Tissue Magnesium Research Articles

Profile of trace element concentrations in the feto-placental unit in relation to fetal growth.

During pregnancy, trace elements are indispensable for life maintenance not only for the mother but also for the fetus. The purpose of this study was to examine whether fetal growth is associated with altered levels of trace elements in maternal blood, fetal blood, and placenta tissue. Twenty-one pairs of healthy mothers and their newborns with intrauterine growth restriction delivered after 34 weeks of gestation were recruited for the study. In addition, 30 pairs of healthy mothers and their appropriate for gestational age newborns were included as controls. Maternal venous blood, umbilical cord venous and arterial blood, and placenta tissue were collected immediately after delivery. Six essential elements, magnesium, manganese, iron, copper, zinc, and selenium, and four other elements, rubidium, strontium, cadmium, and cesium, in those samples were determined by inductively coupled plasma mass spectrometry or inductively coupled plasma atomic emission spectrometry. Compared with appropriate for gestational age cases, intrauterine growth restriction cases showed higher magnesium, copper, and selenium concentrations in umbilical cord arterial sera, and higher magnesium and selenium concentrations in placenta tissue, but no significant differences appeared for the elements measured in maternal and umbilical cord venous sera. The umbilical cord venous vs. maternal sera concentration ratio was elevated for copper, and the umbilical cord arterial vs. umbilical cord venous sera concentration ratios were elevated for copper and zinc, but there were no differences in placenta tissue vs. maternal sera concentration ratios in intrauterine growth restriction cases. Among the trace elements evaluated, magnesium, copper, zinc, and selenium showed elevated concentrations in umbilical cord arterial blood, or elevated umbilical cord arterial vs. umbilical cord venous blood concentration ratios in intrauterine growth restriction cases. Reduced consumption efficiency of these four essential trace elements may be closely associated with retarded fetal development.

Profile of trace element concentrations in the feto-placental unit in relation to fetal growth

Background. During pregnancy, trace elements are indispensable for life maintenance not only for the mother but also for the fetus. The purpose of this study was to examine whether fetal growth is associated with altered levels of trace elements in maternal blood, fetal blood, and placenta tissue. Methods. Twenty-one pairs of healthy mothers and their newborns with intrauterine growth restriction delivered after 34 weeks of gestation were recruited for the study. In addition, 30 pairs of healthy mothers and their appropriate for gestational age newborns were included as controls. Maternal venous blood, umbilical cord venous and arterial blood, and placenta tissue were collected immediately after delivery. Six essential elements, magnesium, manganese, iron, copper, zinc, and selenium, and four other elements, rubidium, strontium, cadmium, and cesium, in those samples were determined by inductively coupled plasma mass spectrometry or inductively coupled plasma atomic emission spectrometry. Results. Compared with appropriate for gestational age cases, intrauterine growth restriction cases showed higher magnesium, copper, and selenium concentrations in umbilical cord arterial sera, and higher magnesium and selenium concentrations in placenta tissue, but no significant differences appeared for the elements measured in maternal and umbilical cord venous sera. The umbilical cord venous vs. maternal sera concentration ratio was elevated for copper, and the umbilical cord arterial vs. umbilical cord venous sera concentration ratios were elevated for copper and zinc, but there were no differences in placenta tissue vs. maternal sera concentration ratios in intrauterine growth restriction cases. Conclusions. Among the trace elements evaluated, magnesium, copper, zinc, and selenium showed elevated concentrations in umbilical cord arterial blood, or elevated umbilical cord arterial vs. umbilical cord venous blood concentration ratios in intrauterine growth restriction cases. Reduced consumption efficiency of these four essential trace elements may be closely associated with retarded fetal development.

