How much gin in the tonic? The problems of writing a provincial medical history,

This paper describes the problems and resources involved in writing a Canadian provincial medical history, (Manitoba Medicine: A Brief History). The first decision was whether it should be a scholarly or a popular history; The authors' background, and the realities of publishing dictated the latter. Resources available were local and easily accessible: archives and records, the Manitoba medical journals, a series of local medical journals (almost continuous for a century), and the Manitoba medical biographies, books variable in length, and content, but relating to a wide variety of physicians. Such a paper leads to a question- "Is local history merely trivial?" The answer to such a question is "no."

Biphasic changes in heart performance with food restriction in rats

To examine effects of food restriction resembling very-low-calorie dieting on heart performance, normal rats were fed 25% of ad libitum food intake for 14 days. Although heart weight decreased (P < 0.05) after 5 days, left ventricular systolic pressure as well as rates of pressure development and fall were increased (P < 0.05) at 7 days and decreased (P < 0.05) after 14 days. Systolic and diastolic blood pressures were also increased from 5 to 7 days and decreased after 14 days. The increased hemodynamic performance of heart was associated with a raised plasma norepinephrine concentration, which peaked at day 7 of food restriction; epinephrine concentration was increased (P < 0.05) also at day 7. An increased catecholamine synthesis was indicated by the raised (P < 0.05) plasma dopamine beta-hydroxylase activity at 3 days, but this was decreased (P < 0. 05) at 14 days. The concentration of dopamine in the heart was increased (P < 0.05) at 2-14 days, of norepinephrine at 7-14 days, and of epinephrine at 10 and 14 days. Food restriction thus appears initially to be associated with an enhanced catecholamine influence on the heart and is followed by a depressed cardiac performance.

Differential changes in sympathetic activity in left and right ventricles in congestive heart failure after myocardial infarction

Although congestive heart failure subsequent to myocardial infarction is known to be associated with increased sympathetic activity, very little information regarding changes in the sympathetic nerves in the left and right ventricles at various stages after infarction is available. Male Sprague-Dawley rats were subjected to coronary artery ligation and studied 4 and 8 weeks later; these animals had mild and moderate stages of congestive heart failure. A sham group, without coronary ligation, was used as control. Four weeks after myocardial infarction, plasma and ventricular (left and right) epinephrine (EPI), unlike norepinephrine (NE), were markedly increased. Whereas plasma catecholamine (EPI and NE) levels were increased 8 weeks after infarction, NE concentration in the left ventricle was unchanged but EPI concentration was increased in comparison with sham control. The right ventricle showed an increased level of both NE and EPI 8 weeks after infarction. Measurement of the rate of change in the specific activity of NE (NE turnover) in the left and right ventricles 8 weeks after infarction revealed an increase in NE turnover in the left ventricle, without any changes in the right ventricle. The concentration of EPI, unlike NE, was increased in the kidney, spleen, and brain 8 weeks after coronary occlusion. These results are interpreted to mean that congestive heart failure caused by myocardial infarction is associated with differential changes in the status of sympathetic nerves in the left and right ventricles; sympathetic activity is increased only in the left ventricle, whereas the right ventricle may play an adaptive role by increasing catecholamine stores during the development of heart failure.

Differential changes in left and right ventricular adenylyl cyclase activities in congestive heart failure

The status of beta-adrenergic receptors and adenylyl cyclase in crude membranes from both left and right ventricles was examined when the left coronary artery in rats was occluded for 4, 8, and 16 wk. The adenylyl cyclase activity in the presence of isoproterenol was decreased in the uninfarcted (viable) left ventricle and increased in the right ventricle subsequent to myocardial infarction. The density of beta1-adrenergic receptors, unlike beta2-receptors, was reduced in the left ventricle, whereas no change in the characteristics of beta1- and beta2-adrenergic receptors was seen in the right ventricle. The catalytic activity of adenylyl cyclase was depressed in the viable left ventricle but was unchanged in the right ventricle. In comparison to sham controls, the basal, as well as NaF-, forskolin-, and 5'-guanylyl imidodiphosphate [Gpp(NH)p]-stimulated adenylyl cyclase activities were decreased in the left ventricle and increased in the right ventricle of the experimental animals. Opposite alterations in the adenylyl cyclase activities in left and right ventricles from infarcted animals were also seen when two types of purified sarcolemmal preparations were employed. These changes in adenylyl cyclase activities in the left and right ventricles were dependent on the degree of heart failure. Furthermore, adenosine 3',5'-cyclic monophosphate contents were higher in the right ventricle and lower in the left ventricle from infarcted animals injected with saline, isoproterenol, or forskolin in comparison to the controls. The results suggest differential changes in the viable left and right ventricles with respect to adenylyl cyclase activities during the development of congestive heart failure due to myocardial infarction.

