The relation between extra- and intracellular electrolytes in patients with hypokalemia and/or diuretic treatment

Case report: Magnesium-A new therapeutic target in gestational diabetes mellitus?

To date, physicians are not aware of a potential connection between magnesium and gestational diabetes mellitus. This case shows that magnesium supplementation can reduce maternal serum glucose, specifically the hard-to-control fasting glucose.

Amiloride prevents thiazide-induced intracellular potassium and magnesium losses

To study the effect of a combination of amiloride, 5 mg, and hydrochlorothiazide, 50 mg (Moduretic), on plasma and skeletal muscle electrolytes in patients on long-term diuretic therapy (greater than 1 year) for arterial hypertension and/or congestive heart failure, 58 patients were recruited. Fifty-five patients completed the study, 27 controls and 28 in the treatment group. The Moduretic group demonstrated a significant increase in skeletal muscle potassium and magnesium values and a significant decrease in systolic blood pressure after 6 months on therapy. There was no significant change in these parameters in the control group. It is concluded that this combination of amiloride and hydrochlorothiazide is capable of preserving the internal and external balance of potassium and magnesium on a long-term basis in the patient categories studied.

Relation between potassium, magnesium and cardiac arrhythmias

Magnesium may influence the incidence of cardiac arrhythmias by 1) a direct effect 2) an effect on potassium metabolism 3) an effect as a calcium blocking agent. In the event of a magnesium deficiency the cell cannot attract potassium against the transmembrane concentration gradient. The reason may be that a magnesium deficiency interferes with the function of membrane ATPase, and thus the pumping of sodium out from the cell and potassium into the cell is impaired. The interference from a magnesium deficiency on the equilibrium of potassium between the intra- and extracellular spaces may result in changes in the resting membrane potential, changes in potassium conductance across the cell membrane as well as disturbances in the repolarization phase.

Serum magnesium in acute myocardial infarction. Relation to arrhythmias

During 1 1/2 years, 768 patients-905 admissions, 342 with acute myocardial infarction (AMI), 563 with other diagnoses-were treated in the CCU at Serafimerlasarettet. On admission, both the AMI and the non-AMI group had significantly lower serum magnesium levels than a reference group. The incidence of serious VEBs, VT and VF on admission was significantly higher in the hypomagnesemic patients with AMI. AV blocks and SVB were more frequently observed in the hypermagnesemic patients, both in the AMI and in the non-AMI group. The incidence of AF and SVT was higher in the hypomagnesemic patients.

Magnesium, potassium and zinc deficiency in subjects with type II diabetes mellitus

The concentrations of magnesium, potassium and zinc were determined in plasma, erythrocytes, muscle biopsies, and in urine collected during 24 hours, in 18 subjects with type II diabetes mellitus (DM). Magnesium was also determined in mononuclear cells. The results were compared with those in 35 (magnesium and potassium analyses) or 26 (zinc analyses) healthy controls. Subjects with type II DM had lower concentrations of magnesium (3.79 +/- 0.32 vs. 4.29 +/- 0.22 mmol/100 g FFDS), potassium (40.5 +/- 5.17 vs. 46.1 +/- 3.81 mmol/100 g FFDS) and zinc (231 +/- 29 vs. 247 +/- 23 ng/mg FFDS) in skeletal muscle. Furthermore, the urinary excretions of magnesium and zinc were higher, as compared with those in healthy controls (5.00 +/- 2.68 vs. 3.62 +/- 1.47 mmol/24 hours, and 683 +/- 285 vs. 326 +/- 205 micrograms/24 hours, respectively). The contents of magnesium, potassium and zinc plasma did not correlate with the corresponding concentrations in skeletal muscle or circulating blood cells, as investigated in healthy controls, diabetics and in all subjects together, implying that the plasma concentrations are not useful in the assessment of electrolyte status. Hence, deficiency of electrolytes frequently occurs, and should be looked for, in subjects with type II DM.

Hypokalemia--clinical spectrum and etiology

This paper is intended to give a review of the etiology and symptoms of potassium deficiency in man, as an introduction to the section on potassium and cardiac arrhythmias of this symposium. A review is given of different conditions where hypokalemia and/or total potassium deficiency is or might be part of the clinical picture, such as conditions with insufficient dietary intake, gastrointestinal potassium losses (e.g. vomiting, fistulas, malabsorption, abuse of laxatives and diarrhea), and renal potassium losses (e.g. primary and secondary hyperaldosteronism, Cushing's syndrome, intake of licorice, diabetic coma, renal disease, diuretic treatment and l-dopa treatment). Common symptoms of hypokalemia and/or potassium deficiency are reviewed as well, such as general and unspecific symptoms (e.g. tiredness, lack of concentration, lack of appetite and vomiting), and symptoms from the heart, kidneys and skeletal muscle.

