Formation Of Oxygen-derived Free Radicals Research Articles

The protective effects of sesamol in a neonatal rat model of necrotizing enterocolitis

Background and aim: Necrotizing enterocolitis (NEC) is a severe gastrointestinal inflammatory disease associated with high rates of morbidity and mortality. Its pathophysiology includes hypoxic-ischemic injury that may be related to oxygen-derived free radical formation. Sesamol is considered to be an antioxidant and free radical scavenger with anti-inflammatory effects. The aim of this study is to investigate the effects of sesamol in a neonatal rat model of NEC.Materials and methods: The study included 1-day-old Wistar albino rat pups (n = 34) that were randomly divided into four groups: Group 1 (NEC), group 2 (NEC + intraperitoneal sesamol), group 3 (NEC + oral sesamol), and a control group. NEC was induced by exposure to hypoxia/reoxygenation, following cold stress and hyperosmolar enteral formula feeding. Sesamol 100 mg kg−1 dose−1 was administered intraperitoneally to group 2 and orally to group 3 for 3 days. On day 4 all rats were sacrificed. Histological injuries, the Bcl-2, caspase-3, malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione-peroxidase (GSH-Px) activities were measured in intestinal samples.Results: The grade of intestinal damage, and Bcl-2 and caspase-3 levels in group 1 were significantly higher than in groups 2 and 3 and the control group, and intestinal damage was significantly more severe in group 1 than in groups 2 and 3. The MDA activity was significantly lower in groups 2 and 3 than in group 1 (112, 89, and 144 nmol mL−1, respectively). Groups 2 and 3 had significantly higher SOD and GSH-Px activities than group 1 (SOD: 1.75, 1.74, and 0.89 U mg−1; GSH-Px: 114, 121, and 110 nmol of NADPH min−1 mg−1, respectively).Conclusions: The present findings highlight that sesamol has beneficial effects on intestinal injury in a rat model of NEC through its antioxidant and anti-inflammatory properties.

Oxidative stress induced by cumene hydroperoxide evokes changes in neuronal excitability of rat motor cortex neurons

Oxidative stress and the production of reactive oxygen radicals play a key role in neuronal cell damage. This paper describes an in vitro study that explores the neuronal responses to oxidative stress focusing on changes in neuronal excitability and functional membrane properties. This study was carried out in pyramidal cells of the motor cortex by applying whole-cell patch-clamp techniques on brain slices from young adult rats. Oxygen-derived free radical formation was induced by bath application of 10μM cumene hydroperoxide (CH) for 30min. CH produced marked changes in the electrophysiological properties of neurons (n=30). Resting membrane potential became progressively depolarized, as well as depolarization voltage, with no variations in voltage threshold. Membrane resistance showed a biphasic behavior, increasing after 5min of drug exposure and then it started to decrease, even under control values, after 15 and 30min. At the same time, changes in membrane resistance produced compensatory variations in the rheobase. The amplitude of the action potentials diminished and the duration increased progressively over time. Some of the neurons under study also lost their ability to discharge action potentials in a repetitive way. Most of the neurons, however, kept their repetitive discharge even though their maximum frequency and gain decreased. Furthermore, cancelation of the repetitive firing discharge took place at intensities that decreased with time of exposure to CH, which resulted in a narrower working range. We can conclude that oxidative stress compromises both neuronal excitability and the capability of generating action potentials, and so this type of neuronal functional failure could precede the neuronal death characteristics of many neurodegenerative diseases.

Iron-ascorbate-mediated lipid peroxidation causes epigenetic changes in the antioxidant defense in intestinal epithelial cells: impact on inflammation.

