Increases in callus formation and mechanical strength of healing fractures in old rats treated with parathyroid hormone.

We studied the effects of intermittent administration of parathyroid hormone (PTH(1-34)) on callus formation and mechanical strength of tibial fractures in 27-month-old rats after 3 and 8 weeks of healing. 200 microg PTH(1-34)/kg was administered daily during both periods of healing, and control animals with fractures were given vehicle. At 3 weeks, PTH treatment increased maximum load and external callus volume by 160% and 208%; at 8 weeks, by 270% and 135%. It also enhanced callus bone mineral content (BMC) by 190% and 388% (3 and 8 weeks). From week 3 to week 8, callus BMC increased by 60% in the vehicle-injected animals, and by 169% in the PTH-treated animals. In the contralateral intact tibia, PTH treatment increased BMC by 18% and 21% (3 and 8 weeks). No differences in body weight were found between the vehicle-injected and the PTH-treated animals during the experiment. In conclusion, PTH treatment enhances fracture strength, callus volume and callus BMC after 3 and 8 weeks of healing.