Mechanisms and causes of hypomagnesemia.

Purpose Of Review: Identification of the mechanisms of magnesium absorption and reabsorption has markedly enhanced our understanding of the causes of hypomagnesemia.

Recent Findings: New gastrointestinal and renal causes of hypomagnesemia have been recently documented.

Summary: The recognition of new mechanisms and causes of magnesium absorption and reabsorption should enhance the ability to monitor patients at risk for hypomagnesemia and improve our ability to mitigate the serious symptoms associated with this disorder.

Commentary: CME and its role in the academic medical center: increasing integration, adding value.

Continuing medical education (CME), as it is currently structured, funded, and institutionalized, plays a marginal role in the academic medical center (AMC). In contrast, several models of more effective, integrated CME exist, and these enable the AMC to better achieve its potential in education, research, and health care delivery. Examples of such models are presented, emphasizing quality and performance improvement; regional, national, and public outreach; faculty and staff development; and research and scholarly activity.

Dietary intake and the risk of coronary heart disease among the coconut-consuming Minangkabau in West Sumatra, Indonesia.

Several nutrition and non-nutritional pathways are recognised in the development and occurrence of cardiovascular disease. In many populations, high intakes of saturated fat are associated with elevated serum cholesterol concentrations and increased coronary heart disease (CHD) mortality. However, several studies report that hyperlipidaemia and heart diseases are not common among populations who consume coconut, a source of saturated fat.

Pseudohyperphosphatemia in a hyperphosphatemic hemodialysis patient.

Hyperphosphatemia is a predictable consequence of end-stage renal disease. Pseudohyperphosphatemia is a spurious elevation of serum phosphate in samples containing a substance that interferes with the laboratory assay for phosphate. The most common cause is a paraprotein in disorders such as Waldenström's macroglobulinemia and multiple myeloma.

Contemporary Minangkabau food culture in West Sumatra, Indonesia.

Diet has a strong relationship with food culture and changes in it are likely to be involved in the pathogenesis of newly emergent degenerative diseases. To obtain in-depth opinions about the food culture of Minangkabau people, focus group discussions were conducted in a Minangkabau region, represented by four villages in West Sumatra, Indonesia, from January to March 1999. The members of the discussion groups were principally women aged from 35 to 82 years old.

Cardiovascular actions of magnesium.

Intracellular magnesium is an important modulator of calcium and potassium channels in cardiac myocytes. Hypomagnesemia is common in hospitalized patients and may contribute significantly to cardiac morbidity and mortality, particularly in states associated with myocardial ischemia. Therefore, it is important to maintain the plasma magnesium concentration within the normal range in asymptomatic patients and in patients with cardiac disease as prophylaxis against the occurrence of significant arrhythmias.

Serum retinol concentrations in children are affected by food sources of beta-carotene, fat intake, and anthelmintic drug treatment.

The provision of vitamin A in food sources of beta-carotene is an alternative to the distribution of high-dose capsules. To examine factors that may influence the success of food-based programs, a study was carried out in Sumatra, Indonesia, of the effect of food sources of beta-carotene, extra dietary fat, and Ascaris lumbricoides infection on serum retinol concentrations in children. Meals and snacks with various amounts of beta-carotene and fat were fed at midday to children 3-6 y of age for 3 wk.

Hypomagnesemia: renal magnesium handling.

Magnesium is an important constituent of the intracellular space that affects a number of intracellular and whole body functions. Magnesium balance depends on intake and renal excretion, which is regulated mainly in the thick ascending limb of the loop of Henle. The complex hormonal modulation that responds to changes in plasma concentration of other ions such as calcium and potassium is lacking for magnesium.

Macronutrient intake of elderly people in the Padang area,West Sumatra, Indonesia.

We examined the macronutrient intake of residents in Padang area, West Sumatra, Indonesia. The daily energy intake (1130±420 kcal) of elderly people in a rural traditional group was significantly lower than that in an urbanised "modernised" group (1700±460 kcal) (p<0.01).

Effects of intracellular magnesium on calcium, potassium and chloride channels.

Intracellular free magnesium activity approximates 0.6-0.8 mM.

Divalent cations modulate the transient outward current in rat ventricular myocytes.

The modulation of the transient outward K+ current (Ito) by divalent cations was studied in enzymatically isolated rat ventricular myocytes with the whole cell patch-clamp technique. At holding potentials negative to -70 mV, 1 mM Cd2+ suppressed Ito, whereas, at potentials positive to -50 mV, the current was augmented. These effects were caused by shifts in the voltage dependence of both activation and inactivation of Ito toward more positive potentials.

