Magnesium sulfate effectively reduces blood pressure in an animal model of preeclampsia

Short-Acting Oral Nifedipine versus Intravenous Labetalol for the Control of Severe Hypertension in the Postpartum Period: A Retrospective Cohort Study

This study aimed to compare the effectiveness of oral short-acting (SA) nifedipine with intravenous (IV) labetalol for the treatment of postpartum (PP) severe hypertension.We conducted a retrospective cohort study of women who delivered at a tertiary care facility between January and December 2018, had not previously received antihypertensive medication, and required treatment for PP severe hypertension defined as systolic blood pressure (SBP) ≥ 160 mm Hg and/or diastolic blood pressure (DBP) ≥110 mm Hg. Exposure groups were defined by the receipt of either oral SA nifedipine or IV labetalol. The primary outcome was time (minutes) to BP control (SBP < 160 mm Hg and DBP <110 mm Hg). Secondary outcomes included number of doses required to achieve BP control, crossover to the alternative medication, and recurrence of severe range BP after the achievement of BP control. t-Tests and Wilcoxon-Mann-Whitney tests were used to analyze continuous variables and chi-square tests or Fisher's exact tests were used to analyze categorical variables. Multivariable linear regression models were conducted for the primary outcome, controlling for potential confounders in a sequential fashion across three models. A Kaplan-Meier plot was also created.Of the 99 women included, 74 received oral SA nifedipine and 25 received IV labetalol. There was no significant difference in minutes to initial BP control between groups (30.5 minutes [interquartile range, IQR: 20.0-45.0] vs. 25.0 minutes [IQR: 14.0-50.0]; p = 0.82) or in the rate of recurrent severe BP. However, patients who received nifedipine required fewer doses to achieve control (p < 0.01) and did not require crossover (0 vs. 12%, p = 0.01).Both oral SA nifedipine and IV labetalol are effective options for treating PP severe hypertension. An initial choice of nifedipine was associated with a lower requirement for subsequent doses of medication and no need for crossover to an alternative antihypertensive medication. · Nifedipine and labetalol effectively treat PP severe HTN.. · Nifedipine requires fewer doses to treat PP severe HTN.. · Both have low recurrence rates of severe HTN..

Radio-Telemetric Assessment of Cardiac Variables and Locomotion With Experimentally Induced Hypermagnesemia in Horses Using Chronically Implanted Catheters

The objective of this study was to characterize the pharmacokinetics and pharmacodynamics of intravenous administration of magnesium sulfate to horses using a novel radio-telemetry system for physiologic signal capture. Five Horses were surgically implanted with a radio-telemetric carotid catheter. Implants were paired with a non-invasive telemetric unit which acquired a six lead ECG and 3-axis acceleration to assess activity acquired wirelessly in real-time for future analysis. Horses were exposed to a new stall environment before (baseline) and after 60 mg/kg (30 mL) of magnesium sulfate (MgSO₄), or the same volume of 0.9% saline, administered intravenously in a blinded, random crossover design. Blood for pharmacokinetics, telemetric data, and body temperature were recorded serially for 24 h. Data were analyzed across time and between treatments. Significance was set at P < 0.05. Ionized magnesium concentration (Mg²⁺) increased and the Ca²⁺ to Mg²⁺ ratio decreased and persisted for 5 h after MgSO₄ administration. Heart rate (HR) increased and mean arterial blood pressure (MAP) decreased for at least 6 h. Electrocardiogram (ECG) intervals (RR) decreased and (PR and QTc) increased in duration compared to controls indicating an increase in heart rate, and slower myocardial conduction in the MgSO₄ group. Acceleration in all planes was less in the MgSO₄ group compared to controls indicating decreased locomotion. This novel method permitted collection of physiologic signals without interference by handlers or animal restraint. An intravenous bolus of MgSO₄ produced cardiac variable changes associated with the reduction of locomotion in these horses, and in a direction that may be causal. Locomotion was decreased when horses were first introduced into a new environment which reflects the calming effect desired in sport horses. Telemetric monitoring can be used as a model to elucidate the behavior and physiologic effects of other drugs. The administration of MgSO₄ may be detected for regulatory purposes with the monitoring of Mg²⁺ and Ca²⁺ concentrations and their ratio.

