Effect of calcitonin administration on young pig trabecular bone remodeling

Ten-week-old pigs were treated with 4 different treatment schedules of porcine calcitonin for 2 months. Groups C 1 and C 4 received continuous treatment: C 1 had daily IM injections (4 IU/kg/BW (body weight) each injection), and C 4 was infused with a minipump implanted subcutaneously delivering 4 IU/kg/BW/day. Groups C 2 and C 3 received intermittent calcitonin treatment (each injection 4 IU/kg/BW): C 2 was given 1 out of every four days, C 3 was injected 5 consecutive days out of 20 days. The total dosage received in C 1 versus C 4 and C 2 versus C 3 were the same. Results were evaluated by histomorphometry after double tetracycline labeling on iliac trabecular bone. Resorption surfaces were decreased in groups C 2, C 3 and C 4, but bone volume, osteoclast surfaces, and interstitial bone thickness were not modified in any group receiving calcitonin. Osteoblast and mineralizing surfaces were increased in group C 2, C 3 and C 4. Plasma 1,25-dihydroxyvitamin D concentration and bone formation rate were increased in groups C 2 and C 4. Plasma immunoreactive parathyroid hormone levels and parathyroid weights were not increased in any treated groups. In conclusion, 2-month calcitonin treatment did not decrease the amount of bone resorbed in growing pigs. Continuous calcitonin infusion and intermittent calcitonin administration induced an increase in the extent of active bone formation which might be in part dependent on an increased production of 1,25 dihydroxyvitamin D.