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 C
Mg/C
Na 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.
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