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.

Modification of catecholamine-induced changes in heart function by food restriction in rats

In view of the common practice of dieting for weight reduction, the influence of severe food restriction (about 25% of ad libitum intake) on adrenergic mechanisms was studied. Cardiac norepinephrine and epinephrine concentrations as well as plasma norepinephrine levels, were increased upon feeding a restricted diet to rats for 14 days in comparison with control rats that ingested about 30 g food/ day. Bradycardia as well as characteristic electrocardiographic abnormalities, including prolongation of the QRS and QT intervals, were observed in food-restricted rats. Diet-restricted rats did not develop ventricular arrhythmias in response to epinephrine injections as readily as control rats. Depression in both + dP/dt and -dP/dt of the heart in situ as well as reductions in the inotropic responses to epinephrine were evident in diet-restricted rats. Beta-adrenergic binding studies revealed a significant decrease in receptor density, but the dissociation constant for binding was also depressed in the food-restricted rat heart. Downregulation of the beta-adrenergic receptors in the heart may explain the lack of an epinephrine-induced increase in contractile force development as well as arrhythmias in food-restricted rats. These data demonstrate that severe food restriction has marked effects on adrenergic mechanisms and heart function, and thus some caution should be exercised at early periods of this therapy for weight reduction.

Mechanisms of subcellular remodelling in post-infarct heart failure

Occlusion of a coronary artery results in myocardial ischemia and subsequent myocardial infarction. Whenever the infarct size is more than 30% of the ventricular wall, the remaining myocardium attempts to compensate for the loss of muscle mass by changing the size and shape of cardiocytes in addition to developing cardiac hypertrophy, cardiac dilatation and congestive heart failure. This remodeling of the heart is associated with changes in the extracellular matrix including collagen proteins and is most probably due to the activation of both sympathetic nervous system and renin-angiotensin system as well as increased formation of various growth factors. Alterations in contractile function of the infarcted heart are associated with remodelling of the sarcoplasmic reticulum with respect to Ca(2+)-pump and Ca(2+)-release channels as well as contractile and regulatory proteins of the myofibrils. Myocardial infarction has also been shown to result in remodelling of the sarcolemmal membrane with respect to Ca(2+)-channels, Ca(2+)-transport systems, cardiac receptors and signal transduction mechanisms. Although information regarding remodelling of mitochondria in the infarcted heart is limited, alterations in energy yielding and Ca(2+)-accumulating systems are suspected. Accordingly, it is suggested that changes in cardiac contractile dysfunction due to myocardial infarction are associated with remodeling of both extracellular matrix and subcellular organelles in the heart.

Role of extracellular matrix proteins in heart function

The cardiac interstitium is populated by nonmyocyte cell types including transcriptionally active cardiac fibroblasts and endothelial cells. Since these cells are the source of many components of the cardiac extracellular matrix, and because changes in cardiac extracellular matrix are suspected of contributing to the genesis of cardiovascular complications in disease states such as diabetes, hypertension, cardiac hypertrophy and congestive heart failure, interest in the mechanisms of activation of fibroblasts and endothelial cells has led to progress in understanding these processes. Recent work provides evidence for the role of the renin-angiotensin-aldosterone system in the pathogenesis of abnormal deposition of extracellular matrix in the cardiac interstitium during the development of inappropriate cardiac hypertrophy and failure. The cardiac extracellular matrix is also known to change in response to altered cardiac performance associated with post-natal aging, and in response to environmental stimuli including intermittent hypoxia and abnormal nutrition. It is becoming clear that the extracellular matrix mainly consists of molecules of collagen types I and III; they form fibrils and provide most of the connective material for typing together myocytes and other structures in the myocardium and thus is involved in the transmission of developed mechanical force. The data available in the literature support the view that the extracellular matrix is a dynamic entity and alterations in this structure result in the development of heart dysfunction.

