OBJECTIVE:To study the effect of methotrexate (MTX) combined with Sanhuang Yilong decoction (SYD) on aquaporin (AQP) expression,and to explore the role of AQPs in the pathogenesis of rheumatoid arthritis (RA).METHODS:A total of 118 dampness-heat blockage type RA patients who were hospitalized in the General Chengdu Military Hospital between January 2014 and December 2016 were selected as subjects in this study (30 patient of these patients with knee joint effusion were assigned to the RA synovial fluid group).For the pre-treatment control groups,30 healthy volunteers were recruited as the healthy control group and 30 osteoarthritis (OA) patients with knee joint effusion were included as OA synovial fluid control group.The RA dampnessheat blockage syndrome treatment groups were divided into 45 cases in the combined group and 45 cases in the MTX group.The combined group received MTX combined with SYD treatment while the MTX group received MTX alone.AQP1,AQP2 and AQP3 expressions were detected in the serum and synovial fluid.RESULTS:AQP1 had the highest expression,followed by AQP3,and AQP2.The serum levels of AQP1,AQP2 and AQP3 were all significantly lower than those in the healthy volunteers (P ＜ 0.05),while the synovial fluid AQP1,AQP2 and AQP3 expression in the RA group were comparable to these in the OA groups (P ＞ 0.05).After treatment for 2 weeks,serum AQP1,AQP2,AQP3 were significantly increased and erythrocyte sedimentation rate,C-reactive protein,disease activity score of 28 joints were decreased in the combined group (P ＜ 0.05).CONCLUSION:Abnormal expression of AQPs inhibits water metabolism in RA dampness-heat blockage syndrome,so liquid is accumulated at the joint,which may play an important role in the pathogenesis of RA.MTX combined with SYD for the treatment of RA can effectively increase AQP expression.