Endogenous xanthine oxidase does not significantly contribute to vascular endothelial production of reactive oxygen species

Antioxidant and anti-inflammatory effects of exercise in diabetic patients

Diabetes is a chronic metabolic disease which is characterized by absolute or relative deficiencies in insulin secretion and/or insulin action. The key roles of oxidative stress and inflammation in the progression of vascular complications of this disease are well recognized. Accumulating epidemiologic evidence confirms that physical inactivity is an independent risk factor for insulin resistance and type II diabetes. This paper briefly reviews the pathophysiological pathways associated with oxidative stress and inflammation in diabetes mellitus and then discusses the impact of exercise on these systems. In this regard, we discuss exercise induced activation of cellular antioxidant systems through “nuclear factor erythroid 2-related factor.” We also discuss anti-inflammatory myokines, which are produced and released by contracting muscle fibers. Antiapoptotic, anti-inflammatory and chaperon effects of exercise-induced heat shock proteins are also reviewed.

Enhanced mitochondrial superoxide in hyperglycemic endothelial cells: direct measurements and formation of hydrogen peroxide and peroxynitrite

Hyperglycemic challenge to bovine aortic endothelial cells (BAECs) increases oxidant formation and cell damage that are abolished by MnSOD overexpression, implying mitochondrial superoxide (O2•−) as a central mediator. However, mitochondrial O2•−and its steady-state concentrations have not been measured directly yet. Therefore, we aimed to detect and quantify O2•−through different techniques, along with the oxidants derived from it. Mitochondrial aconitase, a sensitive target of O2•−, was inactivated 60% in BAECs incubated in 30 mM glucose (hyperglycemic condition) with respect to cells incubated in 5 mM glucose (normoglycemic condition). Under hyperglycemic conditions, increased oxidation of the mitochondrially targeted hydroethidine derivative (MitoSOX) to hydroxyethidium, the product of the reaction with O2•−, could be specifically detected. An 8.8-fold increase in mitochondrial O2•−steady-state concentration (to 250 pM) and formation rate (to 6 μM/s) was estimated. Superoxide formation increased the intracellular concentration of both hydrogen peroxide, measured as 3-amino-2,4,5-triazole-mediated inactivation of catalase, and nitric oxide-derived oxidants (i.e., peroxynitrite), evidenced by immunochemical detection of 3-nitrotyrosine. Oxidant formation was further evaluated by chloromethyl dichlorodihydrofluorescein (CM-H2DCF) oxidation. Exposure to hyperglycemic conditions triggered the oxidation of CM-H2DCF and was significantly reduced by pharmacological agents that lower the mitochondrial membrane potential, inhibit electron transport (i.e., myxothiazol), and scavenge mitochondrial oxidants (i.e., MitoQ). In BAECs devoid of mitochondria (rho0cells), hyperglycemic conditions did not increase CM-H2DCF oxidation. Mitochondrial O2•−formation in hyperglycemic conditions was associated with increased glucose metabolization in the Krebs cycle and hyperpolarization of the mitochondrial membrane.

Doxorubicin increases intracellular hydrogen peroxide in PC3 prostate cancer cells

We studied the effect of doxorubicin on the production of hydrogen peroxide by PC3 human prostate cancer cells, using a sensitive assay based on aminotriazole-mediated inhibition of catalase. PC3 cells exposed to increasing concentrations of doxorubicin had an increase in intracellular hydrogen peroxide that was concentration-dependent up to 1 microM doxorubicin. The apparent hydrogen peroxide concentration in the PC3 cells was 13 +/- 4 pM under basal steady-state conditions and increased to 51 +/- 13 pM after exposure to 1 microM doxorubicin for 30 min. The level of hydrogen peroxide in the medium as measured by Amplex Red did not increase as a result of doxorubicin treatment. PC3 cells overexpressing catalase were no more resistant to doxorubicin cytotoxicity as compared to non-transduced wild-type cells; therefore, the exact role of hydrogen peroxide in anthracycline cytotoxicity remains unproven. This study demonstrates that a specific oxidative event associated with the exposure of PC3 human prostate cancer cells to anthracyclines results in an increase in intracellular hydrogen peroxide.

Regulation of xanthine oxidoreductase protein expression by hydrogen peroxide and calcium

OBJECTIVE

We have previously demonstrated that endothelial xanthine oxidase (XO) levels are dependent on the NADPH oxidase. We postulated that H2O2 may modulate the irreversible conversion of xanthine dehydrogenase (XDH) to XO and sought to examine mechanisms involved.