Pathophysiology of cardiac dysfunction in congestive heart failure

Although various factors, such as myocardial infarction, pressure overload and volume overload, result in the development of congestive heart failure (CHF), the pathogenesis of contractile dysfunction in this situation is poorly understood. Loss of cardiac muscle due to myocardial infarction appears to activate several humoral and hormonal pathways, including the renin-angiotensin and sympathetic systems which serve as adaptive mechanisms to maintain cardiovascular performance at early stages of failure. However, under chronic conditions, an altered hormonal profile produces deleterious effects and permits transition from the compensated heart to the failing heart. Since several risk factors--such as hypertension, hypercholesteremia, stress, diabetes, smoking, ageing, obesity and lack of exercise--precipitate ischemic heart disease, it is possible that development of CHF due to myocardial infarction may vary according to the nature of these pathogenetic entities. While a great deal of research work remains in this area of investigation, it is becoming evident that cardiac dysfunction is intimately associated with calcium handling abnormalities of cardiac cells. In view of the role of sarcolemma, sarcoplasmic reticulum and mitochondria in regulating the intracellular concentration of Ca2+ and the importance of myofibrillar interaction with Ca2+, it appears that Ca2+ handling and Ca2+ interaction abnormalities in the failing heart are due to remodelling of different subcellular organelles. Such a remodelling of the subcellular organelles may be due to changes in gene expression for different protein components or the interactions of proteins with phospholipids. Accordingly, it is proposed that new interventions, which could prevent the remodelling of subcellular organelles, be developed for improving the therapy of CHF.

Role of endothelin in heart function in health and disease

A comprehensive review of the literature has revealed that endothelins belong to a family of vasoactive peptides which are formed and released from the endothelium. By producing constriction of the coronary arteries and peripheral blood vessels, endothelins are known both to reduce coronary bloodflow and increase blood pressure and thus can be seen to affect heart function adversely. On the other hand, endothelins are capable of producing positive inotropic and chronotropic effects by directly affecting both the myocardium and nodal tissues. Prolonged actions of high concentrations of endothelins can be seen to induce relative hypoxia in the myocardium which will eventually result in heart dysfunction. The mechanisms of actions of endothelin on smooth muscle cells and cardiomyocytes include interaction with endothelin receptors on the cell surface, activation of phospholipase C through G-proteins, and increase in the intracellular concentration of Ca2+ through the increase in phosphoinositol turnover. Endothelins were found to exert no effects on sarcolemmal Na+,K(+)-ATPase, Na(+)-Ca2+ exchange and Ca2+ pump systems nor on the sarcoplasmic reticular Ca2+ pump system and myofibrillar ATPase activities in the rat heart. Marked elevation in the levels of plasma endothelins and down-regulation of endothelin receptors in ischemia-reperfusion injury, hypertension and chronic diabetes indicate a significant role of endothelins in the genesis of heart dysfunction under different pathological conditions.

Characteristics and mechanisms of tachyphylaxis of cardiac contractile response to insulin

Although insulin is known to cause internalization of its own receptors, the physiological significance of this phenomenon is not clear. In the isolated rat heart we observed that the positive inotropic effect of 25 munits/ml insulin was completely abolished if the heart was preperfused with insulin for 10 min. This tachyphylactic response to insulin began to appear 3-4 min after starting preperfusion with insulin and was partially reversible after 30 min of washing. Preperfusion with insulin did not affect the action of vanadate, which has insulin-like effect on glucose transport, or the actions of the other positive inotropic agents, isoproterenol and ouabain. The presence of propranolol in the perfusion medium, unlike atenolol, phenoxybenzamine, guanethidine, verapamil or quinidine, modified the inotropic as well as tachyphylactic responses to insulin. The positive inotropic and tachyphylactic responses to insulin were not altered in hearts from reserpine-treated animals. Perfusion of heart with glucose-free solution abolished the tachyphylaxis due to insulin. Likewise, no tachyphylactic response to insulin was evident when iodoacetate, but not sodium fluoride, was added in medium containing glucose. These results suggest that ATP formed during glycolysis may play an important role in insulin-induced tachyphylaxis with respect to cardiac contractile activity.

