Body Magnesium Research Articles

Effects of Treated Wastewater Effluent Irrigation on Terrestrial Salamanders

Since 1983, State Game Lands 176 in Centre Co.,Pennsylvania, U.S.A., has been spray irrigated withtreated wastewater effluent as an alternative to thedirect discharge of treated effluent into surfacewaters. Although the effects of wastewater irrigationon birds and mammals had been studied, its effects onamphibians were unknown. We examined the physiological and behavioral responses of juvenile Jefferson salamanders (Ambystoma jeffersonianum Green) to effluent-irrigated soils and wastewater effluent in the field and laboratory to assess the effects of wastewater irrigation on the terrestrial phase of this species. Salamanders confined to irrigated soils for 35 d showed no difference in six physiological parameters (growth, body water concentration, and body sodium, potassium, calcium, and magnesium levels) compared to those enclosed on unirrigated soils. Salamanders on wastewater effluentsoaked substrates for the same duration in thelaboratory had higher body sodium concentration thanthose on deionized water soaked substrates, likely dueto elevated sodium levels in wastewater effluent.Salamanders demonstrated no `preference' for irrigatedor unirrigated soils over three days when allowed achoice between the two substrates in behavioral tests. These results suggest wastewater effluent irrigationis not acutely toxic to terrestrial A.jeffersonianum under natural conditions. Long-termadverse effects wastewater irrigation on terrestrialJefferson salamanders are still possible, andexaminations of salamander growth and survival overlonger durations are needed to assess the holisticimpacts of wastewater spraying on this species.

Magnesium in disease: a review with special emphasis on the serum ionized magnesium.

This review deals with the six main clinical situations related to magnesium or one of its fractions, including ionized magnesium: renal disease, hypertension, pre-eclampsia, diabetes mellitus, cardiac disease, and the administration of therapeutic drugs. Issues addressed are the physiological role of magnesium, eventual changes in its levels, and how these best can be monitored. In renal disease mostly moderate hypermagnesemia is seen; measuring ionized magnesium offers minimal advantage. In hypertension magnesium might be lowered but its measurement does not seem relevant. In the prediction of severe pre-eclampsia, elevated ionized magnesium concentration may play a role, but no unequivocal picture emerges. Low magnesium in blood may be cause for, or consequence of, diabetes mellitus. No special fraction clearly indicates magnesium deficiency leading to insulin resistance. Cardiac diseases are related to diminished magnesium levels. During myocardial infarction, serum magnesium drops. Total magnesium concentration in cardiac cells can be predicted from levels in sublingual or skeletal muscle cells. Most therapeutic drugs (diuretics, chemotherapeutics, immunosuppressive agents, antibiotics) cause hypomagnesemia due to increased urinary loss. It is concluded that most of the clinical situations studied show hypomagnesemia due to renal loss, with exception of renal disease. Keeping in mind that only 1% of the total body magnesium pool is extracellular, no simple measurement of the real intracellular situation has emerged; measuring ionized magnesium in serum has little added value at present.

