Abstract: AimTo study the effect and mechanism of action of total glucosides of paeony (TGP) on synoviocytes from rats with collagen-induced arthritis (CIA). MethodsChicken type II collagen was used to induce CIA in rats. Synoviocytes were separated by incubation with collagenase and trypsin, and its ultrastructural changes were observed under transmission electron microscope. Synoviocyte proliferation was determined by 3-(4,5-dimethylthiazal-2yl) 2,5- diphenyltetrazoliumbromide (MTT) assay, and IL-1 activity in synoviocytes supernatant was measured by thymocyte proliferation assay. TNFα and PGE₂ produced by synoviocytes were determined by radioimmunoassay. ResultsTGP was shown to protect CIA rats against the ultrastructural damages of synoviocytes. Meanwhile, TGP also suppressed the excessive synoviocyte proliferation and over-production of IL-1, TNFα and PGE₂. ConclusionTGP has inhibitory effect on hyperfunctional synoviocytes of CIA rats and its mechanism of action may be related with the inhibition of abnormal proliferation and secretion of synoviocytes.