Cardiovascular consequences of magnesium deficiency and loss: pathogenesis, prevalence and manifestations--magnesium and chloride loss in refractory potassium repletion

The Effect of Magnesium on Reperfusion Arrhythmias in STEMI Patients, Treated With PPCI. A Systematic Review With a Meta-Analysis and Trial Sequential Analysis

Aims: The restoration of coronary circulation plays a crucial role in treating ST-segment elevation myocardial infarction (STEMI), however successful reperfusion with primary percutaneous coronary intervention (PPCI) may induce life-threatening arrhythmias. The relation between myocardial electrical instability, as a background factor in reperfusion arrhythmia, and magnesium administered periprocedurally is still questionable. Several randomized clinical trials have been conducted predominantly in the thrombolysis era. Due to the contradictory results of these studies, there is little evidence of the potential preventive effect of magnesium on reperfusion arrhythmias. The aim of our study is to review and meta-analytically analyze data from all studies published so far in the PPCI era, comparing STEMI patients who have undergone primary PCI and received either magnesium or a placebo before the reperfusion procedure. Methods and Results: Our meta-analysis follows the points in the PRISMA protocol and, meets all of their criteria. We conducted a search in five scientific databases using the following keyword combination: (myocardial infarction OR myocardial injury OR acute coronary syndrome OR acs OR stemi) AND magnesium. The 7,295 collected publications were filtered with the Endnote program by title, abstract and full-text based on predefined criteria. A statistical analysis was performed on three randomized-controlled trials using three common parameters, involving 336 patients Trial sequential analysis (TSA) was applied to assess the risk of random error associated with sparse data and multiple testing which can affect cumulative meta-analysis. The incidence of ventricular tachycardias (VTs) was not significantly increased in the non-magnesium control group. (OR: 1.36; CI: 0.619; -2.986, P = 0.263). For the ejection fraction (EF), a non-significant decrease was observed in the magnesium group by weighted mean difference calculation. (WMD: 7.262, 95% CI: -0.238; 0.053; P = 0.057). There was significant decrease in the infarct zone wall motion index (IZWMSI) in the magnesium treatment group. (WMD: 0.384, 95% CI: -0.042; 0.811, P = 0.015). Based on the TSA assessments, the results of all parameters are not significant, objectively demonstrating the lack of reasonable data pertaining to our question. Conclusions: The preventive effect of magnesium on reperfusion arrhythmia associated with primary PCI can still be considered contradictory based on previous studies. In our study, we found, that magnesium is ineffective with a very weak evidence, due to the small number of patients and the biases of the included studies, and a well-designed clinical trial is needed in this area, based on the TSA.

Experimental Hypomagnesemia Induces Neurogenic Inflammation and Cardiac Dysfunction

Hypomagnesemia occurs clinically as a result of restricted dietary intake, Mg-wasting drug therapies, chronic disease status and may be a risk factor in patients with cardiovascular disorders. Dietary restriction of magnesium (Mg deficiency) in animal models produced a pro-inflammatory/pro-oxidant condition, involving hematopoietic, neuronal, cardiovascular, renal and other systems. In Mg-deficient rodents, early elevations in circulating levels of the neuropeptide, substance P (SP) may trigger subsequent deleterious inflammatory/oxidative/nitrosative stress events. Evidence also suggests that activity of neutral endopeptidase (NEP, neprilysin), the major SP-degrading enzyme, may be impaired during later stages of Mg deficiency, and this may sustain the neurogenic inflammatory response. In this article, experimental findings using substance P receptor blockade, NEP inhibition, and N-methyl-D-aspartate (NMDA) receptor blockade demonstrated the connection between hypomagnesemia, neurogenic inflammation, oxidative stress and enhanced cardiac dysfunction. Proof of concept concerning neurogenic inflammation is provided using an isolated perfused rat heart model exposed to acute reductions in perfusate magnesium concentrations.

Effect of micronutrient malnutrition on periodontal disease and periodontal therapy

Periodontitis is a complex chronic inflammatory noncommunicable disease, initiated by the development of a dysbiotic microbial plaque biofilm below the gingival margin. Whilst the pathogenic biofilm is a "necessary cause" of periodontitis, it is insufficient on its own to cause the disease, and a destructive immune-inflammatory response is a key to the translation of risk to destructive events. Other exposures or "component causes" include individual genetic predisposition, lifestyle (including smoking and nutrition), and environmental factors. Dietary nutrients are essential for life as they provide crucial energy sources in the form of macronutrients, as well as important cofactors in the form of micronutrients, which regulate the functionality of enzymes during the regulation of anabolic and catabolic processes in human cells. Moreover, micronutrients can regulate gene transcription factors, such as the proinflammatory nuclear factor kappa B and the anti-inflammatory nuclear factor (erythroid-derived 2)-like 2. This review focuses on the role of vitamins (vitamin A, carotenoids, the vitamin B complex, vitamins C, D, and E, and coenzyme Q10) and minerals (calcium, magnesium, iron, zinc, potassium, copper, manganese, and selenium) in human physiology and the impact of their deficiencies upon periodontal health and disease.

Effects of long-term magnesium supplementation on endothelial function and cardiometabolic risk markers: A randomized controlled trial in overweight/obese adults

Long-term magnesium supplementation improves arterial stiffness, a cardiovascular disease risk marker. Effects on endothelial function may be another mechanism whereby increased magnesium intakes affect cardiovascular risk. Therefore, a 24-week, randomized, double-blind, placebo-controlled trial was performed to examine effects of magnesium supplementation on endothelial function and cardiometabolic risk markers. Fifty-two overweight and obese subjects (30 men and 22 women, age 62 ± 6 years) were randomized to receive either three times daily magnesium (total dose: 350 mg) or placebo capsules. Endothelial function was assessed at the start and at the end of the study. Cardiometabolic risk markers were measured at baseline, after 12 weeks, and at week 24. Brachial artery flow-mediated vasodilation did not change following long-term magnesium supplementation (0.49 pp; 95% CI: −0.38 to 1.36 pp; P = 0.26). Changes in reactive hyperemia index, retinal microvascular caliber and plasma markers for microvascular endothelial function (sVCAM-1, sICAM-1 and sE-selectin) were also not different. In addition, no effects on serum lipids, plasma glucose, insulin sensitivity, and low-grade systemic inflammation were observed. In conclusion, a daily magnesium supplement of 350 mg for 24 weeks does not improve endothelial function and cardiometabolic risk markers in overweight and obese middle-aged and elderly adults.

