Calcitonin treatment of immobilization osteoporosis in rats

We studied changes in bone mass induced by immobilization and the ability of salmon calcitonin to inhibit immobilization osteoporosis in rat. The bone mass of the immobilized hind leg of rat was compared with the contralateral non-treated leg. Neurectomy and cast immobilization reduced the bone mineral mass to an equal extent. However, the dose-response of calcitonin was different with these immobilization techniques. Calcitonin 15 IU kg^-1 administered once daily reduced bone ash weight difference significantly after 2 weeks' neurectomy (P < 0.001). This had no significant effect on the bone loss induced by cast immobilization, but the dose had to be delivered as two injections given every 12 h. Two weeks' immobilization decreased the incorporation of ⁴⁵Ca into bones. Calcitonin could not prevent this. However, calcitonin tended to inhibit the overall incorporation of 45Ca into bones in immobilized rats but yet had no effect on ⁴⁵Ca incorporation in non-immobilized rats. Immobilization decreased serum alkaline phosphatase activity in cast-immobilized animals. Neurectomy did not change serum alkaline phosphatase activity from a sham operation level. The tartrate-resistant acid phosphatase to total acid phosphatase ratio in the serum increased significantly in neurectomized rats and in cast-immobilized calcitonin-treated rats.