OBJECTIVETo examine the expression of activin A (ACT A) and transforming growth factor-beta 1 (TGF-beta 1) during mandibular lengthening and elucidate the difference between the role of ACT A and TGF-beta 1 during mandibular distraction osteogenesis.

METHODSkeletally mature white new zealand rabbits were established right mandibular distraction osteogenesis model. The regenerating tissue of animals' lengthened mandibes were harvested at different time points to have immunohistochemistric research of ACT A, TGF-beta 1 protein and analysis ACT A, TGF-beta 1 mRNA by using RT-PCR semiquantitative mean.

RESULTSAT the end of latency period day, positive stain of ACT A were found in the osteoblasts while positive stain of TGF-beta 1 was found in mesenchymal cells. At the end of distraction phase, fibrosis tissue had no stain of ACT A, but had strong stain of TGF-beta 1. At the period of fixation days of 20 days, both cytoplasm of osteoblasts and extracellular matrix in primary mineralization front were strongly stained of ACT A. The osteoblasts, osteoid and osteocytes in peripheral new bone zone were moderately stained of ACT A. TGF-beta 1 had strongly positive stained in fibrosis zone and weekly positive stained in primary mineralization front and peripheral new bone zone. There were also broad activin A stains in cytoplasm of osteoblasts, osteoid and cytoplasm of ACT A, TGF-beta 1 in osteocytes after distraction for 30 days. Activin A mRNA began to express at the end of latency period. Expression for activin A mRNA increased gradually along with the beginning of distraction and at the peak in distraction of 10 days and 20 days, while TGF beta 1 mRNA increased at the peak at the end of latency period.

CONCLUSIONACT A and TGF beta 1 have different role during rabbit mandibular distraction osteogenesis.