Objective      To investigate the effect of tetramethylpyrazine (TMP) on inducible nitric oxide synthase (iNOS) expression and NO synthesis in interleukin-1β (IL-1β)-induced rabbit articular chondrocytes.       Methods      The chondrocytes derived from the joint of rabbits were cultured in vitro. Toluidine blue staining was applied to detect proteoglycan

and immunofluorescence assay was applied to detect type Ⅱ collagen in primary culture of rabbit articular chondrocytes. The primary cultures were incubated with IL-1β 10 ng/ml plus different concentrations of TMP (5

10

15 and 20 μg/ml) for 48 h. Then the gene and protein expression of iNOS was determined by RT-PCR and immunohistochemistry

respectively

and the NO synthesis level was determined by nitrate reduction assay.       Results      The rabbit articular chondrocyte appeared as a triangle or a polygon. Proteoglycan and type Ⅱ collagen were mainly expressed in the cytoplasm

and type Ⅱ collagen was rarely located in the nucleus. Compared with the control group

iNOS expression significantly increased in the articular chondrocytes incubated with IL-1β alone (P0.01)

but the increase was inhibited in the articular chondrocytes incubated with IL-1β plus different concentrations of TMP (P0.05

P0.01).       Conclusion      Tetramethylpyrazine can inhibit iNOS expression and NO synthesis in rabbit articular chondrocytes induced by IL-1β.