Magnesium-induced vasodilation in the dorsal hand vein

Review Article on Molecular Mechanism of Regulation of Hypertension by Macro-elements (Na, K, Ca and Mg), Micro-elements/Trace Metals (Zn and Cu) and Toxic Elements (Pb and As)

Hypertension (HT) is a medical condition arising due to increase in blood pressure (BP) prevalent worldwide. The balanced dietary intakes of macro-elements and micro-elements including Na, K, Ca, Mg, Zn, and Cu have been described to maintain BP in humans by regulating the osmolarity of blood, cells/tissues, prevention of generation of oxidative and nitrosative stress (OANS), and endothelial damage through their functioning as important components of renin-angiotensin-aldosterone system (RAAS), antioxidant enzyme defense system, and maintenance of blood vascular-endothelial and vascular smooth muscle cell (VSMC) functions. However, inadequate/excess dietary intakes of Na/K, Ca/Mg, and Zn/Cu along with higher Pb and As exposures recognized to induce HT through common mechanisms including the followings: endothelial dysfunctions due to impairment of vasodilatation, increased vasoconstriction and arterial stiffness, blood clotting, inflammation, modification of sympathetic activity and higher catecholamine release, increased peripheral vascular resistance, and cardiac output; increased OANS due to reduced and elevated activities of extracellular superoxide dismutase and NAD(P)H oxidase, less nitric oxide bioavailability, decrease in cGMP and guanylate cyclase activity, increase in intracellular Ca2+ ions in VSMCs, and higher pro-inflammatory cytokines; higher parathyroid and calcitriol hormones; activation/suppression of RAAS resulting imbalance in blood Na+, K+, and water regulated by renin, angiotensin II, and aldosterone through affecting natriuresis/kaliuresis/diuresis; elevation in serum cholesterol and LDL cholesterol, decrease in HDL cholesterol due to defect in lipoprotein metabolism. The present study recommends the need to review simple dietary mineral intervention studies/supplementation trials before keeping their individual dietary excess intakes/exposures in consideration because their interactions lead to elevation and fall of their concentrations in body affecting onset of HT.

Magnesium Deficiency and Cardiometabolic Disease

Magnesium (Mg²⁺) has many physiological functions within the body. These include important roles in maintaining cardiovascular functioning, where it contributes to the regulation of cardiac excitation-contraction coupling, endothelial functioning and haemostasis. The haemostatic roles of Mg²⁺ impact upon both the protein and cellular arms of coagulation. In this review, we examine how Mg²⁺ homeostasis is maintained within the body and highlight the various molecular roles attributed to Mg²⁺ in the cardiovascular system. In addition, we describe how nutritional and/or disease-associated magnesium deficiency, seen in some metabolic conditions, has the potential to influence cardiac and vascular outcomes. Finally, we also examine the potential for magnesium supplements to be employed in the prevention and treatment of cardiovascular disorders and in the management of cardiometabolic health.

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.

The effects of subchronic intake of magnesium hydrocarbonate-rich mineral water on body weight and cardiovascular variables in rats with streptozotocin: Induced diabetes

Background/Aim: Optimal intake of magnesium minerals is essential in maintaining the coordinated physiological functions of cells, tissues and organs. The importance of this element is reflected in the fact that it is the fourth most abundant cation in the human body, participating as a cofactor in more than three hundred enzymatic reactions. Its presence is necessary for the proper functioning of a number of vital functions, such as glycaemic control, the work of the heart and the vascular system and it can potentially play a role in the regulation of body weight. Aim of this study was to investigate the effects of subchronic intake of magnesium hydrocarbonate-rich water on changes in body weight, organ weight and cardiovascular variables in rats with streptozotocin-induced diabetes. Methods: Wistar rats (n = 28) were divided into 4 groups: two control groups, on tap water (TW-C, n = 7) and magnesium hydrocarbonate-rich water (MW-C, n = 7); and two experimental groups with streptozotocin-induced diabetes, on tap water (TW-DM, n = 7) and magnesium hydrocarbonate-rich water (MW-DM, n = 7). The values of body weight, organ weight and cardiovascular parameters were compared after 6 weeks between control groups of rats on subchronic treatment with tap water (TW-C) and magnesium hydrocarbonate-rich water (MW-C) and between groups with streptozotocin-induced diabetes on tap water (TW-DM) and with magnesium hydrocarbonate-rich water (MW-DM). Results: By comparing the values of cardiovascular parameters between groups, significant (p < 0.05) positive effects of magnesium hydrocarbonate-rich water were registered on the values of systolic and pulse blood pressure in diabetic rats fed with magnesium hydrocarbonate-rich water (MW-DM) compared to those fed with tap water (TW-DM). In contrast, no significant effect of magnesium hydrocarbonate on changes in body weight and organ weight was observed. Conclusion: Based on the results, the beneficial effects of magnesium hydrocarbonate-rich water in the regulation of blood pressure can be clearly observed. Potential effects on other cardiovascular variables and body weight and organ weight should be further investigated.

