Magnesium metabolism in mice selected for high and low erythrocyte magnesium levels.

A genetic control of blood magnesium (Mg) levels has been suggested. To investigate the mechanisms and the biologic significance of this genetic regulation, a mouse model, ie, mice selected for low magnesium level (MGL) and high magnesium level (MGH), was developed. The purpose of this study was to explore the Mg status and Mg metabolism in female MGL and MGH mice. We observed that MGL mice had reduced total and ionized plasma Mg, lower erythrocyte Mg, lower tibia, and kidney Mg levels. In contrast, total urinary Mg and (25)Mg levels were significantly higher in MGL mice. MGL mice had smaller total Mg exchangeable pool masses compared with MGH, and fractional transport rates of Mg (exchange constant) were different. In vitro (25)Mg enrichments in erythrocytes from MGL mice were significantly lower. Moreover, Mg efflux from erythrocytes was significantly higher in MGL. In conclusion, this work demonstrates that MGL mice present lower body stores of Mg than MGH mice and lower body Mg retention. This is confirmed at a cellular level by a lower enrichment of (25)Mg in erythrocytes. The lower retention of Mg by MGL erythrocyte in comparison to MGH appears to be partly due to a higher Mg efflux in MGL erythrocyte. It can be hypothesized that a genetic factor that modulates Na(+)/Mg(2+) exchanger activity may be important in the regulation of Mg metabolism. Further investigations on the mechanisms responsible for differences in Mg retention between MGL and MGH mice could contribute to a better understanding of the genetic regulation of cellular Mg.

Magnesium involvement in sleep: genetic and nutritional models.

Alterations of peripheral magnesium (Mg) concentration have been reported in association with several behavioral disorders and sleep organization. Blood Mg regulation is under a strong genetic control, whereas brain Mg regulation does not seem to be affected. We have studied peripheral and central levels of Mg and analyzed sleep in two lines of mice selected for low (MGL) and high (MGH) red blood cell (RBC) Mg levels. The same variables were also studied in C57BL/6J mice before and after 3 weeks of Mg deficiency. Whereas blood Mg was highly affected by the selection, brain Mg exhibited only small differences between the two lines. In contrast, Mg deficiency strongly decreased both central and peripheral Mg levels. Sleep analysis indicated that in both models the amount of paradoxical sleep was lower in mice with higher Mg levels. The amplitude of daily variation in sleep and slow-wave sleep delta power was markedly decreased in MGH line. Quantitative electroencephalogram (EEG) analysis also revealed a faster theta peak frequency in MGH mice, irrespective of behavioral states. Central Mg showed significant correlations with the amount of paradoxical sleep and sleep consolidation. However, because the direction of these correlations was not consistent, it is concluded that optimal, (physiological) rather than high or low, Mg levels are needed for normal sleep regulation.

Modulating role of glucose on magnesium transport in rat erythrocytes.

Magnesium efflux from rat erythrocytes has been shown to be inhibited by a plasma fraction containing glucose. Therefore, we investigated the effect of D-glucose on erythrocyte magnesium transport. We show the inhibitory activity of this hexose on sodium (Na(+))-independent erythrocyte magnesium (Mg(2+)E) efflux. Inhibitory effects of D-mannose, 2-deoxy-D-glucose, and D-fructose on Mg(2+)E efflux also were demonstrated. Moreover, the suppression of the inhibitory activity of glucose on Mg(2+)E efflux was shown to be associated with the inhibition of glucose transport by cytochalasin B and phloretin. Together these data suggest a possible implication of the glucose carrier GLUT-1 in the regulation of Mg(2+) transport.

Unexpected association between reproductive longevity and blood magnesium levels in a new model of selected mouse strains.

Two recently described mouse strains, with high (MGH) and low (MGL) blood magnesium (Mg) levels were obtained by selection over 19 generations. Both strains exhibit strong differences for characteristics generally known to be related to blood Mg levels, such as increased stress sensitivity and stress-induced aggressivity in MGL mice. In contrast, while experimental Mg deficiency due to low oral Mg intake has been shown to shorten life span and lower reproductive ability, reproductive longevity was longer in the MGL than in the MGH strain. Interestingly, the life spans of the two strains are very similar. Although this character could have been fixed in the strains by chance, with no relationship to the blood Mg level, the possibility of a causal link with the selection cannot be ruled out and is discussed. Regardless of the mechanisms at stake, the MGH and MGL strains appear to constitute a new model for the study of the relationships between reproductive longevity and blood Mg levels.

