Oral magnesium administration prevents vascular complications in STZ-diabetic rats

The Benefits of Nanosized Magnesium Oxide in Fish Megalobrama amblycephala: Evidence in Growth Performance, Redox Defense, Glucose Metabolism, and Magnesium Homeostasis

This study evaluated the effects of dietary magnesium oxide nanoparticles (MgO NPs) on the growth, redox defense, glucose metabolism, and magnesium homeostasis in blunt snout bream. Fish (12.42 ± 0.33 g) were fed seven diets containing graded levels of MgO NPs (0, 60, 120, 240, 480, 960, and 1920 mg/kg) for 12 weeks. Whole-body Mg retention decreased significantly as the dietary Mg increased. As dietary MgO NPs levels reached 120 mg/kg, the growth performance and feed utilization remarkably improved. When added at 240 mg/kg, oxidative stress was significantly reduced evidenced by the increased Mn-sod transcription and the decreased CAT and GSH-Px activities and the MDA content. Meanwhile, it enhanced glucose transport, glycolysis, and glycogen synthesis, while inhibiting gluconeogenesis, as was characterized by the increased transcriptions of glut2, gk, and pk, and the decreased transcriptions of fbpase and g6pase. In addition, the supplementation of 120 mg/kg MgO NPs promoted Mg transport marked by a significant increase in the protein expressions of TRMP7, S41A3, and CNNM1. In conclusion, the moderate supplementation of MgO NPs improved the growth performance, reduced hepatic oxidative stress, and promoted glucose transport, glycolysis, glycogen synthesis, and magnesium homeostasis in fish while inhibiting glu.

High magnesium mitigates the vasoconstriction mediated by different types of calcium influx from monocrotaline-induced pulmonary hypertensive rats

NEW FINDINGS

What is the central question of this study? The aim was to examine and explore the involvement of Mg²⁺ in mitigating the vasoconstriction in PAs and sPAs in the MCT-PAH rat model. What are the main finding and its importance? 1.Both SOCE- and ROCE-mediated vasoconstriction enhanced in the MCT-PAH model. 2.High magnesium inhibited vasoconstriction due to directly antagonizing Ca²⁺ and increasing NO release. 3.The inhibition effect of high magnesium was more notable in sPA.

ABSTRACT

Increased extracellular magnesium concentration ([Mg²⁺ ]_e ) has been evidenced to attenuate the endothelin-1 (ET-1)-induced contractile response via the release of nitric oxide (NO) from the endothelium in proximal pulmonary arteries (PAs) of chronic hypoxic (CH) mice. Here we further examined the involvement of Mg²⁺ in the inhibition of vasoconstriction in PAs and distal smaller pulmonary arteries (sPAs) in a monocrotaline-induced pulmonary arterial hypertension (MCT-PAH) rat model. The data showed that in control rats, vasoconstriction in sPAs is more intense than that in PAs. In MCT-PAH rats, the store-operated Ca²⁺ entry (SOCE)-, and receptor-operated Ca²⁺ entry (ROCE)-mediated contraction was significantly strengthened. However, there was no upregulation of the vasoconstriction mediated by voltage-dependent calcium entry (VDCE). Furthermore, high magnesium greatly inhibited the VDCE-mediated contraction in PAs instead of sPAs, which was opposite to the ROCE-mediated contraction. Moreover, MCT pretreatment partly eliminated the endothelium-dependent vasodilation in PAs, which in sPAs, however, was still promoted by magnesium due to the increased NO release in pulmonary microvascular endothelial cells (PMVECs). In conclusion, the findings suggest that both SOCE- and ROCE-mediated vasoconstriction in the MCT-PAH model are enhanced, especially in sPAs. The inhibition effect of high magnesium on vasoconstriction can be achieved partly by its direct role as a Ca²⁺ antagonist and partly by increasing the NO release in PMVECs. This article is protected by copyright. All rights reserved.