IntroductionThe gastrointestinal tract is frequently exposed to noxious stimuli that may cause oxidative stress, inflammation and injury. Intraluminal pro-oxidants from ingested nutrients especially iron salts and ascorbic acid frequently consumed together, can lead to catalytic formation of oxygen-derived free radicals that ultimately overwhelm the cellular antioxidant defense and lead to cell damage.HypothesisSince the mechanisms remain sketchy, efforts have been exerted to evaluate the role of epigenetics in modulating components of endogenous enzymatic antioxidants in the intestine. To this end, Caco-2/15 cells were exposed to the iron-ascorbate oxygen radical-generating system.ResultsFe/Asc induced a significant increase in lipid peroxidation as reflected by the elevated formation of malondialdehyde along with the alteration of antioxidant defense as evidenced by raised superoxide dismutase 2 (SOD2) and diminished glutathione peroxidase (GPx) activities and genes. Consequently, there was an up-regulation of inflammatory processes illustrated by the activation of NF-κB transcription factor, the higher production of interleukin-6 and cycloxygenase-2 as well as the decrease of IκB. Assessment of promoter’s methylation revealed decreased levels for SOD2 and increased degree for GPx2. On the other hand, pre-incubation of Caco-2/15 cells with 5-Aza-2′-deoxycytidine, a demethylating agent, or Trolox antioxidant normalized the activities of SOD2 and GPx, reduced lipid peroxidation and prevented inflammation.ConclusionRedox and inflammatory modifications in response to Fe/Asc -mediated lipid peroxidation may implicate epigenetic methylation.

279 Antioxidant Effects of N-Acetylcysteine in a Neonatal Rat Model of Necrotizing Enterocolitis

Background and AimHypoxia and ischemia appear to play an important role in the pathogenesis of necrotizing enterocolitis (NEC) which is related to oxygen-derived free radical formation. This study was designed...

Antioxidant effects of N-acetylcysteine in a neonatal rat model of necrotizing enterocolitis

Background/PurposeHypoxia and ischemia appear to play an important role in the pathogenesis of necrotizing enterocolitis (NEC), which may be related to oxygen-derived free radical formation. This study was designed to evaluate the role of oxidative stress and potentially beneficial effects of N-acetylcysteine (NAC) in a neonatal rat model of NEC. MethodsThirty Wistar albino rat pups were randomly divided into 3 groups: group 1, control; group 2, NEC and saline; and group 3, NEC and NAC treatment. Necrotizing enterocolitis was induced by hyperosmolar enteral formula feeding and exposure to hypoxia after cold stress at 4°C and oxygen. The pups were killed on the fourth day, and their intestinal tissues were harvested for biochemical and histopathologic analysis. ResultsMucosal injury scores and intestinal malondialdehyde levels in group 2 were found to be significantly higher than that in other groups (P ≤ .05). Intestinal superoxide dismutase activities in group 3 were significantly higher than that in group 2 (P = .018). Intestinal tissue tumor necrosis factor α levels were significantly reduced with NAC treatment in group 3 compared with group 2 (P < .003). ConclusionsIt is likely that oxidative stress and inflammatory mediators contribute to the pathogenesis of NEC and that NAC has a protective effect on intestinal injury through its antiinflammatory and antioxidant properties.

Restraint stress up-regulates lectin-like oxidized low-density lipoprotein receptor-1 in aorta of apolipoprotein E-deficient mice

Psychological stress is a risk factor for cardiovascular disease including atherosclerosis, but the mechanisms are unknown. The vascular lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is involved in vascular pathology and early atherogenesis. We hypothesized that LOX-1 is up-regulated by psychological stress via the formation of oxygen-derived free radicals, and that treatment with EUK-8 (a superoxide dismutase and catalase mimetic) prevents production of oxygen-derived free radicals and leads to reduced expression of LOX-1 in the vascular wall. As a model for psychological stress, we exposed male apolipoprotein E-deficient mice to repeated restraint stress by placement in a conical tube for 2 h per day for 14 consecutive days. Stressed and control mice were treated with EUK-8 (n = 4–5) or vehicle (n = 4–5). Reactive oxygen species and peroxynitrite levels, as detected by oxidative fluorescence microscopy, were increased in the aortic root of mice exposed to stress compared to those of controls by 212 ± 22% (mean ± SEM; p < 0.001) and 110 ± 6% (p < 0.001), respectively. LOX-1, as detected by immunohistochemistry, was increased by 443 ± 63% in stressed mice compared to control mice (p < 0.001). EUK-8 reduced reactive oxygen species, peroxynitrite, and LOX-1 levels in stressed mice compared to vehicle-treated stressed mice. To conclude, LOX-1 induced by reactive oxygen species and/or peroxynitrite could be one mechanism by which stress promotes cardiovascular disease.