Assessing Magnesium Status: A Persisting Problem

AbstractMagnesium plays an essential role in a wide range of fundamental biological reactions. Although diets consumed by healthy Americans usually do not lead to clinically significant magnesium depletion, epidemiological and clinical studies have suggested an association between low magnesium status and increased risk of cardiovascular diseases, hypertension, osteoporosis, diabetes, and other chronic diseases. In acutely or chronically ill hospitalized patients, the prevalence of hypomagnesemia has been reported to be as high as 11%. Hypomagnesemia resulting from underlying disease can be due to decreased gastrointestinal absorption or increased renal magnesium losses. Magnesium is principally an intracellular cation. Tissue magnesium status is difficult to accurately estimate with non‐invasive measures due to poor correlations between serum or RBC or WBC magnesium levels and magnesium concentration in major tissue stores in muscle and the skeleton. At present, a comprehensive evaluation of a patient's risk of magnesium deficiency should include consideration of known risk factors and disease conditions possibly contributing to magnesium depletion, estimates of dietary magnesium intake, and clinical observations. The evaluation also should include laboratory measures of magnesium status, including analysis of both extracellular (serum magnesium) and intracellular (RBC, WBC or muscle magnesium) magnesium concentration, if available. Researchers should continue efforts to find a simple, reliable, and useful technique to accurately estimate magnesium status.

The impact of diets with different magnesium contents on magnesium and calcium in serum and tissues of the rat

The impact of three different magnesium diets (70, 1000 and 9000 ppm) on total, ionized and bound magnesium as well as ionized calcium in serum and total calcium and magnesium in femoral bone, skeletal muscle, heart and liver of male Sprague-Dawley rats was investigated. The percentage of ionized serum magnesium was unproportionally high in rats fed a low magnesium (70 ppm) diet. Femoral magnesium was correlated with ionized and total serum magnesium. In contrast, there was generally no correlation between total serum magnesium and the magnesium fractions in skeletal muscle, heart and liver. In rats fed the magnesium deficient diet, total cardiac concentration of magnesium was even significantly increased along with total calcium content, while there were no effects on total muscle and liver magnesium. Within the single groups, ionized serum calcium was never proportional to dietary magnesium, but in all three magnesium diet groups together, it was inversely correlated with dietary magnesium. Moreover, ionized serum calcium was inversely correlated with both ionized and total serum magnesium. In all 3 groups together, the concentrations of total calcium and magnesium in heart and skeletal muscle were correlated, within the single groups correlation existed only in the 1000 ppm group. Magnesium influx via calcium channels during low magnesium intake has been seen in non cardiac tissues [35,36], but nothing similar is known about non selective channels for divalent cations in the heart [33]. Thus, magnesium uptake by cardiac cells along with calcium seems to be possible, especially at low intracellular magnesium concentrations, but is still poorly investigated. We suggest that the calcium-antagonistic effect of magnesium is related to the turnover rate of magnesium rather than to its tissue concentrations.

Elemental content relationships in greenhouse grown apple seedlings supplemented with copper and peat

Apple seedlings from a greenhouse pot experiment, investigating the effects of copper (Cu) and peat amendments on crop performance growing on a Cu‐and potassium (K)‐deficient soil, were characterized for a range of major and trace elements. Concentrations of barium (Ba), calcium (Ca), Cu, iron (Fe), K, magnesium (Mg), manganese (Mn), molybdenum (Mo), sodium (Na), rubidium (Rb), strontium (Sr), and zinc (Zn) in leaf and stem tissues were correlated with treatment and tissue. Addition of Cu, peat and the nature of the tissue had significant impacts on many element concentrations. Generally, increasing Cu resulted in elevated Ba, Fe, Mo, and Sr as well as Cu levels. The presence of peat resulted in reduced levels, generally in both leaf and stem, of Ba, Mg, Mn, Rb, and Zn and increased levels of Fe, K, and Mo. Finally, the vast majority of elemental concentrations were higher in leaf tissue rather than stem, with the exceptions of Na and Zn. Elemental concentration ranges, over all tissues and conditions of added Cu and peat were (mg kg‐1) Ba 9–49, Ca 6380–16340, Cu 2–11, Fe 10–57, K 4070–16950, Mg 900–4260, Mn 22–197, Mo 0.02–0.19, Na 28–124, Rb 0.7–12, Sr 41–58, Zn 18–48.

