Measurement of adrenolutin as an oxidation product of catecholamines in plasma

Oxidative Products of Catecholamines During Heightened Sympathetic Activity Due to Congestive Heart Failure: Possible Role of Antioxidants

The past several decades have shown the functional status of sympathetic activity in congestive heart failure. The results, particularly through clinical and basic studies in heart failure, indicate an increased sympathetic neural activity. The definitive and compelling evidence of the involvement of catecholamines is the demonstration that many drugs that are therapeutically useful in the treatment of heart failure also affect the sympathetic nervous system at various sites, including its synthesis, release and uptake of catecholamines and a decreased plasma norepinephrine level. Although it is not surprising that the sympathetic system is altered as cardiac function is compromised in heart failure, it now appears that this system may overreact in chronic situations. The detrimental cardiovascular problems result in the production of aminochrome and free radicals. Antioxidant therapy to target the production of aminochrome from autooxidation of catecholamines should provide an insight into the future therapeutic goal in situations like congestive heart failure.

Pheochromocytoma/paraganglioma-associated cardiomyopathy

Pheochromocytoma/paraganglioma (PPGL) are neuroendocrine tumors that frequently produce and release catecholamines. Catecholamine excess can manifest in several cardiovascular syndromes, including cardiomyopathy. PPGL-induced cardiomyopathies occur in up to 11% of cases and are most often associated with an adrenal pheochromocytoma (90%) and rarely with a paraganglioma derived from the sympathetic ganglia (10%). PPGL-associated cardiomyopathies can be chronic or acute, with takotsubo cardiomyopathy being the most often reported. These two types of PPGL-induced cardiomyopathy seem to have different pathophysiological backgrounds. Acute catecholaminergic stress inundates myocardial β-adrenoceptors and leads to left ventricle stunning and slight histological apoptosis. In chronic cardiomyopathy, prolonged catecholamine exposure leads to extended myocardial fibrosis, inflammation, and necrosis, and ultimately it causes dilated cardiomyopathy with a low ejection fraction. Sometimes, especially in cases associated with hypertension, hypertrophic cardiomyopathy can develop. The prognosis appears to be worse in chronic cases with a higher hospital mortality rate, higher cardiogenic shock rate at initial presentation, and lower left ventricular recovery rate after surgery. Therefore, establishing the correct diagnosis at an early stage of a PPGL is essential. This mini-review summarizes current data on pathophysiological pathways of cardiac damage caused by catecholamines, the clinical presentation of PPGL-induced cardiomyopathies, and discusses treatment options.

β-1 adrenoceptors and AT1 receptors may not be involved in catecholamine-induced lethal arrhythmias

An excessive amount of catecholamines produce arrhythmias, but the exact mechanisms of this action are not fully understood. For this purpose, Sprague–Dawley rats were treated with or without atenolol, a β1-adrenoceptor blocker (20 mg/kg per day), for 15 days followed by injections of epinephrine for cumulative doses of 4 to 128 μg/kg. Another group of animals were pretreated with losartan, an angiotensin receptor (AT1) blocker (20 mg/kg per day), for comparison. Control animals received saline. Varying degrees of ventricular arrhythmias were seen upon increasing the dose of epinephrine, but the incidence and duration of the rhythm abnormalities as well as the number of episodes and severity of arrhythmias were not affected by treating the animals with atenolol or losartan. The levels of both epinephrine and norepinephrine were increased in the atenolol-treated rats but were unchanged in the losartan-treated animals after the last injection of epinephrine; the severity of arrhythmias did not correlate with the circulating catecholamine levels. These results indicate that both β1-adrenoceptors and AT1 receptors may not be involved in the pathogenesis of catecholamine-induced arrhythmias and support the view that other mechanisms, such as the oxidation products of catecholamines, may play a crucial role in the occurrence of lethal arrhythmias.

Role of catecholamines in the pathogenesis of diabetic cardiomyopathy 1

Although the sympathetic nervous system plays an important role in the regulation of cardiac function, the overactivation of the sympathetic nervous system under stressful conditions including diabetes has been shown to result in the excessive production of circulating catecholamines as well as an increase in the myocardial concentration of catecholamines. In this brief review, we provide some evidence to suggest that the oxidation products of catecholamines such as aminochrome and oxyradicals, lead to metabolic derangements, Ca²⁺-handling abnormalities, increase in the availability of intracellular free Ca²⁺, as well as activation of proteases and changes in myocardial gene expression. These alterations due to elevated levels of circulatory catecholamines are associated with oxidative stress, subcellular remodeling, and the development of cardiac dysfunction in chronic diabetes.

Edaravone protects rats against oxidative stress and apoptosis in experimentally induced myocardial infarction: Biochemical and ultrastructural evidence

OBJECTIVES

The present study was designed to evaluate the cardioprotective potential of edaravone on oxidative stress, anti-apoptotic, anti-inflammatory and ultrastructure findings in isoproterenol (ISO) induced myocardial infarction (MI) in rats.