Combination Therapy with GABA and MgSO4 Improves Insulin Sensitivity in Type 2 Diabetic Rat

BACKGROUND

Gamma-aminobutyric acid (GABA) and magnesium sulfate (MgSO₄) play a crucial role in glycemic control. Therefore, we studied the effect of combination therapy with GABA and MgSO₄ to improve insulin sensitivity in diabetes induced by streptozotocin as well as high-fat diet in a diabetic rat model. Design and Methods. Forty randomly selected rats were assigned to four groups: nondiabetic control group was fed the normal diet, insulin-resistant diabetic rat model was induced by streptozotocin and high-fat diet, GABA + MgSO₄ group received GABA and MgSO₄, and insulin group was treated with insulin. Body weight, abdominal fat, blood glucose, serum insulin, and glucagon concentration were measured. The glucose clamp technique, glucose tolerance test, and insulin tolerance test were performed to study insulin sensitivity. Also, the expressions of glucose 6 phosphatase, glucagon receptor, and phosphoenolpyruvate carboxykinase genes in liver were assessed for the gluconeogenesis pathway. Protein translocation and glucose transporter 4 (Glut4) genes expression in muscle were also assessed.

RESULTS

Combination of GABA + MgSO₄ or insulin therapy enhanced insulin level, glycemic control, glucose and insulin tolerance test, some enzymes expression in the gluconeogenesis pathway, body fat, body weight, and glucagon receptor in diabetic rats. Moreover, an increase was observed in protein and gene expression of Glut4. Insulin sensitivity in combination therapy was more than the insulin group.

CONCLUSIONS

GABA and MgSO₄ enhanced insulin sensitivity via increasing Glut4 and reducing the gluconeogenesis enzyme and glucagon receptor gene expressions.

Effect of oral magnesium sulfate administration on lectin-like oxidized low-density lipoprotein receptor-1 gene expression to prevent atherosclerosis in diabetic rat vessels

AIMS/INTRODUCTION

The purpose of the present study was to investigate the possible effect of oral magnesium sulfate (MgSO4 ) in the reduction of atherosclerosis plaques through inhibition of lectin-like low-density lipoprotein receptor-1 (LOX-1) gene expression in diabetic vessels.

MATERIALS AND METHODS

A total of 50 rats were divided into five groups, including non-diabetic control, Mg-treated non-diabetic control, chronic diabetic, Mg-treated chronic diabetic and insulin-treated chronic diabetic. The induction of diabetes was carried out by streptozotocin. The Mg-treated chronic diabetic and Mg-treated non-diabetic control groups were treated with 10 g/L of MgSO4 added to their drinking water. The insulin-treated chronic diabetic group received 2.5 U/kg of insulin twice per day. The fasting blood glucose level and bodyweight were determined weekly. Blood pressure measurement and the intraperitoneal glucose tolerance test were carried out after 16 weeks, and the plasma levels of Mg, lipid profile and oxidized low-density lipoprotein cholesterol (oxLDL) were determined. The mesenteric bed was isolated and perfused according to the McGregor method. The aorta was isolated for LOX-1 genes and proteins expression, and pathological investigation.

RESULTS

MgSO4 administration improved blood pressure, sensitivity to phenylephrine, intraperitoneal glucose tolerance test, lipid profile and plasma ox-LDL level, and also lowered the blood glucose level to the normal range, and decreased LOX-1 gene and protein expressions. Insulin decreased blood pressure, sensitivity to phenylephrine, blood glucose, lipid profiles and plasma oxLDL level, but it did not decrease LOX-1 gene and protein expressions.

CONCLUSIONS

The present findings suggested that MgSO4 improves blood pressure and vessel structure through decreasing oxLDL, and LOX-1 gene and protein expressions; however, insulin did not repair vessel structure, and LOX-1 gene and protein expressions.