METHODS AND RESULTS

H2O2 (100 micromol/L) decreased bovine aortic endothelial cell (BAEC) XDH protein expression, and metabolic labeling studies indicated that H2O2 stimulated conversion of XDH to XO. The decline in XDH was mimicked by the reactive oxygen species (ROS) generating compounds SIN-1 and Menadione, as well as by stimulating BAECs with angiotensin II (200 nmol/L). BAPTA-AM prevented the decline in XDH by H2O2, indicating that it was calcium-dependent. In keeping with calcium acting downstream of H2O2, the calcium ionophore A23187 (1 micromol/L) caused XDH-to-XO conversion, and this was not prevented by the antioxidants. In addition, XDH-to-XO conversion was blocked by 2-APB and NO donors and induced by thapsigargin and M-3M3FBS, implicating phospholipase C and endoplasmic reticulum calcium stores in this process.

CONCLUSIONS

Endothelial XO and XDH expression are strongly dependent on H2O2 and calcium. Stimulation of XDH conversion to XO may represent a feed-forward mechanism whereby H2O2 can stimulate further production of ROS.

Methods for detection of reactive metabolites of oxygen and nitrogen: in vitro and in vivo considerations

Facile detection of reactive oxygen and nitrogen species in biologic systems is often problematic. This is a result of the numerous cellular mechanisms, both enzymatic and nonenzymatic involved in their catabolism/decomposition, the complex and overlapping nature of their reactivities, as well as the often limited intracellular access of detector systems. This review describes approaches to the direct and indirect measurement of different reactive metabolites of oxygen and nitrogen. Particular attention to a method's applicability for in vivo determinations will be addressed.

Role of xanthine oxidoreductase and NAD(P)H oxidase in endothelial superoxide production in response to oscillatory shear stress

Oscillatory shear stress occurs at sites of the circulation that are vulnerable to atherosclerosis. Because oxidative stress contributes to atherosclerosis, we sought to determine whether oscillatory shear stress increases endothelial production of reactive oxygen species and to define the enzymes responsible for this phenomenon. Bovine aortic endothelial cells were exposed to static, laminar (15 dyn/cm2), and oscillatory shear stress (+/-15 dyn/cm2). Oscillatory shear increased superoxide (O2.-) production by more than threefold over static and laminar conditions as detected using electron spin resonance (ESR). This increase in O2*- was inhibited by oxypurinol and culture of endothelial cells with tungsten but not by inhibitors of other enzymatic sources. Oxypurinol also prevented H2O2 production in response to oscillatory shear stress as measured by dichlorofluorescin diacetate and Amplex Red fluorescence. Xanthine-dependent O2*- production was increased in homogenates of endothelial cells exposed to oscillatory shear stress. This was associated with decreased xanthine dehydrogenase (XDH) protein levels and enzymatic activity resulting in an elevated ratio of xanthine oxidase (XO) to XDH. We also studied endothelial cells lacking the p47phox subunit of the NAD(P)H oxidase. These cells exhibited dramatically depressed O2*- production and had minimal XO protein and activity. Transfection of these cells with p47phox restored XO protein levels. Finally, in bovine aortic endothelial cells, prolonged inhibition of the NAD(P)H oxidase with apocynin decreased XO protein levels and prevented endothelial cell stimulation of O2*- production in response to oscillatory shear stress. These data suggest that the NAD(P)H oxidase maintains endothelial cell XO levels and that XO is responsible for increased reactive oxygen species production in response to oscillatory shear stress.

Oxygen radical inhibition of nitric oxide-dependent vascular function in sickle cell disease