Therapeutic effects of a taurine-magnesium coordination compound on experimental models of type 2 short QT syndrome

Short QT syndrome (SQTS) is a genetic arrhythmogenic disease that can cause malignant arrhythmia and sudden cardiac death. The current therapies for SQTS have application restrictions. We previously found that Mg· (NH₂CH₂CH₂SO₃)2· H₂O, a taurine-magnesium coordination compound (TMCC) exerted anti-arrhythmic effects with low toxicity. In this study we established 3 different models to assess the potential anti-arrhythmic effects of TMCC on type 2 short QT syndrome (SQT2). In Langendorff guinea pig-perfused hearts, perfusion of pinacidil (20 μmol/L) significantly shortened the QT interval and QTpeak and increased rTp-Te (P<0.05 vs control). Subsequently, perfusion of TMCC (1-4 mmol/L) dose-dependently increased the QT interval and QTpeak (P<0.01 vs pinacidil). TMCC perfusion also reversed the rTp-Te value to the normal range. In guinea pig ventricular myocytes, perfusion of trapidil (1 mmol/L) significantly shortened the action potential duration at 50% (APD₅₀) and 90% repolarization (APD₉₀), which was significantly reversed by TMCC (0.01-1 mmol/L, P<0.05 vs trapidil). In HEK293 cells that stably expressed the outward delayed rectifier potassium channels (I_Ks), perfusion of TMCC (0.01-1 mmol/L) dose-dependently inhibited the IKs current with an IC₅₀ value of 201.1 μmol/L. The present study provides evidence that TMCC can extend the repolarization period and inhibit the repolarizing current, I_Ks, thereby representing a therapeutic candidate for ventricular arrhythmia in SQT2.

Mg(2+)-dependent facilitation and inactivation of L-type Ca(2+) channels in guinea pig ventricular myocytes

This study aimed to investigate the intracellular Mg(2+) regulation of the L-type Ca(2+) channels in guinea pig ventricular myocytes. By adopting the inside-out configuration of the patch clamp technique, single channel currents of the L-type Ca(2+) channels were recorded at different intracellular Mg(2+) concentrations ([Mg(2+)]i). At free [Mg(2+)]i of 0, 10(-9), 10(-7), 10(-5), 10(-3), and 10(-1) M, 1.4 μM CaM + 3 mM ATP induced channel activities of 44%, 117%, 202%, 181%, 147%, and 20% of the control activity in cell-attached mode, respectively, showing a bell-shaped concentration-response relationship. Moreover, the intracellular Mg(2+) modulated the Ca(2+) channel gating properties, accounting for alterations in channel activities. These results imply that Mg(2+) has a dual effect on the L-type Ca(2+) channels: facilitation and inhibition. Lower [Mg(2+)]i maintains and enhances the basal activity of Ca(2+) channels, whereas higher [Mg(2+)]i inhibits channel activity. Taken together, our data from the application of an [Mg(2+)]i series suggest that the dual effect of Mg(2+) upon the L-type Ca(2+) channels exhibits long open-time dependence.

Decreased seizure threshold in an eclampsia-like model induced in pregnant rats with lipopolysaccharide and pentylenetetrazol treatments

Objective

Eclampsia is a poorly understood but potentially fatal complication of pregnancy. Research to date on this disorder has been hampered by the lack of a suitable animal model. To correct this deficiency, this report describes the generation of a rat eclampsia-like model using pentylenetetrazol (PTZ) in a previously established rat preeclampsia model.

Method

Rats were administered lipopolysaccharide (1.0 µg/kg) by tail vein injection on gestational day 14 to establish preeclampsia (PE). PE and control rats (non-pregnant, NP; normal-pregnant, P) were injected intraperitoneally (i.p.) with PTZ (40 mg/kg) to induce seizures. In separate experiments, MgSO₄ (270 mg/kg IP) was injected in advance of PTZ into PE rats to observe its effect on PTZ-induced seizures.

Results

PE conditions were verified in rats after LPS administration by significantly higher blood pressure (P<0.01) and urinary albumin excretion (P<0.05), elevated sFlt-1 (P<0.05) and decreased PlGF serum levels (P<0.05), and evidence of hepatic dysfunction compared to control groups. PTZ successfully induced seizure activity in all groups studied. Latency to seizure was significantly (P<0.01) less in the PE-PTZ group (73.2±6.6 sec.) than in PTZ-treated controls (107.0±7.4 sec.). Pretreatment with MgSO₄ prolonged (P<0.05) latency to seizure, shortened seizure duration and decreased seizure rates. Significant increased (P<0.05) in the serum levels of the inflammatory cytokines TNF-α and IL-1β in PE and PE-PTZ groups, and decreased (P<0.05) in their levels following MgSO₄ administration.