Changes in adrenergic receptors during the development of heart failure

Moderate and severe stages of congestive heart failure due to the loss of myocardium upon coronary occlusion in rats was associated with an increase in alpha-adrenergic receptors and a decrease in beta-adrenergic receptors in the viable left ventricle. However, at early stages of heart failure the number of beta-adrenergic receptors was decreased without any changes in the number of alpha-adrenergic receptors. The affinities of these receptors to alpha receptor antagonist (3H-prazosin) and beta receptor antagonist (3H-dihydroalprenolol) were not altered in the failing hearts. On the other hand, the pattern of changes in both alpha- and beta-adrenergic receptors in heart membranes treated with oxygen free radical generating system was different from that seen in the failing hearts. In particular, the affinities for these receptors were decreased whereas the number of beta-receptors was increased and the number of alpha-receptors was decreased or unchanged. These results indicate that alterations in the adrenergic receptors in heart failure are not due to the formation of oxygen free radicals.

Modification of cardiac adrenergic receptors by oxygen free radicals

To examine the effects of oxygen free radicals on alpha- and beta-adrenergic receptors, rat heart crude membranes were incubated with xanthine plus xanthine oxidase, H2O2, or H2O2 plus Fe2+. The assay of beta-adrenergic receptors involving [3H]dihydroalprenolol (DHA) binding revealed that the maximal number of binding sites (Bmax) and dissociation constant (Kd) were increased by xanthine plus xanthine oxidase. H2O2 increased the Kd value for [3H]DHA binding. When a hydrophilic ligand, [3H]CGP-12177, was used for the beta-adrenergic receptor assay, an increase in Kd value without any changes in Bmax value was evident on treating the membranes with xanthine plus xanthine oxidase. The assay of alpha-adrenergic receptors involving [3H]prazosin binding showed a decrease in the number of binding sites and an increase in Kd value only after a prolonged period of incubation. Both H2O2 and H2O2 plus Fe2+ increased the Kd value for [3H]prazosin without changes in Bmax. Changes in both alpha- and beta-adrenergic receptors similar to those with crude membranes were also seen by employing the purified heart sarcolemmal membranes. These data indicate that adrenergic receptors in the sarcolemmal membranes are modified by oxygen free radicals.

Depression in cardiac contractile force induced by cholesterol

Cholesterol, combined with albumin, induced rapid functional changes in the isolated perfused rat heart. Under constant perfusion pressure, the decline in contractile force and the rate of development of force due to cholesterol was accompanied by an increase in resting tension and a decrease in coronary flow. Such effects were not produced by albumin alone. Depression in contractile force and increase in resting tension were also evident when coronary flow was kept constant; these effect of cholesterol were dependent on time and dose. The findings support the view that cholesterol may affect cardiac function independently of the atherosclerotic lesion in the hypercholesterolemic state.

Stimulation of phospholipid N-methylation by isoproterenol in rat hearts

Phosphatidylethanolamine (PtdEtn) N-methyltransferase activities were studied in rat heart sarcolemmal and sarcoplasmic reticular fractions after a single intraperitoneal injection of isoproterenol (0.5-5.0 mg/kg). Three active sites (I, II, and III) for PtdEtn N-methylation were assayed by measurement of [3H]methyl group incorporation from 0.055, 10, and 150 microM S-adenosyl-L-[methyl-3H]methionine into membrane PtdEtn molecules. Total methylation activity for catalytic site I of both sarcolemma and sarcoplasmic reticulum was stimulated within 2 minutes by isoproterenol in a dose-dependent manner. Although the increased methyltransferase activity in sarcoplasmic reticulum was normalized at 10 minutes, the enzyme activity in sarcolemma was normalized at 5 minutes but was again increased at 10-30 minutes after isoproterenol injection. No changes in response to isoproterenol were seen for site II and III N-methylation activities in either membrane. Individual N-methylated phospholipids (phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidylcholine), which specifically formed at each site, showed similar behavior. Pretreatment of the animals with a beta-blocking drug, atenolol, for 2 days prevented the isoproterenol-induced changes in hemodynamic parameters and sarcolemmal methylation without affecting the enhanced methylation activities in sarcoplasmic reticulum. In vitro addition of cyclic AMP-dependent protein kinase (catalytic subunit) plus Mg-ATP enhanced methyltransferase activities in sarcolemma and sarcoplasmic reticulum from control hearts by 2.7- and 2.3-fold, respectively; however, under the same in vitro conditions, only about 20% activation was seen in both subcellular membranes isolated from the heart of isoproterenol-injected animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered sympathetic system and adrenoceptors during the development of cardiac hypertrophy