Abnormal Mitochondrial Function During Ischemia Reperfusion Provides Targets For Pharmacological Therapy

The concept of reperfusion injury has been a subject of intense debate. Some researchers believe that the entire injury develops during the ischemic period, whereas others argue that blood reflow extends tissue injury due to the release of oxygen-derived free radicals, an inflammatory reaction involving influx of various populations of immune cell, and dysregulation of intracellular and particularly mitochondrial calcium concentration. Mitochondrial calcium overload in the presence of oxygen-derived free radicals can result in the opening of the mitochondrial permeability transition pore (mPTP), which further compromises cellular energetics. The resultant low ATP and altered ion homeostasis lead to a rupture of the plasma membrane and cell death. Mitochondria have long been proposed as one of the main players in cell death, since the mitochondria are central to synthesis of both ATP and the formation of oxygen-derived free radicals. These mechanisms are centered on mitochondrial calcium overload as a key component of cell death. Pharmacological strategies that are cardioprotective attempt to reduce mitochondrial calcium overload to decrease the likelihood of arrhythmias and cardiac dysfunction elicited by reperfusion.

The double-edge sword of TNF-α in ischemia-reperfusion injury

The double-edge sword of TNF-α in ischemia-reperfusion injury

Hyperlipidemia induced by a cholesterol-rich diet aggravates necrotizing pancreatitis in rats

The aim of the present study was to investigate whether hyperlipidemia can cause acute pancreatitis or alter its severity. Male Wistar rats were fed a 3% cholesterol-enriched diet or a normal diet for 16 weeks. Edematous and necrotizing pancreatitis was induced with 3x75 mug/kg body weight of cholecystokinin s.c. and 2x2 g/kg body weight of L-arginine i.p., respectively, in separate groups of normal and hyperlipidemic rats. The severity of the pancreatitis was assessed. We studied the influence of hyperlipidemia on the formation of oxygen-derived free radicals, endogenous scavengers, nitric oxide synthases (NOS), peroxynitrite (ONOO(-)), heat shock protein 72 (HSP72) and nuclear factor-kappa B (NF-kappaB) activation in the pancreas during acute edematous and necrotizing pancreatitis. Hyperlipidemia did not worsen edematous, but aggravated necrotizing pancreatitis. The cholesterol-enriched diet significantly reduced the catalase and Mn-superoxide dismutase (SOD) and constitutive NOS (cNOS) activities and increased the inducible NOS (iNOS) in the pancreas relative to those in the rats on the normal diet. The pancreatic nitrotyrosine level, as a marker of ONOO(-), and the NF-kappaB DNA-binding activity in the pancreas, were significantly elevated in the cholesterol-fed rats. The pancreatic HSP72 expression during necrotizing pancreatitis was not influenced by the hyperlipidemia. The pancreatic Mn-SOD, Cu, Zn-SOD, glutathione peroxidase, total glutathione and cNOS activities were significantly reduced, while the catalase, iNOS and NF-kappaB DNA-binding activities were significantly increased in the animals with necrotizing pancreatitis on the cholesterol diet as compared with those with pancreatitis and receiving the normal diet. Hyperlipidemia induced with this cholesterol-enriched diet leads to decreases in endogenous scavenger and cNOS activities, results in iNOS and NF-kappaB activation and stimulates ONOO(-) generation in the pancreas, which may be responsible for the aggravation of acute necrotizing pancreatitis.