Antihypertensive and biochemical effects of different doses of hydrochlorothiazide alone or in combination with triamterene

The antihypertensive and biochemical effects of 25 mg hydrochlorothiazide alone or 50 mg hydrochlorothiazide alone or in combination with triamterene (either 37.5 or 75 mg) once daily were studied in 26 patients with essential hypertension. After a 5-week run-in period the patients were randomized to receive active therapy in a cross-over manner. Each treatment period lasted 3 months. All drugs significantly (p less than 0.01) lowered both systolic and diastolic blood pressure. There were no differences in blood pressure between the medication periods. Serum potassium concentration was slightly lower during all medication periods than during the run-in period. This change was statistically significant (p less than 0.01) only on 50 mg hydrochlorothiazide daily. There were no significant changes in serum magnesium during any of the periods compared to the run-in period. The lowest values were recorded on 50 mg hydrochlorothiazide alone and the highest on 50 mg hydrochlorothiazide plus 75 mg triamterene daily. A slight increase in serum urate was recorded in all medication periods compared to the run-in period. No significant changes were observed in serum total cholesterol, HDL cholesterol or triglycerides between any of the periods. It can be concluded that 25 mg of hydrochlorothiazide is as effective in lowering blood pressure as higher doses of the diuretic. Higher doses of thiazides will in some patients cause adverse metabolic reactions of which the fall in serum potassium and magnesium is effectively hindered by triamterene.

Magnesium deficiency contributing to ventricular tachycardia. Two case reports

Two cases of ventricular tachycardia (VT), possibly caused by magnesium deficiency, are presented. Skeletal muscle biopsies and blood samples were taken before and after magnesium infusions. These infusions resulted in a significant retention of magnesium, and the VT attacks vanished permanently in one case and temporarily in the other.

Ventricular extrasystoles and intracellular electrolytes in hypokalemic patients before and after correction of the hypokalemia

Fifty-four initially hypokalemic patients, 43 of whom were on diuretic treatment, were given potassium supplementation until they showed a repeatedly normal serum potassium level. Muscle specimens obtained by percutaneous biopsy revealed that there were no concomitant increases in muscle potassium content, nor in intracellular potassium concentration, except in the very small group (6 patients) with a muscle magnesium content of greater than or equal to 3.95 mmol/100 g fat free dry solids (FFDS) and an initially lower muscle potassium content (less than or equal to 39.9 mmol/100 g FFDS). ECG, registered for 3 hours on a portable ECG tape recorder before and after correction of the serum potassium level, showed no change in the frequency of ventricular ectopic beats.

Renal excretion of electrolytes in patients on long-term diuretic therapy for arterial hypertension and/or congestive heart failure

Renal excretion, skeletal muscle content and plasma concentration of electrolytes were studied in 108 patients on long-term diuretic therapy for congestive heart failure and/or arterial hypertension. As reference populations served a group of 16 healthy volunteers and a group of 22 patients with liver cirrhosis, but not on diuretic therapy. Diuretic therapy was found to deprive the patients of their ability to conserve potassium and magnesium when there was a simultaneous cellular depletion of these ions. Magnesium excretion was found to be correlated to the skeletal muscle magnesium content. An inverted Na/K ratio in urine and a low magnesium excretion were fair indicators of cellular magnesium depletion.

Plasma and skeletal muscle electrolytes in patients on long-term diuretic therapy for arterial hypertension and/or congestive heart failure

Investigations regarding plasma and skeletal muscle electrolytes were carried out in 537 patients on long-term diuretic treatment (greater than 1 year) for arterial hypertension (n = 240) and/or congestive heart failure (n = 297). In both groups there were significant decreases in both plasma and skeletal muscle K and Mg, while the muscle Na values as well as the total and extracellular water content of skeletal muscle were increased.

Magnesium and potassium interrelationships, experimental and clinical

1) Coexisting Mg and K deficiency may occur with greater frequency than has been previously appreciated. 2) Profound hypokalemia, or refractoriness to K repletion or coexisting hypokalemia and hypocalcemia should suggest the possibility of concurrent Mg and K depletion. 3) The identification and treatment of concurrent K and Mg depletion is especially important in patients with congestive heart failure because of problem of digitalis toxicity. 4) We believe that the role of magnesium in optimizing cardiac function remains to be elucidated, identification and treatment of coexisting Mg and K depletion will be facilitated by making serum Mg a routine electrolyte determination together with Na, K, Cl, CO2.

Magnesium deficiency in congestive heart failure

In congestive heart failure several compensatory mechanisms are operating, and may cause severe disturbances of both the internal and external electrolyte balance. The medical treatment prescribed in congestive heart failure also leads to changes in the handling of electrolytes. These combined effects may prove critical to the patient, especially with regard to the emergence of cardiac arrhythmias.

Problems with potassium and magnesium in diuretic-treated patients

Treatment with thiazides and loop diuretics increase the urinary excretion of potassium and magnesium and the body content of these ions are reduced after long-term treatment. The diuretic-induced magnesium deficiency influences the potassium metabolism. Magnesium is a necessary activator of Na-K-ATPase, which supplies the Na-K pump with energy. Lack of magnesium will therefore impair the pumping of sodium out of the cell and of potassium into the cell. The change of the relationship between extra and intracellular potassium may induce cardiac arrhythmias. Certain groups of patients, such as patients on digitalis therapy, patients with secondary hyperaldosteronism, elderly patients with insufficient dietary habits, and heavy drinkers, run an additional risk of developing potassium/magnesium disturbances. In young patients with uncomplicated essential hypertension, the risk is probably very small.