Increasing experimental evidence suggests that the development of cardiac hypertrophy may involve the sympathetic system and associated receptor mechanisms. However, very little work has been done so far to understand changes in the sympathetic system and cardiac adrenoceptors soon after an increased work load is imposed on the heart. Accordingly rat hearts subjected to aortic banding-induced pressure overload were assessed 3, 7, and 14 days postoperatively. Sham-operated rats without aortic banding were used as a control group. Rats with aortic constriction had increases in heart rate, left ventricular systolic pressure, and total mechanical energy during the entire study period. The cardiac RNA level was increased without a significant increase in left ventricular mass on days 3 and 7 in aortic-banded animals; these results were associated with a decrease in the cardiac norepinephrine (NE) store and an increase in the plasma level of NE and dopamine beta-hydroxylase (DBH) activity. By day 14 a significant increase in left ventricular mass and the NE store were found; both plasma NE and DBH remained elevated. Catecholamines in other tissues such as the spleen and kidney were depleted in the banded group, whereas the dopamine level, particularly in the brain, was significantly higher during the entire study. Furthermore, the density of alpha-adrenoceptors was higher on day 3 of aortic banding, and a reciprocal correlation was evident between cardiac alpha- and beta-adrenoceptors on day 14; the density of beta-adrenoceptors was increased, whereas that of alpha-adrenoceptors was decreased in the banded group.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Influence of verapamil on some subcellular defects in diabetic cardiomyopathy

The effects of verapamil on cardiac myofibrillar adenosinetriphosphatase (ATPase) activity, myosin ATPase, and myosin isoenzyme profile as well as sarcoplasmic reticular Ca2+ uptake and ATPase activities were examined in Sprague-Dawley rats made diabetic with a single injection of streptozotocin (65 mg/kg). Myofibrillar ATPase activity and myosin Ca2+ ATPase activity as well as Ca2+ uptake and Ca2+-stimulated ATPase activities of the sarcoplasmic reticulum were significantly decreased in diabetic hearts in comparison to the control values. The myosin isoenzyme component V3 was prominent in diabetic hearts, whereas V1 isoenzyme was the major myosin component in control hearts. Chronic treatment of diabetic rats with verapamil (8 mg/kg daily for 4-8 wk) resulted in an improvement of the altered myofibrillar ATPase activity, myosin ATPase, myosin isoenzyme distribution, and sarcoplasmic reticular Ca2+-pump activities in ventricular tissue. The ability of verapamil to normalize the observed defects in the subcellular organelles in diabetic cardiomyopathy may be related to its effects in controlling the entry of Ca2+ into the cardiac cell.

Depression of heart sarcolemmal Ca2+-pump activity by oxygen free radicals

Although oxygen free radicals have been implicated as mediators of cellular injury in myocardial ischemia-reperfusion, the exact nature of defects produced by these radicals is not clear. Because sarcolemmal Ca2+-pump is involved in the efflux of Ca2+ from the cell, this study was undertaken to examine the effects of oxygen free radicals on sarcolemmal ATP-dependent Ca2+ accumulation and Ca2+-stimulated Mg2+-dependent adenosinetriphosphatase (ATPase) activities as well as lipid peroxidation of membrane phospholipids. Isolated rat heart sarcolemmal membranes were incubated with xanthine + xanthine oxidase [a superoxide anion radical (O2-)-generating system], H2O2, or H2O2 + Fe2+ [a hydroxyl radical (HO.)-generating system] and assayed for Ca2+-pump activities. O2- inhibited the Ca2+-pump activities in a time-dependent manner; a significant inhibition of Ca2+-stimulated ATPase activity was seen after 1 min of incubation. Superoxide dismutase showed a protective effect on depression in Ca2+-pump activities caused by O2-.H2O2 inhibited Ca2+-pump activities in a dose-dependent manner; this inhibition was protected by the addition of catalase. HO. depressed the Ca2+-pump activities to a greater extent in comparison with H2O2. Mannitol showed a protective effect on HO.-induced inhibition of Ca2+-pump activities. The promotion of lipid peroxidation by free radicals was evident from increased formation of malondialdehyde. These results indicate that the sarcolemmal membrane is altered on exposure to oxygen free radicals, and this may result in depressing the Ca2+-pump mechanism for Ca2+ efflux from the myocardial cell.