Oral herbal supplement containing magnesium sulfate improve metabolic control and insulin resistance in non-diabetic overweight patients: A randomized double blind clinical trial

Background: Magnesium deficiency plays a key role in obesity and decreases insulin sensitivity. In our previous study, significant evidence was provided for the contribution of oral Mg supplement that could improve insulin sensitivity and body weight in animal trials. The purpose of the present study was to investigate the effects of an herbal supplement containing 300 mg magnesium sulfate on lipid profile, as well as insulin resistance and secretion in overweight patients. Methods: Seventy overweight non-diabetic volunteers with Body Mass Index (BMI) >28 kg/m2 were included in a randomized double blind placebo-controlled clinical trial (ethic number HUMS REC.1394.57) and registered in Iranian Registry of Clinical Trials (IRCT2012110124756N2 with registration number 24756). They received either placebo or an herbal supplement capsule containing 300 mg magnesium sulfate (MgSO4) for 6 months on a daily basis. Metabolic control, lipid profile and magnesium status were determined at baseline and every three months. Student t-test, repeated measure ANOVA and ANCOVA were used to compare the groups. Results: There was no significant difference between groups before intervention, but daily Mg supplement for 6 months significantly improved fasting insulin level (6.71±0.11 to 6.27±0.3 three months after Mg therapy, p<0.01 vs. 6.41±0.11 in control group (5.83±0.063) six months after Mg therapy, p< 0.0001), HOMA-IR (1.52±0.03 )in control group to 1.36±0.03 after three months Mg therapy, p<0.05 vs 1.37±0.05 in control group to 1.22±0.02 six months after Mg therapy, p< 0.05), high density lipoprotein cholesterol (HDL) (43.57±0.82 in control group to 43.91±1.92 three months after Mg therapy, p<0.001vs 43.57±0.82 in control group to 46±0.88 six months after Mg therapy, <0.01), triglyceride (TG) (163.17±6.1 in control group to 141.2±5.84 six months after g therapy, p<0.05) and low density lipoprotein cholesterol (LDL) (112.62±3.41 in control group to 104.42±2.35 six months after Mg therapy, p<0.05). Conclusion: Oral herbal supplement containing MgSO4 (300 mg/day) could improve plasma insulin level, lipid profile, and insulin resistance in non-diabetic overweight volunteers.

Magnesium attenuates endothelin-1-induced vasoreactivity and enhances vasodilatation in mouse pulmonary arteries: Modulation by chronic hypoxic pulmonary hypertension

NEW FINDINGS

What is the central question of this study? The central goal of this study was to elucidate the role of magnesium in the regulation of pulmonary vascular reactivity in relationship to hypoxic pulmonary hypertension. What is the main finding and its importance? We found that magnesium is essential for normal vasoreactivity of the pulmonary artery. Increasing the magnesium concentration attenuates vasoconstriction and improves vasodilatation via release of nitric oxide. Pulmonary hypertension is associated with endothelial dysfunction resulting in the suppression of magnesium modulation of vasodilatation. These results provide evidence that magnesium is important for the modulation of pulmonary vascular function.

ABSTRACT

Pulmonary hypertension (PH) is characterized by enhanced vasoreactivity and sustained pulmonary vasoconstriction, arising from aberrant Ca²⁺ homeostasis in pulmonary arterial (PA) smooth muscle cells. In addition to Ca²⁺ , magnesium, the most abundant intracellular divalent cation, also plays crucial roles in many cellular processes that regulate cardiovascular function. Recent findings suggest that magnesium regulates vascular functions by altering the vascular responses to vasodilator and vasoactive agonists and affects endothelial function by modulating endothelium-dependent vasodilatation in hypertension. Administration of magnesium also decreased pulmonary arterial pressure and improved cardiac output in animal models of PH. However, the role of magnesium in the regulation of pulmonary vascular function related to PH has not been studied. In this study, we examined the effects of magnesium on endothelin-1 (ET-1)-induced vasoconstriction, ACh-induced vasodilatation and the generation of NO in PAs of normoxic mice and chronic hypoxia (CH)-treated mice. Our data showed that removal of extracellular magnesium suppressed vasoreactivity of PAs to both ET-1 and ACh. A high concentration of magnesium (4.8 mm) inhibited ET-1-induced vasoconstriction in endothelium-intact or endothelium-disrupted PAs of normoxic and CH-treated mice, and enhanced the ACh-induced production of NO in PAs of normoxic mice. Moreover, magnesium enhanced ACh-induced vasodilatation in PAs of normoxic mice, and the enhancement was completely abolished after exposure to CH. Hence, in this study we demonstrated that increasing the magnesium concentration can attenuate the ET-1-induced contractile response and improve vasodilatation via release of NO from the endothelium. We also demonstrated that chronic exposure to hypoxia can cause endothelial dysfunction resulting in suppression of the magnesium-dependent modulation of vasodilatation.

