Adrenochrome uptake and subcellular distribution in the isolated perfused rat heart

Adrenochrome uptake and its subcellular distribution were examined using isolated perfused rat heart preparation. The heart was perfused for 30 min with a medium containing 1 to 50 mg/l of 14C-adrenochrome and the subcellular fractions were isolated to measure their radioactivities. A decline in contractile force, a rise in resting tension and an increase in adrenochrome uptake by the heart were seen to depend upon the time of perfusion and the concentration of adrenochrome in the medium. The sarcolemmal fraction had the highest uptake of adrenochrome and this was followed by the microsomal fraction; some accumulation of adrenochrome was also observed in the myofibrillar and mitochondrial fractions. Either 10 or 20 min reperfusion of the heart previously exposed to 25 mg/l of adrenochrome, resulted in approximately 50 or 37% of the radioactivity remaining in the heart; this indicates irreversible binding of adrenochrome to the tissue. Reperfusion of the heart showed restoration of the resting tension but the contractile force did not show any recovery. Propranolol and iproniazid, which have been shown to inhibit the adrenochrome induced cardiotoxicity, reduced adrenochrome uptake by the heart, and prevented adrenochrome-induced depression in contractile force and rise in resting tension. These results indicate that adrenochrome is taken up by the heart and induces cardiac disturbances through its action on different subcellular organelles in the myocardium.

Prostaglandins and heart disease

The role of prostaglandins (PGs) in cardiac pathophysiology has been reviewed with special emphasis on clinically applied aspects. Several PGs are synthesized and released by the heart and coronary vessels. Their synthesis is altered by various factors such as physical manipulation of tissue, pharmacological treatments and pathological conditions such as myocardial over-reactivity and ischemia. The involvement of PGs in cardiac dysfunction remains controversial, although it has been proposed that various PGs such as PGI2 or PGB2 may play a role in disaggregating platelets, inhibiting thrombus progression and coronary vasodilatation. The balance between thromboxane A2 (TXA2), a proaggregatory agent released from platelets and PGI2 may have a role in the genesis and management of angina and myocardial infarction. The use of non-steroidal anti-inflammatory agents in these conditions remains controversial; their possible beneficial effects are believed to be due to inhibition of TXA2 synthesis whereas their failure to be effective may be a consequence of concomitant inhibition of PGI2 production. Modulation of endogenous PG synthesis and administration of exogenous PGs or their analogues appear to be two therapeutic approaches in the management of certain cardiac diseases. Accordingly, there is a great need for synthesizing stable and potent PG analogues as well as specific inhibitors of PG synthesis in addition to studying their pharmacology and therapeutics. In this review we have emphasized the involvement of PGs in the pathogenesis of some forms of cardiac disease and have highlighted some therapeutic implications of these substances for the treatment of heart disease.

Biochemical alterations in heart after exhaustive swimming in rats

This study investigated alterations in glycogen, catecholamines, and the function of various subcellular membranes of the heart after exhaustive swimming in rats. The rats were exhausted by daily exercise over 1, 3, or 7 consecutive days. Glycogen content of the heart and three selected skeletal muscles was depleted after a single bout of exhaustive exercise. Repeated bouts of exhaustive swimming elicited a depletion of glycogen in only the plantaris and gastrocnemius skeletal muscles. Plasma norepinephrine and epinephrine levels were highly elevated, and cardiac concentrations of these hormones were significantly depleted immediately after all exercise sessions. Cardiac sarcoplasmic reticulum (SR) Ca2+ transport was depressed after a single exhaustive exercise period. After three exercise bouts SR Ca2+ accumulation remained depressed; however, mitochondrial Ca2+ transport was found to be augmented. If the exhaustive exercise protocol was continued up to seven days, only mitochondrial Ca2+ accumulation was depressed. Various parameters of sarcolemmal membrane function were observed to be unaltered after exhaustive exercise. These findings demonstrate that exhaustive swimming exercise in rats is capable of producing significant alterations in the Ca2+ transport capacity of the SR and mitochondrial membrane systems of the heart but is without apparent effect on the sarcolemmal membrane.