Dehulled Adlay Consumption Modulates Blood Pressure in Spontaneously Hypertensive Rats and Overweight and Obese Young Adults

High blood pressure is a crucial risk factor for many cardiovascular diseases, and a diet rich in whole-grain foods may modulate blood pressure. This study investigated the effects of dehulled adlay consumption on blood pressure in vivo. We initially fed spontaneous hypertensive rats diets without (SHR group) or with 12 or 24% dehulled adlay (SHR + LA and SHR + HA groups), and discovered that it could limit blood pressure increases over a 12-week experimental period. Although we found no significant changes in plasma, heart, and kidney angiotensin-converting enzyme activities, both adlay-consuming groups had lower endothelin-1 and creatinine concentrations than the SHR group; the SHR + HA group also had lower aspartate aminotransferase and uric acid levels than the SHR group did. We later recruited 23 participants with overweight and obesity, and they consumed 60 g of dehulled adlay daily for a six-week experimental period. At the end of the study, we observed a significant decrease in the group's systolic blood pressure (SBP), and the change in SBP was even more evident in participants with high baseline SBP. In conclusion, our results suggested that daily intake of dehulled adlay had beneficial effects in blood-pressure management. Future studies may further clarify the possible underlying mechanisms for the consuming of dehulled adlay as a beneficial dietary approach for people at risk of hypertension.

An evidence-based appraisal of complementary and alternative medicine strategies for the management of hypertension

: Hypertension is a major risk factor for cardiovascular disease and all-cause mortality. Numerous antihypertensive medications and lifestyle changes have proven effective for the reduction of blood pressure (BP). Over the past few decades, the emergence of complementary and alternative medicine (CAM)-based strategies to lower BP have broadened the therapeutic armamentarium for hypertension. CAM is defined as a group of heterogeneous medical treatments that are used to enhance the effect of standard therapy, or, conversely, are implemented as an alternative to standard practice. The available body of evidence does substantiate the BP-lowering effects of certain CAM-based therapies in individuals with and without established hypertension. Collectively, alternative strategies for BP reduction have undergone less rigorous testing than traditional BP-lowering strategies and the lack of robust clinical data has greatly hampered the broad-scale adoption of CAM therapies into clinical practice. Despite these limitations, CAM-based therapies for the reduction of BP require consideration as they could offer substantial public health benefits given the high prevalence of hypertension in the general population. This article reviews some of the most promising CAM-based therapies for the reduction of BP and cardiovascular outcomes based on the current literature.

The Effects of Magnesium Supplementation on Blood Pressure and Obesity Measure Among Type 2 Diabetes Patient: a Systematic Review and Meta-analysis of Randomized Controlled Trials

In this study, we aimed to systematically review the literature to evaluate the effects of magnesium (Mg) supplementation on blood pressure (BP) and obesity measure among patients with type 2 diabetes mellitus (T2DM). Major electronic databases of Web of Science, the Cochrane library, PubMed, and Scopus were searched completely from the inception until 15 October 2019 to identify randomized clinical trials (RCTs) pertaining to the topic of interest. All outcomes were pooled using a random-effects model and expressed as weighted mean differences (WMD) with 95% confidential intervals (CI). Heterogeneity, sensitivity analysis, and publication bias were also assessed using standard methods. The pooled analysis of five RCTs showed that Mg supplementation did not affect body weight (WMD: - 0.01 kg, 95% CI: - 0.36 to 0.33), BMI (WMD: - 0.07, 95% CI: - 0.18 to 0.04), and waist circumference (WMD: 0.12, 95% CI: - 1.24 to 1.48) in T2DM patients compared to the control groups of the patients who received placebo. However, pooling seven RCTs together showed significant reduction of systolic blood pressure (WMD: - 5.78 mmHg, 95% CI: - 11.37 to - 0.19) and diastolic blood pressure (WMD: - 2.50 mmHg, 95% CI: - 4.58 to - 0.41) in T2DM patients. Furthermore, subgroup analysis by dose of intervention, intervention duration, and type of intervention suggested that Mg supplementation for > 12 weeks, in doses higher than 300 mg/day or inorganic forms, could significantly decrease both systolic and diastolic BP in T2DM patients. Based on the findings, Mg supplementation has beneficial effects on BP in type 2 diabetes patients independent of body weight status. However, further investigations are needed to provide more reliable evidences.

