Observations in Experimental Magnesium Depletion*

Abstract

Studies of experimental magnesium depletion have been reported in the past (1)(2)(3)(4)(5)(6)(7)(8). This report describes a re-evaluation of this problem in which some of the previous observations have been confirmed and extended. In particular these studies were concerned with the interrelationships between magnesium deficiency and the metabolism of potassium, calcium, and phosphorus. In addition, the pathologic alterations of the kidneys were examined. These latter observations will be alluded to here, although they have been reported in an abstract (9), and will be the subject of a more detailed discussion in another publication. METHODS A-ND EXPERINIENTAL D)ESIGNFemiale Sprague-Dawley rats were used throughout. The animals were pair-fed by groups a synthetic diet free of sodium, potassium, chloride, phosphate, and magnesium. The composition of this diet is listed in Table I. In additon, each animal received daily by gavage an approp)riate electrolyte solution which will be described in specific terms later. Demineralized water was allowed at will.At the end of each experiment the animals were anesthetized with hexobarbital sodium administered intraperitoneally, and then exsanguinated from the abdominal aorta. Thigh, leg, and lumbar muscles were taken for chemical analysis, and the other tissues obtained for histologic examination. In some experiments total carcass was also analyzed. The preparation of erythrocytes for analysis involved an initial centrifugation in a plastic tube, followed by the removal of plasma and buffy coat. The red cell mass was then recentrifuged at 20,000 g for 15 minutes. At the end of this time the tube was frozen, and then a cut was made just below the top of the erythrocyte mass. In this fashion a quantity of relatively pure red cells was obtained.The chemical methods were as follows: urea nitrogen vith the autoanalyze.r utilizing the calorimetric reaction with diacetyl monoxime (10); sodium and potassium,

Impaired tyrosine-kinase activity of muscle insulin receptors from hypomagnesaemic rats

“…Another mechanism that has been postulated for the low insulin secretion present in hypomagnesaemic rats is a probable low pancreatic K + content [40], Although we did not measure the K + content in pancreas or in skeletal muscle, there is evidence of a low K + content in various tissues of hypomagnesaemic rats; i.e. skeletal muscle, liver and heart, in association with either normal or low serum K + levels [41][42][43]. Therefore, the independent role of Mg +2 and K + on the impaired glucose-induced insulin secretion in hypomagnesaemia remains to be clarified.…”

Magnesium Modulates ROMK Channel–Mediated Potassium Secretion

“…5 Under these conditions, plasma Mg 2ϩ concentrations may fall to one third of normal values. [1][2][3] In cells in culture, cytoplasmic Mg 2ϩ decreases in parallel with that in the extracellular medium. 22 Using these values, we can calculate that, for an apical membrane potential around Ϫ40 mV and a luminal K ϩ of 1 mM, a decrease in cytoplasmic Mg 2ϩ from 1 to 0.5 mM would increase K ϩ conductance by about 30% ( Figure 3C).…”

“…Interactions between Mg 2ϩ and K ϩ cations can affect K homeostasis. [1][2][3] In particular, under conditions of Mg deficiency, it can be difficult to restore K balance unless the Mg deficit is corrected. 4 Recently, Huang and Kuo 5 suggested that Mg 2ϩ block of rat outer medullary K (ROMK) or Kir1.1 channels might play a role in this phenomenon.…”

Mechanism of Hypokalemia in Magnesium Deficiency

“…3,4 Magnesium deficiency impairs Na-K-ATPase, which would decrease cellular uptake of K ϩ . 3 A decrease in cellular uptake of K ϩ , if it occurs along with increased urinary or gastrointestinal excretion, would lead to K ϩ wasting and hypokalemia. Little K ϩ is excreted by the gastrointestinal tract normally; therefore, hypokalemia in magnesium deficiency is likely associated with enhanced renal K ϩ excretion.…”