Biochemical and biomechanical properties of avian callus after local administration of dihydroxylated vitamin D metabolites

In vitamin D-fed chicks 1,25-dihydroxyvitamin D₃ and 24,25-dihydroxyvitamin D₃ were implanted into experimentally-produced fractures of the mid-tibia. The mechanical and biochemical properties of the tibia were evaluated for two weeks, including torsion tests, measurement of alkaline phosphatase activity, ⁴⁵Ca incorporation, and Ca²⁺ content. Both dihydroxylated metabolites of vitamin D₃ had a direct effect on endochondral bone formation. 24,25(OH)₂D₃ strengthened the callus, and raised alkaline phosphate activity in the first seven days after fracture. 1,25(OH)₂D₃ decreased the strength of the callus concomitant with a reduction in ⁴⁵Ca incorporation. It is suggested that local application of 24,25(OH)₂D₃ into fractures may accelerate healing and prevent non-union.