Conclusion

This PTZ-induced eclampsia-like rat model is comparable to the human condition of eclampsia and may serve as a useful research tool for future studies of this disease. The increased inflammatory cytokines in preeclampsia are coincident with a decreased threshold for PTZ-induced seizures, suggesting that an inflammatory mechanism may contribute to the susceptibility to seizure activity and inflammation might have an important role in eclampsia.

Maternal magnesium supplementation reduces intrauterine growth restriction and suppresses inflammation in a rat model

OBJECTIVE

Intrauterine growth restriction (IUGR) is associated with increased inflammatory responses. We sought to investigate whether magnesium (Mg) attenuates inflammation and IUGR in a rat model.

STUDY DESIGN

Pregnant Wistar rats (12 weeks, gestational day 18) were randomly assigned to 1 of 4 groups: normal diet with bilateral uterine artery ligation (BL) (n = 6) or sham surgery (SH) (n = 5); and Mg chloride (MgCl2) 1% (wt/vol) in the drinking water throughout gestation + BL (MgBL) (n = 6) or SH (MgSH) (n = 5). Dams were euthanized 24 hours postsurgery (gestational day 19). Maternal plasma, fetal plasma (pooled), individual amniotic fluid (AF) samples, and placentas (PL) were collected and assessed from live fetal pups only (BL, n = 36; SH, n = 20; MgBL, n = 20; MgSH, n = 20). All samples were analyzed for cytokines/chemokines (interleukin [IL]-6, IL-1β, chemokine [C-X-C motif] ligand 1 [CXCL1], chemokine [C-C motif] ligand 2 [CCL2], and tumor necrosis factor [TNF-α] sensitivity <3 pg/mL) using a multiplex platform. Data were analyzed using Mann Whitney, analysis of variance, and Fisher exact tests.

RESULTS

The incidence of IUGR (pup weight <10th percentile of SH) in the MgBL group was significantly lower (31%) than the BL group (86.3%) (relative risk, 0.36; 95% confidence interval, 0.2-0.6; P < .0001). BL significantly increased AF levels of IL-6, IL-1β, TNF-α (P < .05), and CCL2 (P < .001) vs SH and PL levels of IL-6, IL-1β, CCL2 and CXCL1 (P < .001), and TNF-α (P < .05) vs SH. Maternal MgCl2 supplementation significantly decreased IL-1β, TNF-α, and CCL2 levels in AF and IL-1β in PL tissues of MgBL vs BL rats (P < .0001).

CONCLUSION

Maternal oral MgCl2 supplementation reduced BL-induced IUGR by 64% and suppressed cytokine/chemokine levels in the AF and PL.

Effects of taurine-magnesium coordination compound on ionic channels in rat ventricular myocytes of arrhythmia induced by ouabain

Taurine-magnesium coordination compound (TMCC) has anti-arrhythmic effects. The aim of the present study was to explore the targets of the anti-arrhythmic effect of TMCC and the electrophysiological effects of TMCC on ouabain-induced arrhythmias in rat ventricular myocytes. Sodium current (I(Na)), L-type calcium current (I(ca, L)), and transient outward potassium current (I(to)) were measured and analyzed using whole-cell patch-clamp recording technique in normal rat cardiac myocytes and rat ventricular myocytes of arrhythmia induced by ouabain. In isolated ventricular myocytes, I(Na) and I(to) were blocked by TMCC (100, 200, 400 μM) in a concentration-dependent manner, and the effects of TMCC (400 μM) were equal to that of amiodarone. However, I (ca, L) was moderately increased by TMCC (400 μM) while significantly decreased by amiodarone. Ouabain (5 μM) significantly decreased sodium, L-type calcium, and transient outward potassium currents. TMCC (100 μM) relieved abnormal sodium currents induced by ouabain through facilitation of steady-state inactivation. TMCC (200 and 400 μM) relieved abnormal L-type calcium currents induced by ouabain through facilitation of steady-state activation and retardation of steady-state inactivation. TMCC failed to further inhibit abnormal transient outward potassium currents induced by ouabain. However, amiodarone inhibited the decreasing sodium, L-type calcium, and transient outward potassium currents further. These data suggest that I(Na), I(ca, L), and I(to) may be the targets of the antiarrhythmic effect of TMCC, which can antagonize ouabain-induced changes of ionic currents in rat ventricular myocytes.

