Protective effect of sulfinpyrazone against catecholamine metabolite adrenochrome-induced arrhythmias

Metanephrine and normetanephrine associated with subclinical myocardial injuries in pheochromocytoma and paraganglioma

Objective

To analyze the correlation between metanephrine and normetanephrines (MNs) and subclinical myocardial injuries (SMI) diagnosed by low left ventricular global longitudinal strain (LV GLS) in patients with pheochromocytoma and paraganglioma (PPGL).

Methods

Seventy-six patients who underwent surgery for pheochromocytoma or paraganglioma from September 2017 to April 2022 were examined. All the patients enrolled had normal left ventricular ejection fraction (LVEF) and myocardial injury biomarkers including cardiac troponin I and B-natriuretic peptide. Univariate analysis and multivariate analysis were performed to evaluate the association of MNs and subclinical myocardial injury (SMI)(defined as LV GLS<18).

Results

LV GLS of 13(17.11%) PPGL patients was less than 18. The percentage of patients with elevation of single hormone (metanephrine, normetanephrine, 3-methoxytyramine) or any one of MNs was not significantly correlated with SMI (P=0.987, 0.666, 0.128 and 0.918, respectively). All MNs elevation was associated with SMI (OR: 11.27; 95% CI, 0.94—135.24; P= 0.056). After adjusting for age, All MNs elevation was significantly correlated with SMI (OR: 16.54; 95% CI, 1.22—223.62; P= 0.035).

Conclusion

MNs might be an important factor influencing myocardial function. All MNs elevation might indicate SMI. If all MNs elevated, LV GLS measurement was recommended for PPGL patients to detect SMI in the absence of decrease LVEF or other heart disease in clinical practice.

Future scope and challenges for congestive heart failure: Moving towards development of pharmacotherapy

Heart failure is invariably associated with cardiac hypertrophy and impaired cardiac performance. Although several drugs have been developed to delay the progression of heart failure, none of the existing interventions have shown beneficial effects in reducing morbidity and mortality. In order to determine specific targets for future drug development, we have discussed different mechanisms involving both cardiomyocytes and non-myocyte (extracellular matrix) alterations for the transition of cardiac hypertrophy to heart failure as well as for the progression of heart failure. We have emphasized the role of oxidative stress, inflammatory cytokines, metabolic alterations and Ca2+-handling defects in adverse cardiac remodeling and heart dysfunction in hypertrophied myocardium. Alterations in the regulatory process due to several protein kinases as well as participation of mitochondrial Ca2+-overload, activation of proteases and phospholipases and changes in gene expression for subcellular remodeling have also been described for the occurrence of cardiac dysfunction. Association of cardiac arrhythmia with heart failure has been explained as a consequence of catecholamine oxidation products. Since these multifactorial defects in extracellular matrix and cardiomyocytes are evident in the failing heart, it is a challenge for experimental cardiologists to develop appropriate combination drug therapy for improving cardiac function in heart failure.

Mechanisms of Lian-Gui-Ning-Xin-Tang in the treatment of arrhythmia: Integrated pharmacology and in vivo pharmacological assessment

BACKGROUND

Lian-Gui-Ning-Xin-Tang (LGNXT), a classical traditional Chinese medicine (TCM) formula, has been widely used in clinical practice and has shown satisfactory efficacy in the treatment of arrhythmias. However, its mechanism of action in the treatment of arrhythmias is still unknown. Moreover, the complex chemical composition and therapeutic targets of LGNXT pose a challenge in pharmacological research.

PURPOSE

To analyze the active compounds and action mechanisms of LGNXT for the treatment of arrhythmias.

METHODS

Here, we used an integrated pharmacology approach to identify the potential active compounds and mechanisms of action of LGNXT in treating arrhythmias. Potential active compounds in LGNXT were identified using ultra-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF/MS) and the potential related targets of these compounds were predicted using an integrated in silico approach. The obtained targets were mapped onto relevant databases to identify their corresponding pathways, following the experiments that were conducted to confirm whether the presumptive results of systemic pharmacology were correct.

