Clinical studies with the NOVA ISE for IMg2+

Comprehensive analysis of changes in clinically significant divalent serum cation levels during automated plateletpheresis in healthy donors in a tertiary care center in North India

BACKGROUND

Adverse effects due to apheresis are unusual. The most common apheresis-specific reaction is hypocalcemia due to citrate anticoagulation and induces ionized hypocalcemia and hypomagnesemia by chelating effect during the plateletpheresis; generally transient and self-limiting but has the potential of severely injuring donor. We have investigated total calcium (tCa(++)) and magnesium (tMg(++)) levels in sixty healthy plateletpheresis donors at different intervals during the procedure and 30 min post-procedure.

MATERIALS AND METHODS

A total of 60 procedures were performed on healthy donors. Blood samples were obtained from sterile diversion pouch placed on apheresis circuit. 5 ml sample in plain vials was obtained at different intervals during each procedure and 30 min after the end of the procedure. Samples were used for measurement of tCa(++) and tMg(++) levels.

RESULTS

There is continuous decrease in mean tCa(++) from baseline levels (9.83 ± 0.64 mg/dl) till end of procedure (8.33 ± 0.78 mg/dl), but after 30 min, levels again reached near their respective baseline values (9.42 ± 0.54 mg/dl). Similarly, mean tMg(++) fell from baseline levels (2.36 ± 0.3 mg/dl) till the end of procedure (1.39 ± 0.40 mg/dl). After 30 min, levels were again increased, their respective baseline values (2.25 ± 0.25 mg/dl).

CONCLUSION

There is continuous, gradual, and significant fall (P < 0.05) in mean tCa(++) and mean tMg(++) from baseline levels to till the end of procedure but after 30 min of completion of procedure, levels again reached near their respective baseline values.

A case report: magnesium intoxication occurring in the process of total serum magnesium decrease

Magnesium intoxication is a result of excessively high serum magnesium levels, which are generally represented by a patient's total serum magnesium concentration. This is the first case report in PubMed in which a female patient showed no signs of magnesium intoxication when her total serum magnesium concentration was 4.34 mg/dL, but showed signs of magnesium intoxication (i.e. absent-patellar reflex) when the concentration was 3.66 mg/dL. We concluded that the serum magnesium level cannot be represented by the total serum magnesium concentration to a full extent; a lower total serum magnesium concentration may still lead to magnesium intoxication.

Multiple Measures of Magnesium Status Are Comparable in Mild Asthma and Control Subjects

Magnesium (Mg) may be a significant factor in asthma management. There is debate about how to best assess Mg status. We evaluated multiple indices of Mg status and lung function in 52 people with mild to moderate asthma and 47 controls. Mg measures included serum total, ionized and erythrocyte Mg, intravenous Mg load retention and dietary recall. Methacholine challenge and pulmonary function tests were used to assess diagnosis and severity of asthma. Mg status was similar in asthma and controls, and was not correlated to lung function. Total serum Mg closely reflected ionized Mg and offers a useful clinical diagnostic monitor.

Cerebral spinal fluid and serum ionized magnesium and calcium levels in preeclamptic women during administration of magnesium sulfate

OBJECTIVE

To study the distribution of ionized and total magnesium (Mg) in serum and cerebral spinal fluid (CSF) in preeclamptic women receiving MgSO(4) and how this treatment affects the ionized calcium (Ca(2+)) and ionized Ca:Mg ratios compared with healthy nonpregnant women and pregnant control women (HP).

DESIGN

Controlled clinical study.

SETTING

An academic medical center.

PATIENT(S)

African-American women older than 20 and less than 35 years. The pregnant preeclamptic study and pregnant control groups each consisted of 16 women; the nonpregnant group consisted of 10 subjects.

INTERVENTION(S)

The preeclamptic women received a 6-g bolus of MgSO(4) IV started at least 4.5 hours before delivery during 15-20 minutes, then 2 g/h baseline.

MAIN OUTCOME MEASURE(S)

The CSF and serum levels of Ca(2+) and Mg(2+) and total Mg were measured in all three groups of women. The Ca(2+):Mg(2+) ratios were determined. Physiologic monitoring was done and recorded every 4 hours where appropriate. Bloods were drawn every 6 hours for complete blood count, metabolic panel, lactate dehydrogenase, uric acid, and electrolytes. Serum pH, total Mg, Apgar scores, and general health of the infants born to preeclamptic mothers given MgSO(4) were followed.

RESULT(S)

The HP showed a reduction in mean serum ionized and total Mg, increase in ionized Ca, and a large increase in Ca(2+):Mg(2+) ratios compared with healthy nonpregnant women. Although the CSF ionized and total Mg and Ca(2+):Mg(2+) ratios were not altered with MgSO(4) treatment in the preeclamptic women receiving MgSO(4), the mean serum Mg values increased 3-fold. All infants were full-term, regardless of MgSO(4) treatment, and normal with respect to birth weight, Apgar scores, blood pH, total Mg, and neurologic scores.