Evaluation of magnesium sulfate effects on fetus development in experimentally induced surgical fetal growth restriction in rat

Objective: The objective of this study was to evaluate the effect of magnesium sulfate in the prevention of fetal growth restriction due to the impaired uterine blood supply in the rat model.Methods: A total number of 24 female rats were used in this study. They were mated overnight and randomly divided into control and treatment groups. After anesthesia and incising abdominal midline in day 17 of gestation, the uterine artery was occluded by an atraumatic clamp for 60 min. The rats of the control group received normal saline after surgery and the rats of treatment group received magnesium sulfate subcutaneously. The laparotomy was repeated on day 21 of gestation, and the number of alive and dead fetuses was counted in each horn. The viability of fetuses was evaluated. The weight of the placenta and fetuses and the distance between the head and tail as well as back to the abdomen of the fetuses were also measured. Samples of the amniotic fluid (AF) were collected during both surgeries for biochemical analyses of the glucose, urea, lactate, and pyruvate levels by an AutoAnalyzer.Results: Among the total fetuses in ischemic horn, only 50% survived in the control group. Dead fetuses had less body consistency and had a dark color. In contrary, only 7.6% of the fetuses in the treatment group were absorbed and 92.4% were completely healthy and developed. Parameters related to placenta weight, fetus weight, fetus length, and fetus width had significant differences and those of the treatment group were higher. Glucose and lactate levels of the AF in the treatment group were significantly lower and urea level was significantly higher than the control group in day 21 of gestation. The changes in pyruvate levels were not significant.Conclusion: In conclusion, magnesium sulfate may counteract with the effects of temporary uterine ischemia in pregnant rats and prevent intrauterine growth restriction.

Role of Magnesium Deficiency in Promoting Atherosclerosis, Endothelial Dysfunction, and Arterial Stiffening as Risk Factors for Hypertension

Arterial hypertension is a disease with a complex pathogenesis. Despite considerable knowledge about this socially significant disease, the role of magnesium deficiency (MgD) as a risk factor is not fully understood. Magnesium is a natural calcium antagonist. It potentiates the production of local vasodilator mediators (prostacyclin and nitric oxide) and alters vascular responses to a variety of vasoactive substances (endothelin-1, angiotensin II, and catecholamines). MgD stimulates the production of aldosterone and potentiates vascular inflammatory response, while expression/activity of various antioxidant enzymes (glutathione peroxidase, superoxide dismutase, and catalase) and the levels of important antioxidants (vitamin C, vitamin E, and selenium) are decreased. Magnesium balances the effects of catecholamines in acute and chronic stress. MgD may be associated with the development of insulin resistance, hyperglycemia, and changes in lipid metabolism, which enhance atherosclerotic changes and arterial stiffness. Magnesium regulates collagen and elastin turnover in the vascular wall and matrix metalloproteinase activity. Magnesium helps to protect the elastic fibers from calcium deposition and maintains the elasticity of the vessels. Considering the numerous positive effects on a number of mechanisms related to arterial hypertension, consuming a healthy diet that provides the recommended amount of magnesium can be an appropriate strategy for helping control blood pressure.