Effect of cold-restraint stress on the distribution of trace elements in rat tissues.

The aim of this study was to assess the effects of cold-restraint stress on blood and the other tissue levels of trace elements. The experiment was performed on male Swiss albino rats. The animals were divided to two groups: control and stressed groups. In the stressed group, the rats were subjected to immobilization for 4 h at 4 degrees C. At the end of the experimental period, blood and tissue samples were collected from all of the animals. The levels of zinc, copper, magnesium, and manganese were measured using flame and graphite furnace atomic absorption spectrometry. In rats subjected to stress, the zinc levels of serum were increased, whereas in the duodenum and brain, zinc was found to decrease when compared to the control. The magnesium content of both the stomach and duodenum were reduced, but the manganese levels of the liver, kidneys, and brain significantly increased because of stress. In conclusion, cold-restraint stress may affect the metabolic process by changing the distributions of zinc, magnesium, and manganese in tissues.

Neuroprotective effects of NPS 846, a novel N-methyl-D-aspartate receptor antagonist, after closed head trauma in rats.

The authors sought to determine whether 3,3-bis (3-fluorophenyl) propylamine (NPS 846), a novel noncompetitive N-methyl-D-aspartate receptor antagonist, alters outcome after closed head trauma in rats. The experimental variables were: presence or absence of closed head trauma, treatment with NPS 846 or no treatment, and time at which the rats were killed (24 or 48 hours). The NPS 846 (1 mg/kg) was administered intraperitoneally at 1 and 3 hours after closed head trauma or sham operation. Outcome measures were the neurological severity score (NSS), ischemic tissue volume, hemorrhagic necrosis volume, and specific gravity, water content, and concentrations of calcium, sodium, potassium, and magnesium in brain tissue. The following closed head trauma-induced changes in the injured hemisphere (expressed as the mean +/- the standard deviation) were reversed by NPS 846: decreased specific gravity of 1.035 +/- 0.006 at 24 hours was increased to 1.042 +/- 0.004; the decreased potassium level of 0.583 +/- 0.231 mg/L at 48 hours and at 24 hours was increased to 2.442 +/- 0.860 mg/L; the increased water content of 84.7 +/- 2.6% at 24 hours was decreased to 79.8 +/- 2%; the increased calcium level of 0.592 +/- 0.210 mg/L at 24 hours was decreased to 0.048 +/- 0.029 mg/L; and the increased sodium level of 2.035 +/- 0.649 mg/L was decreased to 0.631 +/- 0.102 mg/L. Administration of NPS 846 also lowered the NSS (improved neurological status) at 48 hours (7 +/- 3) and caused no significant changes in ischemic tissue or hemorrhagic necrosis volumes in the injured hemisphere at 24 or 48 hours. In this model of closed head trauma, NPS 846 improved neurological outcome, delayed the onset of brain edema, and improved brain tissue ion homeostasis.

Effect of Soil Sodicity on the Growth and Cation Composition of Palmarosa and Lemongrass

ABSTRACT The effects of soil sodicity on the growth, yield, and cation composition of palmarosa (Cymbopogon martinii Roxb. Wats) and lemongrass (Cymbopogon flexuosus Steud Wats) were studied in a pot experiment. The plant height, number of tillers, and herb yield of both species significantly decreased as the exchangeable sodium in soil increased. A 50 percent reduction in herb yield over control was recorded at soil exchangeable sodium levels of 52 and 37 percent, respectively, for palmarosa and lemongrass. Increases in exchangeable sodium percentages of soil enhanced the concentration of sodium and decreased that of potassium, calcium and magnesium in vegetative tissues of both plants as compared with control. Palmarosa was lower in sodium and better able to maintain the potassium to sodium and calcium to sodium ratios in vegetative tissues under sodicity stress than lemongrass. Geranyl acetate content in the oil of palmarosa increased with increases in the soil exchangeable sodium percentage.

