Magnesium Chloride Infusion Research Articles

Intravenous infusion of magnesium chloride improves epicenter blood flow during the acute stage of contusive spinal cord injury in rats.

Vasospasm, hemorrhage, and loss of microvessels at the site of contusive or compressive spinal cord injury lead to infarction and initiate secondary degeneration. Here, we used intravenous injection of endothelial-binding lectin followed by histology to show that the number of perfused microvessels at the injury site is decreased by 80-90% as early as 20 min following a moderate T9 contusion in adult female rats. Hemorrhage within the spinal cord also was maximal at 20 min, consistent with its vasoconstrictive actions in the central nervous system (CNS). Microvascular blood flow recovered to up to 50% of normal volume in the injury penumbra by 6 h, but not at the epicenter. A comparison with an endothelial cell marker suggested that many microvessels fail to be reperfused up to 48 h post-injury. The ischemia was probably caused by vasospasm of vessels penetrating the parenchyma, because repeated Doppler measurements over the spinal cord showed a doubling of total blood flow over the first 12 h. Moreover, intravenous infusion of magnesium chloride, used clinically to treat CNS vasospasm, greatly improved the number of perfused microvessels at 24 and 48 h. The magnesium treatment seemed safe as it did not increase hemorrhage, despite the improved parenchymal blood flow. However, the treatment did not reduce acute microvessel, motor neuron or oligodendrocyte loss, and when infused for 7 days did not affect functional recovery or spared epicenter white matter over a 4 week period. These data suggest that microvascular blood flow can be restored with a clinically relevant treatment following spinal cord injury.

Magnesium Administration and Dysrhythmias After Cardiac Surgery

Objective. —To determine whether magnesium administration is effective in reducing postoperative morbidity and mortality after cardiac surgery. Design. —Randomized, double-blind, placebo-controlled trial. Setting. —A tertiary acute-care 500-bed university teaching hospital. Patients. —Over a 6-month period, 100 patients electively scheduled for cardiac surgery involving cardiopulmonary bypass were studied. Interventions. —Fifty patients were randomized to receive an intravenous infusion of magnesium chloride, 2 g, and 50 patients received placebo intraoperatively after the termination of cardiopulmonary bypass. Results. —Magnesium-treated patients had a significantly decreased frequency (P Conclusions. —Total and ultrafilterable hypomagnesemia are prevalent findings in cardiac surgery patients, and postoperative hypomagnesemia is strongly associated with clinically important morbidity. Magnesium administration decreased the frequency of postoperative ventricular dysrhythmias and increased the stroke volume and thereby cardiac index in the early postoperative period. (JAMA. 1992;268:2395-2402)

Magnesium Administration and Dysrhythmias After Cardiac Surgery

To determine whether magnesium administration is effective in reducing postoperative morbidity and mortality after cardiac surgery. Randomized, double-blind, placebo-controlled trial. A tertiary acute-care 500-bed university teaching hospital. Over a 6-month period, 100 patients electively scheduled for cardiac surgery involving cardiopulmonary bypass were studied. Fifty patients were randomized to receive an intravenous infusion of magnesium chloride, 2 g, and 50 patients received placebo intraoperatively after the termination of cardiopulmonary bypass. Magnesium-treated patients had a significantly decreased frequency (P < .04) of postoperative ventricular dysrhythmias (eight [16%] of 50) compared with placebo-treated patients (17 [34%] of 50). Patients who were normomagnesemic postoperatively had new supraventricular dysrhythmias less frequently (P < .03) than patients who were hypomagnesemic postoperatively (eight [17%] of 48 vs 19 [37%] of 52). Compared with placebo-treated patients, magnesium-treated patients had significantly higher (P < .02) postoperative cardiac indices in the intensive care unit (2.8 +/- 0.1 vs 2.5 +/- 0.1 L/min per m2). Patients with postoperative total and ultrafilterable hypomagnesemia had postoperative ventricular dysrhythmias (P < .04) and required prolonged mechanical ventilatory support (P < .01) more frequently than patients without postoperative hypomagnesemia. Total and ultrafilterable hypomagnesemia are prevalent findings in cardiac surgery patients, and postoperative hypomagnesemia is strongly associated with clinically important morbidity. Magnesium administration decreased the frequency of postoperative ventricular dysrhythmias and increased the stroke volume and thereby cardiac index in the early postoperative period.

Cyclosporin-induced hypomagnesaemia and renal magnesium wasting in rats.

