Oxygen free radicals and reperfusion injury; the effect of ischaemia and reperfusion on the cellular ability to neutralise oxygen toxicity

Emerging role for antioxidant therapy in protection against diabetic cardiac complications: experimental and clinical evidence for utilization of classic and new antioxidants

Diabetes mellitus (DM) markedly potentiates the risk of cardiovascular morbidity and mortality among individuals with diabetes as compared to the non-diabetic population. After myocardial infarction (MI), DM patients have a higher incidence of death than do non-diabetics. The excess mortality and poor prognosis of these patients results primarily from the development of recurrent MI and heart failure (HF). Although several lines of evidence support a role for increased oxidative stress in a range of cardiovascular diseases, clinical trials examining the therapeutic efficacy of antioxidants have yielded conflicting results. The reasons for these incongruous results is multifactorial. An underlying theme has been lack of patient inclusion based on elevated indices of oxidative stress which could have diluted the population susceptible to benefit in the clinical trials. Laboratory evidence has accumulated indicating that oxidative stress is dramatically accentuated in cardiac abnormalities inherent in DM. In this review, we provide the emergence of experimental and clinical evidence supporting antioxidant supplementation as a cardioprotective intervention in the setting of DM. Specifically, focus will be directed on preclinical animal studies and human clinical trials that have tested the effect of antioxidant supplements on MI and HF events in the presence of DM.

Reduced antioxidant capacity and diet-induced atherosclerosis in uncoupling protein-2-deficient mice

Vascular dysfunction in response to reactive oxygen species (ROS) plays an important role in the development and progression of atherosclerotic lesions. In most cells, mitochondria are the major source of cellular ROS during aerobic respiration. Under most conditions the rates of ROS formation and elimination are balanced through mechanisms that sense relative ROS levels. However, a chronic imbalance in redox homeostasis is believed to contribute to various chronic diseases, including atherosclerosis. Uncoupling protein-2 (UCP2) is a mitochondrial inner membrane protein shown to be a negative regulator of macrophage ROS production. In response to a cholesterol-containing atherogenic diet, C57BL/6J mice significantly increased expression of UCP2 in the aorta, while mice lacking UCP2, in the absence of any other genetic modification, displayed significant endothelial dysfunction following the atherogenic diet. Compared with wild-type mice, Ucp2(-/-) mice had decreased endothelial nitric oxide synthase, an increase in vascular cell adhesion molecule-1 expression, increased ROS production, and an impaired ability to increase total antioxidant capacity. These changes in Ucp2(-/-) mice were associated with increased aortic macrophage infiltration and more numerous and larger atherosclerotic lesions. These data establish that in the vasculature UCP2 functions as an adaptive antioxidant defense to protect against the development of atherosclerosis in response to a fat and cholesterol diet.

Oxidant injury in coronary heart disease (Part-I)

Oxidative stress damages the heart through a series of reactions beginning with lipid peroxidation, the main process behind atherosclerosis. Antioxidant supplementation has some beneficial effects by binding with metal ions or catalysts to prevent oxidative lipid peroxidation and chain production.

Functional and ultrastructural evidence of myocardial stunning after acute carbon monoxide poisoning

OBJECTIVE

To study human myocardial ultrastructural changes after carbon monoxide (CO) poisoning inducing reversible cardiac failure.

DESIGN

CASE REPORT

clinical, functional and morphologic findings.

SETTINGS

Public university-affiliated hospital and electron microscopy laboratory.

PATIENT

A 25-yr-old woman with functional evidence of cardiac failure after acute CO poisoning.

INTERVENTIONS

Hyperbaric and intensive care treatment over 10 days. Scintigraphic and cardiac angiography with endomyocardial biopsy.

MEASUREMENTS AND MAIN RESULTS

Scintigraphy with 99mTc hexakis 2-methoxy-2-isobutyl isonitrile (sestaMIBI) showed an uptake defect in the left anterior descending artery territory. The cardiac angiography demonstrated a slight hypokinesis of the superior two thirds of the anterior wall and of the septal region with completely normal coronary angiograms. Electron microscopy of left ventricular biopsies showed slight ultrastructural changes in the myocytes. In addition, large glycogen deposits were mostly associated with swollen mitochondria. The patient was discharged in good clinical condition on day 10.

