The production of secondary potassium depletion, sodium retention, nephrocalcinosis and hypercalcaemia by magnesium deficiency

Magnesium in hypertension: mechanisms and clinical implications

Hypertension is associated with increased risk of cardiovascular disease and death. Evidence suggests that Mg2+ depletion contributes to hypertension. It is estimated that 25% or more of the United States population experiences chronic, latent Mg2+ depletion. This review explores mechanisms by which Mg2+ influences blood pressure, modifying risk of hypertension and complicating its treatment. Mechanisms addressed include effects upon i) sympathetic tone, via the modulation of N-methyl-D-aspartate (NMDA) receptor and N-type Ca2+ channel activity, influencing catecholamine release from sympathetic nerve endings; ii) vascular tone, via alteration of L-type Ca2+ and endothelial nitric oxide synthase (eNOS) activity and prostacyclin release; iii) renal K+ handling, influencing systemic K+ balance and potentially indirectly influencing blood pressure; iv) aldosterone secretion from the adrenal cortex; and v) modulation of pro-hypertensive inflammatory processes in dendritic cells and macrophages, including activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome and stimulation of isolevuglandin (IsoLG) production. Discovery of these mechanisms has furthered our understanding of the pathogenesis of hypertension, with implications for treatment and has highlighted the role of Mg2+ balance in hypertension and cardiovascular disease.

The Association Between Serum Magnesium and Premenstrual Syndrome: a Systematic Review and Meta-Analysis of Observational Studies

A number of studies have assessed the association between serum magnesium (Mg) and premenstrual syndrome (PMS) in different population, but the findings have been inconclusive. Herein, we systematically reviewed available observational studies to elucidate the overall relationship between Mg and PMS. PubMed, Cochrane's library, ScienceDirect, Scopus, Google Scholar, and ISI web of science databases were searched for all available literature until January 2019 for studies evaluating the association between Mg and PMS. The Newcastle-Ottawa Quality Assessment Scale was used to assess the quality of observational studies. A total of 13 studies out of 196 met our inclusion criteria and were included in our systematic review and meta-analysis. There were no associations between serum magnesium and PMS (WMD - 0.04; 95% CI, - 0.14 to 0.06; P = 0.46) during follicular or serum/erythrocyte magnesium (WMD - 0.37; 95% CI, - 1.01 to 0.27; P = 0.25)/(WMD - 0.04; 95% CI, - 0.10 to 0.03; P = 0.26) and during luteal phase except for the sub-group of studies done outside of the US in which recent association became significant and means that serum Mg is lower in PMS subjects. According to what have been discussed, although our study did not show any significant association between serum/erythrocyte Mg and PMS except for serum Mg in luteal phase in the sub-group of studies done outside of the USA, heterogeneity between studies should be taken into accounts when interpreting these results. Additional well-designed clinical trials should be considered in future research to develop firm conclusions on the efficacy of magnesium on PMS.Registration number: CRD42018114473 .

Toward a broader understanding of aldosterone in congestive heart failure

Discovered some 50 years ago, aldosterone (ALDO) has come to be recognised as a mineralocorticoid hormone with well-known endocrine properties in epithelial cells that contribute to the pathophysiology of congestive heart failure. This includes Na + resorption at the expense of K+ excretion in classic target tissues: kidneys, colon, sweat and salivary glands. Though less well known, Mg2+ excretion is likewise enhanced by ALDO, while adrenal ALDO secretion is regulated by extracellular Mg2+ ([Mg2+ ]o). An emerging body of information has and continues to identify other endocrine actions of ALDO receptor-ligand binding. They include: promoting an efflux of cytosolic free Mg2+, or [Mg2+]i, in exchange for Na+ in such non-epithelial cells as peripheral blood mononuclear cells; its influence on endothelial cell function; and its central actions that involve regulation of cerebrospinal fluid composition produced by epithelial cells of the choroid plexus, activity of the hypothalamic paraventricular nucleus involved in Na+ appetite, Na+ and H2O excretion and sympathetic nerve activity, and the regulation of TNF-α production from central and/or peripheral sources. Extra-adrenal steroidogenesi and auto/paracrine properties of ALDO generated de novo in the cardiovasculature are now under investigation and preliminary findings suggest they contribute to tissue repair. The past decade has witnessed a revival of interest in this steroid molecule. In years to come, an even broader understanding of ALDO's contribution to the pathophysiology of congestive heart failure will undoubtedly emerge.

