 710 mmHg). 2. Total weight of the toads and total and relative wet weight of liver, kidneys, lungs and heart were not changed by hyperoxic acclimation. 3. In vivo tissue peroxidation increased in lung, decreased in skeletal muscle, and was not changed in liver, kidney, heart and skin after hyperoxic exposure. 4. Hyperoxic acclimation increased catalase activities in the lung, liver, kidney and heart but not in skeletal muscle and skin. 5. Liver showed higher GSH-peroxidase activity with cumene-OOH than with H2O2 as substrate, whereas lung, skeletal muscle and skin presented similar GSH-peroxidase activities with both substrates. 6. GSH-peroxidase activities did not change between hyperoxic and normoxic animals in liver, lung, skeletal muscle and skin. 7. These results show that catalase, not GSH-peroxidase, is the principal H2O2 detoxifying enzyme involved in the adaptation of D. pictus to hyperoxia.     

黑斑蛙精巢MDA和抗氧化酶对铅、镉暴露的生态毒性响应

以健康性成熟黑斑蛙为供试动物,以精巢组织丙二醛(MDA)含量、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽过氧化物酶(GSH-Px)活性为指标,进行了水体铅、镉暴露的生态毒性响应研究.结果表明:(1)精巢MDA含量随铅、镉暴露浓度的升高而明显增加,且呈明显的浓度-效应关系.说明低水平铅、镉的长期暴露对黑斑蛙精巢具有一定的损伤作用;(2)SOD活性在各处理组响应变化不明显,CAT、GSH-Px活性则被显著诱导,说明GSH-Px、CAT在铅、镉引起的精巢抗氧化损伤中起着重要作用;(3)3种抗氧化酶相比,GSH-Px活性对铅、镉暴露响应最敏感,SOD活性的响应最不明显,精巢GSH-Px活性是指示铅、镉暴露的优选生物标志物。     

Species variation in lung antioxidant enzyme activities

Exposure of several different animal models to O2-induced lung injury has revealed marked differences in sensitivity of various species to O2 damage. These differences may be due in part to variation of cellular antioxidant defenses. To characterize lung antioxidant enzyme activities in different species, we measured lung activities of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GSH S-trans) in rat, hamster, baboon, and human lung. Soluble lung fractions were also fractionated on Sephadex G-150-S columns and GSH-Px activity was measured using both cumene hydroperoxide and H2O2. This was done to evaluate non-Se-dependent GSH-Px activity in these lung samples. Human lung was obtained at surgery from patients undergoing lobectomy or pneumonectomy for localized lung tumors. SOD activity was similar for all four groups. GSH-Px activity was higher in rat lung than baboon or hamster lung. Lung CAT activity was variable with the highest activity present in the baboon which revealed a lung CAT activity 10 times higher than activity present in the rat. Lung GSH S-trans activities were higher in hamster, baboon, and human lung than in rat lung. Non-Se-dependent GSH-Px was present in rat lung but absent in hamster, baboon, and human lung. We conclude that the hamster was the best model of the animals studied for mimicking human lung antioxidant enzyme activities. Rat lung antioxidant enzyme activities were markedly different from any of the other species examined.     

Lipid peroxidation and activity of antioxidant enzymes in diabetic rats

We hypothesized that oxygen free radicals (OFRs) may be involved in pathogenesis of diabetic complications. We therefore investigated the levels of lipid peroxidation by measuring thiobarbituric acid reactive substances (TBARS) and activity of antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT)] in tissues and blood of streptozotocin (STZ)-induced diabetic rats. The animals were divided into two groups: control and diabetic. After 10 weeks (wks) of diabetes the animals were sacrificed and liver, heart, pancreas, kidney and blood were collected for measurement of various biochemical parameters. Diabetes was associated with a significant increase in TBARS in pancreas, heart and blood. The activity of CAT increased in liver, heart and blood but decreased in kidney. GSH-Px activity increased in pancreas and kidney while SOD activity increased in liver, heart and pancreas. Our findings suggest that oxidative stress occurs in diabetic state and that oxidative damage to tissues may be a contributory factor in complications associated with diabetes.     