METHODS

Rats were pretreated with edaravone (1, 3, 10 mg/kg body weight-1 day-1) intraperitoneally. MI was induced by subcutaneous administration of ISO (85 mg/kg body weight-1) at two doses with 24h interval.

RESULTS

ISO treated rats showed significant increase in the levels of thiobarbituric acid reactive substances (TBARS) and decreased levels of reduced glutathione, glutathione perdoxidase, glutathione reductase and glutathione-S- transferase in the cardiac tissues. Moreover, significant increase in the levels of lactate dehydrogenase (LDH), creatine kinase-MB (CK-MB), C--reactive protein and caspase-3 activity was observed in ISO treated group. Pretreatment of ISO intoxicated rats with edaravone showed significant decrease in the level of TBARS, increased activities of antioxidant enzymes and significantly decreased levels of LDH and CK-MB. Moreover, results also showed decreased C-reactive protein level, caspase-3 activity and maintained ultrastructure of the myocardial cells.

DISCUSSION

Our study suggests that edaravone possess strong cardioprotective potential. Edaravone may have exhibited cardioprotective effects by restoring antioxidant defense mechanism, maintaining integrity of myocardial cell membrane, reducing apoptosis and inflammation against ISO induced MI and associated oxidative stress.

Role of microangiopathy in diabetic cardiomyopathy

Although heart disease due to diabetes is mainly associated with complications of the large vessels, microvascular abnormalities are also considered to be involved in altering cardiac structure and function. Three major defects, such as endothelial dysfunction, alteration in the production/release of hormones, and shift in metabolism of smooth muscle cells, have been suggested to produce damage to the small arteries and capillaries (microangiopathy) due to hyperglycemia, and promote the development of diabetic cardiomyopathy. These factors may either act alone or in combination to produce oxidative stress as well as changes in cellular signaling and gene transcription, which in turn cause vasoconstriction and structural remodeling of the coronary vessels. Such alterations in microvasculature produce hypoperfusion of the myocardium and thereby lower the energy status resulting in changes in Ca(2+)-handling, apoptosis, and decreased cardiac contractile force. This article discusses diabetes-induced mechanisms of microvascular damage leading to cardiac dysfunction that is characterized by myocardial dilatation, cardiac hypertrophy as well as early diastolic and late systolic defects. Metabolic defects and changes in neurohumoral system due to diabetes, which promote disturbances in vascular homeostasis, are highlighted. In addition, increase in the vulnerability of the diabetic heart to the development of heart failure and the signaling pathways integrating nuclear factor κB and protein kinase C in diabetic cardiomyopathy are also described for comparison.

Modification of epinephrine-induced arrhythmias by N-acetyl-L-cysteine and vitamin E

Sprague-Dawley rats were pretreated for 21 days with N-acetyl-L-cysteine (NAC) or vitamin E to investigate their influence on arrhythmias induced by a bolus injection or by cumulative doses of epinephrine. Electrocardiographic analysis revealed that both NAC and vitamin E decreased the duration and increased the time of onset of epinephrine-induced arrhythmias in a dose-dependent manner. The antiarrhythmic effects of NAC were comparable with those seen in the vitamin E-pretreated animals. The lipid peroxidation due to cumulative doses of epinephrine was reduced in both pretreated groups; however, NAC, unlike vitamin E, failed to decrease the basal level of malondialdehyde. Although the plasma concentrations of both norepinephrine and epinephrine were markedly increased, the level of aminochromes on epinephrine administration was decreased by both NAC and vitamin E pretreatments. The results support the view that antioxidants may prevent the catecholamine-induced heart rhythm disorders by reducing the formation of oxidized catecholamines.

Peroxynitrite and myocardial contractility: in vivo versus in vitro effects

Generation of peroxynitrite (ONOO-) as a result of altered redox balance has been shown to affect cardiac function; however, inconsistencies in the data exist, particularly for myocardial contractility. The hypothesis that the cardiac impact of ONOO- formation depends on its site of generation, intravascular or intramyocardial, was examined. Cardiac contractility was assessed by pressure-volume analysis to delineate vascular versus cardiac changes on direct infusion of ONOO- into the right atria of conscious dogs both with normal cardiac function and in heart failure. Additionally, ONOO- was administered to isolated murine cardiomyocytes to mimic in situ cardiac generation. When infused in vivo, ONOO- had little impact on inotropy but led to systemic arterial dilation, likely as a result of rapid decomposition to NO2- and NO3-. In contrast, infused ONOO- was long lived enough to abolish beta-adrenergic (dobutamine)-stimulated contractility/relaxation, most likely through catecholamine oxidation to aminochrome. When administered to isolated murine cardiomyocytes, ONOO- induced a rapid reduction in sarcomere shortening and whole cell calcium transients, although neither decomposed ONOO- or NaNO2 had any effect. Thus, systemic generation of ONOO- is unlikely to have primary cardiac effects, but may modulate cardiac contractile reserve, via blunted beta-adrenergic stimulation, and vascular tone, as a result of generation of NO2- and NO3-. However, myocyte generation of ONOO- may impair contractile function by directly altering Ca2+ handling. These data demonstrate that the site of generation within the cardiovascular system largely dictates the ability of ONOO- to directly or indirectly modulate cardiac pump function.