CONCLUSION(S)

The data indicate that there is a direct relationship between the serum and CSF Ca(2+):Mg(2+) ratios in HP and this ratio may be crucial in preventing vascular and neurologic complications in preeclampsia-eclampsia.

Magnesium metabolism in type 2 diabetes mellitus, metabolic syndrome and insulin resistance

Type 2 diabetes is characterized by cellular and extracellular Mg depletion. Epidemiologic studies showed a high prevalence of hypomagnesaemia and lower intracellular Mg concentrations in diabetic subjects. Insulin and glucose are important regulators of Mg metabolism. Intracellular Mg plays a key role in regulating insulin action, insulin-mediated-glucose uptake and vascular tone. Reduced intracellular Mg concentrations result in a defective tyrosine-kinase activity, post-receptorial impairment in insulin action, and worsening of insulin resistance in diabetic patients. Mg deficit has been proposed as a possible underlying common mechanism of the "insulin resistance" of different metabolic conditions. Low dietary Mg intake is also related to the development of type 2 diabetes. Benefits of Mg supplementation on metabolic profile in diabetic subjects have been found in most, but not all clinical studies, and larger prospective studies are needed to support the potential role of dietary Mg supplementation as a possible public health strategy in diabetes risk.

Serum ionized magnesium during magnesium sulfate administration for preterm labor and preeclampsia

OBJECTIVE

The purpose of this study is to estimate the relations between ionized and total Mg levels during MgSO4 administration in patients with preterm labor and preeclampsia.

METHODS

Forty-three pregnant patients who were candidates for MgSO4 were studied (preterm labor, 27; preeclampsia, 16). The administration method was intravenous injection of MgSO4 4 g over 30 min followed by 1-2 g/h. Ionized Mg was measured by the selective ion electrode method at bedside, and compared it with total Mg levels.

RESULTS

Significant correlation was existed between levels of ionized and total Mg throughout therapy for both preterm labor (ionized Mg=0.19 x total Mg+0.19; r=0.61, p<0.001) and preeclampsia (ionized Mg=0.20 x total Mg+0.14; r=0.60, p<0.001).

CONCLUSION

There are correlations between ionized and total Mg levels during administration of MgSO4 for both preterm labor and preeclampsia.

Ionized magnesium in the cerebrospinal fluid of patients with head injuries

BACKGROUND

In head injury patients, a decrease in the serum ionized magnesium (iMg) concentration is considered to be related to the severity of the injury, however, this phenomenon is still not completely understood. The cerebrospinal fluid (CSF) iMg concentration has not been well documented under such conditions and, moreover, its normal value has not yet been established. We hereby intended to investigate the role of the iMg concentration and other parameters in both the serum and CSF of head injury patients and identify any relationship with other parameters.

MATERIALS AND METHODS

The subjects consisted of head injury patients without any other serious injuries. Ten healthy volunteers were selected as control subjects. Arterial blood and CSF specimens were simultaneously obtained and measured. We measured the Glasgow Coma Scale scores (GCS), the intracranial pressure (ICP), pH, po2, pco2, sodium, potassium, iCa, iMg, glucose, lactate, urea nitrogen. All data are expressed as the mean+/-SD and the units of iMg and iCa (corrected under pH 7.40) are given in mmol/L.

RESULTS

In the healthy subjects, the iMg concentration in the serum/CSF was 0.48 +/- 0.02 / 0.66 +/- 0.14, and iCa was 1.14 +/- 0.05 / 0.94 +/- 0.07. The GCS of the 15 head injury subjects at examination was 8.7 +/- 4.5. When the subjects were divided into 3 groups according to the GCS level (3 and 4, 5-8, and > or =9) at the time of examination, the serum iMg concentration was thus found to be related to the severity of injury based on the GCS level (p = 0.028), but not the CSF iMg concentration (p = 0.89). No relationship was observed between the iMg concentration in the serum and CSF when all specimens were compared, but an extremely close correlation was seen in the group with GCS 3 and 4 (p < 0.0001, r = 0.995), although no such correlation was seen in the other 2 groups (p = 0.12, r = -0.56 in the group with GCS 5-8, and p = 0.26, r = -0.35 in the group with GCS > or = 9). There was a significant correlation between the serum iMg and iCa (p = 0.0093, r = 0.47), and also between the CSF iMg and iCa concentrations (p < 0.0001, r = 0.67).

CONCLUSION

The serum iMg concentration has been suggested to possibly affect the neurologic state through CSF iMg in patients with the most severe head injury. In patients with moderate or mild head injuries, however, the ionized magnesium concentration is also probably associated with the degree of neurologic deficit based on the ionized calcium level. The CSF and serum ionized magnesium dissociation may thus result from the slow movement of ionized magnesium through the blood brain barrier.