Treatment of ionized hypercalcemia in 12 cats (2006-2008) using PO-administered alendronate

Background

Long‐term treatment of cats with ionized hypercalcemia using alendronate has not been evaluated.

Hypothesis/Objectives

Alendronate is well tolerated in treatment of ionized hypercalcemia in cats.

Animals

A total of 12 cats with ionized hypercalcemia.

Methods

Prospective study of 12 cats with ionized hypercalcemia of idiopathic origin was identified by telephone and email communication with a convenience sample of consulting veterinarians. Cats were treated with alendronate at a dose of 5–20 mg per feline PO q7d. Serum ionized calcium concentration (iCa) was measured before beginning treatment with alendronate, and after 1, 3, and 6 months of treatment. Alendronate dosage was adjusted according to iCa. Evaluation included physical examination, CBC, biochemistry profile, and diagnostic imaging. The owners and referring veterinarians were questioned about any observed adverse effects. The Wilcoxon matched‐pairs signed rank test was used to compare baseline iCa to iCa at different time periods.

Results

Alendronate treatment resulted in a decrease in iCa in all 12 cats. The median percentage change in iCa was −13.2%, −15.9%, and −18.1% (range, −29.6 to +7.6; −30.5 to −1.9; −45.8 to +1.5%) at the 1, 3, and 6 month time points, respectively. Baseline iCa was significantly different from 1 month (P = .0042), 3 months (P = .0005), and 6 months (P = .0015). No adverse effects were reported for any of the cats.

Conclusions and Clinical Importance

Alendronate was well tolerated and decreased iCa in most cats for the 6‐month period of observation.

The influence of the parathyroid glands on the hypercalcemia of experimental magnesium depletion in the rat

Magnesium-deficient rats develop significant hypercalcemia, hypophosphatemia, and hyperphosphaturia. These changes suggest a state of hyperparathyroidism. This study examines the regulation of parathyroid gland activity in magnesium-deficient rats. Magnesium deficiency was induced in intact and chronically parathyroidectomized animals by feeding them a diet free of this cation. Control animals were pair fed and treated identically except for the inclusion of magnesium in their gavage solution.Magnesium-deficient rats with intact parathyroid glands developed significant hypercalcemia and hypophosphatemia. In addition, the concentration of ionic calcium in plasma was significantly elevated. In contrast, magnesium-deficient parathyroidectomized animals did not have a higher level of calcium in plasma than their nondeficient controls; they developed a decreased concentration of ionic calcium in the absence of a difference in the concentration of phosphate in plasma when compared with appropriate controls. The increased urinary excretion of phosphate was independent of the parathyriod status of the animals.It can be concluded that the hypercalcemia and hypophosphatemia of magnesium deficiency demands parathyroid gland activity and that the regulation of this activity is modified in the magnesium-deficient state to permit the maintenance of an elevated concentration of ionic calcium in plasma. Additional explanations must be found for the hyperphosphaturia.

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

The relation between extra- and intracellular electrolytes has been studied by means of percutaneous muscle biopsies in 107 patients with hypokalemia and/or treatment with diuretics. No relation was found between the extra- and intracellular concentrations of Na or Mg. The serum and muscle contents of K correlated weakly. The correlation coefficient tended to be stronger when S-creatinine was normal, total carbonate was between 25 and 30 mmol/l, muscle Mg content was greater than or equal to 3.95 mmol/100 g fat free dry solids, and when no treatment was given with digitalis and/or diuretics.