Magnesium transport in freshwater teleosts

The magnesium handling of freshwater teleost fish is discussed, with an emphasis on the role of branchial, intestinal and renal transport. In response to the eminent threat of constant diffusive losses of minerals such as magnesium, freshwater fish have developed efficient mechanisms for magnesium homeostasis. Magnesium losses are overcome by the uptake of magnesium from the food, making the intestine an important route for magnesium uptake. Some evidence suggests that intestinal magnesium uptake in fish is a regulated, cellular process. The ambient water is an additional magnesium source for fish, implicating the gills as a secondary route for magnesium uptake. Certainly, in some species, direct uptake from the water, probably via branchial routes, ameliorates the effects of a low-magnesium diet. The hard tissues, representing over 50 % of the total body magnesium pool, form a reservoir from which magnesium can be recruited to perform its functions in the cellular metabolism of soft tissues such as muscle. In fish, as in terrestrial vertebrates, the balance of a variety of elements becomes disturbed when the magnesium homeostasis of the soft tissues is disrupted. However, fish appear to be less sensitive than terrestrial vertebrates to these perturbations. Magnesium is reabsorbed in the kidneys to minimise losses. For renal cells, part of a cellular pathway has been elucidated that would allow absorptive magnesium transport (a magnesium conductive pathway in renal brush-border membranes). In some euryhaline teleosts, the kidneys appear to switch instantaneously to rapid magnesium secretion upon magnesium loading, a response common to marine fish that are threatened by diffusive magnesium entry. This enigmatic mechanism underlies the capacity of some euryhaline species to acclimate rapidly to sea water. Despite the progress made over the last decade, much of the cellular and molecular basis of magnesium transport in the gills, intestine and kidneys remains obscure. The application of fluorescent, radioactive and molecular probes, some of which have only recently become available, may yield rapid progress in the field of magnesium research.

Dietary phytate reduces magnesium bioavailability in growing rats

The aim of the present study was to evaluate the effect of dietary phytate on Mg bioavailability in rats. Male rats with an initial average weight of 60 g were fed ad libitum semisynthetic diets based on casein and corn starch containing 300 mg Mg/kg and increasing levels of sodium phytate (0, 4, 8, 12, 16, 20 g/kg) over 21 days. The addition of increasing levels of phytic acid to the diets resulted in a dose dependent decrease of the apparent magnesium absorption. Urinary magnesium declined in tendency with increasing levels of dietary phytate. Similarly to apparent Mg absorption and Mg balance, dietary phytate decreased whole body magnesium retention dose dependently. Higher intakes of phytic acid reduced plasma and femur Mg concentration and impaired body weight and feed efficiency.

Serum phenytoin levels of patients on gastrostomy tube feeding.

Serum phenytoin levels of two groups of brain-injured patients on gastrostomy tube (GT) feeding were retrospectively examined. In the first group (group C = clamped, n = 13), GT was clamped for one hour after the phenytoin dose (2-3 doses per day), and in the second group (group NC = not clamped, n = 9) GT feedings were continued without interruption. Mean +/- SD of the serum phenytoin levels was 14.4 +/- 4.7 micrograms/ml for group C, and 9.2 +/- 6.8 micrograms/ml for group NC. When serum phenytoin levels were adjusted for decreased serum albumin levels, the results were 19.8 +/- 6.4 micrograms/ml for group C and 11.7 +/- 7.9 micrograms/ml for group NC. Statistical analysis showed a significant difference between the means in both the phenytoin and adjusted phenytoin levels between the two groups (p < 0.05). No significant difference was found in phenytoin dosage per kg of body weight, protein intakes, calcium, magnesium and sodium per 24 hours between the means for the two groups. Results of this study suggest that clamping the GT for one hour after the phenytoin dose results in higher serum levels of the drug.

Hypomagnesemia in alcoholic patients.

CUTE AND chronic alcoholism are the most common A settings for hypomagnesemia in everyday clinical practice.' In almost all studies addressing this issue, the total serum magnesium concentration was although there are limitations on its use in evaluating total body magnesium stores.' Recently, commercially available instruments with new ion-selective electrodes for ionized magnesium, the biologically active form of magnesium, have made its measurement possible. However, as has been pointed out,6 the determination of ionized magnesium activity in biological fluids is influenced by several factors, and the values found for it may differ when measured with different instruments. In particular, the usefulness of ionized magnesium determination is problematic in alcoholics, in whom significant differences in ionized magnesium have been found when two different instruments were used.6 We are deeply involved in the study of the acid-base and electrolyte abnormalities observed in chronic alcoholic patients,' and we have extensively studied the pathogenetic mechanisms of hypomagnesemia in a large group (n = 127) of alcoholic patients admitted to our university hospital for causes related to alcohol abuse.' The mean (SD) total serum magnesium level was 0.7 ? 0.2 mmol/L, which was significantly lower than that observed in 203 normal controls (0.9 5 0.3 mmol/L, p < 0.01). These values are in agreement with the results reported by De Marchi et aL3 in a smaller group of patients with chronic alcoholism. Of interest, hypomagnesemia (total serum magnesium < 0.65 mmol/L) was the most common electrolyte disturbance observed in 38 of the 127 patients (29.9%), a value comparable to that reported by De Marchi et al.3 but a lot higher than the values obtained by Hristova et a1.6 The determination of total serum magnesium, the most common method clinically available to assess the magnesium status of patients, reflects only a small part of the total

