Mechanical stimualtions and estrogen play an important role in the formation and maintenance of normal functions in the micro-environment of cartilage.In this study, we investigated the synergistic effect of mechanical pressure and estrogen on the proliferation and alkaline phosphatase (ALP) activity of the rabbit mandibular condylar chondrocytes (MCCs). In vitro cultured MCCs from two-week-old New Zealand rabbits were untreated, treated with 10-6 mol/L, 10-9 mol/L and 10-12 mol/L 17
-estradiol (E2), respectively, or treated with pressure and a combination of hydraulic pressure (90kPa/1h) with each individual concentration of E2. ALP activity and cell proliferation were determined by modified enzyme kinetic method and MTT assay, respectively. Individual treatment with hydraulic pressure or E2 facilitated proliferation of MCCs. Combinational treatment with high or medium concentration of E2 (10-6 mol/L or 10-9mol/L) and pressure significantly decreased the effect of pressure on MCCs proliferation. However, combinational treatment with low concentration of E2 (10-12 mol/L) showed no significant effect on the MCCs proliferation stimulated by pressure. Individual treatment with either E2 or pressure significantly increased the activity of ALP. ALP activity in the MCCs treated with both E2 and pressure was higher than that in MCCs individually treated E2 or pressure. We conclude that (1) presence of pressure does not affect E2-stimulated MCCs proliferation; (2) estrogen significantly inhibits the pressure- induced proliferation and the inhibitory effect is closely related with the concentration of estrogen; (3) pressure and E2 have synergistic effect on the activation of ALP in MCCs.