Mg(2+) differentially regulates two modes of mitochondrial Ca(2+) uptake in isolated cardiac mitochondria: implications for mitochondrial Ca(2+) sequestration

The manner in which mitochondria take up and store Ca(2+) remains highly debated. Recent experimental and computational evidence has suggested the presence of at least two modes of Ca(2+) uptake and a complex Ca(2+) sequestration mechanism in mitochondria. But how Mg(2+) regulates these different modes of Ca(2+) uptake as well as mitochondrial Ca(2+) sequestration is not known. In this study, we investigated two different ways by which mitochondria take up and sequester Ca(2+) by using two different protocols. Isolated guinea pig cardiac mitochondria were exposed to varying concentrations of CaCl2 in the presence or absence of MgCl2. In the first protocol, A, CaCl2 was added to the respiration buffer containing isolated mitochondria, whereas in the second protocol, B, mitochondria were added to the respiration buffer with CaCl2 already present. Protocol A resulted first in a fast transitory uptake followed by a slow gradual uptake. In contrast, protocol B only revealed a slow and gradual Ca(2+) uptake, which was approximately 40 % of the slow uptake rate observed in protocol A. These two types of Ca(2+) uptake modes were differentially modulated by extra-matrix Mg(2+). That is, Mg(2+) markedly inhibited the slow mode of Ca(2+) uptake in both protocols in a concentration-dependent manner, but not the fast mode of uptake exhibited in protocol A. Mg(2+) also inhibited Na(+)-dependent Ca(2+) extrusion. The general Ca(2+) binding properties of the mitochondrial Ca(2+) sequestration system were reaffirmed and shown to be independent of the mode of Ca(2+) uptake, i.e. through the fast or slow mode of uptake. In addition, extra-matrix Mg(2+) hindered Ca(2+) sequestration. Our results indicate that mitochondria exhibit different modes of Ca(2+) uptake depending on the nature of exposure to extra-matrix Ca(2+), which are differentially sensitive to Mg(2+). The implications of these findings in cardiomyocytes are discussed.

Role of magnesium in cardiovascular diseases

Magnesium, the fourth most abundant cation in the human body, is involved in several essential physiological, biochemical, and cellular processes regulating cardiovascular function. It plays a critical role in modulating vascular smooth muscle tone, endothelial cell function, and myocardial excitability and is thus central to the pathogenesis of several cardiovascular disorders such as hypertension, atherosclerosis, coronary artery disease, congestive heart failure, and cardiac arrhythmias. This review discusses the vasodilatory, anti-inflammatory, anti-ischemic, and antiarrhythmic properties of magnesium and its current role in the prevention and treatment of cardiovascular disorders.

Magnesium deficit ? overlooked cause of low vitamin D status?

Like vitamin D deficit, magnesium deficit is considered to be a risk factor for cardiovascular disease. Several steps in the vitamin D metabolism, such as vitamin D binding to its transport protein and the conversion of vitamin D into the hormonal form 1,25-dihydroxyvitamin D by hepatic and renal hydroxylation, depend on magnesium as a cofactor. A new analysis of two National Health and Nutrition Examination Surveys data sets, published in BMC Medicine, investigated potential interactions between magnesium intake, circulating 25-hydroxyvitamin D, which is the generally accepted indicator of vitamin D status, and mortality. Data indicate a reduced risk of insufficient/deficient vitamin D status at high magnesium intake and an inverse association between circulating 25-hydroxyvitamin D and mortality, particularly cardiovascular mortality, among those with magnesium intake above the median. The study provides important findings concerning potential metabolic interactions between magnesium and vitamin D and its clinical relevance. However, results should be considered preliminary since biochemical data on individual magnesium status were lacking, confounding cannot be excluded and questions on the dose?response relationship still remain to be answered. Please see related research article: http://www.biomedcentral.com/1741-7015/11/187.

Magnesium in health and disease

Mammalian cells tightly regulate cellular Mg(2+) content through a variety of transport and buffering mechanisms under the control of various hormones and cellular second messengers. The effect of these hormones and agents results in dynamic changes in the total content of Mg(2+) being transported across the cell membrane and redistributed within cellular compartments. The importance of maintaining proper cellular Mg(2+) content optimal for the activity of various cellular enzymes and metabolic cycles is underscored by the evidence that several diseases are characterized by a loss of Mg(2+) within specific tissues as a result of defective transport, hormonal stimulation, or metabolic impairment. This chapter will review the key mechanisms regulating cellular Mg(2+) homeostasis and their impairments under the most common diseases associated with Mg(2+) loss or deficiency.

A structural equation model for assessment of links between changes in serum triglycerides, -urate, and -glucose and changes in serum calcium, -magnesium and -phosphate in type 2 diabetes and non-diabetes metabolism

Background

This study investigates the associations between changes in serum Triglycerides (S-TG), -Urate (S-Urate), and -Glucose (S-Glu) and changes in serum Calcium (S-Ca), -Magnesium (S-Mg), and -Phosphate (S-P) in patients with type 2 diabetes compared with non-diabetic patients.

Methods

The analysis is based on data collected from a secondary prevention population of women and men (W/M) at risk for cardiovascular disease (type 2 diabetes, 212/200; non-diabetes 968/703). The whole population (n = 2083) had a mean age of 51.0 (9.7) years and was stratified for sex and according to type 2 diabetes or non-diabetes. The patients were followed for, either half a year or one year and changes in risk factors were calculated from follow-up to baseline, the time when patients were admitted to the health center. The pattern of relationships was evaluated using a structural equation model.

Results

Higher S-TG and S-Glu but lower S-Urate was revealed at baseline in type 2 diabetes women and men as compared to their counterparts, non-diabetes patients. Women with type 2 diabetes had higher S-Ca and lower S-Mg than non-diabetes women. Changes in S-Glu were associated with changes in S-Ca (+), baseline S-Ca (+), and S-Urate (-) in type 2 diabetes men. Changes in S-Urate were associated with changes in S-Mg (+) in type 2 diabetes women and non-diabetes men. In men with non-diabetes, changes in S-Glu were associated with changes in S-Mg (-). In women with non-diabetes, changes in S-Glu were associated with changes in S-P (-) and changes in S-Urate with changes in S-Ca (+).

Conclusion

With respect to metabolic disturbances in non-diabetes and the awareness of risk for type 2 diabetes, changes in S-Glu and changes in S-Ca, S-Mg, and S-P should be considered as risk factors for cardiovascular disease. Increased early detection and corrections of high S-Ca, low S-Mg, and S-P in obese patients may improve their metabolism and reduce the risk of CVD in patients with type 2 diabetes.

