Evaluation of body magnesium stores

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Evaluation of body magnesium stores

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The Journal of LABORATORY and CLINICAL MEDICINE Copyright

VOLUME 84

©

1974 by The C. V. Mosby Ca,mpany

AUGUST 1974

NUMBER 2

Clinical and experimental Evaluation of body magnesium stores ALLEN C. ALFREY, NANCY L. MILLER, and DONALD BUTKUS Denver, Colo.

Muscle, erythrocyte, and bone magnesium was studied in patients with reduced, normal, and increased serum magnesium levels. Muscle magnesium content was shown to vary directly with muscle potassium levels and independently of other body magnesium stores. In contrast to the fact that serum magnesium did not consistently reflect muscle magnesium concentration there was a highly significant correlation between serum and bone magnesium levels. It would appear from these resuits that bone and extracellular fluid magnesium are the major magnesium pools in man increased during magnesium excess and decreased during magnesium depletion. Changes in muscle magnesium reflect changes in total body potassium and are not a valid indicator of total body magnesium .

Rasma, erythrocyte, muscle, and bone magnesium levels have all been used to estimate total body magnesium stores. During experimentally induced magnesium depletion the first change appears to be a fall in serum magnesium concentration. 1 However, recent studies by Lim and Jacobs 2 - f have shown reduced muscle magnesium in association with normal serum, erythrocyte, and bone magnesium levels in patients with chronic renal insufficiency, cirrhosis, and chronic diarrhea. The above authors have suggested that muscle magnesium is the most freely exchangeable and thus the first to fall during magnesium depletion. In contrast, Dunn and Walser5 in experimentally induced magnesium From the Veterans Administration Hospital and University of Colorado Medical Center, Denver. This study was supported in part by a grant from the Veterans Administration and by a grant (RR-51) from the General Clinical Research Centers, National Institutes of Hea,lth. Received for publication Nov. 5, 1973. Accepted tor publication May 2, 1974. Reprint requests: Dr. Allen C. Alfrey, Chief, Renal Medicine, Veterans Administration Hospital, 1055 Clermont St., Denver, Colo. 80220.

153

154 .fUlrey, Mill-er, alld Bntk1lS

] . Lab. Clin . Med August. 1974

35 3 .0

2 .5 ULTRAFILTERABLE MAGNESIUM

2 ·0

mEq/ L

1.5

1. 0

.5 ,-0 .99 UF MQ -0.78(10101 Mill ' .01 o+---,---,---,---,,--,,--,,--,,--~

o

.5

1.0

1.5

2 .0

2.5

3.0

35

4 .0

SERUM MAGNESIUM

mEq/L

Fig. 1. Correlation between total serum magnesium and ultrafiltrable magnesium.

Table I. Blood and tissue values in control subjects No.

Serum Mg Ultrafiltrable Mg Erythrocyte Mg Muscle Mg Muscle K Muscle Ca Cortical bone Mg

(31) (22) (27) (8) (8) (8) (6)

Mean

• 1.56 ± 1.15 4.60 75.6 424 12.6 352

±1

S.D.

0.08 mEq./L.

± 0.05 mEq./L. ± 0.34 mEq./L. ± 8.6 mEq./Kg. FFDS ± 28 5.2 ± 20

±

mEq./Kg. FFDS mEq./Kg. FFDS mEq./Kg. Ash

depletion and Muldowney and associates 6 in patients with malabsorption syndrome found reduced serum magnesium levels in association with normal muscle magnesium content. Although bone contains approximately 65 per cent of the total body magnesium and has usually been found to be decreased in experimentally induced magnesium depletion in animals, bone magnesium has rarely been measured in hypomagnesemic patients. Even fewer studies have been carried out in patients with hypermagnesemia to determine whether the elevated serum magnesium concentration is associated with increased magnesium content of other body pools. The purpose of the present study is to correlate serum, erythrocyte, bone and muscle magnesium levels in patients with hypo- and hypermagnesemia and to determine what effect alterations in other intracellular cations have on muscle magnesium levels. Methods Normal values for serum, ultrafiltrable, and erythrocyte magnesium were obtained from blood donors and members of a hemodialysis ;tilff. The normal values for muscle and bone magnesium were obtained from nonhospitaJized patients who experienced sudden death (u~u~Uy auto accident victims). The study group consisted of renal transplant donors and recipients, patients with chronic renal failure, renal tubular acidosis, magnesium-losing

\-olume

Body magnestnm stores

8~

):umber 2

155

4.0

3.0

PLASMA MAGNESIUM

2.0

mEq/L

1.0

REO CELL MAGNESIUM mEq/L

Fig. 2. Correlation between serum and erythrocyte magnesium levels. The normal range for erythrocyte and serum magnesium is shown by the rectangle. The open circles represent patients with chronic renal failure and the closed circles patients with a variety of disorders of magnesium and potassium m~tabolism.

nephropathy, primary hyperaldosteronism, hypokalemia secondary to laxative abuse, and chronic alcoholism. Informed consent was obtained from all patients from whom blood or tissue samples were taken for this study. Heparinized blood was centrifuged at 2,000 r.p.m. for 10 minutes immediately following withdrawal. The plasma was removed for analysis and ultrafiltrable magnesium was determined by the method of Lavietes' under strict anaerobic conditions. The red blood cells were trans· ferred to a 150 mm. by 1.5 mm. (internal diameter) capillary tube and recentrifuged for 2 hours at 2,000 r.p.m. in a refrigerated centrifuge. The tubes were broken 1 to 2 mm. below the buffy coat to obtain the packed red blood cells. Muscle and bone were obtained both at autopsy and by surgical biopsy. Bone was uni· formly taken from the iliac crest; \I"hprpas, muscle "'as obtained from either the abdominal wall or thigh. Tissues were maintainPd in a frozen state from the time of procurement until analysis. The muscle was then thawed and approximately 1 gram Bamples were minced and dried to a constant weight for 16 hours at 130 0 C. The samples were then ground to a fine powder, weighed and extrl1ete