Plasma xanthine oxidase (XO) activity was defined as a source of enhanced vascular superoxide (O(2)( *-)) and hydrogen peroxide (H(2)O(2)) production in both sickle cell disease (SCD) patients and knockout-transgenic SCD mice. There was a significant increase in the plasma XO activity of SCD patients that was similarly reflected in the SCD mouse model. Western blot and enzymatic analysis of liver tissue from SCD mice revealed decreased XO content. Hematoxylin and eosin staining of liver tissue of knockout-transgenic SCD mice indicated extensive hepatocellular injury that was accompanied by increased plasma content of the liver enzyme alanine aminotransferase. Immunocytochemical and enzymatic analysis of XO in thoracic aorta and liver tissue of SCD mice showed increased vessel wall and decreased liver XO, with XO concentrated on and in vascular luminal cells. Steady-state rates of vascular O(2)( *-) production, as indicated by coelenterazine chemiluminescence, were significantly increased, and nitric oxide (( *)NO)-dependent vasorelaxation of aortic ring segments was severely impaired in SCD mice, implying oxidative inactivation of ( *)NO. Pretreatment of aortic vessels with the superoxide dismutase mimetic manganese 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin markedly decreased O(2)( small middle dot-) levels and significantly restored acetylcholine-dependent relaxation, whereas catalase had no effect. These data reveal that episodes of intrahepatic hypoxia-reoxygenation associated with SCD can induce the release of XO into the circulation from the liver. This circulating XO can then bind avidly to vessel luminal cells and impair vascular function by creating an oxidative milieu and catalytically consuming (*)NO via O(2)( small middle dot-)-dependent mechanisms.

Internalization of proteinase 3 is concomitant with endothelial cell apoptosis and internalization of myeloperoxidase with generation of intracellular oxidants

The important issue addressed by the studies presented here is the mechanism of neutrophil-mediated damage to endothelial and epithelial cells during inflammation. Binding of neutrophil-released granule proteins to endothelial cells may be involved in vascular damage in patients with inflammatory vascular diseases. We have determined whether granule proteins proteinase 3(PR3) and/or myeloperoxidase (MPO) are internalized into endothelial cells, as examined by UV light, confocal, and electron microscopy. Coincident induction of apoptosis and/or the generation of intracellular oxidants were monitored. The results indicate that human endothelial cells (human umbilical vein endothelial cells, human umbilical arterial endothelial cells, human lung microvascular endothelial cells) internalize both PR3 and MPO, which are detected on the cell surface, in the cytoplasm, and possibly nuclear. Epithelial cells (small airway epithelial cells) internalized MPO but not PR3, implying that the mechanism of PR3 internalization may be cell-type specific and different from that of MPO. Internalization of PR3, but not MPO, correlated with activation of apoptosis. Internalization of MPO correlated with an increase in intracellular oxidant radicals. The requirement for the proteolytic activity of PR3 for the induction of apoptosis was examined by generating PR3-truncated fragments that did not contain the components of the catalytic triad. An apoptotic function was localized to the C-terminal portion of PR3. These studies reveal novel mechanisms by which the neutrophil granule proteins PR3 and MPO contribute to tissue injury at sites of inflammation.

Chemiluminescent detection of oxidants in vascular tissue. Lucigenin but not coelenterazine enhances superoxide formation

Lucigenin-amplified chemiluminescence has frequently been used to assess the formation of superoxide in vascular tissues. However, the ability of lucigenin to undergo redox cycling in purified enzyme-substrate mixtures has raised questions concerning the use of lucigenin as an appropriate probe for the measurement of superoxide production. Addition of lucigenin to reaction mixtures of xanthine oxidase plus NADH resulted in increased oxygen consumption, as well as superoxide dismutase-inhibitable reduction of cytochrome c, indicative of enhanced rates of superoxide formation. Additionally, it was revealed that lucigenin stimulated oxidant formation by both cultured bovine aortic endothelial cells and isolated rings from rat aorta. Lucigenin treatment resulted in enhanced hydrogen peroxide release from endothelial cells, whereas exposure to lucigenin resulted in inhibition of endothelium-dependent relaxation in isolated aortic rings that was superoxide dismutase inhibitable. In contrast, the chemiluminescent probe coelenterazine had no significant effect on xanthine oxidase-dependent oxygen consumption, endothelial cell hydrogen peroxide release, or endothelium-dependent relaxation. Study of enzyme and vascular systems indicated that coelenterazine chemiluminescence is a sensitive marker for detecting both superoxide and peroxynitrite.