[Not Available]. / Relationship between blood magnesium and psychomotor retardation in drug-free patients with major depression.

In previous reports, we have observed that blood magnesium was significantly higher in drug-free patients with major depression when compared to healthy controls. This was especially true for erythrocyte magnesium. Furthermore, the most severely depressed patients had the highest intracellular magnesium content, showing that intracellular magnesium rate was related to the intensity of symptoms. We report here the results of blood magnesium measured in 88 major depressed patients as compared to 61 controls. We show that the mean erythrocyte and also plasma magnesium contents are both increased in these patients. We observe that about 40% of male and female patients have a very significant increase (25%) in intracellular magnesium content as compared to controls. However, about 60% of the hospitalised depressed patients have normal values. None of the controls has high erythrocyte magnesium. This is less evident concerning the plasma magnesium. No differences are observed between patients when classified according to the intensity of moral pain or anxiety. In contrast, the patients with mild to high psychomotor retardation score, which is an index of hypoexcitability, have significant higher erythrocyte magnesium values compared with other patients. The results of male patients without psychomotor retardation do not differ from control values. Our study suggests that central hypoexcitability might be related to an increase in intracellular magnesium observed at the peripheral level, keeping in mind that hyperexcitability, as observed in various conditions such as stress and cardiovascular disorders, is frequently associated, in contrast, with a decrease in blood magnesium.

Mice selected for low and high blood magnesium levels: a new model for stress studies.

Extra- and intracellular magnesium levels have previously been shown to be genetically controlled in humans and in the mouse. To further study this genetic regulation, mice were selected from a heterogeneous population, for low (MGL mice) and high (MGH mice) red blood cell (RBC) magnesium values. These values diverged rapidly in the two strains, to reach a stable difference between the 14th and 18th generations. MGL mice also exhibited significantly lower plasma, kidney, and skull bone magnesium contents and higher urinary magnesium excretion and total brain weights. Moreover, in stressful conditions, MGL mice displayed a more aggressive behavior that the control MGH strain. Altogether, MGL mice showed a more restless behavior, a higher rectal temperature, and much higher brain (+17%) and urine (+200%) noradrenaline levels than the MGH animals. These strains, thus, constitute a new animal model for the study of magnesium metabolism and its relationships with catecholamines, stress sensitivity, and aggressive behavior.

Relationship between erythrocyte magnesium, plasma electrolytes and cortisol, and intensity of symptoms in major depressed patients.

53 male and female drug-free major depressed patients were separated into three groups according to the severity of the depression. In the entire regrouped population, plasma and erythrocyte magnesium (Mg) were shown to increase as compared with 48 healthy controls, confirming our previous studies. The middle and highly depressed patients had higher erythrocyte and also plasma Mg levels than either lowly depressed patients or controls. Only, a few differences were noticed in plasma sodium, potassium and calcium (Ca) in the three groups of patients, except for ultrafiltrable plasma Ca, measured for the first time in affective disorders. Thus, erythrocyte and also plasma Mg are shown to be associated with the intensity of the depression. As blood hypomagnaesemia is often related to hyperexcitability, further investigations are actually in process to shown whether hypermagnesaemia might be, in contrast, associated with psychomotor retardation as observed in many depressed patients.

The variability of blood pressure in mice selected for low (MGL) and high (MGH) blood magnesium levels.