Trial registration number

ISRCTN: ISRCTN79355192

Stressor states and the cation crossroads

Neurohormonal activation involving the hypothalamic-pituitary-adrenal axis and adrenergic nervous and renin-angiotensin-aldosterone systems is integral to stressor state-mediated homeostatic responses. The levels of effector hormones, depending upon the degree of stress, orchestrate the concordant appearance of hypokalemia, ionized hypocalcemia and hypomagnesemia, hypozincemia, and hyposelenemia. Seemingly contradictory to homeostatic responses wherein the constancy of extracellular fluid would be preserved, upregulation of cognate-binding proteins promotes coordinated translocation of cations to injured tissues, where they participate in wound healing. Associated catecholamine-mediated intracellular cation shifts regulate the equilibrium between pro-oxidants and antioxidant defenses, a critical determinant of cell survival. These acute and chronic stressor-induced iterations in extracellular and intracellular cations are collectively referred to as the cation crossroads. Intracellular cation shifts, particularly excessive accumulation of Ca2+, converge on mitochondria to induce oxidative stress and raise the opening potential of their inner membrane permeability transition pores (mPTPs). The ensuing loss of cationic homeostasis and adenosine triphosphate (ATP) production, together with osmotic swelling, leads to organellar degeneration and cellular necrosis. The overall impact of iterations in extracellular and intracellular cations and their influence on cardiac redox state, cardiomyocyte survival, and myocardial structure and function are addressed herein.

Chronic magnesium deficiency decreases tolerance to hypoxia/reoxygenation injury in mouse heart

AIMS

Magnesium (Mg) deficiency has been reported to be associated with the development of the metabolic syndrome, cardiovascular diseases, and sudden death. We examined the influence of chronic Mg deficiency on cardiac tolerance to hypoxia/reoxygenation injury.

MAIN METHODS

Mice were fed an Mg-deficient diet for 4 weeks, and then their hearts were excised for Langendorff perfusion experiments. The levels of total Mg in the blood and heart were quantified by atomic absorption spectrometry.

KEY FINDINGS

In Mg-deficient mice, the Mg concentration in whole blood was markedly decreased; however, that in the heart remained unchanged. When the hearts of control mice were exposed to hypoxia/reoxygenation, removal of extracellular Mg from a normal Krebs solution containing 1.2 mM Mg resulted in a significant decrease in the recovery of the tension-rate product (TRP) upon reoxygenation. In Mg-deficient mice, the recovery of TRP in the heart was reduced significantly in the absence of extracellular Mg compared to that in controls. The addition of Mg to the perfusate did not improve TRP recovery. During hypoxia/reoxygenation, cardiac damage evaluated by myocardial aspartate amino transferase (AST) release was greater in hearts of Mg-deficient mice than in that of control mice.

SIGNIFICANCE

These results indicate that chronic Mg deficiency causes severe hypomagnesemia and a decrease in cardiac tolerance to hypoxia, without changing the intracellular Mg content. The decreased tolerance to hypoxia was not affected by the presence or absence of extracellular Mg, suggesting that some intracellular metabolic abnormalities develop in the cardiac myocytes of Mg-deficient mice.

Theobromine and the pharmacology of cocoa

The effects of theobromine in man are underresearched, possibly owing to the assumption that it is behaviourally inert. Toxicology research in animals may appear to provide alarming results, but these cannot be extrapolated to humans for a number of reasons. Domestic animals and animals used for racing competitions need to be guarded from chocolate and cocoa-containing foods, including foods containing cocoa husks. Research ought to include caffeine as a comparative agent, and underlying mechanisms need to be further explored. Of all constituents proposed to play a role in our liking for chocolate, caffeine is the most convincing, though a role for theobromine cannot be ruled out. Most other substances are unlikely to exude a psychopharmacological effect owing to extremely low concentrations or the inability to reach the blood-brain barrier, whilst chocolate craving and addiction need to be explained by means of a culturally determined ambivalence towards chocolate.

Alcohol and arrhythmias: a comprehensive review

The use of alcohol as a social lubricant has been ubiquitous in human societies since ancient times. It has also long been recognized that alcohol produces undesirable cardiovascular effects, especially when imbibed in excess. Numerous investigators have noted a causal relationship between alcohol and arrhythmias, as well as sudden cardiac death. We have undertaken a comprehensive review of the literature on alcohol as a potential trigger for arrhythmias. We have reviewed the major epidemiological studies undertaken on this subject. We have also explored pathophysiological mechanisms that drive the arrythmogenic effects of alcohol. In conclusion, although there is definite proof in the literature to implicate alcohol as a culprit in arrhythmias, the relationship is complex.

Potential renovascular hypertension, space missions, and the role of magnesium

Space flight (SF) and dust inhalation in habitats cause hypertension whereas in SF (alone) there is no consistent hypertension but reduced diurnal blood pressure (BP) variation instead. Current pharmaceutical subcutaneous delivery systems are inadequate and there is impairment in the absorption, metabolism, excretion, and deterioration of some pharmaceuticals. Data obtained from the National Aeronautics and Space Administration through the Freedom of Information Act shows that Irwin returned from his 12-day Apollo 15 mission in 1971 and was administered a bicycle stress test. With just three minutes of exercise, his BP was >275/125 mm Hg (heart rate of only 130 beats per minute). There was no acute renal insult. Irwin’s apparent spontaneous remission is suggested to be related to the increase of a protective vasodilator, and his atrial natriuretic peptide (ANP) reduced with SF because of reduced plasma volume. With invariable malabsorption and loss of bone/muscle storage sites, there are significant (P < 0.0001) reductions of magnesium (Mg) required for ANP synthesis and release. Reductions of Mg and ANP can trigger pronounced angiotensin (200%), endothelin, and catecholamine elevations (clearly shown in recent years) and vicious cycles between the latter and Mg deficits. There is proteinuria, elevated creatinine, and reduced renal concentrating ability with the potential for progressive inflammatory and oxidative stress-induced renal disease and hypertension with vicious cycles. After SF, animals show myocardial endothelial injuries and increased vascular resistance of extremities in humans. Even without dust, hypertension might eventually develop from renovascular hypertension during very long missions. Without sufficient endothelial protection from pharmaceuticals, a comprehensive gene research program should begin now.