RESULTS

Eighty-three components were identified in herbal materials and in animal plasma using UPLC-Q-TOF/MS and were considered the potential active components of LGNXT. Thirty key targets and 57 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were identified as possible targets and pathways involved in LGNXT-mediated treatment using network pharmacology, with the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/Ca2+ system pathway being the most significantly affected. This finding was validated using an adrenaline (Adr)-induced rat model of arrhythmias. Pretreatment with LGNXT delayed the occurrence, shortened the duration, and reduced the severity of arrhythmias. LGNXT exerted antiarrhythmic effects by inhibiting cAMP, PKA, CACNA1C, and RyR2.

CONCLUSIONS

The findings of this study revealed that preventing intracellular Ca2+ overload and maintaining intracellular Ca2+ homeostasis may be the primary mechanisms of LGNXT in alleviating arrhythmias. Thus, we suggest that the β-adrenergic receptor (AR)/cAMP/PKA/Ca2+ system signaling hub may constitute a promising molecular target for the development of novel antiarrhythmic therapeutic interventions. Additionally, we believe that the approach of investigation of the biological effects of a multi-herbal formula by the combination of metabolomics and network pharmacology, as used in this study, could serve as a systematic model for TCM research.

Catecholamine-Induced Cardiomyopathy in Pheochromocytoma: How to Manage a Rare Complication in a Rare Disease?

Pheochromocytomas and paragangliomas (PHEOs) are rare neuroendocrine tumors. Clinical manifestations include different cardiovascular signs and symptoms, which are related to excessive secretion of catecholamines. Catecholamine-induced cardiomyopathy in PHEO (CICMPP) is a rare but dreaded complication of PHEO. Once patient is diagnosed with this condition, the prognosis is worse and a surgical risk is much higher than expected. This article focuses on how catecholamines affect the heart and the pathophysiologic mechanism of CICMPP. The cardiovascular responses to catecholamine depend mostly on which catecholamine is released as well as the amount of catecholamine that is released. The acute release of norepinephrine and epinephrine from PHEO increases heart rate, systemic vascular resistance, myocardial contractility, and reduces venous compliance. The excessive adrenergic stimulation by catecholamine results in severe vasoconstriction and coronary vasospasm, myocardial ischemia, and subsequently damage, and necrosis. Chronically elevated catecholamine levels lead to significant desensitization of cardiac β-adrenoceptors. The increased levels of the enzyme β-adrenoceptors kinase (βARK) in the heart seems to mediate these biochemical and physiological changes that are consistently correlated with attenuated responsiveness to catecholamine stimulation. Through these mechanisms different types of cardiomyopathy (CMP) can be formed. This review discusses extensively the 3 types of cardiomyopathies that can be present in a PHEO patient. It also provides the clinical presentation and diagnostic and therapeutic algorithm in managing patients with CICMPP.

Effects of phosphodiestrase type 5 inhibitors in epinephrine-induced arrhythmia in rats: Involvement of lactate dehydrogenase and creatine kinase downregulation and adiponectin expression

Cardiac arrhythmia is a common cause of mortality, and its progression may be due to abnormal sympathetic nerve activity and catecholamine release. Besides, lactate dehydrogenase (LDH) and creatine kinase (CK) downregulation and adiponectin expression play important roles in promoting coronary artery disease. The study aimed to examine the possible cardioprotective effect of members of phosphodiesterase type 5 (PDE-5) inhibitors in epinephrine-induced arrhythmia in rats. Arrhythmia was induced by cumulative boluses of epinephrine (4, 8, 16, 32, 64, and 128 mg/kg) given at 10-min intervals. Rats were randomly allocated into five groups. Group I: Normal control group received only saline. Group II: Rats injected with epinephrine and served as arrhythmia group. Groups III, IV, and V: Rats received daily oral sildenafil (0.5 mg/kg), vardenafil (3 mg/kg), and tadalafil (10 mg/kg), respectively, for 30 days prior to epinephrine injections. Injection of epinephrine to rats decreased heart rate and QTc interval but increased RR interval and duration of arrhythmia. Epinephrine group had lower serum reduced glutathione (GSH) and adiponectin levels and higher serum malondialdehyde (MDA), nitric oxide (NO), heart LDH, and CK contents. Histopathological investigations of epinephrine group provoked necrotic changes with strong positive immunoreactivity for caspases-3. While pretreatment of rats with PDE-5 inhibitors improved GSH and adiponectin contents, ameliorated serum MDA and NO levels and heart LDH and CK contents and corrected epinephrine-induced histopathological changes. PDE-5 inhibitors may delay epinephrine-induced arrhythmia through expression of adiponectin and downregulation of heart LDH and CK.