Adverse effects of free fatty acid associated with increased oxidative stress in postischemic isolated rat hearts

The mechanisms of the adverse effects of free fatty acids on the ischemic-reperfused myocardium are not fully understood. Long-chain fatty acids, including palmitate, uncouple oxidative phosphorylation and should therefore promote the formation of oxygen-derived free radicals, with consequent adverse effects. Conversely, the antianginal agent trimetazidine (TMZ), known to inhibit cardiac fatty acid oxidation, could hypothetically lessen the formation of reactive oxygen species (ROS) and thus improve reperfusion mechanical function. Isolated perfused rat hearts underwent 30 min of total global ischemia followed by 30 min of reperfusion. Hearts were perfused with glucose 5.5 mmol/l or palmitate 1.5 mmol/l with or without TMZ (100 micromol/l). Ascorbyl free radical (AFR) release during perfusion periods was measured by electron spin resonance as a marker of oxidative stress. Post-ischemic recovery in the palmitate group of heart was lower than in the glucose group with a marked rise in diastolic tension and reduction in left ventricular developed pressure (Glucose: 85 +/- 11 mmHg; Palmitate: 10 +/- 6 mmHg; p < 0.001). TMZ decreased diastolic tension in both glucose- and in palmitate-perfused hearts. Release of AFR within the first minute of reperfusion was greater in palmitate-perfused hearts and in hearts perfused with either substrate, this marker of oxidative stress was decreased by TMZ (expressed in arbitrary units/ml; respectively: 8.49 +/- 1.24 vs. 1.06 +/- 0.70 p < 0.05; 12.47 +/- 2.49 vs. 3.37 +/- 1.29 p < 0.05). Palmitate increased the formation of ROS and reperfusion contracture. TMZ, a potential inhibitor of palmitate-induced mitochondrial uncoupling, decreased the formation of free radicals and improved postischemic mechanical dysfunction. The novel conclusion is that adverse effects of fatty acids on ischemic-reperfusion injury may be mediated, at least in part, by oxygen-derived free radicals.

The l-arginine nitric oxide pathway: avenue for a multiple-level approach to assess vascular function

Endothelial dysfunction is an early stage of atherosclerosis and has been attributed to impaired nitric oxide (NO) bioactivity and enhanced formation of oxygen-derived free radicals. Given that endothelial dysfunction is at least in part reversible, the assessment of altered NO availability is of important diagnostic and prognostic significance. Identification of such alterations may help to target asymptomatic individuals who are at risk for cardiovascular diseases and would likely benefit from preventive measures. Focusing on a single signaling pathway, we present here a multi-level approach for the early diagnosis of cardiovascular diseases by assessing molecular, biochemical, structural, and functional changes in the vascular wall.

Endothelium-dependent contractions in hypertension.

1. Endothelial cells, under given circumstances, can initiate contraction (constriction) of the vascular smooth muscle cells that surround them. Such endothelium-dependent, acute increases in contractile tone can be due to the withdrawal of the production of nitric oxide, to the production of vasoconstrictor peptides (angiotensin II, endothelin-1), to the formation of oxygen-derived free radicals (superoxide anions) and/or the release of vasoconstrictor metabolites of arachidonic acid. The latter have been termed endothelium-derived contracting factor (EDCF) as they can contribute to moment-to-moment changes in contractile activity of the underlying vascular smooth muscle cells. 2. To judge from animal experiments, EDCF-mediated responses are exacerbated by aging, spontaneous hypertension and diabetes. 3. To judge from human studies, they contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients. 4. Since EDCF causes vasoconstriction by activation of the TP-receptors on the vascular smooth muscle cells, selective antagonists at these receptors prevent endothelium-dependent contractions, and curtail the endothelial dysfunction in hypertension and diabetes.