Neurogenic inflammation and cardiac dysfunction due to hypomagnesemia

Hypomagnesemia continues to be a significant clinical disorder that is present in patients with diabetes mellitus, alcoholism, and treatment with magnesuric drugs (diuretics, cancer chemotherapy agents, etc.). To determine the role of magnesium in cardiovascular pathophysiology, we have used dietary restriction of this cation in animal models. This review highlights some key observations that helped formulate the hypothesis that release of substance P (SP) during experimental dietary Mg deficiency (MgD) may initiate a cascade of deleterious inflammatory, oxidative, and nitrosative events, which ultimately promote cardiomyopathy, in situ cardiac dysfunction, and myocardial intolerance to secondary stresses. SP acts primarily through neurokinin-1 receptors of inflammatory and endothelial cells, and may induce production of reactive oxygen and nitrogen species (superoxide anion, NO*, peroxynitrite, hydroxyl radical), leading to enhanced consumption of tissue antioxidants; stimulate release of inflammatory mediators; promote tissue adhesion molecule expression; and enhance inflammatory cell tissue infiltration and cardiovascular lesion formation. These SP-mediated events may predispose the heart to injury if faced with subsequent oxidative stressors (ischemia/reperfusion, certain drugs) or facilitate development of in situ cardiac dysfunction, especially with prolonged dietary Mg restriction. Significant protection against most of these MgD-mediated events has been observed with interventions that modulate neuronal SP release or its bioactivity, and with several antioxidants (vitamin E, probucol, epicaptopril, d-propranolol). In view of the clinical prevalence of hypomagnesemia, new treatments, beyond magnesium repletion, may be needed to diminish deleterious neurogenic and prooxidative components described in this article.

Dietary magnesium intake can affect mechanical properties of rat carotid artery

The purpose of the present study was to determine the effects of Mg deficiency and supplementation on the mechanical properties of the rat common carotid artery. The internal diameter and intra-arterial pressure of carotid artery were measured continuously using an echo-tracking device. Systolic, diastolic and mean intra-arterial pressures were not significantly different in Mg-deficient, -supplemented or control rats. Histological examination showed a larger cross-sectional area, increased intima-media thickness and a greater media:lumen value in carotid artery of Mg-deficient rats, indicating that Mg deficiency may directly stimulate growth and/or proliferation of arterial wall components. In addition, we observed a negative linear relationship between intima-media thickness and plasma Mg concentration, suggesting that increased Mg intake may counteract arterial wall hypertrophy. Neither Mg deficiency nor supplementation modified the arterial distensibilityv.intra-arterial pressure curve or the Eincv.wall stress curve, indicating that dietary Mg intake did not modify wall stiffness in young rats. At mean intra-arterial pressure, the stress and Eincvalues were, however, significantly lower in Mg-deficient rats (P<0·05 in both cases); this finding could be related to the alteration in the geometry of the carotid artery. In conclusion, these findings suggest that Mg deficiency modifies the mechanical properties of the common carotid artery in young rats. Since Mg deficiency is considered a risk factor, these mechanical alterations could contribute to the development of atherosclerosis, hypertension and cardiovascular diseases.

Long-term moderate magnesium-deficient diet shows relationships between blood pressure, inflammation and oxidant stress defense in aging rats

Epidemiological and experimental studies have indicated a relationship among aging, dietary Mg, inflammatory stress, and cardiovascular disease. Our aim in the present study was to investigate possible links between dietary Mg, oxidant stress parameters, and inflammatory status with aging in rats. We designed a long-term study in which rats were fed for 22 months with moderately deficient (150 mg/kg), standard (800 mg/kg), or supplemented (3200 mg/kg) Mg diets. Comparisons were made with young rats fed with the same diets for 1 month. Compared to the standard and supplemented diets, the Mg-deficient diet significantly increased blood pressure, plasma interleukin-6, fibrinogen, and erythrocyte lysophosphatidylcholine, particularly in aging rats, it decreased plasma albumin. The impairment of redox status was indicated by increases in plasma thiobarbituric acid reactive substances and oxysterols and an increased blood susceptibility to in vitro free-radical-induced hemolysis. We concluded that Mg deficiency induced a chronic impairment of redox status associated with inflammation which could significantly contribute to increased oxidized lipids and promote hypertension and vascular disorders with aging. Extrapolating to the human situation and given that Mg deficiency has been reported to be surprisingly common, particularly in the elderly, Mg supplementation might be useful as an adjuvant therapy in preventing cardiovascular disease.

The nerve-heart connection in the pro-oxidant response to Mg-deficiency

Magnesium is a micronutrient essential for the normal functioning of the cardiovascular system, and Mg deficiency (MgD) is frequently associated in the clinical setting with chronic pathologies such as CHF, diabetes, hypertension, and other pathologies. Animal models of MgD have demonstrated a systemic pro-inflammatory/pro-oxidant state, involving multiple tissues/organs including neuronal, hematopoietic, cardiovascular, and gastrointestinal systems; during later stages of MgD, a cardiomyopathy develops which may result from a cascade of inflammatory events. In rodent models of dietary MgD, a significant rise in circulating levels of proinflammatory neuropeptides such as substance P (SP) and calcitonin gene-related peptide among others, was observed within days (1-7) of initiating the Mg-restricted diet, and implicated a neurogenic trigger for the subsequent inflammatory events; this early "neurogenic inflammation" phase may be mediated in part, by the Mg-gated N: -methyl-D-aspartate (NMDA) receptor/channel complex. Deregulation of the NMDA receptor may trigger the abrupt release of neuronal SP from the sensory-motor C-fibers to promote the subsequent pro-inflammatory changes: elevations in circulating inflammatory cells, inflammatory cytokines, histamine, and PGE(2) levels, as well as formation of nitric oxide, reactive oxygen species, lipid peroxidation products, and depletion of key endogenous antioxidants. Concurrent elevations of tissue CD14, a high affinity receptor for lipopolyssacharide, suggest that intestinal permeability may be compromised leading to endotoxemia. If exposure to these early (1-3 weeks MgD) inflammatory/pro-oxidant events becomes prolonged, this might lead to impaired cardiac function, and when co-existing with other pathologies, may enhance the risk of developing chronic heart failure.