Polyethylene glycol-attached antioxidant enzymes decrease pulmonary oxygen toxicity in rats

When exposed continuously to hyperoxia (100% O2, 760 Torr barometric pressure), rats pretreated with polyethylene glycol (PEG)-attached superoxide dismutase and catalase (PEG-SOD + PEG-CAT) lived longer (79.1 + 7.6 h) than rats pretreated with saline (60.7 +/- 2.1 h) or PEG-inactivated-SOD + PEG-inactivated-CAT (62.3 +/- 1.6 h). Rats pretreated with PEG-SOD + PEG-CAT also had less hyperoxia-induced acute oxidative edematous lung injury, as assessed by increases in lung oxidized glutathione (GSSG) contents, pleural effusions, and lung lavage albumin concentrations than saline-pretreated rats. Rats pretreated with the long-lived conjugates PEG-inactivated-SOD + PEG-inactivated-CAT or PEG-albumin also had decreased acute oxidative edematous lung injury compared with rats pretreated with PEG, SOD + CAT + PEG, SOD + CAT, or saline. In vitro studies suggested that PEG itself may have contributed to protection by scavenging hydroxyl radical (.OH) but not superoxide (O2-.) or H2O2. Compared with more effective endogenous (via preexposure to hypoxia) or exogenous (via liposomes) means for increasing lung antioxidant enzymes, PEG enzymes are less protective against lung injury from continuous hyperoxia.     

Antioxidant defenses and biochemical changes in pacu (Piaractus mesopotamicus) in response to single and combined copper and hypoxia exposure

The effect of combined-factors (hypoxia+copper) on the biochemical parameters and antioxidant defenses were studied in the neotropical fish Piaractus mesopotamicus. Fish were exposed for 48 h to 0.4 mg Cu(2+) L(-1) (0.4Cu), hypoxia=50 mm Hg (Hpx), and 0.4 mg Cu(2) L(-1)+hypoxia=50 mm Hg (0.4CuHpx). The exposure to 0.4Cu increased the reactive oxygen species (ROS) in the liver, accompanied by increases in superoxide dismutase (SOD) and decreases in catalase (CAT) activity, showing the influence of copper in this protection. The exposure to Hpx decreased the activity of glutathione peroxidase (GSH-Px) and CAT. Exposure to a combined-factor caused an increase in the ROS production followed by an increase in SOD and a decrease in GSH-Px and CAT. At 0.4Cu, fish presented a reduction in CAT, while in Hpx decreases in SOD, CAT and GSH-Px were observed in red muscles. Single-factors were insufficient to cause ROS production. In combined-factors, increased ROS formation and decreased SOD, CAT and GSH-Px were observed. RBC increased in all groups, but only under combined-factors was there an increase in hemoglobin. Copper plasma concentration increased in groups exposed to copper. Na(+)/K(+)-ATPase activity in gills decreased in 0.4Cu and 0.4CuHpx, and increased in Hpx. Metallothionein concentration in gills increased under combined-factors. Combined-factors caused significant disturbances in the antioxidant defenses and biochemical parameters than single-factors.     

镉对长江华溪蟹精巢抗氧化酶活性及脂质过氧化的影响

在实验条件下,将健康性成熟雄性长江华溪蟹Sinopotamon yangtsekiense暴露于0、7.25、14.5、29、58和116 mg/L浓度的镉(Cd2+)溶液中,分别于1 d、3 d、5 d和7 d时测定精巢中超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)、过氧化氧酶(CAT)活性及脂质过氧化产物丙二醛(MDA)的含量.结果显示,不同时间段3种酶活性和MDA含量均具有浓度和时间效应关系,表明急性镉暴露对精巢有明显的毒性作用,其作用机制与抗氧化酶活力变化和脂质过氧化加剧有关.     

Protection of PC12 cells from hydrogen peroxide-induced injury by EPS2, an exopolysaccharide from a marine filamentous fungus Keissleriella sp. YS4108

A number of studies indicate that free radicals are involved in the neurodegeneration in Parkinson's and Alzheimer's diseases. EPS2, an exopolysaccharide with a mean molecular weight of 1.3 x 10(5) Da, was isolated by ion-exchange and sizing chromatography from the culture of Keissleriella sp. YS4108, a marine filamentous fungus. Compositionally, it is composed of galactose, glucose, rhamnose, mannose and glucuronic acid in an approximate proportion of 50:8:1:1:0.4. The protective effects of EPS2 on peroxide hydrogen (H2O2)-induced cell lesion, level of lipid peroxidation, antioxidant enzyme activities were investigated in the rat pheochromocytoma line PC12 cells. Following a 1-h exposure of the cells to H2O2, a significant reduction in cell survival and activities of glutathione peroxidase (GSH-Px) and catalase (CAT), as well as increased levels in malondialdehyde (MDA) production and lactate dehydrogenase (LDH) release were observed. However, preincubation of the cells with EPS2 prior to H2O2 exposure elevated the cell survival and GSH-Px and CAT activities, and decreased the level of MDA and LDH activity in a dose-dependent manner. In conclusion, EPS2 possesses pronounced protective effects against H2O2-induced cell toxicity. The finding is of a higher value in searching for new therapeutic agent for treating oxidative damage-derived neurodegenerative disorders.     