Sarcolemmal Na+-Ca2+ exchange and Ca2+-pump activities in cardiomyopathies due to intracellular Ca2+-overload

In order to identify defects in Na+-Ca2+ exchange and Ca2+-pump systems in cardiomyopathic hearts, the activities of sarcolemmal Na+-dependent Ca2+ uptake, Na+-induced Ca2+ release, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase were examined by employing cardiomyopathic hamsters (UM-X7.1) and catecholamine-induced cardiomyopathy produced by injecting isoproterenol into rats. The rates of Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities of sarcolemmal vesicles from genetically-linked cardiomyopathic as well as catecholamine-induced cardiomyopathic hearts were decreased without any changes in Na+-induced Ca2+-release. Similar results were obtained in Ca2+-paradox when isolated rat hearts were perfused for 5 min with a medium containing 1.25 mM Ca2+ following a 5 min perfusion with Ca2+-free medium. Although a 2 min reperfusion of the Ca2+-free perfused hearts depressed sarcolemmal Ca2+-pump activities without any changes in Na+-induced Ca2+-release, Na+-dependent Ca2+ uptake was increased. These results indicate that alterations in the sarcolemmal Ca2+-efflux mechanisms may play an important role in cardiomyopathies associated with the development of intracellular Ca2+ overload.

Norepinephrine storage, distribution, and release in diabetic cardiomyopathy

The ability of hearts to store, distribute, and release norepinephrine (NE) was investigated in rats 8 wk after the induction of diabetes by an injection of streptozotocin (65 mg/kg iv). Chronic diabetes was associated with increased content and concentration of NE in heart and in other tissues such as kidney, brain, and spleen. Reserpine or tyramine treatment resulted in depletion of endogenous cardiac NE in control and diabetic rats. The depletion of NE stores at different times after a dose of reserpine was greater in diabetic hearts. On the other hand, NE stores in diabetic hearts were less sensitive than control hearts to low doses of tyramine but were more sensitive to high doses. The uptake of [3H]NE was greater in diabetic hearts in isolated perfused preparations. In comparison with the control values, diabetic hearts showed a decrease in [3H]NE in the granular fraction and an increase in the supernatant fraction. Diabetic hearts also showed an accelerated spontaneous release of [3H]NE. The increased cardiac NE and the uptake and release of NE in diabetic animals were reversible upon treatment with insulin. These results are consistent with the view that sympathetic activity is increased in diabetic cardiomyopathy and indicate that cardiac NE in diabetic rats is maintained at a higher level partly due to an increased uptake of released NE by adrenergic nerve terminals.

Pathophysiological aspects of myocardial hypertrophy

Heart hypertrophy in response to increased workload is a complex process in which this organ adapts to the environment by increasing the muscle mass in terms of additional contractile units and formation of different types of contractile proteins (myosin isozymes). In addition, augmentation of membrane function with respect to calcium transport activities of sarcolemma and sarcoplasmic reticulum occurs at early stages of cardiac hypertrophy associated with hyperfunction of the myocardium. However, if cardiac hypertrophy is left unattended beyond a certain period, physiological hypertrophy is converted to pathological hypertrophy whereby the cardiac muscle is unable to generate an adequate amount of contractile activity. It appears that the sympathetic nervous system is activated for producing beneficial effects at early stages but an elevated level of sympathetic tone for a prolonged period could result in dysfunction of the cardiac muscle. The transition of physiological hypertrophy to pathological hypertrophy seems to be due to the occurrence of intracellular calcium overload in the myocardial cell as a consequence of defects in the membrane calcium transport systems. It is suggested that careful attention should be paid not only to removal of the stimulus responsible for cardiac hypertrophy but also to lowering sympathetic tone. Efforts should also be made to prevent the occurrence of intracellular calcium overload due to membrane defects.

Biphasic changes in the sarcolemmal phosphatidylethanolamine N-methylation activity in catecholamine-induced cardiomyopathy

Phosphatidylethanolamine (PE) N-methylation activity was studied in rat heart sarcolemma at 1, 3, 9 and 24 h after an intraperitoneal injection of isoproterenol (40 mg/kg). Three reaction sites for PE N-methylation were examined by assaying the incorporation of radiolabeled methyl groups from S-adenosyl-L-methionine (AdoMet) into sarcolemmal PE molecules under optimal conditions. Total methylation activity at catalytic site I (studied by employing 0.055 microM AdoMet) was increased at 1 and 3 h after the isoproterenol injection and depressed at 24 h; 9 h samples showed no change. Similar biphasic alterations were seen for phosphatidyl-N-monomethylethanolamine, the major methylated product formed at site I. Alterations in the methylation activity at site I were associated with changes in Vmax values but the apparent affinity for AdoMet remained unaltered. No alterations were found in total methylation activities at sites II and III in isoproterenol treated preparations when studied by employing 10 and 150 microM AdoMet, respectively. An increase and a decrease in the PE N-methylation activity at site I were also observed in the sarcoplasmic reticular (microsomal) fraction from experimental hearts after 1 h and 24 h of the isoproterenol injection respectively, without changes at sites II and III. On the other hand, no changes were seen in the mitochondrial fraction. These results indicate biphasic alterations in the sarcolemmal and microsomal PE N-methylation activities during the development of catecholamine-induced cardiomyopathy.

