MAGNESIUM PARTITION STUDIES IN GRAVES' DISEASE AND IN CLINICAL AND EXPERIMENTAL HYPOTHYROIDISM

The influence of the parathyroid glands on the hypercalcemia of experimental magnesium depletion in the rat

Magnesium-deficient rats develop significant hypercalcemia, hypophosphatemia, and hyperphosphaturia. These changes suggest a state of hyperparathyroidism. This study examines the regulation of parathyroid gland activity in magnesium-deficient rats. Magnesium deficiency was induced in intact and chronically parathyroidectomized animals by feeding them a diet free of this cation. Control animals were pair fed and treated identically except for the inclusion of magnesium in their gavage solution.Magnesium-deficient rats with intact parathyroid glands developed significant hypercalcemia and hypophosphatemia. In addition, the concentration of ionic calcium in plasma was significantly elevated. In contrast, magnesium-deficient parathyroidectomized animals did not have a higher level of calcium in plasma than their nondeficient controls; they developed a decreased concentration of ionic calcium in the absence of a difference in the concentration of phosphate in plasma when compared with appropriate controls. The increased urinary excretion of phosphate was independent of the parathyriod status of the animals.It can be concluded that the hypercalcemia and hypophosphatemia of magnesium deficiency demands parathyroid gland activity and that the regulation of this activity is modified in the magnesium-deficient state to permit the maintenance of an elevated concentration of ionic calcium in plasma. Additional explanations must be found for the hyperphosphaturia.

A method for distinguishing ionized, complexed and protein-bound Mg in normal and diseased subjects

Since 1932, it has been known that Mg exists in blood in several forms: protein-bound, complexed to certain anions, and ionized. However, there is discrepancy and debate on what these fractions are, how to accurately assess them, and whether they are important in diagnosis and prognosis of disease syndromes. Using the NOVA ISE for IMg2+, a controlled method for ultrafiltration of Mg and atomic absorption spectrophotometry, we have found four distinct fractions of Mg in healthy normal plasma and serum: 1. ultrafilterable Mg (81%) (made up of ionized and complexed); 2. ionized Mg (67%); 3. protein-bound Mg (19%); and 4. complexed Mg (14%). The amount of each fraction appears to depend upon the pathophysiologic state of the patients. Previous observations on the amount of complexed and ionized Mg are at best, only approximations, due to the absence of a device (i.e., ISE) to measure accurately IMg2+.

The discrimination between magnesium and manganese by serum proteins

Magnesium and manganese have proved physically and functionally interchangeable in many isolated biological systems investigated in vitro. This lack of discrimination contrasts sharply with the high biological specificity exhibited by intact mammals under a large variety of conditions. The dichotomy between intact animals and their isolated systems might be due at least partially to presence vs. absence of an intact circulation. Hence the capability of mammalian plasma to discriminate between the alkaline earth and the transition metal was investigated by means of equilibrium dialysis, exchange, ultrafiltration, ultracentrifugation, and zone electrophoresis. The states of the respective elements are thus contrasted as follows: (a) Magnesium is partially bound, manganese totally. (b) Magnesium is nonselectively bound by serum proteins, manganese selectively by a beta(1)-globulin. (c) Under conditions approaching physiological, the two metals do not interchange. This is interpreted as indicating that the plasma proteins contribute to biological specificity by discriminating between a trace metal and a macronutrient.