Anti-oxidative therapy protects renal function in cardiac surgery patients

Objectives: Oxygen-derived free radical formation induced by cardiopulmonary bypass (CPB) may contribute to renal dysfunction associated with cardiac surgery. As anti-oxidants have been shown to attenuate free radical-induced renal dysfunction in medical patients, we hypothesized that the anti-oxidant N-acetylcysteine (NAC) protects renal function in patients subjected to cardiac surgery on CPB. Material and Methods: Forty coronary artery surgery patients (66±9[SD] years, 9 women and 31 men) with normal preoperative renal function (serum creatinine <0.9mg/dl) subjected to CPB and CA were randomized in a double-blind fashion to receive either NAC (100mg/kg into CPB prime followed by infusion at 20mg/kg/h; n=20) or Placebo (n=20). We measured serum creatinine levels pre- and post-operatively (1. day post CPB) as well as urinary output and diuretic medication. Creatinine clearance was calcuted using the Cockroft equation. Results: In the Placebo group, serum creatinine increased from 93.1±35.4 mmol/l pre-operatively to 115.9±47.2 mmol/l on post-op day 1 (p<.001, 95% CI for mean change: 13.9 to 31.7). In the NAC group, change in serum creatinine was not statistically significant (92.3±31.3 mmol/l pre-operatively; 99.3±25.4 mmol/l on post-op day 1; p=.084, 95% CI for mean change: –0.5 to 14.5). Creatinine clearance decreased significantly in the Placebo group compared to NAC (–16.9±3.2ml/min vs. –7.5±4.2ml/min, p=0.04). Hemodynamics as well as clinical outcome were similar between NAC and Placebo. Conclusions: Our data show that NAC protects renal function post CPB, thus, radical-scavenging may reduce renal dysfunction associated with cardiac surgery.

過酸化水素処理による骨芽細胞様細胞株ＭＣ３Ｔ３‐Ｅ１のｂｏｎｅ ｎｏｄｕｌｅ形成への影響―石灰化物の結晶学的検索―

The ability of osteoblasts to form bone greatly diminishes with aging, which may be due to the rise of oxygen-derived free radical formation. However, changes that occur in the mineral crystallinity of bone nodules formed by osteoblasts under conditions of oxidative stress have not been sufficiently clarified. The aim of this study was to elucidate the effects of oxidative stress on osteogenesis. We investigated bone nodule formation in an osteoblast-like cell line, MC3T3-E1, using von Kossa staining and micro-X-ray diffraction (micro-XRD). For the micro-XRD examinations, the bone nodules were analyzed after removal from the culture plate and placed on a slide glass or a silver membrane filter. We found that nodule formation was lower on day 30 following treatment with H2O2 and mineral crystallinity in H2O2-treated cells was also lower than in the controls. These results suggest that osteoblasts damaged by oxygen free radicals produced during the aging process show a decline in their bone nodule formation ability.

Inhibition of inducible nitric oxide synthase reduces lipopolysaccharide‐induced renal injury in the rat

1. Gram-negative bacterial lipopolysaccharide (LPS) release and subsequent septic shock is a major cause of death in intensive care units. Lipopolysaccharide has been reported to increase the production of nitric oxide (NO) and the formation of oxygen-derived free radicals (OFR) in different organs. The aim of the present study was to evaluate the role of an inducible form of NO synthase (iNOS) and OFR production in LPS-induced renal impairment. 2. Measurement of vitamin E as the most important fat-soluble anti-oxidant was used as a marker of tissue oxidative stress. Lipopolysaccharide (10 mg/kg), L-iminoethyl lysine (L-Nil; 3 mg/kg, i.p.; a specific inhibitor of iNOS activity) and dimethyl thiourea (DMTU; 500 mg/kg i.p.; a well-known OFR scavenger) were used. Four groups of eight rats were studied. One group received LPS, whereas a second group received LPS + L-Nil. A third group received LPS + DMTU and the fourth group, receiving saline, acted as a control group. To evaluate renal function, plasma creatinine and blood urea nitrogen (BUN) were measured. High-pressure liquid chromatography and ultraviolet detection were used to measure plasma and tissue vitamin E levels. Light microscopy was used to examine histopathological changes in the four groups. 3. Lipopolysaccharide markedly decreased the vitamin E content of renal plasma and tissue (P < 0.05). Administration of L-Nil attenuated renal dysfunction and preserved vitamin E levels. However, DMTU failed to prevent renal injury, as indicated by plasma BUN levels and renal histology, despite the fact that it maintained renal vitamin E levels and increased plasma vitamin E levels. Thus, the overproduction of NO by iNOS may have a role in this model of LPS-induced renal impairment.