Tissue magnesium and calcium affect arbuscular mycorrhiza development and fungal reproduction

Applications of high levels of MgSO4 resulted in reduced root colonization and sporulation by Glomus sp. (INVAM isolate FL329) with sweet potato and onion in aeroponic and sand culture, respectively. Onion shoot-Mg concentrations were elevated when a nutrient solution containing 2.6 or 11.7 mM MgSO4 was applied. Magnesium application depressed tissue-Ca levels. With lower Ca in the tissue, colonization was reduced from > 30% of root length to < 10%, and sporulation from > 1200 to ca. 200 spores per plant, 10 weeks after transplantation and the start of nutrient application. These effects on colonization and sporulation were independent of changes in tissue-P concentration. High Mg/low Ca tissue concentrations induced premature root senescence, which may have disrupted the mycorrhizal association. Our results confirm the importance of Ca for the maintenance of a functioning mycorrhiza.

The Influence of Sodium Chloride and Waterlogging Stresses on Alnus Cordata

Sodium chloride solutions were applied as a root drench to containerized Alnus cordata trees grown in freely drained or waterlogged compost substrates. Leaf chlorophyll fluorescence; cell electrolyte leakage; plant mortality; leaf necrosis; time to bud burst; and leaf, shoot, and root macronutrient concentrations were evaluated. Waterlogging using distilled water caused no significant stress compared to controls, apart from increasing root iron and manganese concentrations. Complete mortality ^vas recorded in trees watered with a sodium chloride solution &gt; 4.5% or waterlogged in sodium chloride solutions &gt; 2%. Watering or waterlogging with distilled water had no,significant effect on mortality, while 66.6% of trees watered with a 2% sodium chloride solution died. Applications of sodium chloride tended to increase time to bud burst compared to controls. Irrespective of whether trees were grown in freely drained or waterlogged compost, applications of sodium chloride to roots decreased leaf chlorophyll fluorescence and increased cell electrolyte leakage and leaf necrosis for up to 15 days after bud burst. Significant reductions in chlorophyll fluorescence was detected by day 3 following bud burst; however, significant increases in cell electrolyte leakage and leaf necrosis were not detected until day 6. Applications of sodium chloride significantly increased sodium and chloride concentrations in root, leaf, and shoots irrespective of drainage, with higher concentrations reflecting applications of stronger salt solutions. Calcium, phosphorous, magnesium, and potassium concentrations in cell tissues were unaffected by treatments. Depressed leaf and shoot copper, zinc, and iron concentrations were recorded in trees waterlogged in sodium chloride solutions &gt; 4.5%. Irrespective of treatment, no significant effects on manganese concentrations of leaf and shoot tissue were found, but significantly lower concentrations of manganese were recorded in roots. Greater reductions generally reflected stronger applications of sodium chloride.

Induction of fungal disease resistance in Vicia faba by dual inoculation with Rhizobium leguminosarum and vesicular-arbuscular mycorrhizal fungi.

Infection of Vicia faba with Bothytis fabae causes significant decreases in growth vigour, total nitrogen content, number of nodules and nutrient accumulation. Na-uptake and phenolics concentration increased compared to that of noninfected plants. In contrast, dual inoculation of Rhizobium and VA mycorrhizae increased all above parameters suggesting a distinct improvement of the plants. The results also revealed that an inverse correlation may exist between phenolic, calcium, magnesium and zinc concentrations in mycorrhizal plant tissues grown in presence of rhizobial bacteria and the disease severity. From these findings we conclude a possible role of both VA mycorrhizal fungi and rhizobial bacteria in the decrease of susceptibility of plants.