Effect of adrenalin, adrenochrome, and adrenolutin on connexin proteins in the cardiovasculature

Reported myocardial pathology resulting from increased levels of catecholamines in vivo has led us to investigate the effect of adrenalin on the gap junction proteins connexin 40 (Cx40) and Cx43 and the possible relationship to vascular toxicity. Adrenalin and its known metabolites, adrenochrome and adrenolutin, were used in this study. Utilizing the A7r5 rat aortic cell line, we evaluated the effects of adrenalin, adrenochrome, and adrenolutin on the expression and function of connexin 40 and 43 that are present in both cardiac and vascular tissues.

The separation and quantification of aminochromes using high-pressure liquid chromatography with electrochemical detection

There is increasing evidence that oxidative stress plays an important role in the pathogenesis of many neurodegenerative diseases including Parkinson's disease (PD). In particular there is support for the participation of oxidized catecholamines in PD. Catecholamines are highly reactive and are readily oxidized to aminochromes. While aminochromes have been shown to be toxic, their formation in oxidative stress and subsequent participation in disease has yet to be confirmed. We propose that the characterization of aminochromes, specifically dopaminochrome, is important in clarifying the role that oxidized catecholamines play in PD. We have developed a novel method for the separation and quantification of aminochromes using high-pressure liquid chromatography with electrochemical detection (HPLC-ED). Our method utilizes the separation principles employed in measuring catecholamines by HPLC except that the electrochemical detection of aminochromes is achieved by reversing the detector's electrode. We have used this method to separate and quantify aminochrome standards, prepared by oxidizing catecholamines with sodium periodate (NaIO(4)) and we have also shown that aminochromes can be measured in plasma and cell lysates. Furthermore, we have characterized aminochromes to facilitate forthcoming studies on aminochromes and the role oxidized catecholamines may play in neurodegenerative disease.

Leucoisoprenochrome-o-semiquinone Formation in Freshly Isolated Adult Rat Cardiomyocytes

Sustained high levels of circulating catecholamines can lead to cardiotoxicity. There is increasing evidence that this process may result from metal-catalyzed catecholamine oxidation into semiquinones, quinones, and aminochromes. We have previously shown that Cu2+-induced oxidation of isoproterenol into isoprenochrome induces toxic effects in isolated cardiomyocytes. The aim of this study was to characterize the isoproterenol oxidation process and to locate the formation of semiquinone radicals in cardiomyocyte suspensions. Freshly isolated rat cardiomyocytes were incubated with 1 or 10 mM isoproterenol and 20 microM Cu2+ for 4 h. The formation of an isoproterenol oxidation radical was detected in the extracellular medium, cells, membranes, and heavy organelles by electron spin resonance spectroscopy. An electron spin resonance signal assigned to leucoisoprenochrome-o-semiquinone increased in a time-dependent manner in the extracellular medium. A second electron spin resonance signal, characteristic of an immobilized radical, was also found in the cardiomyocytes. The latter was attributed to leucoisoprenochrome-o-semiquinone immobilized on cellular components such as membranes, cytoskeleton, nucleus, and heavy organelles. In addition, the levels of leucoisoprenochrome-o-semiquinone decreased in the presence of glutathione. Computer simulations of the experimental spectra indicate the formation of two distinct isomeric leucoisoprenochrome-o-semiquinone radicals during isoproterenol oxidation. The present study shows that the isoproterenol oxidation in isolated rat cardiomyocytes correlates with the formation of leucoisoprenochrome-o-semiquinone in the cells and in the extracellular medium, suggesting that it might be involved in cardiotoxicity induced by the oxidation of catecholamines.

Neurohormones and oxidative stress in nonischemic cardiomyopathy: relationship to survival and the effect of treatment with amlodipine

OBJECTIVES

The purpose of this study was to assess the effects of amlodipine on neurohormones and oxidative stress in nonischemic cardiomyopathy, and determine the relationship between baseline and posttreatment levels of these markers with survival.

BACKGROUND

Neurohormones and oxidative stress are important in the pathophysiology of heart failure. Calcium-channel blockers are associated with poor outcomes in patients with heart failure, in part due to neurohormonal activation. In contrast, amlodipine, a second-generation dihydropyridine, has a more favorable clinical profile.

METHODS

In the Prospective Randomized Amlodipine Survival Evaluation 2 (PRAISE-2) trial, a subset of 181 patients with nonischemic cardiomyopathy were randomized to amlodipine (10 mg/day) or placebo. Blood samples were evaluated at baseline, 2 weeks and 26 weeks for norepinephrine, epinephrine, angiotensin II, dopamine, N-terminal pro-atrial natriuretic peptide (Nt-pro-ANP), brain natriuretic peptide (BNP), adrenolutin and malondialdehyde.