1. Twenty-four hour clearance studies were performed on three groups of rats to determine the hypomagnesaemic effect of cyclosporin. Group I rats served as controls, whereas group II rats received 10 mg of cyclosporin/kg and group III rats received 20 mg of cyclosporin/kg daily. 2. After 7 days of cyclosporin treatment, plasma magnesium concentration was 1.04 +/- 0.01 mmol/l in control rats compared with 0.85 +/- 0.01 mmol/l in group II and 0.81 +/- 0.02 mmol/l in group III. After 14 days of cyclosporin administration, group III rats developed severe hypomagnesaemia (0.67 +/- 0.01 mmol/l). This reduction in plasma magnesium was associated with an increase in the urinary excretion of magnesium. 3. This reduction in plasma magnesium and increment in magnesium excretion returned to normal 7 days after cessation of treatment. 4. Additional three-phase acute clearance experiments were performed on eight normal and 12 cyclosporin-treated rats (20 mg/kg). These animals were subjected to acute magnesium chloride infusion. After graded magnesium chloride infusion, despite a similar rise in plasma magnesium, the fractional magnesium excretion was significantly higher in the cyclosporin-treated animals. 5. Analysis of the fractional intestinal absorption of magnesium suggested that the development of hypomagnesaemia after cyclosporin treatment is due to magnesium loss by the kidney. Furthermore, this effect of cyclosporin on magnesium transport is only present during cyclosporin treatment and is reversible when treatment with cyclosporin is withdrawn.

Renal magnesium wasting and hypocalciuria in chronic cis-platinum nephropathy in man.

1. The renal handling of calcium and magnesium was studied in six patients with persistent hypomagnesaemia after cis-platinum treatment for testicular tumours. 2. In comparison with normal subjects, the patients showed hypomagnesaemia (mean 0.54 mmol/l), which was associated with a normal urinary magnesium excretion (mean 4.83 mmol/24 h). Urinary calcium excretion was significantly lower in the patients than in the normal subjects (mean 2.05 vs 5.15 mmol/24 h, respectively; P less than 0.01), despite slightly higher total serum calcium levels (2.53 vs 2.38 mmol/l, respectively; P less than 0.05). During magnesium chloride infusion, when serum magnesium levels were comparable in patients and controls, urinary calcium excretion remained lower in the patients, indicating that hypomagnesaemia was not the cause of the hypocalciuria. 3. Dietary magnesium supplementation resulted in a significant increase in the serum magnesium levels in the patients, while dietary magnesium deprivation resulted in a comparable decrease in urinary magnesium excretion in patients and controls (to 1.46 and 2.00 mmol/day, respectively), although the serum magnesium level fell further (to 0.46 mmol/l) in the patients. 4. The dissociation of renal calcium and magnesium excretion appears to be part of the intrinsic tubular defect caused by cis-platinum. This dissociation of urinary calcium and magnesium excretion, which resembles that seen in Bartter's syndrome, may result from a lesion in the distal convoluted tubule.

Renal excretion of magnesium in a freshwater teleost, Salmo gairdneri.

Infusion of magnesium salts into the body cavity of freshwater-adapted rainbow trout led to elevated plasma magnesium concentrations and to stimulation of renal tubular secretion of magnesium. The majority of the infused load was excreted renally, no net branchial excretion being detected. Magnesium sulphate infusion led to increased tubular secretion of sulphate. Magnesium chloride infusion led to reduced tubular reabsorption of chloride. Magnesium could either be reabsorbed or secreted in control freshwater-adapted trout, apparently as a function of nutritional status. Fish could switch from reabsorption to secretion in response to magnesium loading. It is suggested that freshwater fish eliminate excess dietary magnesium renally.

Foetal plasma magnesium levels during maternal hypo- or hypermagnesaemia in ewes.

1. The influence of maternal hypo- or hypermagnesaemia of foetal plasma magnesium levels was studied in pregnant ewes between the 120th and the 145th day of gestation using a permanent catheter inserted in utero into the left aorta of the foetus on the 115th day of gestation. 2. In seven ewes, carrying eleven foetuses, the injection of 1 alpha-hydroxycholecalciferol induced a hypomagnesaemia which lasted 72 h. This had no significant effect on foetal plasma Mg levels. 3. In five ewes, carrying six foetuses, hypermagnesaemia induced by a 2 h magnesium chloride infusion had no significant effect on foetal plasma Mg levels. 4. These results provide evidence that in sheep during the last 20 d of gestation the foetal regulation of plasma Mg is independent of the maternal plasma Mg levels.

Effect of hypermagnesemia on the urinary concentrating mechanism in the rat and the dog.

