Electrolyte content of serum, erythrocyte, kidney and heart tissue in salt induced hypertensive rats

Effects of magnesium supplementation on electrophysiological remodeling of cardiac myocytes in L-NAME induced hypertensive rats

Hypertension is one of the major risk factors of cardiac hypertrophy and magnesium deficiency is suggested to be a contributing factor in the progression of this complication. In this study, we aimed to investigate the relationship between intracellular free Mg(2+) levels and electrophysiological changes developed in the myocardium of L-NAME induced hypertensive rats. Hypertension was induced by administration of 40 mg/kg of L-NAME for 6 weeks, while magnesium treated rats fed with a diet supplemented with 1 g/kg of MgO for the same period. L-NAME administration for 6 weeks elicited a significant increase in blood pressure which was corrected with MgO treatment; thereby cardiac hypertrophy developing secondary to hypertension was prevented. Cytosolic free magnesium levels of ventricular myocytes were significantly decreased with hypertension and magnesium administration restored these changes. Hypertension significantly decreased the fractional shortening with slowing of shortening kinetics in left ventricular myocytes whereas magnesium treatment was capable of restoring hypertension-induced contractile dysfunction. Long-term magnesium treatment significantly restored the hypertension-induced prolongation in action potentials of ventricular myocytes and suppressed Ito and Iss currents. In contrast, hypertension dependent decrement in intracellular Mg(2+) level did not cause a significant change in L-type Ca(2+) currents, SR Ca(2+) content and NCX activity. Nevertheless, hypertension mediated increase in superoxide anion, hydrogen peroxide and protein oxidation mitigated with magnesium treatment. In conclusion, magnesium administration improves mechanical abnormalities observed in hypertensive rat ventricular myocytes due to reduced oxidative stress. It is likely that, changes in intracellular magnesium balance may contribute to the pathophysiology of chronic heart diseases.

Inhibitory Effect of Fluoride on Na+,K+ ATPase Activity in Human Erythrocyte Membrane

The present study was performed to evaluate the role of long-term consumption of excessive fluoride on electrolyte homeostasis and their transporting mechanisms in erythrocytes of subjects afflicted with dental and skeletal fluorosis. A total of 620 adult (20-50 years) Indian residents participated in this study: 258 men and 242 women exposed to high concentrations of fluoride and 120 age and gender-matched control subjects. Erythrocytes were isolated from blood samples, washed, and used for the estimation of intraerythrocyte sodium and potassium concentrations. Na+,K+ ATPase activity was determined spectrophotometrically from a ghost erythrocyte membrane prepared by osmotic lysis. Erythrocyte analytes were correlated with the water and serum fluoride concentrations by Pearson's bivariate correlation and regression analysis. Results indicated a significant increase in intraerythrocyte sodium (F=14306.265, P<0.0001) in subjects from endemic fluorosis study groups as compared to controls. A significant (P<0.05) positive correlation of intracellular sodium was found with water and serum fluoride concentrations. Mean concentration of intraerythrocytic potassium ions showed significant reduction (F=9136.318, P<0.0001) in subjects exposed to fluoride. A significant (P<0.05) negative correlation of potassium ions was noted with water and serum fluoride concentrations. Na+,K+ ATPase activity was significantly declined (F=1572.763, P<0.0001) in subjects exposed to fluoride. A significant (P<0.05) inverse relationship of Na+,K+ ATPase activity was revealed with water and serum fluoride concentrations.

The effects of medicinal plants on renal function and blood pressure in diabetes mellitus

Abstract

Diabetes mellitus is one of the most common chronic global diseases affecting children and adolescents in both the developed and developing nations. The major types of diabetes mellitus are type 1 and type 2, the former arising from inadequate production of insulin due to pancreatic β-cell dysfunction, and the latter from reduced sensitivity to insulin in the target tissues and/or inadequate insulin secretion. Sustained hyperglycaemia is a common result of uncontrolled diabetes and, over time, can damage the heart, eyes, kidneys and nerves, mainly through deteriorating blood vessels supplying the organs. Microvascular (retinopathy and nephropathy) and macrovascular (atherosclerotic) disorders are the leading causes of morbidity and mortality in diabetic patients. Therefore, emphasis on diabetes care and management is on optimal blood glucose control to avert these adverse outcomes.

Studies have demonstrated that diabetic nephropathy is associated with increased cardiovascular mortality. In general, about one in three patients with diabetes develops end-stage renal disease (ESRD) which proceeds to diabetic nephropathy (DN), the principal cause of significant morbidity and mortality in diabetes. Hypertension, a well-established major risk factor for cardiovascular disease contributes to ESRD in diabetes. Clinical evidence suggests that there is no effective treatment for diabetic nephropathy and prevention of the progression of diabetic nephropathy. However, biomedical evidence indicates that some plant extracts have beneficial effects on certain processes associated with reduced renal function in diabetes mellitus. On the other hand, other plant extracts may be hazardous in diabetes, as reports indicate impairment of renal function. This article outlines therapeutic and pharmacological evidence supporting the potential of some medicinal plants to control or compensate for diabetes-associated complications, with particular emphasis on kidney function and hypertension.

Magnesium sulfate in emergency department patients with hypertension

To compare the effect of IV magnesium with other antihypertensives in emergency department (ED) patients with hypertension. ED patients with a systolic BP > 135 mmHg or diastolic BP > 85 were approached for entry into the study. Those granting consent were randomly placed into one of three treatment groups: (1) 1.5 gm IV MgSO(4) (n = 42), (2) a parenteral or oral antihypertensive agent (n = 41), (3) both IV MgSO(4) and an antihypertensive agent (n = 44). Systolic and diastolic blood pressures were measured at entry into the study and at 15, 30, 45, and 60 min after magnesium or other antihypertensive medications were given. The main outcome measure was blood pressure at 60 min, and results were compared using one-way analysis of variance with the post hoc Tukey HSD test. Compared to systolic and diastolic blood pressures at time 0, both were lower at 15, 30, 45, and 60 min in all groups (p < 0.05). No significant difference in systolic or diastolic BP at any time point was observed when response to treatment was compared between the three groups. Intravenous MgSO(4) is as effective as antihypertensives at lowering BP in emergency department patients.

