Changes In Plasma Magnesium Concentrations Research Articles

Magnesium flux caused by coronary artery bypass operation: Three patterns of deficiency

We undertook a study to evaluate the patterns of magnesium deficiency that may develop during and following coronary artery bypass operation without cardioplegia. In 18 patients intraoperative measurements of plasma magnesium and potassium concentrations and measurements of cardiac and skeletal muscle content of these ions were taken. The changes in plasma concentrations and excretion were evaluated postoperatively. Hemodilution at initiation of cardiopulmonary bypass caused a 17.3% decrease in plasma magnesium concentration ( p < 0.01), which persisted until the first postoperative day. By the fifth postoperative day the level was 19.5% greater than the preoperative value. Urinary excretion of magnesium reflected changes in plasma magnesium concentration. Cardiac muscle content of magnesium decreased by 133%. Plasma potassium concentration was elevated by hemodilution ( p < 0.01), and muscle potassium was not depleted. We conclude that three patterns of magnesium depletion occur: hemodilution, intraoperative cellular depletion, and postoperative cellular depletion. The findings support the need for magnesium supplementation during and after cardiac operation.

Effects of acute hypermagnesemia on the threshold for lidocaine-induced seizures in the rat

The effects of acute changes in plasma magnesium concentration on the threshold for lidocaine-induced seizures were evaluated in mechanically ventilated rats receiving 70% nitrous oxide and 30% oxygen. In experiment 1, male rats were intravenously administered either 0.9% sodium chloride (group I) or 5.0% magnesium sulfate to elevate plasma magnesium levels to 5.8 +/- 0.1 (group II) or 10.5 +/- 1.0 mg/dl (group III). In experiment 2, pregnant rats were intravenously administered either 0.9% sodium chloride (normomagnesemia) or magnesium sulfate, resulting in a plasma magnesium concentration of 7.8 +/- 1.4 mg/dl. Thirty minutes later, a continuous intravenous infusion of lidocaine (2.3 mg/kg per minute) was begun in both experiments. Biparietal electroencephalographic activity was monitored continuously. At the onset of electroencephalographic seizure activity, arterial plasma magnesium and lidocaine concentrations were measured. In groups I and III (experiment 1), brain parenchymal magnesium was also assayed. There were no differences in plasma lidocaine concentrations (in experiments 1 or 2) between saline solution and hypermagnesemic groups at onset of seizures. Brain magnesium level was unaltered by magnesium sulfate infusion. We conclude that acute administration of magnesium sulfate alters neither brain magnesium level nor the plasma lidocaine concentration associated with onset of electroencephalographic seizures.

The effect of age on erythrocyte magnesium concentrations of dairy cows during late pregnancy and early lactation

Blood samples were taken at weekly intervals from fifty four dairy cows (mainly Friesians and Jerseys) during the periods 8 weeks before and 8 weeks after calving. The cows were divided into two age groups; Group 1 consisting of 26 cows 2 1/2 to 4 years old and Group 2 consisting of 28 cows over 4 years old. The changes in erythrocyte magnesium (EMg) and plasma magnesium (PMg) concentrations before and after calving were expressed as the slope of each blood parameter regressed on weeks. The post-partum EMg concentration slope (increase) was greater (P less than 0.05) in the older cows than in the young ones. The older cows also had higher (P less than 0.05) mean EMg concentrations than the young cows. Between cow EMg concentrations variations were significant (P less than 0.05) in both age groups while the weekly EMg concentration variations were only significant (P less than 0.05) in the older cows after calving. Age did not influence the changes in PMg concentrations before or after calving. Nor did the PMg concentrations vary significantly either between cows or between weeks.

The effect of induced hypomagnesaemia and hypermagnesaemia on the erythrocyte magnesium concentration in cattle

Hypomagnesaemia was induced in ten yearling Friesian heifers by starving them for forty hours while hypermagnesaemia was induced in seven Friesian calves (about two and half months old) by intramuscular magnesium sulphate (MgSO4) injection. The plasma magnesium (PMg) concentration decreased (P less than 0.05) during starvation and increased (P less than 0.05) following MgSO4 administration. However the erythrocyte magnesium (EMg) concentration did not show any significant change either with starvation or following the MgSO4 administration. These results show that sudden and significant changes in PMg concentration do not have any significant effect on EMg concentration. Accordingly EMg concentration may be a better indicator of long-term body Mg status and during hypomagnesaemic tetany could show whether the decrease in PMg concentration was sudden or gradual.

Plasma magnesium during epidural anaesthesia. A study in patients undergoing transurethral prostatectomy.