Cardioprotective and Antioxidant Effects of Apomorphine

Apomorphine is a potent antioxidant that infiltrates through biological membranes. We studied the effect of apomorphine (2 μM) on myocardial ischemic-reperfusion injury in the isolated rat heart. Since iron and copper ions (mediators in formation of oxygen-derived free radicals) are released during myocardial reperfusion, apomorphine interaction with iron and copper and its ability to prevent copper-induced ascorbate oxidation were studied. Apomorphine perfused before ischemia or at the commencement of reperfusion demonstrated enhanced restoration of hemodynamic function (i.e. recovery of the work index (LVDP × HR) was 69.2±4.0% with apomorphine pre-ischemic regimen vs. 43.4±9.01% in control hearts, p<0.01, and 76.3±8.0% with apomorphine reperfusion regimen vs. 30.4±11.1% in controls, p<0.001). This was accompanied by decreased release of proteins in the effluent and improved coronary flow recovery in hearts treated with apomorphine after the ischemia. Apomorphine forms stable complexes with copper and with iron, and inhibits the copper-induced ascorbate oxidation. It is suggested that these iron and copper chelating properties and the redox-inactive chelates formed by transition metals and apomorphine play an essential role in post-ischemic cardioprotection.

LONG TERM PRODUCTION OF REACTIVE OXYGEN SPECIES DURING PERINATAL ASPHYXIA IN THE RAT CENTRAL NERVOUS SYSTEM: EFFECTS OF HYPOTHERMIA

The formation of oxygen-derived free radicals in hypoxic and ischemic/reperfused brains has been proposed as an important step that links brain injury to neuronal death. Previously, we have demonstrated that reactive oxygen species (ROS) production was significantly increased in rat neostriatum during acute perinatal asphyxia (PA) in pups. In this article, we have studied the time course of ROS production in the neostriatum and neocortex of adult rats subjected to PA using electron spin resonance spectrometry (ESR) in order to record ROS production. Further more, we analyzed the actions of hypothermia on ROS release in pups and adult rats. We used for this study 6-month-old rats that suffered sub-severe and severe PA when they were pups. The most significant production of ROS was detected either in the neostriatum or neocortex at 19 and 20 min of PA. Hypothermia during 20 and 100 min at 15°C prevented ROS formation either in pups and adult rats. These data further support the concept that free radicals may contribute to the brain injury alterations and that hypothermia can prevent long-term sequelae induced by PA.