Correction of ionized plasma magnesium during cardiopulmonary bypass reduces the risk of postoperative cardiac arrhythmia

We conducted this randomized controlled trial to determine whether the intraoperative measurement and correction of ionized plasma magnesium can reduce the risk of cardiac arrhythmia after cardiopulmonary bypass. Eighty-five patients presenting for coronary artery bypass grafting were randomly assigned either to the magnesium-corrected group, which received magnesium sulfate on the basis of measured levels of ionized plasma magnesium (n = 43), or to the control group, in which magnesium levels were identified but not corrected (n = 42). Ionized magnesium was determined with an ion-selective electrode with minimal delay, and further samples were taken for laboratory analysis of total plasma magnesium. All patients had Holter electrocardiogram monitoring for 72 h after surgery. Total hypomagnesemia (45 patients; 53% of all patients) was more common than ionized hypomagnesemia (11 patients; 13%) before cardiopulmonary bypass. Both total and ionized magnesium levels declined further during the course of cardiopulmonary bypass in the control group. The incidence of ventricular tachycardia in the first 24 h was less frequent in the magnesium-corrected group (3 patients; 7%) than the control group (12 patients, 30%; P < 0.01). Patients in the magnesium-corrected group were more likely to display continuous sinus rhythm (Lown Grade 0) in the first 24 h (14 patients; 34%) than patients in the control group (2 patients, 5%; P < 0.001). Our results suggest that the intraoperative correction of ionized magnesium is associated with a reduction in postoperative ventricular arrhythmia in cardiac surgical patients.

IMPLICATIONS

In this study the correction of ionized plasma magnesium during cardiopulmonary bypass was guided by measurements from an ion-selective electrode. This intervention resulted in a reduction in the incidence of postoperative ventricular tachycardia and an increased frequency of continuous sinus rhythm. Ion-selective electrodes constitute a convenient near-patient test, providing a basis for the targeted replacement of ionized plasma magnesium.

Optical spectroscopy and prevention of deleterious cerebral vascular effects of ethanol by magnesium ions

Previously, it has been suggested that acute ethanol (alcohol) administration can result in concentration-dependent vasoconstriction and decreased cerebral blood flow. Here, we present in vivo results using rapid (240 nm/min) optical backscatter measurements, with an intact cranial preparation in the rat, indicating that acute infusion of ethanol directly into the rat brain rapidly produces dose-dependent vasoconstriction of the cerebral microcirculation associated with a pronounced reduction in tissue blood content, pronounced rises in deoxyhemoglobin, significantly increased levels of reduced cytochrome oxidase and microvascular damage as the dose increases. Furthermore, we present in vivo experiments demonstrating the capability of magnesium ions (Mg(2+)) to attenuate and prevent these deleterious responses. Optical backscatter spectra (500-800 nm) were obtained by directing a single sending and receiving fiber to a portion of the left parietal cranium (in anesthetized rats), shaved to a translucent appearance to facilitate optical penetration. In the absence of added Mg(2+), infusion of a 10% solution of ethanol at 0.34 ml/min ( approximately 26.8 mg/min) produced prompt vasoconstriction as evidenced by a greater than 90% loss of oxyhemoglobin from the field-of-view and increases in levels of reduced cytochrome oxidase to between 50% and >90%. These effects were partially, to nearly completely, attenuated by the addition of MgCl(2) to the infusate containing added ethanol. Of special interest was the observation that attenuation of the vasoconstrictive effect of ethanol by Mg(2+) persisted despite a subsequent ethanol challenge without added Mg(2+). The results obtained demonstrate that, depending on dose, ethanol can produce prompt and severe vasoconstriction of the intact cerebral microcirculation and that infusion of moderate doses of Mg(2+) can largely attenuate and prevent this response. We conclude that appreciable, graded changes in cerebral cytochrome oxidase aa(3), blood volume and the state of hemoglobin occur at minimal tissue levels of ethanol which can be modulated by Mg(2+).

Hydroxyurea therapy associated with declining serum levels of magnesium in children with sickle cell anemia

OBJECTIVE

To obtain quantitative serum levels of total and ionized magnesium (Mg(2+)) in children with homozygous sickle cell anemia (SCA) undergoing therapy with hydroxyurea.

STUDY DESIGN

Five children, ages 11 to 14 years with homozygous SCA, were enrolled in a dose-escalating trial of hydroxyurea over an 18-month period. Serum levels of total and ionized magnesium together with ionized K(+), Na(+), and Ca(2+) were measured before hydroxyurea and every 6 months during hydroxyurea therapy.

RESULTS

Before treatment, 4 of the 5 patients had low or below-normal serum concentrations of Mg(2+) (normal range, 0.51-0.67 mmol/L). All 5 became Mg(2+)-deficient during hydroxyurea therapy, with no indication of recovery until after 12 to 18 months of drug administration (P <.05). Similar changes were noted for total magnesium concentrations. Mean serum levels of K(+), Na(+), and Ca(2+) remained consistently within normal ranges.