Magnesium in drinking water and body magnesium status measured using an oral loading test

Epidemiological studies have shown an inverse relationship between magnesium in drinking water and death from ischaemic heart disease. The question is whether magnesium in drinking water can be critical for the body magnesium status. The aim of this study was to investigate, using an oral loading test, whether a change in body magnesium status could be found among people who change from drinking water with a low magnesium concentration to water with higher concentrations. The subjects participating in the study were 9 men and 3 women 65-70 years old, living in the city of Göteborg, Sweden, where the magnesium concentration in the tap water is low (1.6 mg/l). Drinking water was prepared with 200 mg MgCl2.6H2O added per litre to a level of 25 mg/l, and was distributed to the subjects twice a week for 6 weeks. Excretion of magnesium, potassium and creatinine, basal and after oral magnesium loading (tablets containing 575 mg), was measured in 24 h urine before and after the supplementation period. Calculations were made for the total excretion (mmol/24 h), and in relation to creatinine. The subjects' intake of magnesium via food and water was estimated using a questionnaire. There was a difference between the post load excretion of magnesium, expressed as the magnesium/creatinine ratio, before and after the supplementation period. The mean percentage change was a 14.6% (p=0.047) increase. No changes were found for potassium. In summary, the results indicate that magnesium in drinking water can affect body magnesium status.

Metabolic response to dietary phosphorus intake in rainbow trout ( Oncorhynchus mykiss)

The objectives of this study were to determine which indicators were most responsive to suboptimal phosphorus intake in fingerling rainbow trout, and to observe the magnitude of these changes over time. Fish with an initial mean weight of 1.8 g were hand-fed one of five semipurified wheat-gluten based diets containing between 0.23%–1.16% dietary phosphorus, or a fish meal control diet (1.8% P) for 8 weeks. Phosphorus, calcium and magnesium concentrations in whole body, skin (with scales), and plasma were measured bi-weekly. Alkaline phosphatase activity was determined in plasma and in a crude intestinal homogenate. There was no correlation between dietary phosphorus concentration and body weight of rainbow trout. Of all tissues and metabolites examined, skin was the most responsive to differences in dietary phosphorus concentration. Dietary treatment had a significant effect on the concentrations of ash, phosphorus, calcium and magnesium in rainbow trout skin at weeks 4 and 8. Whole body ash, phosphorus, calcium, and magnesium concentrations were also highly responsive to graded levels of dietary phosphorus at week 8. Rainbow trout fed suboptimal phosphorus diets had significantly lower plasma phosphorus concentrations and alkaline phosphatase activity, and significantly higher whole body lipid than those fed adequate phosphorus diets. Alkaline phosphatase activity of the intestinal homogenate was not significantly correlated with dietary phosphorus intake.

Erythrocyte Magnesium in Elderly Patients: not a Reliable Guide to Magnesium Status

To assess body magnesium status in various illness states in older people by measurement of serum magnesium (S Mg) and erythrocyte magnesium (E Mg) and to explore the limitations of E Mg measurement. S Mg and E Mg were measured in 150 consecutive out-patients, mean age 77 years, and in 100 consecutive in-patient admissions, mean age 80 years. Results were analysed for different diagnostic groups S Mg was normally distributed for both in-patients and out-patients, mean values 0.79 mmol/l and 0.77 mmol/l respectively. In-patient E Mg concentrations were often higher but the distribution was considerably skewed, median 2.28 mmol/l, mean 2.35 mmol/l. Out-patient E Mg concentration followed a near normal distribution, median 2.32 mmol/l, mean 2.30 mmol/l. There was a significant correlation between E Mg and S Mg for out-patients, R = 0.29 (p < 0.001). In-patients with infections and pressure sores had significantly raised E Mg concentrations but normal or low S Mg. High E Mg concentrations in illness are likely to be due to alterations in characteristics of the erythrocytes themselves rather than an indication of body magnesium excess. E Mg concentrations in illness should be interpreted with caution.