Magnesium depletion in chronic terminal liver cirrhosis

Serum ionized magnesium represents less than 1% of the total body magnesium. The most reliable method to evaluate magnesium status is the magnesium loading test: In magnesium depletion its uptake is increased (20-50%) and is about 6% in normal magnesium status. There are no studies on magnesium status in chronic cirrhotics who may be in depletion. We performed magnesium loading test in 10 chronic cirrhotics listed for liver transplantation and in six healthy control patients. Magnesium sulphate 30 mmol was infused and urine magnesium was determined over 24 h. Serum ionized magnesium increased similarly in all patients. The uptake of magnesium was 8 +/- 8% in control patients and 34 +/- 26% in cirrhotics (p < 0.01). Chronic terminal cirrhotics are magnesium depleted which should be taken into account in case of liver transplantation and also in other interventions. Spot sampled serum ionized magnesium revealed magnesium depletion poorly.

Magnesium: a useful adjunct in the prevention of cerebral vasospasm following aneurysmal subarachnoid haemorrhage

Despite recent advances in the management of aneurysmal subarachnoid haemorrhage delayed ischaemic deficits from cerebral vasospasm remains a major cause of morbidity and mortality. As magnesium is a potent cerebral vasodilator we have introduced routine supplementation in patients presented with subarachnoid haemorrhage to determine whether there has been a reduction in the incidence of cerebral vasospasm.

METHOD

All patients presented with aneurysmal subarachnoid haemorrhage from February 1997 were included except those who presented after day 5 following bleed. Identical management protocol was used except intravenous magnesium supplementation which was introduced to all patients from May 1999. Incidence of cerebral vasospasm on angiograms among the two groups was analysed.

RESULTS

Seven out of 10 patients who did not receive magnesium supplement developed vasospasm requiring intra-arterial papaverine compared with 2 of 13 patients among the treated group (P<0.008).

CONCLUSIONS

From our pilot study it appears that magnesium supplement has a beneficial role in the prevention of cerebral vasospasm following aneurysmal subarachnoid haemorrhage. Further studies would seem justified.

Magnesium deficiency in patients with chronic pancreatitis identified by an intravenous loading test

Magnesium deficiency is a common clinical condition that may exist despite a normal serum magnesium concentration. Patients with chronic pancreatitis could develop magnesium deficiency due to either malabsorption, diabetes mellitus, or chronic alcoholism. Since serum levels of magnesium are a poor indicator of magnesium deficiency, the retention of a low-dose intravenous magnesium load (0.1 mmol/kg body weight) was determined in 13 patients with chronic pancreatitis (10 due to alcoholism) and eight healthy controls. Percentage magnesium retention was greater in patients with chronic pancreatitis than controls (59.8+/-37.3% S.D. versus 22.0+/-38.2% S. D.: P=0.038), and 10 of 13 patients showed evidence of magnesium deficiency. Routine evaluation of magnesium status could allow appropriate supplementation and conceivably symptomatic improvement in patients with severe chronic pancreatitis.

Effect of potassium magnesium citrate on thiazide-induced hypokalemia and magnesium loss

The study was performed to ascertain the value of potassium magnesium citrate, magnesium citrate, and potassium citrate in overcoming thiazide-induced hypokalemia and magnesium loss. Sixty-two healthy subjects were first administered hydrochlorothiazide, 50 mg/d. After 3 weeks of thiazide treatment (or earlier for potassium level </=3.5 mEq/L), they were randomized to receive one of three drugs while continuing to receive thiazide: potassium magnesium citrate (49 mEq of potassium, 24.5 mEq of magnesium), magnesium citrate (24.5 mEq/d of magnesium), or potassium citrate (49 mEq/d of potassium). Outcome measures were changes in serum potassium and magnesium levels and urinary potassium, magnesium, pH, and citrate values. All three drugs increased serum potassium concentration compared with that resulting from thiazide alone. Potassium magnesium citrate increased serum potassium levels from 3.3 +/- 0.2 to 3.8 +/- 0.3 mEq/L (P < 0.001), potassium citrate increased serum potassium levels from 3.4 +/- 0.4 to 3.9 +/-0.3 mEq/L (P < 0.001), and magnesium citrate from 3.4 +/- 0.4 to 3.7 +/- 0.3 mEq/L (P < 0.001). Potassium magnesium citrate led to a significant increase in urinary magnesium levels by the third week of supplementation (from 120 +/- 34 to 149 +/- 58 mg/d; P < 0.01) and produced a small but significant increase in serum magnesium level. Magnesium citrate significantly increased 24-hour urinary magnesium after the first week of supplementation and maintained this increase throughout the study. Potassium magnesium citrate and potassium citrate, but not magnesium citrate, significantly increased urinary pH and citrate values. Potassium magnesium citrate not only corrects thiazide-induced hypokalemia, but also may avert magnesium loss while providing an alkali load.