Vitamin E improves bone quality in the aged but not in young adult male mice

It is generally viewed that with advancing age, humans and other animals including mice experience a gradual decline in the rate of bone formation. This, in part, may be due to the rise in oxygen-derived free radical formation. Vitamin E, a strong antioxidant, functions as a free radical scavenger that potentially can suppress bone resorption while stimulating bone formation. Although the effects of vitamin E on immune functions are well documented, there is a paucity of information on its effect on skeletal health in vivo. The purpose of this study was to explore the influence of vitamin E supplementation on bone in young adult and old mice. Six and twenty-four month-old male C57BL/6NIA mice each were divided into two groups and fed a diet containing either adequate (30 mg/kg diet) or high (500 mg/kg diet) levels of vitamin E. Thirty days later, mice were killed and bones were removed for analyses including biomechanical testing using three-point bending and mRNA expressions of insulin-like growth factor-I (IGF-I), osteocalcin, and type 1α-collagen using Northern blot. In old but not the young adult mice, high-dose vitamin E enhanced bone quality as evident by improved material and structural bone properties in comparison with adequate. This improved quality was accompanied by increases in bone dry weight, protein, and mRNA transcripts for osteocalcin, type Iα−collagen, and IGF-I. These data demonstrate that high-dose vitamin E has pronounced effects on bone quality as well as matrix protein in old mice by augmenting bone matrix protein without reducing bone mineralization as evidenced by unaltered bone density.

Downregulation of Metabolic Gene Expression in Failing Human Heart before and after Mechanical Unloading

Background: We have previously shown that several metabolic genes are downregulated in the failing human heart. We now tested the hypothesis that mechanical unloading might reverse this process. Methods: Clinical data and myocardial tissue were collected from 14 failing hearts paired for the time of implantation and explantation of a left ventricular assist device (LVAD) and compared to 10 non-failing hearts. Transcript levels for key regulators of energy metabolism and for atrial natriuretic factor (ANF) were measured by real-time quantitative RT-PCR. Results: The expression of the glucose transporter 1 and 4 (GLUT1, GLUT4), muscle carnitine palmitoyl transferase-1 (mCPT-1), and uncoupling protein 3 (UCP3) were downregulated by up to 80% in the failing heart. Although LVAD treatment improved clinical markers of heart failure (decrease of left ventricular diastolic dimension and normalization of serum sodium), only UCP3 expression reversed to non-failing transcript levels following mechanical unloading. Conclusions: LVAD treatment only partially reverses depressed metabolic gene expression in the failing human heart. Reversal of depressed UCP3 expression may be an important mechanism for reducing the formation of oxygen-derived free radicals. Further studies are necessary to define the effects of mechanical unloading on post-transcriptional mechanisms.

Reactive oxygen species contribute to contractile dysfunction following rapid ventricular pacing in dogs

Background: Ventricular tachyarrhythmias may produce subsequent myocardial dysfunction through the formation of oxygen-derived free radicals. We tested the hypothesis that the antioxidant N-acetylcysteine enhances recovery of contractile function after rapid ventricular pacing. Methods: Barbiturate-anesthetized dogs were instrumented for measurement of systemic and coronary hemodynamics and subendocardial segment shortening (%SS). All dogs were subjected to 3 h of rapid ventricular pacing (230 beats/min) followed by a 2 h recovery period. In three groups ( n=8 each), dogs received intravenous 0.9% saline or N-acetylcysteine (50 or 150 mg/kg over 60 min) in a random manner before pacing. Results: N-acetylcysteine did not affect systemic and coronary hemodynamics or alter regional myocardial contractility. Rapid ventricular pacing significantly ( P<0.05) increased rate-pressure product and left ventricular end-diastolic pressure and decreased +d P/d t max. Rapid ventricular pacing produced equivalent degrees of contractile dysfunction in dogs receiving saline or N-acetylcysteine (e.g. %SS of 14.7±1.8 to −3.8±2.7% before and during pacing in saline-pretreated dogs). Dogs receiving the 150 mg/kg dose of N-acetylcysteine demonstrated greater recovery of contractile function than those pretreated with saline or the 50 mg/kg dose (e.g. %SS of 12.3±1.7% compared to 7.0±2.0% 2 h after pacing in dogs receiving saline). No differences in systemic and coronary hemodynamics were observed between groups during recovery from pacing. Conclusions: The results indicate that the N-acetylcysteine enhances recovery of contractile function after rapid ventricular pacing independent of alterations in systemic and coronary hemodynamics and imply that reactive oxygen species are an important component of the contractile dysfunction following rapid pacing in vivo.