Magnesium and potassium interrelationships, experimental and clinical

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

Regulation of L-type Ca2+ channels in the heart: overview of recent advances

Regulation of L-type Ca2+ channels is complex, because many factors, such as phosphorylation, divalent cations, and proteins, specified or unspecified, have been shown to affect the channel activities. An additional complication is that these factors interact with one another to achieve final outcomes. Recent molecular technologies have helped to shed light on the mechanisms governing the activity of L-type Ca2+ channels. In this review article, three major topics concerning regulation of L-type Ca2+ channels in the heart are discussed, i.e. c-AMP dependent channel phosphorylation, role of magnesium (Mg2+), and the phenomenon of channel run-down.

Aldosteronism revisited: perspectives on less well-recognized actions of aldosterone

Aldosterone is a mineralocorticoid with protean actions in both epithelial and nonepithelial cells. These include endocrine properties of circulating aldosterone that promote Na(+) resorption at the expense of well-recognized K(+) excretion and less well-recognized Mg(2+) excretion in classic target tissues: kidneys, colon, and sweat and salivary glands. The regulation of adrenal aldosterone secretion by [Mg(2+)](o) is also less well appreciated. More recently recognized endocrine actions of aldosterone include induction of Mg(2+) efflux in exchange for Na(+) in such nonepithelial cells as peripheral-blood mononuclear cells and influence on epithelial cells of the choroid plexus, where aldosterone alters the composition of cerebrospinal fluid that contributes to blood-pressure regulation. An association between primary aldosteronism and idiopathic intracranial hypertension has recently been reported. Extraadrenal steroidogenesis with de novo aldosterone production by the cardiovasculature, where its auto-/paracrine properties may contribute to tissue repair at sites of injury, has been observed. These less well-recognized actions of aldosterone have led to a revival of interest in how this steroid molecule contributes to the pathophysiology of various clinical disorders.

The determination of magnesium in biological fluids and tissues by flame spectrophotometry

A flame spectrophotometric method for estimating magnesium in biological fluids and tissues is described. It may be applied to the Zeiss spectrophotometer PMQ II with flame attachment. Interferences are small, and recoveries from plasma and urine and from ashed faeces, soft tissue, and bone are satisfactory. Calcium can be measured on the same dilutions of plasma and urine and faecal ash. Sodium, potassium, calcium, and magnesium can be estimated on the same dilutions of soft tissue and bone ash. The plasma magnesium concentration of normal subjects falls within a narrow range. Differences between mean normal values previously reported may be partly attributed to the magnesium salt used in preparation of standard solutions.

The estimation of magnesium in small biological samples by flame spectrophotometry

Studies of human magnesium metabolism in this laboratory called for a simple and reliable method of estimating the magnesium content of large numbers of small biological specimens (Montgomery, 1960). It has been found that a technique involving the Unicam S.P. 900 flame spectrophotometer fulfils this need. Estimations have been made on serum, red cells, urine, and acid digests of muscle and faeces. A standard instrument was used, burning acetylene and air, with a new standard atomiser containing a metal jet. Readings were made at the atomic line of 285.2 mmu.

Plasma magnesium in health and disease

Simpler and more accurate flame spectrophotometric techniques are now available for estimating magnesium. Because of the development of modern electrolyte therapy, cases of hypo-magnesaemia are now encountered more frequently. The condition may lead to dangerous convulsions without sufficient warning. Some causes of hypomagnesaemia and hypermagnesaemia are presented.

Stability of brain content of magnesium in experimental hypomagnesemia

Magnesium is important in cerebral function. If there is a deficiency and neurological symptoms accrue, we hypothesised that Mg2+ deficiency causes neurological symptoms by decreasing the level of Mg2+ in cerebral tissue. The content of magnesium was determined in 12 brain structures in magnesium-deficient rats. Experiments were carried out for 40 days in two groups of Wistar male rats made magnesium-deficient (MD) by a well-controlled diet (50 mg of Mg2+/kg of food), and a control group (CG) rats fed normal diet (1 g of Mg2+/kg of food). At the end of the 40 days, the clinical signs of hypomagnesemia were sought in the MD rats and Mg2+ concentration levels were measured in the blood and brain. The results showed variable distribution of Mg2+ in the different brain structures, both in CG and MD rats; in the MD rats there is an important stability of global Mg2+ content of the brain. Although the global values for Mg2+ in the brain did not decline in MD rats, there was a significant decrease in Mg2+ in the brainstem. We conclude that the brain is able to maintain a stable concentration of Mg2+ during chronic hypomagnesemia, but its topographic variations could account for some of neurological signs accompanying this condition.