Sodium-dependent recovery of ionised magnesium concentration following magnesium load in rat heart myocytes

Our objectives were to investigate regulation of intracellular ionised Mg2+ concentration ([fMg2+]i) in cardiac muscle and cardiac Na+/Mg2+ antiport stoichiometry. [fMg2+]i was measured at 37 degrees C in isolated rat ventricular myocytes with mag-fura-2. Superfusion of myocytes with Na+ and Ca2+ free solutions containing 30 mM Mg2+ for 15 min more than doubled [fMg2+]i from its basal level (0.75 mM). Re-addition of Na+ caused [fMg2+]i to fall exponentially with time to basal level, the rate increasing linearly with [Na+]. Log(recovery rate) increased linearly with log([Na+]), the slope of 1.06 (95% confidence limits, 0.94-1.17) suggesting one Na+ ion is exchanged for each Mg2+. [fMg2+]i recovery was complete even if the membrane potential was depolarised to 0 mV or if superfusate [Mg2+] was increased to 3 mM. Recovery was rapid in normal Tyrode (0.3 min(-1)) with a Q10 of 2.2. It was completely inhibited by 200 microM imipramine but was unaffected by 20 microM KB-R7943 or 1 microM SEA0400, suggesting the Na+ /Ca2+ antiporter is not involved. Membrane depolarisation by increasing superfusate [K+] to 70 mM, or voltage clamp to 0 mV, increased recovery rate in Na+ containing solutions more than threefold. We conclude [fMg2+]i recovery is by Mg2+ efflux on a 1 Na+:1 Mg2+ antiport.

Benefits and risks of sex hormone replacement in postmenopausal women

Because cardiovascular disease (CVD), which is far less common in young women than in men, but increases in prevalence in the postmenopausal years to that of men, estrogen repletion therapy (ERT) or combined hormone replacement therapy (HRT), has been widely used to protect against development of both CVD and osteoporosis, and possibly to delay or prevent cognitive loss or Alzheimer's disease (AD). To test the validity of favorable findings in many small-scale studies, and in clinical practice, a large-scale trial: the Women's Health Initiative (WHI) was undertaken by the National Institutes of Health (NIH), a trial that was prematurely ended because of increased CVD complications, despite some lessening of hip fractures. This paper suggests that the customary high intake of calcium (Ca)-advised to protect against osteoporosis, and the marginal magnesium (Mg) intake in the USA, might well be contributory to the adverse CV effects, that were all thromboembolic in nature. The procoagulant effect of estrogen is intensified by Ca; Mg-which counteracts many steps in the coagulation cascade and inhibits platelet aggregation and adhesion-is commonly consumed in sub-optimal amounts. The high American dietary Ca/Mg ratio might also be contributory to the WHI failure to confirm ERT's favorable mental effects. Discussed are mechanisms by which Mg enhances estrogen's central nervous system protective effects. Mg's improvement of cerebral blood flow, which improves brain metabolism, can also enhance removal of the beta amyloid peptide, accumulation of which is implicated in AD.

Magnesium decreases cardiac injury in patients undergoing coronary artery bypass surgery

BACKGROUND

The calcium-channel blocking effect of magnesium might have protective effects in patients undergoing cardiopulmonary bypass surgery. We assessed the effects of magnesium on hearts undergoing coronary artery bypass surgery with intermittent warm blood hyperkalemic cardioplegia in the antegrade fashion.

PATIENTS AND METHODS

Twenty patients undergoing coronary bypass surgery were randomly divided into two groups, a control group who received intermittent antegrade warm blood hyperkalemic cardioplegia for myocardial protection, and a study group who received the same solution with the addition of magnesium to the cardioplegia. Extracellular substrates (creatinine phosphokinase, creatinine phosphokinase-MB group, lactate dehydrogenase, c-reactive protein, and cardiac troponin I were measured preoperatively and postoperatively.

RESULTS

There were significant differences in the post-operative concentrations of creatinine phosphokinase, creatinine phosphokinase-MB group, c-reactive protein, and lactate dehydrogenase after cardiopulmonary bypass (P<0.001) in the study group compared with the control subjects. Cardiac troponin I levels were also significantly lower in the study group after cardiopulmonary bypass (P<0.005).

CONCLUSIONS

Our study indicates that if magnesium is added to intermittent antegrade warm blood hyperkalemic cardioplegia, blood levels of many markers of cardiac myocardial injury after cardiopulmonary bypass are lowered. This finding may have implications for myocardial protection.

Iron-catalyzed lipid peroxidation in aortic cells in vitro: protective effect of extracellular magnesium

Low serum Mg2+ has been associated with an increased incidence of cardiovascular pathology in human populations. We investigated the effect of extracellular Mg2+ on Fe-catalyzed lipid peroxidation in rat aortic segments and in human aortic smooth muscle cells. Products of phospholipid oxidation [malonaldehyde (MDA) and 4-hydroxyalkenals (4-HA)], loss of fatty acyl double bonds (by proton-NMR) and glutathione levels indicated that exogenous ferric ions were several-fold more effective than ferrous ions in causing lipid peroxidation. Increased peroxidation was detectable at <1.0 microM Fe3+. Exogenous ferric iron-ionophore, 8-hydroxyquinoline, did not increase peroxidation by ferric ion, suggesting that Fe-catalyzed lipid peroxidation occurred at the cell surface. As ionized serum [Mg2+](o) was lowered from the physiological (0.7-0.96 mM) into the pathophysiological range (0.3-0.5mM) in Fe3+-containing medium, MDA/4-HA levels increased two to three-fold, with a concomitant loss of fatty acyl double bonds and decreased extracellular glutathione. Conversely, MDA/4-HA decreased as ionized Mg2+ was increased, accompanied by a rise in extracellular glutathione. The results indicate that Mg2+ protects aortic cell plasma membranes from ferric iron-catalyzed lipid peroxidation and that this is a contributing factor in the protective action of ionized Mg2+ on the cardiovascular system.

Catecholamine-induced Regulation in Vitro and ex Vivo of Intralymphocyte Ionized Magnesium

Despite the importance of the adrenergic activity and of the metabolism of magnesium in some important cardiovascular pathologies, very little is known about how intracellular ionized magnesium (Mgi2+) is regulated by catecholamines. We made an in-vitro study of the variations in the concentration of ionized magnesium in human lymphocytes using the fluorescent probe furaptra in response to different catecholamines. We also made an ex-vivo study of the changes in intracellular ionized magnesium in lymphocytes in 20 subjects with essential arterial hypertension, 10 treated with 120 mg/d of propranolol and 10 with placebo. Norepinephrine and isoproterenol significantly decrease Mgi2+ and this effect is blocked by beta-blockers but not by alpha-blockers. The EC50 of the effect of norepinephrine is within the range of concentrations physiologically present in plasma. The substitution of extracellular sodium with choline blocks the decrease in intracellular ionized magnesium induced by norepinephrine, which leads us to suppose that the magnesium-reducing effect of catecholamines is a result of the activation of a Na+-Mg2+ exchanger. We were not able to demonstrate any change in intracellular ionized magnesium after 1 and 17 days of active treatment in essential hypertensives. The impossibility of demonstrating ex vivo the mechanism of catecholamine-mediated regulation that is evident in vitro is perhaps due to our experimental conditions or to substances which in vivo inhibit the action of the catecholamines on magnesium, such as insulin and/or glucose.