Cytosolic magnesium modulates calcium channel activity in mammalian ventricular cells.

The effect of cytosolic free Mg2+ concentration on the regulation of myocardial function was studied by dialyzing isolated guinea pig ventricular myocytes with different internal Mg2+ concentrations [( Mg2+]i). We found that elevation of [Mg2+]i shortened the action potential and suppressed the Ca2+ current. Mean values recorded for action potential duration in cells dialyzed with solutions containing 0, 1.

Benzodiazepines inhibit transport-related oxygen consumption in thick ascending limb.

Specific binding sites for benzodiazepines (BZD) have been identified in several nonneuronal tissues including the kidney where they are localized predominantly to the tubular epithelium of the thick ascending limb of Henle's loop (TALH). The physiological function of these nonneuronal (peripheral) BZD-binding sites is undefined, but it has been suggested that they may represent receptors for putative endogenous ligands that may modulate cell function. In the current study, we examined the in vitro effects of diazepam and Ro5-4864, a specific peripheral BZD-receptor agonist, on the oxygen consumption of medullary TALH tubule suspensions of rabbit kidney.

Benzodiazepines stimulate sodium ion transport in frog skin epithelium.

Benzodiazepine binding sites are present in a variety of non-neuronal tissues including the kidney where they are localized to distal nephron segments. It is postulated that renal binding sites are involved in modulating ion transport. This study examined the effects of two benzodiazepines on sodium transport in frog skin epithelium, a model system for sodium transport in renal collecting duct.

Role of calcium in chloride-secreting epithelia.

There are a number of well-characterized chloride-secreting epithelia. The role of cyclic AMP in mediating chloride secretion in these tissues is well established. The role of calcium is less well established, although a substantial body of evidence points to a significant mediator role of calcium in the modulation of chloride secretion.

Thiazides stimulate calcium absorption in urinary bladder of winter flounder.

Thiazides inhibit voltage-independent NaCl absorption in the urinary bladder of the winter flounder presumably by blocking an electroneutral mucosal Na/Cl co-transporter. As thiazides stimulate calcium absorption in mammalian distal convoluted tubule while inhibiting NaCl absorption, we studied the effects of hydrochlorothiazide (HCTZ) on unidirectional 45Ca fluxes and intracellular electrical potential in short-circuited bladders to examine possible mechanisms of HCTZ effects on calcium transport. Basal secretory calcium flux was, on average, slightly larger than absorptive flux, reflecting small net calcium secretion.

Case-control study of risk factors for idiopathic calcium nephrolithiasis.

We compared epidemiological risk factors and urine excretion of calcium, phosphate, uric acid, urea nitrogen, sodium, potassium, and fluid volume in recurrent idiopathic calcium stone-formers and in a control group of age- and sex-matched normal volunteers. Stone-formers were less likely than normal subjects to have followed a low-calorie diet, but body weight did not differ between the two groups. Daily urine calcium excretion was a graded risk factor for stone formation throughout its range.

Relationships between calcium and chloride transport in frog skin glands.

Frog skin gland, a furosemide-sensitive Cl(-)-secreting epithelium, exhibits Cl(-)-dependent Ca2+ secretion in response to stimulation by beta-adrenergic agonists. In this study, we further explored the relationships between Cl- and Ca2+ secretion in frog skin using 45Ca fluxes and short-circulating technique. On addition of isoproterenol (ISO) or 8-(p-chlorophenylthio)-cAMP, a significant positive correlation was demonstrated between Ca2+ secretion and Cl- secretion.

cAMP- and beta-adrenergic-stimulated chloride-dependent Ca2+ secretion in frog skin.

This study examined the possible existence and nature of Ca2+ transport in frog skin using 45Ca fluxes and short-circuiting technique. Following the addition to full-thickness frog skin (FTFS) of 8-[p-chlorophenylthio]cAMP (8-CPT-cAMP), forskolin, or 1-methyl-3-isobutylxanthine, the secretory Ca2+ flux increased severalfold, inducing net Ca2+ secretion. The absorptive flux was unchanged.

The uricosuric effect of oxaprozin in humans.

The effects of oxaprozin, a new investigational propionic acid analogue, and indomethacin on uric acid metabolism were compared in 12 healthy volunteers receiving either agent, first as a single dose and then daily for seven days. While indomethacin did not alter either serum or urinary uric acid values, oxaprozin caused a fall in serum uric acid levels from 5.8 +/- 0.