Impaired tyrosine-kinase activity of muscle insulin receptors from hypomagnesaemic rats

The effect of magnesium deficiency on glucose disposal, glucose-stimulated insulin secretion and insulin action on skeletal muscle was investigated in rats which were fed a low magnesium-containing diet for 4 days. Control rats were fed a standard diet. Compared to the control rats, the rats fed with low magnesium diet presented: 1) lower serum magnesium levels (0.45 +/- 0.02 vs 0.78 +/- 0.01 mmol/l, p < 0.001), 2) higher basal serum glucose (6.8 +/- 0.02 vs 5.5 +/- 0.2 mmol/l, p < 0.05) and similar basal serum insulin, 3) 40% reduction (p < 0.001) in the glucose disappearance rate after its i.v. administration, and 4) 45% reduction (p < 0.05) in the glucose-stimulated insulin secretion. The insulin action upon the glucose uptake by skeletal muscle was determined by means of hindquarter perfusions. Compared with control rats, magnesium-deficient rats presented: 1) normal basal glucose uptake, 2) lower stimulatory effect on the glucose uptake by insulin at the concentrations of 5 x 10(-10) mol/l (3.0 +/- 0.9 vs 5.4 +/- 0.6, p < 0.05) and 5 x 10(-9) mol/l (6.3 +/- 0.5 vs 8.0 +/- 0.5, p < 0.05), 3) normal glucose uptake at a maximal insulin concentration of 1 x 10(-7) mol/l, and 4) 50% reduction in the insulin sensitivity (ED50: 1.3 +/- 0.3 vs 0.55 +/- 0.1 mol/l, p < 0.05). In partially purified insulin receptors prepared from gastrocnemius muscle, 125I-insulin binding was similar in both groups of rats. However, the autophosphorylation of the beta-subunit of the insulin receptor was significantly reduced by 50% in magnesium-deficient rats and the tyrosine kinase activity of insulin receptors toward the exogenous substrate Poly Glu4; Tyr 1 was also reduced (p < 0.05) by hypomagnesaemia. The abundance of the insulin-sensitive glucose transporter protein (muscle/fat GLUT4), measured by Western blot analysis using polyclonal antisera, was similar in muscles of control and hypomagnesaemic rats. These findings indicate that hypomagnesaemia has a deleterious effect on glucose metabolism due to an impairment of both insulin secretion and action. The insulin resistance observed in skeletal muscle of magnesium-deficient rats may be attributed, at least in part, to a defective tyrosine kinase activity of insulin receptors.

Mechanism of increased erythrocyte membrane fluidity during magnesium deficiency in weanling rats

The erythrocyte membrane was investigated in weanling male rats pair fed with magnesium-deficient and control diets for 8 days. Fluorescence polarization studies revealed a 15% increase in the fluidity of membranes from deficient rats. A similar increase in the fluidity of liposomes indicated that protein was not involved. The change was associated with decreased osmotic fragility of intact erythrocytes; the cells lost their biconcavity and had a flattened appearance with surface irregularities. Analysis of the membranes showed decreased amounts of magnesium, cholesterol, and sphingomyelin in the deficient group. The reduced ratios of cholesterol to phospholipid and sphingomyelin to phosphatidylcholine were consistent with the increased fluidity. Addition of physiological amounts of magnesium to the medium rigidified membranes incubated in tris(hydroxymethyl)-aminomethane buffer, and this was prevented by the presence of EDTA. Cross-incubation experiments with erythrocyte ghosts and plasma from the two groups of rats showed that magnesium-deficient plasma increased the fluidity of control ghosts and control plasma rigidified ghosts from magnesium-deficient rats. Addition of sufficient magnesium chloride to raise the magnesium content of deficient plasma to normal had no significant effect. These results show that the increased fluidity of the erythrocyte membrane in magnesium deficiency is due to physicochemical exchange with the plasma. Although magnesium can directly influence membrane fluidity, the change during its deficiency in vivo is mainly mediated indirectly via disturbances in lipid metabolism.