Relation Between Severity of Magnesium Deficiency and Frequency of Anginal Attacks in Men With Variant Angina

Objectives. We evaluated whether the severity of magnesium deficiency was correlated with the frequency of attacks of variant angina.Background. Magnesium deficiency may be associated with the development of variant angina. However, the relation between the activity of variant angina and magnesium deficiency remains to be elucidated.Methods. We assessed the body magnesium status of 18 men with variant angina: Group 1 (≥4 attacks/week, n = 7) and Group 2 (<4 attacks/week, n = 11). Concentrations of magnesium were determined in serum, urine, mononuclear cells and erythrocytes, and the 24-h magnesium retention rate was determined.Results. Group 1 showed a higher 24-h magnesium retention rate (mean ± SEM 63.5 ± 7.6% vs. 24.9 ± 2.7%, p < 0.01) and a lower intracellular concentration of magnesium in mononuclear cells and erythrocytes than did Group 2 (respectively, 156.3 ± 13.5 vs. 212.1 ± 6.9 fg/cell, p < 0.01; and 3.5 ± 0.5 vs. 5.2 ± 0.4 fg/cell, p < 0.05), demonstrating the presence of magnesium deficiency in Group 1. The 24-h magnesium retention rate and intracellular concentrations of magnesium in mononuclear cells and erythrocytes correlated well with the frequency of anginal attacks (r = 0.78, p < 0.01; r = −0.78, p < 0.01; r = −0.62, p < 0.01, respectively) for all patients.Conclusions. Data suggest that the magnesium status of men with variant angina is closely related to disease activity.

Magnesium flux during and after open heart operations in children

Hypomagnesemia and depletion of the body's magnesium stores is known to be associated with an increased incidence of both cardiac arrhythmias and neurological irritability. In a two-part prospective study we have evaluated whether magnesium deficiency is a significant occurrence in children treated in the intensive care unit after open heart operations, and subsequently have sought to identify how intraoperative metabolic changes were related to the resultant findings. In 41 children studied after operation the plasma magnesium concentration showed a significant decrease from 0.92 mmol/L (10th to 90th centile, 0.71 to 1.15 mmol/L) immediately after operation to 0.77 mmol/L (0.65 to 0.91 mmol/L) on the following morning. The subsequent change in grouped values was not significant but 14 (34.2%) and 7 (17.1%) possessed values of less than 0.7 mmol/L and 0.6 mmol/L, respectively. The occurrence of cardiac arrhythmias was not statistically related to the occurrence of hypomagnesemia. In 21 children perioperative changes in extracellular and tissue magnesium, potassium, and calcium content were measured. It was found that hemodilution with a prime low in magnesium caused a reduction from a median of 0.81 mmol/L to 0.61 mmol/L (p < 0.01). Plasma potassium level, however, was elevated from 3.7 mmol/L to 4.15 mmol/L (p < 0.05) and the ionized calcium content from 1.17 mmol/L (1.07 to 1.25 mmol/L) to 1.49 mmol/L (1.25 to 2.56 mmol/L) (p = 0.0009). The myocardial content of magnesium did not change significantly but skeletal muscle content was depleted from 6.75 mumol/g (2.85 to 8.35 mumol/g) to 5.65 mumol/g (2.45 to 7.2 mumol/g) (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Biological variation of serum and urinary magnesium in apparently healthy males.