Protective role of curcumin in myocardial oxidative damage induced by isoproterenol in rats

This study was designed to investigate the effect of oral curcumin pretreatment (200 mg/kg) on isoproterenol-induced myocardial injury in rats. Isoproterenol (85 mg/kg, s.c., in two divided doses at 24 h intervals) administration induced a statistically significant increase ( P < 0.01) in serum lactate dehydrogenase, creatine kinase, aspartate transaminase, and alanine transaminase activities and significant increase ( P < 0.01) in myocardial lipid peroxides levels as compared to vehicle control rats. Furthermore, significant depletion ( P < 0.01) of myocardial endogenous antioxidants viz. superoxide dismutase, catalase, and tissue glutathione levels were also found in the pathogenic control group, that is, isoproterenol only treated animals. Curcumin (200 mg/kg) pretreatment for 20 days in isoproterenol treated rats significantly lowered ( P < 0.01) the serum lactate dehydrogenase, creatine kinase, aspartate transaminase, alanine transaminase, and myocardial lipid peroxides levels and increased the levels of myocardial endogenous antioxidants (superoxide dismutase, catalase, and tissue glutathione) as compared to pathogenic control rats. Furthermore, histological examination of rat’s heart section confirmed myocardial injury with isoproterenol administration and near normal pattern with curcumin pretreatment. The results of our study provide clear evidence that the curcumin pretreatment enhances the antioxidant defense against isoproterenol-induced oxidative myocardial injury in rats and exhibit cardioprotective property.

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.

Targeting platelets for prevention and treatment of cardiovascular disease

Platelets play an important role in the development of thrombosis, atherosclerosis, hypertension, heart attack and stroke. As a result, pharmacologic interventions that influence platelet functions, such as adhesion, aggregation and the release of different factors, are considered useful for the prevention and treatment of cardiovascular disease. Although classical anti-platelet agents have proven beneficial effects for the treatment of some specific cardiovascular diseases, there are limitations for their use as these drugs target platelet function directly. In contrast, newly developed anti-platelet agents have broad applications for the treatment of cardiovascular disease as they not only influence platelet function but are also considered to affect cardiac and vascular smooth muscle cell functions. Natural food products and nutraceutical agents also appear to modify cardiovascular abnormalities by affecting various platelet functions; however, the mechanisms of their actions remain to be investigated. Accordingly, this article is focused to discuss emerging pharmacologic, nutritional and nutraceutical interventions that may influence the prevention or progression of a broad range of cardiovascular diseases.

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.

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.

Electrospray tandem mass spectrometry of aminochromes

The catecholamines adrenaline, noradrenaline, dopamine, dopa and isoprenaline were oxidized into their respective aminochromes: adrenochrome, noradrenochrome, dopaminochrome, dopachrome and isoprenochrome. Tandem mass spectrometry (MS/MS) fragmentation patterns were examined for the five aminochromes in order to establish a general structural assignment of these oxidation products by electrospray mass spectrometry. Although protonated aminochromes undergo similar fragmentation patterns with a characteristic consecutive loss of two carbonyl groups, the presence of different substituents in the parent compounds led to significant changes in the CID spectra. This feature is more evident for isoprenochrome and dopachrome, especially for the latter where the MS/MS spectrum is dominated by the loss of formic acid. A general pattern of fragmentation for aminochromes is proposed, which should provide a suitable basis to aid their characterization in studies in vivo or in vitro.