Nutritional and toxicological aspects of the Maillard browning reaction in foods

The Maillard, or nonenzymatic, browning reaction between carbonyl and amino groups is a common reaction in foods which undergo thermal processing. The Maillard reaction is a desirable consequence of many industrial and domestic processes and is responsible for the attractive flavor and brown color of some cooked foods. An early recognized consequence of the Maillard reaction was the destruction of some essential amino acids, such as lysine. More recently, research interest has focused on the production of toxic and antinutritive compounds. This review examines the nutritional and toxicological consequences of the Maillard reaction in light of the findings of such research. In particular, the effect of Maillard reaction products on the digestion, absorption, and excretion of nutrients is considered. The cytotoxicity, mutagenicity, and immunochemical aspects of selected Maillard reaction products are also examined and suggestions are made for future areas of investigation.

On the prevention and treatment of calcification disorders of old age

From several investigations it is known that magnesium oxide or hydroxide therapy causes a considerable delay of kidney stone recurrence in man. Further, it is known that the mortality of populations due to cardiovascular disease in areas with hard drinking water containing more magnesium and having a higher Mg/Ca ratio than soft water, is considerably lower than in soft water areas. In the present study a physiological model for the homeostasis of calcium and phosphate is given. It is shown that and why a slight magnesium deficiency causes the pH of bone extracellular fluid to decrease at or below the pH level of the other body fluids. This decrease makes the other body fluids supersaturated with octocalcium phosphate and this is the prime reason for calcification disorders in the soft tissues. Therefore, the hypothesis is proposed that soft tissue calcifications can be stopped and even prevented by magnesium therapy. However, they are not reversible and treatment with chelate therapy is contraindicated.

Muscle involvement during postnatal protein calorie malnutrition and recovery in rhesus monkeys

The effect of protein calorie malnutrition (PCM) and, thereafter, nutritional rehabilitation on neuromuscular dysfunction was evaluated electromyographically, histopathologically and biochemically in 24 young, growing, healthy rhesus monkeys. There were 2 control and 2 PCM groups with 6 animals in each group. Animals of one control and one PCM group were killed at 10-12 weeks and those of the second PCM group were rehabilitated and killed together with the second control group at 20-22 weeks. The animals with PCM demonstrated irritability, muscular wasting, weight loss and reduced physical activity. The electromyographic findings showed a myopathic pattern revealed by significant reduction in motor unit potential duration and amplitude, and amplitude of interference pattern at maximum effort. The histopathological abnormalities were non-specific and consisted of rare obliterations of cross striations and streaming fibrillar appearance, mild increase in epimysial and perimysial tissue and 29-34% reduction in fibre size. A statistically significant reduction in motor nerve conduction velocity of median, ulnar, common peroneal and tibial nerves was found. The muscle Na and K were evaluated in all groups of animals. Muscle K content was reduced and Na concentration was augmented following PCM. The change in concentration of electrolytes within the fibres and reduction in the diameter of muscle fibres could be related to the observed functional alterations. These changes returned to normal in rehabilitated group.

Magnesium deficiency: pathogenesis, prevalence, and clinical implications

Hypomagnesemia is probably the most underdiagnosed electrolyte deficiency in current medical practice. Patients with cardiovascular disease who are at greatest risk for the development of magnesium deficiency are those treated with diuretics or digitalis. Both potassium and magnesium deficiencies are associated with increased ventricular ectopy and may increase the risk of sudden unexpected death. Refractory potassium repletion can be caused by concomitant magnesium depletion, and can be corrected with magnesium supplementation. Routine serum magnesium determination is recommended whenever the testing of electrolyte levels is required, especially in patients taking diuretic drugs or digitalis. Because hypomagnesemia is not necessarily present in a magnesium-deficient state, it is recommended that both potassium and magnesium be repleted in patients with hypokalemia. Potassium-/magnesium-sparing diuretics may be helpful in the prevention of these electrolyte deficiencies.