RESULTS

There was no difference in levels of neurohormones or oxidative stress markers between the amlodipine and placebo groups at the different times. Both Nt-pro-ANP and BNP decreased at 2 weeks and at 26 weeks. Baseline Nt-pro-ANP correlated with survival in multivariate analysis (P =.001). A strong relationship was found between a reduction in BNP at 26 weeks and survival, with a hazard ratio of 0.153 (95% CI 0.051-0.461, P =.017). No relationship was found between markers of oxidative stress and survival.

CONCLUSIONS

We conclude that amlodipine does not affect circulating neurohormones and oxidative stress markers in patients with nonischemic cardiomyopathy treated with angiotensin-converting enzyme inhibitors, digoxin and diuretics. In addition, low circulating Nt-pro-ANP and a reduction in BNP over time confers a good prognosis.

Prognostic importance of the oxidized product of catecholamines, adrenolutin, in patients with severe heart failure

OBJECTIVES

The purpose of this study was to assess whether adrenolutin, the inert product of the highly reactive molecules aminochromes, is increased in severe chronic heart failure and whether it is associated with a poor prognosis.

BACKGROUND

Experimental evidence suggests that oxidative products of catecholamines, aminochromes, are more cardiotoxic than unoxidized catecholamines and may be increased in heart failure.

METHODS

Adrenolutin was measured at baseline and at 1 and 3 months in 263 patients with chronic New York Heart Association class III or IV heart failure and a left ventricular ejection fraction of 22% +/- 7%. Adrenolutin levels were compared with normal levels, and their relation to prognosis was evaluated.

RESULTS

Baseline adrenolutin was increased (55 +/- 90 pg/mL vs 8.4 +/- 9.1 pg/mL for control, P <.02) and remained increased at 1 month (49 +/- 65 pg/mL). During a mean follow-up of 309 +/- 148 days (22-609 days), 57 patients died. Baseline adrenolutin levels correlated with mortality rates by univariate and multivariate analyses (relative risk 1.06, 95% CI 1.01-1.10 for each 17.9-pg/mL rise, P =.032). Left ventricular ejection fraction (P =.013) and New York Heart Association class (P =.009) were the only other variables associated with survival. Age, sex, plasma creatinine, plasma N-terminal atrial natriuretic peptide, and plasma norepinephrine levels were not retained in our model. Adrenolutin levels 1 month after random assignment were not significantly correlated with total mortality rate (P =.061) but were correlated with mortality rate from low output (relative risk 1.14, 95% CI 1.06-1.22, P =.002).

CONCLUSIONS

Plasma adrenolutin is increased in patients with heart failure and correlates with a poor prognosis independent of other important predictors of survival. This finding has potentially important pathophysiologic, prognostic, and therapeutic implications.

Identification of serum soluble ST2 receptor as a novel heart failure biomarker

BACKGROUND

Using genomic technology, we previously identified an interleukin-1 receptor family member, ST2, as a gene markedly induced by mechanical strain in cardiac myocytes. The soluble receptor form of ST2 is secreted and detectable in human serum. This study tested the hypothesis that soluble ST2 levels in the serum of patients with severe chronic heart failure are increased in patients with neurohormonal activation.

METHODS AND RESULTS

Serum samples, clinical variables, and neurohormone levels from the PRAISE-2 heart failure trial (NYHA functional class III-IV; end point, mortality or transplantation) were analyzed. ST2 serum measurements were performed with ELISA on samples from 161 patients obtained at trial enrollment and from 139 of the same patients obtained 2 weeks after trial enrollment. Baseline ST2 levels were correlated with baseline B-type natriuretic peptide (BNP) levels (r=0.36, P<0.0001), baseline proatrial natriuretic peptide (ProANP) levels (r=0.36, P<0.0001), and baseline norepinephrine levels (r=0.39, P<0.0001). The change in ST2 was significant as a univariate predictor of subsequent mortality or transplantation (P=0.048), as was baseline BNP (P<0.0001) and baseline ProANP (P<0.0001). In multivariate models including BNP and ProANP, the change in ST2 remained significant as a predictor of mortality or transplantation independent of BNP and ProANP.

CONCLUSIONS

Serum soluble ST2 is a novel biomarker for neurohormonal activation in patients with heart failure. In patients with severe chronic NYHA class III to IV heart failure, the change in ST2 levels is an independent predictor of subsequent mortality or transplantation.