Binding of xanthine oxidase to vascular endothelium. Kinetic characterization and oxidative impairment of nitric oxide-dependent signaling

Concentrations of up to 1.5 milliunits/ml xanthine oxidase (XO) (1.1 micrograms/ml) are found circulating in plasma during diverse inflammatory events. The saturable, high affinity binding of extracellular XO to vascular endothelium and the effects of cell binding on both XO catalytic activity and differentiated vascular cell function are reported herein. Xanthine oxidase purified from bovine cream bound specifically and with high affinity (Kd = 6 nM) at 4 degreesC to bovine aortic endothelial cells, increasing cell XO specific activity up to 10-fold. Xanthine oxidase-cell binding was not inhibited by serum or albumin and was partially inhibited by the addition of heparin. Pretreatment of endothelial cells with chondroitinase, but not heparinase or heparitinase, diminished endothelial binding by approximately 50%, suggesting association with chondroitin sulfate proteoglycans. Analysis of rates of superoxide production by soluble and cell-bound XO revealed that endothelial binding did not alter the percentage of univalent reduction of oxygen to superoxide. Comparison of the extent of CuZn-SOD inhibition of native and succinoylated cytochrome c reduction by cell-bound XO indicated that XO-dependent superoxide production was occurring in a cell compartment inaccessible to CuZn-SOD. This was further supported by the observation of a shift of exogenously added XO from extracellular binding sites to intracellular compartments, as indicated by both protease-reversible cell binding and immunocytochemical localization studies. Endothelium-bound XO also inhibited nitric oxide-dependent cGMP production by smooth muscle cell co-cultures in an SOD-resistant manner. This data supports the concept that circulating XO can bind to vascular cells, impairing cell function via oxidative mechanisms, and explains how vascular XO activity diminishes vasodilatory responses to acetylcholine in hypercholesterolemic rabbits and atherosclerotic humans. The ubiquity of cell-XO binding and endocytosis as a fundamental mechanism of oxidative tissue injury is also affirmed by the significant extent of XO binding to human vascular endothelial cells, rat lung type 2 alveolar epthelial cells, and fibroblasts.

Xanthine oxidase reaction with nitric oxide and peroxynitrite

Nitric oxide (.NO) and peroxynitrite (ONOO-) inhibit enzymes that depend on metal cofactors or oxidizable amino acids for activity. Since xanthine oxidase (XO) is a 2(2Fe2S) enzyme having essential sulfhydryl groups linked with Mo-pterin cofactor function, the influence of .NO and ONOO- on purified bovine XO was determined. Physiological (</=1 microM) and supraphysiological (</=100 microM) concentrations of dissolved .NO gas did not inhibit the catalytic activity or alter the spectral characteristics of XO at 25 degreesC and pH 7.0, differing from reports showing XO inhibition by .NO. The apparent decrease in XO activity observed previously was the result of depressed rates of uric acid accumulation in XO assay systems, due to ONOO--mediated oxidation of uric acid upon reaction of residual .NO with XO-derived superoxide (O*-2). Nitric oxide derived from S-nitrosoglutathione also did not inhibit cultured vascular endothelial cell XO activity. In contrast, purified and vascular endothelial cell catalase, a heme enzyme reversibly inhibited by .NO, was inhibited by similar concentrations and rates of production of . NO. In contrast to .NO, ONOO- inhibited XO (0.2 microM, 50 mU/ml) with an IC50 of 57 microM (for 3 microM/min infusion of ONOO-) or 120 microM (for bolus addition of ONOO-). Addition of 1% bovine serum albumin, 50 microM xanthine, or 10 microM uric acid protected XO from inactivation by ONOO-. Thus, in the presence of purine substrates and other more readily oxidized components of the biological milieu, XO should not be inhibited by either .NO or ONOO-. These observations reveal that .NO will not serve as an indirect antioxidant by inhibiting XO-derived production of reactive species and that the XO-derived products O*-2 and uric acid readily modify the reactivities of .NO and ONOO-.

Adenosine prevents permeability increase in oxidant-injured endothelial monolayers

Adenosine is thought to prevent or reduce the increase in permeability, which is a hallmark of oxidant injury to endothelium. However, the effect of adenosine on endothelial cells directly exposed to oxidant species has not been demonstrated in vitro. By measuring the passage of Evan's blue dye-labeled albumin across confluent monolayers, we demonstrated the ability of adenosine (0.1-100 microM) to lower basal permeability of human umbilical vein endothelial cells in a concentration-dependent fashion and prevent the permeability increase induced by exposure of the cells to xanthine plus xanthine oxidase (X/XO). Whereas pretreatment of monolayers for 10 min with adenosine (10 and 100 microM) prevented the X/XO-induced permeability increase, these same concentrations of adenosine failed to increase intracellular adenosine 3',5'-cyclic monophosphate in X/XO-exposed cells. The protective effect of adenosine on endothelial monolayers was mimicked by adenosine amine congener and 5'-(N-ethylcarboxamido)adenosine but not by other agonists examined. Hence, the protective effect of adenosine against oxidant injury may include an adenosine 3',5'-cyclic monophosphate-independent mechanism by direct action of adenosine at A1 receptors on endothelial cells.

