Effects of magnesium and lactose supplementation on bone metabolism in the X-linked hypophosphatemic mouse

Effect of dietary lactose on salt-mediated changes in mineral metabolism and bone composition in the rat

The effects of salt (sodium chloride) supplementation of rat diets (80 g/kg diet), with or without lactose (150 g/kg), were studied in weanling rats over 14 d. Dietary salt increased water intake and reduced weight gain and food conversion efficiency, but these variables were unaffected by lactose. Salt-supplemented rats exhibited a three- to fivefold increase in urinary calcium excretion and a small increase in urinary magnesium and phosphorus excretion, irrespective of dietary lactose content. In addition, salt supplementation reduced plasma alkaline phosphatase (EC 3.1.3.1) activity. Lactose increased urinary Ca and Mg excretion and plasma Ca and P concentrations. Salt reduced tibia mass but not tibia mass expressed relative to body-weight, but neither variable was affected by lactose. Both tibia Mg content and concentration were reduced by salt but unaffected by lactose, and neither tibia P content nor concentration was affected by salt or lactose. Tibia Ca content was reduced by salt but this was prevented by lactose. Tibia Ca concentration was unaffected by salt or lactose, although there was a reduction (not significant) in tibia Ca concentration in animals fed on the lactose-free diet. These results show that lactose had no independent effect on bone and that reduced accretion of bone mass and mineral content in rats fed on the high-salt diets was due, at least in part, to reduced growth. Failure to offset sodium-induced hypercalciuria by a compensatory increase in net Ca absorption may have contributed to reduced bone Ca accretion. The protective effect of lactose against reduced bone Ca accretion may be due to increased Ca absorption.

On the prevention and treatment of calcification disorders of old age

From several investigations it is known that magnesium oxide or hydroxide therapy causes a considerable delay of kidney stone recurrence in man. Further, it is known that the mortality of populations due to cardiovascular disease in areas with hard drinking water containing more magnesium and having a higher Mg/Ca ratio than soft water, is considerably lower than in soft water areas. In the present study a physiological model for the homeostasis of calcium and phosphate is given. It is shown that and why a slight magnesium deficiency causes the pH of bone extracellular fluid to decrease at or below the pH level of the other body fluids. This decrease makes the other body fluids supersaturated with octocalcium phosphate and this is the prime reason for calcification disorders in the soft tissues. Therefore, the hypothesis is proposed that soft tissue calcifications can be stopped and even prevented by magnesium therapy. However, they are not reversible and treatment with chelate therapy is contraindicated.

Contrasting effects of 1,25-dihydroxyvitamin D3 on bone matrix and mineral appositional rates in the mouse

In order to determine the effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on bone matrix appositional rate (Ma AR) and bone mineral appositional rate (Mi AR), three doses (0.06, 0.13 and 0.20 microgram/kg/d) of 1,25(OH)2D3 were continuously infused for seven days in young mice. Histologic parameters of bone formation and resorption were evaluated by morphometric and autoradiographic methods. All doses of 1,25(OH)2D3 increased serum calcium and produced a dose-related increase in the metaphyseal osteoclastic surface and in the number of acid phosphatase-stained osteoclasts. The Mi AR evaluated by double tetracycline labeling was enhanced at all dosage levels. By contrast the Ma AR evaluated by double 3H-proline labeling was decreased at the two highest doses of 1,25(OH)2D3 which also produced growth impairment. We concluded that the continuous administration of 1,25(OH)2D3 in the mouse produces contrasting effects on bone matrix synthesis and calcification, resulting in a dose-related reduction in the amount of osteoid.

Influence of magnesium supplementation on bone turnover in the normal young mouse

The effect of magnesium (Mg) supplementation on bone metabolism has been studied in the normal young mouse. Weanling male mice were given Mg-supplemented drinking water (5 mM or 32 mM Mg) for 4 weeks. Mineral and skeletal changes were assessed by biochemical methods and by histomorphometric analysis of endosteal bone formation and resorption parameters evaluated on tetracycline double-labeled, undecalcified caudal vertebrae. Magnesium supplementation increased serum and urinary Mg concentrations and bone Mg content. Both the calcification rate and the extent of tetracycline double-labeled osteoid surface increased progressively in Mg-treated mice, whereas the mineralization lag time was shortened. The osteoblastic surface was reduced, leading to a fall in osteoid surface. Stimulation of bone mineralization was associated with a rise in extracellular calcium (Ca) and phosphorus (P) concentrations whereas serum 25-OHD and 1,25(OH)2D levels remained normal. The Mg supplementation increased the number of acid phosphatase stained chondroclasts and osteoclasts and the extent of resorbing surface showing histochemically stained osteoclasts. Although urinary OH-proline increased above normal, Ca, P, and cyclic adenylic acid (cAMP) excretion and phosphate concentration (TmP/GFR) remained normal, suggesting that parathyroid hormone (PTH) secretion was not altered. The trabecular bone volume remained normal, showing that the increased bone resorption was balanced by the stimulated bone mineralization. The results show that Mg supplementation influenced both bone formation and resorption in the young mouse, and that the stimulation of bone mineralization was the result of increased extracellular mineral availability.(ABSTRACT TRUNCATED AT 250 WORDS)