Irwin Clark

The effects of alterations in dietary magnesium on calcium, phosphate and skeletal metabolism

The effect of increasing dietary magnesium on calcium and phosphate absorption and excretion by adult rats was investigated. Chemical and morphologic studies of the femora of these animals also were made. As the dietary level of magnesium was raised, absorption, balance and retention of calcium, magnesium and phosphate were increased; urinary calcium and magnesium were elevated, but urinary phosphate was decreased; skeletal content of calcium and magnesium were increased but that of phosphate was decreased; serum calcium was unchanged, a variable effect was seen on serum phosphate and serum magnesium was increased. Dietary deficiency of magnesium for 48 days was without significant effect on body weight gain of adult rats. The optimal level of magnesium for maximal bone activity in adult rats, as judged by histologic and alpharadiographic techniques was about 0.25% if the diet contained 0.8% calcium and 0.4% phosphorus. Levels much below or above 0.25% dietary magnesium resulted in bone of abnormal appearance and chemical composition.RésuméLes effects de laugmentation du magnésium alimentaire sur labsorption et lélimination du calcium et du phosphate sont étudiés chez le rat adulte. Des analyses chimiques et des examens morphologiques des fémurs de ces animaux ont été réalisés. En augmentant le magnésium alimentaire, labsorption, léquilibre et la rétention du calcium, magnésium et phosphate sont augmentés, le calcium et le magnésium urinaires sont augmentés, mais le phosphate urinaire est abaissé. Le calcium et le magnésium osseux sont augmentés, mais le phosphate osseux est abaissé. Le caclium sérique est inchangé: le phosphate sérique subit des variations inconstantes et le magnésium sérique est augmenté. Une insuffisance alimentaire en magnésium pendant 48 jours a peu deffet sur laugmentation pondérale des rats adultes. La quantité optimale de magnésium, permettant dobtenir la meilleure activité dapposition osseuse, est denviron 0.25%, lorsque lalimentation contient 0.8% de calcium et 0.4% de phosphate. Ce fait est mis en évidence par des méthodes histologiques et autoradiographiques. Le magnésium alimentaire, supérieur ou nettement inférieur à 0.25%, donne un os daspect atypique et de composition chimique anormale.ZusammenfassungDie Wirkung auf die Calcium- und Phosphat-Absorption und-Ausscheidung durch eine größere Aufnahme von Magnesium in der Nahrung wurde an erwachsenen Ratten untersucht. Chemische und morphologische Untersuchungen der Oberschenkelknochen der Tiere wurden vorgenommen. Bei Steigen des Magnesiumgehaltes in der Nahrung stiegen auch die Absorption, das Gleichgewicht und die Retention von Calcium, Magnesium und Phosphat an; Calcium- und Magnesiumgehalt im Urin stiegen ebenfalls, aber der Phosphatgehalt fiel; der Knochengehalt von Calcium und Magnesium stieg an, der Gehalt von Phosphat fiel; der Serum-Calciumgehalt blieb unverändert, unterschiedliche Befunde wurden bezüglich des erum-Phosphatgehaltes erhoben, und Magnesium im Serum war erhöht. Magnesiummangel inoder Nahrung während 48 Tagen war ohne deutliche Wirkung auf die Gewichtszunahme Svn erwachsenen Ratten. Der optimale Magnesiumspiegel für maximale Knochenaktivität in erwachsenen Ratten, bemessen durch histologische und alpharadiologische Verfahren, betrug etwa 0,25%, wenn die Nahrung 0,8% Calcium und 0,4% Phosphor enthielt. Werte bedeutend unter oder über 0,25% Magnesium in der Nahrung riefen Abnormalitäten in der Knochenstruktur und in ihrer chemischen Konstitution hervor.

Prevention of phosphate-induced nephrocalcinosis by parathyroidectomy.

Summary Intact rats, fed diets high in phosphate, develop nephrocalcinosis; but parathyroidectomized rats do not. Neither intact nor parathyroidectomized rats, fed diets high in calcium, have mineral deposits in their kidney. Intact rats, but not parathyroidectomized rats, fed diets high in calcium and phosphate, develop kidney calcification. The mineral deposits consist of at least calcium, magnesium, and phosphate.

Acid hydrolases in slices of articular cartilage and synovium from normal and abnormal joints.