Superoxide dismutase, glutathione peroxidase, catalase, and lipid peroxidation in the major organs of the aging rats

Glutathione peroxidase (GSh-Px), superoxide dismutase (SOD), catalase (CAT) activities and malon-dialdehyde (MDA) content were determined in heart, liver, kidney and brain of rats. Two different age groups (4 months; 24 months) were considered. GSH-Px and SOD activities decrease significantly for the aged liver and kidney. During aging, the activity of catalase increase in cardiac muscle and, in contrast, decrease in other organs. Lipids peroxidation, expressed in term of MDA formation, decrease in all the organs of the aged rats. The results indicate that: 1) the liver and kidney antioxidative defense decrease with age; 2) the enzymatic activities evolve in a different manner for different enzymes and organs. Furthermore, the results suggest that there is not any correlation between the SOD, CAT, and GSH-Px activities and the peroxidative status of the organs; thus, the age-related increase in the MDA content proposed as a criterion of aging process should be considered with caution.     

Protective Effects of Selenium,Zinc, or Their Combination on Cadmium-Induced Oxidative Stress in Rat Kidney

The present study was conducted to investigate whether the combined treatment with Se and Zn offers more beneficial effects than that provided by either of them alone in reversing Cd-induced oxidative stress in the kidney of rat. For this purpose, 30 adult male Wistar albino rats, equally divided into control and four treated groups, received either 200 ppm Cd (as CdCl₂), 200 ppm Cd + 500 ppm Zn (as ZnCl₂), 200 ppm Cd + 0.1 ppm Se (as Na₂SeO₃), or 200 ppm Cd + 500 ppm Zn + 0.1 ppm Se in their drinking water for 35 days. The results showed that Cd treatment decreased significantly the catalase (CAT) and glutathione peroxidase (GSH-Px) activities, whereas the superoxide dismutase (SOD) activity and the renal levels of lipid peroxidation (as malondialdehyde, MDA) were increased compared to control rats. The treatment of Cd-exposed rats with Se alone had no significant effect on the Cd-induced increase in the MDA concentrations but increased significantly the CAT activities and reversed Cd-induced increase in SOD activity. It also partially prevented Cd-induced decrease in GSH-Px activity. The treatment of Cd-exposed animals with Zn alone increased significantly the CAT activity and partially protected against Cd-induced increase in the MDA concentrations, whereas it had no significant effect on the Cd-induced increase in SOD activity and decrease in GSH-Px activity. The combined treatment of Cd-exposed animals with Se and Zn was more effective than that with either of them alone in reversing Cd-induced decrease in CAT and GSH-Px activities and Cd-induced increase in MDA concentrations. Results demonstrated beneficial effects of combined Se and Zn treatment in Cd-induced oxidative stress in kidney and suggest that Se and Zn can have a synergistic role against Cd toxicity. I. Messaoudi and J. El Heni have equally contributed to this work.     

Hydrogen peroxide detoxification in the midgut of the blood-sucking insect, Rhodnius prolixus

Here we investigated H2O2 production and detoxification in the hematophagous hemiptera, Rhodnius prolixus. Superoxide dismutase (SOD) catalyzes the dismutation of superoxide radical (O2-). This reaction produces hydrogen peroxide, which is scavenged by antioxidant enzymes such as catalase (CAT). SOD and CAT activities were found in all tissues studied, being highest in the midgut. CAT was dose-dependently inhibited in vivo by injections of 3-amino-1,2,4-triazole (AT). Insects treated with AT showed a twofold increase in H2O2 levels. Injection of DL-buthionine-[S, R]-sulfoximine (BSO), an inhibitor of glutathione synthesis, also resulted in a fourfold increase in H2O2, together with stimulation of CAT activity. Simultaneous administration of both AT and BSO had a synergistic effect on midgut H2O2 content. Taken all together, our results suggest that CAT and glutathione-dependent mechanisms cooperate to control H2O2 concentration in the midgut cell and prevent hydroxyl radical generation by Fenton reaction in this tissue.