Magnesio en líquido cefalorraquídeo en la isquemia cerebral aguda: relación con la neurotoxicidad por el glutamato

In animal models it has been shown that there is an increase in tissue magnesium concentration during cerebral ischemia. We studied the changes in magnesium levels in the cerebrospinal fluid (CSF) during the acute phase of cerebral ischemia. We included 95 patients with first ischemic cerebral infarcts admitted to hospital within the first 24 hours and also 37 controls. CT scan was done on admission and between four and seven days later (when the volume of the infarct was determined). The neurological defect was evaluated on the Canadian scale on admission, after 48 hours, on the seventh day and after three months. The CSF magnesium concentration was determined using a colorimetric method and the glutamate by HPLC. The CSF magnesium concentrations were significantly higher in the patients than in the controls (2.6 +/- 0.6 mmol/l vs 2.2 +/- 0.6 mmol/l p = 0.0001). The magnesium concentration was higher in the larger infarcts (Pearson's coefficient = 0.2901, p = 0.0043), and in those presenting greater neurological defects after 48 hours (Spearman's coefficient = -0.4649, p < 0.0001). The magnesium concentration was not related to the presence of early signs on the initial CT scan and the Canadian scale rating on admission. The concentration of magnesium was significantly correlated with that of glutamate (Pearson coefficient = 0.7735, p < 0.0001). The levels of magnesium in the CSF were satisfactorily related to the volumes of the infarct and the intensity of the neurological defect. However, this association was late, occurring more than 48 hours after onset of the condition.

Seasonal variations in nutrient and carbohydrate levels of tall fescue cultivars in Japan

Quality (color and density) of tall fescue (Festuca arundinacea Schreb.) as a turfgrass is reduced during both the winter and summer in Japan. Seasonal variations in nutrient and carbohydrate levels of six cultivars of tall fescue were measured to determine if these changes are related to the reduction in the turf quality. There were significant differences among the cultivars in nutrient and carbohydrate levels. The nutrient and carbohydrate levels of tall fescue cultivars changed seasonally. Levels of calcium (Ca) and zinc (Zn) were below the sufficiency, but the concentrations of other nutrients were sufficient during the summer suggesting that the reduction in the quality of tall fescue cultivars during the summer in Japan may not be related to the lack of these nutrients in the plant tissues. The nitrogen (N), Ca, magnesium (Mg), phosphorus (P), Zn, iron (Fe), and copper (Cu) levels in the plant tissues were below the adequate range in the spring which could be attributed to high growth rate since no deficiency symptom was observed. With exception of Ca content, plants contained sufficient or more than sufficient nutrients in their tissues during the fall. Though concentrations of other nutrients were sufficient in the plant tissues in the winter, levels of N, Ca, Mg, P, molybdenum (Mo), Zn, and Cu were lower than plant's requirement which could be due to low temperature since availability of the nutrients reduces under low temperature. There were no deficiency symptoms of these nutrients, but lack of N in the plant tissue could be the cause of the reduction in the color of the tall fescue cultivare in winter. Levels of glucose, fructose, sucrose, fructan, and starch in the summer were higher or equal to those carbohydrate levels in the spring or fall suggesting that decline in tall fescue quality in Japan during the summer may not be related to carbohydrates shortages. Though starch levels were lower in the winter than other seasons, other carbohydrate levels were equal or higher than the levels in the spring and the total carbohydrate content was much higher in the winter than other seasons, suggesting that reduction in tall fescue quality in Japan during the winter may not be related to carbohydrates shortages.

Tissue magnesium levels and the arrhythmic substrate in humans.