CONCLUSIONS

These findings warrant a controlled study of the effects of magnesium supplementation in patients with SCA receiving hydroxyurea. Potentially, such therapy could alleviate or prevent vaso-occlusive crises.

Evaluation of two Mg2+-selective electrodes by means of a flow-through device

Monitoring the ionized magnesium (Mg2+) concentration in critically ill patients can prevent development of serious and potentially fatal complications. The analyzers KONE Microlyte 6 (KONE Instruments, Espoo, Finland) and NOVA CRT (NOVA Biomedical, Waltham, MA, USA) provide the discontinuous measurement of Mg2+ and were evaluated in several studies. It was our objective to integrate the Mg2+-selective electrodes into a device for continuous on-line measurements. This device is suitable not only for research but also for a specific evaluation of electrode characteristics. It allowed us to compare the genuine electrodes and reference systems independently of their specific analyzers. Precision, accuracy, response time, limit of detection, drift and interferences were assessed by continuous flow-through measurements and discussed in comparison to the results of previous studies. The NOVA electrode proved to be superior regarding accuracy, sensitivity and selectivity, especially with respect to calcium. It was demonstrated that current commercial serum-like control materials were not appropriate for quality control of the assessed Mg2+-electrodes. However, despite the fact that the electrodes are commercially used for discontinuous measurements, both sensor types can be used for continuous on-line measurements in an extracorporeal circulation in a rat model. The NOVA electrode showed superior characteristics with this application as well. This study should also be understood as a contribution to the development of devices for online analyzers used in point-of-care-testing.

Antioxidants prevent depletion of [Mg2+]i induced by alcohol in cultured canine cerebral vascular smooth muscle cells: possible relationship to alcohol-induced stroke

Low serum concentrations of Mg(2+) ions have been reported, recently, in patients with coronary disease, atherosclerosis, and stroke as well as in patients with cerebral hemorrhage. The aim of the present study was to determine whether potent antioxidants [alpha-tocopherol and pyrrolidine dithiocarbamate (PDTC)] can prevent or ameliorate intracellular Mg(2+) ([Mg(2+)](i)) depletion associated with cerebral vascular injury induced by alcohol. Exposure of cultured canine cerebral vascular smooth muscle cells to alcohol (10-100 mM) for 24 h induced marked depletion in [Mg(2+)](i) (i.e., approximately 30-65%, depending upon alcohol concentration). Treatment of the cultured cells with either PDTC (0.1 microM) or alpha-tocopherol (15 microM) for 24 h, alone, failed to interfere with basal [Mg(2+)](i) levels. However, preincubation of the cells with either alpha-tocopherol or PDTC for 24 h completely inhibited the depletion of [Mg(2+)](i) induced by exposure to 10-100 mM ethanol. These results indicate that alpha-tocopherol and PDTC prevent decreases in [Mg(2+)](i) produced by ethanol. Moreover, these new results suggest that such protective effects of alpha-tocopherol and PDTC on cerebral vascular cells might be useful therapeutic tools in prevention and amelioration of cerebral vascular injury and stroke in alcoholics.

The effects of magnesium supplementation on exercise performance

PURPOSE

To determine the effects of magnesium (Mg2+) supplementation on performance and recovery in physically active women using the sensitive and recently advanced measure of ionic Mg2+ (iMg).

METHODS

Participants (N = 121) were screened for [iMg] in plasma, with 44 (36.4%) exhibiting [iMg] below the normal range of 0.53-0.67 mmol.L-1 (4). Thirty-two subjects (21 +/- 3 yr) representing a broad range of [iMg] (0.54 +/- 0.04 mmol.L-1) completed the main 14-wk study. At baseline, participants submitted to a resting blood pressure measurement, and they completed both an anaerobic treadmill test and an incremental (aerobic) treadmill test. For the latter, values for workload, oxygen uptake, and heart rate were obtained at both anaerobic threshold and maximal effort. Blood samples for iMg, total serum Mg2+ (TMg), erythrocyte Mg2+ (EMg), Ca2+, K+, Na+, hemoglobin, hematocrit, lactate, and glucose were also collected pretest, and 4, 10, 30 min, and 24 h posttest. Subjects received 212 mg.d-1 Mg oxide or placebo in a double-blind fashion and were retested after 4 wk. After a 6-wk washout period, the testing was repeated with a treatment crossover.

RESULTS

Ionic Mg2+ increased with Mg2+ treatment versus placebo (P < 0.05); however, performance and recovery indices were not significantly affected.

CONCLUSION

Four weeks of 212 mg.d-1 Mg oxide supplementation improves resting [iMg] levels but not performance or recovery in physically active women.

