Strong effect of PTH (1-34) on regenerating bone - A time sequence study in rats

This study compares the effects of parathyroid hormone (PTH) treatment on n ew bone formation and normal baseline remodelling in rats. To study new bon e formation we used a titanium bone chamber, and to study normal remodellin g me used the femur and vertebrae from the same animals. One titanium bone chamber was inserted in the proximal tibia of each of 37 rats. The rats wer e randomly assigned to daily injections of human PTH (1-34) 60 mug/kg) or v ehicle control and killed after 2, 4 or 6 weeks. The total distance of bone growth into the chamber was slightly increased b y PTH. Body weight was not affected, and there was only a minor increase in trabecular density of the vertebral and femoral cancellous bone after 6 we eks. The only dramatic effect of PTH was seen in the chambers, In the controls, a marrow cavity formed in the chamber so that the cancellous density decrea sed from 44% to 24%, and 11% over 2, 4 and 6 weeks. In the PTH-treated anim als, a dense network of bone trabeculae was found in the entire bone chambe r at all times. The cancellous density increased from 48% to 60%, and 73% a t 2, 4 and 6 weeks, respectively. The results suggest that PTH treatment can reduce the development of a reso rption cavity. Thus, PTH in this model had a net antiresorptive effect, pro bably solely because it stimulated osteoblastic activity. Even though osteo clastic activity was present throughout the PTH specimens, it was not suffi cient to resorb all newly formed bone. Since PTH seemed to have a greater effect on new bone formation in the cham ber than on normal bone remodeling, it might become useful for improving th e incorporation of orthopedic implants and stimulating fracture repair.