Magnesium deficiency has been implicated in the pathogenesis of sudden death, but the investigation of arrhythmic mechanisms has been hindered by difficulties in measuring cellular tissue magnesium stores. To see if magnesium deficiency is associated with a propensity toward triggered arrhythmias, we measured tissue magnesium levels and QT interval dispersion (as an index of repolarization dispersion) in 40 patients with arrhythmic complaints. Magnesium was measured in sublingual epithelium using X-ray dispersive analysis. QT interval dispersion was assessed on 12-lead surface ECGs in all patients, and programmed stimulation was performed in 28. The sublingual epithelial magnesium level ([Mg]1), but the not the serum level, correlated inversely with QT interval dispersion in 40 patients (r = 0.58, P < 0.005); in 12 patients undergoing repeat testing on therapy, the change in magnesium also correlated inversely with the change in QT dispersion (r = 0.61, P < 0.05). Patients with left ventricular ejection fractions > 40% had significantly higher tissue magnesium and lower QT dispersion (34.5 +/- 0.5 mEq/L, 81 +/- 8 msec) than those with left ventricular ejection fractions < 40% (32.7 +/- 0.5 mEq/L, P < 0.01, and 114 +/- 9 msec, P < 0.05). There was no difference in either [Mg]1 or QT dispersion in the 16 patients with inducible monomorphic ventricular tachycardia versus the 12 noninducible patients. Reduced tissue magnesium stores may represent a significant risk factor for arrhythmias associated with abnormal repolarization, particularly in patients with poor left ventricular systolic function, but may not represent a risk for excitable gap arrhythmias associated with a fixed anatomic substrate (e.g., monomorphic ventricular tachycardia).

Shoot growth, plant tissue elemental composition, and soil salinity following irrigation of alfalfa and tall fescue with high‐sulfate waters1

Groundwater contaminated with sulfate (SO4 2‐) at concentrations higher than allowable for drinking water might still be usable for irrigation. Objectives were to determine the growth response and mineral uptake of two forage crops irrigated with waters containing SO4 2‐ at concentrations ranging from 175 to 1743 mg/L, and with electrical conductivities (EC) ranging from 1.2 to 3.6 dS/m. Plants were grown for 12 weeks in 8‐L pots containing a calcareous sandy loam and were harvested at 4, 8, or 12 weeks for plant growth measurements and tissue analysis. Digested leaves, stems, and reproductive tissues were analyzed by inductively coupled plasma (ICP) spectroscopy at each harvest, as were saturated soil paste extracts. Shoot growth of tall fescue (Festuca arundinacea Schreb.) was not affected by irrigation water treatment, whereas shoot growth of alfalfa (Medicago sativa L.) was increased by a moderate level of soil solution SO4 2‐ Sulfur (S), boron (B), magnesium (Mg), sodium (Na), and zinc (Zn) concentrations in shoot tissues of both species showed a tendency to increase with increasing SO4 2‐ content of irrigation water. Shoot tissue concentration of molybdenum (Mo) increased with maturation in both species, while the concentrations of B, potassium (K), manganese (Mn), Na, and Zn decreased. Soil saturated paste extract concentrations of Mg and Na increased with irrigation water Mg and Na concentrations, while Ca and S concentrations in the soil solution became saturated at the higher irrigation water concentrations of these elements.

Detection of Salt and Waterlogging Stresses in Alnus Cordata by Measurement of Leaf Chlorophyll Fluorescence

The measurement of chlorophyll fluorescence for use as a rapid diagnostic tool which detected stress interactions in Italian alder (Alnus cordata Desf.) is reported. Containerised trees in well-drained or waterlogged conditions were subjected to foliar applications of various concentrations of sodium chloride (NaCI). Measurements of leaf chlorophyll fluorescence provided strong correlations with visual necrosis (r2adj = 63.5%), and cell electrolyte leakage (r2adj = 84.6%). Leaf chlorophyll fluorescence was not correlated with stem growth. Foliar applications of NaCI increased sodium and chloride concentration in leaves irrespective of whether trees were planted in well-drained or waterlogged compost, with higher leaf Na and Cl concentrations reflecting the application of stronger salt solutions. Except for decreased calcium, phosphorous, magnesium and potassium in leaf tissue from trees grown in waterlogged compost and sprayed with distilled water or 2% NaCI, no treatment effects upon macronutrient concentrations were identified. Chlorophyll fluorescence values &lt; 0.8 indicated the onset of stress. The opportunities offered by measurements of chlorophyll fluorescence to provide a diagnostic tool for arborists are discussed.

