Magnesium status and excretion in age-matched subjects with normal and elevated blood pressures

Transient receptor potential melastatin 6 and 7 channels, magnesium transport, and vascular biology: implications in hypertension

Magnesium, an essential intracellular cation, is critically involved in many biochemical reactions involved in the regulation of vascular tone and integrity. Decreased magnesium concentration has been implicated in altered vascular reactivity, endothelial dysfunction, vascular inflammation, and structural remodeling, processes important in vascular changes and target organ damage associated with hypertension. Until recently, very little was known about mechanisms regulating cellular magnesium homeostasis, and processes controlling transmembrane magnesium transport had been demonstrated only at the functional level. Two cation channels of the transient receptor potential melastatin (TRPM) cation channel family have now been identified as magnesium transporters, TRPM6 and TRPM7. These unique proteins, termed chanzymes because they possess a channel and a kinase domain, are differentially expressed, with TRPM6 being found primarily in epithelial cells and TRPM7 occurring ubiquitously. Vascular TRPM7 is modulated by vasoactive agents, pressure, stretch, and osmotic changes and may be a novel mechanotransducer. In addition to its magnesium transporter function, TRPM7 has been implicated as a signaling kinase involved in vascular smooth muscle cell growth, apoptosis, adhesion, contraction, cytoskeletal organization, and migration, important processes involved in vascular remodeling associated with hypertension and other vascular diseases. Emerging evidence suggests that vascular TRPM7 function may be altered in hypertension. This review discusses the importance of magnesium in vascular biology and implications in hypertension and highlights the transport systems, particularly TRPM6 and TRPM7, which may play a role in the control of vascular magnesium homeostasis. Since the recent identification and characterization of Mg2+-selective transporters, there has been enormous interest in the field. However, there is still a paucity of information, and much research is needed to clarify the exact mechanisms of magnesium regulation in the cardiovascular system and the implications of aberrant transmembrane magnesium transport in the pathogenesis of hypertension and other vascular diseases.

Diet and arterial hypertension: is the sodium ion alone important?

Hypertension is a widespread phenomenon whose ultimate cause is still unknown. Many factors contribute to this disease, and partially for this reason, hypertension responds to different treatments in different individuals. It is difficult to generalize about therapies for general populations. In particular, the role of electrolytes in hypertension varies widely across individuals. This review focuses its attention on sodium, potassium, calcium, and magnesium ions in order to investigate whether these electrolytes play a role in the pathogenesis of arterial hypertension and its treatment. Some individuals are especially sensitive to sodium, and changing their intake of dietary sodium may lead to variations in the levels of the other electrolytes. These changes in electrolyte levels can complicate treatments for arterial hypertension in some patients.

Relationship of serum and dietary magnesium to incident hypertension: the Atherosclerosis Risk in Communities (ARIC) Study

PURPOSE

To examine the relationship of serum and dietary magnesium (Mg) with incident hypertension. The setting was the Atherosclerosis Risk in Communities (ARIC) Study, which included a biracial cohort, aged 45-64 years, from four U.S. communities.

METHODS

This analysis included 7731 participants (4190 women and 3541 men) free of hypertension at baseline and followed six years. Fasting serum Mg was measured, and usual dietary intake was assessed with a food frequency questionnaire.

RESULTS

After adjustment for age, race, and a number of other risk factors, the odds of incident hypertension across ascending quartiles of serum Mg were 1.0, 0.79, 0.85, and 0.70 in women (p trend = 0.01) and 1.0, 0.87, 0.87, and 0.82 in men (p trend = 0.16). We found no association between dietary Mg intake and incident hypertension. These associations were attenuated after the addition of baseline systolic blood pressure to the models.

CONCLUSIONS

This study suggests that low Mg may play a modest role in the development of hypertension.

Urinary phosphate/creatinine, calcium/creatinine, and magnesium/creatinine ratios in a healthy pediatric population

OBJECTIVE

To determine reference values for urinary phosphate/creatinine (Cr) concentration ratios and to complete reference values for urinary calcium/creatinine and magnesium/creatinine ratios in the second morning urine sample of healthy infants, children, and adolescents.

DESIGN

Urinary P/Cr, Ca/Cr, and Mg/Cr ratios were determined from the second morning urine sample. Two urine samples were obtained 1 week apart from most subjects to assess reproducibility.

SETTING

Kindergartens and schools of Lausanne, Switzerland.

PARTICIPANTS

A total of 410 healthy children aged 1 month to 17 years (197 girls and 213 boys) participated in the study.

RESULTS

The 5th and 95th percentiles were estimated from 664 urine samples. There were no differences related to sex. A nonlinear regression in terms of age was used to smooth the estimated percentiles yielding reference curves from which critical values may be obtained for any given age. The 95th percentile for urinary Ca/Cr and Mg/Cr agreed with previously reported values in children older than 7 years. The upper limit of the three solute/creatinine ratios decreased significantly with age: for urinary P/Cr from 19.0 mol/mol at 1 month to 2.7 at 14 years; for urinary Ca/Cr from 2.2 to 0.7 mol/mol, and for urinary Mg/Cr from 2.2 to 0.6 mol/mol. Lower limits varied little. Interindividual and intraindividual variations decreased with age.

CONCLUSIONS

Urinary P/Cr, Ca/Cr, and Mg/Cr ratios vary strongly with age. We provide reference values, expressed both in SI and in mass units, for urinary P/Cr, Ca/Cr, and Mg/Cr in children aged one month to 17 years.

Effect of renal perfusion pressure on excretion of calcium, magnesium, and phosphate in the rat

Abnormalities in renal handling of calcium, magnesium, or phosphate have been implicated in the development and/or maintenance of human hypertension. We have shown recently that renal excretion of these ions is correlated to blood pressure in Dahl salt-sensitive as well as salt-resistant rats. The present study was designed to determine whether renal perfusion pressure per se could affect excretion of these ions. Urinary excretion of calcium, magnesium, and phosphate was studied in anaesthetized Sprague-Dawley rats under basal conditions and during an intravenous infusion of angiotensin II (ANG II), vasopressin (AVP) or phenylephrine (PE). A cuff, placed around the aorta between the two renal arteries, allowed maintenance of normal perfusion pressure in the left kidney, while that in the right kidney was allowed to rise. Infusion of pressor agents raised mean arterial blood pressure to comparable levels (means +/- SE): ANG II (n = 7), before = 102 +/- 4, during = 133 +/- 3 mmHg, AVP (n = 8), before = 110 +/- 7, during = 136 +/- 5 mmHg, PE (n = 6), before = 111 +/- 6, during = 141 +/- 6 mmHg. Although there was no difference in excretion of calcium, magnesium and phosphate between the two kidneys under basal conditions, infusion of ANG II or PE induced hypercalciuria, hypermagnesiuria and hyperphosphaturia in the right kidney which was exposed to the increased arterial pressure. Such effects did not appear in the pressure-controlled left kidney. Infusion of AVP was associated with reduced excretion of calcium and magnesium, and increased excretion of phosphate, in the normotensive kidney. The response to the similarly increased renal perfusion pressure in this group was also reduced for calcium and magnesium, and enhanced for phosphate. The results indicate (1) renal excretion of calcium, magnesium and phosphate is renal perfusion pressure-dependent; the higher the renal perfusion pressure, the greater the excretion of these ions. (2) Independently of perfusion pressure, AVP can inhibit phosphate reabsorption and stimulate divalent cation reabsorption.