Magnesium upregulates insulin receptor and glucose transporter-4 in streptozotocin-nicotinamide-induced type-2 diabetic rats

Objective. We investigated the effects of magnesium supplementation on glucose tolerance, insulin sensitivity, oxidative stress as well as the concentration of insulin receptor and glucose transporter-4 in streptozotocin-nicotinamide induced type-2 diabetic (T2D) rats. Methods. Rats were divided into four groups designated as: 1) control (CTR); 2) diabetic untreated (DU); 3) diabetic treated with 1 mg of Mg/kg diet (Mg1-D); and 4) diabetic treated with 2 mg of Mg/kg diet (Mg2-D). T2D was induced with a single intraperitoneal (i.p.) injection of freshly prepared streptozotocin (55 mg/kg) aft er an initial i.p. injection of nicotinamide (120 mg/kg). Glucose tolerance, insulin sensitivity, lipid profile, malondialdehyde (MAD) and glutathione content, insulin receptors (INSR) and glucose transporter-4 (GLUT4), fasting insulin and glucose levels were measured, and insulin resistance index was calculated using the homeostatic model assessment of insulin resistance (HOMA-IR). Results. Magnesium supplementation improved glucose tolerance and lowered blood glucose levels almost to the normal range. We also recorded a noticeable increase in insulin sensitivity in Mg-D groups when compared with DU rats. Lipid perturbations associated T2D were significantly attenuated by magnesium supplementation. Fasting glucose level was comparable to control values in the Mg-D groups while the HOMA-IR index was significantly lower compared with the DU rats. Magnesium reduced MDA but increased glutathione concentrations compared with DU group. Moreover, INSR and GLUT4 levels were elevated following magnesium supplementation in T2D rats. Conclusion. These findings demonstrate that magnesium may mediate effective metabolic control by stimulating the antioxidant defense, and increased levels of INSR and GLUT4 in diabetic rats.

Role of GABAB receptor and L-Arg in GABA-induced vasorelaxation in non-diabetic and streptozotocin-induced diabetic rat vessels

Background:

Hypertension is considered an independent risk factor for cardiovascular mortality in diabetic patients. The present study was designed to determine the role of gamma amino butyric acid B (GABA_B) receptor and L-arginine (L-Arg) in GABA-induced vasorelaxation in normal and streptozotocin-induced diabetic rat vessels.

Methods:

Diabetes was induced by a single i.p. injection of streptozotocin (STZ, 60 mg/kg). Eight weeks later, superior mesenteric arteries of all groups were isolated and perfused according to the McGregor method.

Results:

Baseline perfusion pressure of STZ diabetic rats was significantly higher than non-diabetic rats in both intact and denuded endothelium. In the presence of faclofen, a selective GABA_B receptor blocker, GABA-induced relaxation in intact and denuded endothelium mesenteric beds of STZ diabetic rats was suppressed, but this response in non-diabetic rats was not suppressed. Our results showed that in the presence of L-Arg, a nitric oxide precursor, GABA induced vasorelaxation in both diabetic and non-diabetic vessels.