The variations of plasma magnesium concentration in relation to protein concentration and plasma volume were studied in 12 patients during epidural anaesthesia for transurethral prostatectomy. The most significant changes in plasma magnesium concentration were observed during the onset of anaesthesia. From the arrival in the operating theatre to the start of operation, the concentration of plasma magnesium decreased from 0.88 (SD 0.10) mmol/l to 0.82 (SD 0.10) mmol/l. At the same time, the increase of 16 per cent in plasma volume was associated with a rise of 8.4 per cent in the total amount of magnesium in plasma. After commencement of surgery, the plasma magnesium concentration was unchanged throughout the remainder of the study period. The total plasma protein concentration and the erythrocyte volume fraction decreased during the onset of anaesthesia, remained stable during surgery and returned to initial values one hour postoperatively. The pre-operative changes in the plasma magnesium concentration may have been the result of haemodilution and mobilisation of magnesium ion from its bone stores. Postoperatively, an increased urinary loss of magnesium must have followed the injection of frusemide at the end of surgery. The consequences of these variations in plasma magnesium concentration are unlikely to be of clinical significance, except in patients with pre-existing subclinical magnesium deficiency.

The effects of hypermagnesaemia on calcitonin secretion in vivo.

SUMMARY The influence of magnesium on calcitonin (CT) secretion rate has been studied in pigs by perfusion of porcine thyroid glands, isolated in situ, under controlled conditions of flow rate and blood electrolyte composition. At concentrations of 4·4–12·7 mequiv./l, magnesium stimulated CT secretion in the presence of a normal calcium concentration in the perfusate. The maximum effect was reached at a concentration of about 7 mequiv. Mg/l. At higher magnesium concentrations, the secretion rate of CT tended to revert towards that found with concentrations of calcium and magnesium within the normal range. When hypermagnesaemia was superimposed on hypercalcaemia there was a fall in the secretion rate of CT as the Mg: Ca ratio in the perfusing blood plasma approached 1. The stimulatory effect of hypermagnesaemia was usually less than that caused by an equimolar increase in plasma calcium concentration. The results suggest that changes in plasma magnesium concentration probably do not influence CT secretion under normal conditions.

Magnesium metabolism in thyroid dysfunction.

The accuracy of estimation of magnesium in plasma and urine by atomic absorption spectrophotometry was discussed. The normal range of plasma magnesium by this method was 1.63-2.13mg/100ml. Among 23 hyperthyroid patients, 15 subjects were hypomagnesemic. The plasma magnesium levels in 4 hypothyroid patients were within the normal range but always higher than those in hyperthyroid patients. A significant inverse relationship was noted between plasma magnesium concentrations and parameters of thyroid function. Plasma magnesium concen-trations increased in hyperthyroid patients and decreased in hypothyroid patients during therapy. A significant positive relationship was noted between magnesium clearance and parameters of thyroid function. During the therapy, the changes in magne-sium clearance did not always correspond to the changes in plasma magnesium con-centration or parameters of thyroid function. On the contray, the changes in CMg/CNa ratio corresponded to the changes in plasma magnesium concentration or parameters of thyroid function. This may suggest that magnesium and sodium share a common pathway in the renal tubule and are reabsorbed competitively. A negative correlation was noted between plasma protein concentration and mangesium clearance. From these results, the main cause of abnormality in plasma magnesium concentration in thyroid dysfunction seems to be the changes in magnesium clearance by the influence of thyroid hormone. Magnesium clearance might be influenced, in part, by the changes in plasma protein concentration.

An investigation into the parathyroid origin of calcitonin.

SUMMARY To investigate the part played by the parathyroids as a source of calcitonin under controlled conditions, conscious, thyroidectomized animals have been used, in which a superior parathyroid was perfused with blood of variable composition and parathyroid venous blood could be collected at will. Hypercalcaemic perfusion of such a parathyroid gland usually resulted in a prompt systemic hypocalcaemic response but it was impossible to conclude with certainty that this was not merely due to the cessation of parathyroid hormone secretion. Although no effect was observed in acute experiments, cross-transfusion of parathyroid venous plasma during hypercalcaemic perfusion of the gland in conscious sheep was followed by a small hypocalcaemic response in the two recipient lambs. The time-course of this response was similar to that obtained in sheep following the intravenous injection of extracts of bovine superior parathyroid glands. However, pure parathyroid hormone, injected intravenously into a sheep, was also found to cause an initial hypocalcaemia, followed later by hypercalcaemia. In general, similar changes in plasma magnesium concentration accompanied those of plasma calcium concentration as a result of hypercalcaemic perfusion of a parathyroid gland or the intravenous injection of bovine parathyroid extracts. It is impossible to conclude with certainty that, in the sheep, the parathyroid glands secrete calcitonin in response to the stimulus of hypercalcaemia, although the possibility cannot be entirely eliminated.

Changes in plasma magnesium concentration during hibernation in the golden-mantled ground squirrel ( Citellus lateralis)

1. 1. Plasma magnesium concentrations of active (37°C) and hibernating (3°C) ground squirrels ( Citellus lateralis) have been compared over the whole hibernation period. 2. 2. In general, hibernating animals have a significantly higher plasma magnesium concentration than active animals. The increase is higher in females than males, but there is no difference between sexes in active animals. 3. 3. Over the whole hibernation period females have a declining plasma magnesium concentration eventually reaching the active level, which may be responsible for the terminal arousal. The hibernating behaviour of the animals has been related to the changes in plasma magnesium. 4. 4. The evidence suggests that the changes in plasma magnesium going from a hibernating to an aroused state, and vice versa, are active physiological processes.