Significance of adaptation mechanisms in adriamycin induced congestive heart failure

Natural history of myocardial dysfunction due to chronic contractile deficit consists of physiological and pathophysiological adaptations culminating in congestive heart failure. Among the mechanisms considered is the combination of compensatory as well as the harmful overcompensatory role of the adrenergic system during the genesis of a congestive heart failure "spiral" due to the chronic treatment with adriamycin. Refractoriness of this spiral to various inotropic agents may involve reduced sympathetic support of the myocardium, structural loss of contractile elements and abnormalities of the Ca2+ metabolism.

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.

Direct and respiratory chain-mediated redox cycling of adrenochrome

Adrenochrome is reduced by ascorbate in a reaction accompanied by a large and rapid oxygen uptake. The rates of adrenochrome reduction and the concomitant oxygen uptake are decreased in the presence of superoxide dismutase or catalase. The species formed on the one-electron reduction of adrenochrome (i.e., the semiquinone) was shown by pulse radiolysis to rapidly react with oxygen (9.10(8) M-1.s-1), indicating the occurrence of a redox cycling in a system formed by adrenochrome, a reducing agent, and oxygen. Adrenochrome is also reduced to the corresponding semiquinone by complex I of beef heart submitochondrial particles supplemented with NADH, while succinate is unable to support this reduction. The o-semiquinone is the intermediate species in the superoxide-generating cycle resulting from both non-enzymatic and enzymatic reduction. The toxic effects of adrenochrome and its pathophysiological role can be explained, at least in part, on the basis of the demonstrated cycle.

Toxicity of aminochromes

The first part of the present review deals with the chemical and enzymatic synthesis of adrenochrome and other aminochromes from the corresponding catecholamines. A description of the most significant pathways of formation and the reactivity of the aminochromes is presented. In the second part of the toxicity of aminochromes, mainly at the cardiac and CNS level, is described and some of the molecular mechanisms of the toxic action are outlined. The toxicity of the aminochromes appears to depend mainly on the production of reduced oxygen species through redox cycling. The interaction of aminochromes with sulfhydryl groups and the induced depletion of oxygen, ascorbate and glutathione are additional mechanisms resulting in noxious effects at a cellular level.

Measurement of adrenolutin as an oxidation product of catecholamines in plasma

Using the reverse phase high-performance liquid chromatography (HPLC) with mobile phases composed of simple acids, we have developed an assay technique for the measurement of adrenolutin, one of the oxidation products of catecholamines, in rat plasma. Ion-pairing chromatography permits the separation and quantitation of plasma adrenolutin (microM) in a linear manner. Sample preparation involved the precipitation of plasma proteins with perchloric acid and it is easier to handle a large number of samples at a time. However, we were unable to demonstrate the presence of adrenochrome, another oxidation product of catecholamines, in plasma since adrenochrome was rapidly destroyed in acid as well as in blood and was quickly changed into adrenolutin. Adrenolutin peak in HPLC was confirmed by 1) the retention time; 2) co-injection of adrenolutin and; 3) the appearance of 3H-adrenolutin after injection of 3H-norepinephrine. Administration of different catecholamines as well as adrenochrome and adrenolutin in rats also increased the level of adrenolutin in plasma. Adrenolutin was found to be present in plasma in other species including dog, rabbit and pig. High level of adrenolutin, which may represent total concentration of aminolutin in plasma, suggests the presence of an efficient mechanism for the oxidation of catecholamines under in vivo conditions.

A direct protective effect of sulphinpyrazone on ischaemic and reperfused rat hearts

Initiation of 60 min ischaemia to rat isolated hearts produced a depression in developed tension and heart rate. Subsequent reperfusion caused a greatly exacerbated creatine phosphokinase (CPK) efflux and limited functional recovery. Sulphinpyrazone (100 ng ml-1 and 1 microgram ml-1) significantly reduced CPK release, particularly after reperfusion, the lower concentration being more effective. A reduction in the mechanical depression during ischaemia and enhanced recovery after reperfusion were seen only with 100 ng ml-1 sulphinpyrazone. Heart rate and coronary perfusion pressure were unaffected by drug treatment. The reduction in reperfusion-induced CPK efflux by 100 ng ml-1 sulphinpyrazone was maximal when the drug was present throughout the perfusion period although some protection was evident when sulphinpyrazone was present either during ischaemia or reperfusion only. An enhanced recovery in contractility was seen only when the drug was present throughout all phases of perfusion. It is suggested that sulphinpyrazone exerts a direct protective effect on the heart particularly during reperfusion. The degree of protection is critically dependent on the concentration of sulphinpyrazone.