Reduced NO signaling during pregnancy attenuates outward uterine artery remodeling by altering MMP expression and collagen and elastin deposition

Recent findings indicate that endothelial nitric oxide (NO) plays a key role in uterine artery outward circumferential remodeling during pregnancy. Although the underlying mechanisms are not known, they likely involve matrix metalloproteinases (MMPs). The goal of this study was to examine the linkage among NO inhibition, expansive remodeling, and MMP expression within the uterine vascular wall. Adult female rats were treated with N(G)-nitro-L-arginine methyl ester [L-NAME (LPLN)] beginning on day 10 of pregnancy and until death at day 20 and compared with age-matched controls [late pregnant (LP)]. Mean arterial pressure of LPLN rats was significantly higher than controls. LPLN fetal and placental weights were significantly reduced compared with controls. Main uterine arteries (mUA) were collected to determine dimensional properties (lumen area and wall thickness), collagen and elastin content, and levels of endothelial nitric oxide synthase (eNOS) and MMP expression. Circumferential remodeling was attenuated, as evidenced by significantly smaller lumen diameters. eNOS RNA and protein were significantly (>90%) decreased in the LPLN mUA compared with LP. Collagen and elastin contents were significantly increased in LPLN rats by ∼10 and 25%, respectively, compared with LP (P < 0.05). Both MMP-2 and tissue inhibitors of metalloproteinase-2 as assessed by immunofluorescence were lower in the endothelium (reduction of 60%) and adventitia (reduction of 50%) of LPLN compared with LP mUA. Membrane bound MMP-1 (MT1-MMP) as assessed by immunoblot was significantly decreased in LPLN. These data suggest a novel contribution of MMPs to gestational uterine vascular remodeling and substantiate the linkage between NO signaling and gestational remodeling of the uterine circulation via altered MMP, TIMP-2, and MT1-MMP expression and activity.

Animal models of pre-eclampsia

The cardinal features of human pre-eclampsia, hypertension and proteinuria, are mimicked in animal models. Increasingly, the accuracy of inducing 'pure' systemic endothelial dysfunction is regarded as critical in differentiating mechanisms of pre-eclampsia from other conditions which induce hypertension (e.g. glomerulonephritis, renal denervation or manipulation of the renin-angiotensin system). A recent study in baboons has identified the timing of induction of maternal endothelial damage after acute uteroplacental ischaemia (UPI). The endothelial changes in the glomerulus are indicative of a direct endothelial toxin and mimic the lesions seen in human pre-eclampsia; the extent of hypertension and proteinuria are also similar. This animal model identifies systemic and placental sFLT-1 (soluble fms-like tyrosine kinase-1) as a potential mediator of endothelial damage. This research involving primates with haemomonochorial placentas makes translation of these results to humans very compelling for understanding the mechanisms of human disease. Similar endothelial dysfunction has been identified in baboons treated with anti-inflammatory inhibitors. Similar studies in rodents have identified a relationship between angiotensin II agonistic antibodies, UPI/reduced uteroplacental perfusion pressure, angiogenic markers, and cytokines. We can now identify vasoconstrictive mediators of the hypertensive and endothelial response such as endothelin 1, the renin-angiotensin system, or other hormones such as oestrogens in primate models.

Effects of magnesium on central arterial compliance in preeclampsia

OBJECTIVE

The objective of the study was to investigate the effect of MgSO4 infusion on central arterial compliance, using radial artery applanation tonometry in women with preeclampsia.

STUDY DESIGN

Seventy women with preeclampsia were prospectively recruited. Radial pulse waveforms were obtained and the aortic waveforms constructed. The arterial compliance surrogates, augmentation pressure (AP) and augmentation index (AIx-75), were derived from the aortic waveform and then compared: prior to MgSO4 (t1), 1 hour after MgSO4 bolus (t2), 4 hours after MgSO4 infusion (t3), and 24 hours after MgSO4 cessation (t4). Statistical analysis was performed using differences of least squared means with Tukey Kramer adjustments.