The biological variations of serum (S-) magnesium and urinary (U-) magnesium concentrations and excretions have been investigated. Serum samples, 24-h and fasting urinary samples were collected from each of 60 supposedly healthy male volunteers. In addition, 12 volunteers collected additional samples 7 and 112 days after the initial sample. The reference interval for S-magnesium was 0.765-0.997 mmol l-1. The biological variation for S-magnesium was 3.2% within subjects and 7.4% between subjects. This indicated an index of indivduality of 0.5, which means that significant changes in S-magnesium can occur within the limits of the reference interval, and that serial determinations of S-magnesium might prove useful as an indicator of changes in whole body magnesium status. It is, on the other hand, unlikely that a single determination of S-magnesium can be used in assessing whole-body magnesium status in the individual. The reference interval for the 24-h U-magnesium excretion, corrected for surface area, was 1.306-4.762 mumol min-1 1.73 m-2. The 24-h U-magnesium excretion exhibited a biological within-subject variation of 36% and a between-subject variation of 26%. The 24-h U-magnesium excretion did not correlate with S-magnesium, and only slightly (r = 0.58) with the fasting U-magnesium/creatinine concentration. This, and the very large coefficients of variation, make it unlikely that the renal magnesium excretion can be used as a measure of whole body magnesium status, or that changes in the renal magnesium excretion can be used as a measure of changes in whole body magnesium status.

Consider Magnesium Homeostasis: III: Cytochrome P450 Enzymes and Drug Toxicity*

The serum contains only 0.3% of the body's magnesium (sMg). More than half is in bone and nearly half is intracellular. The bone Mg is in equilibrium with sMg, whereas red blood cell Mg (rbcMg) reflects sMg concentration while each cell is maturing. The kidney controls the sMg by reabsorption up to a serum level of 3mg/dL, and the amount saved varies with the Mg balance. Normal humans retain less than 25% of an intravenous Mg load test. When the sMg is normal and the load test and/or rbcMg values are abnormal, normomagnesemia Mg deficiency (MgD), Type I, exists. The earliest stage is latent MgD, which has been defined as more than 25% but less than 50% retention of Mg in a load test. In those with more severe stages of MgD, the Mg retention is more than 50%. Occult MgD is when there is more than 50% retention. Whenever the rbcMg level is also decreased, subclinical MgD is present. Type II MgD is clearly understood by everyone, because of the presence of hypomagnesemia. There are multiple causes of minimal urinary Mg wasting, plus other causes of MgD, and there are many subtle symptoms of MgD. Over 300 enzyme systems require Mg to function optimally, including the cytochrome P450 enzymes (CYP450). In vitro evaluation of CYP450 metabolism of drugs require a NADPH-generating system, which contains MgCl2 and requires NADPH cytochrome P450 reductase. NADPH-CYP450-reductase also requires Mg. Drug toxicity might well be due, in part, to CYP450 enzymes not being in an adequate environment when MgD is present. Symptoms and signs of both noncardiac and cardiotoxic drug reactions to theophylline and some of the second-generation antihistamines are similar to those found in MgD. MgD is a known risk factor for torsades de pointes TdP, which has been treated with Mg sulfate. Moreover, many of the causes of MgD are present in patients with drug intolerance. A comprehensive evaluation of Mg status should be done in all patients with drug reactions when CYP450 enzymes are involved, before, during and after intervention. This should include a sMg, rbcMg, and a 24-hour urine Mg levels. A urine creatinine/Mg ratio should be calculated using 24-hour urine concentrations. The metabolism of these drugs need to be studied in a population of patients with known normomagnesemia MgD.

Ultrastructural detection of calcium and magnesium in the chromatoid body of mouse spermatids by electron spectroscopic imaging and electron energy loss spectroscopy.

