Objective To investigate the effect of parathyroid hormone related protein（PTHrP） on proliferation of human osteoblasts（MG-63） under the circumstance of tension force in vitro. Methods An apparatus was designed and fabricated by which force was loaded onto the cultured cells in vitro. Reverse transcription-polymerase chain reaction（RT-PCR） was used for measuring the expression of PTHrP mRNA and c-fos mRNA. The effect of tension force and different PTHrP dose（0, 0.01, 0.1, 1 nmol/L） on the proliferation of human osteoblasts were examined using flow cytometry. Results Various forces of the mechanical stretching exerted different influences on the intensities of the mRNA′ expression. The strain of 12% induced the most remarkable mRNA′ expression. The mitogenesis happened in the group with tension force（12%） combined with PTHrP was more active than that in the group with PTHrP or tension force only. Tension force combined with PTHrP induced significantly more c-fos mRNA than that of tension force only. Conclusion The mechanical stretching can inevitably influence the expression of PTHrP mRNA. The most active mitogenesis happened in the group with tension force combined with PTHrP. The effect may be related with the signaling pathways of c-fos.