Summary Five acid hydrolases, i.e., glu-cosaminidase, sulfatase, phosphatase, cathepsin, and glucuronidase were identified in normal articular cartilage and synovium of rabbit knee joints by incubating tissue slices with appropriate substrates. These enzymes were also assayed in cartilage and synovium of rabbit knee joints which had been subjected to continuous compression from 1 to 21 days. Significant elevation of enzyme activity occurred in the first two enzymes in the cartilage and in the first four enzymes from the synovium of the treated joints. Studies with tissue slices preincubated with and without substrate suggest that most of the hydrolysis of substrate occurs within the tissue, rather than as a result of enzyme liberation into the incubation medium.

Alterations in Thyroidal Calcitonin Content of Rats Fed Diets of Varying Ca:P Ratios

Summary The thyroidal content of CT was measured by bioassay and radioimmu-noassay in intact, parathyroidectomized, and adrenalectomized rats fed diets with varying Ca:P ratios for 4 to 8 weeks. There was a good correlation between values obtained with the two assay methods. In intact, parex, and adrex rats, thyroidal CT content was higher 4 and 8 weeks after feeding a diet with a Ca:P ratio of 1:8. However, there was a little difference in overall CT content between intact, parex, and adrex rats despite marked differences in the levels of serum calcium. CT content appeared to be related to the length of time the rats were fed the high phosphate diet. In intact rats fed diets with Ca:P ratios ranging from 8:1 to 1:8 and prepared by varying the calcium content (P constant at 0.4%), the CT content of thyroid gland and serum was elevated only in those animals fed the 1:8 diet. In other intact rats fed with diets having the same range of ratios but prepared by varying the phosphorus content (Ca constant at 0.4%), thyroidal CT increased progressively with the diets having a Ca:P ratio below 1:1. The results indicate that changes in thyroidal CT stores produced by feeding diets with varying Ca:P ratios cannot be explained solely on the basis of changes in the levels of serum calcium.

EFFECT OF MAGNESIUM IONS ON REMOVAL OF RADIOSTRONTIUM FROM RATS

Summary Magnesium is effective in increasing the elimination of Sr-89 by rats which had been given the isotope either one or 30 days before treatment. It is effective when given orally or parenterally. Oral administration of magnesium decreases fecal Sr-89; however, the sum of urinary and fecal Sr-89 is significantly greater than those of control animals. Supplementation of magnesium with citrate ions or Prednisolone was no more effective than magnesium alone.

An improved fluorometric procedure for the estimation of magnesium in biological materials

Abstract An improved, highly specific method is described for the fluorometric estimation of magnesium in biological materials. Interfering substances such as phosphate ions, which depress fluorescence, and calcium ions, which enhance fluorescence, have been eliminated. This method is reliable and reproducible over a wide range of calcium and phosphate levels and is convenient for routine analyses.

Effect of hypervitaminosis D upon the phospholipids of metaphyseal and diaphyseal bone.

Summary The phospholipids of the diaphyseal and metaphyseal portion of the long bones of rats have been analyzed. Lecithin, phosphatidylethanolamine, sphingomyelin and lysolecithin constitute the major phospholipids with small amounts of cardiolipin and phosphatidic acid also being present. Hypervitaminosis D was found to cause a significant increase in all phospholipids without a selective action on any one component. The incorporation of P32 into the phospholipids was found to be increased indicating an increased synthesis rather than a decreased break-down. It is suggested that the accumulation of lipid material may be related to the failure of the osteoid in hypervitaminosis D to calcify properly.

PERSISTENT PROTEASE ACTIVITY IN BONE FOLLOWING ACETONE FIXATION AND EDTA DEMINERALIZATION.

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The Effect of Vitamin D Deficiency on the Lipids of Bone Matrix

Summary The bones of control and vitamin D-deficient animals have been analyzed to determine whether the D-deficient state affects the lipids extractable from these bones. A decrease in serum calcium and an increase in serum phosphorus was noted and all D-deficient animals had an increase in the percentage of the organic fraction of the bones. There was an increase in the total lipids extractable from the epiphysis, metaphysic, and diaphysis; and a significant increase was found in the diaphyseal phospholipids and cholesterol. Significant decrease was noted in the metaphyseal fatty acid and an increase in the diaphyseal fatty acid, There was a decrease in the metaphyseal triglyceride and an increase in the diaphyseal triglyceride. It is concluded that perhaps there is an arrest in the conversion of neutral fats to phospholipids but that vitamin D-deficiency does not have a primary effect on phospholipid metabolism.