Progress and problems in understanding the involvement of calcium in heart function

In this article we have briefly reviewed the role of Ca2+ in the excitation contraction coupling in the myocardium and have indicated that cardiac contraction and relaxation are initiated upon raising and lowering the intracellular concentration of free Ca2+, respectively. Different mechanisms for the entry of Ca2+ through sarcolemma as well as release of Ca2+ from sarcoplasmic reticulum and possibly mitochondria have been outlined for initiating cardiac contraction. Relaxation of the cardiac muscle appears to be intimately dependent upon efflux of Ca2+ through sarcolemma as well as sequestration of Ca2+ by the intracellular storage sites, particularly sarcoplasmic reticulum and possibly mitochondria. The actions of some pharmacological and pathophysiological interventions have been explained on the basis of changes in subcellular Ca2+ movements in myocardium. Quinidine, which produced an initial positive inotropic action on rat heart was also found to increase sarcolemmal Ca2+-ATPase activity without any changes in the Na+-K+ ATPase. Other antiarrhythmic agents, procainamide and lidocaine, also increased sarcolemmal Ca2+-ATPase activity without affecting the Na+-K+ ATPase. On the other hand, both Ca2+-ATPase and Na+-K+ ATPase activities were increased in heart sarcolemma obtained from cardiomyopathic hamsters. In this model the increased Ca2+-ATPase activity may promote the occurrence of intracellular Ca2+ overload in the cardiac cell whereas the increased Na+-K+ ATPase activity may increase Ca2+ efflux through Na+-Ca2+ exchange systems as an adaptive mechanism. It has been suggested that some caution should be exercised while interpreting the data from in vitro experiments in terms of functional changes in the myocardium. Furthermore, it has been proposed that the pathophysiology and pharmacology of Ca2+ movements at different membrane sites be understood fully in normal and diseased myocardium in order to improve the therapy of heart disease.

Defect in the adrenergic receptor-adenylate cyclase system during development of catecholamine-induced cardiomyopathy

We have investigated alterations in adrenergic receptors and adenylate cyclase activity in cardiac membranes from rats injected with 40 mg/kg intraperitoneal isoproterenol. Reduction in the number of beta-adrenergic and alpha-adrenergic receptors, as assessed by changes in specific binding of 3H-dihydroalprenolol (DHA) and 3H-dihydroergocryptine (DHE), was observed only at 9 and 24 hours after isoproterenol injection, respectively. On the other hand, epinephrine-stimulated, NaF-stimulated, and Gpp (NH)p-stimulated adenylate cyclase activity was decreased as early as 3 hours after isoproterenol treatment without changes in the basal adenylate cyclase activity. These results demonstrate a defect in the adrenergic receptor-adenylate cyclase system during the development of catecholamine-induced cardiomyopathy and may partly explain the attenuated inotropic adrenergic response of the heart under stressful situations.

Involvement of calcium in coronary vasoconstriction due to prolonged hypoxia

In this study we employed a hypoxic rat heart model for investigating the mechanisms of coronary spasm. Perfusion of the isolated heart with hypoxic medium resulted in initial coronary dilatation followed by sustained constriction. Pretreatment of rats with 5 mg/kg reserpine did not alter the rate of the magnitude of constriction during 60 minutes of hypoxic perfusion. The hypoxia-induced vasoconstriction was not affected by the inclusion of either 1 or 10 micrograms/ml phentolamine in the perfusion buffer, but phenoxybenzamine (0.1 and 1 microgram/ml) significantly attenuated the degree of constriction. Since phenoxybenzamine and phentolamine were equally effective in preventing the phenylephrine-induced coronary constriction, it is unlikely that the effect of phenoxybenzamine was due to an alpha-receptor blocking property but instead may be accounted for by its calcium channel blocking action. Two calcium channel blockers, verapamil and D-600 (0.1 and 1 microgram/ml), were also effective. The rate of rise in coronary pressure was substantially reduced by decreasing the concentration of calcium and was increased by elevating the concentration of calcium in the perfusion medium, but the magnitude of hypoxia-induced constriction was not affected. These results are consistent with the suggestion that the coronary constriction seen during hypoxia does not involve adrenergic mechanisms but is dependent upon the availability of calcium.

Dr. Albert Clifford Abbott: pioneer surgeon of western Canada

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Stimulation of calcium pump activity in heart sarcolemma by timolol

The effects of beta-adrenergic blocking agents, timolol and atenolol (1-1000 microM), were studied on rat heart sarcolemmal ATPase and Ca2+ binding activities. Timolol, unlike atenolol, increased both Ca2+-stimulated ATPase and ATP-dependent Ca2+ binding; the maximal effects were seen at 1 microM concentration of timolol. Both timolol and atenolol did not alter the sarcolemmal Mg2+ ATPase and nonspecific Ca2+ binding activities. Sarcolemmal Ca2+-stimulated ATPase was also activated by concanavalin A (6-66 micrograms/mL) which is known to alter membrane fluidity; however, Mg2+ ATPase was unaffected by this agent. These results indicate that timolol may stimulate Ca2+ pump activity in heart sarcolemma by changing membrane fluidity in a manner similar to that of concanavalin A.

