Effect of calcitonin on the magnesium-induced bone resorption in the mouse

This study was performed to evaluate whether Mg directly influences the activity of bone resorbing cells in vivo. Young male mice were given oral Mg supplementation (10 mM) in drinking water for 14 days. In order to inhibit bone resorption, a group of animals received 1 IU/kg/day of salmon calcitonin (CT) concurrently with Mg supplementation. The effects of CT alone were also tested separately. Skeletal changes were evaluated by histomorphometric analysis of parameters of endosteal bone resorption and formation after double tetracycline and double 3H-proline labelings. Two weeks of Mg supplementation induced a significant increase in the number of acid phosphatase-stained chondroclasts (+21.1%) and osteoclasts (+12.2%) and in the extent of osteoclastic resorbing surface (+40.5%) without change in serum mineral concentrations. Treatment with CT alone decreased the number of actively resorbing chondroclasts by 11% and decreased the osteoclastic resorbing surface by 22.4% without change in the number of active osteoclasts. Despite this 'escape' phenomenon, treatment with CT concurrent with Mg administration completely abolished the stimulatory effect of Mg on bone-resorbing cells. CT also inhibited the Mg-induced stimulation of the bone mineralization rate and produced a slight inhibition of the bone matrix apposition rate. The data indicate that Mg activates the bone resorbing cells in vivo and that CT administration blunts the Mg-induced stimulation of bone resorption.