Disorders of divalent ions and vitamin D metabolism in chronic alcoholism

This chapter reviews the pathogenesis of disordered divalent mineral and bone metabolism in alcoholism, emphasizing the role of impaired vitamin D physiology. Normally, vitamin D metabolites are derived principally from cholecalciferol, which is synthesized in the skin via the energy of sunlight. Most alcoholics have subnormal levels of 25-hydroxyvitamin D [25(OH)D]. Those with Laennec's cirrhosis also have low levels of vitamin D binding protein due to impaired hepatic protein synthesis and as a result, have low serum concentrations of total, but not free, 1,25-dihydroxyvitamin D. The causes of 25(OH)D deficiency in alcoholics include reduced hepatic 25-hydroxylase activity, lack of sun exposure, inadequate dietary intake, and malabsorption. Hypomagnesemia and hypophosphatemia, which are very common in hospitalized alcoholics, result from deficient intake, malabsorption, excessive renal losses, and cellular uptake of both ions. Hypocalcemia in alcoholics is caused primarily by hypoalbuminemia but can result also from deficient intake, malabsorption, hypomagnesemia, and renal calcium wastage. Low vitamin D activity may contribute significantly to the calcium and phosphate deficiencies. Osteoporosis is extremely common in alcoholics whereas osteomalacia is exceptional. However, both bone disorders respond well to vitamin D therapy. Thus, alcoholics should be screened periodically for vitamin D deficiency and osteopenia, and when either is detected they should receive vitamin D supplements.

Magnesium deficiency. Causes and clinical implications

The many causes of clinical magnesium deficiency can be placed into 2 categories: diminished intake of magnesium, and enhanced losses of magnesium, either through the gastrointestinal tract or through the kidneys. Examples of the first category include alcoholism, starvation, anorexia due to neoplastic disease and/or chemotherapy. Examples of the second category include severe diarrhoeal states, gastrointestinal fistulae, malabsorption, diuretic therapy and gentamicin therapy. Estimates of the prevalence of clinical hypomagnesaemia range from 6 to 11% in hospitalised patients. Serum predictors of associated clinical magnesium depletion include hypokalaemia (42%), hyponatraemia (23%), hypophosphataemia (22%) and hypocalcaemia (20%). Experimental and clinical observations strongly support the view that magnesium and potassium are closely linked at the cellular level. Magnesium has been demonstrated to be important in cell energetics (Mg++-activated ATPase), in maintenance of the integrity of cell membranes, retardation of cell loss of potassium, as well as enhancing repletion of cell potassium. While translation of these experimental observations into clinical terms encompasses a wide spectrum of illnesses, there is special relevance in considering the role of magnesium in repletion and maintenance of cell potassium in 2 clinical instances: (a) patients treated with digitalis and diuretics; and (b) hypertensive patients. In these types of patients not only potassium but also magnesium should be administered together to avoid the problem of cell potassium depletion and refractory potassium repletion associated with coexisting and uncorrected magnesium depletion.