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.

Role of free radicals in catecholamine-induced cardiomyopathy

Effects of an antioxidant, vitamin E, and a membrane stabilizing agent, zinc, were examined on the isoproterenol-induced changes in the rat myocardium. Isoproterenol treatment (80 mg/kg given over 2 days in two equal doses) caused arrhythmias and 25% mortality within 24 h of the last injection. The ultrastructural changes in the subendocardium and in focal areas of the subepicardium included swelling of mitochondria, loss of myofibrils, cell necrosis, fibrosis, and infiltration of the affected areas by polymorphonucleocytes. Both creatine phosphate and adenosine triphosphate levels were markedly decreased in hearts from isoproterenol-treated animals. Pretreatment of the animals with vitamin E (10 mg X kg-1 X day -1 for 2 weeks) or zinc (10 mg/kg ZnSO4, twice a day for 7 days) prevented these deleterious effects of isoproterenol. Animals maintained on vitamin E deficient diet for 8 weeks were found to be more sensitive to isoproterenol-induced changes and this increased sensitivity was reversed by a 2-week feeding of the animals on the normal diet coupled with vitamin E treatment. Based on the data obtained in this study it is proposed that catecholamine-induced changes may involve free radicals, which by promoting lipid peroxidation may increase membrane permeability and lead to the development of cardiomyopathy.

Cardiac alpha- and beta-adrenergic receptor alterations in diabetic cardiomyopathy

The effect of chronic experimental diabetes on the adrenergic receptors in the rat heart was investigated. Diabetes was induced by streptozotocin (65 mg/kg; i.v.) administration, animals were sacrificed 8 weeks later, and positive as well as negative dF/dt values were determined in isolated papillary muscle preparations. Stimulation of the contractile force generation by isoproterenol and methoxamine was attenuated in diabetic preparations. Beta- and alpha-adrenergic receptor bindings were determined in cardiac membranes by employing 3H-dihydroalprenolol and 3H-dihydroergocryptine respectively. Reduced number of beta- and alpha-receptor binding sites without changes in the affinity constants were observed in diabetic myocardium. Such a decrease in alpha- and beta-receptor density in the heart may account for the depressed contractile responsiveness to adrenergic stimuli in diabetic cardiomyopathy.

Myocardial cell damage and cardiovascular changes due to i.v. infusion of adrenochrome in rats

In vivo effects of adrenochrome (1-32 mg/kg), an oxidation product of catecholamines, on the heart ultrastructure, ECG and blood pressure were studied in rats over a period of 60 min following a single i.v. injection of the drug. One milligram of the drug had no influence on the myocardium or the cardiovascular system, whereas maximum changes in these parameters were recorded at 32 mg/kg of adrenochrome. The maximum structural damage, reached within 5-10 min, included marked swelling of mitochondria and sarcotubular system, intracellular and perinuclear oedema, hypercontraction of myofibrils and partial separation of the intercalated disc. Ultrastructural changes in the myocardium due to 4 and 8 mg of adrenochrome were not accompanied by any cardiovascular effects and the changes were fully reversed within 60 min of the injection of the drug. However, at 16 and 32 mg/kg of adrenochrome both heart rate and blood pressure were depressed within 5 min of drug administration. At these concentrations of adrenochrome arrhythmias, mainly due to premature ventricular contractions, were also noticed. Ultrastructural and cardiovascular changes seen at these higher concentrations of adrenochrome showed only a partial recovery. The data indicates that adrenochrome-induced ultrastructural changes in the heart are due to a direct myocardial effect of the drug which may not involve haemodynamic changes and the latter are most probably a consequence of this effect. However, the present study has not been able to rule out direct vascular effects at higher concentrations of adrenochrome.