CONCLUSIONS

Presence of glycogen deposits associated with abnormal mitochondria may be signs of the incapability of myocardial cells in utilizing energy substrata. In the presence of normal myocardial perfusion, our findings are consistent with the presence of a stunned myocardium-like syndrome. Early recognition and treatment of this clinical syndrome allow the prevention of myocardial infarction.

Effect of desferrioxamine cardioplegia on ischemia-reperfusion injury in isolated rat heart

BACKGROUND

The protective effect of desferrioxamine against myocardial ischemia-reperfusion injury remains uncertain. In this study we examined a broad range of ischemia-reperfusion indices to determine the effect of desferrioxamine cardioplegia in a model that reflects surgical practice.

METHODS

Isolated rat hearts were subjected to 90 minutes of ischemia with cold cardioplegia, with or without 0.5-mmol/L desferrioxamine. Left ventricular mechanical function and the levels of thiobarbituric acid-reactive substances and nonprotein thiol compounds were measured after reperfusion. Electron microscopic analysis of mitochondria was performed using diaminobenzidine staining, together with histochemical staining for glycogen and marker enzymes in left ventricular muscle and the atrioventricular node.

RESULTS

The desferrioxamine group showed better preservation of diastolic function (chamber stiffness coefficient at 15 minutes and maximum rate of decrease of left ventricular pressure at 45 minutes of reperfusion). Histochemical analysis showed that mitochondria-specific succinate dehydrogenase and the nonspecific esterase of the atrioventricular node were better preserved in the desferrioxamine group.

CONCLUSIONS

The findings from this study indicate that there is added protection against ischemia-reperfusion injury when desferrioxamine is added to the cardioplegic solution; however, the study also highlighted that, in this clinically applicable model, desferrioxamine is not universally protective against all aspects of ischemia-reperfusion injury.

Role of oxidative stress in transition of hypertrophy to heart failure

OBJECTIVES

In an attempt to define the role of increased oxidative stress in the transition from compensatory hypertrophy to heart failure, this study examined the effects of long-term vitamin E therapy on the occurrence of heart failure subsequent to chronic pressure overload in guinea pigs.

BACKGROUND

Hyperfunctional heart hypertrophy has been shown to be accompanied by an increase in the endogenous antioxidant reserve, whereas congestive heart failure is accompanied by a decrease in this reserve. The effects of vitamin E, a naturally occurring antioxidant, on the development of heart failure from a hypertrophic stage were examined.

METHODS

The ascending aorta in guinea pigs was coarcted. For vitamin treatment, slow-release pellets were implanted at the time of the operation. The animals were assessed at 10 and 20 weeks for hemodynamic function, myocardial structure, antioxidant agents and oxidative stress.

RESULTS

Banding of the ascending aorta in guinea pigs resulted in hyperfunctional hypertrophy at 10 weeks, which was followed by congestive heart failure at 20 weeks. Hypertrophied hearts showed decreased oxidative stress, as evidenced by a higher oxidation-reduction (redox) state and less lipid peroxidation, whereas the failure stage was characterized by increased oxidative stress. Supplementation of animals with timed-release vitamin E tablets resulted in an increased myocardial content of the vitamin, and the banded animals did not develop any signs of heart failure at 20 weeks. Hemodynamic function at 20 weeks in these vitamin E-treated animals was also better maintained. The myocardial reduced glutathione/oxidized glutathione ratio of vitamin E-treated animals at 20 weeks was higher and lipid peroxidation was less compared with the untreated animals. Ultrastructural abnormalities were significantly less in the vitamin E-treated hearts compared with the untreated failing hearts at 20 weeks.

CONCLUSIONS

An improved myocardial redox state with vitamin E therapy, coupled with the modulation of the development of heart failure, may indicate a pathophysiologic role for increased oxidative stress in the pathogenesis of heart failure. This study suggests the potential therapeutic value of long-term antioxidant treatment in modulating or preventing the pathogenesis of heart failure.