Role of nitric oxide in poly(I-C)-induced endothelial cell expression of leukocyte adhesion molecules

Polyinosinic-polycytidylic acid [poly(I-C)] is a synthetic double-stranded RNA (dsRNA) that simulates a viral-infected state in cells. It has been shown that viral infection, as well as poly(I-C), stimulates leukocyte adhesion to endothelial cell (EC) monolayers and that this is mediated through the surface expression of the adhesion molecules E-selectin, vascular cell adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule 1. We have tested the involvement of nitric oxide (NO) in poly(I-C)-induced monocytic cell adhesion to human vascular EC. Using primary cultured EC for these studies, we confirmed the results from previous reports that these cells have higher basal levels of NO production than passaged cells. Poly(I-C)-induced monocytic cell adhesion to primary EC was concentration-dependently inhibited by 40-74% by the nitric oxide synthase (NOS) inhibitor NG-methyl-L-arginine (L-NMA), as well as three other NOS inhibitors, without significantly affecting interleukin-1 beta-induced adhesion. L-NMA inhibited poly(I-C)-induced surface expression of E-selectin and VCAM-1 by 25 and 45%, respectively, and mRNA levels of E-selectin and VCAM-1 by 62 and 74%, respectively. Primary EC transiently transfected with a plasmid containing an E-selectin promoter-driven luciferase reporter gene showed that L-NMA treatment reduced poly(I-C)-induced E-selectin promoter activity to basal levels. Electrophoretic mobility shift analysis indicated that poly(I-C)-induced nuclear factor-kappa B (NF-kappa B) binding to a radiolabeled oligonucleotide corresponding to the consensus NF-kappa B binding domain of the E-selectin promoter was decreased by L-NMA pretreatment. Hence, NO appears to augment E-selectin gene expression in response to poly(I-C) at the transcriptional level in vascular EC. Collectively, these data support the hypothesis that NO augments poly(I-C)-induced EC activation. These data suggest a novel role for NO as a response mediator in dsRNA-induced leukocyte adhesion to EC.

Cyclic strain induces an oxidative stress in endothelial cells

Hypertension imposes an oxidant stress on the aorta and also causes mechanical deformation of the aortic wall. To assess whether deformation causes an oxidative stress, isolated porcine aortic endothelial cells (PAEC) were subjected to cyclic strain, and the cumulative amount of thiobarbituric acid reactive substances (TBARS, an index of lipid peroxidation) and H2O2 (a reactive oxygen species) was measured in the eluent at 2, 6, and 24 h. TBARS were increased by 40.5 +/- 9.2% after 24 h in cells exposed to cyclic strain vs. static controls (P < 0.05). No difference was seen at 2 and 6 h. H2O2 release was increased after 6 and 24 h of cyclic strain by 22.0 +/- 8.0 and 57.6 +/- 11.1 nmol H2O2/mg, respectively (P < 0.005), but was not increased after 2 h of strain. In vascular smooth muscle cells, TBARS were not observed and H2O2 release was not increased by cyclic strain. To investigate a potential source of H2O2 induced by strain, the activity of NADH/NADPH oxidase, a superoxide-generating enzyme, was measured by chemiluminescence. After 2 h, cells exposed to cyclic strain had greater activity than static controls (531.0 +/- 68.4 vs. 448.3 +/- 54.2 pmol O2- x mg(-1) x s(-1), respectively, when incubated with NADH, P < 0.005; 85.8 +/- 8.9 vs. 71.6 +/- 3.8 pmol O2- x mg(-1) x s(-1) when incubated with NADPH, P < 0.05). No effect on NADH/NADPH oxidase activity was seen after 6 or 24 h. The following conclusions were made: 1) cyclic strain induces an oxidant stress in PAEC monolayers as measured by TBARS formation and H2O2 release, 2) NADH/NADPH oxidase is a potential source of H2O2 release in cyclically strained cells, and 3) mechanical deformation of endothelial cells may play a critical role in the generation of oxidative stress within the vessel wall.