We studied at the ultrastructural level the presence of calcium and magnesium in the chromatoid body (CB) in mouse spermatids. In addition, the presence of these two cations was also examined in the nucleolus. By electron spectroscopic imaging (ESI) and electron energy loss spectroscopic (EELS) analyses on glutaraldehyde/pyroantimonate-fixed material, we showed the association of pyroantimonate precipitate granules containing calcium and/or magnesium with the CB. The granules in both active (primary spermatocytes) and inactive (spermatids) nucleoli contain mainly calcium. Our results confirm that although the pyroantimonate technique used alone suffers from a lack of specificity, it can be useful for in situ immobilization of different cations that are further resolved with methods of elemental analysis. Without pyroantimonate fixation, only very few spots containing calcium can be localized by ESI and EELS.

Magnesium in the 1990's: Implications for Veterinary Critical Care

SummaryMagnesium is the second most abundant intracelular cation, exceeded only by potassium. The majority of magnesium is found in bone and muscle. This cation is required for many metabolic functions, most notably as a coenzyme for the sodium‐potassium ATPase pump. Magnesium functions to maintain the electrolyte gradient across all membranes. Interference with this gradient may result in changes in the resting membrane potential and disturbances in repolarization, resulting in cardiovascular and neuromuscular abnormalities.Hypomagnesemia may be the most underdiagnosed electrolyte disorder. Incidence rates greater than 50 percent have been reported in critically ill human patients. Currently there is little or no information available regarding the incidence and significance of hypomagnesemia in hospitalized animals. Causes of magnesium deficiency can be divided into four general categories: gastrointestinal, renal, endocrine and miscellaneous. The diagnosis of magnesium depletion can be difficult since less than one percent of total body magnesium is located in serum. Alternative methods of evaluating magnesium status include determining ultrafilterable magnesium levels, mononuclear blood cell magnesium levels or by quantifying magnesium retention of an administered loading dose.

Laboratory Evaluation of Magnesium Status: Renal Function and Free Intracellular Magnesium Concentration

In summary, magnesium plays an essential role in both extracellular and intracellular metabolism. Even though biologists recognize the importance of magnesium, clinicians often are unaware of the frequency and significance of magnesium disturbances. Some clinicians recommend routine measurement of magnesium when other electrolyte analyses are required for the care of patients. Others have reported a high frequency of hypomagnesemia in hospitalized patients, but the clinical significance of this observation was not evident. Patients with coexisting hypokalemia of any cause require particular attention however, and it is important to assess magnesium status in that setting. The assessment of magnesium status is difficult because of the distribution of magnesium within the intracellular compartment. The majority of body magnesium is located within soft and hard tissues and most intracellular magnesium is complexed and not available for measurement. Accordingly, no single determination is available to accurately assess magnesium status. The simplest and most useful approach is the determination of serum magnesium and renal magnesium clearance and interpretation of these parameters in light of complete history and clinical evaluation of the patient. Accordingly, one combines the laboratory assessment with the clinical evaluation. Other tests, such as determination of serum and intracellular free Mg2+ activity by either fluorescent or 31P-NMR techniques, are not particularly useful in the routine laboratory. These approaches currently are being used on an experimental basis to assess the role of magnesium in health and disease, which may lead to better indices of clinical evaluation in the future.

Mononuclear blood cell magnesium in older subjects: evaluation of its use in clinical practice.

Serum and mononuclear blood cell (MBC) magnesium were measured in 24 healthy community subjects, average age 76 years (67-93), and in 21 ill hospitalized subjects, average age 79 years (65-90). MBC magnesium, expressed as mumol/mg protein, was significantly lower in the in-patient group (P < 0.001), but tended to be higher in the same group when expressed as fmol/cell (not significant). Further samples from community subjects on the same day, and again at 7 days, revealed coefficients of variation for intrasubject analysis of 12% and 22%, respectively (fmol/cell). The equivalent intrasubject values for serum were 2.8% on the same day and 4% at 1 week. MBC magnesium values for inpatients were probably distorted by changes in cell size and cell protein content caused by illness. Biological variability and the effects of illness on the composition and size of cells seem to limit the usefulness of MBC magnesium measurement as a clinical tool for assessment of body magnesium status.