Optimal nutrition: calcium, magnesium and phosphorus

In the past, a major challenge for nutrition research was in defining indicators of nutritional adequacy. More recently, the research base related to the role of nutrition in chronic disease has expanded sufficiently to permit moving beyond deficiency indicators to other indicators with broader functional significance. Thus, nutrition research is faced with the new challenge of defining 'optimal nutrition'. One definition of optimal nutrition with respect to any particular nutrient could be when a functional marker reaches an 'optimal value' or plateau beyond which it is not longer affected by intake or stores of the nutrient. A functional marker of nutrient status could be defined as a physiological or biochemical factor which (1) is related to function or effect of the nutrient in target tissue(s) and (2) is affected by dietary intake or stores of the nutrient (which may include markers of disease risk). Examples of such indicators or markers are those related to risk of chronic diseases such as osteoporosis, CHD, or hypertension. The present review focuses on the concept of optimal nutrition with respect to three nutrients, Ca, Mg and P. However, for P and Mg there are as yet no functional indicators which respond to dietary intake, and in such cases nutrient requirements are established using more traditional approaches, e.g. balance data. For Ca, there has been interest in using maximal Ca retention, which is based on balance data, bone mass measurements and biomarkers of bone turnover as useful functional indicators of the adequacy of Ca intake.

[Magnesium and calcium changes in serum and atrial muscle caused by open heart surgery and the effect of preoperative oral magnesium administration]

The study was undertaken to compare magnesium and calcium serum concentration levels and magnesium and calcium atrial muscle content of between the non-magnesium group (20 patients) and the magnesium group (11 patients) in the perioperative period of open heart surgery. In addition, the incidence of arrhythmias was compared between the two groups. Late ventricular potentials and postoperative ventricular arrhythmias were evaluated in both groups. The patients of the magnesium group were administered a daily oral intake of 3.0 g of magnesium oxide for ten days before operation. In both groups, serum concentration of magnesium decreased abruptly due to hemodilution after the operation and began increasing gradually from 24 hours after the operation. However, in the non-magnesium group the concentration decreased below the normal range in the 24 hour period after the operation and elevated to above the preoperative value from the third to fifth postoperative days. In the magnesium group serum concentration of magnesium was higher during the 24 hours after the operation and lower from the third to fifth postoperative days than the non-magnesium group. Thus, the fluctuation was smaller in the magnesium group than the non-magnesium group. Serum concentration of calcium also decreased abruptly after the operation and gradually increased in the postoperative days in both groups. However, the level was always higher in the magnesium group than the non-magnesium group. The concentration ratio of serum calcium to magnesium was relatively unchanged postoperatively in the magnesium group, whereas it decreased significantly from the second to seventh postoperative days in the non-magnesium group. Magnesium and calcium contents in the atrial muscle were measured before and after cardiopulmonary bypass. Before bypass, magnesium and calcium contents were higher in the magnesium group than the non-magnesium group. However, in the non-magnesium group the calcium content increased significantly after bypass compared to pre-bypass levels, whereas it was unchanged in the magnesium group. Ventricular arrhythmias severer than grade 3 were found in 4 cases in the non-magnesium group. On the other hand, no ventricular arrhythmias severer than grade 3 were found in the magnesium group. As to the incidence of supraventricular arrhythmias, no difference was demonstrated between both groups. The appearance of late ventricular potentials on signal averaged electrocardiograms was found variable and often transient, and no association was found between the appearance of late ventricular potentials and the incidence of ventricular arrhythmias. Smaller fluctuations of magnesium and calcium concentrations in serum as well as in the atrial muscle were observed in the postoperative days in the magnesium group. Magnesium and calcium ratio also showed smaller fluctuations in the postoperative days in the magnesium group. In conclusion, these factors, along with suppression of calcium influx in the cardiac muscle, appeared to serve to reduce the incidence of ventricular arrhythmias in the magnesium group.

Current concepts in cardiopulmonary resuscitation

The "chain of survival" is important in the resuscitation of a patient who has had a cardiac arrest. The provision of Basic Life Support (BLS) and Advanced Cardiac Life Support (ACLS) is essential in this "chain of survival." Both BLS and ACLS have undergone several revisions since their initial inception. This article reviews (1) the current established and investigational issues of cardiopulmonary resuscitation, (2) the incidence and outcomes of anesthesia-related cardiac arrest, (3) the use of cardiopulmonary bypass in resuscitation, and (4) cerebral protection during and after resuscitation.

Functional magnesium deficiency in critically ill patients identified using a magnesium-loading test

OBJECTIVE

To determine the feasibility of the magnesium-loading test in the critically ill and to validate serum ionized magnesium assay using the magnesium-loading test as a reference in this same patient population.