Antioxidants prevent elevation in [Ca(2+)](i) induced by low extracellular magnesium in cultured canine cerebral vascular smooth muscle cells: possible relationship to Mg(2+) deficiency-induced vasospasm and stroke

Low serum concentrations of Mg(2+) ions have been reported, recently, in patients with coronary disease, atherosclerosis and stroke as well as in patients with cerebral hemorrhage. The aim of the present study was to determine whether potent antioxidants [alpha-tocopherol and pyrrolidine dithiocarbamate (PDTC)] can prevent or ameliorate intracellular Ca(2+) ([Ca(2+)](i)) overload associated with cerebral vascular injury induced by low extracellular free Mg(2+) ([Mg(2+)](o)). Exposure of cultured canine cerebral vascular smooth muscle cells to low [Mg(2+)](o) (0.15-0.6 mM) vs. normal [Mg(2+)](o) (1.2 mM) for either 10 min or 2 h induced concentration-dependent rises in [Ca(2+)](i). Treatment of the cultured cells with either PDTC (0.1 microM) or alpha-tocopherol (15 microM) for 24 h, alone, failed to interfere with basal [Ca(2+)](i) levels. However, preincubation of the cells with either alpha-tocopherol or PDTC for 24 h completely inhibited the elevation of [Ca(2+)](i) induced by exposure to low [Mg(2+)](o), not only for 10 min, but also for 2 h. These results indicate that alpha-tocopherol and PDTC prevent rises in [Ca(2+)](i) produced by low [Mg(2+)](o), which probably result from low [Mg(2+)](o)-induced lipid peroxidation of cerebral vascular smooth muscle cell membranes. Moreover, these new results suggest that such protective effects of alpha-tocopherol and PDTC on cerebral vascular cells might be useful therapeutic tools in cerebral vascular injury associated with low [Mg(2+)](o) and accumulation of [Ca(2+)](i).

Serum ionized magnesium and calcium and sex hormones in healthy young men: importance of serum progesterone level

OBJECTIVE

To determine the serum concentrations of the sex hormones with respect to the concentrations of the biologically active fractions of magnesium (Mg) and calcium (Ca) in healthy young men and to compare them with those in young and older women.

DESIGN

Controlled clinical study.

SETTING

An academic research environment.

PATIENT(S)

Twenty-five healthy young male volunteers.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Concentrations of the sex steroid hormones testosterone, estrogen, and progesterone, and levels of ionized Ca (Ca2+) and Mg (Mg2+) were measured in the serum of healthy young men. These levels were compared with those in young women at different phases of the menstrual cycle and with those in older women.

RESULT(S)

The Mg2+ and total Mg concentrations in young men were not different from those during the follicular phase in young women or from the mean concentrations in menopausal women. The Ca2+ levels in young men were similar to the levels in young women during the follicular phase but significantly lower than the levels in older women. The Mg2+ concentration in the young men was directly and significantly related to the progesterone level, and the Ca2+/Mg2+ ratio was inversely related to the progesterone level.

CONCLUSION(S)

Progesterone may be a more important steroid hormone in men than previously believed.

Association of alcohol in brain injury, headaches, and stroke with brain-tissue and serum levels of ionized magnesium: a review of recent findings and mechanisms of action