Arterial blood pressure has been determined using a tail cuff method in 164 unanaesthetized, adult mice with genetically low (MGL) or high (MGH) erythrocyte magnesium levels. The mice came from the 9th, 10th, 11th and 12th generations of a bidirectional selective breeding undertaken at the CSAL-CNRS (Orleans). The two lines differed significantly by the magnesium contents of their erythrocytes, plasma, kidney and bone. Ten successive measurements of systolic blood pressure were recorded from each animal, without habituation, within a single period of about 2 min. All mice had elevated blood pressures presumably due to the stress of the experimental procedure. The first, the tenth and the average values of these 10 measurements yielded similar results in both sexes and in both lines. Younger animals (4 months of age) had significantly higher values (180 mmHg) than older ones (10-13 months, 161 mmHg), and this difference was more pronounced in the MGL than in the MGH strain. In both age-groups and lines, about two-thirds of all mice tested showed an increasing arterial pressure during the testing period while the remaining third exhibited decreasing values. Whatever the age-group or the variation pattern during the course of the blood pressure measurements. MGL mice had median values (mean of the fifth and sixth measurements) higher than those of MGH mice. The difference observed between the two strains can be attributed to a greater sensitivity and/or reactivity of the MGL mice to the stress induced by the manipulation, heating and immobilization required for blood pressure measurement.

Brain catecholamines, serotonin and their metabolites in mice selected for low (MGL) and high (MGH) blood magnesium levels.

Brain noradrenaline, dopamine, DOPAC (3-4 dihydroxyphenylacetic acid), HVA (homovanillic acid), serotonin and 5-HIAA (5-hydroxyindolacetic acid) were determined by high performance liquid chromatography with amperimetric detection in adult male mice from three different strains : mice with genetically low (MGL) or high (MGH) blood magnesium levels, obtained by selective breeding and outbred Swiss albino mice. Noradrenaline levels were significantly higher (P < or = 0.001) in MGL than in MGH and Swiss mice : DOPAC levels were lower (P < or = 0.001) in MGL than in MGH and Swiss. Little or no differences were found for these variables between MGH and Swiss mice. MGL and MGH animals had similar brain dopamine, HVA and serotonin contents. These results suggest that the mere selection for genetic traits inducing low blood magnesium levels increases the synthesis of noradrenaline or decreases its catabolism. The above data together with the higher urinary noradrenalin excretion previously observed in the MGL line might account for the higher sensitivity and/or reactivity of MGL animals to stress. Swiss mice had significantly lower (P < or = 0.001) brain dopamine and serotonin contents than both MGL and MGH lines; indeed Swiss mice and MGL/MGH mice were issued from very different populations and had vastly different stocks of genes. Brain 5-HIAA content was also found higher (P < or = 0.01) in MGH than in MGL and Swiss mice; this latter result needs to be confirmed by further research.

[Psychopharmacological properties of three magnesium salts: pidolate, lactate and aspartate]. / Propriétés psychopharmacologiques de trois sels de magnésium: pidolate, lactate et aspartate.

The psychopharmacological activities of three organic magnesium salts were estimated on the spontaneous and amphetamine-induced motility, the barbital-induced sleep and the NMDA toxicity of Swiss mice fed with a normal diet, rich in magnesium. Magnesium aspartate had a stimulant effect whereas lactate did not clearly modify the animal behaviour and pidolate induced a clear cut neurosedative effect. None of these salts afforded protection against NMDA toxicity, moreover, aspartate and lactate increased NMDA toxicity. These results indicate that depending on the anion, magnesium salts do not have the same psychopharmacological activities and that pidolate only seems to respect and enhance magnesium basic pharmacological properties.

Effect of pyridoxine and magnesium on stress-induced gastric ulcers in mice selected for low or high blood magnesium levels.

Gastric ulcers were induced by immobilization in adult female mice with genetically low (MGL) or high (MGH) blood magnesium levels, obtained by selective breeding at the CSAL-CNRS (Orléans, France). All animals, fed with the same standard diet rich in magnesium, were divided into four groups of 20 animals and injected subcutaneously every 2 days for 10 days with isotonic saline (group 1), pyridoxine chlorhydrate 1.11 mg/kg in saline (group 2), magnesium lactate 149 mg/kg in saline (group 3) or both pyridoxine and magnesium (group 4). Subsequently, animals were submitted to a complete fast and an immobilization stress for 17 h. Then, they were sacrificed and the gastric mucosa was dissected for ulcer count. Among the controls (group 1), the mean number of gastric ulcers per mouse was significantly larger in the MGL than in the MGH line (p = 0.0003). In the MGH line, no significant differences were observed between control and treated groups. In the MGL line, pyridoxine associated or not with magnesium (groups 2 and 4) significantly reduced the mean number of ulcers. Magnesium treatment alone (group 3) had little effect. These results can be compared with the greater vulnerability to stress previously observed in Swiss mice fed with a magnesium-deficient diet. However, in this latter group, the number of stress ulcers was reduced not only by pyridoxine but also by the sole magnesium treatment, contrary to our present findings in MGL mice.