Protection from arrhythmias of cultured heart cells by nonsteroidal antiinflammatory drugs

The nonsteroidal antiinflammatory drugs: acetylsalicylic acid, salicylic acid, sulfinpyrazone and indomethacin were tested at 10(-10) - 10(-5) M for their effect on arrhythmias of monolayer cultures of neonatal rat heart myocytes. Arrhythmias produced by reoxygenation were prevented or significantly reduced (p less than or equal to 0.05) by either indomethacin or salicylic acid at 10(-9) M. Acetylsalicylic acid and sulfinpyrazone, while not significantly anti-arrhythmic, produced consistent numerical inhibition of arrhythmias at 10(-9) M.

Potential oxidative pathways of catecholamines in the formation of lipid peroxides and genesis of heart disease

Effects of vitamin E, a fat soluble antioxidant, on the isoproterenol-induced changes in the lipid peroxide activity as determined by a quantitation of malondialdehyde (MDA) content in the myocardium were examined. Isoproterenol treatment (80 mg/kg given over two days in two equal doses) caused more than 100 percent increase in the MDA content which was prevented by pretreatment of the animals with vitamin E (alpha-tocopherol acetate, 10 mg/kg) for two weeks. Animals maintained on vitamin E deficient diet for 8 weeks were found to be more sensitive to isoproterenol-induced increase in the MDA content. A small increase in MDA content was also seen due to vitamin E deficiency alone. These changes were found to be reversible upon a 2 week feeding of the animals on the normal diet coupled with vitamin E treatment. Based on these data it is proposed that free radical mediated increase in lipid peroxide activity may have a role in catecholamine-induced heart disease.

Effects of sulfinpyrazone on ventricular vulnerability in the normal and the ischemic heart

The effects of sulfinpyrazone were studied in 33 chloralose-anesthetized dogs. Ventricular fibrillation thresholds, mid diastolic thresholds and duration of the effective refractory period were determined in the normal heart after intravenous administration of sulfinpyrazone, 30 mg/kg body weight. The drug significantly raised the ventricular fibrillation threshold by 24 percent and the mid diastolic threshold by 36 percent and prolonged the effective refractory period by seven percent. The influence of sulfinpyrazone during acute myocardial ischemia was evaluated before and during a 10 minute occlusion of the left anterior descending coronary artery and after abrupt release of the occlusion. Although the drug afforded significant protection during coronary occlusion, it had no effect on the ventricular fibrillation threshold after reperfusion. Because potent cardiocardiac reflexes are elicited during ischemia, the influence of sulfinpyrazone on the ventricular fibrillation threshold was studied during norepinephrine infusion. Sulfinpyrazone attenuated the reduction of the ventricular fibrillation threshold during sympathetic humoral stimulation. Its effect was additive to beta adrenergic blockade with practolol and membrane stabilization with lidocaine. This investigation suggests that sulfinpyrazone exerts significant effects on ventricular vulnerability of both the normal and the ischemic myocardium. Further studies are needed to elucidate its precise mechanism of action.

Electrophysiological and mechanical effects of sulphinpyrazone on isolated rat atria

Clinical trials suggest that sulphinpyrazone reduces the incidence of sudden death in patients having suffered a myocardial infarction. To investigate possible direct antiarrhythmic properties of sulphinpyrazone, we carried out experiments on spontaneously beating and electrically stimulated isolated rat atrial preparations. Dose-response curves for electrophysiological and mechanical effects of sulphinpyrazone were obtained. Increasing doses of sulphinpyrazone decreased the spontaneous atrial frequency, prolonged the sinus node recovery time after overdrive pacing, slightly increased the electrical threshold for excitation and decreased the contractile force. Although the mechanism by which sulphinpyrazone may reduce the incidence of sudden cardiac death is still not settled, the present study demonstrates direct electrophysiological and mechanical effects of the drug at high concentrations.