Although there is general agreement that chronic ingestion of alcohol poses great risks for normal cardiovascular functions and peripheral-vascular homeostasis, a direct cause and effect between the real phenomena of alcohol-induced headache and risk of brain injury and stroke is not appreciated. "Binge drinking" of alcohol is associated with an ever-growing number of strokes and sudden death. It is becoming clear that alcohol ingestion can result in profoundly different actions on the cerebral circulation (e.g., vasodilation, vasoconstriction-spasm, vessel rupture), depending upon dose and physiologic state of host. Using rats, it has been demonstrated that acute, high doses of ethanol can result in stroke-like events concomitant with alterations in brain bioenergetics. We review recent in vivo findings obtained with 31P-NMR spectroscopy, optical reflectance spectroscopy, and direct in vivo microcirculatory studies on the intact brain. Alcohol-induced hemorrhagic stroke is preceded by a rapid fall in brain intracellular free magnesium ions ([Mg2+]i) followed by cerebrovasospasm and reductions in phosphocreatine (PCr)/ATP ratio, intracellular pH, and the cytosolic phosphorylation potential (CPP) with concomitant rises in deoxyhemoglobin (DH), mitochondrial reduced cytochrome oxidase aa3 (rCOaa3), blood volume, and intracellular inorganic phosphate (Pi). Using osmotic mini-pumps implanted in the third cerebral ventricle, containing 30% ethanol, it was found that brain [Mg2+]i is reduced 30% after 14 days; brain PCr fell 15%, whereas the CPP fell 40%. Such animals became susceptible to stroke from nonlethal doses of ethanol. Human subjects with mild head injury have been found to exhibit early deficits in serum ionized Mg (IMg2+); the greater the degree of early head injury (30 min-8 h), the greater and more profound the deficit in serum IMg2+ and the greater the ionized Ca (ICa2+) to IMg2+ ratio. Patients with histories of alcohol abuse or ingestion of alcohol prior to head injury exhibited greater deficits in IMg2+ (and higher ICa2+/IMg2+ ratios) and, unlike the subjects without alcohol, did not leave the hospital for at least several days. Women, for some unknown reason, exhibit a much higher incidence of morbidity and mortality from subarachnoid hemorrhage (SAH) than men. Data on 105 men and women with different types of stroke indicate that, on the average, a 20% deficit in serum IMg2+ is seen; total Mg (TMg) or blood pH is usually near normal. Women with SAH, however, exhibit much lower IMg2+ and higher ICa2+/IMg2+ ratios; the presence of ethanol in the blood is associated with even more depression in IMg2+ in SAH in women. It is possible that prior alcohol ingestion is, in large measure, responsible for a great deal of this unexplained higher incidence of SAH in women. It has recently been reported that the cyclical changes in estrogenic hormones appear to control the serum IMg2+ level in young women. A surge in estrogenic levels prior to SAH could thus precipitate, in part, the SAH. In other human studies, it has been shown that migraines and headache, dizziness, and hangover, which accompany ethanol ingestion, are associated with rapid deficits in serum IMg2+ but not in TMg. The former, and the alcohol-associated headache, can be ameliorated with IV administration of MgSO4. Premenstrual tension-headache (PTH) and its exacerbation by alcohol in women is also accompanied by deficits in IMg2+, and elevation in serum ICa2+/IMg2+; IV MgSO4 corrects the PTH and the serum deficit in IMg2+. Animal experiments show that IV Mg2+ can prevent alcohol-induced hemorrhagic stroke and the subsequent fall in brain [Mg2+]i, [PCr], pHi, and CPP. Other recent data indicate that alcohol-induced cellular loss of [Mg2+]i is associated with cellular Ca2+ overload and generation of oxygen-derived free radicals; chronic pretreatment with vitamin E prevents alcohol-induced vascular injury and pathology in the brain. (ABSTRACT TRUNCATED)

Alterations in ionized and total blood magnesium after experimental traumatic brain injury: relationship to neurobehavioral outcome and neuroprotective efficacy of magnesium chloride

Experimental evidence suggests that magnesium plays a role in the pathophysiological sequelae of brain injury. The present study examined the variation of blood ionized and total magnesium, as well as potassium, sodium, and ionized calcium, after experimental fluid percussion brain injury in rats. Blood ionized magnesium concentration significantly declined from 0.45 +/- 0.02 to 0.32 +/- 0.02 mM by 30 min postinjury and stayed depressed for the 24-h study period in vehicle-treated rats. Blood total magnesium concentration was 0.59 +/- 0.01 mM and remained stable over time in brain-injured vehicle-treated animals. When magnesium chloride (125 micromol/rat) was administered 1 h postinjury, ionized magnesium levels were restored by 2 h postinjury and remained at normal values up to 24 h following brain trauma. Magnesium treatment also significantly reduced posttraumatic neuromotor impairments 1 and 2 weeks after the insult, but failed to attenuate spatial learning deficits. A significant positive and linear correlation could be established between ionized magnesium levels measured 24 h postinjury and neuromotor outcome at 1 and 2 weeks. We conclude that acute ionized magnesium measurement may be a predictor of long-term neurobehavioral outcome following head injury and that delayed administration of magnesium chloride can restore blood magnesium concentration and attenuate neurological motor deficits in brain-injured rats.

Sex steroid hormones modulate serum ionized magnesium and calcium levels throughout the menstrual cycle in women

OBJECTIVE

To determine the serum concentrations of the sex steroid hormones with respect to the concentrations of the biologically active fractions of magnesium and calcium during the different phases of the menstrual cycle.

DESIGN

Controlled clinical study.

SETTING

An academic research environment.

PATIENT(S)

Six parous and four nulliparous healthy cycling female volunteers.

MAIN OUTCOME MEASURE(S)

Concentrations of the sex steroid hormones estrogen, progesterone, and testosterone as well as the ionized Ca and Mg levels were measured in the serum of normal cycling women during five different stages: the menstrual, early follicular, late follicular, ovulatory (ovulatory/early luteal), and luteal phases.

RESULT(S)

In each woman, there was a comparatively high ionized Mg level coincident with the early follicular phase, a statistically significant decrease in ionized Mg around the time of ovulation, a significant decrease in ionized and total Mg when the serum progesterone concentration peaked, and a significant increase in the serum Ca2+/Mg2+ ratio at both the ovulatory and luteal phases. In addition, a decrease in ionized Mg was found with increased testosterone levels.