Beneficial Role of Mg2+ in Prevention and Treatment of Hypertension

Hypertension constitutes one of the most widespread pathological conditions in developed and developing countries. Currently, more than 1 billion people worldwide are affected by the condition, either as frank hypertension or as prehypertension, raising the risk for major long-term complications and life-threatening pathologies. The costs in terms of health care services, medications for the treatment of hypertension and its complications, and associated loss in productivity represent a major economic burden for the various countries. The necessity of developing treatments that are economically more sustainable and with better compliance has been increasing alongside the incidence of the pathology. Along these lines, attention has been paid to the implementation of affordable but nutritious diets that deliver appropriate levels of macro- and micronutrients as integral part of the diets themselves or as supplements. In particular, experimental and clinical evidence suggests that an appropriate intake of dietary magnesium can be beneficial in controlling blood pressure. Additional advantages of a more diffuse therapeutic and/or preventive utilization of magnesium supplements are the virtual absence of side-effects and their affordable costs. The present review will attempt to frame our knowledge of how magnesium exerts its beneficial effects on blood pressure maintenance, which may lead to the development of more effective treatments of hypertension and its main complications.

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.

Effects of Magnesium Supplementation on Blood Pressure

The antihypertensive effect of magnesium (Mg) supplementation remains controversial. We aimed to quantify the effect of oral Mg supplementation on blood pressure (BP) by synthesizing available evidence from randomized, double-blind, placebo-controlled trials. We searched trials of Mg supplementation on normotensive and hypertensive adults published up to February 1, 2016 from MEDLINE and EMBASE databases; 34 trials involving 2028 participants were eligible for this meta-analysis. Weighted mean differences of changes in BP and serum Mg were calculated by random-effects meta-analysis. Mg supplementation at a median dose of 368 mg/d for a median duration of 3 months significantly reduced systolic BP by 2.00 mm Hg (95% confidence interval, 0.43–3.58) and diastolic BP by 1.78 mm Hg (95% confidence interval, 0.73–2.82); these reductions were accompanied by 0.05 mmol/L (95% confidence interval, 0.03, 0.07) elevation of serum Mg compared with placebo. Using a restricted cubic spline curve, we found that Mg supplementation with a dose of 300 mg/d or duration of 1 month is sufficient to elevate serum Mg and reduce BP; and serum Mg was negatively associated with diastolic BP but not systolic BP (all P <0.05). In the stratified analyses, a greater reduction in BP tended to be found in trials with high quality or low dropout rate (all P values for interaction <0.05). However, residual heterogeneity may still exist after considering these possible factors. Our findings indicate a causal effect of Mg supplementation on lowering BPs in adults. Further well-designed trials are warranted to validate the BP-lowering efficacy of optimal Mg treatment.

Magnesium in health and disease

Mammalian cells tightly regulate cellular Mg(2+) content through a variety of transport and buffering mechanisms under the control of various hormones and cellular second messengers. The effect of these hormones and agents results in dynamic changes in the total content of Mg(2+) being transported across the cell membrane and redistributed within cellular compartments. The importance of maintaining proper cellular Mg(2+) content optimal for the activity of various cellular enzymes and metabolic cycles is underscored by the evidence that several diseases are characterized by a loss of Mg(2+) within specific tissues as a result of defective transport, hormonal stimulation, or metabolic impairment. This chapter will review the key mechanisms regulating cellular Mg(2+) homeostasis and their impairments under the most common diseases associated with Mg(2+) loss or deficiency.

Nutrient-enhanced diet reduces noise-induced damage to the inner ear and hearing loss

Oxidative stress has been implicated broadly as a cause of cell death and neural degeneration in multiple disease conditions; however, the evidence for successful intervention with dietary antioxidant manipulations has been mixed. In this study, we investigated the potential for protection of cells in the inner ear using a dietary supplement with multiple antioxidant components, which were selected for their potential interactive effectiveness. Protection against permanent threshold shift (PTS) was observed in CBA/J mice maintained on a diet supplemented with a combination of β-carotene, vitamins C and E, and magnesium when compared with PTS in control mice maintained on a nutritionally complete control diet. Although hair cell survival was not enhanced, noise-induced loss of type II fibrocytes in the lateral wall was significantly reduced (P < 0.05), and there was a trend toward less noise-induced loss in strial cell density in animals maintained on the supplemented diet. Taken together, our data suggest that prenoise oral treatment with the high-nutrient diet can protect cells in the inner ear and reduce PTS in mice. The demonstration of functional and morphologic preservation of cells in the inner ear with oral administration of this antioxidant supplemented diet supports the possibility of translation to human patients and suggests an opportunity to evaluate antioxidant protection in mouse models of oxidative stress-related disease and pathology.

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.