Aminosulfonic acid buffer preserves myocardium during prolonged ischemia

Prevention of myocardial acidosis during global ischemia in operative cardiopreservation was explored in two series of dogs where acid-base control was the only variable. A specifically designed aminosulfonic acid buffer composition, 3:1 molar equivalents NaMOPS to HEPES, 0.2 mol/L, was compared with NaHCO3 (pH 8). Dissolved in standard cardioplegic solution it was given every 30 minutes by coronary infusion at 20 degrees C during 3 hours of global ischemia. Glass electrode intramyocardial pH, adenosine triphosphate (ATP) level, left ventricular contractility (Dp/Dt) and compliance (-Dp/Dt), and other cardiovascular parameters were measured frequently throughout ischemia and for 75 minutes thereafter. In the buffer group (n = 6) myocardial pH remained above entry levels throughout the study period, adenosine triphosphate level remained normal during ischemia, and Dp/Dt and -Dp/Dt at 75 minutes of reperfusion were above entry levels. In the NaHCO3 group (n = 6) pH declined and remained depressed throughout ischemia, adenosine triphosphate level fell steadily and significantly throughout the experiment, and Dp/Dt and -Dp/Dt never regained entry levels. The difference in each parameter between the two groups was statistically significant (p < 0.05). We conclude that control of myocardial acid-base equilibrium alone during global ischemia will preserve myocardial function and minimize reperfusion injury.

Evidence for the involvement of oxygen-derived free radicals in ischaemia-reperfusion injury

Six patients undergoing vascular reconstructive surgery were examined for evidence of oxygen-derived free radical (ORF) damage to the protein, immunoglobulin G (IgG). OFR damage was determined as an increase in the fluorescence (ex 360 nm em 454 nm) to ultraviolet absorption (280 nm) ratio of IgG, representing N-Formyl kynurenine and other as yet unidentified fluorophores. The IgG ratio was found to increase slightly during ischaemia and to undergo marked elevation upon reperfusion (275 +/- 405% baseline value at 40 min post-clamp; mean +/- sd). A high ratio was maintained post-reperfusion, even after 60 min reperfusion. Determination of thromboxane B2, (TXB2), leukotriene B4, (LTB4) and 6-keto prostaglandin F1 alpha, (PGF1a), revealed a decrease in their concentrations during ischaemia and a transient, marked increase on reperfusion. Only TXB2 concentrations were found to correlate with the IgG ratio (negative correlation, p < 0.05). No correlation was observed between von Willebrand antigen factor, a marker of endothelial cell damage and fluorescent IgG ratio. However, levels of the factor increased slightly during ischaemia and more sharply upon reperfusion. These preliminary results therefore suggest that a more likely source of the OFRs responsible for IgG damage is endothelial cell xanthine oxidase, rather than cyclo-oxygenase or lipoxygenase.

Intracellular catalase inhibition does not predispose rat heart to ischemia-reperfusion and hydrogen peroxide-induced injuries

The objective of this study was to determine whether inhibition of intracellular catalase would decrease the tolerance of the heart to ischemia-reperfusion and hydrogen peroxide-induced injuries. Isolated bicarbonate buffer-perfused rat hearts were used in the study. Intracellular catalase was inhibited with 3-amino-1,2,4-triazole (ATZ, 1.5 g/kg body weight, two hours prior to heart perfusion). In the ischemia-reperfusion protocol, hearts were arrested with St. Thomas'II cardioplegic solution, made ischemic for 35 min at 37 degrees C, and reperfused with Krebs-Henseleit buffer for 30 min. The extent of ischemic injury was assessed using postischemic contractile recovery and lactate dehydrogenase (LDH) leakage into reperfusate. In the hydrogen peroxide infusion protocol, hearts were perfused with increasing concentrations of hydrogen peroxide (inflow rates 0.05-1.25 mumol/min). Inhibition of catalase activity (30.4 +/- 1.8 mU/mg protein in control vs 2.4 +/- 0.3 mU/mg in ATZ-treated hearts) affected neither pre-ischemic aerobic cardiac function nor post-ischemic functional recovery and LDH release in hearts subjected to 35 min cardioplegic ischemic arrest. Myocardial contents of lipid hydroperoxides were similar in control and ATZ-treated animals after 20 min aerobic perfusion, ischemia, and ischemia-reperfusion. During hydrogen peroxide perfusion, there was an increase in coronary flow rate followed by an elevation in diastolic pressure and inhibition of contractile function in comparison with control hearts. The functional parameters between control and ATZ-treated groups remained unchanged. The concentrations of myocardial lipid hydroperoxides were the same in both groups. We conclude that inhibition of myocardial catalase activity with ATZ does not predispose the rat heart to ischemia-reperfusion and hydrogen peroxide-induced injury.