Synthesis and analysis of aminochromes by HPLC-photodiode array. Adrenochrome evaluation in rat blood

The catecholamine oxidation process induces cardiotoxicity and neurotoxicity. Catecholamines can oxidize to aminochromes through autoxidation or by enzymatic or non-enzymatic catalysis. Although some toxic effects seem to be related to the formation of aminochromes there is still scarce information concerning the identification and evaluation of these compounds in in vivo models. In this study five catecholamines were oxidized to their respective aminochromes: adrenaline/adrenochrome; noradrenaline/noradrenochrome; dopa/dopachrome; dopamine/dopaminochrome; and isoproterenol/isoprenochrome. The evaluation of the catecholamines oxidation profile was performed by HPLC with photodiode array detection and using either enzymatic (tyrosinase) or non-enzymatic [Ag(2)O, CuSO(4), NaIO(4) and K(3)Fe(CN)(6)] catalytic systems. The NaIO(4) was found to be the most efficient oxidant of catecholamines. An isocratic reverse-phase HPLC method was developed to analyse each pair of catecholamine-aminochrome. The analytical system was then applied to the detection of adrenochrome in rat blood at 490 nm. Thus, adrenochrome was administered i.p. to rats and its concentration in whole blood was monitored after 5, 15 and 25 min. Blood treatment for adrenochrome evaluation consists of an acidification for protein precipitation followed by a rapid neutralization. The results showed a rapid decrease of adrenochrome concentration in blood after its administration. The adrenochrome present in blood was characterized by UV and tandem mass spectrometry.

Cu2+-induced isoproterenol oxidation into isoprenochrome in adult rat calcium-tolerant cardiomyocytes

Sustained high levels of circulating catecholamines may induce cardiotoxicity. There is increasing evidence that this could result from catecholamine oxidation into aminochromes, which is catalyzed by transition metals. In fact, it has already been shown that copper-induced oxidation of the beta-agonist isoproterenol decreases the viability of isolated cardiomyocytes. Thus, the aim of this work was to contribute for the clarification of the mechanisms underlying the toxic effects of isoproterenol, Cu2+ and their concomitant effect in isolated rat cardiomyocytes. Freshly isolated calcium-tolerant cardiomyocytes from adult rat were incubated with 1 mM isoproterenol, 20 microM Cu2+ or with both during 4 h. Isoproterenol and its aminochrome (isoprenochrome), and reduced and oxidized glutathione were measured at each hour in the incubation medium and in the cells. The intracellular activities of the selenium-dependent glutathione peroxidase, glutathione reductase, and glutathione-S-transferase were determined after 4 h of incubation. Isoprenochrome was found in both cells and incubation medium in samples incubated with isoproterenol alone. However, in the isoproterenol plus Cu2+ samples, a greater depletion of isoproterenol accompanied by a proportional increase of isoprenochrome was observed. This higher ISO oxidation resulted in the depletion of intracellular glutathione and in the release of oxidized glutathione to the incubation medium. The content of total glutathione (intra- and extracellular) and the intracellular activity of the selenium-dependent glutathione peroxidase, glutathione reductase, and glutathione-S-transferase were also decreased in the isoproterenol plus Cu2+ samples. These results seem to indicate that the oxidative stress resulting from catecholamine/transition metal association may contribute to catecholamine cardiotoxicity.

Toxicology update: the cardiotoxicity of the oxidative stress metabolites of catecholamines (aminochromes)

This toxicology update reviews the oxidative stress metabolites of catecholamines, postulated to be the biochemical initiators of cardiotoxicity. A brief overview of catecholamine metabolism is provided with several noteworthy historical observations relating to the autoxidation and rearrangement of epinephrine. The basic chemical and physical properties of adrenochrome and adrenolutin are discussed. The autoxidative, enzymatic and cellular basis for the transformation of catecholamines to oxidative metabolites is reviewed. Mechanisms seeking to account for the observed cardiotoxic changes in isolated heart perfusion studies and in vivo models are described.

Role of Oxidative Stress in Catecholamine-Induced Changes in Cardiac Sarcolemmal Ca2+ Transport

Although an excessive amount of circulating catecholamines is known to induce cardiomyopathy, the mechanisms are poorly understood. This study was undertaken to investigate the role of oxidative stress in catecholamine-induced heart dysfunction. Treatment of rats for 24 h with a high dose (40 mg/kg) of a synthetic catecholamine, isoproterenol, resulted in increased left ventricular end diastolic pressure, depressed rates of pressure development, and pressure decay as well as increased myocardial Ca2+ content. The increased malondialdehyde content, as well as increased formation of conjugated dienes and low glutathione redox ratio were also observed in hearts from animals injected with isoproterenol. Furthermore, depressed cardiac sarcolemmal (SL) ATP-dependent Ca2+ uptake, Ca2+-stimulated ATPase activity, and Na+-dependent Ca2+ accumulation were detected in experimental hearts. All these catecholamine-induced changes in the heart were attenuated by pretreatment of animals with vitamin E, a well-known antioxidant (25 mg/kg/day for 2 days). Depressed cardiac performance, increased myocardial Ca2+ content, and decreased SL ATP-dependent, and Na+-dependent Ca2+ uptake activities were also seen in the isolated rat hearts perfused with adrenochrome, a catecholamine oxidation product (10 to 25 microg/ml). Incubation of SL membrane with different concentrations of adrenochrome also decreased the ATP-dependent and Na+-dependent Ca2+ uptake activities. These findings suggest the occurrence of oxidative stress, which may depress the SL Ca2+ transport and result in the development intracellular Ca2+ overload and heart dysfunction in catecholamine-induced cardiomyopathy.