Conclusion:

From the results of this study, it may be concluded that the vasorelaxatory effect of GABA in diabetic vessel is mediated by the GABA_B receptor and nitric oxide, but it seems that in non-diabetic vessel GABA_B receptor does not play any role in GABA-induced vasorelaxation, but nitric oxide induced GABA relaxation in non-diabetic vessel.

Protective effect of magnesium on renal function in STZ-induced diabetic rats

Background

Diabetic nephropathy is a serious complication of T1D (type one diabetes mellitus). Persistent hyperglycemia and subsequent hypomagnesemia is believed to develop kidney damage by activation of oxidative stress. We conducted this study to investigate the renoprotective effect of magnesium sulfate (MgSO₄) on renal histopathology and oxidative stress in diabetic rats.

Methods

The study included 70 male rats. The animals were divided into seven groups: control (CRL), control receiving MgSO₄ (CRL + Mg1 & CRL + Mg8), diabetic (DM1 & DM8) and diabetic receiving MgSO₄ (DM + Mg1 & DM + Mg8). Rats were given 20 mg/kg (i.p) Streptozocin (STZ) for 5 consecutive days in (MLD) multiple low doses to induce T1D. At day 10 treatment groups were received MgSO₄ (10 g/l) in drinking water, for 1 or 8 weeks. The blood glucose, BUN and creatinine levels were measured. Renal tissue levels of malondialdehyde (MDA) were measured by thiobarbituric acid (TBA) method to evaluate the oxidative stress. Renal histopathology was done using H & E staining method.

Results

Treatment with MgSO₄ significantly decreased the blood glucose in DM + Mg1 and DM + Mg8 groups as compared with DM1 and DM8. Magnesium treatment also decreased serum BUN and tissue level of MDA significantly in both short and long term treatment. The body weight loss and kidney weight to body weight ratio was improved by MgSO₄. Histological results showed there were no differences between DM and DM + Mg groups.

Conclusion

Our findings showed that diabetic nephropathy is associated with high blood glucose level and oxidative stress (significant increase in MDA level). The renal dysfunction and oxidative stress can be improved by magnesium sulfate administration. It is suggested that protection against development of diabetic nephropathy by MgSO₄ treatment involves changes in the blood glucose and oxidative stress.

Modulation of GLUT4 expression by oral administration of Mg(2+) to control sugar levels in STZ-induced diabetic rats

It has been previously shown that oral magnesium administration decreases the levels of glucose in the plasma. However, the mechanisms are not fully understood. The aim of this study was to determine the potential role of GLUT4 on plasma glucose levels by orally administering magnesium sulfate to diabetic rats. Animals were distributed among 4 groups (n = 10 rats per group): one group served as the non-diabetic control, while the other groups had diabetes induced by streptozotocin (intraperitoneal (i.p.) injection). The diabetic rats were either given insulin by i.p. injection (2.5 U·(kg body mass)(-1)·day(-1)), or magnesium sulfate in their drinking water (10 g·L(-1)). After 8 weeks of treatment, we conducted an i.p. glucose tolerance test (IPGTT), measured blood glucose and plasma magnesium levels, and performed in-vitro and in-vivo insulin level measurements by radioimmunoassay. Gastrocnemius (leg) muscles were isolated for the measurement of GLU4 mRNA expression using real-time PCR. Administration of magnesium sulfate improved IPGTT and lowered blood glucose levels almost to the normal range. However, the insulin levels were not changed in either of the in-vitro or in-vivo studies. The expression of GLU4 mRNA increased 23% and 10% in diabetic magnesium-treated and insulin-treated groups, respectively. Our findings suggest that magnesium lowers blood glucose levels via increased GLU4 mRNA expression, independent to insulin secretion.

Effect of oral administration of magnesium on Cisplatin-induced nephrotoxicity in normal and streptozocin-induced diabetic rats

Background

Cisplatin (CP) therapy as the most common potent chemotherapeutic process is accompanied by nephrotoxicity. The diabetic state may protect rat kidney against this toxicity, and magnesium (Mg) on the other hand may reduce the glucose level in diabetic animals.