N-Methyl-d-aspartate Receptor Blockade Inhibits Cardiac Inflammation in the Mg2+-Deficient Rat

Elevated plasma levels of the neuropeptide substance P (SP) precede the perivascular inflammatory infiltrate seen in hearts of Mg(2+)-deficient (MgD) animals. The N-methyl-d-aspartate (NMDA) receptor is found in neurons, and activation of this receptor participates in SP release; under normal circumstances, this release can be blocked by Mg(2+). Therefore, we reasoned that blockade of the NMDA receptor with dizolcipine maleate (a noncompetitive NMDA receptor antagonist) would prevent SP release from C-fibers due to MgD. In this study, animals were implanted with slow-release pellets containing dizolcipine or placebo and were fed with diet sufficient in Mg(2+) or deficient with only 9% of USDA-recommended Mg(2+). SP immunostaining of dorsal root ganglia showed a time-dependent depletion of SP in the MgD animals, with a dramatic decrease of SP by week 2; this depletion was prevented by pretreatment with dizolcipine maleate. The significant increase in plasma prostaglandin E(2) levels during MgD was prevented by dizolcipine, and the loss of total red blood cell glutathione content was significantly attenuated by NMDA blockade after 3 weeks of MgD (p < 0.01 versus controls). Immunohistochemical and Western blot analyses of ventricular tissue demonstrated that NMDA receptor blockade abolished MgD-related increase of endothelium adhesion molecule CD54 (weeks 1 and 2; p < 0.05), and of monocyte/macrophage surface protein CD11b expression (week 3; p < 0.05). We conclude that NMDA receptor blockade with dizolcipine maleate prevented SP depletion and reduced perivascular inflammatory infiltrates, thus decreasing cardiac injury due to Mg(2+) deficiency.

Low Serum Magnesium Predicts Neurological Events in Patients With Advanced Atherosclerosis

Background and Purpose— Magnesium (Mg) deficiency is thought to be a risk factor for cerebrovascular atherosclerosis and complications. We investigated the prognostic impact of Mg serum levels with respect to the occurrence of neurological events in patients with advanced atherosclerosis.

Methods— We prospectively studied 323 patients with symptomatic peripheral artery disease and intermittent claudication (197 men; median age, 68 years). Serum Mg was determined, and patients were followed for a median of 20 months (interquartile range, 12 to 25 months) for the occurrence of neurological events, defined as ischemic stroke and/or carotid revascularization (carotid endarterectomy or carotid stenting). Multivariate Cox proportional hazards analysis was applied to assess the association of serum Mg (in tertiles) and neurological events.

Results— Neurological events occurred in 35 patients (11%) (15 patients with stroke, 13 with carotid revascularization, and 7 with stroke and subsequent revascularization). Compared with patients in the highest tertile of Mg serum levels (>0.84 mmol/L), patients with Mg serum values <0.76 mmol/L (lowest tertile) exhibited a 3.29-fold increased adjusted risk (95% CI, 1.34 to 7.90; P=0.009) for neurological events, but patients with Mg serum values of 0.76 mmol/L to 0.84 mmol/L (middle tertile) had no increased risk (adjusted hazard ratio, 1.10; 95% CI, 0.35 to 3.33; P=0.88). Mg serum levels were not associated with all-cause mortality (P=0.87) or coronary events (P=0.67) during follow-up.

Conclusions— Low Mg serum levels indicate an increased risk for neurological events in patients with symptomatic peripheral artery disease, favoring Mg substitution therapy in those patients with advanced atherosclerosis.

Effect of magnesium on mRNA expression and production of endothelin-1 in DOCA-salt hypertensive rats

The aim of this study was to investigate whether or not the decrease in blood pressure induced by dietary magnesium supplementation in DOCA-salt hypertensive rats is associated with modifications in expression and tissular production of endothelin-1. DOCA-salt treatment increased blood pressure, induced renal and cardiac hypertrophy, and increased endothelin-1 expression and production in the kidney, heart, and aorta. Mg supplementation for 8 weeks lowered blood pressure in DOCA-salt hypertensive rats and prevented hypertrophies and the increase of endothelin-1 expression and production in the heart, aorta, and kidney. Treatment with a receptor ETA antagonist, ABT-627, was used to clarify the relationship between the lowering effect of Mg supplementation on blood pressure and endothelin-1 production. When DOCA-salt rats were treated with ABT-627 for 8 weeks, Mg supplementation failed to lower blood pressure. In conclusion, these findings suggest that the lowering effect of Mg supplementation on blood pressure requires an inhibitory effect on endothelin-1 activity and/or endothelin-1 production in DOCA-salt hypertensive rats.

Dietary magnesium intake influences circulating pro-inflammatory neuropeptide levels and loss of myocardial tolerance to postischemic stress

