AIM: To investigate the abnormity of rat colon caused by depression and the ameliorative effects of Radix Acanthopanacis Senticosi (RAS) capsule on colon and their mechanisms in rat depression model. METHODS: Chronic stress-induced model of depression of Wistar rats was produced. The experimental animals were randomly divided into model control, 5-aminosalicylic acid (5-ASA) therapy group and three RAS capsule therapy groups. These five groups were intracolonically treated daily (8:00 a.m.) for 2 wk with normal saline, 5-ASA (100 mg/kg) and RAS capsule at the doses of 300, 600 and 900 mg/kg, respectively. A normal control group of rats was also included in the study. Colonic activities of nitric oxide (NO) and superoxide dismutase (SOD), levels of malondialdehyde (MDA) and inducible nitric oxide synthase (iNOS) were determined by ultraviolet spectrophotometry. The expression of cyclooxygenase-2 (COX-2) in colonic tissue was detected by immunohistochemistry. RESULTS: Enhanced colon inflammatory response and oxidative stress were observed in the chronic stress-induced rat depression model, which manifested as the significant increase of MDA, iNOS and NO levels, as well as the expressions of COX-2 in the colon tissue, but the colonic SOD activity was significantly decreased compared with the normal control (MDA: 10.34±2.77 vs2.55±0.70; iNOS: 1.11±0.44 vs 0.25±0.16; COX-2: 53.26±8.16 vs 4.87±1.65; NO: 11.28±5.66 vs 4.76±1.55; SOD: 53.39±11.15 vs 84.45±22.31; P<0.01). However, these parameters were significantly ameliorated in rats treated locally with RAS capsule at the doses of 300, 600 and 900 mg/kg (iNOS: 0.65±0.31,0.58±0.22 and 0.64±0.33; NO: 5.99±2.73, 6.87±1.96 and 6.50±1.58; MDA: 2.92±0.75, 3.19±1.08 and 3.26±1.24; SOD: 70.81±12.36, 73.30±15.30 and 69.09±11.03, respectively). The expressions of COX-2 in the colon were significantly ameliorated (28.83±9.48 and 27.04±9.56, respectively) when RAS capsule was administered at the doses of 600 and 900 mg/kg. CONCLUSION: Administration of RAS capsule intracolonically may have significant therapeutic effects on the colon of rat depression model, which are probably due to its antioxidative action and inhibition of arachidonic acid metabolism. AIM: To investigate the abnormity of rat colon caused by depression and the ameliorative effects of Radix Acanthopanacis Senticosi (RAS) capsule on colon and their mechanisms in rat depression model. METHODS: Chronic stress-induced model of depression of Wistar rats was produced. The The experimental animals were randomly divided into model control, 5-aminosalicylic acid (5-ASA) therapy group and three RAS capsule therapy groups. These five groups were intracolonically treated daily (8:00 am) for 2 weeks with normal saline, 5-ASA (100 mg / kg) and RAS capsule at the doses of 300, 600 and 900 mg / kg, respectively. A normal control group of rats was also included in the study. Colonic activities of nitric oxide (NO) and superoxide dismutase The expressions of cyclooxygenase-2 (COX-2) in colonic tissue were detected by immunohistochemistry. RESULTS: Enhanced colon infl (iNOS) were determined by ultraviolet spectrophotometry ammatory response and oxidative stress were observed in the chronic stress-induced rat depression model, which manifested as the significant increase of MDA, iNOS and NO levels, as well as the expressions of COX-2 in the colon tissue, but the colonic SOD activity was significantly decreased compared with the normal control (MDA: 10.34 ± 2.77 vs 2.55 ± 0.70; iNOS: 1.11 ± 0.44 vs 0.25 ± 0.16; COX-2: 53.26 ± 8.16 vs 4.87 ± 1.65; NO: 11.28 ± 5.66 vs 4.76 ± 1.55; SOD: 53.39 ± 11.15 vs 84.45 ± 22.31; P <0.01). However, these parameters were significantly ameliorated in rats treated locally with RAS capsule at the doses of 300, 600 and 900 mg / kg (iNOS: 0.65 ± 0.31, 0.58 ± 0.22 and 0.64 ± 0.33; NO: 5.99 ± 2.73, 6.87 ± 1.96 and 6.50 ± 1.58; MDA: 2.92 ± 0.75, 3.19 ± 1.08 and 3.26 ± 1.24; SOD: 70.81 ± 12.36, 73.30 ± 15.30 and 69.09 ± 11.03, respectively.) The expressions of COX-2 in the colon were significantly ameliorated (28.83 ± 9.48 and 27.04 ± 9.56, respectively) when RAS capsule was administered at doses of 600 a nd 900 mg / kg. CONCLUSION: Administration of RAS capsule intracolonically may have significant therapeutic effects on the colon of rat depression model, which are probably due to its antioxidant action and inhibition of arachidonic acid metabolism.