DESIGN

Double-blind, randomized, controlled clinical investigation.

SETTING

Tertiary level intensive care unit.

PATIENTS

Forty-four consecutive critically ill patients without evidence of renal insufficiency.

INTERVENTION

Patients were randomly allocated to receive 30 mmol (7.5 g) of magnesium sulfate daily for 3 days, or an equivalent amount of normal saline.

MEASUREMENTS AND MAIN RESULTS

We recorded baseline characteristics, and serial serum biochemical measurements included creatinine, glucose, sodium, potassium, phosphate, total calcium, ionized calcium, total magnesium, and ionized magnesium. Serum assays were accompanied by 24-hr urine collections of creatinine and magnesium over the 3-day period. Baseline characteristics were comparable in both groups. In patients receiving magnesium, serum ionized magnesium and total magnesium concentrations were increased by 43% (p = .0001) and 59% (p = .0002), respectively, on day 1 as compared with the control group. Magnesium excretion in the control group averaged 4.8 +/- 2.3 mmol/day during the 3-day study period, while the magnesium excretion in the magnesium-loaded group was significantly increased to 22.7 +/- 10.9 mmol/day (p < .0001). Following day 1 magnesium loading, patients who excreted < 70% of the total magnesium (30 mmol infused magnesium plus 4.8 mmol basal excretion) were termed as functionally magnesium-deficient retainers (n = 12), and patients who excreted > 70% of the total magnesium were termed as nonretainers (n = 7). In addition, magnesium retainers on day 2 (nine of ten patients) and day 3 (five of six patients) excreted > 70% of the total magnesium, indicating a replenishment of body magnesium stores. In contrast, nonretainers on day 2 (four of five patients), and day 3 (four of four patients) continued to excrete excess amounts of magnesium. In the retainer group, only two patients had a low serum ionized magnesium concentration, while two other patients had low total serum magnesium values. In addition, magnesium retention was associated with low ionized calcium and high phosphate values.

CONCLUSIONS

The magnesium-loading test is feasible and appears to be valid based on its performance during the 3-day evaluation. Using the magnesium-loading test as a reference, serum ionized magnesium appears to be an insensitive biochemical marker of functional hypomagnesemia. Larger cohort studies using the magnesium-loading test will help establish the true prevalence of magnesium deficiency and its associated risk factors in critically ill patients.

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 (> or = 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 sulfate for conversion of supraventricular tachycardia refractory to intravenous adenosine

The use of magnesium sulfate infusion for the management of cardiac dysrhythmia has recently gained popularity. Magnesium sulfate has been advocated for the management of torsade de pointes and other ventricular dysrhythmias. We report the case of a 38-year-old firefighter with atrial tachycardia that was treated unsuccessfully according to Advanced Cardiac Life Support guidelines with IV adenosine. Subsequently, 2 g of magnesium sulfate was administered intravenously over 5 minutes with resulting conversion of the patients' supraventricular tachycardia to normal sinus rhythm, with complete resolution of symptoms.

Noninvasive measurement of tissue magnesium and correlation with cardiac levels

BACKGROUND

Intracellular magnesium ([Mg]i) plays an important role in the regulation of myocardial metabolism, contractility, and the maintenance of transsarcolemmal and intracellular ionic gradients. An understanding of the role of magnesium in the clinical setting, however, is hampered by the lack of an assay of intracellular tissue magnesium levels.

METHODS AND RESULTS

We used energy-dispersive x-ray analysis to measure [Mg]i in sublingual epithelial cells and to correlate the level with those in atrial biopsy specimens from the same patients during cardiopulmonary bypass. Levels were also measured in acute myocardial infarction (AMI) patients before and after intravenous magnesium sulfate administration and compared with those from intensive care unit (ICU) patients and healthy individuals. A strong correlation between sublingual epithelial cell (mean, 32.1 +/- 0.3 mEq/L) and atrial tissue (mean, 32.1 +/- 0.3 mEq/L) [Mg]i was present in 18 cardiac surgery patients (r = .68, P < .002). Epithelial and atrial [Mg]i levels were lower than in healthy individuals (33.7 +/- 0.5 mEq/L, P < .01) studied at that time and correlated poorly with serum magnesium. Mean [Mg]i in 22 AMI patients was 30.7 +/- 0.4 mEq/L, which was significantly lower than in 21 ICU patients and 15 healthy individuals (35.0 +/- 0.5 mEq/L and 34.5 +/- 0.7 mEq/L, respectively, P < .001). Intravenous magnesium sulfate was administered to most of the AMI patients (mean dose, 36 +/- 6 mmol). [Mg]i rose significantly in the AMI patients over the first 24 hours, and the magnitude of the increase was greater in those who received higher doses of intravenous magnesium sulfate.

CONCLUSIONS

Sublingual epithelial cell [Mg]i correlates well with atrial [Mg]i but not with serum magnesium. [Mg]i levels are low in patients undergoing cardiac surgery and those with AMI. Intravenous magnesium sulfate corrects low [Mg]i levels in AMI patients. Energy-dispersive x-ray analysis determination of sublingual cell [Mg]i may expedite the investigation of the role of magnesium deficiency in heart disease.