Magnesium transport in hypertension

Epidemiological, clinical and experimental evidence indicates an inverse association between Mg(2+) levels (serum and tissue) and blood pressure. Magnesium may influence blood pressure by modulating vascular tone and structure through its effects on numerous biochemical reactions that control vascular contraction/dilation, growth/apoptosis, differentiation and inflammation. Magnesium acts as a calcium channel antagonist, it stimulates production of vasodilator prostacyclins and nitric oxide and it alters vascular responses to vasoactive agonists. Mammalian cells regulate Mg(2+) concentration through specialized influx and efflux transport systems that have only recently been characterized. Magnesium efflux occurs via Na(2+)-dependent and Na(2+)-independent pathways. Mg(2+) influx is controlled by recently cloned transporters including Mrs2p, SLC41A1, SLC41A1, ACDP2, MagT1, TRPM6 and TRPM7. Alterations in some of these systems may contribute to hypomagnesemia and intracellular Mg(2+) deficiency in hypertension. In particular increased Mg(2+) efflux through altered regulation of the vascular Na(+)/Mg(2+) exchanger and decreased Mg(2+) influx due to defective vascular and renal TRPM6/7 expression/activity may be important. This review discusses the role of Mg(2+) in vascular biology and implications in hypertension and focuses on the putative transport systems that control vascular magnesium homeostasis. Much research is still needed to clarify the exact mechanisms of Mg(2+) regulation in the cardiovascular system and the implications of aberrant transcellular Mg(2+) transport in the pathogenesis of cardiovascular disease.

Magnesium ion inhibits spontaneous and induced contractions of isolated uterine muscle

AIM

Magnesium sulfate, mainly used in obstetrics to treat eclamptic convulsions, is currently questioned as to its clinical tocolytic effect. We aimed to study the relaxant action (if any) of magnesium sulfate on in vitro pregnant and non-pregnant myometrium.

METHODS

Myometrial strips, harvested from five pregnant women (35-39 gestational weeks) during Cesarean procedures indicated for dystocia or scared uterus and five non-pregnant women during hysterectomy or myomectomy for benign conditions, were placed in a Krebs-Henseleit solution organ bath and the isometric force was registered. We assessed the effect of Mg2+ (magnesium sulfate) at different concentrations (0.50-10 mM) on spontaneous and oxytocin-induced (1 microM) myometrial contractility.

RESULTS

Mg2+ temporarily reduced spontaneous myometrial contractions in a dose-dependent manner, with efficient regimens at 2.0-2.5 mM, and arrested contractility completely at 3 mM. Oxytocin-induced contractions were reduced by 30-40% at 8 mM and decreased further at 9-10 mM. Induced contractions were reduced, in a dose-dependent and time-dependent manner (maximum effect at 20 min), at higher Mg2+ concentrations and with non-significant proportional differences between pregnant and non-pregnant myometrium.

CONCLUSIONS

The present in vitro study suggests a possible benefit of Mg2+ in the inhibition of spontaneous myometrial contractility, but not of uterine-induced hyperactivity.

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.

Risk factors and clinical outcomes of pulmonary interstitial emphysema in extremely low birth weight infants

OBJECTIVE

We studied the ante- and postnatal risk factors and clinical outcomes associated with pulmonary interstitial emphysema (PIE) in extremely low birth weight infants (ELBW, <1000 g at birth) in the present era of tocolytics, antenatal steroid and postnatal surfactant administration.

STUDY DESIGN

This was a retrospective case-controlled study of all ELBW admitted consecutively during a designated study-period in a level III nursery. Data were analyzed by performing univariate and multivariate analysis as applicable.

RESULTS

Infants with PIE had lower 1 and 5 min Apgar scores (P=0.04 and 0.003 respectively), increased surfactant utilization (P=0.004), higher maximum inspired oxygen concentration (P=0.04) and mean airway pressure administration (P=0.02) during the first week of life, and increased neonatal mortality (P=0.01). They received higher antenatal doses of magnesium sulfate (MgSO(4)) (P=0.02). 56% of infants with PIE were exposed to more than 10 g of MgSO(4) (Mg10), compared to 15% in non-PIE group (P=0.01). The multivariate logistic regression analysis including significant co-variates revealed an independent association between Mg10 and PIE (P=0.01, Odds ratio 19.8, 95% CI 1.5-263).

CONCLUSION

Pulmonary interstitial emphysema is associated with increased mortality in ELBW infants. Mg10 is an independent risk factor for PIE in this population.