Brain weight and noradrenaline content in mice selected for low (MGL) and high (MGH) blood magnesium.

Brain noradrenaline content was determined by high performance liquid chromatography in adult male mice from three different strains: 40 mice with genetically low (MGL) or high (MGH) blood magnesium levels, obtained by selective breeding and 20 outbred Swiss albino mice. Brain wet weight and noradrenaline levels were significantly higher in MGL than in MGH and Swiss mice. Few or no differences were found between MGH and Swiss mice. MGL and MGH animals had a similar mean body weight, were raised in identical conditions, and were fed with a normal diet, rich in magnesium. These results together with the higher urinary noradrenaline excretion previously observed in the MGL line, indicate that the mere selection for genetic traits inducing low blood magnesium levels entails an increased catecholamine production. This phenomenon most probably accounts for the higher sensitivity and/or reactivity of MGL animals to stress. The possible role of magnesium-controlling genetic factors in the regulation of brain growth is also suggested.

High cardiac zinc levels in spontaneously hypertensive rats.

OBJECTIVES: Higher cardiac zinc levels have been observed previously in spontaneously hypertensive rats (SHR) compared with Wistar-Kyoto (WKY) rats. However, this difference was established in adult males only and needed to be confirmed on a larger number of animals of both sexes. We also explored the respective roles of genetic and environmental factors in the genesis of this zinc anomaly as well as the causal relations with hypertension. DESIGN: Cardiac zinc levels were determined in adult male and female SHR and WKY rats originating from various colonies and submitted to various experimental conditions (anaesthesia, stress). These determinations were also performed in 3-week prehypertensive SHR and in adult Wistar rats submitted or not to deoxycorticosterone acetate-salt-induced hypertension. METHOD: Zinc levels were measured by flame atomic absorption spectrophotometry. RESULTS: In adults, cardiac zinc content was significantly higher in SHR than in WKY rats irrespective of sex and experimental conditions. In young prehypertensive rats, the difference between SHR and WKY cardiac zinc levels was also very significant. Experimental hypertension induced in Wistar rats did not entail any significant rise in cardiac zinc levels. CONCLUSIONS: These findings indicated that the higher cardiac zinc of SHR is not secondary to blood pressure elevation. High erythrocyte zinc, previously described in SHR, together with the present data suggest the occurrence of a primary genetic defect leading to high intracellular zinc in SHR. The possible role of this zinc anomaly in the development of hypertension and/or cardiac hyperplasia is discussed.

Effect of pyridoxine on mice gastric ulcers and brain catecholamines after an immobilization stress.

Fifty adult female Swiss albino mice were injected with either 1.11 mg/kg body weight pyridoxine or saline, subsequently they were all submitted to an immobilization stress with a complete fast for 17 h. At the end of this period, the animals were sacrificed, the gastric mucosa was dissected for ulcer count, and brain noradrenaline, dopamine and serotonin were determined by liquid chromatography. In addition, 26 nonstressed mice were used as controls, 16 of them being fed at libitum and 10 submitted to the same fasting period as the first two groups. In the stressed animals, the average number of gastric ulcers per mouse was twice as large in the saline-treated group than in the pyridoxine-treated group (p < 0.05). With a single exception, no ulcer was found in the non stressed controls. Brain norepinephrine content was almost identical in fasting controls and in stressed mice treated with pyridoxine; in the stressed animals treated with saline, the average norepinephrine content was higher by 15% and in the fed controls lower by 11% than in the two preceding groups. Pyridoxine treatment entailed a very significant reduction (p < 0.002) of norepinephrine variability, mainly due to the absence of high values (> or = 750 ng/g of fresh brain) which occurred only in the saline-treated group. Similar results were yielded for brain dopamine. No variations were observed for brain serotonin. These results suggest the antistress effect of pyridoxine.

Tissue and blood magnesium levels in spontaneously hypertensive rats, at rest and in stressful conditions.