The magnesium loading test: reference values in healthy subjects

The magnesium loading test is a useful tool in the diagnosis of magnesium deficiency. In order to establish a reference range in normal subjects, 88 healthy men and women aged between 18 and 66 years were given 30 mmol magnesium intravenously during eight hours as a loading test, urine was collected from start of infusion for 24 h for measurement of magnesium excretion. The magnesium mean retention was 6.3 +/- 10.3% of the loading dose, and the 0.025 and 0.975 fractiles were -19.5% and 27.5%, respectively. There was no significant difference between the sexes or in the different age groups studied. There was no correlation between the magnesium retention and serum magnesium or with basal urinary magnesium excretion. An excess excretion of magnesium was observed the postload day compared to baseline, but the excretion 24 and 48 h after the magnesium loading were closely correlated, suggesting that 24 h urinary sampling is sufficient. In order to examine the reproducibility of the test 23 of the subjects underwent two magnesium loading tests 4 weeks apart. The mean difference between two repeat magnesium loading tests was 2.0% with a SD of 8.1% and a 95% confidence interval of -1.6-5.5%. Normal saline did not affect baseline magnesium excretion. Concomitant administration of ethanol or physical exercise caused greater variation in magnesium excretion, whereas furosemide was without effect. The 8 h magnesium loading test with 24 h urine sampling seems to be fairly reproducible, is adequate for clinical use, but the normal range is wide.

Magnesium status in healthy free-living elderly Norwegians

OBJECTIVE

Magnesium (Mg) status has previously not been properly assessed among healthy elderly subjects.

METHODS

Thirty-six healthy elderly subjects participated. Their Mg status was assessed by serum Mg, basal urinary Mg output, and with a Mg loading test (30 mmol infused during 8 hours; urine sampled 24 hours), and compared with 53 healthy younger subjects. Their dietary intake was assessed by a quantified food frequency questionnaire. Fourteen of the subjects received 300 mmol Mg to study the effect on Mg status.

RESULTS

With the exception of vitamin D in women, average energy and nutrient intakes were adequate. All subjects had serum Mg levels within the reference value of the laboratory. Basal urinary Mg excretion was 3.3 +/- 1.1 mmol/day and 24-hour Mg retention after a Mg load was 28 +/- 16% compared to 6 +/- 11% in younger controls, suggesting Mg deficiency in the elderly. In the 14 subjects who received oral Mg supplementation there was a statistically significant increase in basal urinary Mg excretion and creatinine clearance, and decreases in Mg retention, serum Mg and serum creatinine.

CONCLUSIONS

This study suggests that a significant subclinical Mg deficit, not detected by serum Mg, was present in many of these healthy elderly subjects. Mg supplementation improved Mg status and renal function.

Effects of intravenous magnesium sulfate on arrhythmias in patients with congestive heart failure

Intravenous magnesium is an effective treatment for ventricular tachycardia of some etiologies, and in patients with congestive heart failure low serum magnesium concentrations are associated with frequent arrhythmias and high mortality. This suggests that magnesium administration may decrease the frequency of ventricular arrhythmias in patients with heart failure. We therefore assessed the impact of an intravenous magnesium infusion upon the frequency of ventricular premature depolarizations in 40 patients with New York Heart Association (NYHA) class II to IV heart failure and serum magnesium < or = 2.0 mg/dl. Within 1 week of a baseline 6-hour ambulatory electrocardiographic recording, an infusion of 0.2 mEq/kg of MgSO4 was given over 1 hour and a repeat 6-hour recording was obtained. There was an inverse relationship between the change in magnesium concentration and the change in frequency of premature ventricular depolarizations; premature ventricular depolarizations declined by 134 +/- 207 hr-1 in patients in whom serum magnesium concentration increased > or = 0.75 mg/dl, but increased by 72 +/- 393 hr-1 in patients with a change < 0.75 mg/dl (p < 0.05). For all patients, the frequency of premature ventricular depolarizations was 283 +/- 340 hr-1 pretreatment and 220 +/- 269 hr-1 following magnesium infusion (p = 0.21). Patients with > or = 300 premature ventricular depolarizations hr-1 demonstrated a decrease from 794 +/- 309 to 369 +/- 223 hr-1 (p < 0.001). Intravenous magnesium administration decreased the frequency of couplets from 233 +/- 505 to 84 +/- 140 (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of magnesium versus verapamil on supraventricular arrhythmias

Magnesium has previously been used in the treatment of various arrhythmias, but few randomized and prospective studies are available. In a single-blind study, the efficacy and safety of intravenous magnesium sulfate (bolus doses of 5 + 5 mmol followed by infusion of 0.04 mmol/min) versus verapamil (5 + 5 mg followed by 0.1 mg/min) was evaluated in 57 patients with supraventricular arrhythmias (supraventricular tachycardia, atrial fibrillation, and atrial flutter) of recent onset (less than 1 week). Fifteen (58%) of the patients receiving magnesium (n = 26) converted to sinus rhythm within 4 h, and 16 (62%) within 24 h. Verapamil caused a lower ventricular rate, but only six (19%) of the patients (n = 31) converted to sinus rhythm within 4 h (p < 0.01) and 16 (52%) within 24 h (NS). No side effects were observed during magnesium infusion, whereas six patients receiving verapamil had to be withdrawn from further study medication due to symptomatic side effects (hypotension in three, cardiac failure in three). Magnesium appears to be an effective and safe drug for the treatment of supraventricular arrhythmias. The overall efficacy for conversion to sinus rhythm is at least as effective as with verapamil, and its action is more rapid.