Inactivation of catecholamines by superoxide gives new insights on the pathogenesis of septic shock

A major feature of septic shock is the development of a vascular crisis characterized by nonresponsiveness to sympathetic vasoconstrictor agents and the subsequent irreversible fall in blood pressure. In addition, sepsis, like other inflammatory conditions, results in a large increase in the production of free radicals, including superoxide anions (O(2)) within the body. Here we show that O(2) reacts with catecholamines deactivating them in vitro. Moreover, this deactivation would appear to account for the hyporeactivity to exogenous catecholamines observed in sepsis, because administration of a superoxide dismutase (SOD) mimetic to a rat model of septic shock to remove excess O(2) restored the vasopressor responses to norepinephrine. This treatment with the SOD mimetic also reversed the hypotension in these animals; suggesting that deactivation of endogenous norepinephrine by O(2) contributes significantly to this aspect of the vascular crisis. Indeed, the plasma concentrations of both norepinephrine and epinephrine in septic rats treated with the SOD mimetic were significantly higher than in untreated rats. Interestingly, the plasma concentrations for norepinephrine and epinephrine were inversely related to the plasma concentrations of adrenochromes, the product of the autoxidation of catecholamines initiated by O(2). We propose, therefore, that the use of a SOD mimetic represents a new paradigm for the treatment of septic shock. By removing O(2), exogenous and endogenous catecholamines are protected from autoxidation. As a result, both hyporeactivity and hypotension are reversed, generation of potentially toxic adrenochromes is reduced, and survival rate is improved.

Effect of behavioral stress on coronary artery relaxation altered with aging in BHR

Behavioral stress and aging are associated with an increase in vascular disease. This study determined the mechanisms contributing to changes in endothelium-dependent relaxation of isolated coronary arteries (300-350 micrometers) induced by exposure to 10 days of air-jet stress (2 h/day) in young (3 mo) and old (18 mo) male borderline hypertensive rats (BHR). Aging, alone, did not alter endothelium-dependent relaxation to acetylcholine (ACh) quantitatively but did alter the mechanisms contributing to relaxation to ACh, which was largely dependent on nitric oxide synthase (NOS) in vessels from old, but not young, BHR. Behavioral stress resulted in an enhanced relaxation to ACh that was dependent on NOS in vessels from young stressed compared with young control BHR. Conversely, relaxation to ACh was reduced in coronary arteries from old stressed compared with old control BHR. In vessels from old control BHR, there was an NOS-independent component of relaxation mediated by opening of K+ channels that was absent in vessels from old stressed BHR. The superoxide anion scavenger, tiron, partially restored relaxation, and inhibition of cyclooxygenase largely restored relaxation to ACh in vessels from old stressed BHR. In summary, the effect of behavioral stress was age dependent. ACh-induced relaxation of coronary arteries was enhanced in an NOS-dependent manner in young BHR and was impaired in old BHR due to superoxide anions, vasoconstrictor cyclooxygenase products, and a loss of K+ channel-mediated relaxation.

Behavioral stress alters coronary vascular reactivity in borderline hypertensive rats

BACKGROUND

Behavioral stress has been proposed to contribute to the occurrence of myocardial ischemia. Objective To investigate the effect of chronic exposure to behavioral stress on the function and structure of the coronary artery of borderline hypertensive rats (BHR).

DESIGN

BHR were either exposed to an air-jet stress for 2 h/day for 10 days or kept in their cage for 10 days.

METHODS

After 10 days, hemodynamic measurements in conscious animals were recorded, and their hearts were removed for isolation of a left ventricular coronary artery for functional studies or for fixation by retrograde perfusion for study with scanning electron microscopy. Vascular reactivity was measured in isolated coronary arteries (approximately 250 microm) maintained at an intraluminal diameter of 40 mmHg while the intraluminal diameter was recorded continuously.

RESULTS

The resting mean arterial pressure and heart rate in conscious, unrestrained BHR were not altered significantly by exposure to 10 days of 2 h/day air-jet stress. Coronary artery relaxation in response to the endothelium-dependent vasodilator acetylcholine was impaired in rats exposed to the air-jet stress compared with that in controls. An attenuated response to exogenous nitric oxide in coronary arteries from stressed BHR was confirmed by the finding of a reduced sensitivity to nitroprusside, which releases nitric oxide independently from the endothelium. However, relaxation of coronary arteries in response to isoproterenol, which acts independently from nitric oxide, was not altered. Coronary artery contraction in response to endothelin-1 and phenylephrine was not altered in vessels taken from BHR exposed to behavioral stress compared with that in vessels from control rats. Scanning electron microscopy of the endothelial surface of the septal coronary artery showed no difference between vessels from control and stressed BHR.

CONCLUSION

These results indicate that behavioral stress impairs endothelium-dependent and nitric oxide-mediated coronary relaxation, but does not alter alpha1-adrenoceptor or endothelin-1-mediated contraction. By impairing coronary artery vascular relaxation, chronic exposure to behavioral stress may contribute to myocardial ischemia.