Magnesium (Mg) levels were measured by flame atomic absorption spectrophotometry in the blood (plasma, erythrocytes) and soft tissues (liver, brain, heart, aorta, kidneys, adrenals, spleen, thymus) of adult spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar Kyoto (WKY). In experiment 1, Mg determinations were performed on eight animals of each strain at rest. Mg levels were lower in brain (P less than or equal to 0.05), kidneys (P less than or equal to 2.10(-4] and erythrocytes P less than or equal to 0.01) in SHR than in WKY rats. Tissue water content was the same in the two strains. These results suggest the occurrence of lower intracellular Mg levels in SHR than in WKY. In experiment 2, 15 SHR and 15 WKY were submitted either to acute (1 d) or subacute (22 d) stresses or reared in restful conditions. Acute stress induced important Mg shifts leading to a decreased difference between SHR and WKY in most tissues and to an increased and more significant difference (P less than or equal to 0.01) in spleen and plasma Mg levels. Subacute stress was milder and had little effect. It is concluded that the results of experiment 1 cannot be attributed to the greater sensitivity of SHR to laboratory manipulations. When compared with previously published data our results nevertheless suggest an association between stress sensitivity and genetic factors regulating Mg metabolism.

A plasma factor inhibiting erythrocyte magnesium efflux.

When incubated at 37 degrees C for 5 h in a magnesium- and calcium-free phosphate buffer solution (PBS), rat and mouse erythrocytes lose 30-40% of their Mg content. However, no Mg loss is observed if these erythrocytes are incubated in their own plasma. In order to investigate this phenomenon, murine erythrocytes were incubated in PBS, in human and murine blood plasmas, and fetal calf serum diluted in PBS (1/4), and in PBS supplemented with MgCl2, CaCl2, and crystallized plasma proteins at concentrations equal to those obtained in plasma/PBS solutions. Erythrocyte Mg efflux was significantly inhibited (P = 10(-8] by diluted human and rat plasmas but the time course of this inhibition was different with these two kinds of plasmas (P = 10(-4]. Mouse plasma and fetal calf serum also entailed a significant inhibition of Mg efflux, while the addition of Mg, Ca, and purified plasma proteins in the incubation medium had little effect. Blood plasma thus contains a factor inhibiting Mg efflux from murine erythrocytes and this effect is not explained by its content of magnesium, calcium, and proteins.

Blood and tissue zinc levels in spontaneously hypertensive rats.

Zinc (Zn) determinations were performed on blood plasma and red cells, liver, heart, adrenals, and spleen of spontaneously hypertensive (SHR) and control normotensive (WKY) male rats, 20 weeks of age. SHR revealed higher red cell (p = 2 x 10(-5)) and heart (p = 0.007) Zn levels than WKY rats. The water content of organs was the same in the two strains. When compared with published data, these results suggest an association between high cell Zn levels and hypertension, the meaning of which is briefly discussed.

HLA- and H-2-associated variations of intra- and extracellular magnesium content.

Erythrocyte and plasma magnesium (EMg, PMg) levels have been shown to be genetically controlled in human and mouse. The possible association of these genetic factors with the major histocompatibility complex (MHC) (HLA and H-2) was investigated. Among unrelated adult male blood donors, HLA-B35 carriers have PMg (P less than 0.01) and EMg (P less than 0.0005) levels lower than those of noncarriers, while HLA-B38 carriers exhibit a significant (P less than 0.05) increase of both PMg and EMg levels when compared to the other individuals. Furthermore, HLA identical sibs have EMg values more similar than those of HLA different sibs. In the mouse, erythrocyte (P less than 0.001), plasma (P less than 0.001), liver (P less than 0.03), and spleen (P less than 0.04) Mg contents vary significantly according to H-2, with higher values being found in H-2k than in H-2q or H-2b congenic strains. However, non-MHC genes also have an influence on erythrocyte (P less than 10(-10], plasma (P less than 10(-10], spleen (P less than 10(-5], and kidney (P less than 10(-6] Mg contents as shown by differences between H-2 identical strains, which differ by the C3H and B10 genetic backgrounds. In conclusion, genetic factors controlling intra- and extracellular Mg levels are composed of at least three components: MHC (HLA and H-2)-associated genes, non-MHC genes, and tissue factors modulating the respective importance of the first two sets of factors. The mechanisms underlying this genetic system are discussed.