Preconditioning: a new technique for improved muscle flap survival

Musculocutaneous regional and distal flaps have become an important tool available to the head and neck surgeon. Vascularized autogenous muscle transplants allow single-stage reconstruction of complex defects. Ischemic muscle necrosis is a well-recognized complication with serious potential morbidity. It has been shown that myocardial muscle is protected from ischemic damage by brief periods of coronary artery occlusion and reperfusion subsequent to prolonged ischemia. This is called preconditioning. To our knowledge, this technique has never been extrapolated to skeletal muscle. This article presents a discussion of preconditioning and the potential benefits of this new technique as a means to enhance skeletal muscle survival to sustained normothermic global ischemia. Theories behind ischemic muscle injury are presented. A review of the development of preconditioning in myocardial muscle is discussed. Experimental models used to investigate this phenomenon are also presented. In addition, results of our laboratory investigations using the latissimus dorsi porcine model are discussed. Preconditioning is a new, nonpharmacologic means to improve muscle flap survival. This simple technique may have great clinical application in reducing ischemic muscle necrosis in regional and distal muscle transplantation.

Glutathione mobilization during cerebral ischemia and reperfusion in the rat

1. Cerebral ischemia applied for 15 min and followed by a 30 min reperfusion did not change the glutathione (GSH) levels and beta-adrenoceptor density (Bmax) in brain cortex. 2. A significant increase in erythrocyte-lysate GSH concentration (vs control) and a significant decrease of Bmax values in erythrocyte membranes (vs control) was found at the same time. 3. Pretreatment with the alpha-adrenoceptor antagonist phentolamine (5 mg/kg i.p.) prevented the erythrocyte GSH increase but not the decrease of Bmax value. Pretreatment with the beta-antagonist propranolol (2 mg/kg i.p.) did not influence the increase in erythrocyte GSH but circumvented the decrease of Bmax.

The role of post-ischaemic reperfusion in the development of microvascular incompetence and ultrastructural damage in the myocardium

To determine the contribution of oxygenated reperfusion to the development of myocardial microvascular incompetence and ultrastructural damage following ischaemia, isolated buffer perfused rat hearts were subjected to either temporary (n = 15) or permanent (n = 15) ischaemia for 15, 30 or 45 minutes. The temporarily ischaemic hearts were reperfused for 5 min with oxygenated Krebs Henseleit buffer. All hearts were then fixed by perfusion fixation with nitrogen-bubbled glutaraldehyde. The transmural development of microvascular incompetence was determined quantitatively by scanning electron microscopy using nuclear track photographic emulsion as an intravascular marker of competent capillaries, and ultrastructural damage was examined by transmission electron microscopy. Thirty or more minutes of ischaemia where required to significantly reduce the mean density of competent capillaries in the subendocardial third of the left-ventricular wall. Such ischaemic myocardium contained relatively normal, open unobstructed vessels, indicating that the microvascular incompetence arising during ischaemia per se was not due to ultrastructural change in the capillaries. Subendocardial myocardium reperfused following 15 min ischaemia also showed little ultrastructural change, but did show a significant reduction in the density of competent capillaries. However, reperfusion of more severely ischaemic myocardium resulted in obvious ultrastructural damage as well as significant further reduction in capillary competence. These findings demonstrate that oxygenated reperfusion of ischaemic myocardium paradoxically results in the further development of microvascular incompetence and, in severely ischaemic myocardium, also to additional ultrastructural damage.

The occurrence of oxidative stress during reperfusion in experimental animals and men

Reperfusion is the prerequisite for the ischemic myocardium to recover its metabolic and mechanical function. However, reperfusion after a prolonged period of ischemia in the experimental animal may exacerbate, or at least accelerate, the occurrence of ischemic injury, whilst in humans at the least it is not beneficial. This entity has been called reperfusion damage, since much of the damage is believed to be caused by events occurring at the moment of reperfusion rather than by changes occurring during ischemia. The existence of reperfusion damage, however, has been questioned, and evidence in favour of the concept is sparse. At the moment the molecular events occurring at the time of reperfusion are not completely understood, and the relative importance of several proposed deleterious mechanisms is not yet established. One of the most fashionable ideas for the cause of reperfusion damage is that the function of cell membrane is modified by oxygen radicals generated at the moment of reperfusion. Evidence in favour of and against this hypothesis is described in detail in the present article.