Mechanisms of alterations in cardiac membrane Ca2+ transport due to excess catecholamines

The occurrence of excessive catecholamine release is often associated with stress due to the lifestyle of Western societies. Contrary to the general thinking that excess catecholamines produce cardiotoxicity mainly via binding to adrenoceptors, there is increasing evidence that catecholamine-induced deleterious actions may also occur through oxidative mechanisms. In this overview it is shown that a high dose of isoproterenol induces a biphasic change in cardiac Ca2+ transport in the sarcolemma and in sarcoplasmic reticulum. Both sarcolemmal and sarcoplasmic reticular Ca2+-transport activities are initially increased to maintain Ca2+ homeostasis and then are impaired, which may be associated with the occurrence of intracellular Ca2+ overload. On the other hand, mitochondrial Ca2+-transport activities exhibited a delayed increase. Pretreatment with vitamin E partially prevented the deleterious changes in cardiac membranes as well as the depressed energetic status of the heart muscle cell. It is concluded that excess catecholamines affect Ca2+-transport mechanisms primarily via oxidation reactions involving free radical-mediated damage. Thus drug approaches that reduce circulating catecholamines and/or prevent their oxidation should prove beneficial. A combination therapy involving inhibitors of catecholamine release, blockers of adrenoceptors, and antioxidants may be indicated for stress-induced heart disease.

Functional effects of adrenochrome in isolated rabbit heart

The cardiotoxic effects of catecholamines have been explained in part by the generation of oxygen free radicals and aminochromes. The role of aminochromes remains however controversial. It has previously been demonstrated that adrenochrome, an oxidation product of adrenaline, shows cardiotoxic properties only at very high concentrations, and it has been suggested that the deleterious effects observed may be caused by a worsening in myocardial perfusion. The functional properties of adrenochrome were examined in isolated spontaneously-beating rabbit hearts with depleted catecholamine stores (reserpin 7.0 mg/kg 16-24 hr before preparation, Langendorff, constant pressure: 70 cm H2O, Tyrode solution, [Ca++]sol. 1.8 mmol/l, 37 degrees). Cumulative concentration-response curves show an adrenochrome-concentration-dependent increase of contractility (left ventricular pressure, EC50 = 3.6 x 10(-6) M; +dp/dtmax, EC50 = 1.6 x 10(-5) M), whereas myocardial relaxation was impaired (-dp/dtmax, EC50 = 2.6 x 10(-5) M; -dp/dtmax/+dp/dtmax = 0.68 at 10(-4) M). Heart-rate was only slightly enhanced (+10% at 10(-4) M), and the coronary flow was markedly influenced only by adrenochrome 10(-4) M (-17%). The relative coronary flow (= global coronary flow/pressure-rate product) was concentration-dependently reduced (EC50 = 10(-5) M; -49% at 10(-4) M). We conclude that in isolated rabbit hearts, adrenochrome has a positive inotropic action but impairs myocardial relaxation, and coronary constrictor activity prevents an increase of myocardial oxygen supply, thus worsening myocardial oxygen-demand/supply balance.

The pathophysiology of cocaine cardiotoxicity

Cocaine use is accompanied by a high risk of serious adverse effects involving the cardiovascular system. The basic cellular mechanisms of cocaine consist in [1] a potentiation of catecholamine effects by inhibition of the presynaptic uptake carrier [2] local anesthetic effects by the block of sodium-channels. Acute ischemic events can be induced by cocaine through coronary spasms in a situation of physiologic stress already accompanied by an enhanced myocardial oxygen demand. Procoagulant properties of cocaine may, moreover, favor coronary thrombosis formation and the development of myocardial infarction. Ischemia, reperfusion and the direct action of catecholamines on cardiocytes are accompanied by enhanced cytoplasmic calcium levels, inducing delayed after-potentials, repetitive action-potential generation and premature ventricular beats. Conduction velocity impairments caused by the local anesthetic effects of cocaine and inhomogeneous repolarization phenomena related to potassium channel inhibition may form a substrate for re-entrant circuits inducing ventricular fibrillation. Cocaine abuse may also cause degenerative and inflammatory alterations of the myocardium. Besides secondary ischemic changes, hypersensitivity-myocarditis and toxic cardiomyopathies that may be due to the cardiotoxic effects of catecholamines have been described in cocaine abusers. Moreover, persons using cocaine intravenously seem to be particularly endangered by bacterial endocarditis compared to the users of other intravenous drugs, for still unknown reasons.