Early albumin leakage in pulmonary endothelial monolayers exposed to varying levels of hyperoxia

We assessed the effect of varying levels of hyperoxia on 14C-albumin flux across bovine pulmonary artery endothelial cell (BPAEC) monolayers. Endothelialized nitrocellulose filters were mounted in Ussing-type chambers which were filled with cell culture medium (M 199). Equimolar amounts of 14C-labeled and unlabeled albumin were added to the "hot" and "cold" chambers, respectively, and the monolayers were exposed to 3 hours of varying levels of oxygen (16%, 30%, 40%, 60%, and 95%). When compared to 16% O2, exposure to hyperoxic gas mixtures of 40% or greater progressively increased albumin permeability across endothelial monolayers within 3 hours to a value 2.5 times higher at 95% O2 compared to 16% O2 (p < 0.001). Hyperoxia-induced permeability increases were prevented by catalase, superoxide dismutase, desferrioxamine, and allopurinol. Our data indicate that hyperoxia induces endothelial permeability changes more rapidly than previously reported even at O2 concentrations as low as 40%.

Blood radicals: reactive nitrogen species, reactive oxygen species, transition metal ions, and the vascular system

Free radicals, such as superoxide, hydroxyl and nitric oxide, and other "reactive species", such as hydrogen peroxide, hypochlorous acid and peroxynitrite, are formed in vivo. Some of these molecules, e.g. superoxide and nitric oxide, can be physiologically useful, but they can also cause damage under certain circumstances. Excess production of reactive oxygen or nitrogen species (ROS, RNS), their production in inappropriate relative amounts (especially superoxide and NO) or deficiencies in antioxidant defences may result in pathological stress to cells and tissues. This oxidative stress can have multiple effects. It can induce defence systems, and render tissues more resistant to subsequent insult. If oxidative stress is excessive or if defence and repair responses are inadequate, cell injury can be caused by such mechanisms as oxidative damage to essential proteins, lipid peroxidation, DNA strand breakage and base modification, and rises in the concentration of intracellular "free" Ca(2+). Considerable evidence supports the view that oxidative damage involving both ROS and RNS is an important contributor to the development of atherosclerosis. Peroxynitrite (derived by reaction of superoxide with nitric oxide) and transition metal ions (perhaps released by injury to the vessel wall) may contribute to lipid peroxidation in atherosclerotic lesions.

Endogenous reactive oxygen metabolites mediate sublethal endothelial cell dysfunction during reoxygenation

PURPOSE

Endothelial cells (EC) secrete vasoactive eicosanoids, which maintain organ blood flow. Because EC are a major source of eicosanoids, we studied the effects of reoxygenation on EC prostacyclin production.

METHODS

Bovine aortic EC cultures were exposed to 2 hours of normoxia, then 1 hour of hypoxia (PO2 = 10 +/- 3.5 mm Hg), followed by 1.5 hours of reoxygenation in either normal medium or medium plus either superoxide dismutase (SOD, 300 units/ml), catalase (1200 units/ml), allopurinol (5.0 x 10(-4) mol/L), or dinitrophenol (10(-4) mol/L).

RESULTS

Prostacyclin production decreased to 40% (p < 0.05) of basal prostacyclin production after 1 hour of hypoxia. EC reoxygenated with control medium recovered to 48% of basal prostacyclin production. EC reoxygenated in SOD resulted in recovery (p < 0.05) to 154% of basal prostacyclin production after 60 minutes. Catalase treatment resulted in recovery to 105% (p < 0.05) of basal prostacyclin production within 30 minutes of reoxygenation. Allopurinol treatment resulted in 77% recovery (p < 0.05) of basal prostacyclin production only during 30 minutes of reoxygenation. Dinitrophenol treatment resulted in significant (> or = 85%, p < 0.05) sustained recovery of basal prostacyclin production at 30, 60, and 90 minutes of experimental reperfusion.

CONCLUSIONS

The hypoxia-induced decrease in EC prostacyclin does not recover during reoxygenation. Catalase/SOD allowed return to baseline prostacyclin production during reoxygenation, implicating reactive oxygen metabolites as mediators of decreased eicosanoid biosynthesis. Recovery of prostacyclin production after 60 minutes reoxygenation with dinitrophenol but not allopurinol suggests a mitochondrial origin of the oxygen metabolites responsible for decreased prostacyclin biosynthesis.