Severe dietary Mg restriction (Mg(9), 9% of recommended daily allowance [RDA], plasma Mg = 0.25 mM) induces a pro-inflammatory neurogenic response in rats (substance P [SP]), and the associated increases in oxidative stress in vivo and cardiac susceptibility to ischemia/reperfusion (I/R) injury were previously shown to be attenuated by SP receptor blockade and antioxidant treatment. The present study assessed if less severe dietary Mg restriction modulates the extent of both the neurogenic/oxidative responses in vivo and I/R injury in vitro. Male Sprague-Dawley rats maintained on Mg(40) (40% RDA, plasma Mg = 0.6 mM) or Mg(100) (100% RDA, plasma Mg = 0.8 mM) diets were assessed for plasma SP levels (CHEM-ELISA) during the first 3 weeks and were compared with the Mg(9) group; red blood cell (RBC) glutathione and plasma malondialdehyde levels were compared at 3 weeks in Mg(9), Mg(20) (plasma Mg = 0.4 mM), Mg(40), and Mg(100) rats; and 40-min global ischemia/30-min reperfusion hearts from 7-week-old Mg(20), Mg(40), and Mg(100) rats were compared with respect to functional recovery (cardiac work, and diastolic, systolic, and developed pressures), tissue LDH release, and free radical production (ESR spectroscopy and alpha-phenyl-N-tert butylnitrone [PBN; 3 mM] spin trapping). The Mg(40) diet induced smaller elevations in plasma SP (50% lower) compared with Mg(9), but with a nearly identical time course. RBC glutathione and plasma malondialdehyde levels revealed a direct relationship between the severity of oxidative stress and hypomagnesemia. The dominant lipid free radical species detected in all I/R groups was the alkoxyl radical (PBN/alkoxyl: alpha(H) = 1.93 G, alpha(N) = 13.63 G); however, Mg(40) and Mg(20) hearts exhibited 2.7- and 3.9-fold higher alkoxyl levels, 40% and 65% greater LDH release, and lower functional recovery (Mg(20) < Mg(40)) compared with Mg(100). Our data suggest that varying dietary Mg intake directly influences the magnitude of the neurogenic/oxidative responses in vivo and the resultant myocardial tolerance to I/R stress.

Effects of oral magnesium therapy on exercise tolerance, exercise-induced chest pain, and quality of life in patients with coronary artery disease

Previous studies have demonstrated that magnesium supplementation improves endothelial function in patients with coronary artery disease (CAD). However, the impact on clinical outcomes, such as exercise-induced chest pain, exercise tolerance, and quality of life, has not been established. In a multicenter, multinational, prospective, randomized, double-blind and placebo-controlled trial, 187 patients with CAD (151 men, 36 women; mean +/- SD age 63 +/- 10 years, range 42 to 83) were randomized to receive either oral magnesium 15 mmol twice daily (Magnosolv-Granulat, total magnesium 365 mg provided as magnesium citrate) (n = 94) or placebo (n = 93) for 6 months. Symptom-limited exercise testing (Bruce protocol) and responses given on quality-of-life questionnaires were the outcomes measured. Magnesium therapy significantly increased intracellular magnesium levels ([Mg]i) in a substudy of 106 patients at 6 months compared with placebo (35.5 +/- 3.7 vs 32.6 +/- 2.9 mEq/L, p = 0.0151). Magnesium treatment significantly increased exercise duration time compared with placebo (8.7 +/- 2.1 vs 7.8 +/- 2.9 minutes, p = 0.0075), and lessened exercise-induced chest pain (8% vs 21%, p = 0.0237). Quality-of-life parameters significantly improved in the magnesium group. These findings suggest that oral magnesium supplementation in patients with CAD for 6 months results in a significant improvement in exercise tolerance, exercise-induced chest pain, and quality of life, suggesting a potential mechanism whereby magnesium could beneficially alter outcomes in patients with CAD.

Does magnesium have a role in the treatment of patients with coronary artery disease?

Hypomagnesemia is common in hospitalized patients, especially in elderly patients with coronary artery disease (CAD) and/or those with chronic heart failure. Hypomagnesemia is associated with increased all cause mortality and mortality from CAD. Magnesium supplementation improves myocardial metabolism, inhibits calcium accumulation and myocardial cell death; it improves vascular tone, peripheral vascular resistance, afterload and cardiac output, reduces cardiac arrhythmias and improves lipid metabolism. Magnesium also reduces vulnerability to oxygen-derived free radicals, improves endothelial function and inhibits platelet function, including platelet aggregation and adhesion, which potentially confers upon magnesium physiologic and natural effects similar to adenosine-diphosphate inhibitors such as clopidogrel. However, data regarding the use of magnesium in patients with acute myocardial infarction (AMI) are conflicting. Although some previous relatively small randomized clinical trials demonstrated a remarkable reduction in mortality when intravenous magnesium was administered to relatively high risk AMI patients, two recently published large-scale randomized clinical trials (the Fourth International Study of Infarct Survival [ISIS 4] and Magnesium in Coronaries [MAGIC]) were unable to demonstrate any advantage of intravenous magnesium over placebo. Nevertheless, the theoretical benefits of magnesium supplementation as a cardio-protective agent in CAD patients, promising results from animal and human studies, its relatively low-cost and ease of handling requiring no special expertise, together with its excellent tolerability, gives magnesium a place in treating CAD patients, especially in those at high risk, such as CAD patients with heart failure, the elderly and hospitalized patients with hypomagnesemia. Furthermore, magnesium therapy is indicated in life-threatening ventricular arrhythmias such as torsades de pointes and intractable ventricular tachycardia.

Early administration of intravenous magnesium to high-risk patients with acute myocardial infarction in the Magnesium in Coronaries (MAGIC) Trial: a randomised controlled trial

BACKGROUND

The benefits of supplemental administration of intravenous magnesium in patients with ST-elevation myocardial infarction (STEMI) are controversial. Despite promising results from work in animals and the ready availability of this simple, inexpensive treatment, conflicting results have been reported in clinical trials. Our aim was to compare short-term mortality in patients with STEMI who received either intravenous magnesium sulphate or placebo.

METHODS

We did a randomised, double-blind trial in 6213 patients with acute STEMI who were assigned a 2 g intravenous bolus of magnesium sulphate administered over 15 min, followed by a 17 g infusion of magnesium sulphate over 24 h (n=3113), or matching placebo (n=3100). Our primary endpoint was 30-day all-cause mortality. At randomisation, patients were stratified by their eligibility for reperfusion therapy. The first stratum included patients who were aged 65 years or older and eligible for reperfusion therapy, and the second stratum included patients of any age who were not eligible for reperfusion therapy. Analysis was by intention-to-treat.

FINDINGS

At 30 days, 475 (15.3%) patients in the magnesium group and 472 (15.2%) in the placebo group had died (odds ratio 1.0, 95% CI 0.9-1.2, p=0.96). No benefit or harm of magnesium was observed in eight prespecified subgroup analyses of patients and in 15 additional exploratory subgroup analyses. After adjustment for factors shown to effect mortality risk in a multivariate regression model, no benefit of magnesium was observed (1.0, 0.8-1.1, p=0.53).

INTERPRETATION

Early administration of magnesium in high-risk patients with STEMI has no effect on 30-day mortality. In view of the totality of the available evidence, in current coronary care practice there is no indication for the routine administration of intravenous magnesium in patients with STEMI.