Altered norepinephrine turnover and metabolism in diabetic cardiomyopathy

Cardiac norepinephrine turnover and metabolism were examined in rats 8 weeks after the induction of chronic diabetes by an intravenous injection of streptozotocin (65 mg/kg). Cardiac norepinephrine concentration, norepinephrine turnover, and norepinephrine uptake were markedly increased in chronic diabetes in comparison with control values; these changes were reversible by 28-day insulin therapy. When the animals were exposed to cold for 6 hours, norepinephrine turnover rate constant increased in control and decreased in diabetic animals; cold exposure also increased norepinephrine concentration in diabetic hearts. Both cardiac norepinephrine concentration and turnover rate in diabetic rats were restored toward control values by ganglionic blockade with pentolinium. The conversion of [3H]tyrosine to [3H]catecholamine was enhanced and tyrosine hydroxylase as well as dopa decarboxylase activities were increased in diabetic hearts. The higher concentrations of [3H]normetanephrine and deaminated catechols indicated a faster metabolic rate of norepinephrine metabolism in hearts from diabetic rats; both monoamine oxidase and catechol-O-methyltransferase activities were also increased. The increased activities of the enzymes for the synthesis and metabolism of norepinephrine were not evident on treating the diabetic animals with insulin. These data not only support the view that chronic diabetes in rats is associated with increased sympathetic activity but also indicate that the cardiac norepinephrine concentration in diabetic rats may be maintained at a higher than normal level by an increased synthesis and uptake of norepinephrine in the adrenergic nerve terminals.

Calcium pump activity of sarcoplasmic reticulum in diabetic rat skeletal muscle

Ca2+ pump activity of skeletal muscle microsomes containing fragments of sarcoplasmic reticulum was examined in rats 8 wk after the induction of chronic diabetes by an intravenous injection of streptozotocin (65 mg/kg). In comparison with the control values, both ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities were increased in the microsomal fraction from diabetic rats. These changes were seen as early as 7 days after streptozotocin injection and were apparent at various times of incubation (1-10 min) as well as at different concentrations of free Ca2+ (10(-7)-5 X 10(-5) M Ca2+). Insulin administration to diabetic animals for 2 wk reversed Ca2+ uptake and ATPase activities to control levels. The increase in microsomal ATPase activity of the diabetic preparation due to cAMP-dependent protein kinase or calmodulin was greater than in the control microsomes and the depression by a specific inhibitor of protein kinase, but not of calmodulin, was greater in diabetic muscle. The enhanced Ca2+ pump activity was associated with altered phospholipid composition and protein profile of the diabetic preparations. The rate of Ca2+ release from microsomal vesicles was unaffected by the diabetic condition. Isometric contractile force development as well as positive dF/dt and negative dF/dt of the skeletal muscle from diabetic animals were higher at different pulse strengths (0.5-100 V) and at different Ca2+ concentrations (0.25-2.5 mM). These results suggest that diabetes is associated with enhanced sarcoplasmic reticular Ca2+ pump activity, and this may account for the hyperfunction of skeletal muscle in this disease.

Effect of adrenochrome on adenine nucleotides and mitochondrial oxidative phosphorylation in rat heart