CONCLUSION(S)

Healthy women of reproductive age demonstrate recurring cycling of ionized Mg and cyclic alterations in the ionized Ca to Mg ratio in their serum. The changes in serum concentrations of these important physiologically active cations, in the range at which they occur, can affect such entities as the vasculature, synaptic transmission, and excitation-secretion coupling and thus can produce the well-known premenstrual syndromes during the luteal phase in women who are somewhat deficient in Mg or in those who have an unusually increased Ca2+/Mg2+ ratio.

Blood-free magnesium concentration declines following graded experimental traumatic brain injury

Traumatic brain injury has been shown to result in a decrease in brain-free magnesium concentration that is associated with the development of neurologic motor deficits. Although these changes have been well characterized in the brain, changes in free magnesium homeostasis have not been characterized in other fluid compartments. The current experiments use ion selective electrodes to measure alterations in blood-free magnesium concentration following graded experimental brain injury in rats and to compare these changes with subsequent neurologic outcome. After severe impact-acceleration-induced injury, blood-free magnesium levels significantly declined (p < 0.05) by 25% and remained depressed for at least 4 days after injury. After moderate injury, the decline in blood-free magnesium was less than that observed in the severe injury group with respect to both degree of decline and duration of decline. The post-traumatic blood-free magnesium concentration correlated to observed motor deficits as assessed by rotarod evaluation (p < 0.001). We conclude that blood-free magnesium levels may be a prognostic indicator of outcome following severe traumatic brain injury.

Serum ionized magnesium in chronic alcoholism: is it really decreased?

Chronic alcoholism is associated with a marked deficit in total magnesium (tMg). However, little is known about the status of the physiologically active form, ionized magnesium (iMg). We assessed serum iMg (measured with two ion-selective electrodes, AVL 988-4 and NOVA CRT) and tMg concentrations in chronic alcoholics at admission (n = 31) and after abstinence (n = 13) and compared these results with those for a control group (n = 40). At admission, the tMg and NOVA iMg concentrations in alcoholics (0.78 ± 0.020 and 0.38 ± 0.016 mmol/L, respectively) were significantly less (P &lt;0.001) than in the controls (0.85 ± 0.008 and 0.50 ± 0.006 mmol/L). The AVL iMg results, however, did not differ significantly between the two groups: 0.53 ± 0.013 vs 0.56 ± 0.006 mmol/L, respectively (P &gt;0.05). The mean iMg between the two analyzers differed significantly in both groups (P &lt;0.001). After 3 weeks of abstinence, the alcoholics showed a significant increase in tMg (P &lt;0.001) and in both NOVA and AVL iMg values (P &lt;0.01 for each). tMg concentrations were positively correlated with the AVL iMg values in both alcoholics and controls but correlated positively with the NOVA iMg results only in the controls. Thus, the altered status of iMg is instrument-dependent, and the usefulness of the measurement in alcoholics is yet to be determined.

Homeostatic disruption and depression

A putative model is presented for the nature of depression. It relies upon changes in core and defense homeostatic activity, subjecting the person either to minor or major depression. The former corresponds with the interaction between assessed brain emotion and altered organic elements which disrupt homeostasis. This is in contrast to the latter, which corresponds with the disruption of several homeostatic systems. We suggest that the frequency and severity of depression may be regulated by biological markers that represent the homeostatic baseline of biochemical, biophysical and mutual data system appraisals. In this framework, the relationship of the coefficient to the baseline of the homeostatic threshold levels evaluates the intensity of depression. The type of depression depends on the properties of the negative feedback mechanism which are replaced either by abnormal (retarded depression), or by a positive feedback mechanism (agitated depression). Homeostasis eliminates depression.

Reference interval for whole blood ionized magnesium in a healthy population and the stability of ionized magnesium under varied laboratory conditions

OBJECTIVE

To establish a reference interval for ionized magnesium (iMg), to evaluate the stability of whole blood iMg under varied laboratory storage conditions, and to study the correlation between total and iMg in healthy volunteers and in an intensive care unit (ICU) population.

METHODS

Blood specimens were collected anaerobically from 125 healthy volunteers and 200 ICU patients into tubes containing lithium heparin, transported to the laboratory on ice, stored at 4 degrees C and analyzed within 2 h on a NOVA 8 Electrolyte Analyzer. Additional specimens were stored under different conditions before analysis to assess the stability of iMg.

RESULTS

In healthy volunteers, the mean whole blood iMg level was 0.52 mmol/L with a range of 0.44 to 0.59 mmol/L. The iMg/total serum Mg ratio was at 0.60 (0.50-0.69). Regression analysis of iMg vs total Mg produced a correlation coefficient (r) of 0.48 (p < 0.0001). Ionized Mg levels were comparable between males and females (0.52 +/- 0.04 vs 0.51 +/- 0.03, p = 0.38). In the ICU group, a wider range of iMg results was observed (0.35-0.78 mmol/L) and the correlation between iMg and total Mg was r = 0.71 (p < 0.0001). Storage of whole blood specimens in uncapped tubes at room temperature resulted in a small, but significant, decrease in iMg over a 6-h period. Little change was seen in capped tubes stored either at room temperature or at 4 degrees C. over 6 h, or at 4 degrees C. over 5 days.