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.

Role of magnesium in hypertension

Magnesium affects blood pressure by modulating vascular tone and reactivity. It acts as a calcium channel antagonist, it stimulates production of vasodilator prostacyclins and nitric oxide and it alters vascular responses to vasoactive agonists. Magnesium deficiency has been implicated in the pathogenesis of hypertension with epidemiological and experimental studies demonstrating an inverse correlation between blood pressure and serum magnesium levels. Magnesium also influences glucose and insulin homeostasis, and hypomagnesemia is associated with metabolic syndrome. Although most epidemiological and experimental studies support a role for low magnesium in the pathophysiology of hypertension, data from clinical studies have been less convincing. Furthermore, the therapeutic value of magnesium in the management of hypertension is unclear. The present review addresses the role of magnesium in the regulation of vascular function and blood pressure and discusses the implications of magnesium deficiency in experimental and clinical hypertension, in metabolic syndrome and in pre-eclampsia.

Magnesium influx enhanced by nitric oxide in hypertensive rat proximal tubule cells

An abnormal handling of renal magnesium has been suggested to cause salt-sensitive hypertension. The filtered magnesium is first reabsorbed in the proximal tubule. Amiloride has been shown to enhance renal magnesium conservation, but the regulatory mechanisms are unknown yet. High-salt (8% NaCl) diet decreased serum magnesium concentration, while increased urinary magnesium in Dahl salt-sensitive (DS) rat. Furthermore, the expression of nitric oxide synthase type 3 and nitric oxide (NO) content were decreased in high-salt loaded DS rat. In isolated proximal tubule cells, amiloride (0.1 mM) increased intracellular free magnesium concentration ([Mg(2+)](i)). However, the net [Mg(2+)](i) increase in the high-salt loaded DS rat was smaller than other groups. NOR1 (0.1 mM), a NO donor, restored the increase of [Mg(2+)](i) to the same level of other groups. On the contrary, L-NMMA (0.1 mM), an inhibitor of NO production, inhibited the increase of [Mg(2+)](i) in all groups. These results suggest that intracellular NO has an important role to up-regulate amiloride-elicited magnesium influx.

Physiological and pathophysiological role of magnesium in the cardiovascular system: implications in hypertension

Attention is growing for a potential role of magnesium in the pathoetiology of cardiovascular disease. Magnesium modulates mechanical, electrical and structural functions of cardiac and vascular cells, and small changes in extracellular magnesium levels and/or intracellular free magnesium concentration may have significant effects on cardiac excitability and on vascular tone, contractility and reactivity. Thus, magnesium may be important in the physiological regulation of blood pressure whereas alterations in cellular magnesium metabolism could contribute to the pathogenesis of blood pressure elevation. Although most epidemiological and experimental studies support a pathological role for magnesium in the etiology and development of hypertension, data from clinical studies have been less convincing. Furthermore, the therapeutic value of magnesium in the management of essential hypertension is unclear. The present review discusses the molecular, biochemical, physiological and pharmacological roles of magnesium in the regulation of vascular function and blood pressure and introduces novel concepts relating to magnesium as a second messenger in intracellular signaling in cardiovascular cells. In addition, alterations in magnesium regulation in experimental and clinical hypertension and the potential antihypertensive therapeutic effects of magnesium are addressed.

Alterations in heart and kidney membrane phospholipids in hypertension as observed by 31P nuclear magnetic resonance

Abnormalities of phospholipids in hypertension have previously been described in human erythrocyte, platelet, and plasma lipoproteins. Since the heart and kidney are adversely affected by hypertension, we investigated possible alterations in their membrane phospholipids, which could play a role in the derangement of intracellular ion balance widely observed in hypertension. The phospholipid compositions of heart and kidney from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were determined by using 31P nuclear magnetic resonance (NMR) spectroscopy. Absolute contents of all phospholipids in hypertensive hearts and kidneys were significantly higher than in normotensive hearts and kidneys. Expressed as a fraction of total phospholipid, cardiolipin (CL) and phosphatidylethanolamine plasmalogen (PEp) were significantly increased in SHR hearts compared to WKY hearts (CL and PEp were 7.95+/-0.22% and 13.16+/-0.35% in SHR vs. 7.01+/-0.20% and 11.19+/-0.42% in WKY rats, P< or =0.05), but phosphatidylethanolamine (PE) and phosphatidylcholine (PC) were significantly decreased in SHR (PE and PC were 22.46+/-0.37% and 44.81+/-0.43% in SHR vs. 24.02+/-0.44% and 46.01+/-0.50% in WKY rats, P< or =0.05). In the phospholipids extracted from rat kidneys, the percentage of PE was significantly higher for SHR than for WKY rats (20.37+/-0.60% vs. 18.43+/-0.37%, P< or =0.05), while PEp and phosphatidylserine (PS) were significantly lower for SHR (PEp and PS were 10.22+/-0.36% and 8.42+/-0.28% in SHRs vs. 11.29+/-0.36% and 9.71+/-0.40% in WKY rats, P< or =0.05). The above alterations in phospholipid composition might contribute to the higher oxygen consumption in the hypertensive heart and abnormal intracellular ion concentrations and ion transport in the heart and the kidney in hypertension.