Effects of adrenochrome, an oxidation product of epinephrine, on myocardial energy production were investigated by studying changes in adenine nucleotide content and mitochondrial oxidative phosphorylation activities in the isolated rat heart. Perfusion of the heart with 50 mg/L adrenochrome induced a marked decline in contractile force within 5 min and this was associated with a rapid decline in the myocardial ATP/AMP ratio. A significant decrease in ATP and ATP/ADP ratio as well as a significant increase in ADP and AMP content was observed at 10 min of perfusion with adrenochrome. Furthermore, mitochondrial oxidative phosphorylation activities were unchanged except that an increase in state 4 respiration and a decrease in RCI value were seen in the heart perfused with adrenochrome for 10 min. Autoradiography of the sections from hearts perfused with 14C-adrenochrome revealed the localization of a significant amount of radioactivity on mitochondria. Adrenochrome at concentrations of 20 mg/L or higher was found to inhibit the oxidative phosphorylation activities of heart mitochondria under in vitro conditions. The depressant effects of adrenochrome on mitochondrial oxidative phosphorylation were additive to those seen with calcium. These data suggest that adrenochrome in the presence of excess calcium in the myocardial cell may impair the process of energy production in mitochondria and this may result in contractile failure of hearts exposed to this cardiotoxic metabolite of epinephrine.

Sarcolemmal Na+-Ca2+ exchange during the development of genetically determined cardiomyopathy

The UM-X7.1 myopathic and control hamsters at 40, 120 and 280 days of age were employed for the examination of heart sarcolemmal Ca2+-transport activities. Na+-dependent Ca2+ uptake activities were significantly depressed in myopathic animals at 120 and 280 days of age in comparison to the control values. No difference in Na+-induced Ca2+ release activities was found between control and experimental sarcolemmal vesicles. ATP-dependent Ca2+ binding and Ca2+-stimulated, Mg2+ ATPase activities were depressed in the experimental animals at 120 and 280 days of age. Similar alterations in the sarcolemmal Na+-dependent Ca2+ exchange and Ca2+-pump activities were seen upon treating the control hamsters with 40 mg/kg isoproterenol for 24 hr. It is suggested that a depression in the sarcolemmal Ca2+ transport activities may contribute to the development of intracellular Ca2+ overload in the genetically determined cardiomyopathy in hamsters and such a defect may be due to excessive amount circulating catecholamines in these animals.

Pathogenesis of cardiac dysfunction in diabetes mellitus

The use of insulin by diabetics has largely removed the threat of death from ketotic coma but cardiovascular dysfunction remains a major cause of death in patients with diabetes. Recent research has indicated a generalized membrane defect, which may cause abnormalities of calcium metabolism in nerves, cardiac and smooth muscle as well as endothelial cells and thus may lead respectively to the development of neuropathy, primary cardiomyopathy, microangiopathy and atherosclerosis in the diabetic population. Each of these pathogenic processes, which are associated with insulin deficiency, alone or in combination with others, may result in cardiac dysfunction in chronic diabetes. Activation of the sympathetic nervous system and abnormalities in catecholamine metabolism have been identified in diabetes; their involvement in the genesis of cardiac pump failure as well as large and small vessel disease is likely. The membrane defects as indicated by changes in both plasma membrane and glycocalyx in diabetic cardiomyopathy appear to be complex and may involve alterations in the metabolism of lipids and pyrimidine nucleotides. It seems that intracellular calcium overload is intimately involved in the development of diabetic cardiomyopathy; however, a concentrated research effort is required to understand the primary biochemical lesion in the pathogenesis of cardiac dysfunction in diabetes. In the meantime, a heightened awareness on the part of clinicians concerning the susceptibility of diabetic patients to cardiovascular problems may help in reducing mortality and morbidity in the diabetic population.

Adaptive changes in subcellular calcium transport during catecholamine-induced cardiomyopathy

Rats were injected intraperitoneally with isoproterenol in dosage of 40 mg/kg body weight and heart microsomal and mitochondrial fractions were isolated 3, 9 and 24 h later. The heart/body weight ratio increased at 9 and 24 h after injection without any changes in the yield of subcellular organelles. Microsomal calcium uptake was significantly elevated at 3 h but returned to normal at 9 h and then became depressed 24 h post-injection. Mitochondrial calcium uptake was significantly increased 9 and 24 h after isoproterenol administration. Kinetic parameters of the calcium transport function indicated that the apparent affinity for Ca2+ remained unchanged, whereas Vmax values were altered in the experimental groups. Although there was no significant change in the phospholipid composition, the total phospholipid contents were increased (at 3, 9 and 24 h for microsomes; 3 and 9 h for mitochondria) in both types of organelles. The protein composition, as determined by gel electrophoresis, was altered in microsomes, but not in mitochondria. These results demonstrate rapid structural and functional changes in subcellular organelles. Such alterations may play an adaptive role in maintaining the intracellular calcium homeostasis during the development of catecholamine-induced cardiomyopathy.