CONCLUSIONS

Using the NOVA 8 Electrolyte Analyzer, we established a reference interval for whole blood iMg in a healthy Canadian population. The correlation between ionized Mg and total Mg was weak, but statistically significant. Ionized Mg levels in lithium heparin tubes were stable over 5 days when specimens were stored at 4 degrees C, suggesting that specimens may be stored at least overnight prior to processing.

Extracellular Mg2+ modulates intracellular Ca2+ in acutely isolated hippocampal CA1 pyramidal cells of the guinea-pig

Using digital imaging microscopy and fluorescent probes, isolated hippocampal CA1 pyramidal neurons of the guinea-pig were used to examine the roles of [Mg2+]o in regulation of [Ca2+]i and [Mg2+]i. Low extracellular Mg ([Mg2+]o) (0.3 mM) significantly increased [Ca2+]i compared to 1.2 and 4.8 mM [Mg2+]o. In contrast, [Mg2+]i levels remained relatively constant, irrespective of alterations of [Mg2+]o. The sustained rise in [Ca2+]i induced by low [Mg2+]o was reduced 70% by 1 microM verapamil and 42% by 1 mM Ni2+, and completely abolished by 5 mM Ni2+. The data suggest that [Mg2+]o regulates [Ca2+]i in hippocampal neurons, probably by modulating Ca2+ entry via voltage-sensitive Ca2+ channels, which may play important roles in epileptogenesis, memory, learning and brain trauma. Furthermore, the results demonstrate that intracellular Mg2+ concentration does not follow passively the concentration of Mg2+ in the extracellular solution.

Alcohol-associated acute head trauma in human subjects is associated with early deficits in serum ionized Mg and Ca

Acute head trauma (AHT) (caused by motor vehicle accidents that did not produce loss of consciousness or observed brain lesions on CT scan, or falls) was found to result in early (1-8 h after injury) serum deficits in ionized magnesium (IMg2+) and ionized calcium (ICa2+) assessed with ion-selective electrodes (ISEs). Total Mg (TMg) and other electrolytes as well as serum biochemical analytes were all within the normal reference ranges. AHT patients with acute alcohol intoxication (BAC > or = 150 mg/dl) or alcohol abuse (BAC > 200 mg/dl) demonstrated deficits (15-35% less than normal) in IMg2+, but serum TMg levels were normal as were electrolytes and serum biochemical analytes. AHT patients with alcohol intoxication or alcohol abuse required hospitalization for 1-3 days prior to release, whereas AHT patients without alcohol intoxication were released in less than 24 h. The ICa2+/IMg2+ ratio, a sign of increased vascular tone and vascular reactivity, was significantly elevated in AHT patients with alcohol intoxication but not in AHT patients without alcohol intoxication or abuse. These serum divalent cation changes early after traumatic brain injury could be of considerable practicable diagnostic value in the assessment of alcohol-associated head injury. Use of ion-selective electrodes to accurately measure IMg2+ could serve as a logical basis for monitoring the response of the body to AHT.

Measurement of free magnesium in blood, serum and plasma with an ion-sensitive electrode

The fraction of total magnesium bound to protein and other substances depends upon the pH. pH-dependency of ionized free magnesium (iMg2+) in serum is expressed by the Siggaard-Andersen equation: iMg2+ (pH) = iMg2+ (7.4) x 10x(7.4 - pH). During preparation of serum or plasma, considerable pH changes occur which have to be corrected on the basis of the above mentioned equation. For pH correction of iMg2+, x < 0.1 has so far been used. However, this is correct only for new Mg(2+)-sensitive electrodes. During the lifetime of Mg2+ electrodes used in the "Microlyte Magnesium" (Kone Instruments, Finland) x increases and x = 0.2 was found to be a suitable approximation for most of the lifetime. By instantaneous iMg2+ measurements in whole blood samples pH changes and the uncertainty of x can be avoided. Dilution of blood by intravenous infusions decreases x nearly proportionally to the decrease of protein concentration in blood. Various methodological influences such as temperature and delay time before centrifugation, storage of serum and venous occlusion were studied. The circadian rhythm of iMg2+ was found to be considerably more pronounced than that of total Mg and was negatively correlated to changes of free fatty acids. To avoid variations of iMg2+ due to circadian changes, blood collection should be carried out between 6 and 10 a.m. The normal range of iMg2+ in blood of 179 healthy subjects was found to be between 0.46 and 0.60 mmol/l and the quotient of free and total Mg between 0.59 and 0.71. The accuracy of "Microlyte Magnesium" (Kone Instruments, Finland) is sufficient in a wide range of iMg2+.