Efficacy of long duration resuscitation and magnesium sulphate treatment in amitriptyline poisoning

A single dose of cyclic antidepressants leads to death in childhood. Myocardial depression and ventricular arrhythmia are the severe side effects in cyclic antidepressant overdose. A 23-month-old boy was brought to hospital because 36 mg/kg of amitriptyline had been taken. Cardiopulmonary resuscitation was applied for 70 minutes due to cardiac and respiratory arrest. Circulation was restored after resuscitative efforts. However, ventricular tachycardia was detected which did not respond to lidocaine, bicarbonate and cardioversion treatment. Magnesium sulphate treatment was started and cardiac rhythm normalized. No side effects were observed. The duration of resuscitation should be extended in cases of cardiopulmonary arrest secondary to tricyclic antidepressants intoxication. It should be continued at least for 1 hour. Magnesium sulphate was found to be extremely effective in a case of amitriptyline intoxication refractory to treatment.

Increased phagocytosis and production of reactive oxygen species by neutrophils during magnesium deficiency in rats and inhibition by high magnesium concentration

Recent studies underline the importance of the immunoinflammatory processes in the pathology of Mg deficiency. Neutrophils possess a superoxide anion-generating NADPH oxidase and its inappropriate activation may result in tissue damage. The aim of the present study was to assess the effect of experimental Mg deficiency in the rat on polymorphonuclear leucocytes (PMN) activity and the role of increasing extracellular Mg. Weaning male Wistar rats were fed either a Mg-deficient or a control diet for 8 d. In Mg-deficient rats, the characteristic inflammatory response was accompanied by a marked increase in the number of PMN. Higher plasma interleukin 6 and NO concentrations and increased lipid peroxidation in the heart were found in Mg-deficient rats as compared with control rats. As shown by chemiluminescence studies, basal neutrophil activity from Mg-deficient rats was significantly elevated when compared with neutrophils from control rats. Moreover, the chemiluminescence of PMN from Mg-deficient rats was significantly higher than that of control rats following phorbol myristate acetate or opsonized zymosan activation. PMN from Mg-deficient rats also showed an increased activity of phagocytosis in comparison with neutrophils from control animals. Increasing extracellular Mg concentration in the incubating medium of PMN (0.8 v. 8.0 mM) decreased the chemiluminescence activity of PMN from control rats following opsonized zymosan activation. Chemiluminescence activities of PMN from Mg-deficient rats following phorbol myristate acetate or opsonized zymosan challenge were also decreased by high extracellular Mg concentration. From this work, it appears that PMN activation is an early consequence of Mg deficiency and that high extracellular Mg concentration inhibits free radicals generation.

Prevalence and prognostic importance of hypomagnesemia and hypocalcemia in horses that have colic surgery

OBJECTIVE

To determine the prevalence of hypomagnesemia and hypocalcemia in horses with surgical colic.

ANIMALS

35 horses with surgically managed colic.

PROCEDURE

Serum concentrations of total magnesium (tMg2+) and calcium (tCa2+), as well as ionized magnesium (iMg2+) and calcium (iCa2+) were analyzed before surgery and 1, 3, 5, and 7 days following surgery. A lead-II ECG and pertinent clinical data were also obtained at each time.

RESULTS

Preoperative serum tMg2+ and iMg2+ concentrations were below the reference range in 6 (17%) and 19 (54%) horses, respectively. Serum concentrations of tCa2+ and iCa2+ were less than the reference range in 20 (57%) and 30 (86%) horses before surgery. Horses with strangulating lesions of the gastrointestinal tract had significantly lower preoperative serum concentrations of iMg2+ and iCa2+, as well as a higher heart rate than horses with nonstrangulating lesions. Horses that developed postoperative ileus had significantly lower serum concentrations of iMg2+ after surgery. Serum concentrations of magnesium and calcium (total and ionized) correlated significantly with the PR, QRS, QT, and corrected QT (QTc) intervals. Horses that were euthanatized at the time of surgery (n = 7) had significantly lower preoperative serum concentrations of iMg2+, compared with horses that survived. Neither serum magnesium nor calcium concentrations were predictors of hospitalization time or survival.

CONCLUSIONS AND CLINICAL RELEVANCE

Hypomagnesemia and hypocalcemia were common during the perioperative period, particularly in horses with strangulating intestinal lesions and ileus. Serum concentrations of tMg2+ and tCa2+ were less sensitive than iMg2+ and iCa2+ in detecting horses with hypomagnesemia and hypocalcemia.

Oral magnesium therapy improves endothelial function in patients with coronary artery disease

BACKGROUND

Magnesium blocks many of the physiological actions of calcium. Nevertheless, the impact of magnesium supplementation on endothelial function and exercise tolerance in stable coronary artery disease (CAD) patients has not been assessed.

METHODS AND RESULTS

In a randomized, double-blind, placebo-controlled trial, 50 stable CAD patients (41 men and 9 women, mean+/-SD age 67+/-11 years, age range 42 to 82 years) were randomized to receive either magnesium (n=25) (30 mmol/d Magnosolv-Granulat; Asta Medica Company, Inc) or placebo (n=25) for 6 months. Before and after 6 months, endothelium-dependent brachial artery flow-mediated vasodilation (FMD) and endothelium-independent NTG-mediated vasodilation were assessed with high-resolution (10-MHz) ultrasound. Exercise stress testing was performed with use of the Bruce protocol. Intracellular magnesium concentrations ([Mg(2+)](i)) were assessed from sublingual cells through x-ray dispersion (EXA) (normal mean+/-SD values 37. 9+/-4.0 mEq/L). The magnesium therapy significantly increased postintervention ([Mg(2+)](i) versus placebo (36.2+/-5.0 versus 32.7+/-2.7 mEq/L, P<0.02). There was a significant correlation in the total population between baseline [Mg(2+)](i) and baseline FMD (r=0. 48, P<0.01). The magnesium intervention resulted in a significant improvement in postintervention FMD (15.5+/-12.0%, P=0.02 compared with baseline), which was not evident with placebo (4.4+/-2.5%, P=0.78 compared with baseline). There was better exercise tolerance (9.3+/-2.0 versus 7.3+/-3.1 minutes, P=0.05) and less ischemic ST-segment changes (4 versus 10 patients, P=0.05) in the magnesium versus placebo groups, respectively.

CONCLUSIONS

Oral magnesium therapy in CAD patients is associated with significant improvement in brachial artery endothelial function and exercise tolerance, suggesting a potential mechanism by which magnesium could beneficially alter outcomes in CAD patients.