Oxygen content of the fixative is important in the interpretation of the ultrastructure of ischaemic myocardium

Isolated rat hearts were subjected to 15, 45, or 60 minutes of global ischaemia and then fixed by perfusion at 37 degrees C with glutaraldehyde containing various amounts of oxygen. This either had been bubbled with 100% oxygen (PO2 620 mm Hg) or with 100% nitrogen (PO2 40 mm Hg) immediately before use, or it had been routinely prepared and stored exposed to atmospheric oxygen (PO2 245 mm Hg). The ultrastructure of myocytes and endothelial cells subjected to 15 minutes of ischaemia was not affected by the treatment of the fixative. However, when the tissue subjected to longer periods of ischaemia was fixed with routinely prepared or oxygen-bubbled glutaraldehyde, ultrastructural changes characteristic of reoxygenation damage were uniformly evident in both the microvasculature and myocytes. These qualitatively distinct changes included mitochondrial swelling, cell swelling, endothelial bleb formation, and narrowing of capillary lumina. These abnormalities were not observed in tissue fixed with nitrogen-bubbled glutaraldehyde. These findings indicate that deliberate steps should be taken to reduce or eliminate dissolved oxygen from the fixatives used to study ischaemic tissues. Otherwise artefactual reoxygenation damage in vitro may occur and make valid ultrastructural interpretation difficult or impossible.

Superoxide dismutase therapy for myocardial ischemia

Oxygen derived free radicals have been shown to be generated during reperfusion of ischemic myocardium by a variety of approaches including spin trap probes. Three levels of injury have been described for the reperfused heart. Periods of ischemia of only several minutes can trigger lethal arrhythmias on reperfusion. Anti-oxidants including SOD and or catalase, as well as iron chelators reduce the incidence of these arrhythmias in both dog and rat. Xanthine oxidase inhibitors are equipotent with SOD in this model suggesting that xanthine oxidase is the source of the radicals. Periods of occlusion lasting 10-15 minutes produce a recoverable defect in contractility termed "stunning". SOD plus catalase has been shown to reduce the incidence of stunning in a variety of models including the xanthine oxidase deficient rabbit. Neither agent on its own seemed to be effective against stunning in either the rabbit or the dog. Stunning is more difficult to demonstrate in the rabbit heart, presumably due to its lack of xanthine oxidase. Periods of ischemia in excess of 20 minutes will result in some irreversible cell death (infarction) with reperfusion. While studies using histochemical methods suggesting that SOD plus catalase given at the time of reperfusion could limit necrosis in the dog model, histological studies reveal that infarct size was not modified but rather, SOD appears to interfere with the ability of tetrazolium to histochemically discriminate between living and dead cells. While PEG SOD with its extended plasma half life was reported to reduce infarct size in the dog, it was unable to protect the reperfused rabbit heart. To date, none of the scavengers have been proven to limit infarction suggesting that free radicals contribute to arrhythmias and stunning, but do not kill cells in the reperfused heart.

The effect of desferal on rat heart mitochondrial function, iron content, and xanthine dehydrogenase/oxidase conversion during ischemia-reperfusion

Cardiac mitochondrial function as measured by oxidative phosphorylation is impaired by ischemia; and, this deteriorates even further on reperfusion of the heart. Free oxygen radicals, especially the formation of hydroxyl radicals via the iron-catalyzed Haber-Weiss and Fenton reactions have been implicated in the reperfusion injury. In this study, the effect of desferrioxamine (desferal) in the perfusate on mitochondrial function of isolated rat hearts during different periods of normothermic ischemic cardiac arrest (NICA), and subsequent reperfusion was investigated. Mitochondrial functions measured were the QO2 (state 3); ADP/O ratio and oxidative phosphorylation; the mitochondrial, loosely bound (chelateable) iron (LB-iron); the xanthine dehydrogenase and xanthine oxidase activities. Inclusion of desferal in the perfusion solution significantly improved mitochondrial function during the different NICA periods, and prevented the deterioration of mitochondrial function resulting from reperfusion. Desferal did not significantly affect the LB-iron content of the mitochondria or the ratio of xanthine dehydrogenase/xanthine oxidase activities in the mitochondria during NICA or reperfusion. Our experiments suggest that iron, which is free to be chelated by desferal, plays a role in this injury to the rat myocardium.