RESULTS

The AP and AIx-75 at t2-t4 were significantly lower compared with t1, with the greatest decrease in arterial stiffness at t3 (P<.05).

CONCLUSION

In preeclampsia, MgSO4 improved central arterial compliance. This effect was most exaggerated after 4 hours of infusion and remained 24 hours following MgSO4 completion, suggesting either a sustained arterial compliance effect or resolution of the vasoconstrictive effect of preeclampsia.

Magnesium in obstetrics

Magnesium is a critical physiological ion, and magnesium deficiency might contribute to the development of pre-eclampsia, to impaired neonatal development and to metabolic problems extending into adult life. Pharmacologically, magnesium is a calcium antagonist with substantial vasodilator properties but without myocardial depression. Cardiac output usually increases following magnesium administration, compensating for the vasodilatation and minimising hypotension. Neurologically, the inhibition of calcium channels and antagonism of the N-methyl-d-aspartic acid (NMDA) receptor raises the possibility of neuronal protection, and magnesium administration to women with premature labour may decrease the incidence of cerebral palsy. It is the first-line anticonvulsant for the management of pre-eclampsia and eclampsia, and it should be administered to all patients with severe pre-eclampsia or eclampsia. Magnesium is a moderate tocolytic but the evidence for its effectiveness remains disputed. The side effects of magnesium therapy are generally mild but the major hazard of magnesium therapy is neuromuscular weakness.

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.

Magnesium sulfate for the treatment of eclampsia: a brief review

BACKGROUND AND PURPOSE

Magnesium sulfate is used extensively for prevention of eclamptic seizures. Empirical and clinical evidence supports the effectiveness of magnesium sulfate; however, questions remain as to its safety and mechanism. This review summarizes current evidence supporting the possible mechanisms of action and several controversies for magnesium sulfate treatment.

SUMMARY OF REVIEW

Several mechanisms are presented, including the effects of magnesium sulfate on peripheral and cerebral vasodilation, blood-brain barrier protection, and as an anticonvulsant.

CONCLUSIONS

Though the specific mechanisms of action remain unclear, the effect of magnesium sulfate in the prevention of eclampsia is likely multi-factorial. Magnesium sulfate may act as a vasodilator, with actions in the peripheral vasculature or the cerebrovasculature, to decrease peripheral vascular resistance or relieve vasoconstriction. Additionally, magnesium sulfate may also protect the blood-brain barrier and limit cerebral edema formation, or it may act through a central anticonvulsant action.

Vascular endothelial growth factor attenuates Nomega-nitro-L-arginine methyl ester-induced preeclampsia-like manifestations in rats

OBJECTIVES

To verify the hypothesis that vascular endothelial growth factor (VEGF) attenuates Nomega-Nitro-L-arginine Methyl Ester (L-NAME)-induced preeclampsia-like manifestations in rats.

STUDY DESIGN

Forty pregnant Wistar rats were randomly divided into four groups: control, preeclampsia model, VEGF treatment, and VEGF prophylactic. On day 5 of gestation, L-NAME was injected subcutaneously in rats of the preeclampsia model, VEGF treatment, and VEGF prophylactic groups. VEGF was given after the occurrence of hypertension and proteinuria in the VEGF treatment group and from day 5 in the VEGF prophylactic group. Blood pressure was monitored and urine protein was assayed. Blood platelet was counted, and serum nitric oxide metabolites, endothelin-1, 6-keto-PGF-1alpha, and TXB2 were determined.

RESULTS

Blood pressure increased significantly on day 8 of gestation in the preeclampsia model and VEGF treatment groups compared with control (p < 0.05 for both) and remained elevated through the pregnancy in the preeclampsia model group. Blood pressure was significantly decreased after the administration of VEGF in the VEGF treatment group (p < 0.05). There was no significant difference in blood pressure between the VEGF prophylactic group and control (p > 0.05). Urine protein, platelet count, serum nitric oxide metabolites, endothelin-1, 6-keto-PGF-1alpha, and TXB2 were significantly different between control and the preeclampsia model group (p < 0.05), but not between control and the VEGF treatment or VEGF prophylactic groups (p > 0.05 for all).

CONCLUSION

VEGF attenuates L-NAME-induced preeclampsia-like manifestations in rats, suggesting the important role of VEGF in preeclampsia and providing a potential strategy for the prevention and treatment of preeclampsia.