Influence of reducing agents on adrenochrome-induced changes in the heart

To elucidate the role of oxidation products of catecholamines play in myocardial necrosis, we examined the effects that adrenochrome in the presence of some reducing agents and that autoxidized solution of adrenochrome have on the ultrastructure and force of contraction in the isolated rat heart. Addition of ascorbic acid (1 mM) or cysteine (0.5 mM) into a perfusion medium containing 25 mg/L of adrenochrome produced ultrastructural damage greater than that seen with adrenochrome alone, whereas addition of dithiothreitol (0.5 mM) did not. The rate of failure of the heart due to adrenochrome was accelerated by use of ascorbic acid and dithiothreitol. Reduction of adrenochrome into other oxidation products of catecholamines by these reducing agents was indicated by the results of spectral analysis studies. Myocardial damage or contractile failure did not occur if the adrenochrome solution was allowed to autoxidize for 24 hours before perfusion. These data indicate that oxidation products of epinephrine other than adrenochrome are involved in the genesis of catecholamine-induced cardiotoxicity. This effect may occur through the formation of cardiotoxic free radicals, as well as through interaction of these oxidation products with sulfhydryl groups.

Adrenochrome-induced coronary artery constriction in the rat heart

Adrenochrome, an oxidation product of epinephrine, has been demonstrated to produce cardiotoxic effects. In this study, we have investigated whether this agent can alter coronary resistance in isolated rat hearts. Concentrations of adrenochrome from 1 to 1000 ng/ml increased coronary pressure in a dose- and time-dependent manner. The highest concentration produced a 3-fold elevation in pressure after a 1-hr perfusion. Myocardial contractile force decreased only with either 100 or 1000 ng/ml of adrenochrome and this effect was evident after substantial elevations in coronary pressure. The elevation in coronary pressure was significantly reduced by two calcium antagonists, verapamil and D-600. Furthermore, the degree of constriction by adrenochrome was dependent on the CaCl2 concentration in the perfusion medium. High concentrations of indomethacin or propranolol attenuated the degree of coronary pressure elevation, whereas acetylsalicylic acid and phenoxybenzamine were without effect. Sulfinpyrazone, which has been shown to reduce the arrhythmogenic action of adrenochrome in vivo, significantly reduced the coronary pressure increases. These results suggest that adrenochrome is a potent coronary constricting agent in the rat heart and its action is seemingly dependent on external Ca++ availability.

Ventricular dysfunction and necrosis produced by adrenochrome metabolite of epinephrine: relation to pathogenesis of catecholamine cardiomyopathy

We have examined the effects of adrenochrome and other metabolites of epinephrine on the ultrastructure and contractile activity of isolated rat hearts perfused under conditions in which the heart rate and coronary flow were controlled. Perfusion of hearts with epinephrine or metanephrine significantly increased contractile force; vanillylmandelic acid and dihydroxymandelic acid did not alter contractile force development, whereas adrenochrome (50 mg/L) declined contractile force with epinephrine (50 mg/L) was associated with increased resting tension and maximum rates of force development and relaxation, and decreased time for peak tension development and 1/2 relaxation. On the other hand, hearts perfused with adrenochrome showed early decline followed by steady increase in resting tension; maximum rates of force development and relaxation were reduced and times for peak tension development and 1/2 relaxation were increased. Hearts perfused or 10 minutes or more with adrenochrome (50 mg/L), but not epinephrine, metanephrine, dihydroxymandelic acid or vanillylmandelic aicd, showed ultrastructural damage. Adrenochrome concentrations of 10 or 25 mg/L altered the appearance of mitochondria after 30 minutes of perfusion. Infusion of epinephrine (1 mg/L) during perfusion with adrenochrome partially maintained contractile force during the first 15 minutes of perfusion but did not alter the severity of ultrastructural changes due to adrenochrome. These results are consistent with the concept that oxidation products of catecholamines such as adrenochrome are partly responsible for inducing myocardial necrosis and failure following massive catecholamine injections in intact animals.

Protective effect of sulfinpyrazone against catecholamine metabolite adrenochrome-induced arrhythmias

Single intravenous injection of adrenochrome (10 to 50 mg/kg body weight), an oxidation product of catecholamines, has been shown to induce arrhythmias and cause death in anesthetized rats in a dose-dependent manner. Sulfinpyrazone, which is an inhibitor of platelet aggregation, was found to protect animals from these adrenochrome effects. It is suggested that sudden death due to arrhythmias in patients following the first attack of myocardial infarction of during other stressful situations may be linked to the formation of adrenochrome from abnormally high catecholamine levels in blood. Furthermore, results presented here also suggest that the reduction in the mortality rate of patients on sulfinpyrazone therapy may involve an antiarrhythmic property of the drug.