Control of oxidative damage in rheumatoid arthritis by gold(I)-thiolate drugs

The roles of anti-arthritic gold(I)-thiolate drugs such as disodium aurothiomalate ('Myocrisin') in the modulation or promotion of oxygen radical-mediated oxidative damage in vivo are reviewed. In particular, the precise molecular mechanisms by which these novel second-line agents exert their therapeutic effects are discussed in terms of (i) the direct and indirect control of enzymes involved in the generation or scavenging of reactive oxygen species (ROS) such as superoxide ion, hydrogen peroxide and hydroxyl radical, (ii) the protection of proteins and relevant enzyme systems against attack by ROS and (iii) their direct involvement in the production (at appropriate 'target' sites) or scavenging of ROS in vivo. In addition, the role of the orally-effective gold(I)-phosphine complex auranofin in the control of oxidative damage in rheumatoid arthritis is also discussed.

Use of salicylate as a probe for .OH formation in isolated ischemic rat hearts

Salicylic acid was used as a probe for .OH formed during reperfusion of the ischemic myocardium. .OH adds to the phenolic ring of salicylate to yield dihydroxybenzoic acid species. The two principal dihydroxybenzoic acids formed are the 2,3- and 2,5-derivatives and can be isolated and quantitated using HPLC combined with electrochemical detection. In these experiments, dihydroxybenzoic acids were detectable in the f molar range. Rat hearts were perfused in the Langendorff mode with Krebs-Henseleit buffer containing 100 microM salicylate. Following 20 min of global ischemia a 173% increase in tissue content of 2,5-dihydroxybenzoic acid was detected after 2.5 min of reperfusion. The duration of ischemia did not significantly affect tissue content of 2,5-dihydroxybenzoic acid peaked at 250 to 300% of control within 2.5 min of reperfusion. The inclusion of 100 microM salicylate in the perfusion buffer had no effect on myocardial function during the duration of the experiments. The results indicate that salicylate can be used as a very sensitive probe for .OH in the isolated ischemic heart.

Oxygen free radical-mediated heart injury in animal models and during bypass surgery in humans. Effects of alpha-tocopherol

There is evidence that oxygen free radicals play a role in myocardial ischemic and reperfusion injury. We investigated the effect of ischemia and reperfusion on glutathione status. Reperfusion after prolonged ischemia (60 min) induced an important release of reduced (GSH) and oxidized (GSSG) glutathione, concomitant with an increase of tissue GSSG and no recovery of mechanical function, indicating that reperfusion results in oxidative stress. These alterations are associated with tissue and mitochondrial calcium accumulation, loss of mitochondrial function, and membrane damage. We also determined the arteriocoronary sinus difference for GSH and GSSG of 16 CAD patients undergoing coronary artery bypass. Patients were divided in two groups according to the length of clamping period: 25 +/- 2 min (group 1), and 55 +/- 6 min (group 2). In group 1, reperfusion resulted in a transient release of GSH, GSSG, CPK, and lactate, with return to preclamping values in 10 minutes. In group 2, reperfusion determined a sustained and pronounced release of GSH, GSSG, CPK, and lactate during declamping, suggesting the occurrence of an oxidative stress. Using an in vitro model, administration of alpha-tocopherol bound with albumin showed protection of mitochondrial function, improved recovery of contraction, and reduced oxidative stress during reperfusion.

The effect of ischemia and recirculation, hypoxia and recovery on anti-oxidant factors and beta-adrenoceptor density. Is the damage in the erythrocytes a reflection of brain damage caused by complete cerebral ischemia and by hypoxia?

This investigation was focussed on the gravity of tissue injury caused by complete ischemia (for five min) and hypoxia (for three weeks) in the cerebral cortex (homogenate) and the erythrocyte lysate or the erythrocyte membrane of the rat in order to investigate if the changes that occur in brain tissue are reflected in the erythrocyte. To this end, glutathione (GSH), superoxide dismutase (SOD) and catalase were measured, also alterations in beta-adrenoceptor density under these two conditions were examined. It was found that in ischemia partial parallelism in changes that occur in the central nervous system (cerebral cortex) and the erythrocyte exists. The SOD activity became higher and the beta-adrenoceptor density (measured as specific (-)-[125I] iodocyanopindolol binding) was decreased in both tissues. However after the hypoxic condition we established a decrease in the number of beta-adrenoceptors in the cerebral cortex but an increase in beta-adrenoceptor density in the erythrocyte.