In previous microperfusion studies in the rat, increasing luminal fluid magnesium concentration from 1.5 to 6.0 mEq/1 resulted in a 62% fall in proximal and a 74% fall in distal tubular osmotic water permeability. To determine whether this reduction in rat proximal tubular osmotic water permeability produced osmotic dysequilibrium between proximal tubular fluid and plasma, proximal (TF/P)osm were measured during isotonic saline and magnesium chloride infusion. In 11 rats, proximal (TF/P)osm was 0.99 ± 0.01 during isotonic saline and 0.98 ± 0.01 during magnesium chloride infusion; plasma magnesium concentration increased from 1.76 ± 0.12 to 6.03 ± 0.30 mEq/1. The effect of magnesium on the ability of hydropenic anti-diuretic rats and dogs to reabsorb free water was examined during hypertonic mannitol and saline diuresis. In the rat free water reabsorption was not affected by hypermagnesemia. In the dog hypermagnesemia caused a reduction in free water reabsorption at low levels of solute excretion and formation of a urine hypotonic to plasma at high levels of solute excretion. The reduction in rat proximal and distal tubule osmotic water permeability is not sufficient to affect osmotic equilibration across these tubular segments. Free water reabsorption, reflecting solute reabsorption in the ascending limb of Henle’s loop, is decreased by magnesium in the dog but not in the rat.

Interaction between sites of magnesium absorption in the digestive tract of the sheep

The effect of magnesium chloride infusion to different sites in the gastrointestinal tract of sheep upon the net absorption of magnesium from different regions of the digestive tract has been examined. Four Merino wethers were each prepared with cannulas sited in the rumen, in the duodenum adjacent to the pylorus and in the terminal ileum. The basal diet provided 18.45 mmoles magnesium/ day and an additional 65 mmoles magnesium/day as magnesium chloride was continuously infused into (A) the rumen, (B) the rumen and duodenum in equal portions, (C) the duodenum and (D) the terminal ileuni. A continuous infusion of Cr-EDTA to the ruinen enabled digcsta and magnesium flow rates to be estimated from digesta samples obtained from the intestinal cannulas at 4 hr intervals over 3 days. For treatments A, B, C and D respectively, the mean net absorption of magnesium (mmoles/day) from the rumen was 20.4, 11.4, 1.4 and 3.4; from the small intestine –0.5, 1.7, –5.1 and –9.8; from the large intestine 4.6, 2.2, 12.7 and 12.3; and from the total gastrointestinal tract 24.6, 15.4, 9.1 and 4.9. In each case the effect of treatment was significant. The total net absorption of magnesium caudal to the pylorus was unaffected by treatment. Plasma magnesium levels were reduced during post-ruminal infusion of magnesium, but these changes were not obviously linked to the changed net absorption from the intestinal segments. The urinary and faecal excretion of magnesium, but not the magnesium balance, was strongly related to the total net absorption of magnesium. The results emphasize the major contribution of the stomach to the gastrointestinal net absorption of magnesium and show that although the amount absorbed from this region may influence separately the net absorption from the large and small intestine, it does not appear to influence the overall intestinal net absorption of magnesium.

Abolition of magnesium-induced hypocalcaemia by acute thyro-parathyroidectomy in the cat.

ABSTRACT Intravenous infusion of isotonic magnesium chloride into young cats with a resultant mean plasma magnesium concentration of 7.7 meq./100 g protein was followed by a significant lowering of the plasma calcium concentration in 90 minutes. The rate of decrease of plasma calcium is consistent with the hypothesis that calcitonin is released by magnesium in high concentrations. There was no decrease in the plasma calcium concentration in cats of the same weight thyroparathyroidectomized 60 min before an identical magnesium chloride infusion or an infusion of isotonic sodium chloride at the same flow rate. The hypercalciuric effect of magnesium could not account for the hypocalcaemic effect of magnesium. Plasma magnesium concentration during magnesium infusion into cats with an intact thyroid-parathyroid gland complex was slightly, but not significantly higher than in acutely thyroparathyroidectomized cats.

Interrelation between renal transport systems of magnesium and calcium.

Infusion of magnesium chloride markedly increased the excretion of calcium in dogs. A slight but significant increase in the excretion of magnesium occurred following the infusion of calcium chloride. Utilizing the stop-flow technique it was noted that magnesium and calcium achieved minimal concentration ratios in the distal segments of the nephron. Infusion of magnesium chloride during stop-flow studies increased U/PCa/U/PCr ratios both in the proximal and distal samples. These observations support the postulate that magnesium and calcium compete for a common reabsorptive system in the renal tubules. In several stop-flow experiments Mg28 and Ca45 were injected along with inulin 1 or 2 minutes before releasing the ureteral occlusion. Mg28 and Ca45 appeared simultaneously in the urine prior to the appearance of inulin, suggesting transtubular flux of these cations. Such observations, while indicating bidirectional movement of these ions across the tubular epithelium, do not imply active or net secretion.