Magnesium, electrolyte transport and coronary vascular tone

Coronary heart diseases (CHD) have high indices of mortality and morbidity. A number of CHD and myocardial ischaemic syndromes such as unstable angina pectoris, sudden death ischaemic heart disease, acute myocardial infarction and ventricular arrhythmias have been associated with losses of myocardial magnesium and potassium. Mg++ ions are essential for regulation of Na+ and K+ transport across cell membranes, including those found in cardiac and vascular smooth muscle cells. Mg++ activates an Na+-K+-ATPase pump which in turn plays a major role in regulating Na+-K+ transport. Loss of cellular Mg++ results in loss of critically important phosphagens: MgATP and creatine phosphate. Thus, under conditions where cellular Mg++ is depleted (e.g. hypoxia, ischaemia, anoxia), the Na+-K+ pump and phosphagen stores will be compromised, leading to alterations in resting membrane potentials. Cellular Mg++ depletion has been found to result in concomitant depletion of K+ in a number of cells, including cardiac and vascular muscles. The consequences of these events are often production of cardiac arrhythmias. Myocardial and vascular injury lead to disturbances in electrolyte transport across cell membranes, whereby Na+ and Ca++ uptakes are enhanced and, just prior or concomitantly, Mg++ and K+ are lost. Such electrolyte disturbances often lead to necrotic foci. Considerable evidence has accumulated to indicate that the extracellular concentration of Mg++ is important in control of arterial tone and blood pressure via pressure via regulation of vascular membrane Mg++-Ca++ exchange sites. A reduction in the extracellular Mg++ concentration can produce hypertension, coronary vasospasm and potentiation of vasoconstrictor agents by allowing excess entry of Ca++; concomitantly, the potency of vasodilator agents is reduced. Alterations in vascular membrane Mg++ results in arterial and arteriolar membranes which are 'leaky', thus contributing to the cellular reduction in K+ and gain of Na+ and Ca+. Alterations in extracellular K+ or Na+ concentrations over physiological ranges, in the face of a Mg++ deficit, can exacerbate the coronary vasospasm noted with reduction in only extracellular Mg++. Since free Mg++ ions are necessary for maintaining Ca+ ions (both plasma membrane-bound and sarcoplasmic reticulum membrane-bound via Ca++ ATPases), intracellular free Mg++ would rise in conditions which result in cellular loss of Mg++, thereby exacerbating and contributing to elevation of blood pressure and coronary vasospasm.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on the nutrition of rainbow trout (Salmo gairdneri). Magnesium deficiency: the effect of feeding with a Mg-supplemented diet

1. For a period of 8 weeks, rainbow trout (Salmo gairdneri), mean initial weight 21 g, were given either a low-magnesium or control diet containing 0·03 and 0·58 g Mg/kg diet respectively. Both groups of trout were then given the control diet for a further 11 weeks.

2. Weight gains over the initial 8-week period were lowest in the Mg-deficient trout. Feeding the deficient fish the control diet rapidly improved growth rate until it was the same as that of the control trout.

3. Plasma Mg was significantly lower in the Mg-deficient trout at week 8. Feeding with the control diet for 11 weeks did not increase plasma Mg. Few changes were observed in the plasma concentrations of the other electrolytes.

4. Renal calcium concentrations were unaffected by dietary Mg levels. Similarly, the renal levels of phosphorus, sodium and potassium all fell within the range found in normal rainbow trout.

5. Muscle Mg concentrations were reduced in those trout given the Mg-deficient diet. Feeding with the control diet for a further 11 weeks increased muscle Mg but the level was still significantly lower than that found in trout given the control diet for 19 weeks.

6. The bone ash Mg concentration was significantly lower, and the Ca higher, in the deficient fish at week 8, when compared with the control group.

7. When compared with the value at the start of the experiment, total bone Mg fell slightly in the deficient trout over the initial 8-week period, but increased in the control group of fish. Feeding with the control diet for a further 11 weeks increased total bone Mg in both Mg-deficient trout and control trout.

8. The results show that the Mg deficiency imposed on the rainbow trout was of limited severity and almost complete recovery was obtained when the control diet was fed.

Magnesium deficiency after ileal resections for Crohn's disease

The magnesium status of the body was studied in 87 patients with various lengths of small-bowel resections for Crohn's disease. The urinary magnesium excretion decreased with increasing resection length, and so did the concentration of magnesium in muscle. Muscular fatigue, an early symptom of magnesium deficiency, was positively correlated to a pathologically low concentration of muscle magnesium. It was concluded that clinically important magnesium deficiency, which was not detected by determination of serum magnesium, occurred in patients with ileal resections exceeding 75 cm.

Hypomagnesemia and hypokalemia in 1,000 treated ambulatory hypertensive patients

This study reports on the prevalence of hypomagnesemia (4.5%), by the stringent criterion of less than or equal to 1.25 mEq/L, and hypokalemia (17%) in 1,000 ambulatory hypertensive patients under treatment at the VA Medical Center, Oklahoma City. The hypomagnesemic group required a greater number of antihypertensive medications than the nonhypomagnesemic patients to maintain their blood pressure in the acceptable range. These observations suggest the possibility that magnesium may play an important role in blood pressure control and indicate the need for further studies.