Cardiotoxicity of adrenochrome in isolated rabbit hearts assessed by epicardial NADH fluorescence

Noradrenaline in a micromolar concentration has recently been shown to contribute to ischemic tissue injury by direct cardiotoxic effects independent of functional alterations. Oxygen free radicals, generated during the auto-oxidation of catecholamines, are important mediators of catecholamine cardiotoxicity. However, the role of the oxidative products (aminochromes) is still unclear. We examined the effects of adrenochrome on functional parameters and on regional myocardial ischemia (MI) in isolated electrically-driven rabbit hearts with depleted catecholamine stores (reserpine 7.0 mg/kg i.p. 16-24 h before preparation, Langendorff, constant pressure: 70 cm H2O, Tyrode solution, Ca++ 1.8 mmol/l, 37 degrees C). Repetitive MI, separated by a reperfusion period of 50 min, was induced by coronary artery branch ligature, and MI was quantitated from epicardial NADH fluorescence photography. Adrenochrome-treatment (10(-6) M or 10(-4) M) was started after a reperfusion period of 20 min. The left ventricular pressure (LVP) was significantly enhanced by adrenochrome (p < 0.05), but it fell thereafter to below its initial value in hearts treated with adrenochrome 10(-4) M. The global coronary flow (CF) was not affected by adrenochrome 10(-6) M (P > 0.05), but it was significantly decreased by adrenochrome 10(-4) M (P < 0.05). The relative CF (= CF/LVP x heart-rate) was numerically decreased by adrenochrome 10(-6) M (p > 0.05) and more markedly by adrenochrome 10(-4) M (p < 0.05). Whereas epicardial NADH fluorescence was similar after repetitive coronary artery occlusions in controls and in hearts treated with adrenochrome 10(-6) M (p > 0.05), it was significantly enhanced by adrenochrome 10(-4) M (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Observations on atrial natriuretic peptide, sympathetic activity and renal Ca2+ pump in diabetic and hypertensive rats

The relationship between atrial natriuretic peptide (ANP) and peripheral sympathetic nervous system function was studied in diabetic and hypertensive rats. Animals were studied in diabetic and hypertensive rats. Animals were divided into four groups: control, diabetic, hypertensive and diabetic plus hypertensive. Diabetes was induced by streptozotocin (65 mg/kg) injection and hypertension by abdominal aortic constriction. Studies were performed at 1 and 6 weeks. Plasma ANP was increased at 1 week in all groups except controls. Noradrenaline turnover, an index of sympathetic activity in kidney, was attenuated in all pathological groups unlike controls. These changes were associated with increased activity of Ca2++Mg2+ ATPase, which is known to serve as a Ca2+ pump in kidney cortex basolateral membrane. In contrast, at 6 weeks, Ca2++Mg2+ ATPase was significantly decreased only in the diabetic plus hypertensive group which also showed signs of congestive heart failure, increased sympathetic activity and decreased plasma ANP levels. Intracerebral microdialysis of the extracellular space around the paraventricular nucleus (PVN) of the hypothalamus showed a decreased concentration of ANP in the diabetic plus hypertensive group. Infusion of ANP and pentolinium, a ganglionic blocker in diabetic plus hypertensive Ca2+ restored pump activity towards control values; ANP alone had no effect. Our results indicate decreased plasma ANP levels, increased sympathetic drive and a depressed kidney Ca2+ pump in diabetic plus hypertensive rats with heart failure. The relationships between these factors, and the potential modulating role of ANP is discussed.

Biochemical and toxicological properties of the oxidation products of catecholamines

The normal catabolism of catecholamines proceeds through enzymatic pathways (monoaminooxidase, catechol-o-methyltranserase, and phenolsulphotransferase). In addition, nonenzymatic oxidative pathways might take place since catechols are readily oxidized. In this review article, the pathways of formation of the oxidation products of catecholamines and their reactions are described. The interactions of these products with different biological systems and their toxicity are examined. Among the reactions known to occur is that with sulfhydryls, which results in either a covalently linked adduct or disulfide production. Another interesting pathway to toxicity involves the oxidation of these catecholamine products by oxygen, with the formation of damaging oxygen-derived species. The action of the oxidation products of catecholamines is outlined, with special attention to the nervous and cardiac systems.

Impaired inotropic responses to adrenergic stimulation following aortic constriction: role of oxidation product of catecholamines

In order to support the hypothesis that oxygen free radicals derived from persistent sympathetic drive play an important role in the modulation of receptor-mediated effect in cardiac hypertrophy, rat hearts subjected to aortic banding-induced pressure overload were assessed on postoperative days 3, 14, and 28. Sham-operated rats without aortic banding were used as a control group. Cardiac alpha-adrenoceptors were increased at day 3 whereas beta-adrenoceptors were increased at postoperative days 14 and 28; these results were associated with increased amount of circulating norepinephrine and adrenolutin, one of the oxidation products of catecholamines. The hearts of these animals were also perfused by Langendorff technique in the presence and absence of adrenergic agonists. Banded animals had a diminished inotropic response to alpha agonists in addition to their reduced inotropic responsiveness to beta-adrenergic stimuli. These changes were however, reversible in animals pretreated with alpha-tocopherol, a powerful antioxidant. Furthermore, the circulating level of adrenolutin was normalized by such treatment. These results indicate that an oxidation product of catecholamines may be responsible for impaired inotropic responses to adrenergic stimulation following aortic constriction.