Objectives

Current study was planned to investigate the effect of oral administration of magnesium supplementation on CP-induced nephrotoxicity in normal and Streptozocin (STZ)-induced diabetic rats.

Materials and Methods

Male Wistar rats were divided into seven groups and underwent two experiment protocols. As protocol 1, group 1 was considered as the sham group. Group 2 (CP group) received CP (2 mg/kg/d) for five consecutive days. Group 3 (CP + Mg group) received magnesium sulphate (MgSO4, 10 g/L added to the drinking water) for 10 days and then treated with CP from sixth day. As protocol 2, animals received a single dose of STZ (65 mg/kg i.p.). Three days after diabetes induction, animals were divided into four groups; Groups 4 (D group), 5 (D + CP group), and 7 (D + Mg + CP group) followed the same manner as groups 1 to 3, respectively; and group 6 (D + Mg group) was treated with MgSO4 alone for 10 days. Finally, blood samples were obtained, and all animals were killed for kidney tissue investigation.

Results

CP administration in normoglycemic rats significantly elevated the serum levels of blood urea nitrogen (BUN) and creatinine (Cr) (P < 0.05). However, coadministration of CP and Mg statistically increased the serum levels of BUN and Cr in both normoglycemic and diabetic animals when compared to the rats treated with CP alone (P < 0.05), while the serum level of Mg was significantly increased in nondiabetic groups (P < 0.05). No significant changes were observed in serum and kidney levels of nitrite; as well as the testis weight between all normoglycemic groups, whereas Mg decreased kidney levels of nitrite in diabetic groups when accompanied by CP (P < 0.05). The kidney and serum levels of malondialdehyde (MDA) enhanced significantly in nondiabetic rats treated with Mg and CP (P < 0.05). Kidney tissue damage score (KTDS), kidney weight, and body weight loss were significantly different among normoglycemic groups (P < 0.05), and Mg promoted the KTDS in diabetic animals treated with CP.

Conclusions

Oral Mg supplementation did not protect the CP induced nephrotoxicity in diabetic rats.

Effect of the administration of Solanum nigrum fruit on blood glucose, lipid profiles, and sensitivity of the vascular mesenteric bed to phenylephrine in streptozotocin-induced diabetic rats

Background

Solanum nigrum fruit is traditionally used in Asia to manage, control, and treat diabetes but there is no scientific evidence of the efficacy of Solanum nigrum fruit in treatment of diabetes. We designed this study to investigate the effect of the administration of oral doses of aqueous extract from Solanum nigrum fruit on plasma glucose, lipid profiles, and the sensitivity of the vascular mesenteric bed to Phenylephrine in diabetic and non-diabetic rats.

Material/Methods

Animals were divided into 5 groups (n=10): 2 groups served as non-diabetic controls (NDC), and the other groups had diabetes induced with a single injection of streptozotocin (STZ). Solanum nigrum-treated chronic diabetic (CD-SNE) and Solanum nigrum-treated controls (ND-SNE) received 1g/l of Solanum nigrum added to drinking water for 8 weeks. The mesenteric vascular beds were prepared using the McGregor method.

Results

Administration of Solanum nigrum caused Ca/Mg ratio, plasma glucose, high-density lipoprotein (HDL), low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), total cholesterol, and triglyceride concentrations to return to normal levels, and was shown to decrease alteration in vascular reactivity to vasoconstrictor agents.

Conclusions

Our results support the hypothesis that Solanum nigrum could play a role in the management of diabetes and the prevention of vascular complications in STZ-induced diabetic rats.