Postmoult Uptake of Calcium by the Blue Crab (Callinectes Sapidus) in Water of Low Salinity

ABSTRACT After moulting, blue crabs (Callinectes sapidus) acclimated to a salinity of 2 ‰ were able to calcify as rapidly and accumulate as much calcium as crabs in sea water. Immediately after moult, the total masses of calcium, magnesium and strontium present in the whole body were 4.6, 15.6 and 3.0%, respectively, of their intermoult values. During the time of most rapid calcification, calcium uptake was 5.4±1.4mmol l−1, which is comparable to the maximum rate found in seawater-acclimated crabs. The concentrations of bound and free calcium in the blood changed very little with acclimation salinity, remaining at approximately 3 and 8 mmol l−1. respectively, both during intermoult and 1 day postmoult. Free calcium changed relatively little through the moult cycle, varying between 6.9 and 8.1 mmol l−1, but bound calcium rose to a peak of 6.4 mmol l−1 prior to moult then dropped to 2.6 mmol l−1 after moult, concurrent with a decrease of approximately 80% in the protein concentration of the blood. The concentration of total magnesium in the blood increased from a premoult low of 9.0 mmol l−1 to a postmoult high of 11.7 mmol l−1 and remained elevated throughout the period of rapid mineralization. During the postmoult period of rapid calcium uptake, the internal-to-external concentration ratio for total calcium was 6.6 to 1. The activity ratio, however, was only 2.5 to 1 because 28% of the calcium in the blood was bound to protein, and because the lower ionic strength of the medium resulted in a 2.5-fold higher activity coefficient for the water compared to blood. The transepithelial potential at postmoult (–5.4±0.7mV) was significantly more negative than at intermoult (–3.1±0.6mV). In artificial 2‰ sea water, the transepithelial potential (–9.3±0.7 mV) was higher than the equilibrium potential for calcium (–12.0±0.5 mV), implicating active transport in the uptake of calcium.

Magnesium deficiency: Recognition and treatment in the emergency medicine setting

Magnesium deficiency and its clinical manifestations are common in palients presenting to the emergency department. Assessment of the total body magnesium status of a patient is problematic since the serum magnesium concentration, the only readily available clinical test for this condition, may not be accurate in predicting the intracellular magnesium concentration. Therefore, empiric magnesium therapy should be considered in high-risk patients. Since magnesium participates in numerous metabolic processes in the body, a deficiency can affect multiple organ systems and present clinically in a variety of ways. Magnesium deficiency is reviewed in this paper with regard to therapeutic implications; specific treatment guidelines are given including dose, infusion rate, and magnesium preparation. Magnesium is also reviewed with regard to its homeostasis and metabolic role in the body. Special mention is made regarding precautions for use of magnesium in the setting of renal insufficiency.

Magnesium Content of the Human Heart

Although changes in the body's magnesium status have been linked to ischemic heart disease, sudden death and arrhythmia, there is as yet no recommended, established procedure for evaluation of magnesium homeostasis. We therefore explored the relationship between the magnesium content of the heart and that of serum, lymphocytes and skeletal muscle in 50 men undergoing cardiac surgery, using biopsies from the right auricula, right atrium and skeletal muscle and simultaneously drawn venous blood for measurement of lymphocyte and serum electrolyte concentration. Median magnesium values (mumol/g wet weight) were 7.42 (3.98-8.89) in skeletal muscle, 5.49 (3.44-7.66) in right auricula and 5.80 (2.60-7.53) in right atrium. The magnesium concentration in skeletal muscle was found to correlate with that in right auricula (r = 0.46, p less than 0.01) and right atrium (r = 0.43, p less than 0.01), whereas values in serum and lymphocytes showed no correlation with the heart's magnesium content. When myocardial biopsy is not available, skeletal muscle magnesium concentration seems to be the best predictor of the human myocardium's magnesium status.