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

We studied the effects of intermittent administration of parathyroid hormon e (PTH(1-34)) on callus formation and mechanical strength of tibial fractur es in 27-month-old rats after 3 and 8 weeks of healing. 200 mug PTH(1-34)/k g was administered daily during both periods of healing, and control animal s with fractures were given vehicle. At 3 weeks, PTH treatment increased ma ximum 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 3 88% (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 2 1% (3 and 8 weeks). No differences in body weight were found between the ve hicle-injected and the PTH-treated animals during the experiment. In conclu sion, PTH treatment enhances fracture strength, callus volume and callus BM C after 3 and 8 weeks of healing.