Magnesium attenuates chronic hypersensitivity and spinal cord NMDA receptor phosphorylation in a rat model of diabetic neuropathic pain

Neuropathic pain is a common diabetic complication affecting 8-16% of diabetic patients. It is characterized by aberrant symptoms of spontaneous and stimulus-evoked pain including hyperalgesia and allodynia. Magnesium (Mg) deficiency has been proposed as a factor in the pathogenesis of diabetes-related complications, including neuropathy. In the central nervous system, Mg is also a voltage-dependent blocker of the N-methyl-d-aspartate receptor channels involved in abnormal processing of sensory information. We hypothesized that Mg deficiency might contribute to the development of neuropathic pain and the worsening of clinical and biological signs of diabetes and consequently, that Mg administration could prevent or improve its complications. We examined the effects of oral Mg supplementation (296 mg l(-1) in drinking water for 3 weeks) on the development of neuropathic pain and on biological and clinical parameters of diabetes in streptozocin (STZ)-induced diabetic rats. STZ administration induced typical symptoms of type 1 diabetes. The diabetic rats also displayed mechanical hypersensitivity and tactile and thermal allodynia. The level of phosphorylated NMDA receptor NR1 subunit (pNR1) was higher in the spinal dorsal horn of diabetic hyperalgesic/allodynic rats. Magnesium supplementation failed to reduce hyperglycaemia, polyphagia and hypermagnesiuria, or to restore intracellular Mg levels and body growth, but increased insulinaemia and reduced polydipsia. Moreover, it abolished thermal and tactile allodynia, delayed the development of mechanical hypersensitivity, and prevented the increase in spinal cord dorsal horn pNR1. Thus, neuropathic pain symptoms can be attenuated by targeting the Mg-mediated blockade of NMDA receptors, offering new therapeutic opportunities for the management of chronic neuropathic pain.

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.

Effect of oral magnesium sulfate administration on blood pressure and lipid profile in streptozocin diabetic rat

Approximately one-third of patients with type 1 diabetes develop a variety of complications as a result of mechanisms that are not completely understood. However, insufficient metabolic control seems to play a major role. Other factors such as magnesium (Mg) could also be of importance. We designed this study to elucidate the effect of oral magnesium administration on plasma lipid profile and mesenteric fat in male Wistar rats. Animals were divided into 4 groups (n=10 in each group): one group served as control, while the other groups were made diabetic with a single i.v. injection of 40 mg/kg streptozocin. Animals in which the diabetic state lasted for 10 days were referred as acute diabetic rats, whereas those in which the diabetes lasted for 8 weeks were defined as chronic diabetics. Mg-treated chronic diabetic received 10 g/l of MgSO(4) added to the drinking water (0.46 g/24 h) for eight weeks following which the left common carotid artery was cannulated for continuous recording of blood pressure. Blood glucose, magnesium and lipid profiles levels were also determined. Diabetes induction caused plasma glucose, high density lipoprotein (HDL), low density lipoprotein (LDL), very low density lipoprotein (VLDL), total cholesterol and triglyceride concentrations to increase, however plasma Mg level was decreased. Administration of MgSO(4) for eight weeks caused the return of the above factors to their normal levels. Mg concentrations also increased but failed to reach normal levels. Diabetes induction caused mesenteric fat/body weight ratio to increase, but administration of MgSO(4) reduced the ratio to normal levels. In addition, Mg administration returned systolic blood pressure to the normal level. Our results support the hypothesis that Mg may play a part in the management of diabetes and the prevention of its vascular complications in streptozocin-induced diabetic rats and it may be useful in the treatment of hyperlipidaemia in diabetic case.

Magnesium metabolism in type 2 diabetes mellitus, metabolic syndrome and insulin resistance

Type 2 diabetes is characterized by cellular and extracellular Mg depletion. Epidemiologic studies showed a high prevalence of hypomagnesaemia and lower intracellular Mg concentrations in diabetic subjects. Insulin and glucose are important regulators of Mg metabolism. Intracellular Mg plays a key role in regulating insulin action, insulin-mediated-glucose uptake and vascular tone. Reduced intracellular Mg concentrations result in a defective tyrosine-kinase activity, post-receptorial impairment in insulin action, and worsening of insulin resistance in diabetic patients. Mg deficit has been proposed as a possible underlying common mechanism of the "insulin resistance" of different metabolic conditions. Low dietary Mg intake is also related to the development of type 2 diabetes. Benefits of Mg supplementation on metabolic profile in diabetic subjects have been found in most, but not all clinical studies, and larger prospective studies are needed to support the potential role of dietary Mg supplementation as a possible public health strategy in diabetes risk.