Effects of Qing Kai Ling injection on experimental cerebral hematoma in rabbits

To observe the effect of "Qingkailing" (QKL) on cerebral hematoma. The experimental cerebral hematoma models were produced by injecting autogenous clot in the rabbit. The influences of QKL on blood gas, brain index, contents of water, sodium, potassium, calcium, magnesium in brain tissues and changes of cerebrovascular permeability, histomorphology at the third day, seventh day, fourteenth day after cerebral hematoma were observed. In the pathological group brain index and contents of water, sodium, calcium of brain tissue, ventilation of lung were increased progressively, cerebrovascular permeability were raised obviously, especially in the side of hematoma (right brain). After the forming of cerebral hematoma cerebral edema was reduced, brain index, contents of water, sodium, calcium in brain tissue and cerebrovascular permeability, hyperventilation were all less than pathological group and close to the control group. QKL was advantageous in the treatment of encephal edema induced by experimental cerebral hematoma.

Effect of Salinity on Ionic Shifts in Mesohaline Scyphomedusae, Chrysaora quinquecirrha.

Mesohaline populations of the scyphomedusae Chrysaora quinquecirrha are found in salinities ranging from 5{permill} to 25{permill}. Osmotic and ionic adjustments within this salinity range were investigated using C. quinquecirrha ephyrae budded from polyps in the laboratory and young medusae collected from the mid-salinity region of the Patuxent River, Maryland. When medusae were transferred from 20{permill} salinity to lower salinities (8{permill}, 12{permill}), concentrations of sodium and magnesium in tissue and mesogleal fluid fell rapidly and approached those of dilute seawater within 6 hours. There was some recovery of these levels relative to the 8{permill} medium, and they were significantly higher than the dilute seawater concentration after 1 week. Tissue concentrations of calcium showed no evidence of being regulated, whereas potassium was strongly regulated such that levels did not fall significantly following transfer of medusae to lower salinities. However, after 1 week, the concentration of potassium in mesogleal fluid approached that of the dilute medium. Extracellular space measured by direct blotting and weighing or using 35S was about 40%. As a result, estimates for intracellular potassium were revised to 17 mM1-1. The concentration of potassium in tissue remained stable following transfer to lower salinity, despite a substantial osmotic influx of water. This influx was measured as a >20% gain in body weight over 24 h following transfer of medusae from 16{permill} to 8{permill}. Mesogleal fluid was slightly hypo-osmolar to the medium at 15% and 20{permill} and slightly hyperosmolar to the medium at 5{permill} and 12{permill}. Sulfate concentrations in mesogleal fluid were 66%-70% those of the external medium. Medusae died or were unable to achieve positive buoyancy at 5%{permill}, which is probably very close to a lower salinity limit for C. quinquecirrha in the mesohaline Chesapeake Bay.

Serum Magnesium Levels May Not Indicate Low Tissue Magnesium Levels

I recently read an article by Madias et al1entitled "Admission Serum Magnesium Level Does Not Predict the Hospital Outcome of Patients With Acute Myocardial Infarction," which appeared in the August 12/ 26, 1996, issue of theArchives. While the determination of magnesium (Mg) levels may be very useful to a practicing clinician, not only in patients with myocardial infarction but also in patients with other problems such as bronchial asthma and fibromyalgia,2,3it should be pointed out that just because a serum Mg level is within normal range the patient's total body Mg status may not be normal. In a patient with myocardial infarction, one should be interested not only in the serum Mg levels but also in the myocardial (ie, tissue) Mg level. I am a rheumatologist and have found that my patients with fibromyalgia as a group have a lower mean red blood cell Mg

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