A comparison of the potassium and magnesium-sparing properties of amiloride and spironolactone in diuretic-treated normal subjects

1. The relative potencies of amiloride (5 and 20 mg) and spironolactone (25 and 100 mg) for plasma and erythrocyte electrolytes were investigated in a double-blind, randomised, balanced, crossover study in 12 normal men treated concomitantly with hydrochlorothiazide 100 mg daily for 1 week. 2. Participants satisfied an a priori requirement for a fall in plasma potassium concentration of at least 0.5 mmol l-1 after 7 days of treatment with hydrochlorothiazide alone. 3. After hydrochlorothiazide alone, plasma potassium and sodium concentrations fell (P < 0.001). There were associated reductions in erythrocyte sodium (P < 0.01). Plasma magnesium concentration did not change, although erythrocyte magnesium decreased (P < 0.001). 4. Both amiloride and spironolactone attenuated the thiazide-induced fall in plasma potassium (relative potency, amiloride:spironolactone 10:1, 95% confidence interval 6.3-16.2:1). Amiloride but not spironolactone was associated with a dose-related increase in plasma magnesium; a relative potency estimation was precluded. There was little evidence of influences of amiloride or spironolactone on erythrocyte electrolytes. 5. On a weight basis, amiloride is ten times more potent than spironolactone as a potassium-sparing agent in diuretic-treated subjects but neither agent had major effects on erythrocyte potassium. The drugs may have divergent actions on magnesium handling; hydrochlorothiazide alone had no influence on plasma magnesium.

Correlation between magnesium and potassium contents in muscle: role of Na(+)-K+ pump

In young rats fed a Mg(2+)-deficient diet for 3 wk, Mg2+ and K+ contents in soleus and extensor digitorum longus muscles were significantly reduced and closely correlated. In isolated soleus muscles, Mg2+ depletion induced an even more pronounced loss of K+, and Mg2+ and K+ contents were correlated over a wide range (r = 0.95, P < 0.001). Extracellular Mg2+ (0-1.2 mM) caused no change in total or ouabain-suppressible 86Rb influx. After long-term incubation in Ca(2+)-Mg(2+)-free buffer with EDTA and EGTA, cellular Mg2+ and K+ contents were reduced by 35 and 15%, respectively, without any reduction in ATP and total or ouabain-suppressible 86Rb influx. In Mg(2+)-depleted muscles 42K efflux was increased by up to 42%, and repletion with Mg2+ produced a graded decrease. We conclude that Mg2+ and K+ contents are closely correlated in muscles Mg2+ depleted in vivo or in vitro and that neither extracellular nor moderate intracellular Mg2+ depletion affects total or Na(+)-K+ pump-mediated K+ influx. The reduced K+ content may rather be related to increased K+ efflux from the muscles.

Oral magnesium supplementation restores the concentrations of magnesium, potassium and sodium-potassium pumps in skeletal muscle of patients receiving diuretic treatment

In 76 consecutive patients who had received diuretics for 1-17 years for arterial hypertension or congestive heart failure, muscle concentrations of magnesium, potassium, and sodium-potassium pumps were significantly reduced compared to 31 age- and sex-matched controls. Thirty-six patients with muscle magnesium and/or potassium below the control level received oral magnesium hydroxide supplement for 2-12 weeks (n = 20) or 26 weeks (n = 16). After short-term (2-12 weeks) magnesium supplementation muscle parameters were increased, but far from normalized. After magnesium supplementation for 26 weeks, the muscle concentrations of magnesium, potassium and sodium-potassium pumps were normalized in most cases. Oral magnesium supplementation may restore diuretic-induced disturbances in the concentrations of magnesium, potassium and sodium potassium pumps in skeletal muscle. A supplemental period of at least 6 months seems to be required before complete normalization can be expected.