Role of Cav1.2 L-type Ca2+ channels in vascular tone: effects of nifedipine and Mg2+

Ca(2+) entry via L-type voltage-gated Ca(2+) channels (LVGCs) is a key factor in generating myogenic tone (MT), as dihydropyridines (DHPs) and other LVGC blockers, including Mg(2+), markedly reduce MT. Recent reports suggest, however, that elevated external Mg(2+) concentration and DHPs may also inhibit other Ca(2+)-entry pathways. Here, we explore the contribution of LVGCs to MT in intact, pressurized mesenteric small arteries using mutant mice (DHP(R/R)) expressing functional but DHP-insensitive Ca(v)1.2 channels. In wild-type (WT), but not DHP(R/R), mouse arteries, nifedipine (0.3-1.0 microM) markedly reduced MT and vasoconstriction induced by high external K(+) concentrations ([K(+)](o)), a measure of LVGC-mediated Ca(2+) entry. Blocking MT and high [K(+)](o)-induced vasoconstriction by <1 microM nifedipine in WT but not in DHP(R/R) arteries implies that Ca(2+) entry via Ca(v)1.2 LVGCs is obligatory for MT and that nifedipine inhibits MT exclusively by blocking LVGCs. We also examined the effects of Mg(2+) on MT and LVGCs. High external Mg(2+) concentration (10 mM) blocked MT, slowed the high [K(+)](o)-induced vasoconstrictions, and decreased their amplitude in WT and DHP(R/R) arteries. To verify that these effects of Mg(2+) are due to block of LVGCs, we characterized the effects of extracellular and intracellular Mg(2+) on LVGC currents in isolated mesenteric artery myocytes. DHP-sensitive LVGC currents are inhibited by both external and internal Mg(2+). The results indicate that Mg(2+) relaxes MT by inhibiting Ca(2+) influx through LVGCs. These data provide new information about the central role of Ca(v)1.2 LVGCs in generating and maintaining MT in mouse mesenteric small arteries.

Oral magnesium administration prevents thermal hyperalgesia induced by diabetes in rats

BACKGROUND

Peripheral neuropathy is a common complication of diabetes mellitus. It has been shown that hyperglycemia may contribute to its development but the exact pathophysiology underlying this complication is not fully understood. Since oral magnesium supplementation can normalize hyperglycemia induced by diabetes in rats, this study was designed to examine the effect of oral magnesium administration on thermal hyperalgesia in streptozocin-induced diabetic rats.

MATERIAL AND METHODS

Twenty-four male adult wistar rats were divided equally into control, magnesium-treated control, diabetic and magnesium-treated diabetic groups. In magnesium-treated diabetic rats, magnesium sulfate (10g/l) was added into the drinking water once diabetes was established (10 days after STZ injection) and continued for 8 weeks. Mg-treated control animals received magnesium sulfate in the same dose and over the same time period. The other two groups; control and diabetic animals, only received tap water. At the end of the 8 weeks, thermal pain threshold was assessed by tail flick test and magnesium and glucose plasma levels were measured in all groups.

RESULT

A significant decrease (p<0.001) in thermal pain threshold and plasma magnesium levels and an increase in plasma glucose levels (p<0.001) were seen in diabetic rats 8 weeks after diabetes induction. After 8 weeks of oral magnesium, thermal hyperalgesia was normalized and plasma magnesium and glucose levels were restored towards normal.

CONCLUSION

It is concluded that oral magnesium administration given at the time of diabetes induction may be able to restore thermal hyperalgesia, magnesium deficiency and hyperglycemia and in diabetic rats.

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.