The effect of 1alpha-hydroxycholecalciferol on the healing of experimental fractures in adult rats.

Unilateral tibial fractures were produced in adult, 1-year-old, male Sprague-Dawley rats. The animals were then treated for 6 weeks with daily doses of 2.5 micrograms, 1.25 micrograms or 0.125 microgram 1alpha-hydroxycholecalciferol (1alpha-OH-D3). The aim of the investigation was to study the effect of this treatment on the healing process of the fracture and on the composition of the fractured bone. The general effect of 2.5 micrograms of 1alpha-OH-D3 was a significant loss of body weight (20 per cent) and hypercalcaemia. The lower dose levels, however, did not affect the body weight, and with a dose of 0.125 microgram the serum calcium level did not increase significantly. The healing rate of the fractures increased in all treatment groups as compared with the controls. The water content of the fractured tibias increased in the rats treated with 2.5 micrograms doses but decreased in the other groups. On the other hand the mineral content increased in the groups treated with 1.25 micrograms and 0.125 microgram doses and decreased in the largest dose group. Furthermore the amount of organic material per wet weight increased with the 2.5 micrograms dose and was mainly unchanged in the other groups. The hydrated bone density and the cortical thickness of the tibia increased most significantly in the group treated with 0.125 microgram but the trabecular bone area of the periosteal callus did not increase significantly. The conclusion is drawn that treatment with small doses of 1alpha-OH-D3 has a beneficial effect on the healing rate and on the mineralization of the fracture callus, and on cortical bone formation.