Mononuclear cell magnesium and retention of magnesium after intravenous loading in patients with acute myocardial infarction

A magnesium (Mg++) retention test was performed in 19 patients with acute myocardial infarction (AMI) 4-11 days after admission to the coronary care unit. The retention of Mg++ was 45 +/- 23% of the 30 mmol given intravenously. It has been proposed that a retention of more than 20% represents Mg++ deficiency. The mononuclear cell Mg++ concentration before the retention test was on an average slightly higher in the AMI patients than in 25 healthy volunteers (72.5 +/- 24.2 vs. 62.9 +/- 9.2 mumol g-1 protein) indicating no Mg++ depletion in the first group. The reason why patients during the phase of AMI show an increased retention of Mg++ is unknown, but changes in concentrations of several hormones and a reduction in blood glucose could be of importance. Serum concentrations of Mg++ were lower on admission than after 4-11 days. These initial reductions are probably due to increased concentrations of circulating catecholamines during the early hours of AMI.

Oral magnesium supplementation improves metabolic variables and muscle strength in alcoholics

Magnesium deficiency is common among chronic alcoholics, but the knowledge of oral magnesium supplementation to this group is limited. We, therefore, randomized 49 chronic alcoholics, moderate to heavy drinkers for at least 10 years to receive oral magnesium or placebo treatment for 6 weeks according to a double-blind protocol. Effects on metabolic variables and muscle strength were analyzed. Significant reduction of aspartate-aminotransferase (ASAT), alanine-aminotransferase (ALAT) and gamma-glutamyl-transpeptidase (GGT) were seen after magnesium, whereas no change was observed with placebo. Bilirubin decreased in both groups. Serum Na, Ca, and P increased significantly during magnesium therapy compared with no statistically significant change in the placebo group. Serum K and Mg increased slightly after magnesium supplementation and decreased in the placebo group, resulting in a significant difference between the two groups at the end of the study. Muscle strength increased significantly during magnesium treatment, contrasting to no change with placebo. Blood pressure, heart rate, hematological variables, serum lipids (cholesterol, HDL, TG), glucose tolerance, and creatinine were unchanged in the two groups after treatment. Alcohol consumption was similar before and during the trial and does not explain the differences between the two groups The results shows that short-term oral magnesium therapy may improve liver cell function, electrolyte status, and muscle strength in chronic alcoholics.

Can the magnesium content of mononuclear blood cells be altered by oral magnesium supplementation?

A randomized, double-blind, placebo-controlled trial was performed on a rigorously defined group of normal subjects to see if magnesium (Mg) supplementation could affect serum Mg levels or Mg content of mononuclear blood cells. Forty-nine subjects were randomized to either placebo, tablets containing 90% United States recommended daily allowance (USRDA) of Mg, or tablets containing 180% USRDA of Mg. We were unable to demonstrate a statistically significant increase in Mg content of mononuclear blood cells.

Magnesium deficiency diagnosed by an intravenous loading test

Magnesium deficiency is common but difficult to diagnose and to assess in clinical practice. The use of a magnesium loading test was therefore evaluated to diagnose magnesium deficiency in 661 hospitalized patients with medical conditions assumed to interfere with magnesium uptake and excretion. Thirty millimoles of magnesium sulphate were administered intravenously during 8 h as a loading test and related to the urinary excretion in the following 24 h. A group of 30 patients without any known predisposition for magnesium deficiency and a group of 27 healthy volunteers served as controls. The mean (with 95% confidence interval) magnesium retention was 4 (-2-10)% in the control group of patients and 3 (-2-8)% in healthy subjects. A significantly higher retention was observed in all the groups of the patients: atrial fibrillation 18 (11-25)%, other arrhythmias 18 (11-24)%, hypertension 27 (20-33)%, coronary artery disease 25 (20-30)%, congestive heart failure 31 (26-37)%, cerebrovascular events 38 (24-51)%, gastrointestinal disorders 22 (14-29)%, diabetes mellitus 16 (9-22)%, and alcoholics 33 (29-36)%. The percentage of patients with a retention greater than mean + 2 SD of the two control groups varied between 22% and 54% among the different patient groups. The mean serum magnesium among the patient groups was similar to the control group of patients, except for the alcoholics, hypertensives and young healthy controls, who had significantly reduced levels. Magnesium retention was significantly correlated to age and renal function, and among the alcoholics negatively correlated to serum magnesium.(ABSTRACT TRUNCATED AT 250 WORDS)

An evaluation of plasma and erythrocyte magnesium concentration and the activities of alkaline phosphatase and creatine kinase as indicators of magnesium status

Rats were fed diets containing magnesium at concentrations ranging from 3.3 to 26.7 mmol/kg of diet (80 to 650 mg/kg). The magnesium concentration of their plasma and erythrocytes, and the activities of plasma alkaline phosphatase and creatine kinase were investigated to determine their usefulness as indices of magnesium status. All the indices increased with increasing dietary magnesium levels. The best correlations were observed between dietary intake and plasma concentration of magnesium (r = 0.846, p less than 0.001) and between intake and femur concentration (r = 0.811, p less than 0.001). There was an extremely high correlation between plasma concentration and femur concentration (r = 0.930, p less than 0.001). Although significant, the correlations between intake and the enzyme activities were not strong. It is concluded that plasma magnesium concentration is the most useful indicator of magnesium status and that the activities of the two magnesium-requiring enzymes can only be used for the purpose of diagnosing severely deficient magnesium status.