Modification of adrenochrome-induced cardiac contractile failure and cell damage by changes in cation concentrations

Adrenochrome has been shown to produce cardiac necrosis as well as failure in the isolated rat hearts. These effects of adrenochrome were influenced by alterations in the Ca2+, Na+, K+, and Mg2+ concentrations of the perfusion medium. Increasing the Ca2+ or K+ concentration or decreasing the Na+ concentration of the adrenochrome-containing perfusion medium partially maintained contractile force but increased the severity of ultrastructural damage. Reducing the K+ concentration of the medium did not alter the failure of contractile force development but increased the severity of ultrastructural damage due to adrenochrome. Reducing the Ca2+ or increasing the Mg2+ concentration of the perfusion medium completely prevented myocardial necrosis due to adrenochrome. Omission of Mg2+ from the perfusion medium neither altered the time course of contractile failure nor effected the severity of necrosis due to adrenochrome. These results for the most part parallel the influence of similar ionic interventions on the severity of necrosis produced by excessive amount of catecholamines.

Effects of adrenochrome on calcium accumulating and adenosine triphosphatase activities of the rat heart microsomes

The influence of adrenochrome (1-100 microgram/ml or 5.6 x 10(-6)-5.4 x 10(-4) M) on microsomal calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent adenosine triphosphatase (ATPase) activities was studied in vitro. Adrenochrome decreased microsomal calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent ATPase activities. The inhibitory effect of adrenochrome on microsomal calcium uptake activity of the isolated membrane was independent of pH (6.0-8.0), calcium concentrations (10-200 muM), protein concentration (0.02-0.10 mg/ml), temperature (25-37 degrees C) and incubation time (2-30 min). Kinetic study of calcium uptake activity in different concentrations of ATP showed that the inhibition was of a mixed type. Perfusion of hearts with adrenochrome resulted in marked depression in contractile force and the microsomal fraction obtained from these hearts showed depressed calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent ATPase activities. The depression in microsomal The influence of adrenochrome (1-100 microgram/ml or 5.6 x 10(-6)-an irreversible nature. It is proposed that cardiodepressant action of adrenochrome may partly be explained on the basis of its inhibitory effect on the calcium transporting ability of the sarcoplasmic reticulum.

Protection against adrenochrome-induced myocardial damage by various pharmacological interventions

Perfusion of the isolated rat heart with Krebs-Henseleit solution containing adrenochrome (25 or 50 mg/l), and oxidation product of catechalmines, resulted in contractile failure and myocardial necrosis. Various pharmacological agents known to protect the myocardium against catecholamine-induced necrosis were also found to be effective against adrenochrome-induced changes in the ultrastructure of the isolated perfused rat heart. The alpha-receptor-blocking drugs tolazoline and Dibenamine (dibenzylchlorethamine), and the adrenergic neurone-blocking agents guanethidine and bretylium did not alter the development of contractile failure and necrosis due to adrenochrome. The beta-receptor-blocking compounds propranolol and practolol effectively protected the heart from adrenochrome-induced necrotic damage, and partially prevented contractile failure. The hydrazine-type monoamine oxidase inhibitor iproniazid completely prevented ultrastructural damage and partially maintained contractile-force development in adrenochrome perfused hearts. The non-hydrazine-type monoamine oxidase inhibitor tranylcypromine partially protected the isolated rat heart against adrenochrome necrosis, but disruption of mitochondrial structure was still seen. Tranylcypromine did not significantly improve contractile force development during adrenochrome perfusion. The calcium antagonist D-600 reduced the severity of adrenochrome-induced ultrastructural damage. These results provide strong support for the view that catecholamine-induced cardiotoxicity is mediated through the formation of adrenochrome.

Ambulant management of patients with recent myocardial infarction

Thirty-two patients who had remained ambulant and active after suffering an acute myocardial infarction were observed for 6 months. Complications were present initially in 11 but proved transient. One patient died of a new coronary thrombosis 15 weeks after the initial episode. There were no recurrences among the 31 surviving patients. After the 6 months all but two patients were as well as before the attack; 21 were free of symptoms and there was no undue incidence of objective findings that could be attributed to failure to rest after the attack. It is therefore concluded that, for patients who suffer an acute myocardial infarction, immediate diagnosis and admission to a coronary care unit need not be equated invariably with immobilization in bed. Our experience suggests that selected patients can be allowed moderate activity without ill effects and thus avoid the undesirable consequences of enforced bed rest.